Engine build progress

[sawood12]

ORIGINAL: DivineE

ORIGINAL: sawood12 With the only apparent disadvantage of E85/biofuels causing you to stop more frequently at petrol stations for a fill up, wouldn't a more elegant solution for those short sharp bursts of extreme speed be to run lower boost pressures (thereby preserving the engine and transmission) and using NOS?

I've never liked NOS, it doesn't seem like 'real' power to me as you only get it in a few second bursts. Something like a high octane fuel lifts the performance of the car for a whole tank. I also hear its very hard to accurately account for in the mapping, but that's just what I heard.

I see what you're saying but I think that achieving big power by simply increasing boost pressure just as false too - it is a real blunt instrument. The end result is the same - you are looking to enrichen the mixture with air - one does it by enabling you to increase boost pressure the other does it by introducing it directly into the air/fuel mix. Simply increasing boost pressures more and more introduces more problems largely around heating of the air as you compress it - and using the turbo over a larger operating range thereby spending more time out of their efficiency window. By running lower boost pressures you are operating the turbo within its narrow window of efficiency, reducing stress on the engine and super cooling the charge as it goes into the engine. It is a far more elegant solution and perfect for those quick bursts of speed - so ultimately the same benefit as E85 as you will be using it about the same % of time you would be using the benefits of E85. It would not really be any good for trackdays though. Biofuels only have about 70% if the energy yield of petrol so to achieve the same power you have to work the engine harder. And having to plan journeys around E85 stations would be a real PITA. It was difficult enough planning journeys around Shell V-Power garages. Paul - nice try with the eco-trump card but i'm not sure about the environmental credentials of biofuels too. They are consuming more and more rain forest than ever!

 

[Diver944]

ORIGINAL: sawood12 Paul - nice try with the eco-trump card but i'm not sure about the environmental credentials of biofuels too. They are consuming more and more rain forest than ever!

Ssshh [:-] how else will I get it past the Missus []

 

[sawood12]

ORIGINAL: Diver944

ORIGINAL: sawood12 Paul - nice try with the eco-trump card but i'm not sure about the environmental credentials of biofuels too. They are consuming more and more rain forest than ever!

Ssshh [:-] how else will I get it past the Missus []

Flowers, chocolates, a nice meal out, loads of compliments. Oh, and lie about the costs!!!! Of course if you're the romantic sort who already ply's your wife with flowers, chocolates, romantic meals out and compliments then you are only left with lying!

 

[George Elliott]

Scott, I agree boost pressure is a blunt instrument in some ways, but back in the F1 turbo era, the qualifying engines ran 58psi (4 bar) and produced 1400bhp from 1500cc. I guess the fact they were known as "grenade" engines just proves the bluntness of raw boost. I can hardly grasp how an engine can stand that. George 944t

 

[DivineE]

Kind of on topic but I'd to know where the maximum power/efficiency point is for boost pressure on a 944. When my Audi S3 was running 1.85bar on the road (dropping to about 1.5bar at the redline) it makes you wonder what the optimum density/pressure level assuming you have a turbo designed to be in maximum efficiency is? How far can you compress air with an efficient turbo and intercooler set up before losses start to outweigh gains? I think the trick with those F1 cars was the oxygen stored in the fuel gel. Its kind of a licence to cheat.

 

[333pg333]

ORIGINAL: sawood12

ORIGINAL: DivineE

ORIGINAL: sawood12 With the only apparent disadvantage of E85/biofuels causing you to stop more frequently at petrol stations for a fill up, wouldn't a more elegant solution for those short sharp bursts of extreme speed be to run lower boost pressures (thereby preserving the engine and transmission) and using NOS?

I've never liked NOS, it doesn't seem like 'real' power to me as you only get it in a few second bursts. Something like a high octane fuel lifts the performance of the car for a whole tank. I also hear its very hard to accurately account for in the mapping, but that's just what I heard.

I see what you're saying but I think that achieving big power by simply increasing boost pressure just as false too - it is a real blunt instrument. The end result is the same - you are looking to enrichen the mixture with air - one does it by enabling you to increase boost pressure the other does it by introducing it directly into the air/fuel mix. Simply increasing boost pressures more and more introduces more problems largely around heating of the air as you compress it - and using the turbo over a larger operating range thereby spending more time out of their efficiency window. By running lower boost pressures you are operating the turbo within its narrow window of efficiency, reducing stress on the engine and super cooling the charge as it goes into the engine. It is a far more elegant solution and perfect for those quick bursts of speed - so ultimately the same benefit as E85 as you will be using it about the same % of time you would be using the benefits of E85. It would not really be any good for trackdays though. Biofuels only have about 70% if the energy yield of petrol so to achieve the same power you have to work the engine harder. And having to plan journeys around E85 stations would be a real PITA. It was difficult enough planning journeys around Shell V-Power garages. Paul - nice try with the eco-trump card but i'm not sure about the environmental credentials of biofuels too. They are consuming more and more rain forest than ever!

