<<Now I can understand the need. The excitement of competition can do
that sort of thing to one's right foot.
My experience is that the tach always reads higher than actual. If,
however, the generator pulley is larger than standard, as the company
recommended for racing MGBs, then the the tach would be read lower. Ouch.
The suggestion of a screw stop on the throttle would not do you much
good, since long downhills would allow the revs to get up. Maybe someone
on the list knows about electrical rev limiters. I note that a number of
new cars are said to have them, and they are installed in almost all
large diesel trucks. Maybe a trip to the Cummins dealer or a truckstop
would result in some ideas that you could incorporate.>>
Allow me my .02 in regard to 'T' type matters of which I know relatively
little. Some of the racing experience might cross over.
First, generator driven tachs - not very good! As stated, for competition use
at higher revs, a larger pulley is normally fitted, which throws your tach
off. In cars that rev higher normally, like the Twinkies, we have sustantially
larger stock pulleys just so tht the generators don't puke their windings as
often.
There are two alternatives - fit an electronic tach, or, the one I think I'd
favour for a 'T' type, if it works, - fit a distributor with a tach drive in
it. I've done this on the later MG engines - you simply need:
1 - a TR 6 distributor
2 - the breaker plate and weights from your MG distributor (so as to get 4
cyl, and the right advance curve
3 - someone that can make up the correct (smaller) end for the distributor end
of your tach cable
This sort of arrangement will be accurate unless you somehow manage to destroy
your distributor, in which case tachometer accuracy will be the least of your
concerns.
Next question - rev limiters. I have in the past used the following:
1 - rotor from a Rotus Cortina - mechanical limiting at 6500 rpm, adjustable
if you need to by carefully changing the weight of the limiter slug by
removing/changing the tiny screws in it or grinding the weight itself. This
set up has a weight that is attached to the centre of the rotor by little
springs. The faster the engine turns, the farther out the weight goes, until
(you guessed it - at 6500 rpm) it touches a stop thus grounding the spark and
limiting the engine. Works great, probably hard to find now, and likely
expensive. Good for the traditionalists. I have also seen a 6 cylinder model
that limits at 4500 rpm, if there are any Austin-Tractor, sorry, Healey
owners out there.
2 - Use an electronic limiter. I use an MSD unit which also, of course, gives
much better spark. The rev limiting part is adjusted by changing little two-
pronged plastic bits into a plug on the outside of the MSD unit. They are, as
I recall, available in about 200 rpm increments. By the way, it is great fun
to sneak over to a friend's car just before a practice session (not a race -
not sporting, you know) and slip a 6000 rpm chip in place of the 6800 one that
was in there. Wonderful puzzled look on his face as you pass him at the end of
the straight!
These units are reliable and very useful for their spark enhancing properties
as well.
Best mounted, I think, under the firewall or somewhere else out of sight, so
as not to look too out of period for the cars. Obviously only useful if your
rules allow them (otherwise they must be mounted _well_ out of sight :)
Bill S.
(Twinkie with MSD, TVR with Rotus Lotor)
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