Getting ready for a 2F rebuild how much to shave the head?

[oregonfj]

Hi there, my 78 2F is getting kinda tired so I'm beginning the planning stage of rebuilding a 78 2F motor I got form a wreck. Its a domed piston open chamber motor that looks like will need to be bored at least .030 over. My question is how much should I ask the machinist to shave from the head for a little better performance? I've read through every post I can find on the subject and the numbers seem to vary from .030 to .100. Im just looking at mild mods so far including the existing motors header and weber 32/36 carb. I will have the motor balanced, install a RV cam kit and probably do some port matching. Im still studying oiling system mods also but dont know if this is required for a low rpm cruiser. Any info would be helpful.

Thanks,

 

[ingomar]

I have never rebuilt a 2F. Other guys can give specifics on what they did, but I think I can offer a couple suggestions. Today's regular gas probably has less octane than the regular of the late 70's, and any real increase in comp. will likely require premium fuel. Also, .1 is a ton of head milling, and will affect rocker arm/valvetrain geometry if nothing else.
If you have the time to research this, ROSS pistons has a nice comp. calculator on their website. You will need to know the displacement of the piston dome in CC's, and the comb. chamber volume of the head. The latter can usually be measured by the shop pretty easy, and most piston mfg's can tell you what your piston will displace. Gasket thickness has an effect, and the amount the piston sits down in the hole at TDC ( piston deck height).
If you do a little research, and your shop is willing to work with you, you can mill the head to achieve the chamber CC and thus the comp. ratio you want. For regular gas, especially in a low-rpm, "lug-it" style motor, 8-1 is plenty.
For some guys this is fun, but if all this is a hassle to you, offhand I'd say go no more than .020 unless premium fuel is used.

 

[oregonfj]

Cool, I'll look into that ingomar. Anyone know what the original 2F compression is supposed to be?

 

[Mark W]

The F series engines will run on Mexican ditch water for gasoline.

They were never designed for high octane.

1978 2F nominal compression is 7.8:1

I have rebuilt a few 2fs. I have cut a lot of heads the full .100 and have never needed to worry about the gas I put in them and never have any valvetrain problems.

.02 - .03 is not going to make enough difference to bother.


Mark...

 

[Sonny 1]

if you take it to a good machine shop then they will let you know what it needs. but you also need to take into acount for the newer gasket thickness to the older ones. for example on a small block chevy they came from the fractory with a stamped steel head gasket and when you replace the head gasket with a new compstion head gasket the new one will be measured at around 35 thousands thick and the old ones are around 14 thousands thick, and then if your puting new pistons in you will need to find out if they are de stroked or not, and if they are then you need to figure for that also. what you want is to get it as close as possiable to factory . in a chevy they call it ("0" decking it) so you need to find out what the factory called for. then find a good machine shop and explain what you want it to do, and they will let you know what needs to be done, and how much needs to be taken off of the head, and the top of the block. just my 2 cents

 

[Sonny 1]

sorry i didnt look to see where you were from if you dont have a good machine shop in eagle point , i can tell you where one is in Mcminville Or. and witch machinest to ask for also thats where i get all my work done at

 

[oregonfj]

Yeah I need to get off my lazy butt and figure actual compression ratio with whatever pistons I will end up using after the bore job. Probably want 9:1 or less. I'm not too worried about quench area on this build. I had a lot of fun figuring proper quench area and compression on this other current project motor

 

[ingomar]

Well oregonfj, looks like you have been thru this! Could I ask, why not consider block decking to help get your quench closer to optimum? I know nothing is cheap, but you wouldn't have to mill the head quite as much, and I think you already know the benefits of good quench. Have fun!