Vilhuer

Don't tell me we have to build more complex fuel delivery for Niklas. It sounded so good.

ptuomov

We're exploring engine oil spray to the floor, but so far no success.

We've got the computers under control, so it's easier for us. The custom wider maps from JDS help.

If one is building a turbo 928, the '87 S4 is by far the best starting point. combustion chamber shape and the compression ratio are the most favorable.

If you guys want to buy a couple of Fuelab Prodigy pumps and/or EFPR, I'll sell mine... caveat emptor, neither John nor me got that setup to work.

Here's the curret setup, which is keeping it simple stupid, but appears to be very reliable. The second pump comes only at >5psi and >4000rpm:




The car cooled down and is now doing 703 Dynapack hp at the axle with the old boost profiles.

Next up is more boost.

I think Todd Tremel's pump gas record is something like 722 rwhp (https://rennlist.com/forums/9927441-post121.html), so let's see if that record breaks before the engine breaks.

Lizard928

Tuomo,

What went wrong with the fuelab pump/FPR?

What model of pump do you have again? I may be interested......

BC

Tell me more. They also have PWM fuel pressure regulators.

BC

Think higher.

BC

So am I!

I know its just a proper control from a real ECU.

blau928

Tuomo,

Great job on your car. It's terriffic!

I would like to know if I can contact you in future about your datalogs to understand what you are observing during the tuning of your motor.

Keep up the great work!

ptuomov

I don't know. Fuelab tested both 42401 pump units and the 52901 electronic regulator. They work fine in their test bench. On a car they are fine, except about an hour into a dyno session there are localized temperature or control problems. The global fuel temperature is low (at about 75F in tank), the tank is 3/4 full, and the pickup is not a restriction. I've been troubleshooting this with Fuelab for a while, and it's some sort of interaction between the way I've run my pipes, the pump, and the control signal from the EFPR. We eliminated every obvious source of problems and after that didn't help John quickly fabbed a pickup for a dual bosch setup.

On other news, we hit another wall in terms of the boost control. We can't accurately control the internal wastegate above 20 psi with the exhaust flow and pressure that we see. So we failed again, this time at 711 SAE hp at the rear axle:





Also see:
As you can see from the graph, there would be plenty of room to give the motor more boost above 6000 rpm, but just couldn't get it to give a precise boost control high up there. We should be at minimum able to extend the torque curve at the 650 ft-lb level all the way to 6700 rpm, instead of letting it fall of the cliff with the stock cams.

Back to the drawing board... The stock engine wins again.

ptuomov

Absolutely. There's a lot electronic data as well as observation notes. The exhaust back pressure data is recorded by hand from a mechanical gauge. Turbo speed sensor max is from the memory recall function. The fuel temp and intercooler temp are with IR gun. The boost pressure is static pressure only and therefore underestimates the total pressure. Definitely not the type of instrumentation that some of the sensor-**** Rennlisters have at their dynos, but we're not letting the best be the worst enemy of good here and take notes wherever we can.

blau928

Hi Tuomo,

Thanks very much for the offer!! I will certainly take you up on it, as I definitely want to understand what the motor is doing with relation to IAT, CLT, Boost (more Mass flow than boost, as the pressure could be higher with less flow in many situations, and I don't know what my system will flow like under test conditions..) Spark, Fuel temp and pressure, Cam and crank position, and a bunch of stuff that makes no sense to anyone but an nut lke myself!!

BTW, I had spoken to John about a "twin charged" motor... All I would need is his "hot side parts" as everything else on by system will work with that.. A stock motor would surely die at higher levels, but it would make for a really interesting experiment....!

ptuomov

John's hot side components are certainly worth more than the price.

"Surely die?" I haven't been able to find the limits of the stock motor in terms of what power it can handle. All the things that have been giving me trouble were (a) made after the 1980's and (b) by someone else than Porsche. Nothing that came from the factory is breaking at 711 axle hp on a dyno so far.

