Inlet and exhaust upgrades???

[sawood12]

ORIGINAL: 333pg333

So Scott are you saying that if you achieved greater flow numbers it could still actually hurt you? You can attain greater flow numbers if done correctly at a price and I agree that ultimately if you were able to optimise the variocam system it would be ideal. This has been done but it is expensive as you know.

Yes. When you optimise the design of a manifold (or any other component for that matter e.g. turbo, airbox, size and diameter of valves) you are setting it up to be an optimal shape and size to suit one set of conditions only. It is impossible to have a fixed design of a component that is optimised for a variety of conditions. You will design your manifolds to either give you good characteristics at high revs at the expense of low end performance or visa versa. Porsche have settled on a design that gives you the best compromise across the whole rev range. A typical exapmple is the comment earlier in this thread that the Lindsay Racing manifold fitted to Marks 400bhp car was not putting out as much power or torque as a standard car at low RPM, so the Linday Racing maniflod is obvously optimised for flow delivery at high RPM at the expense of power and torque low down. If that is what you're after then fine, if not then it's the wrong piece of kit for you.

Air flowing through a curved tube behaves in a very complex manner and just by increasing it's diameter you may be completely destroying the flow characteristics and causing areas of high or low pressures or turbulance in the wrong places that will destroy any improvements you are chasing or even mean you end up with something that is worse than what you started with. Sometimes the right thing to do might be to reduce the diameter of the headers or volume of the manifold to get the characteristics you want.

 

[eastendr]

I believe the standard 951 intake manifold to be a very good design given the space limitations of the engine bay. Certainly it posesses reasonably long inlet tracts as required to make good midrange torque. WUF has a modified version of the 951 intake manifold. The modifications are internal to promote better flow and external to fit an air temp sensor for the engine management - something the standard 951 / DME setup is in serious neglect of. The throttle body is also matched and the butterfly modified.

I have to say that the torque curve of MarkK's car bears out my thoughts about the LR intake manifold - the runners are too short and consequently move the power and more importantly torque curve too far to the right (higher rev range). I'm sure that this is OK for an outright race spec engine running consistently in the 5500 - 7500 rev range and relying on high RPM power (and probably with a suitable shorter diff ratio to match).

However, I question its suitability for a road car, partly because a lot of work would be needed to get the engine to rev that high (as Andrew says above, solid lifters would help here) and partly that the 951 engine can otherwise be made to produce good torque, which is wasted by the LR manifold design.

With LR products, not all that glitters is gold ... ask me how I know and have the graphs to confirm it.

During the early summer I assembled a number of parts for a proposed new air intake system (pre-turbo) that will address some issues with WUF's current intake setup that I'm not entirely happy with. I'll be doing a before / after mockup and test at Allan's (Weltmeister) when I get time next year to prove my theory right or wrong before I go to full fabrication. In essence the modification is about increasing torque by changing the way that air enters the turbocharger, and reducing heat soak. I'll publish on this on my website when I've carried out the necessary tests.

Since April (?) I haven't made any mechanical changes except the new mapped boost control system that I fitted subsequent to the last dyno session at Allan's. I have, however, covered around 6,000 trouble free miles, some of it at full chat around Scotland among other places and tours. Only oil changes and one inspection of the plugs has shown that I'm happy with the ignition setup. Oh, and a new set of 245 front tyres. The cars is still on the standard cylinder head and cam (as it has been all year).

I can get well over 400 miles on a tank of Tesco 99 when trying, or about 340-360 in normal use including 85-90 motorway cruising mixed with horrendous London traffic. The car pulls cleanly from 28mph in 5th gear and a lot of the very low rpm mapping was done on the M1 in the 40 mph section!

I strongly believe that a proper engine management system and thorough mapping to be essential to getting proper drivability and shaping an engine's characteristics to get the best of the mechanical mods. The two parts have to work in harmony to create the synergy that separates a good driving experience from a great one. Even slight mechanical changes need to be accounted for to get them to work for you.

Over the winter I hope to get to rebuild the bottom end that now has over 130,000 miles and is suffering a lot of blow-by. Capacity will remain at 2.5 Litres. At the same time the big valve head and a revised cam should make a re-appearance. The original reason the BV head was removed was that I wasn't happy with the compression ratio. I had lowered this in anticipation of running a higher level of boost, but after a lot of road miles changed my opinion based on the altered engine's characteristics.

I now believe that rather than sacrificing CR to the alter of boost, I want to go the other way and use the benefit of the development work I've done with the engine management and ignition setup to allow an increased boost headroom to work with the original or maybe even slightly higher CR.

