Doug,
Here is some additional info that might help you with your decision:
TR6 Compression Ratios:
1972-76 PI Models : 9.5 - 1
Pre-1972 Carb Mdl: 8.5 - 1
1972-76 Carb Mdl: 7.75 - 1
>From the Competition Prep Manual:
"The first operation with the cylinder head is to measure from the
combustion chamber face to the valve cover surface so present compression
ratio can be determined. The stock compression of 8.5 is present if the
cylinder head is 3.460" thick. Later engines have thicker cylinder heads
i.e. up to 3.550" thick."
For 10.0-1 CR the head should measure 3.375"
For 10.25-1 CR use the above figure and machine block for zero deck
clearance.
Hope this helps,
Hugh Barber
Hollister, CA
'73 TR6
-----Original Message-----
From: doug shook [mailto:dirtbeard@pacbell.net]
Sent: Sunday, July 13, 2003 8:30 PM
To: Hugh Barber
Cc: 6pack@autox.team.net
Subject: Re: cutting down cyl head for '74 TR6, octane, etc.
> Doug,
>
> This is a question that is more complicated than it appears on the
surface.
> Generally cars with higher compression ratios (even the UK TR6) have other
> engine caracteristics optimised to the higher compression. For instance,
my
> TR6 has 10:1 CR. However it also has a different camshaft, a modified
> distributor curve, triple webers, and a header. The modified camshaft
allows
> me to run 10:1 CR without problems - indeed, with that particular camshaft
> you need to run higher compression to gain the whole benefit. I must use
> premium fuel, but rarely have any pinging. Merely raising your compression
> without changing cam or ignition timing can give you negligable power
> benefits along with a tendency toward knocking or pinging. For a good
> synopsis of this, go to: http://www.elgincams.com/campaper.html (its
> primarily about camshafts, but touches on compression ratio and other
> factors)
>
> Hope this helps,
>
> Hugh Barber
> Hollister, CA
> '73 TR6
Hi Hugh,
Thank you very much for your feedback and
insightful information. I have a NOS cam, header
and will ultimately move over to SK's or Webers,
but will not do a different cam for the near future.
I do know the more aggressive cams have more
overlap so that one needs to go to higher
mechanical compression to retain the same applied
compression, so that a higher compression with a
milder cam can lead to detonation.
But what I was hoping to figure out was with a
basically stock engine (better carbs and freer
flowing exhaust), was how many thousands should I
mill off the head without resorting to aviation fuel?
I know that the BP Northwest and others sell
shorter pushrods for a milled head, but I just
hoped to hear what others had done to at least
regain the lost HP form the lower compression of
the 1970's motors.
Again, Hugh, thank you very much for your
response. I really should have included my
exhaust, cam, carb configuration in the original
request -- my apologies. I hate it when people
post questions like:
"My engine won't start, what is wrong?" In
hindsight, I realize that my initial post is in
the same category.
My apologies.... :(
shook
los angeles
'72 BSA B50SS
'74 Triumph TR6
'01 HD XL883
'03 GMC Cargo Van
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