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He is right that there is a lot to be gained with compression, there are
also some negative tradeoffs, like higher maintenance and lower engine
life. Based on my experience, I don't believe the 40-50% figure. In
addition, compression won't do it alone. To increase the horsepower of
your engine, you have to look at cylinder head porting and combustion
chamber profiling, valve grind geometry, and flow around the valve stems
and guides. Also important are carburetor and manifold porting, and
matching of manifold to head and carburetor body, camshaft grind, valve
springs, and rocker geometry. All of these items help get more air/fuel
into the combustion chamber. Without improving these, compression by
itself will help, but not nearly as significantly as your machinist
suggests.
You also need to be able to get the exhaust out. This was always the
restriction on the TR-4 heads, due to the poor shape of the exhaust port.
Again, cam, porting, matching of ports, and headers are all important.
When I first started racing, I was always looking for the one 'magic
secret' which was going to give me that amazing horsepower that everyone
else seemed to have. A lot of well meaning people were willing to give me
advice as to the 'magic secret'. Unfortunately, I eventually learned that
there is no magic secret. It isn't magic which makes horsepower. As Kas
said in his book, it's attention to all the little things. If you do all
of the things I mentioned above, you will find 100 other 'little things'
that you will also have to fix or improve along the way. For instance,
rocker pedestal studs will break as you go to higher lift cams, so better
designed pedestals and stronger studs need to be used. More stress
requires better quality and lighter weight valve spring retainers. Higher
RPM's are also required to generate more horsepower. This means Carillo
(or other aftermarket) rods, billet cranks, etc. On the TR-4, the stock
rear seal leaks pretty badly at 7,000 RPM's, thus a new seal design is
required.
I could go on and on. I'm sure most of the people on the FOT list could as
well. Don't be fooled into thinking that more compression will give you
lots of horsepower without fully developing the rest of the engine, and
beefing it up to withstand the additional stresses.
Good luck.
-----Original Message-----
From: Bob Kramer [SMTP:rgk@flash.net]
Sent: Monday, October 11, 1999 10:09 AM
To: FOT
Subject: TR compression vs. HP
FOT,
I know that some of the more seasoned and/or engineering types out there
know the answer to this question. My machinist claims that an increase in
compression from 10.5 to 1 to 12.5 to 1 will produce serious HP gains,
something like 40 to 50%. Is that true?
Bob Kramer
TR3A, TR6, TR4A, Devin TR3
Hill Country Triumph Club
Corinthians Vintage Auto Racing
rgk@flash.net
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