I am thinking of picking up a used portflow head. The head has the combustion chambers taken out to 84mm, and I want to run it on my 81mm block for now. Is there going to be any sealing/headgasket issues with this combo? And if not, how much will this drop my compression? I will be installing some new flat-faced valves to help raise the c/r again. Is there anything in particular I should be weary of?

 

You don't want a larger chamber than cylinder bore. I would not run that head on anything other than an 84+mm bore.

 

Good advice, heed it.

 

What are some of the risks of running a smaller cylinder bore than combustion chamber? I have been told I would be fine if I stayed with N/A. I was also told that if I ran boost, my main problem would be head-gaskets.

 

It would drop your compression significantly, create issues with head gasket sealing but it also creates a space where the combustion expansion would get trapped outside of the bore.....bad things just waiting to happen.

 

just get a b20 block then...

 

Detonation will happen. You'll get an ara filled with red hot combustion deposits. Plus you'll have nice sharp edge right at the top of the cylinder, where most of the heat is concentrated.

 

x2, sharp edges pick up and hold heat. think about a scratch on top of the cylinder, perfect place for detonation/pre-ignition to happen.

if youve ever noticed there are no sharp edges exposed inside any cylinder. the edge of the piston is slightly radiused, the valves dont have sharp edges........everything has at least a very slight radius.

 

I am currently looking..... Just hate to get rid of such a fresh block before it was even ran.

 

then find another head.

 

Why? I can find another block......... and I'll get more torque. Can't complain about that. Just want to know exactly what my options are with the pressure of making a sale on some machine work involved.

 

make up you mind.

 

If you don't have any more info on the topic then just don't post. I don't need advise on which way to go......... I can make that decision on my own. The shortblock was just assembled, so I am sure you can see why one might not want to retract on such an endeavor.

 

this coming from a kid who cant even spell vtec right....lol

 

c'mon....easy now..

 

That was a good joke about 3000 times ago......... Go be annoying elsewhere please! Or else post some pertinent info.