On the intake ports, I ground open the actual intake using a gradual slope
until it was slightly bigger then the matching ports on the HS4 intake
manifold. I did not polish the intake venturi too much as the Comp Manual
did not recommend it. Rather, I removed all the burs and smooth the
surface just a bit.
The exhaust ports were smoothed until almost polished. Very difficult to
get in there. I've heard two opinions on this. One says that the exhaust
isn't worth the effort b/c it's going to carbon up anyway. THe other says
that a very smoothe port will cause a great deal of the carbon that would
have normally stuck to continue to blow out the exhaust. You choose.
Under the valves, I chose to make nice deep D shaped pockets, for good
puffing action. Go straight down from the valve seat and make a relatively
sharp cut in to the rest of the port. Relative to stock, that is. The goal
is to make the turn into the shape of a D rather than the shape of an O.
Standard valves and hardened seat inserts complete with dual valve springs
and standard guides. No combustion chamber modifications although the Comp
manual has a description and diagram of their modifications. Be sure to cc
the intake ports so that the pockets are matched.
Vizard's book on cylinder head modification was invaluable for the job.
Very precise and very in depth.
I used a Craftsman Rotory Tool with aluminum oxide stones on a flex shaft.
The machine shop that did the engine machining and assembly did the ccing of
the head, and matched all the ports as my work was a little off.
THis was my first time, but I learned alot doing it. Good luck and if the
guides are in place, don't grind off too much when making the pockets.
MIchael
'78 Midget
-----Original Message-----
From: Vic Whitmore [mailto:vicwhit@home.com]
Sent: Tuesday, October 17, 2000 12:26 PM
To: Spitfires Maillist
Subject: Porting and Polishing
If you have ported and polished your head (1500 engine) yourself, I would
like
to hear of your experience and helpful hints you can add. Where and how much
material did you grind on the intake ports? Any problems?
I have read the Standard Abrasives guide to Porting and Polishing which is
very
good but is not specific to the Spitfire/Midget 1500 engine.
Vic Whitmore
76 Spitfire
Thornhill, Ontario
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