I've managed to reduce EGT by a significant margin so far and hope the the BV head with suitably modified chambering in conjunction with the special B10 sparkplugs will allow me to reduce EGT even further, allowing a higher level of boost before the onset of det. The aim of this is to produce a broad torque curve for even better drivability and economy and extended power band at the top end. Quite a holy grail I know, but I do like a challenge. There's just something about a GT spec car ...

I'm also considering mapping for 95 octane to get around some of the problems we've experienced in trying to get decent petrol in a number of places including Scotland and Isle of Wight. The advanced J&S knock control system copes admirably with low grade petrol and both retards ignition correctly and displays whats happening, but I think that I 'll develop a 95 map all the same. I've still got to setup the launch control and full throttle gearchange capabilities that I've already designed in to the system.

WUF also has (LR) vernier cam timing so there will be some work with cam profile and lift and then adjustment on the car to fine tune.

All of this work is bespoke. The intake, head and cam design will be to my specification in conjunction with CTM, who will also get to do all the machining on the bottom end etc. The ignition system is entirely bespoke (and has now to a large extent also been tested in another 951 as well).The mappable boost control system is developed in conjunction with Random EMS - the official WOLF-3D distributors in Seattle.

To get a good rounded package by merely purchasing a selection of off the shelf items is at best a gamble. If you add an air filter (+8%), chip (+25%), Exhaust (+15%), would you honestly expect to get a 38% increase in power ? If your answer to that is yes, then your optimism knows no bounds.

Baby WUF (944S) has an ESS rear exhaust system, Blitz chip and cone air filter. Standard rating of the engine is 192 BHP. At Allan's it currently produces 173 BHP with the mods listed. Yes, that's 192-173 = 19BHP nett LOSS! This is almost certainly due to valve guide wear (it has new ignition system, bits of wiring loom, knock sensors etc to try to locate the problem).

If you're going to modify your car, you need a baseline figure to work to from an accurate dyno to make sure the engine's healthy first. Compare two examples. Back to baby WUF. Cost of exhaust £299, chip £50, intake £25. Additional insurance premium for 3 modifications £150. Additional cost for year say £525 for a nett 19 BHP power loss (this excludes the additional petrol costs from an under-performing engine). Alternative - repair fundemental problem and probably be back to around 190 BHP. Next year spend the money and probably see the right side of 200 BHP.

The cycle of change, test, change, test etc. is the only way I've ever found of getting a full picture and reaching your goals (which will always move!). I've seen some really silly little tricks make a big improvement, and big shiny expensive things produce a nett loss.

In short, get a baseline engine health check - dyno output, 4-way gas analysis, compression (or preferrably a leak down test) and see if your engine is healthy to begin with. If not, spend the money on getting it fixed.

If it's healthy and you want more power, you have a baseling figure to work from. Fit (or have fitted) your modifications, the go back to the SAME dyno.

If you happen to go to Allan's (WRC at Silverstone) you can also compare like for like with other cars / modifications as extensively published on my website.

Either you'll get the improvement that's claimed, or you get your money back and try alternatives.

What does it cost ? Probably £40-60 for the base run (cheaper if you're trade) and you can probably do a deal with the dyno operator in that you get a cheaper price when you bring the car back for an 'after' run), then the same again after the modifications. If you're going for a mid range power hike, then the costs involved are small compared with your outlay for parts / fitting etc. This is the same for both Turbo and normally aspirated cars. Make sure the fuelling is safe.

My advice above applies to ANY make of car and ANY tuner / vendor / part supplier. Either you want to KNOW what's really working, or why not just save your money on the car and spend it down the pub largering a power output of your own choosing (or buy an M316i, get it slammed and fit neons - I know a venue with an inexhaustable supply). This is just sound practice and also the process that would normally be used to develop products / packages as part of bringing them to market.

Sorry for the long post. What was I thinking of! [] []

 

[333pg333]

Not at all Rick. Great post. Really constructive, unbiased, and based on true experience.
Also thanks to Fen, and Scott for your thoughts too. All very good reading.
I'd still be curious about increasing the cfm #'s and the capacity of the motor. I'm looking to Darton mids out to 3.0ltr so am looking at what else could be done. Obviously plenty but that would include plenty wrong possible too. In theory the extra capacity could make up for shifting the power to the right, increasing the flow and lowering the egts. In theory anyway...

 

[Guest]

ORIGINAL: sawood12

I'm not convinced that investing alot of time and effort on inlet and exhaust manifolds is necessarily worth it. Maybe on very very highly turned cars where the manifolds are the weakest link in the chain. Also it's something you have to be sure you know exactly what you're after before you start as the manifolds are fixed designs they are only ever going to be optimised for one set of conditions, i.e. a specific RPM, temp, pressure etc. and as soon as you are outside of those conditions it is no longer an optimised design and in fact might even be hurting you. That is why some cars feature variable geometry inlet manifolds that change their volume and shape to a more optimised shape through the whole rev range and all driving conditions.

