Jim
One suggestion that has been recommended to me for the engine in my 2500S that
you may like to consider.
You will more than likely need to do a rebore. Mazda produced a 1500 engine
that used pistons that were 100 thou wider than the Triumph bore. I am told
there is no problem as there is plenty of meat in the bore. The height, gudgeon
to piston top, is marginally longer but within a whisker of the 2500 engine,
although the gudgeon hole itself would need to be reemed out to accept the
Triumph gudgeon pin. The piston top itself is flat as is the Triumph design.
Compression should remain the same, or be raised only slightly.
Here in NZ there are two types of Mazda engine, one being standard with one
carb, or the twin carb (sport) model which utlisises a forged piston design.
The latter is the better piston to use obviously.
This mod will take the engine capacity to around 2700cc.
Condiser a reprofiling the camshaft as well, as you will probably need to
regrind it anyway. I gather the US spec engine used the standard 2500 TC grind.
The 2500 PI grind or TR6 PI grind will give longer and higher lift for better
breathing.
Also, get the motor balanced, ie, pistons, conrods, crankshaft (front pulley to
clutch) and anything else I have forgotten - smoothness brings better revs
brings more useable power.
I don't know what mods will be required for the caburettor needles and jets
(assuming you are still using Stromberg or SU carbs) - perhaps someone else
could comment.
Although I have not done it yet (finance being the main problem and engine
currently not using any more oil than expected), I will be doing these mods
when the time comes, as they won't add significantly (if at all) to the
existing rebuild cost.
David Greed
1979 2500S
+++++++++++++++++++++++++++++++++++++++++++++++++++++
I am about to rebuild my '71 TR6 engine and would like some suggestions
as to some cost-effective means to get some moderate performance increase.
While I have done a number of engine rebuilds in the past, they have
generally been with stock components. What I am looking for is a good
daily driver with just a little less tri and a little more umph.
As I say, cost is a definite consideration, so a ranking by most effective
mods would be appreciated. New dual Webers are definitely out.
A specific question regarding porting and polishing heads: I have the tools
(die grinder, etc) to port and polish heads, though I have never done this.
Is this something that a mechanically inclined amatuer can do. Exactly
what/how much material would you remove. (I am assuming that this is primarily
to smooth out casting marks.) Does anyone know of any literature to give
instructions on this? How much effect does this have without othernengine mods?
Any input will be greatly appreciated.
Jim Snyder
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