Basal Skull

been re-reading TB993tt and fc-racer's posts on this tread.
I have a FVD ECU and also notice a surge in power to about 4000-4500 rpms, feel a little dip, then power rebuilding/increase in acceleration from about 5000 and up until redline/rev limit.
If the ecu is pulling timing/activating wastegates at 4000 rpm d/t knock/high boost (with standard turbos/standard boost levels), why do you get more power with larger turbos and more boost - why is there no knocking and ecu pulling timing etc. and limiting power with larger turbos?
May be I just don't understand turbos/engines enough...?

Basal Skull

sorry thread I am refering to
https://rennlist.com/forums/showthre...ferrerid=28499

Kevin

What turbochargers are you running? What octane are you running in BC?

K24madness

Please attach a boost gauge and tell me what is does then I can help you. I have several way I can suggest to work around the poorly controlled factory manner of boost control. I can't suggest a solution until I know what your boost is doing.

K24madness

Some things to consider.

Larger compressor, properly sized = less intake charge heat.
Less intake charge heat = less detonation

Larger turbine & AR =less revesion
Less reversion= less detonation

Better boost control = less boost spikes
less boost spikes = less detonation

This applies to ANY turbocharged motor regardless of fuel used. FWIW I blend in race gas for a added measure of safety.

CP

To answer your original questions: why larger turbos, and higher boost yield more power? In a nut shell: more fuel in the combustion chamber.

The fact is, more fuel (burned properly) means more power. Since the engine displacement is fixed at 3.6L, the way to get more fuel to burn is to squeeze more air (read oxygen) into the chamber for combustion needs. Bigger turbo and higher boost squeeze more air into the combustion chamber.

Obviousely this is the simplistic explanation. The proper execution requires the proper tuning of the ECU, the fuel injectors, the boost control, engine cooling, (more power= more heat), and down stream air flow, as the more air you squeeze in up front, the more air must flow out after combustion. So it is a very complicated tuning art, more so than just up the turbo size and boost pressure.

If I'm wrong I'm sure other turbo gurus will jump in and make it right.

CP

K24madness

You nailed it CP. This is why the K24's work so well. They are sooooo much more free flowing on the exhaust side than any K16 based turbo could ever be.

Basal Skull

I guess K24's second post answers some of it. I will also video what the boost guage is doing next time I am 'pushing' it.
I understand about getting more fuel/air into a given displacement. I was wondering if timing is being pulled already with stock turbos, this implies to me that the motor is reached some sort of limit and adding more boost (fuel/air with larger turbos) wouldn't improve on this?
My turbo's are stock, 94 octane gas (r+m/2 I think), FVD ecu for stock turbos/'premium' gas.

K24madness

Here is what we do. You show me the boost video and I will tell you expected compressor outlet temps of your turbos. Then I will show you expected compressor outlet temps of another compressor option. It is this temp difference that will largely dictate the density difference between the two turbos.

Lower temps= denser air
denser air+ more fuel = more power.
colder air makes the car more restant to detonation.

Your car would benifit from larger turbos with your current program. You have several options available to you.

Kevin

Well, in stock form the K16's will struggle to run at your 1bar ECU settings consistantly. If you jump under your car and adjust the wastegates 2mm+2 turns you will improve the bump or transition that you feel.

Basal Skull

Kevin, so my waste gates may be opening prematurely/K16's struggling to maintain boost rather then timing being pulled?
I've read your previous posts on waste gate adjustement - so 2mm or 2 turns clockwise/shortening the rod may help?

I think I'm starting to understand - larger/more efficient turbos = lower temps = more power (not just shoving more air/fuel in at higher pressures).

K24madness

It is a bad idea to adjust the wastegates in this manner. You must pressurize the accuators and measure movement. This is how the ECU opens them. This is how the factory adjusts them. You must be sure that they are in sync. If not one turbo will be working harder than the other and be subject to failure.

This is true. If slightly better boost response is more important to you than HP then K16 based turbos are the better choice.

Clearancing the turbine wheels will help K16's. They will never come close to the flow rate of a K24 turbine wheel with AR or 1.0

The tuner you refer to has it available both ways. It is his (and mine) belief that the EBC is a far superior method of controlling boost on motronic 5.2. You can retain the stock manner of boost control with said software. It is offered as a upgrade for those willing to do the extra work.

K24madness

I guess you assume that all turbos are perfectly adjusted from the factory. You of all people should know the variances seen on factory wastegate adjustments.


Yes of course the N75 valve itself is wonderful. Its the FACT that the ECU has no meens of sensing accual boost is the problem.

Tuner write XX program with XX components. Mr customer does not have same XX components and his wastegates are adjusted slightly different. Guess what? Now your mail order program is out of calibration and you end up with less boost than was tuned for or you have boost spikes.

I have no doubt that Gunther tunning any car will get the boost logs nailed. Its how it behaves in the other 25 cars thats the difference. EBC's don't share the same problem. They look at accual boost to make adjustments.

Kevin

Basil, yes you want to shorten the rod. With your new boost gauge installed, you can watch how the boost comes on through the midrange then starts being pulled. If knock counts are low, boost will come up to a certain point in the RPM range. At 5200-5400 at 1bar things are pretty much spent. What one has to realize that when you install a larger compressor wheel on the same turbine wheel, the actual shaft speed slow down and actually reducing the exhaust backpressure. The reason is because the larger more efficient (hopefully) compressor wheel is producing more air per revolution. In the end the the target boost is reached sooner and one shifts.. the cycle is repeated. Please note that through my latest round of dyno data logging with factory and aftermarket IC, I have found that up to 1.35 bars of boost and 6000RPM the factory Intercooler does very well at keeping the charge air temps below 100 degrees.. However, over 6K the temps increase dramatically.. This data changes in very hot climates..

Basal Skull

Thanx Kevin , I'll watch my boost gauge and give adjusting the waste gate a try. Not quite sure what happened/I must of missed something because all of Tom's posts seemed to have dissappeared..

Ryojo