1.2 BAR with stock turbos is not the same as 1.2 BAR with GT30s. The total volume of air produced is tremendously different between the two...hence why you make more power with larger turbos than you do with smaller ones at the same boost level.

It just seems to me to be a heck of a lot of pressure to place on the stock internals without the safety of high octane fuel. I mean, we aren't running huge displacement Viper engines. These are little 3.6 liter pumps. Anyway, I'm not a tuner...just an enthusiast. I'm very excited about your car and Tym's accomplishment with it thus far. The "1.2 BAR on GT30's on only 93 octane" thing just caught me way off guard.

 

ok so i rode this thing tonight all i had to say after the ride was nothing.... i couldnt say anything i was blown away.... i swear this car went from 30 to 160 to 70 in like 6 seconds, then not even 5 seconds after we hit 70 theres a statie!! lol This build is incredible i could not believe it... it pulled so hard i could not lean forward to put the window up its incredible... just incredible..

 

Looks like you've got quite the beast on your hands!

 

Its the density that makes the power difference, 1Bar is 1Bar, it isn't variable, however its the density of that 1Bar that makes the difference.

 

Exactly.
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Turbochargers compress air to make it more dense, which is what allows more oxygen to enter the engine thus increasing power. They increase density by compressing a volume of air into a static space. A larger turbo compresses more air than smaller one does, but at the same boost level (more CFM = more density at the same PSI).
So, the more air you compress, the higher density you have, the more power you make. But also, the higher density you have, the greater chance you have of causing detonation...and the more important it becomes to use the proper octane fuel to prevent it.
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Durr yeah.. sorry being stuck in bed after surgery is getting to me

 

OK then with a larger turbo 1BAR = 1BAR but the air density is higher, so if 1BAR = 1BAR wouldn't you then also state that with the larger turbo we're looking at GREATER-PSI's @ the same BAR-Level? Isn't the absolute PSI the number that comes out in the end?

 

1Bar is 1Bar, 1PSI is 1PSI, and 1Bar=14.5PSI, I had an article I need to dig up that really explains it all, because on every car forum there's always a discussion about this.

 

Think about it this way, Speed:

You have a fire hose and a garden hose. The fire hose is giving you 100 gpm at 5 psi. The garden hose is giving you 5 gpm at 5 psi. Both are flowing water at the same psi, but a LOT more water is coming from the fire hose.

Now, convert the water to air, and then think of that is terms of density. The more density you have in a combustion chamber, the greater chance you have of inducing detonation.

Detonation is when fuel pre-ignites in the combustion chamber. This produces multiple flames instead of a single flame. When these multiple flames collide, they do so with explosive force that produces a sudden rise in cylinder pressure that creates a sharp metallic pinging or knocking noise.

These shock waves can subject the head gasket, piston, rings, spark plug and rod bearings to severe overloading. Mild detonation can occur in almost any engine and usually causes no harm (i.e., "pinging"). But heavy detonation can be very damaging (i.e., "blown engine").

When low octane fuel is present, the threshold of the engine to resist detonation is lowered. OEM knock sensors (sensors mounted on the engine that are designed to detect the high-frequency vibrations caused by detonation) do a good job at protecting your engine from harm, but they can only do so much.

Higher octane fuel raises the threshold of the engine to resist detonation. That's why we use race gas like C16 (117 octane) when running high boost in our little engines. High octane fuel doesn't add power in and of itself, it protects your engine when you increase boost allowing your turbos to safely add power.

Now, take a car like the Viper, who's huge 505 cubic inch displacement allows power in the 900 rwhp range using only 93 octane fuel with a TT setup. Why? Because the more displacement you have, the less external air required to make the same power as an engine with a smaller displacement would require. The less air, the less density, the less chance of detonation. To make 900 rwhp on a 3.6 Liter (219 cubic inches)...we have to run lots of boost and high octane fuel.

 

I think Davids AFRs where at 11.5 when tested this set up and made this power with 93 pump...

 

through most of the curve it was 11.5. near the top, we were extremely conservative and was closer to 10.5.

 

So there shouldnt be detonation but is there more stress on the engine...

 

Of course there will be more stress on the engine, that is why you need to build the innards for the engine to survive at those power levels, also you need to find a way to dissipate all that heat generated, extra oil coolers,bigger radiators, better intercoolers, etc., there is no free ticket here!

 

I don't see how this argument comes up time after time.
1.1 bar at 6,000 RPM and 120*F in a 3.6 L motor = 1.1 bar at 6,000 RPM and 120*F in a 3.6 L motor!!!!

It doesn't matter if the oxygen came from a Gold-plated Gt40R or Oprah's fart. Once you have put a defined amount of air into a defined space it is all the same.

Assuming both turbos are operating within their efficiency range (READ: SAME INTAKE TEMPURATURES) it doesn't matter how big the turbo is that the compressed air came out of. For anyone that wants to argue against this then please answer this question.

How is 3.6L of 120*F air @ 17psi more air than 3.6L of 120*F air @ 17psi?

When people compare 17psi out of a gt30r to 17psi out of the stock turbos they are forgetting that the stock turbos will taper boost (aka, torque) towards redline and HP will plummet.

If you really want a visual of this I'm sure we can pull up some dyno's comparing two large turbos at low boost levels where both turbos are within their efficiency range and hold the same boost all the way to redline. On these graphs you will see there is a small difference, but it is usually negligible.

Anyhow, BEAUTIFUL CAR and excellent work! Enjoy it!

 

I think what everyone is saying is that turbo A can produce 17psi from 3000-6000rpm on a 3.6l motor, and turbo B can also produce the same 17psi, but since turbo B is larger or more efficiently matched to the 3.6l motor the IAT from turbo B will be maintained evenly across the rpm range while turbo A will start putting alot of heat into the intake since the compressor impellers are spinning much faster than turbo A