Hi all,
I'm going to solicit for anyone' s experiences here to try and cut down on my
development time. The Triumph TR4/4A Comp. Prep. Manual says that compression
can be raised to 10.2 for a hot "street motor" by milling 0.090" from the head.
Being the nervous sort, and since I'm using a shim steel head gasket, I opted to
only have 0.080" milled. I calculated my compression ratio at around 9.8 to
9.9, depending on which deck height I used and how thick the compressed height
of the gasket turns out to be (see other message). I still have to grind out
the shroud around the intake valve, and radius in the squish area a little bit,
which will drop my compression a little more I'm sure.
Here's the rub: my little shareware compression calculator program says that I
can go up to a 10.3 compression ratio and get away with 94 octane fuel.
However, an article published in Grassroots Motorsports magazine last month said
that their VW GTI detonated a set of pistons at a 10.0 compression ratio because
they were running less than 100 octane.
I realize this is comparing apples and oranges, but it got me wondering. Have
any of you milled your heads, and how much? What were your fuel requirements?
I figure I'm in a pretty good position right now, cuz I will lower the
compression further by removing that intake shroud and radiusing the squish
area, but I could raise it by having an additional 0.005" to 0.010" milled off
the face. BTW, I'm also running 87mm pistons and the 'D' type cam profile. The
intake valves are 0.100" oversize.
Any advice, comments, or experiences greatly appreciated!
Thanks,
David Rupert
75701.242@compuserve.com
1967 TR4A (rigid axle)
1980 TR7 convertible
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