Engine build progress
- Thread starter TTM
- Start date
My understanding is different. You are right when you say it is heat that drives the turbo but to increase spool up you retard the timing and in doing so increase the Exhaust Gas Temperature. If you just lean out the mixture or lean it out too much as the turbo is coming on boost you risk inducing knock as spoolup is the most sensitive time for knock to occur. Generally speaking it is advancing or retarding the timing that is used to control the onset of boost via tuning. Advanced to reduce spoolup as more advance reduces EGT's and retarded to increase spoolup as this increases EGT's.
sawood12
New member
Yes, the mass flow rate must remain largely constant, it is the speed and pressure that varies.
I think both ways work don't they? The downside to leaning out the mixture is increased risk of knock and the downside to retarding ignition is that although it increases turbo spool up you get reduced power out of the engine while it is doing it. I guess it depends on the trade off between how quickly you can spin up the turbo and/or which method is easier to achieve with regards to tuning. Maybe certain setups and engines respond better to specific methods. I've seen the AFR method used on some of the cars at the Weltmiester rolling road days.
Both ways dont work for increasing spoolup. Leaning out will increase power, but in theory prior to boost coming on you should be running at the optimum lean point anyway if tuned correctly so you shouldnt really have far to go safely. So leaning out will not improve spoolup significantly as this doesnt increase temps enough within safety margins. The other reason its the wrong way to go is because you get far better results if you richen the mixture at boost onset to maximise the charge and leave unburnt fuel to ignite in the manifold further increasing heat to drive the turbo. You can just richen the mixture, or just retard the timing, or a bit of both, only trial and error will determine the best results. This is the way all anti lag systems work albeit in a more extreme fashion with very late ignition something like 45 degrees ATDC burning hardly any fuel in the cylinder, instead most of it ignites in the manifold driving the turbo. This method is not recommended for your average turbo car though as it will kill the turbo and other components pretty fast! However all of this theory is good, but unless you have an oversized turbo and really need to punch it to get it going you just tune it as per normal as there is no point in making a turbo that is working fine work harder and producing more heat just for the sake of a hundred or so rpm. Also, advancing the timing and richening the mixture can often make the engine feel worse even though you get quicker spool compared to an engine running the optimum fuel and advance for power. In the end a good tuner will be able to balance all this out for the optimum result which will usually be somewhere in between.
TTM
Well-known member
MOT'd my car today; zero mentions. The CO level was joked as being "too low" [
] Had an interesting long chat with the chap, who owns a Sierra Cosworth 4X4, a Fiesta with a 1.6T putting down 280bhp, a 924CGT and a pair of Renault 5 Alpine Turbo. A gentleman with taste I would say [] My car still drives like nuts at only 15psi, awaiting delivery of SFR front mount IC with which I plan to safely up the boost to eventually give this brilliant SPS turbo the ability to perform like it should [][] Sly's 2.5 rebuild about complete, should wake up again in a couple of days, back with a vengeance and a few optimised details [][][]
] Had an interesting long chat with the chap, who owns a Sierra Cosworth 4X4, a Fiesta with a 1.6T putting down 280bhp, a 924CGT and a pair of Renault 5 Alpine Turbo. A gentleman with taste I would say [] My car still drives like nuts at only 15psi, awaiting delivery of SFR front mount IC with which I plan to safely up the boost to eventually give this brilliant SPS turbo the ability to perform like it should [][] Sly's 2.5 rebuild about complete, should wake up again in a couple of days, back with a vengeance and a few optimised details [][][]
TTM
Well-known member
Hi Paul, Yes, I did a lot of reading on Rennlist about this intercooler, and from all the pictures I could find it seems the main problem is caused by the two "charge pipes" that come in 2.5", as they seem to require machining the front cross brace holding the bumper. I ordered the intercooler with intercooler pipes in 2.25", which is about the same size as the original intercooler pipes. They can be ordered in 2.5" but from the measurements I took on the car it seems any size bigger than the original pipes won't clear the bar raising the pop ups. Tim at SFR then said to me he could provide 2.25" tubing all the way, for both the intercooler pipes and the "charge pipes", so that makes me hope I shouldn't need to machine the front cross brace. Will see! To be honest I doubt this intercooler will perform much better, if any, than the original, which everybody I have talked to tell me it is of a very good design and can hardly be bettered if running less than 18psi. The main reason to replace the IC is to get it further away from the engine to avoid heat soak. In a perfect world the 951 would have an extractor in the hood like the 968TRS but with the fussy hood latch mecanism I don't see anything easily doable on this point without modifying the shell, and anyway I'd rather retain the clean look of our car and I don't feel like making holes here and there to improve the mechanical side of things. I don't have any device to measure the temp - are you refering to a particular "kit"?
