I dont think that your problem is there.. The LT-4 intake is a great from GM. Those flow numbers on the AFR heads are a little low for a big cube stroker IMO.. Your cam seems to be in the right range to make decent power. My opinion is your heads are choking the motor.

 

30 lb injectors with stock fuel pressure are good to about 460 rwhp.

 

Not very good with flywheel numbers as I’ve never had an engine dynoed that way so I'll reserve any comments regarding the numbers being low or high. The new dynoject software measures parasitic drivetrain loss and someday for grins we are going to put mine on the dyno and see what it says.

However…….. You’re leaving about 10 hp on the table by not having the LT4 intake welded and ported making a straighter path into the head. There is a restriction around the fuel injectors that should be taken care of for max hp.

The rule of the thumb as I know it is about 2hp per cfm of head flow. In other words if the heads were ported more, you’d pick up power there.

Put the thing on a rear wheel dyno and have it tuned to see what it does before you get too carried away. That way you have numbers that you can directly compare to others with similar combo’s.

My guess is your getting what you got into it.

 

It was a chassis dyno, not an engine dyno.

I also have RearWheel HP numbers, but I'm worried about FlyWheel hp, because if something is wrong with FWHP, you even shouldn't look at RWHP until you fix the problem.

Its 417 rwhp btw. I added the RWHP numbers (First Page)

I think I should see at least 500 FWHP.

I didn't connect my laptop during dyno, so I couldn't look at my inj. duty cycle. My fuel system is Racetronix kit with Walbro 255lph.

I tuned my advance back to 27-29* area. No knock retard.

 

You should definitely check injector duty cycle etc. But if everything else is good, your tune in probably off. I would say around 430-440rwhp would be more like what you should be looking at. your cam should peak a little higher so something is going on there. Keep in mind though, that is not an incredibly agressive cam, and those heads are a little short on flow for a 383. a more thorough porting on those heads (to around 295-300cfm) and a more agressive cam (something like .600int/.600exh 242/250 110LSA) would probably be a different story.

 

Think maybe both of us are confused. You've got me.

Flywheel numbers are done at a shop with the engine out of the car using a dyno with the engine on an engine stand. Obviously rear wheel is dynoing with the engine in the car on a chassis dyno. Apples and oranges as no one I know of has produced factual drive train loss data where they did a direct comparison of each method to determine true loss.

If your making 417 rwhp... that's not all that bad for your particular combo and typical of most stroker motors regardless of what you hear on this list. Don't believe all the BS as most people telling you it aren't making what they are telling you.You might be able to eak out a little more through tuning, but forget all about flywheel numbers as rear wheel is what hits the road.

Frankly considering no porting on the intake and no porting on the heads I say that was damn good.

 

My dyno sheet shows the Flywheel HP and Rearwheel HP at the same time. I think this is a magical chassis dyno lol. So you say there is no way to dyno the Flywheel hp on a chassis dyno?

Yes Out of Box AFRs and unported LT4 is the biggest reason why I can't be near of 450rwhp.

BTW this is a DD street car (also in dead traffic), so even this cam surge a lot!!
I'm thinking to swap my pistons and cam, and going with FI. But I'll wait a while. I only did 250 miles with new engine.

 

Usually you lose around 17% to the drivetrain on a manual car, and up to 30% on an auto (depending on stall). For your numbers to be the same at the flywheel and the wheels is impossible.

You need to get those heads opened up..youve got a bigger cubic inch engine, an awesome set of headers to let it exhale but restricted by the heads on the intake side. Its all about moving volume. I really dont think switching pistons and cam will do much. The key is the heads. More so than anything.

 

A good tune will take care of most, if not all, of that surge. You need to have the car dyno and street tuned. What was the a/f?

I beg to differ. I ran out of fuel making 360 rwhp. It's good now after I replaced it with a Walbro 255 (340).

 

What I find interesting is that your calculated drive train losses are around 7 to 9% from the two numbers I checked. That is very low. I would expect your flywheel numbers to be larger as I think there is more of a drive train loss.

 

Denny this mainly depends on VE(and a few others) I would say closer to 460 flywheel hp is the limit of 30lbers and stock fuel pressure.



David

 

Try a bigger cam.

Steve

 

My 8:8.1 CR 383 w/ ported LT1 heads dyno'd 529fwhp on the stand @ 6200rpm w/ a cam a lot smaller in size. Something isn't right.

 

Here is your issue, You are 5-10* off of where you should be for best power.

Bret

 

QFT

That was the first thing I saw. They say keep adding timing until you don't gain ~7hp/degree. All of my heads/cam combos have liked more than 34 degrees timing.

If you just kept pulling timing to remove knock, there is a good chance that the knock was false, or you had some bad gas in the car. I would certainly look into the knock issue and see what is causing it, but these cars seem to be notorious for false knock issues which will automatically make the car pigish.