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Help on selecting Cam for optimum Performance no more than 5500 RPMS.
Current Setup: (19ft stern drive, fresh water)
350 bored over .040 (flat top pistons)
Edelbrock RPM Aluminum heads (64cc), max lift .550
Harland Shape Rockers 1.5 ratio
Edelbrock RPM Intake
Holley 750 Double Dumper
MSD Ignition
4 inch exhaust

Not sure what compression would be now with this new setup (guesing start was at 8 :1)
Investigating Comp Cams - Help

jaroot

flat tappet or roller?

traviss

with flat tops
.025" deck clearance ( stock blocks),
.015" shim gasket,needed to keep quench around .040"
64cc heads.

Will be a little less if I had the valve pocket cc's

CR is around 11:1. if all my numbers are correct

will require more then 93 octane.

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Wanted to use normal gas (not over 93 octane)
What can I do?
Flat tappet was my thought, Comp Cams I was looking at (but have to idle)

12-240-4
226/236 intake/exhaust
480/489 valve lift
112 LSA

or
12-236-3
218/224 intake/exhaust
462/477 valve lift
112 LSA

or
XE 258 H
224/230 intake/exhaust
477/488 valve lift
110 LSA

traviss

which pistons did you put in it? stock or aftermarket? trying to find a part# to look and see how many cc's the valve pockets are.


I would think you would have to switch to a dished piston.

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Not sure what type (already installed). The have 4 smile type grooves (2 on each side), and have the .040 punched on the top. Motor is a 1972 block (if that helps). I belive pistons are nothing special?
Again thanks for the reply. I am leaning towards the Comp Cam 12-240, but a little worried about reversion, idle, and being able to plain off. Is that Cam too much?
I thought max range was 1600 to 5800 (will never get to 5800), that what the JEGS magazine indicated.

traviss

those are normal replacment pistons. universal, thats way they have 4 reliefs on each piston. With those 4 valve releifs your CR might be a little lower, maybe around 10.5-10.6 :1 maybe, just a estimate.

You should have no problems with that cam. I ran a 234/242 duration on a 112 lsa roller and had no reversion. I had it set to idle around 800.

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See your other 'thead' going (to cool.... similiar boats). So stay with the Comp Cam 12-240-4 ?? With all other setup stuff as stated in my original thead message, you think I should be all right ie: 750 double pumper, RPM Heads, RPM intake. What cam are you rocken at ?. Pretty darn fast in a 18.5 footer (what waterway). Any other motor suggestions?

traviss

that cam sounds good. If you haven't ordered the heads yet, see if you can get them with a larger combustion chamber to drop your CR to under 10:1. I had great luck running the edelbrock air gap intake on my first 383. A 750 will work great on it.

Can you measure and see what your deck clearance is, aka how far your piston is in the cylinder at TDC. Stock blocks are .025" but piston pin heights can change that. That will determine waht thickness head gasket you need.

I just put a crane solid roller in my motor, 250/258 dur. .598/.598 lift


We have a house up on van ettan lake in oscoda. spend most of my time there, and a few runs in the saginaw river/bay

traviss

I got a # of 6.1cc for 4 valve releifs. So that brings your CR down to 10.3:1 if my calculator was right

I see those heads come in 70cc versions too. That would put your CR at 9.6:1 which is perfect for 93 octane.