Horsepower is flatlined from 4,800-5,500. Need opinions

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?

Originally posted by G2 LS1
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.


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.

Originally posted by 1LEThumper
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?


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

Air fuel is perfect.

Originally posted by INTMD8


12psi-

559rwhp 608rwtq

17psi-

662rwhp 692rwtq

21psi-

724rwhp 748rwtq


[/B]


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...

From the other post(s) im not seeing why this cam would be contaminating the intake charge.

What do you mean by bleeding off boost?

A 214/222 on a 114 LSA gives NEGATIVE 7 degrees overlap, which is a good thing for a turbo cam. Of course I would like the lobes swapped around giving more intake and less exh. but I don't think the cam is contaminating your intake charge.

Originally posted by 1994B4C
A 214/222 on a 114 LSA gives NEGATIVE 7 degrees overlap, which is a good thing for a turbo cam. Of course I would like the lobes swapped around giving more intake and less exh. but I don't think the cam is contaminating your intake charge.


Higher Exhaust duration is a GOOD thing on a FI car, you shouldn't have any problems at all getting the air/fuel into the chamber..its getting it all out that is a problem. You want the least restrictive exhaust path as possible...and that start with how long the door is open for it all to get out. At least thats what I have always seen. But maybe thats just me, I've never been a fan of wrong way duration cams.

I agree that a big exhaust duration is a great thing on a supercharged car. I think its a different story on a turbo engine as the shorter exhause duration will increase the velocity the air moves out of the motor as the pistons pushes it out, and spinning the turbine faster. But I still thin the cam he is using will work and isn't the culprit for the flatlined HP he is seeing.

Originally posted by 1994B4C
From the other post(s) im not seeing why this cam would be contaminating the intake charge.

What do you mean by bleeding off boost?

A 214/222 on a 114 LSA gives NEGATIVE 7 degrees overlap, which is a good thing for a turbo cam. Of course I would like the lobes swapped around giving more intake and less exh. but I don't think the cam is contaminating your intake charge.


It has negative 7 deg overlap @.050, but it has a good amount of seat to seat overlap. I'll find the adv duration numbers and figure out exactly how much.

Most turbo cams I have seen are single pattern, or an intake-biased split.

If you are looking for a cam with no overlap seat-to-seat it will be extremely small. My cam is 232/226 on a 114 and has 1 degree overlap at .50.

The guys that make around 2000HP run alot of overlap just because they have to with the size of lobes they are using. You can't get a cam with no overlap and 280 degrees of duration.

My question was you peaked at 4800 @ 23psi. You made the same HP at 5500, what was the boost? What was the boost @ 5800?

Originally posted by INTMD8
It has negative 7 deg overlap @.050, but it has a good amount of seat to seat overlap.

True but how much does a head flow at less than .050? I think it is rather insignificant.

As can be seen in the torque curves of this post:

http://web.camaross.com/forums/showthread.php?s=&threadid=139358&highlight=NOVI

a roots blower and a turbocharger, both of which produce flat boost curves, will multiply the naturally aspirated TORQUE CURVE by the same factor across the board. In this particular case, the roots blower produced a torque curve multiplier of 1.37 and the turbocharger did 1.60. If you plot those torque curves in Excel, like I did, it will become clear that the curves match the naturally aspirated curve, only higher.

The centrifugal superchargers, however, produce more boost with rpm, shifting the torque and hp peaks to a higher rpm.

So, with the AFR heads and the small 214 cam, would you expect a naturally aspirated LT1 to produce peak hp in the 4,800 - 5,500 rpm range? If so, then I tend to think that everything is working properly.

Mike

Originally posted by 1LEThumper
Higher Exhaust duration is a GOOD thing on a FI car, you shouldn't have any problems at all getting the air/fuel into the chamber..its getting it all out that is a problem. You want the least restrictive exhaust path as possible...and that start with how long the door is open for it all to get out. At least thats what I have always seen. But maybe thats just me, I've never been a fan of wrong way duration cams.

Well, if you want to minimize exhaust restriction, then for goodness sakes don't bolt a turbo to it. ;) It's not uncommon for the exhaust to intake pressure ratio to be 2:1 in a turbo combination for a street application. With that kind of exhaust backpressure the main problem is during the overlap period you can actually push exhaust gas back into the chamber and stop fresh charge from coming in. Rather than doing that it's better to shorten the exhaust duration and limit the overlap. Now, as you get a higher flow turbine housing and get your pressure ratio closer to 1:1 you can start creeping back up on exhaust duration, but it was rare that I would spec a split duration cam with more exhaust duration for a turbo car.

Originally posted by INTMD8
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.

BINGO!

thats my guess........you cant expect a supercharger cam to be optimal for a turbo charger.

Optimal NO, will it work yes...the cam has negative overlap. That doesn't explain why it gets to 4800 and makes the same power to 5500.

The guestion was never answered that I asked. Are you seeing a decrease in boost after 4800 while still making the same power?

Originally posted by INTMD8
It reaches peak boost at about 4,400. It has an electronic boost controller, and boost control is solid.



Once it reaches peak boost, it stays there until redline.

I'm going to try a larger cam, and also change the exhaust housing to a .96 to try and achieve a broader hp curve.

I would guess the cam and possibly the intercooler.


How much power/ cfm is the procharger intercooler good for?

Procharger claims 1000hp for the sheetmetal IC.

I plan to test pressure drop across the IC, and also turbine inlet pressure.

Yeah I guess you are right, I got to talkin with a buddy of mine that does a lot of DSM turbo stuff and he said that all of their cars that are running really big turbo's will use a reverse split cam in their cars to help it out. Still got a lot more to learn on turbo cams.

Either way that cam needs to come out of that car if you want to get rid of that flat line.

You don't think the primaries/collectors are choking it off too early?

They seem small for the heads and turbo you're running. 215 AFRs, the RR version, right (don't know since the flow #s you quoted seem low)?

Originally posted by JSK333
You don't think the primaries/collectors are choking it off too early?

They seem small for the heads and turbo you're running. 215 AFRs, the RR version, right (don't know since the flow #s you quoted seem low)?


ive seen mustang guys making over 800rwhp with 1 5/8 primaries and 2 1/2 crossover

but i would guess thats pretty much maxing out that size pipe.

i've been told that 1 5/8th primaries and 2.5 collector is good for around 1000rwhp.


remember, on a turbo setup the exhaust system is "in boost" also, probably 2:1 on his setup!