Personally that is where I think the 944 crowd is severely lacking. Experience has shown me on various other non-944 cars of similar displacement (and some with similar SOHC heads) that larger throttle bodies, larger IC pipes, a larger intake plenum with moderately sized runners, etc all provide worthwhile gains when you start moving past the 300rwhp level. On a stock 951 or one with bolt-on mods, the stock stuff is pretty well optimized. Personally, I feel the stock 52mm throttle body is a bit too small (even at bolt-on power levels) considering the displacement, however I'm not too sure if the size of the stock intake plenum would really lend itself to producing any significant horsepower gains using a larger throttle body. Not to mention the IC pipes are relatively small and would restrict any potential gain anyways.

The stock manifold is designed very well for torque production, though not so much so for maintaining torque/hp at high rpm. As far as the intake runners, IMO the Speed Force Racing and Lindsey Racing intakes both have runners that are a bit too short. They are obviously designed for higher rpm and higher horsepower usage, though I think an intake runner length somewhere between the stock runners and these 2 aftermarket units would be a more worthwhile compromise and would provide improved low to mid range torque. Plenum size on both units is a good improvement over stock, especially for higher hp levels. IMO the stock manifold has much too small of a plenum size for a high horsepower application as you really need a significantly larger plenum volume to efficiently handle the significantly increased airflow volume. True, there are people that have used all of these stock components on some relatively high horsepower 951's. Though, personally I think the question needs to be asked.....how much hp, torque and top-end power is everyone sacrificing by keeping these components? In my experience with other cars, I'd tend to think quite a bit once you've reached the 350-400+rwhp level. Unfortunately very few have really experimented with this stuff on our cars, and it seems many in our world just completely ignore any non-Porsche results with these components. It's all about optimizing airflow/velocity, besides all engines are just air pumps anyways and ours are not all that different. I've seen lots of 951 dyno charts, and even some of the ones with fairly large turbos have relatively poor top end hp curves with torque dropping off too early.

 

[Indi9xx]

My opinion, for what its worth, is that far too many people chase a peak BHP level, which quite frankly mad. Torque is king, or more to the point a package that makes a good spread of power, is king.

The Lindsey is a good manifold for making peak power, if thats what you want. I would be interested in hooking up pressure take off's to each runner in the lindsey manifold and watching the pressures during some power runs on a dyno, as I am not sure how impressed I would be with the balance of the design.

The standard manifold is good for making torque, but not perfect.. just a good production car which met the criteria of production cost, packaging and performance. But it has some serious limitations which need to be addressed and are being addressed at the moment by many different people in different ways.. it will be interesting to see how they all pan out.

Exhausts are another issue... again the standard one is a great design, for what it was designed for. Unfortunately very few manufacturers of performance exhausts want to make a great exhaust... most of them want to make an exhaust which either looks sexy, sounds sexy, or gives 10BHP at 6500 rpm at the expense of 30lbs of torque at 3500 rpms (random example), as the peak figure is what everyone hunts for..... I technically good exhaust design, for the application its intended for, will make gains which on balance are overall gains.. in other words will make gains accross the spectrum, rather than at the expense of low or midrange power... or at very least will make good gains with an acceptable loss lower down (like a gain of 35 bhp at the expense of 3 or 4 lbs of torque lower down...)

Again... everyone talks about peak bhp.. so its no shock that most of the vendors and manufacturers will be happy to develop and sell items which make peak gains, even if it makes the car overall slower than a seemingly less powerfull car..

The best way to think about it, is to seek a dyno graph which will have a maxium average area bellow the torque and bhp graphs if you want a fast... In other words, use some graph paper to plot your chart for bhp, and count the squares under the bhp curve... then do the same for torque... then possibly average the two against each other and should have an indication of which car would have more WORTHWHILE power.

 

[Indi9xx]

Rick,

Are you going for an alusil or nickasil bore?

Are you going for a block with or without piston squirters?

Standard or custom pistons?

As I said earlier this year, I think the performance you have made from your worn bottom end will be improved by a great proportion once you have a good fit bottom end. So I look forward to seeing what you gain at the next dyno day.

