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Unless you're doing the work yourself, it's arguable that tuning a 951 / 952 for significant & reliable performance by current standards (400+whp) is extortionately expensive & the money might be more constructively deployed towards a 996 / 997 GT3, M2 Comp or C63. We all know that modifying cars is the equivalent of fuelling your camp fire with $100 bills, but when a £600 remap can give your M2 Comp 510 bhp & with the BMW BBK it'll circulate the track all day & then comfortably get you home - you've got to question the whole 951 / 952 thing - I know I am - never again. I'd go more modern & get a modest remap & be driving it rather than constantly building it or fixing it.
I've tried to address the 952's weaknesses i.e. lack of a dry-sump, Alusil bores, open deck design, tiny old-fashioned high back pressure turbo, tiny cam, antiquated ECU - but I don't think it was worth it - I've wasted too much money on this thing - now I've got to own it for life.
Blade - I think going to whatever 911 turbo, GT3 or M-car fits your budget would be a wise move.
....and you haven't even driven it yet! Trouble is when you started it was probably a good idea but cars move on very fast! I still wouldn't swap mine for a 997 Turbo, I would swap it for a 997 GT3 though!
I think he found the crossover was restrictive at high boost levels, between 25 psi and 30 psi....I think others are using the standard crossover without issues at more normal boost levels, say 15 psi to 20 psi.
There doesn't seem to be any shortage of bare heads so aftermarket cams might be a possibility. Or just find a whole 968/ S2 engine and start with that.
There is no way I would go 3.0 8v again but that is just my personal experience.
I'd be very curious to see what kind of EBR others are seeing with various crossover and turbo hot sides sizes. I've seen upwards of ~1.7 EBR @1.0bar of boost depending on gear/conditions on my stock 2.5L 8V with a #6 hot side modified by Evergreen.
It's sort of a double edged sword b/c you want back pressure for spool, but you want to minimize it if you're after mega boost/power levels. Really depends what type of car/drivability you are after I suppose. With a properly calibrated ECU I don't think you will hurt anything running high back pressure with a stock crossover though. I bet the references to melted pistons in this thread are likely from not running a well setup knock control, and EFI control in general, rather than restrictive crossovers...
As a data point for reference here's a random 3rd - 4th gear pull @ 1.22bar from my car:
I know we act like it but WA's not a seperate country yet.
You need to get more creative with your shipping if your paying double, but yes I've spent a lot of money on shipping and GST/tariffs lately.
West Oz? Yeah, you guys are in a different country lol!
I mean we pay stupid amounts for anything down here. Look at the price of a 2nd hand Porsche and not the old ones that have escalated in price. Crazy! Look at even n/a 944's these days. Stupid money down here.
I'd be very curious to see what kind of EBR others are seeing with various crossover and turbo hot sides sizes. I've seen upwards of ~1.7 EBR @1.0bar of boost depending on gear/conditions on my stock 2.5L 8V with a #6 hot side modified by Evergreen.
It's sort of a double edged sword b/c you want back pressure for spool, but you want to minimize it if you're after mega boost/power levels. Really depends what type of car/drivability you are after I suppose. With a properly calibrated ECU I don't think you will hurt anything running high back pressure with a stock crossover though. I bet the references to melted pistons in this thread are likely from not running a well setup knock control, and EFI control in general, rather than restrictive crossovers...
As a data point for reference here's a random 3rd - 4th gear pull @ 1.22bar from my car:
1.5 to 1.7 is ok. The log shows 1.44 at full throttle and max rpm and at 1.2 bar that is actually pretty good for a kkk hotside. Move to a 3.0 though and the back pressure will go through the roof. Once it gets over a ratio of 2.0 the engine, although it can be mapped to be safe, will be fairly knock restricted. Far better to use a turbo that keeps things at 1.5 or lower. Excess back pressure is definitely an engine killer but when you say high back pressure I guess it depends what you call high. Personally I would like to aim for 1.5 or less especially on a 3.0 as the bigger the bores, the harder it is to get the head gasket to hold at higher boost levels so every little helps. Less back pressure also increases the knock threshold so you can run more timing and ultimately get more power at a given boost level. Another advantage of 16v over 8v is the combustion chamber is a more modern design which also helps with resistance to knock.
West Oz? Yeah, you guys are in a different country lol!
I mean we pay stupid amounts for anything down here. Look at the price of a 2nd hand Porsche and not the old ones that have escalated in price. Crazy! Look at even n/a 944's these days. Stupid money down here.
