Don
Your question
>I know that the euro-spec TR-6's had fuel injection and developed 40-50hp
>more then the NA carbed versions. Was the fuel injection the only reason
>for the hp difference or were there other differences. (ie a different
>camshaft)
The following is an extract from the March 1991 edition of the magazine of
the Triumph Car Club of Victoria (Australia) - written by "PI Pete". These
should explain all the engine differences. I am not aware of any drivetrain
differences.
Peter H
73/74 TR6
*******************
For those wishing to convert a US TR6 to a real (PI) one, here are some
pointers which may help. Essentially, the vehicles differ in five main
areas:
1) Camshafts
2) Cylinder Heads
3) Manifolds and injection equipment
4) Ignition System
5) Exhaust System.
1 Camshafts
A number of different camshafts were used during the production of the
2000/2500 motors. The following table lists some of the more common
varieties plus a couple of locally available after market units.
PART# APPLICATION TIMING VALVE LIFT IDENTIFICATION
? Carburettor 24-64/64-24 0.345"
311 399 Carburettor (LATE) 18-58/58-18 0.360" 3 rings
307 689 TR5/Early TR6(150BHP)35-65/65-35 0.375" 2 Rings
311 399 Late TR6 PI (124BHP) 18-58/58-18 0.360" 3 Rings
308 778 EarlyPI Sedan 132BHP 25-65/65-25 0.345" Groove
154C Wade Road Cam 31-70/70-31 0.398"
5569 ACE Road Cam 30-70/70-30 0.402"
It is possible to simply bolt PI equipment onto an ex carb motor with a
considerable amount of success as the carb cams are usually similar to the
late TR6 Sedan PI cams. Power output will be in the range of 120 135 BHP
depending on the other components used.
If you want 150 BHP or so then you'll have to use camshaft 307689 or an
equivalent regrind if you can find one. As an alternative you could use one
of the aftermarket road cams which will give similar performance. An
advantage with the two aftermarket cams listed is that they exhibit
smoother idle characteristics as a result of the smaller amount of valve
overlap than the original TR5 camshaft.
Production cams are identified by a part no. engraved on the shaft (not the
one cast into it) and/or by a number of grooves/rings between the timing
gear mounting face and the keeper plate groove. Avoid cams with no
identification rings/grooves as these will more than likely be early 2000
cams with very tame timing.
2 Cylinder Heads
There are 4 things to look out for here :
1)compression ratio
2)intake port spacing
3)Valve size
4)Valve spring set-up
All PI heads use a compression ratio of 9.5:1 whereas most carb heads use a
8.5:1 (some US heads use even lower).
Some of the early US TR6 heads employed different spacing of the intake
ports and the PI manifolds will not line up with these.
If port spacing is OK you can have your head machined to lift the
compression ratio to 9.5:1 (You need to take something like 0.060" off on a
8.5:1 head).
Another area to watch is valve size. Earlier heads tended to have larger
valves. The hottest production set-up uses a 1.44" intake and a 1.28"
exhaust valve.
Finally make sure your head uses twin valve springs as you may experience
valve bounce with singles at high speeds (which the PI vehicles can more
readily achieve).
If you run an alternative cam, make sure that you have enough lift
available with the spring set-up used.
If all this seems a bit much you should be able to pick up a head off an
early (pre 1973) PI sedan which will do the job perfectly.
3 Manifold and Injection Equipment
Metering units, pumps, filters etc. can usually be located off another
model. The metering unit for the late model TR6 PI is the same as the late
model sedans.
The early TR6 metering unit employs different calibration springs to all
other models. However, it should be possible to adjust any metering unit to
give reasonable fuel consumption with best performance.
Intake manifolds varied slightly between models. Late model TR6's and
sedans use manifolds that are not appropriate if you want lS0 BHP or more.
The early manifolds were used on TR5s, early TR6s, Mk I PI & early Mk II
sedans. The early manifolds have fully circular ports and far better gas
flow characteristics.
If you only want 130BHP or so then the late model manifolds will do.
Another area to watch is the throttle linkage assemblies. Only the linkages
as used on the original TR5/early TR6s or Mk I sedans will bolt straight
onto your TR6. The problem with the Mk II sedan linkages (early intake
manifolds only) is that they are slightly bulkier and foul on the exhaust
manifold (only the twin pipe variety).
All is not lost as there is a simple tweak to make the Mk II sedan linkages
work. You have to use spacers to mount the linkages an extra 1/4" or so off
the manifolds. With a bit of careful adjustment and light grinding of the
linkage where they foul, the set-up can be made to work. This is convenient
as Mk II linkages are easier to get hold of.
The linkages an the late model manifolds are very simple and do not pose
any problems.
4 Ignition System In order to get maximum performance from the set-up, you
will find it nessarv to alter the distributor advance characteristics.
The ideal set-up is to try and get hold of an original early TR6
distributor (Lucas part # 41219). You may even be able to get Lucas to
rebuild your unit to this spec.
Alternatively you could use an early 2000 sedan distributor as the curve is
very close to that of the 41219. (Lucas part # 41543 or 41582)
If you are building a TR6 to the late PI spec then you could use the late
PI sedan distributor (Lucas part #41502).
You will find that you will have to use your original distributor body as
the sedan distributors do not have a mechanical tacho drive.
5 Exhaust System
Two types of system were employed. Single and twin pipe.
For maximum performance you need the twin pipe exhaust manifold set-up (or
even better extractors). The single pipe set-up will yield a system very
similar to the PI sedan.
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