nonstop

Quick question guys. Put a crane cam/springs Hyd flat tappet 571/556- 238/242 @ 50 with a 114. Its a 496 with 6.38 H bean scatt rods, scatt forged steel crank, 502 retc port iron heads, Wont go past 5000 rpm with a holly 850 dp 78/83, a 24 3 blade and tops out at 60 to 62 on flat water and 65 on 1 to 2 foot chop. Pistons are forged 9:25/1. The cam called for a min of 10/1. Is that the reason for low rpm? Cam and intake are good for 6800 rpm. I am running stock manifolds and risers with custom down tubes to stop reversion. Are they holding the engine back?

mike tkach

iTrader: (3)

what are u running total timing at?the stock exhaust is very restrictave and may be part of the problem.

FIXX

iTrader: (2)

is this engine in a tug boat??? year make and model would help also..

nonstop

Timing is at 30 full advance. I did bump it up a bit to about 35 but had a bit of piston splatter on the the plugs so I went back to 30. Rpm was about the same. The boat is a 1988 Scarab Concept 23 ft. Single step hull, about 1 inch. weight is 3400lbs

nonstop

Have seen several dyno pulls with 9:1/ cast iron heads pull in 550 hp range. My engine seems to fall off at 4600 rpm. It will go to 4900/5000 trimmed to the max but no more speed.

mike tkach

iTrader: (3)

that combination should like 35 total timing,when installing the cam did you degree it in.when you say piston splatter,do you mean detonation?

sprink58

Consider trying lower prop pitch. You don't mention what your drive ratio is but with any thing less than 1.5 you are biting too much water. In any case...try a 22" or 23" and see if that lets that rig wind on out. I think you might be on to something with running less compression than the cam card calls for.

There will be those here that will think I'm nuts for suggesting this but you might see some benefit in advancing the cam 2*~ 4* to move the power curve to a lower RPM....just an idea to consider.

Good luck with this. After all of your efforts you must be pi$$ed off.

bajabob

check fuel pressure . 7 1/2 pd check wot see if it drop???? if thats ok ? try added more jet in the sec. maybe 88. the best thing is a a/f box that works the best for dail in the carb.. i had a 454 30 over with 500hp and my timing was 36degree and 850holley with 84jets prim 88 sec . ti ran 5200rpm take the check vale out of the tank

FIXX

iTrader: (2)

put timing @ 32*..the jet sizes your running are close to what im running on my 355.78/82.just remember 4 sizes either way on the carb,if you need to go bigger you will need to open up the holes behind the power valve's..

nonstop

Thinking back to my bracket racing days. We ran nitrous, the added fuel wasn't there to make power, it was there to help cool the cyl temps when the nitrous was added. We also took out timing when on the bottle. When I had my timing bumped up I am now thinking I was off with my jetting. This is the reason for the aluminum splatter, detonation to what I thought was to much timing when in fact it might have been just not enough fuel.