I feel your pain, the car prices over there are a nightmare!
Patrick do you know what turbo Sean runs on his 16v engines?
Nick, although they've been on a different journey, pushing limits of this platform, if you look at the expense & pain that Patrick & Gustaf have endured, surely there must have been times when they questioned whether it was worth persisting with this relatively underdeveloped and unsupported platform when there are easier alternatives. How much are you prepared to pay to be different?
While my car has been in build, I've pursued my love of the V12 engine & although I've owned a V12 BMW for 23 years I got into the quad cam (M120 - two C140's) & bi-turbo V12 (M275) Mercedes coupes (two C215's & one C216). While these are an entirely different type of car (although the M275 Mercs donated their gearbox to the 996 turbo & 997 turbo) the quality & performance are on another level.
I put Quaife diffs in all three Bi-turbos & had them remapped by Kleemann in Denmark to 650 bhp / 750 lb/ft. What is most impressive is the ABC suspension - no springs, just computer controlled hydraulic struts which provide a magic carpet ride with negligible roll or pitch - Mercedes at it best. When I contrast this with Gantspeed's struggles to build an enhanced 952 which should look like it was built by the factory - I realise I probably started with the wrong car. I don't think I'll have another four cylinder car - they just sound cheap.
Apologies if this has been so negative - but it probably explains why interest in this platform is declining & why 951 racers are migrating to more robust power plants.
Nick, although they've been on a different journey, pushing limits of this platform, if you look at the expense & pain that Patrick & Gustaf have endured, surely there must have been times when they questioned whether it was worth persisting with this relatively underdeveloped and unsupported platform when there are easier alternatives. How much are you prepared to pay to be different?
While my car has been in build, I've pursued my love of the V12 engine & although I've owned a V12 BMW for 23 years I got into the quad cam (M120 - two C140's) & bi-turbo V12 (M275) Mercedes coupes (two C215's & one C216). While these are an entirely different type of car (although the M275 Mercs donated their gearbox to the 996 turbo & 997 turbo) the quality & performance are on another level.
I put Quaife diffs in all three Bi-turbos & had them remapped by Kleemann in Denmark to 650 bhp / 750 lb/ft. What is most impressive is the ABC suspension - no springs, just computer controlled hydraulic struts which provide a magic carpet ride with negligible roll or pitch - Mercedes at it best. When I contrast this with Gantspeed's struggles to build an enhanced 952 which should look like it was built by the factory - I realise I probably started with the wrong car. I don't think I'll have another four cylinder car - they just sound cheap.
Apologies if this has been so negative - but it probably explains why interest in this platform is declining & why 951 racers are migrating to more robust power plants.
No need to apologise, we have all had our dark moments with these cars. I completely agree....why bother, but modifying cars rarely makes any sense no matter the platform. I think it is an illness we all share!
I think most of the hard work has been done though. The 16v cars I know of run very nicely and with great power at manageable boost levels with turbos such as the Garret Stage 5 or the GTX 3576 etc. Once you get into track cars it gets a little harder no doubt, but it can be done as Jet951 and others have shown. Plenty of reliable 3.0 8v cars (and 2.5's) out there too.
In my humble opinion, the real weakness comes when you are at the mercy of some of the so called specialists, who may or may not produce you a good build and install. No doubt there are some good ones out there but a bit like builders....how do you know, or is a good one about to turn bad. For me, in the end, it has to be a self build to be sure and if that takes longer then so be it. At least I know every little detail is right and every day you learn something knew.
I didn't watch the whole thing but both of these youtube videos are talking about post turbine back pressure. This would be like playing around with the side of your downpipe or going from a 2.5 inch exhaust to a 3 inch exhaust.
The back pressure issues we are discussing relate to pre turbine back pressure. This is a weak point on our cars, partly due to the crossover design and partly due to the more restrictive (compared to Garrett) kkk turbine housings. This is the real killer is once you get above a ratio of 2 times boost pressure you are getting into serious risk of detonation and the engine is also not efficient. The best analogy is like trying to blow through a straw. The build up in the crossover is immense if the turbine housing and/ or turbine wheel are too small. This is hugely more important when you step up in engine size and run out of bolt on housing options, people compromise, stick with bolt on (as I did) and then back pressure becomes the limiting factor on your engine. Hence why it is always worth measuring if possible to see if you are within safe levels.