Scott, I have to disagree with some of this. While just cramming more boost into the motor is perhaps inelegant, essentially most of the time performance engineers have used higher boost (if it's a forced induction motor) coupled with increased VE and a good tune to make big advancements in hp. Of course lighter components help too. With a standard throttle body, intercooler, hardpipes, possibly inlet, head, extractors, and exhaust you are limited by the ceilings of these components (separately and in concert). I have seen on my car where we bang our head at the limits and increasing boost yielded very little change. With a pretty big cam, and larger intercooler / pipes I am probably hitting the throttle body and then I also have an n/a head which will be even less efficient than the stock 951 head. No ceramic liners. So, yes there is certainly a psi level where you just stop gaining, it's still worth the extra cooling of the E85 at these levels. To do a track day you will have to take some spare fuel in jerry cans but that is standard practice. You have to take quite a lot more than when running 98 super. I did a day last week and went through 5 x 20ltr cans and also a 3/4 tank when I arrived. So, yes it is a lot, but as Thom has mentioned, it is a lot cheaper than 98 and way less than race fuel. For the street, well yes you are restricted to just how available it is in your neck of the woods. For a daily driver I probably wouldn't bother so much, but having said that, we have rigged up two dash mounted switches in my car to shift between timing and fuel types. So if I run out of E85 I can switch over to normal pump fuel. Thom, you can do this too with the V Flex. The only thing you can't do with the VFlex is tune the ign, so you are left with whatever timing has been set in the 'images'. I think of NOS as something the streetracer kids use. No skill level and not what I term 'racing'. []

 

[TTM]

I am beginning to wonder if the problem with coolant overflowing isn't actually caused by a subtle combination of developing hot spots in the head with a gradually-failing headgasket. I have been reading back and forth Corleone's thread on Rennlist and what I have been seeing since I have been running E85 is similar to what he describes [link=http://forums.rennlist.com/rennforums/7103087-post151.html]here[/link].

 

[nick_968]

Thom, have you thought about trying Evans Coolant to reduce the hot spots? Its something I have been thinking about for my car but not got round to trying it yet.

 

[DivineE]

TTM I tend to side with your new theory. I read that through also.

 

[TTM]

I am scratching my head at what to do with the headgasket. Wether we're talking about Cometic or widefire I have read as much good as bad on both types. Also, shall I stick with Raceware head studs or try original ones? Shall I add a vent on the head on cyl #4 only or on each cylinder? Lots of questions...[8|] Nick, do you mind me asking what headgasket and studs you are using?

 

[nick_968]

I am using factory studs and headgasket. So far no problems up to 18psi but only done 3k miles since build and a lot of that just going to and from workshops/ dynos etc. I like the look of the new 3.0 headgasket just released by the 928 supercharger guy over on rennlist who just made the new 968 sc kit. I couldnt justify the cost of raceware studs at the time of my build so after doing some limited research decided to stick with the factory ones. The obvious solution should I run into the hot spots issue would be to run Evans coolant but I dont know enough about it yet/ or have had a need to do anything about it.

 

[TTM]

Do you mean the factory NA 968 headgasket? The original 968 turbo unit is made of unobtainium... and I'm not sure if the "widefire" unit made by supplier Reinz is identical.

 

[333pg333]

This is the one Thom. http://forums.rennlist.com/rennforums/968-forum/584907-new-high-performance-head-gasket-for-968-944s2.html Corleone has been talking about hot spots in the head for a few years. I can't see the harm in following his lead? Having said that Thom, I think if you use plenty of hylomar and even between layers on a Cometic, you will be fine. We have also installed a secondary overflow tank for hot days at the track. The coolant flows into it until which time it cools and flows back to the primary expansion tank. It's a large drink bottle sitting in the left guard. We also removed the stock headstuds. My motor is actually an '83 n/a block and head so these studs were pretty old. Put in Raceware and torqued them to 85lb. Perhaps a bit of hit and miss, but so far, so good. On the street you would be fine 100% IMHO.

 

[nick_968]

My studs were all new in a new bare block. Factory NA gasket.

 

[GPF]

ORIGINAL: Diver944 speak to Simonp and get one of his ball bearing hybrids ££££££££

Hi Paul, do you (or anyone else) have a link to these? Regards

 

[TTM]

You can send Simon an e-mail and ask for his phone number : http://www.porscheclubgbforum.com/showprofile.asp?memid=6368 He has always been very helpful on the phone, the turbo he built for me is brilliant.

 

[George Elliott]

I did that and ended up with another car, no regrets though, the Turbomeister saved me loads of work and provided a turn key solution. George 944t

 

[GPF]

ORIGINAL: TTM You can send Simon an e-mail and ask for his phone number : http://www.porscheclubgbforum.com/showprofile.asp?memid=6368 He has always been very helpful on the phone, the turbo he built for me is brilliant.

OK, thanks Thom - I thought he would be a vendor with a website etc. I'll drop him an email. Cheers

 

[TTM]

Pleased to say there is still some life in the headgasket, I did a 50 miles troublefree test drive today with no boost, which means I should be able to drive the car safely to Sly's workshop next month to replace the headgasket. Decided to go for original 2.7 headstuds and use an original 968 NA headgasket again. Will add a Lindsey steam vent, one should be plenty enough for my humble engine, thinking back about it now, assumng for a second that I might have the same hot spot issues as Corleone whose engine is perhaps 50% more powerful than mine was certainly a bit presomptuous from me [8|] Anyone have an idea where to find a fitting for original oil line couplers? I need one to add another original oil cooler.

 

[nick_968]

Try Think Automotive. They have a good online catalogue. They are also local to me so if you are stuck you could mail me the fitting you need and I could go there and get them to match it up.