TTM
Well-known member
Sly's engine complete. What's new since the previous build : - Pauter rods - pistons rings - upgraded fuel pump - Tial 38mm wastegate plugged in dual port - SFR MAF pipe with K&N cone filter, we will see how well/bad a K&N cone filters. - Lindsey Racing intercooler pipes - Oil catch can - Cruise control Sure thing already is that the engine is more responsive off boost than with the airbox.
Thom, one of the reasons the factory IC works so well is because it has its own dedicated ducting enabling airflow to be directly forced through the core. I am not sure but I assume the SFR unit will be standing in free air with no ducting and possibly in front of the radiator? It is very important to get proper ducting to the IC with a smaller entry point than where it meets the face of the IC for a charge air effect and to stop the air from turning around and going back out the duct. It is also important to make sure that the IC is big enough on the cross section of the core so that it provides enough airflow through the inside for the charge air and does not act as a restriction. This is a calculation based on the area of the tubes available for the air to flow through. With the SFR IC being only 8 inches high it is a little low in terms of the flow requirement for your engine at say 400hp according to the textbook. However in the real world it will probably be ok just not quite flowing as well as it could. With the speed your turbo spools up it prob wont effect spool much but it may have to work a little harder (hotter) to make the same boost as with a less restrictive core. It will be interesting to see the real world results though, be sure to log before and after intake temps at given boost levels to see if you are better of worse off with no other changes.
TTM
Well-known member
Thanks for that Nick, I'm replying now as I saw yours posts on RL in the 968 supercharger thread. I checked the SFR IC cross section before ordering, it has about 10% more than the standard IC so this should be good. With regards to spool I have disabled the boost controller for now, meaning the turbo is working only against the wastegate spring at the moment, as I have found pointless to put unnecessary boost load on the engine at low revs when it's not in the rev range where it naturally makes most of its torque (which seems to be a bit around 4000rpm, and the turbo seems to blow most of it lungs out at about 4200rpm). I was advised that building boost "too soon" would greatly increase intake temp, not good, but I will have lots of extra spool left in the boost solenoid if I need to when I install the SFR IC. Interesting comment on the IC only needing 1/3 of its frontal area for its air intake duct. I guess that's why the original IC works so well, and I was sort of concerned how to bring fresh air to the whole frontal area of the SFR IC which will be "hidden" behind the front bumper. Now If I only need to duct 1/3 of its frontal area somewhere through the bumper then it should perform well, if I understand you correctly? Is the 1/3 rule universal? I have the feeling it might vary with the thickenss of the core? If so, and as the SFR core is less thick than the original unit, perhaps I will need more ducting than 1/3 of the frontal area? Did 600 miles last week with the car, the engine is feeling freeer the more I drive it. It's getting worrying at 120+mph though as the rear end squats so much when I floor the throttle that my new set of rear S02 feel on the limit of traction. One great thing though about the 3.0 is that it's sooooooooooo much more flexible that the 2.5. Even when boosting it at only 10psi it takes off so effortlessly on a subtle but vigorous wave of torque that I hardly ever feel the need to floor it at those speeds. I LOVE it so hard it's almost embarassing.[] Sly has done 500miles since the rebuild, engine feels more responsive at low revs and less exhilirating than before, certainly caused by having ditched the airbox - less restriction, more linear torque delivery.
] Sly has done 500miles since the rebuild, engine feels more responsive at low revs and less exhilirating than before, certainly caused by having ditched the airbox - less restriction, more linear torque delivery.
