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Has anyone on here cut the cylinder head down on a 94 onwards 56 cu in oval port engine and got good results ?

I ask this because I have a spare cylinder head that is a fair bit on the pitted side after the spare engine had a piston fail.
if I can get that head cut down a bit it would be a good spare or infact be put on my good engine to raise compression.
at the moment my compression is 145-147-145 with stone cold engine empty carbs etc.
I would like to get as high as possible without filling in the relief holes in the bore's.

if you have done this , how much can be taken off the head before it hits and causes trouble. ?

I am not a racer so scrutinising is no problem, its just for my own use and no club rules to worry about.

also how much gain in psi can be expected with a shaving of 50 thou and what would this mean in horsepower ?

Any info guys ?

Hi
In the 90's I played around with the OMC 56ci heads and found that the most that can be shave is 50 thou off the standard SST 60 head. any more than that and the heads start to crack. The thickness of these STD heads vary and that will also impact on what can be shaved. From memory the std SST 60 combustion chamber measures to a depth of 0.450 so you can go to .040 but I can not remember what compression that gives. To be on the safe side I would take 0.030 off the std SST 60 to measure 0.420.

Stephen Medaris

100 thou gives you 50lbs on the fishing head. None of ours ever cracked. You need to relieve the water channels also to ensure water can still pass thru.

Not on the 56 cid head. There are no water channels. I think you are referring to the 49.7 cid heads with water channels. You can cut the head until the thickness of the water passage at the thermostat area is 0.100" thick. Less than that, and heads will warp. That will raise compression with SST-60 porting to 175-180 psi. Better punch, no top end gain.

[quote="phillnjack"]Has anyone on here cut the cylinder head down on a 94 onwards 56 cu in oval port engine and got good results ?

You guys are missing an important part of the post. THE QUOTE above. The motor he is referring to is an oval port. Unlike the bridge port SST 60 you are referring to. The stock oval port is 140 to 147 without cutting the head. I think the compression would jump to 180 to 200 if you cut the head.

All he needs to do is surface the block and head. Change the reeds. Change the carbs to the larger bridge port SST60 carbs. Run 77 to 79 jets. The result is 10 hp more with lots of torgue.

Hounddog, if that was your play motor would you do a bit of port work while you are at it?
I wonder how that block would react to finger ports.
My best running 56 cu was my oval port

I have never been a person to mod motors. I have always thought that the engineers that developed the motor are much smarter than me. I do believe that blue printing and balancing does make a difference in performance and in engine life. Finger ports, porting and other mods can make a difference. Most times you gain in some areas and lose in others. I have raced people that spend thousands of dollars on a 10 hour life powerhead. If they can afford it, good for them. So to answer your question. If that was my powerhead. I would put the most perfect crank I had, 3 perfectly matched rods, bore 30 over and use OMC Pistons. Match port the
Sleeves, surface the head and block, run the SST 60 carbs with 79 jets, late 80's 49 OMC ignition (they were made in the U.S. and Mexico), a mod 50 OMC flywheel. I think the motor would turn between 7000 and 7300 rpm and pull like jack the bear from 4000 to 7000! And last for years.

Thanks for the info. The oval ports powerheads are hard to come by though.

no internal mods to ports or pistons will be done on this engine until it needs them (hopefully a long time yet)

carbs are now biggest bore carbs (late 70hp carbs 1.5 inch venturi with standard jets )

cylinder head is the standard one piece late flat back head (no waterways to get to ).same as sst60 head just not shaved at all (YET).

just wanted to know what gain would be made with say 80 though skimmed off, as the head I am wanting to know about is a
damaged head from my spares engine.
there is nothing at all wrong with the head on my engine and that will stay like it is once I get the other head done (if its worth doing ).
if I wouldn't get atleast 3hp from raising the compression alone then I will have a re-think about getting it shaved.

would I get say 10 psi more by shaving 60 thou . and what could just 10psi give in bhp ?

this might sound like a daft question as nothing else will be done at same time. but every little bit helps ha ha

the reason I dont want a fully high performance engine is reliability and longevity, the more I keep it standard the longer it will live (I hope).
ive already gone up 10bhp by putting on the bigger 70hp carbs from my smaller original 60hp 1.25 inch carbs that engine was originaly fitted with.

I am just looking for simple mods without a complete teardown.