 

[333pg333]

I don't have the knowledge to challenge any of you guys but in my research I find I have to agree somewhat with Porschefile here. There seems to be some sort of inheirent trepidation in the 951 world when it comes to improving the breathing to our cars. I understand the hesitation from creating a car that needs to be pumping 20+ psi and rev to 7500 to get the benefits of modifications but why does improving our stock system have to mean this? We can still do some improvements and retain good low to mid range torque surely? If it improves flow it should be able to improve spoolup and the benefit is possibly reducing temperatures as well. Hey I don't want a dyno queen car just to post numbers on Rennlist, I want a car that can power out of corners but also not start loosing boost by 5000rpm, or too much anyway. I can't see why we can't have a happy medium without sacrificing what we want which is driveability yet still make significant improvements to what we have to admit is a limited design. Heck, a current Toyota Corolla probably has better CFM's than our cars.

 

[944Turbo]

There are a number of factors. If you are retaining the standard head with ceramic liners this is always going to be a restriction, whatever you do with the intake or exhaust side. The engine being a very large 4 cylinder with an anchor for a crank is never going to enjoy being at high revs. There is only a finite amount of space.
Developing the best set up would require a slide trombone style runner and lots of hours on a dyno. Alternative plenums would also need to be considered.

I also wonder how important flow is compared to equal length paths / pulse effects etc. when the incoming air is well presurised.

Tony

 

[Guest]

I think the point that some people seem to be missing in our 944 community is the fact that many people are adding 100-200+hp over the stock 951's power levels. The stock components were designed very well for production pieces, and were nicely optimized for the stock 951's power levels. Personally I still feel the stock throttlebody is a bit small for our displacement, but that's besides the point. When talking of adding over 100hp to a car you are making your engine flow a huge volume of air over what the stock components were designed for. In short, the stock stuff is no longer optimal. True, lots of people have pushed the stock components to some fairly high horsepower levels, but doing so will require a larger, laggier turbo and more boost. That's fine if that's the route you want to take, however that generally isn't going to result in the nicest powerband and you will see things like torque and hp dropping off relatively low in the rpm. The result of going that route? Basically you build a setup that generates lots of midrange torque with a crappy top-end curve and hp/tq dropping well before 6k rpm. That's a pretty generalized statement, though if you look at lots of 951 dynos it is very true. Why not just do it right the first time? Going with a larger than stock intake or exhaust at these higher hp levels does not necessarily mean you are sacrificing torque or hp. Though, you have to consider quite a few factors to choose and properly size pieces for you new hp level otherwise you can end up loosing low-end power and torque. If you properly optimize all of these things though, it will alow you to run a much smaller, more responsive turbo and you'll be able to make more horsepower on pump gas.

As far as intake manifolds go, sizing one for higher hp generally consits of using a larger intake plenum, larger throttle body, and modifying the intake runner length for either horsepower (shorter) or torque (longer). The stock intake has runners that are already long enough, so you certainly don't want to lengthen them on a higher hp setup. Though, IMO some of the aftermarket offerings such as the SFR and LR manifolds have runners that are much too short. Somewhere in between stock and those 2 aftermarket pieces is a happy medium. There are several mathematical ways you can determine optimal runner length, however I'm not going to get into that right now as I'm pretty tired. Honestly, I'm no expert when it comes to this stuff, however most of it is a matter of simple physics and can easily be understood by the average individual. I just did a quick google search and here are a few good links if you want to learn more about intake manifold design:
http://www.team-integra.net/sections/articles/showarticle.asp?ArticleID=466 Make sure to read the 2nd page
http://www.mne.psu.edu/me415/SPRING02/intake/intake.html A few nice examples of various intake designs
http://www.mne.psu.edu/me415/fall05/SAE/intake.html

And here's a link showing an excellent example of what I'm talking about: http://advancedinductionresearch.com/photo_gallery.htm Check out the Performance Data section. This is a relatively small Honda motor with a 60-1 T4 setup. Notice how the intake only improved CFM across all valve lifts, which resulted in more torque throughout the entire rpm band, as well as an improvement in torque and a substantial improvement in horsepower. The specifics are different from the 944 but, the same general physics apply and it just goes to show you that properly optimizing parts can be a very beneficial thing to do. In the 944's case, the stock plenum is relatively small in volume which would pose a flow restriction when pushing a decent amount more airflow. I don't have any hard numbers as proof of this, though judging by what I've seen from other similar sized non-944 engines, I'd tend to think around the ~350rwhp level or so and it might be a good idea to think about modifying the intake. You'd also want to shorten the runners a bit, though there is really no reason to shorten them as much as the SFR and LR units as it just sacrifices too much torque. It's alot like modifying ports in a head. There are lots of little "tricks" you can do when redesigning the plenum and runners, such as introducing a gradual tapered angle to the plenum (the link above shows a very shallow angle taper) shape which can be used to increase the velocity in airflow. You can also taper the runners themselves to create the same effect, plus you can use things like velocity stacks, resonance tuning, etc.

