3.0 16V engine mods, etc

[Thom]

Well, I was initially kind of bummed as everybody said that a 16v setup would always run cooler than an 8V with lower EGTs but I suppose there are engines and engines and after advancing ign timing to the max it did help but I'm too close to the knock threshold to make any more gains. This is a street car and with the current level of performance there will probably never be enough room to keep EGTs high enough to cause any damage, even with sustained high load runs on the Autobahn. The 8V engine in comparison turned into a heat pump quite quickly at high speeds in top gear and I saw 1050°C several times with the previous GTX3076R, but it was absolutely fine when I took it off to replace it with the GTX3576R. If Porsche put the turbo that far away from the head there must be a reason - such huge cylinders are probably always going to generate more heat than smaller ones, and we probably just have to live with that design feature.

[gruhsy]

I am very curious what your back pressure reading would be with your turbo as it is relatively newer.
My LR Super 75 with a . 58 AR was 20 psi at 18lbs boost.
Your turbo must be better than that as it’s much more modern in comparison.
I was running a dump to atmosphere waste gate.
If I remember correctly you also had a super 75 on your 2V 3.0L yes?

[Thom]

I measured back pressure with the GTX3076R on the 3L 8V after upgrading from a Garrett/KKK Hybrid and the difference in how the engine was eager to rev was almost like and night and day. The ratio was like yours, like 20psi to 18psi of boost and pretty stable up to 7k rpm. With the 16V engine the turbo holds boost all the way up, and as the engine wants to rev beyond 7k rpm in a way the 8V never did I doubt that back pressure is reaching a level high enough to justify upsizing the hotside, though I concede than being sure would be better than assuming.

A friend runs a LR75/8 on his 2.5 8V, not me. Backpressure must have been brutal though as he ended up breaking the temp sensor in the cross over port which went through the turbine wheel.

[SirLapsalot]

They have always been liked that. They are just a little higher now when cruising than with the previous engine, but under load they actually climb up less quickly than with the 8V engine that was running at 18 psi. There is nothing to be done, and believe me, I have tried. That's just where they are with the probe in the cross over port.

Yes that turbo is proving great now that it can run in its comfort zone with pressures like 23 psi rather than 18 psi on the 8V engine. On that log it even spikes to 27 psi when reopening the throttle whilst entering 4th gear. I will try again to turn up the boost, not that the engine needs it but for the sake of science.

Yea I saw that spike there. Logging rate is slow but the WG control looks a little bit goofy. Transients like that on the road are a bit more difficult to calibrate but you could definitely clean that up with some PID work. I had my closed loop boost control dialed near perfect on the dyno, then as soon as I hit the road I had to make a lot more changes than I expected ( I had overshoot like you show there at first). Good learning experience not to waste so much time and effort trying to calibrate something to perfection on the dyno when it will most certainly need messaged on the road!

Well, I was initially kind of bummed as everybody said that a 16v setup would always run cooler than an 8V with lower EGTs but I suppose there are engines and engines and after advancing ign timing to the max it did help but I'm too close to the knock threshold to make any more gains. This is a street car and with the current level of performance there will probably never be enough room to keep EGTs high enough to cause any damage, even with sustained high load runs on the Autobahn. The 8V engine in comparison turned into a heat pump quite quickly at high speeds in top gear and I saw 1050°C several times with the previous GTX3076R, but it was absolutely fine when I took it off to replace it with the GTX3576R. If Porsche put the turbo that far away from the head there must be a reason - such huge cylinders are probably always going to generate more heat than smaller ones, and we probably just have to live with that design feature.

Agreed, for sure some design features we just have to live with. However there’s a number of things you could try over and above just advancing the timing to reduce those EGTs. Unfortunately just about all of them require some decent amount of time/effort/money. Since you’re not worried about the temps on the street then probably not with going down those rabbit holes I suppose!

[Thom]

Many other folks experience high EGTs on these cars and the previous engine ran 70k miles like that without suffering from it so I do not think there is anything to worry about. Perhaps it is just the sensor/calibration giving false readings still after checking, or as I said perhaps it is just the nature of these engines, how they are designed, etc. The way EGT in/decreases is probably more significant than the absolute values, and I cannot see anything wrong there.

