Richard,
Most vintage groups would like you to stay with an 87mm bore, and SCCA
requires that. This is only a 1mm increase over the stock TR4 motor but
does aid compression and displacement a small amount. It is also quite
economical with the kits running about $450 or so.
Pitfalls? Be sure and check the liner protrusion from the block with rge
figure 8 gaskets installed. I think the book call for .004-.006" I use
about 3 layers of copper-coat on the figure 8 gasket and head gasket.
Before installation be sure and radius any sharp edges on the bottom of the
piston skirt, the piston dome and the top inner edge of the liner. Don't
radius the ring lands.
Some other resonable changes during your engine build,
1.a good 3 angle valve job and small compression increase by shaving the
head a bit. Shoot for about 3.200" total head thickness.
2. Have your crankshaft, pistons, rods, flywheel, clutch assembly and front
pulley balanced.
3. Try to find a machine shop who will turn your flywheel and reduce the
weight of it. There is a good section in the factory competition prep
manual about that. And the later flywheels are already lighter than the
earlier.
4. I think most of us have changed to the rubber rear oil seal kit. You
will need to have your crank turned to eliminate the spiral groove. But
these babies work well.
5. And then there is the camshaft....John Lye, what is the BFE grind you
have in your car? That may be a good one for this application.
125 HP is a resonable goal and will result in a very reliable engine with
minimal expense and maintenance. Good luck!
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From: Richard Taylor[SMTP:n196x@mindspring.com]
Sent: Tuesday, July 15, 1997 4:34 AM
To: fot@autox.team.net
Subject: Big Bore Kits
Fellow FOTers,
I recently located an old clapped-out TR-4 motor to re-build for my '66
street-legal/vintage racing Triumph. In the great American tradition, my
first thought is that the road to power is paved with cubic inches.
Contrary to my personal MO of "ready, fire, aim," I thought this time I
might take advantage of our august pool of experience and first ask you
guys for any advice you could offer. Admittedly I'm still on the uphill
slope of the learning curve but if I can lean on you all a little, I bet
next year I can bring a much better car to the track.
My questions about Big Bore Kits are:
1. Is there an optimum size?
2. What are the biggest pitfalls?
3. Is the concept of lots more cc's the right one?
4. Is much (any) special machining necessary?
5. What is the best source and cost?
My ultimate goal is to build a strong, tourqy motor; not a super high
compression fire breather. If 150 hp is somewhere around optimum for a TR-4
motor, I will shoot for 125. For you real racers this may be some sort of
perverted heresy, but for me, I will rely heavily on torque and reliabilty
until (& if) my driving skills warrant a more aggressive approach. Any
other advice you can offer will be greatly appreciated (other than to
pursue Kwaun Do or astronomy.) Thanks for your comradery.
Richard
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