Bob:
Didn't measure the head thickness. All measurements were relative to
the volume of the combustion chamber. According to Goodparts, the head
thickness would be about 3.415" or so. Goodparts compression ratio table
agrees VERY closely with the numbers I came up with. With a 0.020" overboard,
they claim that I would need to shave the head 0.123" to achieve 9.6:1
compression. I had actually computed 0.125" to achieve 9.5:1, but lowered it a
bit when I decided to have the block decked.
If you are raising the compression ratio, decking the block is
superior to shaving the head, and should be done first. Decking the block
decreases the distance between the top of the piston and the head, increasing
squish. The higher the squish, the more efficient the combustion process, and
the more power you extract at a given compression ratio. High squish heads are
all the rage on modern engines.
The squish area on the 6 engine is relatively small, but it does have
some. Decking the block takes advantage of the squish area and enhances it's
effectiveness. This is why Kastner states emphatically in his book that the
TR6 block should be decked to 0 deck height, to maximize squish.
As for how much power I gained, I can't give you real numbers, but
Dyno2000 engine simulation predicts 12 HP by raising the compression from
7.75:1 to 9.5:1. What Dyno2000 doesn't show you is how the fuel economy jumps
way up because of increased thermal efficiency. It is a win-win-lose deal; You
win power, win fuel economy, and lose emissions because NOx increases.
Dyno2000 also does not model increased squish, except in a very broad sense by
choosing the head design (hemi, wedge, bathtub, etc).
Other modifications: Pocket porting (easy as pie with a Dremel!!), 3
angle valve job, back cut intake valves, 270/272 RV cam, lightened flywheel,
and (last minute addition) smoothed the interior of the intake manifold
(removed the casting flash). I don't think the intake manifold work gets you
anything, as the valve pocket is where the flow restriction occurs. I did the
manifold work just because I'm a lunatic; but the amount and size of the
casting flash was pretty impressive. No plans yet on a header; I will probably
not install one because I am looking for (visual at least) originality.
I did notice that port openings in the intake manifold gasket are
slightly SMALLER than the intake ports. So now I am looking for a way to
cleanly enlarge the gasket holes. Any suggestions?
Merry Christmas,
Vance
-----Original Message-----
From: RazorBobSr@aol.com [mailto:RazorBobSr@aol.com]
Sent: Sunday, December 21, 2003 2:10 PM
To: Navarrette, Vance
Subject: Re: Does 0.120" really get 9.5:1 compression?
HOW thick was the head AFTER u take 120 off??? How much HP do u think u gained
by going to 9.5,and what else have u done to eng??
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