Carl Heideman
Carl Heideman
3/11/09 9:45 a.m.

The TR6 can climb from zero to 60 mph in 10 seconds. At least, that’s what Triumph claimed early in the car’s production history.

These numbers have always seemed pretty ambitious to us, as 12 to 14 seconds seems normal for TR6s in the real world. However, even if we give Triumph the benefit of the doubt, those acceleration numbers are pretty lackluster in these days of 10-second minivans. While the TR6 is a beautiful car, it can’t get by on looks and iffy claims alone. To return some street cred to the TR6, we set out to make some tried-and-true performance improvements on the car.

Our subject car is a very nice 1975 model that came to us with bone-stock running gear, including the engine, carbs and ignition. Before starting, we baselined its acceleration and horsepower figures. The car covered the zero-to-60 sprint in about 13.5 seconds—disappointing, but what we expected—while its engine produced a maximum of 74 horsepower at the rear wheels. That horsepower number was also right where we expected it to be.

Our goal was simple: We wanted to improve performance without sacrificing drivability. Additionally, we didn’t want to rebuild the engine or make overly expensive changes. To that end, we decided on some mild changes that would give our TR6 the desired performance boost while maintaining its docile street manners.

The meat of our recipe would be a ported and shaved cylinder head. To help get more air and fuel through that head, we’d also be adding a new camshaft, a pair of side-draft carburetors and a performance exhaust. Finally, we’d give the engine a good tune-up.

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roverguy New Reader
1/9/20 1:50 p.m.

If you have a pre 72 car you should look for a later Wide port circle B head, they are known to have better flow out of the box. There are plenty of late model engines around for short money.

FYI you will need a wide port intake manifold also; Exhaust is the same.

I picked up a wide port head for $125 (stalled project) that had a recent valve job for my 70 TR6 that I intend on installing.

Never heard of the new Weber, but they are much less expensive that DCOE's; bet they are not made in Italy either.

I installed SU HS6's on my TR250 and that was a nice upgrade.

wspohn Dork
1/9/20 5:34 p.m.

The TR6 suffered from the same issue that the TR250 had - it was a car that was very little faster than the TR-4A, because there was only a scant few more horsepower in the emission gutted straight six than the old four banger. It was down 46 bhp on the injected home market version that did 0-60 in the 8 second range.

It also had some interesting design eccentricities that required eliminating for those wanting to race them.  Like only half the thrust washer shims a regular engine had which lead to early end float issues, and rear driveshafts that had a tendency to lock the sliding shafts under hard acceleration and cornering. Racers changed the thrusts regularly and replaced the rear axle shafts with units that carried a much better design that would actually slide reliably when called on to do so.

Credit where credit is due, though. The cut-rate styling overhaul done on the TR4 shape transformed that car's looks and cost far less than a normal redesign normally did. It is a handsome car.  If only it didn't look like a female dog squatting for a whizz when under hard acceleration, due to excessively soft rear springs being specified.


1/10/20 9:48 a.m.

I'd like to have a word with the guy that considers head porting to be an "easy upgrade". Unless you consider writing the check to the mechanic to be the hard part.

keithstewart None
1/17/20 5:30 p.m.

It would be interesting to know the similarities and differences between this kit and the Weber 45MCHH kit that was put together a few years ago. Obviously, the air cleaners are a bit different with a KN type air filter being provided on the earlier 45MCHH. I have a set of these on my wife's TR6 and they have been bullet-proof - requiring no tuning in the eight years we have owned the car. We also have the GP2 cam - a great combination. BTW, although you mention the carb is 1/2 a Weber 45, I believe the MCHH refers to the fact that it is a Motor Cycle Half Height carb.

wspohn Dork
1/18/20 11:59 a.m.

FWIW, a lot of Mikuni HSR carbs are being used on things like TRs and MGs as well.


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