[usnavyame70]

So I just got back from the chassis dyno which was a dynojet. My combo is in my signature.I was hoping for at least 380hp and 380 torque at the wheels but the best i could get out of the 383 was 312 hp and 315 ft-lbs.Both peak horsepower and torque where right at 5300 rpms.After that the carb ran out air for the motor.So if I go to a bigger carb do you guys think i can get more horsepower and torque or ahould i just be happy with what i got out of it.

 

[rustbucket79]

Your carb isn't the restriction.

 

[usnavyame70]

if my carb isnt the problem then what is.

 

[rustbucket79]

A full list of specifications is necessary.

Did you have an O2 sensor installed to determine air/fuel mixture?
Did you try different timing?
Did you try different jetting?
Did you try running w/o air cleaner?
Do you have a fuel pressure gauge?

Saying that your combo produced numbers lower than expected without follow up of what you tried unfortunately doesn't help much. The car's driveline may be eating up a large percentage of power, without knowing what power the engine made in itself, you won't know if the driveline is responsible or if the engine itself isn't making the power.
Having your HP and Torque peak at the same RPM is odd and makes me wonder where the choke is in your engine.

I made 600 HP with my first 408 using a 750 holley turning 6200, you have enough CFM unless you plan to spin the engine 7000 RPM.

 

[onovakind67]

if my carb isnt the problem then what is.

Got a stock exhaust system? Is your carb opening all the way? How's the timing? Can you post the graph? Dynojet also produces a printout of the results and the time between rpm points.

 

[usnavyame70]

timing was 36 all in at 3000rpm, the jetting in the carb is stock.i have hooker super comps with 3 in exhaust into hokker aero chamber then dump right at the rear axle.here is the graph from the 2 pulls.

 

[jbird]

One thing I see is they used the SAE correction factor. Most engine dyno's use the "standard" correction factor. SAE will net lower numbers than standard. Looks like something odd started happening right at 5300. Almost like valve float or some other problem?

 

[usnavyame70]

I am new to this whole performance engine and dynos.what do you mean by SAE and standard correction factor.Is there anyway to check for valve float.i was thinking maybe running out of fuel since i have a holley 170 gph fuel pump with the stock fuel lines going to it.or the rockers maybe not adjusted right.any other ideas on what could be my problem would help out alot.

 

[jbird]

I am new to this whole performance engine and dynos.what do you mean by SAE and standard correction factor.Is there anyway to check for valve float.i was thinking maybe running out of fuel since i have a holley 170 gph fuel pump with the stock fuel lines going to it.or the rockers maybe not adjusted right.any other ideas on what could be my problem would help out alot.

"Standard" The older J607 standard considers that the engine was run on a 60°F day with 0% humidity and a barometric pressure of 29.92 in-Hg.

SAE J1349 standard of 77°F (25°C) day with 0% humidity and a barometric pressure of 29.234 in-Hg.

It amounts to correcting to different conditions. The A/F ratios on the chart don't show going lean or rich. In fact, they look almost perfect. It is really hard to say not being present at the time of testing. What lifters and valve springs are you running?

 

[curley8788]

something is definetly up. your cam and heads should let you rev a lot higher than 5300 rpm...

 

[usnavyame70]

the motor pulls past 5300rpm the power seems to drop from there.the motor pulls to 6000rpm pretty easy.any idea on what could be wrong

 

[curley8788]

what size fuel line are you running? mine had a fuel delivery problem, but mine went very lean on the air/fuel ratio...

 

[usnavyame70]

what ever the chevelle had from the factory i believe it is a 3/8

 

[curley8788]

what ever the chevelle had from the factory i believe it is a 3/8

well double check and make sure it isnt 5/16. it doesnt cost anything to see.

 

[usnavyame70]

thanks for the help.any other way to check valve float with out being on a dyno

 

[jbird]

Look at the A/F ratio on the dyno sheet. Nice flat line all the way to the end of the pull. And right between 12.5-13:1. If it was running out of fuel it would show up there.

You can have the spring pressures checked.

 

[curley8788]

Look at the A/F ratio on the dyno sheet. Nice flat line all the way to the end of the pull. And right between 12.5-13:1. If it was running out of fuel it would show up there.

You can have the spring pressures checked.

thats what i figured.


he would hear valve float as popping/backfiring right?

 

[Wolfplace]

the motor pulls past 5300rpm the power seems to drop from there.the motor pulls to 6000rpm pretty easy.any idea on what could be wrong

Your torque curve starts looking decent at about 4000 & up until it goes to hell at 5300 so it does not look like the peak torque & HP are at the same RPM but I agree you should have more power unless your drive train is eating a ton
The STP numbers would be about 6% higher

If I had to guess I would say you have a valve train control issue
What spring did you get with the heads?

 

[jbird]

he would hear valve float as popping/backfiring right?

I wouldn't say that's true 100% of the time.

 

[Wolfplace]

he would hear valve float as popping/backfiring right?

Not necessarily, not til it gets crazy