end up calling it, if I ever get around to doing more than I have lately.
mjb.
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The Triumph 6 is a cast iron block, cast iron head pushrod engine of 2
or 2.5 liter displacement. The 2 liter (1998cc) engine was found in
the GT6, as well as the Triumph 2000 sedan. An earlier version of
1600 cc or so was fitted to the Vitesse, I believe. This 2 liter 6
has a bore of 2.94 inches and a stroke of 2.992 inches. Basically
square. The 2.5 liter engine, actually 2498cc, uses the same bore but
increases the stroke three quarters of inch to 3.74 inches. The early
TR-250 and TR5 cars even used the same block as the GT6, but later the
larger displacement cars got a slightly different block with a bit
more clearence at the bottom for the crank throws.
The early GT6 Mark I engine (66-68) had a head with pushrod guides being
pressed in tubes, while later cars of both displacements used the same head
casting with integral guides. In the long stroke motor the head was used as
cast, but the 2 liter got it trimmed down to maintain good compression.
[Actually some early cars had different port spacing than later cars.] This
will be covered in more detail in the section on heads and intake systems.
Rather than write a lot of confusing numbers, here's a chart in which all the
confusing numbers are well organized. I will use the US of A market and model
designations and specs unless noted.
[Redo chart in vertical format, add late GT6 and 106 bhp TR6]
GT6 Mk. I GT6+ GT6 Mk. III TR250 TR6a TR6b
Years 66-68 69-70 71-73 68 69-73 74-76
disp. 1998 1998 1998 2498 2498 2498
stroke 2.992 2.992 2.992 3.74 3.74 3.74
CR 8.5:1 9.25:1 9.25:1 8.5:1 8.5:1 7.75:1
bhp 95@5000 95@4700 95@4700 111@4500 104@4500 101@4900
torque 117@3000 117@3400 117@3400 152@3000 142@3000 128@3000
There is some discrepency as to when the low-compression TR6 came about, and
what the actual power output is for that motor. Maybe I should have thrown in
the specs for 9.5:1 injected TR6 just for fun. Anyway, later cars (75-76?) had
106 bhp but same torque and compression. Look at page 43 of the Bentleys for
some further info about which year did what. 72 and 73 TR6s were actually
different enough to warrant their own column above, but the chart is wide
enough as is. Also, the GT6 Mk. III was manufactured up until december of 73,
so you may actually come across a car labeled as a '74 model year car.
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