MC...Thanks for the post

the cam was installed at 0 degrees which is where both AZSM and Comp state to put it as far as cam advance

https://forums.iboats.com/filedata/f...otoid=10536803

Just getting thru a phone melt-down and replacement, however will go out and pull back timing to about 8 degrees and see what the results are.. Also moving the motor to the bed of the truck to run it outside and video it with the cam-corder vs the crappy phone mic

ignition is a YLM-624-AV mallory dizzy

still plan on longer pipes as I need to clear the hatch and snake around a bit. already have one set cut apart, after today, will have the others marked up. they will be re-welded this week

I’m guessing you mean the timing chain set was installed at 0, the screen shot you have there says install at 110* but what did you come up with when measured with a degree wheel?

the intake CL is 110, was measured at 110
the valve events were verified on cylinder 1.
lobe separation is 114
I specifically asked the question to both Comp and AZSM, install at 0 degrees or at 4 degrees, they both stated install at 0

Just trying to clarify to help, you installed it at 110*. 0*advance or retard.

If you installed it at 110 ICL, then it is NOT installed straight up or 0.
110 ICL means the profile is shifted +4 advanced, which IS what I would have recommended as well.
"Straight up" or 0 would be with the lobes symmetrical with each other - 114 LSA installed at 114 ICL is "Straight up" or Zero.

MC

Just getting back to this, got replacement phone late Saturday and got water back at the house on Sunday (found water line with post hole digger).

Sunday dialed timing back to 8 BTDC. while running at 820 RPM, a significant drop in reversion, however there is still some vapor getting back to the manifolds. next step will be the longer elbow runs

moved the motor from inside the garage to running outside.

https://forums.iboats.com/filedata/f...otoid=10539257

I’m assuming that 4* is already accounted for when the cam was ground and the dowel installed.

Yes, it definitely is.
And a normal installation using standard timing set and normal dowels/keys, a person has to figure that the cam will end up more or less at the advertised 110 ICL.

But if anybody is bolting on a degree wheel and using a piston stop for TDC reference, then you PUT the cam where you want it to be. Manufacturing tolerances can allow the actual installed position to vary a few degrees one way or another.
For that reason, installed cam position will always be referenced off of "straight up" regardless of where the dowels would have put it.

Zero = "Straight up" = symmetrical across the lobes.
+4 = advanced 4 crankshaft degrees from above.
-4 = retarded 4 crankshaft degrees from above.
Today's modern lobes being sometimes assymetrical, it can be important to find the centerlines of the lobes at a certain lift (half-lift is a good rule of thumb, since your accel/decel ramp schemes shouldn't be in play at that point.).

Anyhow, just trying to help the situation.

As far as timing, you can go as low as 2 degrees at idle without EGT spiking as long as your idle mix isn't too rich. The lower the initial timing, the lower the intake vacuum, and the less chance of reversion.
As long as you bring your timing back in by 1500 revs, you won't suffer any performance or efficiency loss.

MC

By the way, an OPEN HOLE phenolic spacer may free up a little HP at higher rpm, while also slightly reducing idle vacuum. You mentioned you were running a spacer, but you didn't say whether it was an open spacer or a 4 hole or 2 pocket..
Your carb choice with this package will probably keep you under 430hp. Not sure what your goals are..
The cam you are running is about the right size. Pushing 600 lift, though, I hope you notched your bores, else you missed out on a few cheap hp.

Your peak rpm will be in the 5400 neighborhood.
By the way, what rotating assembly (crank/rods/fasteners) are you running? In a boat you don't want to spin a cast bottom end past 5,000 except for short bursts.

the spacer is blended from the 4 individual throttle plates to two pocket to match the intake. bores were notched for both intake and exhaust.

post one tells you about the rotating assembly - GM performance forged crank, scat forged rods. neutral balanced with SFI flywheel and damper I have no concerns spinning the lower end at any RPM it will go.

never said i wasnt going to improve the carb if needed, things like that can be bolted on without the wife knowing in the future, however it is a 715CFM holley. so the carb should run out of steam about the same time the cam and intake does which is about 5800 RPM. same size carb on my old truck pulled 550hp at 5800 RPM