Engine Mods for a standard marine engine.

[Robin Little]

Hi all.

I have had a slight change in my engine building plans. ( mainly due to a change in circumstances/Finances)

So I have a new standard 302 marine engine which I have stripped as it has been sitting for a while.

So I am looking at skimming the heads and fitting another cam.

So the question is how far to go with head skimming? Heads are E5AE CA with I think 68cc combustion chambers.

I want to stay using UK unleaded without adding Octane booster.

10-1 comp ratio ? if so without having to measure the heads how much do I need to remove? or is this too high

Also can anybody recommend a cam that is basically a fast road cam ( dont mind an lumpy tickover) adds to the character. Hydraulic lifters fitted just now.

Thanks in anticipation of your help.

 

[Jim Cowden]

what octane rating is pome fuel.

Its easy to measure the chambers.
a peice of perspex with a small hole in it, some grease on the head face to seal it.
Buy a large hypodermic syringe with increments on it.
Then fill it through the hole

expensive if the chamber its not what you think?

The comp will be dependant on the cam selection

What ever comp you bleed off with the larger cam you need to put back in with the comp ratio.

Jim

 

[Andy Green]

Hi Robin,
I think you need to calculate what your existing compression ratio is with the std pistons. If they are dished, I think it’s unlikely to achieve a 10.0:1 ration by skimming the heads alone, mainly as it will upset the valve train geometry and require shorter pushrods. It may be easier to bite the bullet and get a set of higher CR (flat top or raised crown, ~£150 from RealSteel)<?xml:namespace prefix = o ns = "urn:schemas-microsoft-com<img src=" /><o></o>
Regards<o></o>
Andy<o></o>

 

[Mike Huddart]

Even if you allready have flat top pistons, which I doubt, you're never going to get 10-1 compression with those heads. As a rule of thumb you need to skim the head .007" to get a 1cc reduction, even if you skimmed .070" to 58cc you would still be only about 9.5-1 and before you ask you CANNOT skim .070 off the heads unless you want to be constantly blowing gaskets.
By the way, flat top pistons are £76.50 plus VAT.

Mike

 

[flatchat(Chris)]

Basic compression Ratio calculator
RSR Static Compression Ratio Calculator

 

[Jac Mac]

Get the piston to head clearance in th 0.040" 0.045" range before you even think about skimming heads etc.

 

[flatchat(Chris)]

"Quench" or "squish band" -- (to do with detonation prevention) explained :- www.rbracing-rsr.com/squishcalc1.html

 

[Robin Little]

Sorry for the delay in replying to my own thread.

UK fuel will be about 95 ron upto approx 98/99 on some of the supers.

As for the pistons, they are flat top with only very small valve cutouts.

existing comp ration is 8.75-1 and with some material removed I am now upto 9.25-1 still not quite where i want to be but ok for now can always take a rethink after the vehicle is on the road.

still struggling on the cam selection though Summit have recommended the Comp Cams CL31-218-2 so will have a think about it but would prefer somthing that is available locally in the UK. ??????


Thanks