boschvette

I have just built a 383 using a lunati stroker kit with 6cc pistons matched to CNC ported CBM 64 cc 243 heads with 1.8 rockers gives it approx 10.8 compression it has a vcm 13 cam which is a 238 242 603 112 spec cam. It has a edelbrock single plane high rise manifold and a 850cfm dominator carbie with a dry sump so why am I only making 420 rwhp? I have checked the cam timing and it is setup dot to dot. And it runs a edelbrock timing module that is fully programable. It also has a crank driven dry sump.
When I do a compression test all cylinders have 160 psi.
It should make a lot more power why isn't it?

bosco022

We have a near identical set up in one of our road race cars, save for it uses a 750 carb and stock 1.7 rockers with a similar cam. Ours made 550 at the flywheel with the current cam, and 570 with a bigger cam. Probably about 500 to the wheels. It is a very strong performer.

Something is amiss, Could the cam have a wiped lobe or something? Geometry with the 1.8 rockers wrong? We use the MSD 6012 box. On the track, our motor with the smaller cam outperforms the big cam version. The torque comes in much earlier. My 346 LS6 with ASA type cam and CNC heads makes more than 420 at the wheels.

LateBreak

I know you said you checked the cam timing at the sprocket and it was dot-to-dot, but have you actually 'checked' it to verify with a degree wheel and dial indicator? That'd be my first step if you haven't already, there's no guarantee that the dots are correct.

Also, how's the carb tuning and ignition timing curve look? Either one of those could easily hurt your peak power.

Black89Z51

Can you post a scan or pic of the dyno graph with AFR?

FASTFATBOY

Put 1.7 rockers back on it.

Did you buy .100 longer valves for the 1.8 rockers?

I bet the 1.8 rockers are the issue and/or pushrod length.

boschvette

I am not sure why 1.8 rockers would make about 80 rwhp difference.
No I haven't put longer valves in but I had these heads on the car before I rebuilt the bottom end and they are untouched and worked perfectly

LateBreak

I don't know that it'd cause 80hp loss, but running them with stock valves and PR's can cause longevity issues because the geometry is probably wrong. When we were building OHC Ford 2300's, bad valvetrain geometry would cause motors to almost immediately spit followers, which made it a critical part of the build. An LS1 valvetrain will hide a lot more geometry sins in the short-term but will still be hurt by them in the long run, especially in a race application.

Ultimately, I think it's important in your case to verify cam timing and lift at the valve with a degree wheel and dial indicator and take it from there

FASTFATBOY

Post the timing and A/F ratio maps.

boschvette

I think I have found the problem. It has massive crank case pressure because the dry sump pump isn't pumping fast enough to cause a vacumn and all the breathers were blocked off.i will re plumb the lines through my catch cans and bang it back on the dyno and then post the results. It had that much crank case pressure when we took it to the track for its first run it blew the rocker cover gasket out.

FASTFATBOY

Why would the dry sump cause this?

Vacuum pump maybe. But the dry sump?

boschvette

I should clarify that I will plumb up some breathers through my rocker covers so the the motor can breath through these

LateBreak

Glad to hear you found the problem, eager to hear the real numbers

Many dry sump engines have so much scavenging versus the oil they pump back in, that they'll actually pull a vacuum in the engine, just like a PCV system that uses engine vacuum on the crankcase. Because they function this way, you can generally 'seal' the engine and just vent the dry sump tank, ensuring that any oil vapor is contained in the oil system, rather than spraying in the engine bay or pulling into the intake.

Pulling a vacuum on the crankcase is good for a number of reasons, but at a minimum it needs to be ventilated to evacuate pressure that builds from normal combustion and engine operation. If that pressure build rate is higher than the dry sump can overcome on an airtight engine, it will build pressure in the crankcase, which in his case is blowing gaskets and using up horsepower by adding another force for the pistons to overcome