Over the past couple of years I have been upgrading the engine in my
Midget (a 1500 - same as the Spitfire). With every upgrade, the power
of the engine has been increased, to the point that I think I am getting
about 90hp (at about 6500 rpm), the engine runs slightly rough at idle,
and the power starts to come in at about 3000 rpm. However it is a
great improvement over the anemic stock engine. Here is a list
of some of the mods that I have made.
1- 4-branch exhaust manifold leading to a Monza silencer.
2- Lucas competition distributor
3- 11:1 compression pistons
4- Head shaved
5- Weber downdraft carb
6- Flex fan
7- Allison ignition
8- Kent fast road camshaft
If I were you, I would not increase the compression above 10:1, and
remember that emissions will be destroyed.
Over the winter I shall be performing the following mods :
9- Port and polish the cylinder head
* At the moment you need to get a head with bigger valves, Inlet and Exhaust,
as you are not realising the full power created by the other modifications.
10- lighten the flywheel
11- install a pair of 1 1/4" SU's
* 1 1/2's may be better.
If I were you, I would do the following (in this order) :
(I am assuming the the bottom end of you engine is healthy, because
by adding more more, you will put more stress in the bottom end)
1- Install a different set of carbs, either the Weber or a pair of SU's.
If the installation of a pair of SU's on my Midget works out how I
expect, I may have a Weber & manifold going spare. BTW the manifold
for the twin SU's is not available in the USA, but I know where to
get them (~$130)
* In a comparison between webers and SU's, the Su's give marginally more bottom
end power (better fuel/air mix) and the Webers give slightly more top end power
( > 4000 rpm).
2- Install a 4-branch manifold and freeflow exhaust (there are some
excellent manifolds available from the UK)
*Try Triumphtune. They have a really good catalogue with lots of tuning tips.
3- Install electronic ignition, and performance distributor
4- Install a flex-fan
5- Install a good camshaft (Piper cams I think are better than Kent)
Except for (5), all these changes are external to the engine, so they
are easy modifications. If you want more Oomp, do the following, which
will entail removing the engine :
6- Fit 10:1 piston and shave the head
7- Lighten the flywheel
8- Port and polish the head
9- fit roller rockers (expensive !!!)
BTW - if you are going to do any sort of spirited driving, the 1500
engine
really does need an oil cooler added.
*It really needs it as standard!
While I was in the UK last week,
I found an oil cooler adoptor plate with integral thermostat.
*Triumphtune have them.
Gerry
kevinh@hasler.ascom.ch
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