Well I previously wiped a cam and recently put the engine back together with essentially the same components. Problem is I lost 400-500 RPM in the process.
460 Ford .030 over, different block
KB Hypers, new rings and gapped to marine specs
Comp Cam 585/305, 1/4 turn lash on hydronic lifters
New lifters and push rods
Same valves lapped & shimmed
Eagle H Beam rods
Rotating assembly balance way within 1/2 gram
Dual Holley 600’s with tunnel ram
Aggressor A impeller.
The only changes were a different block (not decked) and the Eagle rods which replaced stock rods. Compression test showed 120PSI across the board and the plugs look clean almost too clean like it’s running lean. Idles perfect and runs good except I stay at 4500 rpm with a lot of peddle left. Vacuum at WOT is essentially zero.
Can not decking the block create this much of a compression loss? Do I need to re check valve lash and timing? I’m at a loss and pretty disappointed.
Thanks for any help in advance.
B
What your cranking compression on your previous build?
Here are s few thoughts:
The first thing that jumps out at me is the 120 PSI. Every engine that i have had with less than 160 PSI has been an absolute lazy dog. 120 PSI is indicative of a low effective compression ratio. The combustion gasses only expand so much. With an unnecessarily low static compression ratio, power and efficiency suffer.
You mentioned that the block and rods were changed. If the block is on the high end of its tolerance, the piston will not travel as close to the combustion chamber.
Is it possible that the rods are, for some reason shorter? This will further lower the piston in the bore.
I am not familiar with Ford head gaskets, but if they are anything like Chevy and Mopar, there are several different thicknesses and bore diameters available. Just changing the head gaskets alone will not make or break your compression but, in an already compression challenged engine, it all adds up.
The clearance between the cylinder head and the top of the piston is the quench distance. You should make every effort to get this below .055 inches. This has a big effect on power, efficiency, and detonation resistance.
Everything written above is strictly static compression ratio. The intake valve closing point determines the dynamic compression ratio. Basically, the intake valve closes at some point after BDC. The piston can't start compressing the air/fuel mixture until both valves are closed (theoretically).
Increasing duration, with Installed Centerline the same, delays the intake valve closing point. When the intake valve closes later, the piston is further up the cylinder, effective stroke AND compression are reduced.
Advancing the cam will make all timing events occur earlier relative to crankshaft rotation. The intake valve closes earlier, building more cylinder pressure.
I would look into advancing your camshaft 4-degrees. Be advised that advancing the cam will decrease intake valve to piston clearance. The intake valve starts opening well before the piston reaches TDC. I have never worked with a Ford 385 series, so I can't give any advice as to what is safe. Contact your cam grinder and check your piston to valve clearance.
Another other thing to consider is, was true TDC verified on your timing pointer and damper? That won't change your 120 PSI cranking pressure, but if you aren't getting the ignition timing advance that you think you are, you won't be making the power.
You can power tune your timing. Make a pass while noting your MPH and RPM. Advance your ignition timing 2-degrees, and make another pass. Repeat until further advance shows indication of detonation or the boat slows down. Then back off the timing 2-degrees.
Lastly, you need to get your AFR sorted out before anything else.