DivineE
New member
Tell me about it! That's one thing I will always miss about my 3.2, it was effortlessly easy to make progress. With a big turbo 2.5 you have to adapt your driving to the car and work at it to get it to go fast, which is quite rewarding sometimes but stressful when your not in the mood! In a 3ltr 944 the car is fast no matter how you drive it. Interesting stuff on the intercooler and turbo, the two discussions are very closely linked. Nick's suggestion is spot on with what I've read, the reason stated as to why its so important to have sealed ducting and an inlet approx 30% the frontal area of the intercooler is because passing the air through the intercooler creates a restriction, the volume of air that is able to flow through that size vent is just about right to continue on through the larger area of the intercooler. If you have more, the air starts to back up, slow down and heat up forcing air round the edges and creating an area of higher pressure, slower moving air around the intercooler. I'm not sure I see the turbo theory the same way as you though Scott. Same stuff, just a different understanding that I can't get my head round. Obviously with the variable vane turbos altering the angle at low speeds to create more restriction, more pressure and thus spin the turbo faster with less flow of air makes sense. Then you reduce the angle of the blades at higher rpm when there is more airflow to reduce restriction and keep the desired level of pressure constant. What I don't understand is that everything I've read leads me to believe that its the pressure pulses of the air from the combustion that hits the blades and has the greatest effect of spinning a turbo. So its the pressure created by the restriction of the blades causing the trapped volume of air to slow and not the temperature that drives the turbo. I thought temperature was more the bi product? i.e. if you've got more temperature you must have more pressure?ORIGINAL: TTM One great thing though about the 3.0 is that it's sooooooooooo much more flexible that the 2.5. Even when boosting it at only 10psi it takes off so effortlessly on a subtle but vigorous wave of torque that I hardly ever feel the need to floor it at those speeds. I LOVE it so hard it's almost embarassing.[
sawood12
New member
Pressure drives turbines - temperature is the way to achieve pressure. The torque comes from the pressure drip across the turbine stage. All engines work by extracting heat out of the fuel to generate high pressure that can then be used to do useful work e.g. push down on a piston, force high pressure gas through a turbine nozzle to turn a shaft or even dump to atmosphere via a nozzle like a rocket/turbojet engine. Pressure pulses and turbines are not good bedfellows. They want nice laminar constant speed gasflow. Pulses create shocks, and the speed of the gasflow dictates the angle the rotor vanes should be, so if you have a pulsing gasflow you ideally want the rotor vanes to change angle to ensure you don't stall the vanes, generate losses and lose efficiency. The vanes ahead of the rotating turbine (in the 997 turbo VGV turbo - normal turbo's don't have vanes ahead of the rotor) is primarily there to sort the gas flow out from a pulsing, turbulent stream of varying pressure into a smooth, constant speed stream to be presented to the rotor to extract maximum work out of the gas flow - as well as to change angle and generate drive at different gas flow speeds over the entire rev range - think of it as effectively gearing the turbo relative to the exhaust flow. Regarding IC's - a good example is the radiator arrangement on a Lotus Elise. Here you'll see the intake area is much much smaller than the exit area. This is effectively what you've got with the 944T - the single slot feeding the IC and the area of the IC is dumping the warmed air into the engine bay through a much larger area. By presenting more airflow to the IC you are not improving its efficiency (unless it was pretty poor before) and in fact you could be hampering its efficiency. You shouldn't show it more air than it can extract or you'll get a bow wave effect in front of the IC which can cause turbulence ahead of the IC or even cause a back-pressure forcing air away from the IC thereby reducing the flow through the IC. The best IC arrangement i've seen was on a 968 turbo on Rennlist where the IC was mounted horizontally with the intake air being fed underneath the IC and the extraction occurring through bonnet vents. You need to spend as much time on the extraction of the air as you do the intake. It is difficult when you've got a dirty great lump of an engine sat right behind the IC though.
