Horsepower dropping off at 5-6 grand on Tac

[7mgt45r]

Hello everyone need a little help pls. I went to dyno my car yesterday and couldn't reach 400hp only 396.The car ran fine and had enough fuel.The problem was it would boost up to 18psi and at 5-6 grand the boast would rise and the horse power would drop everytime.So we chked the boost contoller it was okay.Disconnected boost controller and tried just on waste gate samething the car just stop making power up top. Build sheet is(Bored 40over JE piston 8:9:1 comp.,all ARP Hardware,Eagle Rods, clevette bearings,Brain Crower valves and valve springs,head ported/polished,T67 comp turbo, big intercooler cus. 2 1/2 pipes, cus.4inch exhaust, Ebay 40mm SS Chrome waste gate,2 walboro 255lp fuel pumps -8 feed, Precision turbo 680cc injectors, VPC/ SAFC, Greddy Profec b, HKS Twin Power ignition upgrade,18lb flywheel, RPS stage 3 cluthe and 19inch rims. Could someone pls give me some advice. I'm thinking a waste gate problem.

 

[SUPERIUM]

Most likely the wastegate. Same thing happened to my friend but with a stock wastegate on 15-18psi it peaked around 4500rpms then started tappering off. I heard if you shim the wastegate it holds a bit better.

 

[7mgt45r]

Most likely the wastegate. Same thing happened to my friend but with a stock wastegate on 15-18psi it peaked around 4500rpms then started tappering off. I heard if you shim the wastegate it holds a bit better.

Thanks for comment, how would you shim the wastegate? i have a external waste gate

 

[honestabe]

http://www.lmgtfy.com/?q=shimming+a+wastegate

Also did a little quick search for "shimming a wastegate" in the general section and found these

http://www.supramania.com/forums/showthread.php?t=22675&highlight=shimming+wastegate
http://www.supramania.com/forums/showthread.php?t=3311&highlight=shimming+wastegate

 

[jdub]

Thanks for comment, how would you shim the wastegate? i have a external waste gate

Not going to work on an external wastegate

 

[WhtMa71]

^ Nice try..but he has an external gate...Which can't be shimmed to my knowledge.

Edit: Bah..beat by Jdub.

Does the boost stay steady at 18psi throughout the run or does it drop down at those rpms?You could try a stiffer spring in the WG. Do you know what pound spring is in there?

I believe the rule of thumb is to run no more than twice the psi of what the WG spring is. So if you have a 7lb spring, you shouldn't run much above 14psi...but then again, people run more boost all the time. It just doesn't hold steady all of the time either.

 

[Suprapowaz!(2)]

He mentioned his boost would rise, but horsepower would drop.
Would your AFR's start running rich toward the end of the run?

 

[jdub]

Could be several things:
- What cams are you using and did you degree them when the motor was built?
- Without knowing what that turbo flows, could be a restriction in your IC or the piping.
- If the turbo flows enough, you may have achieved critical mach in the IC piping...i.e. it's too small

It doesn't sound like a wastegate to me, but it also won't hurt to check the spring.

 

[7mgt45r]

He mentioned his boost would rise, but horsepower would drop.
Would your AFR's start running rich toward the end of the run?

yes the AFR's would run rich.

 

[7mgt45r]

Could be several things:
- What cams are you using and did you degree them when the motor was built?
- Without knowing what that turbo flows, could be a restriction in your IC or the piping.
- If the turbo flows enough, you may have achieved critical mach in the IC piping...i.e. it's too small

It doesn't sound like a wastegate to me, but it also won't hurt to check the spring.

Using stock cams and yes they were degreed when motor was built. Jdubb give me a call i spoke with you before on a issue i had. 7708704600 Anthony. Jdubb my intercooler piping is 2 1/2 inchs.

 

[paradox616]

what exhaust/dp/cat do you have fitted? (you didn't list it)

did the dyno operator have much to say?