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G'day guys, wondering if anyone has any ideas.
I have a built 5.3, with 243 heads, truck manifolds, 21/4 crossover into a gtx45 turbo,
My goals are about 1000 hp atw.
I had it on the dyno today, and it showed 785 on 26 psi.on 28 psi it only shows another 12 hp hp. Originally I thought the turbo may be too small, but I don't think so,the turbo is rated at about 1300hp.it has a billet 80mm comp wheel, and an 87 turbine wheel.
I know it's not cooler, exhaust, fuel setup etc, as I've made about 950 atw with a 406ci and pt8847.
I'm thinking it may be the cam, specs are
Intake .614, ex.621
Duration @ intake .050 227, ex 235
Lobe sep 113.0 plus 4
Any help is much appreciated

asubennett

iTrader: (6)

Compression test will point you in right direction.

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This is a new engine, runs sweet, I don't understand how a compression test will help.

jay_rich

iTrader: (8)

Have a way of checking the back pressure? At that power level i would be looking into a larger wheel than an 87 depending on what kind of RPM you are spinning. What A/R?

Jay

66Chevellelq4

I think with the relatively small turbine wheel for your goals and the big cam your having back pressure issues

asubennett

iTrader: (6)

New engine or not or "runs sweet" or not you should always start with a compression test. Maybe you have a valve adjustment out of whack and one valve is sticking open. Maybe rings haven't seated very well yet. Myriad of reasons to start with compression test.

Next I would start with a boost leak test.

They are both free to do and will give you peace of mind before getting into more difficult thought processes. It's not your cam unless you installed it weird or your turbo.

How many lb/hr of fuel are you burning when it made 785? Honestly, it seems like 26psi is WAY too much with that turbo to only make 785. Something else is wrong, which leads me back to my first two statements.

Compression test.
Boost leak test.

Forcefed86

iTrader: (4)

What... RPM/trans/rearend/converter/IAT's?

Cam is OK IMO with 5* of overlap though It won't like alot of back pressure. Could you be floating valves? Have you checked converter slippage? Checked your back pressure?

Assuming that's all good, if it only picks up 12hp with 2lbs that usually means the turbo's done. Is it an 87mm exducer or inducer? AR housing?

You can't give a turbo a set HP rating. Depending on the cubes/topend flow the amount of power it can make will vary greatly depending on the engine.

A 243 headed 5.3 probably isn't going to make over 400 crank hp NA. Which means you'll need 30+lbs to hit 1000whp. That turbo may not be suited to make 30+lbs on your engine.

s57_s2k

check your IAT and back pressure , they will tell you what is going on.

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Thanks fellas,
Ar is 1.15,
I was thinking maybe the cam because of the way it was installed, apparently the engine builder put it in 4 degrees advanced, and it's supposed to be dot to dot.

ls3fox

Try adjusting the cam timing but it does sound like the turbo is huffed out