Also, just FYI but, there is no "too large" of an exhaust that will cause a poor powerband when talking about a turbocharged vehicle. The most ideal exhaust would be a very short and straight dump of a generous diameter off the back of the exhaust housing. Over here in the "colonies" [] a few people have done some tests of the stock 2.5" exhaust and a 3" exhaust with a stock K26. Basically it showed that a 3" with no cat provided a minimal gain over the stock 2.5" with a cat bypass. Though, when you get into higher hp levels like the 300-400hp range or even just a larger turbo on the stock setup then a full 3" will work perfectly fine and cover everyone's needs. Some retailers are now offering "graduated" exhausts that enlarge out to 4", though it's been my experience that on a 2.0-3.0L motor this won't offer a significant increase in performance unless you are using a massive turbo and flowing a huge volume of air to the tune of well over 600+hp. There will be some improvement with the 4", though it would be minimal at best, and it wouldn't provide some drastic improvement as some retailers would have you believe.

Sorry to type a novel! [] Anyways, alot of this stuff is just common knowledge in the import crowds I generally hang around with. Unfortunately I think much of it is lost with our specific enthusiast group partially because I don't think all of these issues have been entirely addressed by our aftermarket support. Without full market support regarding these issues, largely it's left up to the individual to learn and figure out for themselves.

 

[Indi9xx]

333, I dont think your challenging any of us, I think we are agreeing with Porschphile and on the same page in turbo applications.

The problem with a modified intake manifold, it needs to be quite a way down on the shopping list due to the cost versus gains... There is no point in anyone spending £1k on an intake manifold that on a 300 BHP car isnt going to release as much power as a £800 hybrid turbo will release.... But once the power levels pass about 350 to 400 BHP the intake manifold becomes a real restriction.

With exhausts, I also agree with Porschphile in a turbo application, although there still needs to be a balancing act... noise versus gains... a straight pipe off of the turbo would be great, but not very civilised as we all know... but many exhaust manufacturers make exhausts with no increase in flow, just an increase in noise.... Not only that, but all the glitters isnt gold... a good example is some of the bigger bore exhausts out there... they may have 3 inch pipes, but due to lack of attention to detail they loose power over a properly designed 3 inch system... the same is true of the larger bore systems.

The other thing is this topic isnt just 944 turbo specific... with NA cars the intake, head and exhaust become even more critical, especially when dealing with the exhaust... I know of several makes of "performance" exhaust for the 944 NA which loose power over a standard system, in particular the loose torque at the expense of a couple of BHP over a well designed system.

My main point is that consumers chase BHP, which is a real shame... Its like expecting food to taste good just on the amount of calories in it... which would probably work for the main, but may lead to dissapointment if you expected a steak dinner and were served a bag of sugar..

 

[DivineE]

I'm really enjoying reading this topic even though I admit I have very little knowledge on the subject.

Surely though if you take the route that most people choose to tune 944's and just tune by up rating the boost, rather than altering the characteristics of the engine so that you can rev higher, changing the length or size of the intake is going to make very little difference because your getting more air thought the same space anyway if its under higher pressure?

I'd have taken a guess that heat generated by more pressure and friction would make more of a difference on power loss? If so maybe addressing temperature would be a more cost effective approach??

I know that in the Jap tuning market all they ever talk about is bigger capacity intercoolers, turbos etc and more airflow but most of the time they seem to be trying to increase hp figures mainly by increasing rpm. Notice all the big power tuner cars coming on boost at 5000-7000rpm and revving to 10,000 or even 13,500rpm I've seen once before on a Supra!

It's an amazing achievement that this can be done with the Toyota Supra and Nissan Skyline engines but its just not possible on the 944 and with the massive extra weight, lag and impracticality of these cars they don't seem to actually go that fast anyway?!

I've been very disappointed by genuine 600hp Supra's which I'm confident are no faster than 320hp 944's I've been in. On top of which my standard 220hp 944turbo was almost identical in speed to my friends 385hp 300zx dyno'd at Jamsport so big figures definitely aren't everything and the engine wear at these pressures/revs cannot be healthy!!

Regards,

Ben

 

[Fen]

ORIGINAL: Indi9xx

The other thing is this topic isnt just 944 turbo specific...

Whaddaya mean NA 944's. Do you get them without Turbos? [][][]

 

[DivineE]

No no no thats impossible he must be talking about the 'N'atural 'A'ir venting that your block had.

 

[sawood12]

ORIGINAL: Indi9xx

The problem with a modified intake manifold, it needs to be quite a way down on the shopping list due to the cost versus gains...

