ayousef

Well, I dont even know if something like this exists, but im sure the cam itself plays a huge role in controling backpressure.

Assuming you're running turbo's that max out at 5500RPMs on a motor built to spin to 7500 easily, the most common thing to do is to switch to bigger turbos, but if that was not an option (read that twice ) how could you "compensate" by a custom grind cam for such a system.

I know a cam can only do so much, but again thats why I used the word "compensate".

My general question is, what could I do to shift the power curve a little to the right without changing the turbos, since the current turbo placement does NOT allow for bigger turbos.

Engine is a 427, and turbos are baby T3/T4 Turbonetics with 0.81 a/r.

onfire

iTrader: (17)

LPE cam was designed just for that problem. T25 turbines on a 427 ci engine.

qqwqeqwrqwqtq

Yes, but all of the dyno sheets I've seen of those cars have a peak at 5300-5400 and fall off hard after 6k.

Would you agree or have you seen differently?

onfire

iTrader: (17)

Mine peaked at 5800-6000 and held to 6400 but the boost controller had a lot to do with the curve.

Bad thing is T25's don't belong on a 427...you just bandaid around the problem they create.

ayousef

jim, with the current cam and no interference from the boost controller the car peaked at 6000rpms which is not bad, but this is at 7.5PSI, at 16PSI im sure it will peak at 5500and fall of hard afterwards, so I dont know if that cam would help me, its just another thing im hesitated about.

I can't think of how the boost controller could help though, other than increasing boost pressure after where power tends to drop, so if on the 7.5PSI run where the car peaked at 6000RPMs, if I increased boost pressure by RPM after 6000RPMs to 9-10PSI, the power curve would have looked pretty nice.

ayousef

how do you set=up a boost controller to compensate for such an issue?

sultan(ZR-1)KSA

Hi Ayousef i am having the same exact problem and i upgrade my turbos from gt2876 to gt3076 and i got the same exact power band

have alook here and maby you can get some ideas , and yes i did order the new cam

http://www.lingenfelter.com/LPEforum...hread.php?t=65
i hope this helps

ayousef

thanks alot bro, the cam recommended to you by LPE is quite similar to my current cam, which was interesting to know.

hmmm...

onfire

iTrader: (17)

Use boost vs rpm and ramp the boost upward at +6000.

VINCE

iTrader: (1)

You said your turbo's max out at 5500rpm? How have you determined this? The reason why I have asked is look at Marks setup.. He has the exact same turbo kit and turbos as you. I can see why his power peaked around 5500rpm by looking at his tiny cam. He wanted STOCK-LIKE characteristics hence the tiny cam. I would think if he went with a cam in the 240's or higher his power band would shift to the right and pick up more peak power at the same boost level, but he would lose some power under the curve. I would prefer his setup if you ask me. It's easier on the valvetrain and he has gobs of power everywhere.

"The motor is a LS7 block with Darton Sleeves. Diamond Pistons (8.5:1 compression), Callies Crank, Howard Rods, 224/224 cam, All Pro LSW heads with Jesel rockers. Fuel system was upgrade but I don't have those specs in front of me but I do know it has a Motoron injector. Rear end, and Trans done by RPM and the clutch is a Twin Tex. Corsa Exhaust as well. "

http://forums.corvetteforum.com/c6-f...-pump-gas.html

BoostnTBSS

iTrader: (-1)

You could change to ex housing to new 1.1 tial and get rid of the .81 that might help and you can add a bigger waste gate to help a bit too. These are not fixes but can help ya

ayousef

Bro, my car maxed at 6000RPMs with its current cam - which is very close to the LPE spec cam - but again its worth mentioning this is at 7.5PSI of boost, and I will turn it up tomorow to 16PSI and expecting the car to peak much much sooner.

Turns out this power is really a waste on the street if you want to run street tires and have daily driving capabilities, especially if you want the drivetrain and supporting mods to stand up to the abuse.

