I've been running my car through a 3.5 in exhaust through the modified stock muffler, and stock tailpipes. I thought this might be the reason it peaked early on the dyno.

Tonight, I dropped the exhaust and ran it with an open downpipe.

With 23psi, it made-

733rwhp from 4,800 to 5,500

798rwtq @ 4,650

fwiw, uncorrected is was 743/809

I am wondering if anyone has any insight as to why the horsepower would peak early and then just flatline.

I'm thinking that the cam may have something to do with it, since it was spec'd out by Cam Motion for my supercharged setup.

Basic setup is- 96 Camaro, 357ci LT1, GT80BB turbo, 1.32 divided ex housing, afr 215cc heads, LT4 intake, 214/222 114lsa cam, procharger sheetmetal intercooler.

As a comparison, I used to have a centrifugal supercharger on the same exact engine/car. With 12psi it made 634/580, and peaked at 6,100. (It also made much less average power across the board.)

 

What are you planning on taking the motor to redline wise? Did you take it past the flatline, if so what did it do?

 

Jim, Im not sure if you want to divulge the info, but what is the cam lift, intake and exhaust flow, header primary size, and how do you have the 2-1 setup on going into the turbo?

What happens if you turn down the boost?

What was the length of the downpipe?

If you turn down the boost to say~ 650rwhp wise, does it peak more like the blower?


Louis

 

1LE Thumper- I'll rev it as high as necessary, but I shut it down at 5,800 because it had allready reached peak HP. It was at 700rwhp at 5,800.

G2 LS1- Cam Lift is approx 533/544 (cam card is at work).

Heads didn't flow great. Approx 280/215 @.600. (again, specs are at work) They were flowed by Rich Groh.

Header primary size is 1 5/8, 2 1/2 collectors and crossover. Both banks merge right at the turbine inlet. Wastegate is plumbed right before turbine inlet. Downpipe is 3.5, and approx 32 inches long at the point the exhaust was disconnected from it for dynoing.

I had previously dynoed these numbers all within about 10 minutes of each other. It was warmer out so the correction factor was 1.03

12psi-

559rwhp 608rwtq

17psi-

662rwhp 692rwtq

21psi-

724rwhp 748rwtq


Tonight I only dynoed it at 23 psi and with the open downpipe. Correction factor was .99

I think that I'm getting some intake charge contamination (EGR) because of the overlap in the cam. When it made 600+rwhp with the blower, I was able to run a stock ignition. I needed to install an MSD Dig6 to keep the ignition from breaking up at the same HP levels with the turbo.

 

I was just wondering if it ever picked back up again.

No problems with boost creep I take it.

 

what is peak power in relation to boost for those #s above?

How does it compare to the blower peaks?

Im trying to figure out where the power peaks in relation to boost.

 

Just thinking out loud

Think its just not producing the right amount of exhaust to spin the turbo fast enought to make any more power above that? Also wouldn't that show up on the A/F tables?
It would be nice to have turbine speed as well.

Suppose you don't have EGT readings do you?

 

It reaches peak boost at about 4,400. It has an electronic boost controller, and boost control is solid.

The blower made peak boost, and peak HP at 6,100.

 

I don't think that's a problem, because it has no problem making boost.

Air fuel is perfect.

 

what were the peaks of those number?

 

For all those runs, even at the different boost levels, HP peaked at 5,500, and torque peaked at 4,400.


HP drops of QUICKLY after 6k.

 

Maybe its just the head cam combo doesn't like the increased air flow from the turbo??

 

i'm thinking its the cam, let me give an example:

turbocobra on turbomustangs.com has a combo similar to you. He used to have a blower combo and switched over to a turbo setup and kept his blower cam

made awesome power but not where it should have for the pressure he was running (like you)

he switched cams to a more specific turbo cam and it picked up over 140rwhp over the RPM range of the motor, not just peak

if i find the thread i'll link it to you

 

Pretty interesting stuff... Once you reach peak HP at whatever boost, does the HP stay pretty flat while maintaining the same boost? Or do you get the same HP as the RPM's increase and boost decreases?

 

I would have to vote cam. I was talking to Comp Cams about specing a turbo cam for mine, and mentioned I was running a Hot Cam and 12 psi boost. He said the cam just bleeds boost off, so anything over 7-8 psi and it just bleeds the boost off. Sounds like what is happening to you..

He did say that was why I was able to run 12 psi and pump gas on stock pistons.. all the boost was just going out the exhaust...