That was the point I was trying to make earlier. You need to match your manifolds to the rest of the engine set up because as soon as you change one other element of the engine your manifold will no longer be optimised for the car. There are so many parameters to consider that through trial and error you can only deal with a handful of parameters at best, therefore even with methodical experimentation like Rick is doing, you will be lucky to stumble across a design that happens to have the correct mix of parameters to provide you with a noticable improvement.

My company uses Kray supercomputers (if Krays are still the thing) to carry out our computational fluid dynamics calculations, just like our competitors do, and you would be surprised at just how different our relative designs end up being. So even the real experts disagree on the best design to achive the same thing - and also you would be very surprised at just how close the performance of the two different designs are - so that is why I am not convinced that manifold design can have a significant effect on any performance increase of your car. Yes it will modify the way the car feels and where the torque and power is delivered, but you wont get that much extra performance out of the car. It all fractions of a percent at most.

Also people have mentioned manifold design that flow more. Surely this isn't necessarily what you want. I would imagine (and please correct me if i'm wrong) that with turbo cars you need to provide a bit of back pressure for the turbo compressor to work against. Without this back pressure the pressure in the exhaust manifold will build up more slowy as there is less resistance to the turbo spinning hence more turbo lag. If you get just the right amount of back pressure working against the turbo compressor the exhaust manifold pressure will build up more quickly and be held further through the rev range. The exact oppisite is required for N/A cars where the air is sucked through the manifold instead of blown through the manifold.

I certainly wouldn't have a clue to where to begin with all this and good luck to all those who are having a go. If the stock manifold is even 80% of the way there (and it sounds like it might be better than that) then that'll do for me!

 

[Indi9xx]

The important thing to visualise about a 944 turbo intake manifold isnt that a redesign will make a % gain, but past a cetain airflow at a certain pressure, it will begin to be a potention % loss. A redesign will be reducing the % loss past that air flow / pressure threshold.

The other thing to remember about intake manifolds and fluid dynamics is that they do not respond to a constant flow fluid model as the flow is running on a 25% duty cycle per runner. Also it needs to be noted that this duty cycle with a ASR (attack sustain and release waveform) rather than a square waveform, for which the fluid analysis needs to model... In particular, there are a couple of aspects of this characteristic which makes or breaks the intake manifold design as to how well it works.

There is a solution to the 944 turbo intake manifold, but I would rather not talk about it too much until development is complete, the design perfected and back to back testing is performed.

 

[Guest]

ORIGINAL: Indi9xx

The important thing to visualise about a 944 turbo intake manifold isnt that a redesign will make a % gain, but past a cetain airflow at a certain pressure, it will begin to be a potention % loss. A redesign will be reducing the % loss past that air flow / pressure threshold.

Very well put Jon! This is the point I'm trying to get across. It's not necessarily about how much hp/torque you make as it is about how much you might be loosing as well as how much of this power you can "free" up. We, or at least I, have yet to really see some definite airflow numbers to establish where you start to reach this point on 944's however I tend to think around the ~350hp range might be close.

 

[Guest]

ORIGINAL: Indi9xx
The problem with a modified intake manifold, it needs to be quite a way down on the shopping list due to the cost versus gains... There is no point in anyone spending £1k on an intake manifold that on a 300 BHP car isnt going to release as much power as a £800 hybrid turbo will release.... But once the power levels pass about 350 to 400 BHP the intake manifold becomes a real restriction.

Again, very well put Jon! I think that first sentence is really the main reason why most in the 944 world just go with the easier and, in most cases, considerably cheaper route of a slightly larger turbo or more boost. As far as our aftermarket goes, we are a much smaller group to cater to which normally means there will be less aftermarket support compared to a more common vehicle. Typically, because of that, parts costs are going to be higher. It's the whole supply and demand thing yet again! [] I've learned much of my knowledge as it applies to forced induction from the import world. Fortunately for that crowd there is a huge aftermarket support. For common cars such as the Nissan 180sx and 200sx, intake/exhaust manifolds and all of those other typical mods are a dime a dozen. As a result, it is much more economical for them to optimize airflow a little better than the average 944 Turbo. On the flip side, it makes it easier for them to lose power and reduce low-end torque as you commonly see very short runner intakes available for lots of stuff in the import world, which would generally be better suited to peak power as opposed to broad power. When you add up the ~£1-1.5k+ for an intake, ~£1-3k for an exhaust manifold and full exhaust, £200+ for a larger throttle body.......It can add up a considerable amount! Those are just rough estimates as I'm not familiar enough with the UK market. Hopefully in the near future there will be a few more aftermarket options available to us for these components, which should generally result in slightly cheaper products then we currently see at the moment (possibly "cheaper" in both ways also). Until then, in many cases you might be forced to fabricate your own components if you are trying to stick with a more realistic budget, and fabrication isn't always feasible for everyone.