The car does pull like crazy, but dies out pretty bad after 6K. Ill see what I can do. I dont want a lower powered car to beat me or be as fast as me just because he can make use of his gearing and high revving engine as opposed to having to short-shift to stay in the power band.

VINCE

iTrader: (1)

So you have concluded it has to be the turbos? You do know you have turbos that flow equal or more than GT35R's. Are you saying you are making 1000rwhp at 7.5psi? Mark also has a 427ci built to the hilt by W2W. The only reason he did not make any more power is due to traction issues on the dyno and it was pointless to push further. Can you post a dyno for us to look at? If it falls on its face then you might have other issues besides turbo.

As for you losing a street race because you cant make power past 6krpm makes no sense to me unless they are making equal power and they have a more usable powerband than you. There is always going to be someone faster and if you think you can build a setup for all scenarios thats not going to happen with the C5 platform unless you make some drastic drivetrain changes.

ayousef

We still did not push it beyond 7.5PSI which was the gate spring pressure. On one end I am jumping to conclusions, and on the other end im willing to see how my guesses put up against what I see in real (tomorow or after that), I would love to be wrong.

You saying that those turbos flow equal or more than GT35rs is meaningless though since I am not complaining about the compressors ability to compress air and boost the motor, its just that the exhaust housing on those turbos are smaller than what they need to be *(thats a fact)

In other words, id rather have a car that makes 800RWHP at 6500RPMs, than a car that makes 900RWHP at 5300RPMs on a motor built to spin as high as 7000RPMs.

Im not saying anything bad about the kit though dont get me wrong, I know those are the largest that can fit in there, and it was a very tight fit especially with the slightly wider Warhawk (vs LS7). I know TTi are coming up with replacement turbine and compressor wheels that they guess are worth 120RWHP!!

The car did 575rwhp at 7.5PSI which is low, and you could see its backpressured looking at the graph (which I dont seem to have with me right now, but will get). I did a few changes to the exhaust, crankcase ventilation, oil and a few things the car should be at 600RWHP now at this boost level, ill then turn it up to 16 and see what it does, at least ill see how far we could go on pump.

Im trying to look for bottlenecks in the system, but I know its the turbos, you can hear it, you can feel it and you can see it on the graph.

It does make 1.5PSI of boost at 1000RPMs though lol.

qqwqeqwrqwqtq

I designed the cam you have to make high rpm power. In my opinion you will not be able to shift your power curve to the right by any appreciable amount with a cam change.

Obviously the fix would be a larger exhaust a/r but that is not available (as far as I know).

As onfire mentioned, you could set up the boost controller to control duty cycle vs rpm, ramping in more boost up top to flatten the power curve.

onfire

iTrader: (17)

If Jim spec'd you cam your golden. The rest is in the tune-up.

VINCE

iTrader: (1)

Well I hope you sort out the issue. Keep us posted.

crashly

it's a combination of too small a comp side and too small a turbine side..

my 355 cube engine did the SAME thing , with very simular turbo's.
on the engine dyno , with twin t3/t404E's 57mm turbos, and the torque dropped off at at 5200- 5300 rpm.
i spent 4 days on the dyno , with many different cams , and they all did the same thing.
when the comp side stops flowing.... it's alll over

Due to the mathamatical equation , with the torque / hp and rpm components , the hp will continue for another 500- 600 rpm before peaking , then dropping off too.

too many cubes OR too small a turbo..

try above ideas , and maybe try more or bigger waste gates.... but i don't think that will work...
other wise, put a smaller cam in , and taller diff gears

rx_treme

iTrader: (9)

You probably just need bigger A/R housings. (i did read the whole thread) There should be no issues with just throwing new turbine housings on bc of same outer dimensions. they're cheap, easy to change and DO have an effect on power.
You should not be maxing out twin t3/t4's compressors with only 575 hp and probably just need to lower your backpressure to allow better breathing.

ayousef

nope I didnt max out the turbos, but I simply dont like the fact that they are making peak power in the center of my power curve as opposed to the top.