Camshaft timing and duration are closely linked to compression ratio. The
longer the duration of the cam, the higher the compression ratio needed to
make it work properly. Properly meaning "make real power" not just give the
ability to rev in the lower gears. I have driven quite a few cars that had
295 degree + seat to seat duration cams in them that felt great and real
fast in 1'st and 2'nd gears, but in 3'rd and top just sat there and made a
lot of noise but would not really continue to accelerate up the rev range as
they should have. In every case the culprit was lack of adequate
compression to go with the cam that had been installed.
The rule of thumb that we use is: duration up to 280 degrees needs 9.5:1
up to 11:1 max
duration from 280
up to 290 needs 10.5 up to 12:1 max
duration from 295
up to 300 needs 11.5 up to 12.7:1 max
duration over
305 degrees needs 12.5 up to 13.5
The other variable in the equation are carburation, exhaust system, and
the efficiency of the porting in the cylinder head. More efficient
breathing means that less compression is necessary.
If you really want to keep the compression ratio under 11:1, then I
would recommend that you use a cam that has less than 290 degrees seat to
seat duration. A modern "fast acting, short track" type cam with lots of
lift in a well ported cylinder head might work well for racing. If it were
not well designed, it could be very hard on the valve gear because of the
high stresses caused by the high lift rates. The TR comp dept "D" cam was a
very gently cam that worked well with this compression ratio but did not
give very high lift. We use a similar cam in our 3/4 race "street and race"
engines. We have never actually dynoed one of these engines but with Weber
believe that they put out around 130 hp and with SUs probably between 120
and 125. The cam is very gentle and we normally use stock springs and
pushrods. with a 3.7 rear axle and 165 x 15 tire with SUs, this cam will
easily pull over 6,000 rpm in top gear. It makes a great road cam. For
racing, we usually recommend a 300 degree cam and 12.25: 1 CR. in an
otherwise well prepared engine.
Regards, Greg Solow
----- Original Message -----
From: <TR3197@AOL.COM>
To: <Catpusher@AOL.COM>; <owner-fot@autox.team.net>; <kaskas@earthlink.net>;
<fot@autox.team.net>
Sent: Friday, October 15, 1999 7:52 AM
Subject: TR compression vs. HP..now pistons and cams...Plus SoCal
PinewoodDerby Car.
> FOT,
>
> Hepolite pistons: oddly, a couple of years ago I came across some NOS
> Hepolites that are 87MM .030 OS. I put them on the shelf awaiting a new
> engine build. I have been slowly assembling the parts to build this engine
> and have now begun.
>
> It is good to hear of such positive remarks regarding these Hepolites, in
any
> case.
>
> BTW, if anyone has any recommendations for an intermediate cam grind for
> running vintage, I would appreciate it.
>
> I plan to be under 11:1 in CR and want power range to be near 3500-5500
RPM
> with an emphasis on reliability with a redline of 6000. I have heard some
> good things about the G-3 and TR-777 Isky cams and then I hear that this
is
> 'Old Technology' and "there are much better cams out there".
>
> I currently use the TR-666 Isky cam, per late Mike Belfer's
recommendation,
> and have done so with great relative success...the car has seen 2:58 a few
> times at Road America and this is likely the extent of our ambition. There
> are times however, when it would be nice to have a little more punch for
> passing, or simply keeping pace with some of my friends.
>
> Sidebar Comments: One note is that when our John Engine Engineering 'flow
> bench' guy examined the TR4A head he indicated that when approaching .500
> lift this engine would/should respond very well. Not being familiar with
this
> engine design he said "it sure reminded him of a tractor engine". :-)
>
> Anyway, I am prepared to take any sage advice that I can. Please
understand
> that I run a stock transmission and final drive, too.
> Regards,
> Joe
> PS: When in San Ramon for the Triumphest, Kent Howard and I enountered a
> SoCal lady who entered a pinewood derby car which was reportedly prepared,
in
> part, by a 50s and 60s Triumph Tuner of the first magnitude (resides in
> Orange County). BTW, her pinewood derby car won going away. The legacy
lives
> on.
>
>
> In a message dated 10/15/99 8:08:33 AM, Catpusher@AOL.COM wrote:
>
> <<In a message dated 10/11/99 11:06:04 AM Pacific Daylight Time,
> kaskas@earthlink.net writes:
>
> <<
> The issue of pop-up pistons has come to the fore several times over the
> years and the information never seems to be saved or passed. >>
>
> <snip>
> Once the good heads were gone, it became clear to me that pop-up pistons
> were the only option that I could think of for a motor to win the ARRC.
>
> It took a large investment of time and money to make it work in the TR3
> motor. I doubt that it was easy for Jack Wheeler, even after I let him
know
> that it could work.
>
> Kas is very correct about the flame front getting upset!
> The likes of Lester Lichty would be appalled.
>
> The increased octane of available, legal, racing fuel; the more exact
timing
> of beyond distributor ignition systems, and legal alternative con rods
> are the major changes to this
> situation since the 60s and early 70s.
>
> I did win many earlier races with the fine Hepolite 87mm pistons.
>
> I also figured out how to make the factory rear crank seal work at high
RPM,
> and always check the flywheel runout.
>
> I had a long call from Steve Froines today (TR4 Natl. Champ and the last
> West Coast JRT Comp Director) He could not help me with my wondering
> about 67 TR3 Natl. Champ Lee Midgley
>
> The Hardy HP
> </XMP>
>
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> From: Catpusher@AOL.COM
> Message-ID: <0.5917b8a1.2537f469@aol.com>
> Date: Thu, 14 Oct 1999 23:07:21 EDT
> Subject: Re: TR compression vs. HP, etc
> To: kaskas@earthlink.net, fot@autox.team.net
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