I am pretty confident that the very responsive turbo combined with a small-ish Tial MVS wastegate are why I cannot get a perfectly controlled boost response by adjusting PIDs, but this is also what makes the car such a responsive and exhilirating drive together with a super strong mid range above 4k rpm, which makes revving the engine much if at all above 6k rpm slightly redundant, to be honest. If anything I find myself instinctively changing to the next gear if only to avoid the urgent build up of momentum which could make me lose traction and the control of the car, and at 100 mph at half load in 6th the bull keeps pulling. Losing any of this response together with that mid range raw beef in order to improve the efficency of the boost controller with smooth curves in the logs does not make much sense to me at this point, and I do not think this would be reachable with the current hardware but I will keep trying. At this stage I see little point in trying a larger turbo and larger wastegate as the balance between fun and efficiency seems IMO very difficult to improve on.

With that engine the car has finally lost all of this slightly numb and frustrating trait that pushes us all into modifying them and with all that performance and liveliness available on tap I have never felt a better connection with the road. The car has never felt that much compact, light and nimble, and the 3L 8V engine was in retrospect an appetiser.
If only this experience could be shared with log files, just to give an idea of how it runs, of that fantastic urge and eagerness to rev... Or maybe not, as the beauty of it is that it should just be experienced. Apologies if this all sounds a little corny but as my friend said when he drove the car it's just a whole new world, at least in our experience modding these cars. That friend had strong doubts about it, and just to give some backgroud he gave up his white collar position to become an independent Porsche specialist and now runs his own business. He has been doing this for 10 years and is now mostly blasé with most car topics but driving my car is the only thing that got him to dust off all the 16V engine spares he had bought 15 years ago to finally build his own. I think that is pretty telling about how my car runs and drives now.

PS : posting this perhaps a little over enthusiastically after a 2.5 hr very early morning drive in very cold and dry weather. The natural pace is at the very least 50% over the speed limit, and even on rather wide secondary empty roads it is as involving as running on a tight rope.

[Jay Wellwood]

Thom...do I recall correctly that you're using a Link 4 ECU?

[Thom]

Jay, it is a Vipec V44, very similar to a Link G4 Storm.

[Thom]

Another quick note on the car's dynamics, though that may be obvious to folks driving full race cars or heavily modified track cars.
About 12+years ago, still in the period of pushing the envelope on the 3L 8V engine, I replaced the stock intercooler with an SFR stage 2 FMIC and noticed right away that the steering got a little heavier, obviously as a result to adding weight over the front overhang. It was not "bad" per se but it was a little let down as I really enjoyed the stock weighting of the steering with all of the stock hardware, especially 16" wheels and M030 brakes. This negative change to the steering feel delayed very much the move to 17" wheels that came several years later and the upgrade to big blacks which I could never really justify with the 8V engine as the performance got pretty good at the end but not enough to justify adding further weight to the steering feel by increasing unsprung weight with bigger brakes.

The custom intercooler which has replaced the SFR Stage 2, despite being closer to the front axle, is yet a little heavier and has therefore made for a yet little heavier steering feel (along with the big blacks) however it has also allowed such a dramatic improvement in performance and response that already under medium engine load the steering lightens up just enough to offer the right amount of feedback needed to keep the car going where we want without having to focus on it. Put differently, all driver inputs have remained to this point as remarkably balanced as on a stock car. There is no "elephant in the room" in the way the car sends various signals and talks to the driver and I believe this is a significant matter in the streetability or user-friendliness of a high performance car and the unconscious will to use it for any reason, if that makes sense. The performance can be huge when required but the envelope that houses it has all remained very compliant.

[Thom]

I recently went back to open loop boost control as I find the car more fun with a slightly overwhelming rush of torque that I have not been able to replicate quite exactly by adjusting PID values with throttle-based boost control. Just for giggles I turned the boost up from 23 to 26 psi. Things do process quite quickly then especially with spikes to near 30 psi and although the Michelins are definitely having a hard time the car still goes about straight in 3rd gear interestingly, but some signs suggest that such boost levels are what it takes for a stock 968 top end to beat the brilliant GTX3576R - more on this later.

Despite running that much boost with used S2 studs torqued to stock spec the overflow hose has remained dry all along - closed deck block FTW.

[333pg333]

That's amazing Thom. 30psi on stock studs and not a drop escaping! Closed decks do seem to be a good idea. But they need to be done correctly. Sounds like yours was. Must be stupidly fast at that psi! Really must shock quite a few Supercar owners!!