 

[Guest]

ORIGINAL: DivineE
Surely though if you take the route that most people choose to tune 944's and just tune by up rating the boost, rather than altering the characteristics of the engine so that you can rev higher, changing the length or size of the intake is going to make very little difference because your getting more air thought the same space anyway if its under higher pressure? I'd have taken a guess that heat generated by more pressure and friction would make more of a difference on power loss? If so maybe addressing temperature would be a more cost effective approach??

That's an excellent point. Though here's the catch. You are forcing lots of pressure through a relatively small area when you reach higher ~350whp+ levels on our cars. Guess what? This airflow restriction actually causes increases in intake and exhaust airflow temperature! [] By properly sizing these components, you are also reducing the effective temperature of the airflow, which in turn can and will result in more power as well as extended life of other associated engine components. Is it starting to make sense now? Thank you for noticing that DivineE! It completely slipped my mind to discuss the thermodynamic side of things, and that's a very integral and vital topic when it comes to forced induction.

Largely, with turbocharging, effects in airflow temperature do cause some drastic effects on power. This is one of the main reasons that some newer turbos (such as the Garrett GT series) generate more power. They have more efficient compressor/turbine wheels which spend more of a percentage of their work generating pressure as opposed to generating heat. Because they generate pressure more efficiently, they can generate lower airflow temperatures which results in an increase in power capability. Now, consider the airflow temperatures with all of the stock components and a higher hp level. Pushing say 1bar or more of boost through a motor is actually a substantial amount of air you are forcing into the motor. If you have a small stock intake, stock TB, stock diameter IC pipes, and a stock outlet size intercooler for example, the volume of airflow you are attempting to force through them might be larger then the optimal airflow volume of components such as the plenum, throttle body, intake runner diameter, IC pipe diameter, etc etc. What effects does this have? It results in increased airflow temperatures as your turbo works harder to force the airflow through the motor, it can also result in slower spool times because the airflow is physically taking longer to travel through the motor. This same logic applies to the exhaust as well, however there are some things that vary between the 2. Actually, on the exhaust side, you WANT to generate heat. Heat (think of it in terms of hot air molecules are expanded more than cold ones) can actually improve spool. With a turbo setup like ours and the relatively long distance from the exhaust ports to the turbine inlet as a result of the turbo not being mounted to the manifold, changes in the exhaust temperature could potentially have a big effect on spool. This is one of the reasons that a few here in the states have seen 100-200rpm quicker spool simply from using exhaust wrap on the header and crossover as you are trapping more heat into the airflow. On the other side of this, if your EGT's get too high you can actually damage certain engine components, though usually you will see this under other conditions such as maxing a turbine wheel out and pushing more boost past it's efficiency levels, improper timing, very lean a/f's, etc.

Ultimately, when pushing larger volumes of air, you need more optimally sized components that, in most cases, are physically larger and can support the increased volume of air. There are some general principles of thermodynamics that need to be taken into account, IMO most notably thermal efficiency and airflow velocity. When enlarging these components, there are many methods you can use in sizing components to still maintain a thermally efficient volume of airflow and still maintain a respectable amount of airflow velocity. If done properly, it will only make more power, a broader powerband, a lower airflow temperature, and in some cases can have beneficial effects on longevity of certain engine components. To summarize things, you ultimately want to size all of your intake and exhaust components (exhaust includes the turbine and turbine housing, especially when upgrading turbos) to maintain a more thermally efficient airflow temperature and as high of an airflow velocity as reasonably possible. It is possible to go too far though. For example, if you size the components too large, there will no longer be an airflow restriction, so your airflow temps will decrease though you will also see a decrease in airflow velocity. That decrease in airflow velocity will make your turbo laggier and hurt your powerband everywhere except generally peak hp numbers on the top-end. Now the real trick is finding the best balance of intake/exhaust components to acheive this ideal middle ground. I'm going to try and do some tests of my own in the not too distant future, and hopefully others will eventually join in so that we can get a better idea of exactly where all of the restrictions are with our stock components, and the most optimal ways to fix these issues. It's my opinion that much of the "sizing" issue doesn't apply to a relatively stock 944 Turbo, and/or one at the full bolt-on power level. There may be some improvements to be made on a relatively stock setup, such as a larger TB, and it's definitely worthwhile to do a straight through 2.5" exhaust (just eliminating the cat is what I mean), though a larger majority of the stock components are pretty well sized for up to at least the 300rwhp range.

I know that in the Jap tuning market all they ever talk about is bigger capacity intercoolers, turbos etc and more airflow but most of the time they seem to be trying to increase hp figures mainly by increasing rpm. Notice all the big power tuner cars coming on boost at 5000-7000rpm and revving to 10,000 or even 13,500rpm I've seen once before on a Supra!

