combustion chamber size

[wildbob]

I'm curious, if you go with a bigger bore, do you need a larger combustion chamber. In looking at the specs for my 4v head, it says it has a 55mm combustion chamber. My BBK is a 58.5.. I'm a noob, so is this a issue?

[wildbob]

all good, tom gave me the info.

[351mustanger]

You should share. I am curious.

[wildbob]

Quoted via email:
First off yes in most
cases the Ruima head can be used with your 58.5 kit. The 55mm chamber of
the head will give you a higher compression ratio as compared to if you
had a 58.5 or larger chamber. What I would check is for valve clearance
between vales and piston. Your 58.5 piston will have 2 valve reliefs. In
most cases there is enough clearance but some of the Ruima heads have
small valves and some large valves. The new improved head uses the larger
valves in which the head has been redesigned to accommodate the larger
valves by putting them at a different angle. I have run into some head/
piston combinations in which clearance was lacking. In this case you will
either have to machine the piston top or go with a 4 valve relief piston.
What you will need to do is to apply some either Play Do or modeling
putty to top of piston covering only the reliefs. Make sure to oil top of
piston and valves so as to keep the putty from sticking. Install the head
and cam then tighten. Rotate the engine a couple times then remove the
head. Carefully remove the putty then using a razor blade slice the putty
through center of indention made by the valves and measure the thickness
using a veneer caliper. Some will run with only .050" clearance which
will be fine but close if ever a valve floats due to over reving or weak
springs. A safer clearance is .075"-.100" if running at high rpms. If
piston hits valves then a 4 valve relief piston will be needed. If
clearance is close then a shim placed under cylinder or doubled up head
gasket will work.

The 4 valve head is a huge improvement over the 2 valve head and not much
should be done in the way of porting. The head can be improved but with
removing much less material as compared to the 2 valve head. I do what I
call finish port for $40.00 with 90% of the work done in the throat area.
Hope I've answered your questions. If you need any further instructions
on checking the valve to piston clearance or whatever you can give me a
call @662-301-1563 or e-mail me but I can explain in greater detail much
quicker over the phone."


TOM

[351mustanger]

Cool. Thanks wildbob