Re exhausts, I've fitted near enough straight through systems on 2 turbo charged cars, and in both cases the car was more laggy. Less back pressure and velocity apparently. From memory, the original system on the old Sierra Cosworth was a twin system with 4 silencers and one 3" tail pipe. I fitted a big bore single pipe system from the turbo back, ending in 1 silencer with a 4" tailpipe, sounded good but onset of boost felt delayed. Similar on my 944 turbo, ditched the first silencer and fitted twin big bore straight through back boxes. It sounded like a tractor at low revs, and again onset of boost seemed delayed. The whistling of the turbo spooling up sounded great though. I fitted absorption type baffles that cut some of the noise and the car drives much better under 3k revs. Sounds a lot better than the Dansk I took off too.
Nick, I think some of the parts vendors for these cars are also quite variable in the quality of their offerings.
The differences between a LHD & RHD build shouldn't be underestimated when using aftermarket vendors.
I know that Robert Gant rejected some parts I had acquired as not fit for purpose & he refused to refit the existing M030 spindles & insisted that these should be new.
To be fair, this has been an entire mechanical restoration & upgrade - so everything should effectively be new or freshly rebuilt - but I'm never going to add up the invoices - it would depress me!
Among the parts he rejected were a camshaft, valve springs, spindles, steering rack, alternator, dry-sump pulleys, cylinder head oprv, Leda rear coilovers which didn't fit, obviously Wossner pistons & rods once we decided to build a 2.7 with Darton MID's, the smaller turbo's (GTX3071Gen I & Gen II) once it became obvious that with a short runner intake & the capacity increase we probably need a bigger hotside etc. He also rejected a carbon fibre replica 924 Turbo vented header panel as an appalling fit.
He unpicked all the spot welds in the header panel to make it removable as the engine had to be fitted & refitted between the mock-up and final assembly. He felt the entire car should be seam welded - but didn't want to go that far for what is fundamentally a road car designed for track days.
The Racewear main bearing studs didn't fit - it turns out these late ('90 & '91) 951 / 952's shared the main bearing bolt pitch thread with the 968.
I just have to think of this as a restoration first & an upgrade second and know that hopefully it should be good indefinitely.
1.5 to 1.7 is ok. The log shows 1.44 at full throttle and max rpm and at 1.2 bar that is actually pretty good for a kkk hotside. Move to a 3.0 though and the back pressure will go through the roof. Once it gets over a ratio of 2.0 the engine, although it can be mapped to be safe, will be fairly knock restricted. Far better to use a turbo that keeps things at 1.5 or lower. Excess back pressure is definitely an engine killer but when you say high back pressure I guess it depends what you call high. Personally I would like to aim for 1.5 or less especially on a 3.0 as the bigger the bores, the harder it is to get the head gasket to hold at higher boost levels so every little helps. Less back pressure also increases the knock threshold so you can run more timing and ultimately get more power at a given boost level. Another advantage of 16v over 8v is the combustion chamber is a more modern design which also helps with resistance to knock.
Yea I was fairly surprised to see the 1.4-1.7 range with a KKK hot side. I’d be curious to see what some of these higher level builds are achieving regarding back pressure, spool, boost, etc.
Oh these engines are definitely knock limited on pump gas regardless, but yes things can be done to raise the threshold for sure.
The 16V head is definitely a better design like you say and should help with knock resistance. However I imagine the primary advantage it has regarding combustion stability is related to combustion speed, bc I think it allows you to run less timing at equivalent power levels. The 8V combustion chamber design is so ancient and has such slow combustion that I think you are allowing so much more opportunity for knock to occur, and having to run more advanced timing, compared to say the 16V head, that you are knock limited at lower boost and power levels comparatively.
Of course you can mitigate a lot of that with alcohol fuels, but anyway I think it’s obvious to everyone that 16V is the way to go. I think it would be great to see some actual data with some of these new builds so people can learn more. Which I think was the original purpose of this thread. We unfortunately seem to see a lot of internet experts arguing (like the 8/10 pages from this thread) about what they think/heard/assume is correct, but little data to back anything up.
I just have to think of this as a restoration first & an upgrade second and know that hopefully it should be good indefinitely.
If you look at the quality and attention to detail someone like Kongsodoken applied during their restoration, it makes a mockery of those Porsche dealer restos, and the prices asked for them. Unless it has been gone through top to bottom properly, or has really low mileage, no road car 944 turbo is worth over £35k IMO.
We unfortunately seem to see a lot of internet experts arguing (like the 8/10 pages from this thread) about what they think/heard/assume is correct, but little data to back anything up.
05-16-2023, 05:04 PM