DivineE
New member
I have no idea how big the window for suitable intercooler through flow is on the 944 but WUF with her 924 badge panel vents was showing a fantastic temperature drop on the pre to aft temperature sensors at anything over about 40mph which is encouraging. I might take something that smokes I lot and burns slowly (like a flare maybe?) to the dyno with me when I go. Have a look with the bonnet closed and open how the air enters the vents to the intercooler when the cooling fan is at full power in front of the car. See if it flows through freely or looks like its backing up.
sawood12
New member
I seem to remember that WUF sports a Lindsay Racing Stage 3 IC so stands to reason that you'd need more flow through the IC if it has a modified core. I guess that the air in the engine bay is extracted through the holes in the undertray? Not sure that the weedy fan put in front of the car during a rolliing road session will in anyway simulate the actual airflow when the car is in motion. One modification i'd imagined was to tilt the IC forward by 45 degrees and make some ducting (somehow) that extract the air up and out of bonnet vents. I think there is room if an IC of the size of a standard one is used and the front member is removed and replaced by something that allows better airflow through it. I think that having the air venting out of the bonnet you'll get a venturi effect and the air will actually be sucked through the IC from the airflow over the bonnet and hugely increase its flow. Similarly for the engine cooling system I'd imagined a split radiator system comprising two smaller rads mounted in the corners behind the PU and angled so the airflow comes in through the front slats, turned through 45 degrees outwards, and vents out of the side of the PU just in front of the front wheels through shark gill style vents. This is sort of similar to the Boxster arrangement. This would leave a space in the middle for power steering cooler, A/C rad and oil cooler. I'm always full of good ideas, whether or not they'd work in reality is another thing.
DivineE
New member
I think Scott you'll be pleased to know that all of those things are being done at the moment - so we'll see. The LR intercooler uses the same core but different end tanks to flow better and even out the flow of air through the cores (or so they say I bought a much bigger intercooler and had some new pipework made up to allow me to run a front mounted intercooler (I still have it all sitting in this room) but I've recently come to the conclusion that the standard design and set-up (especially when you look at the detail they've gone into to maximise its efficiency.. well it's pretty good. Amazingly the air in the intake manifold was usually reading slightly lower than the ambient air temperature outside, even when it was leaving the turbo at over 100*c. If it'll flow enough for over 400hp (as my old 3.2 achieved on a totally standard intercooler), and take all the heat out of the air from the compressor who really needs more? This is just my personal opinion obviously, and lets face it a big front mounted intercooler just visible through the front also looks good[]
I bought a much bigger intercooler and had some new pipework made up to allow me to run a front mounted intercooler (I still have it all sitting in this room) but I've recently come to the conclusion that the standard design and set-up (especially when you look at the detail they've gone into to maximise its efficiency.. well it's pretty good. Amazingly the air in the intake manifold was usually reading slightly lower than the ambient air temperature outside, even when it was leaving the turbo at over 100*c. If it'll flow enough for over 400hp (as my old 3.2 achieved on a totally standard intercooler), and take all the heat out of the air from the compressor who really needs more? This is just my personal opinion obviously, and lets face it a big front mounted intercooler just visible through the front also looks good[]
TTM
Well-known member
Interesting feedback Ben... It would annoy me much not to see any improvement when fitting a front mount IC over the standard unit. I would have guessed the standard unit on your ex car would at least be subjected to serious heat soak on the dyno (which is what Paul reported earlier on his 3.2), or for any sort of track duties? The stock unit works well, yes, but is it going to be that much efficient anywhere else than at constant high speeds, which is where there is enough flow to avoid heat soak? Dyno sessions and track work may tell a different story? (I know, I sound like the chap who wants to protect his investment... )
DivineE
New member
No absolutely fair point. I haven't yet tested it on a track so have no data (soon to be corrected), maybe Rick will know as I think he's done some track days in the car since all the sensors were fitted. Heat soak on a dyno would be massive, when sitting in traffic in Rouen the temperature was up to 55*c with zero intercooler efficiency within 90seconds and not much better rolling around at up to 20mph. The in/out readings on the intercooler were virtually identical under 20mph. Considering after a few full boost moments on the motorway the air from the turbo going into the intercooler got as hot as 120*c (I don't think its the most efficient turbo) if you were on a dyno I would think the engine must be breathing 100*c air after 2-3runs. I wonder how much more power the cars really have on the road when the intake manifold is reading 11*c like my drive here in the UK? Food for thought.
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