L-92's w/ forced induction what's wrong?
 

I have a 402 with Livernois stage 2 L-92's, 28cc dish pistons, Stock Gm multi-layer steal gaskets,l-76 intake, 76mm turbo .96ar exhaust housing, .600/.600 232/230 115+2. Is it the heads that are not performing? Did I figure out the compression wrong? Mis-matched cam? I am only running 6psi on it but it seems weak. It will not break the tires loose at 30mph. Just trying to use others experiences and knowledge to save some head aches. Thanks for any input.

well, i would say you have some pretty low compression with the 28cc dish, but you didnt say what it was and im no expert......but why are you only at 6 psi with your combo???

the easiest way to get it to break the tires loose is reach up and crank the hell out of that knob on the boost controler!!!!!!!!!!!!!

I did a little reverse engineering and determined you're right around 8.5:1 cr. Which I think is perfect for turbo applications. You're idea of what's wrong though isn't very scientific or accurate. Being able to break the tires loose isn't exactly a measurement. Have you ever had the car on the dyno? Is it tuned?

EDIT: PS THIS IS A FUCKING PAIN IN THE ASS TO POST! PS POSTS AREN'T COUNTING! MADE A THREAD ABOUT IT:
https://ls1tech.com/forums/user-support-resources/735044-post-not-counting-continued.html

That is what I got for compression. As far as breaking the tires loose it used to with the same set up on the stocker with a quarter throttle. I am pretty good with seat of the pants feel and this don't have it.Yes the tune is pretty close.

Whats up with the post updates. Not bumping to the top.

How much power are you making on the dyno? How did you tune the car? air fuel? timing? Need more info in order for us to help. :)

In my opinion the cam is too small for the L92 heads. Even though it is a turbo application, it should probably still be bigger. Also the compression is pretty low, especially for the low boost you are running. If you want to run only 6 lbs the compression can be 9.5-1, and if you want to run pump gas and like 10-12 lbs then it needs to be around 9.0-1.

Rick LeBlanc
Livernois Motorsports

Yep, and that 6 pounds isn't even working that 76mm Turbo. I would look at a compressor map to see where the efficency hits.
Where is the timing in relation to the previous setup? Where was the compression in the previous setup?

Robin

Also where did you get that cam? I tried backwards splits 10 years ago and I didn't see anything.

Sounds like you are trying to keep the exhaust velocity up. With your cubic inches you should be able to run a larger cam (like Rick said)

I playe with a bunch of cams with my old 76mm years ago. The wide lobe sep helped reduce intake contamination. But the pressure on the exhaust side dictated where the power would fall off.

Those heads flow very well, no need to have a higher duration in my opinion.

Robin

I plan on putting 15psi to it but was starting off low because I have to hook up my e-boost. Maybe it will really wake up with more boost. I would think it would be stronger than it is now at 6psi.

My old motor was stock with 6 psi so compression was alot higher but I would think the extra cubes of the new motor would make up for it.

I just think a motor that should be cranking out at least 600rwhp at 15psi should be alot stronger at 6psi.

I have not brought it to the dyno yet but it doesn't take a genius to know this thing is slow. I am just really disappointed thus far and am hoping to find out why and fix it.

Car was tuned with HP Tuners and a wideband. Right now the timing is at 20* but it seems like the car wants more. I just didn't feel comfortable jacking the timing up when everyone I know makes good power between 16*-20*. Seems like I would be trying to make up power the wrong way.
Air fuel right know is rich at 11.0 to 1.

Ofcourse the car wants more timing, youre only running 6psi with no compression... turn the boost up :)

I was thinking the same thing - that 6 psi with low compression is only getting him back to the equivalent of a regular compression motor. Crank it up!

-Geoff

Like Robin L. said, you are no where near the efficiency of that turbo. Get a compressor map and put the boost in the range where its at least a little more efficient. If you are still not happy, then come back here and start trying to find a problem. Whenever we are breaking in our GNs, we run 5psi at the most on the street for a while. A 9 sec car feels the same as a 12 sec car, the turbos are way out of range at 5psi! :judge:

Thanks guys! You answered my question. I will try cranking up the boost and see what happens. I will keep you posted on how it does.

i have a 9.27 c/r 408 with a s488....10 psi on the street with full exhaust (cuts power output some) and run 16 deg on 87 octane....you need more timing or boost

Boost is WAY too low for that turbo to work efficiently AND the heads are too big (port size).

HiTech

Bump for update!

the turbo is to small the exhuast side is way to small.Porting the heads made the problem worse. The cam looks spot on to me i do not see where the camshaft is really going to affect output much on the combo of parts.. Change that turbo out for something larger or send it in and have the hot side wheel and housing bumped upto a 1.15 AR. Also might wanna consider getting into a large compressor wheel. T76 is really to small for a 402 a T88 or s488 Borgwerner would have been a better choice.

Collect some IMP and EMP data.

I have a feeling your going to hit a wall with making boost fiarly quickly.

I got pissed and pulled the waste gate hose off and let her eat while monitoring the afr. It made 15psi and started to lean out at 4200rpm. This was through full exhaust. My injectors are at 83% duty cycle at 4400rpm(mototron 60) with my meth kit(big nozzle 100% meth) Car felt o.k. I only reved it to 4500rpms. I have had alot of fast cars this felt like 450 to 500 rwhp. There was no tire spin! I am running a 4l80e,yank 3000 stall,and a 2:73 gear. This car is way down on power. I did notice the header wrap on the down pipe starting to burn or discolor. There is a big problem with it. My question is can the turbo be causing such a dramatic power loss alone or do I have a couple of issues?