Lunac4

Hello Folks

I have a c4 with the following items

383 bottom end
Stock top end (including cam)
Stock Exhaust
efi connection 24x conversion
LS1 computer
60# Fuel injector
255gal fuel pump with regulator
LS7 MAF sensor

The dyno results were as follows

HP 254.90 rwhp @ 4500 rpm
TQ 343.29 rwhp @ 3000 rpm

My concern is the unusual drop in HP & TQ at the 5500 rpm mark.

I am including the dyno graph for all you guru's to chime in on ... Please help me narrow this down... Someone must have experienced this before.

rklessdriver

I'm not sure what were you expecting out of the engine.

You added 30 cubic inches to the motor, increased the piston speed and kept the same airflow capability that the stock engine had.....

It makes the power it should and has a comparable powerband.
Will

DanielRicany

You didn't do any head work, no intake work, no exhaust work, no cam, what were you expecting? You're right where you should be. If you want to see 500 hp, everything I listed above needs to be changed.

Lunac4

Thanks for your response and I couldn't agree with you more I am attaching my graph ... there is an unusual or not so unusual drop off like a cliff drop at the 5500rpm mark that's what has me wondering

rklessdriver

Thats just where the dyno operator cut the throttle (stopped the test).
Will

Lunac4

Ok ... I thought it may have been a sign of weak valve springs floating...or choking at the exhaust side...In your opinion does the graph look healthy?

Lunac4

Thanks Daniel...I am going to add a supercharger to this application first and see what comes of it...My concerned was that the dyno graph showed a sharp drop at the 5500rpm mark....I am not used to reading dynos and needed some opinion on the graph...

rklessdriver

The power curves on the graph look fine. I don't see anything to indicate a mechanical problem.

Dyno operators typically stop the pull shortly after peak power happens as there is no reason to keep turning a motor to the moon when it's not making any additional power....

Your tune looks like it could use a little work.... just judging from the fuel curve thats shown on the dyno sheet. Would probally pick up some power between 4500 and 5000 if you managed to get that rich dip out of it....
Will

Lunac4

That was excellent advice..Thank you very much Will