Here's a theory question: What kind of quantitative benefits do you expect from adding a supercharger to a turbo system? The turbo alone is making 400 ft-lb of torque at 3000 rpm and 650 ft-lb at 4000 rpm. At above 4000 rpm, it's nearly impossible to have the turbos not spooled, so there's no measurable lag. So in which way will the twin charged system improve on a pure turbo system?

TexasDude74

Compound system advantages are throttle response and long term durability due to the fact that neither the supercharger or the turbo have to be spun at max rpm. They were once fairly common in the performance diesel world, but turbo advancements have reduced their benefit. You still see compound setups in the exotic tuner world sometimes, for the throttle response.

blau928

Hi Tuomo,

I say "surely die", as there will come the point when the maximum cylinder pressure will increase to the point that the head gasket will deform.

It is out there even if there is no detonation. I don't know what that cylinder pressure is for a 928 motor, as I don't have one hooked up to a piezo pressure sensor, but I do know it is there, as the engines do blow from the detonation pressure spike.

I also know that if a cylinder pressure is 185psi and you add 30 psi you are only raising the pressure 16%, not including effects of cam and dynamic activities on pressure, so you can in effect triple the power output and only place 30% more load on the components. (This is what you are doing so well in your car, and I again think it is great as you are controlling the detonation very well. (711 at the tires is excellent in a docile looking 87 S4..!) BTW, I spoke to Mahle years ago, and they made a +2 oversize 101mm bore piston for the 944S2 with a thicker #1 ring land (same size as the 944T), and Powerhaus in AZ used them to make 500 RWHP on a turbo 944S2 (exactly 1/2 a 928 motor with similar rods) So, theoretically a 1000 RWHP 928 is possible if the detonation is kept at bay..) I am still trying to track down these pistons in a matched group set of 8, but they may no longer be available....

I also very much agree with you on JK's stuff. Years ago when he first designed the setup, I discussed buying just his hotside parts, and it was a very good deal. I may have gone for an external wastegate, as I think the control is better at the higher end of the pressure spectrum. (but that's just me)

What a twin charged system does is up the pressure ratio of the charge. I don't have the spec sheet of the Garrett's you are using in front of me, but if they are 1.3 and the SC is 1.4 then the overall pressure ratio will go to 1.3 x 1.4 or 1.82. In addition, the total area under the power curve will grow, and the torque table will be flatter. (that is the cliff note version, I can do an in depth write, but I think you understand the pressure ratio aspect)

Instead of a ramp up at 2k rpm, there will be a table from 2k-6.5k or higher. If the turbos are sized larger than the SC, then the SC will also give back the crankshaft power used to drive it, as the turbos will pressure feed the SC...

Hope that explains it....

Best Regards,

blau928

Hi Tuomo,

I found this chart I posted here years ago.. It is from a 4.6L Ford Cobra that was supercharged and measured on a Dynojet, so it is in Dynojet units..

My insanity for looking at the twin charged situation is to have the earlier part of the curve "table" left of 3500 RPM be filled in twith the SC, and the area to the right by the turbos..

It should overlay on your chart and fill in the area to the left, so that total area under the curve, or line is what the engine is delivering.... That's the theory.. I have never built a twin charged motor yet...

Best Regards,

ptuomov

I can see the point of twin charging with a 1.8 liter Lancia run at 30 psi of boost and 450+ hp. But it doesn't really make sense on a 5.0L V8. It's completely gratuitous -- and that's why I love it! The answer is "Because I can." ;-)

I am at pressure ratio of about 2.5 at this point, but only at high rpms where the natural volumetric efficiency has already dropped. At the natural peak volumetric efficiency rpm, the pressure ratio has to be kept under 2.

In terms of the cylinder pressures, I am not sure I follow your math. I know that the peak cylinder pressure doesn't scale linearly with the pressure ratio. But the mean pressure has to scale about linearly, and the peak pressure probably also has to increase by much more than just the boost pressure.

I almost bought a pressure logging system from TFX, but didn't pull the trigger as I didn't know if I'd have the time to install it. The system is too expensive to just sit inside a box for months or years.