With Japanese cars, I've noticed that it is fairly common to find very short runner manifolds, and other peak hp oriented components, however for many of these cars there are still plenty of options for more properly sized components oriented more for maintaining a broad powerband. They aren't all dyno queens! [] Some of the stuff you are talking about are more commonly full on drag cars, so that's not really the greatest example. One example of that is the http://www.exvitermini.com/ Skyline. He's revving to ~13.5k and generating around 1350AWHP! That's a complete drag car though. At the point that you are building a sub ~3.5l car to generate say around 900-1000+rwhp, then extremely high rpm boost thresholds and extremely high redlines are going to be necessary modifications to work with the size turbochargers you'll need to use. That's just the fact of the matter. Unfortunately there is no simple way for us to bolt on a few relatively inexpensive valvetrain mods and a huge Garrett Gt42r then rev to 9k and generate 800rwhp in a 944. It would certainly be nice though there isn't enough demand for products like that with our cars, not to mention our drivetrains aren't as well equipped to handle such insane hp increases.

It's an amazing achievement that this can be done with the Toyota Supra and Nissan Skyline engines but its just not possible on the 944 and with the massive extra weight, lag and impracticality of these cars they don't seem to actually go that fast anyway?!

Skylines/Supras are relatively heavy, though that's probably a good thing (for stability, more weight/grip on the drive wheels for traction, etc) considering some of the ridiculous hp levels you see on some of these street driven vehicles. Can you imagine trying to hook up in an 800rwhp 944? [] As far as actually going fast, you should see some of the crazy Supras here in the states! http://www.boostlogic.com/ is a company that's located here in my city. They recently ran a 7.88 at 181 in the 1/4 (0-400m)! I can't even begin to tell you how many 800-1000whp Supras there are in my state, some of them being 9 second cars, and largely alot of them are driven on the street. There are plenty of videos of some of these guys pulling Hayabusa's and other insanely fast streetbikes, so these cars definitely don't have any problem in the speed category.

I've been very disappointed by genuine 600hp Supra's which I'm confident are no faster than 320hp 944's I've been in. On top of which my standard 220hp 944turbo was almost identical in speed to my friends 385hp 300zx dyno'd at Jamsport so big figures definitely aren't everything and the engine wear at these pressures/revs cannot be healthy!!

Regards,

Ben

Lots of people talk big and inflate claims about their cars, so always take everything with a grain of salt. Not to mention, when you reach those kind of hp levels, tuning is such a vital thing yet alot of people screw that part up pretty badly. Tuning can make or break a car. A true 600rwhp Supra that was built and tuned properly is not something to be taken lightly and is truly a fast car. Also, you have to factor in that Supras are 6 cylinders, so at any power level compared to an engine with less cylinders, the one with the larger number of cylinders is typically less stressed because you are generating less hp per cylinder. My statement is a generalization, as it doesn't take into account things like the structural rigidity of the block, thickness of cylinder walls, etc that ultimately define how stressed a motor will be at a given power level. The Supra's (assuming we are mainly speaking of the Mk4) 2JZ motor is an iron block and aluminum head. If you've ever seen those motors dissassembled, they are considerably reinforced and insanely durable in stock form. Here in the states, people have pushed the stock block (meaning no sleeves or other block mods) up to around the 1000-1100rwhp level.

Sorry guys, I can't ever seem to keep my posts short and condensed. I'd highly recommend picking up a good thermodynamics book and start reading! Much of it is really common sense and understanding thermodynamics can really help you further understand forced induction.

 

[333pg333]

Now this is what I'm talking about! I think we're all after the same thing here. An improvement to our cars in a balanced, efficient way. My point, and I'll make this with an odd simile, is that keeping it all stock and maybe turning up the boost is to me like being deserted on an Island and deciding to all stick together and huddle in a cave until someone rescues us. I like the idea of people going off in different directions looking for a way out of there or to improve on the cave conditions. As I said before, there is and must be a way of improving all the facets we've been talking about without sacrificing the driveability of the car. I support the guys who want to go off and explore the island rather than sit in the cave. There is absolutely no offence intended in my comments, in fact I believe that it's discussions like these and people like you that can come up with changes to our fairly staid 951 world. These are great cars and they deserve to approach their potential that was stolen from them by their premature demise ...Churchill would be proud of that one.[][][]

 

[944Turbo]

ORIGINAL: porschphile
Sorry guys, I can't ever seem to keep my posts short and condensed. I'd highly recommend picking up a good thermodynamics book and start reading! Much of it is really common sense and understanding thermodynamics can really help you further understand forced induction.

Impressive first 5 posts [] forgot to say welcome to the forum!
Tony