There are three engine combinations for the spridget. The 948 had the same
stroke as the Mini 998, but a smaller bore. VARAC rules allow a .065"
overbore, which was intended to allow the 948 to accept stock bore 998
pistons, which are readily available 'cause they used to be used in the 1
litre class of Mini Miglia racing in the UK. We tend to get 85 - 90 hp out
of a good vintage 948 engine. If you remember my white Midget, I had about
80 hp. in that car.
The 1100 used the same bore as the 998 transverse motor, but a longer
stroke. The longer stroke may enhance low rpm torque, but puts a limit on
the red line so that I'd say it was a wash between the 1100 and the 948 in
terms of max HP in a well developed race engine. Somewhere in the 1100
they went to a larger main bearing size so that crank strength may be
improved to gain back some of the rpm range. FWIW I have a set of barely
used 1100 Powermax pistons at .020" over that I have absolutely no
conceivable use for.
1275 gives a similar stroke to the 1100 but a bigger bore, so thatalong
with way better rods and crankshaft they get a big increase in torque and
power with no real reduction in red line ability. These things can make
excellent power and the big increase in torque makes them far faster on the
track. I built two motors for my Midget - both of identical spec except
that one was 998 cc, and one was 1301 cc actual displacement. Both motors
used the same type cam, the same head and carb (jetted to suit but not
dyno'd). My all-time best lap at Mosport with the small engine was a 1:55,
my best time with the big motor was a 1:48 using the same tires and
suspension setup. The best 1275 type motor I've ever heard of made about
150 hp without going to monster stroke and bores. you can get 1500 cc out
of the 1275 engine if you try...
If I was trying to get a fast under 1 litre car, I'd probably go with a
billet crank ground to the Mini 970 S stroke, use the 1100cc Formula Junior
or modified Cooper S block to get 1275 size pistons in it, run a shortened
stock oil pan with extensive windage built in and the XSP dry-sump pump,
and use an external oil reservoir to simulate a dry-sump type of setup
(note that by using a stock type oil pan you're not really creating a
drysump, and oil reservoirs a-la Accusump are common. You could say it's
just an "oil de-airation tank"). You'd likely be best to modify a 1275
Cooper S block and have Carrillo make up some extra long rods to get the
best out of this combo...also have custom pistons made up with a pop-up
into the combustion chamber to get the 14:1 compression that this would need.
This combo could probably put out 115 hp at 10,000 rpm, and would probably
last three races between rebuilds. You'd need an ultra-light flywheel and
5.25" clutch to really make it worth while. I'd build this engine for no
labour charge just to see what it would do ;)
Be fun while it lasted...:)
brian
At 09:44 AM 04/19/2000 -0400, Gregory_Schulz@mil-elect-tool.com wrote:
>On 4/19/00 you wrote:
> >I think it would be a great car - I did after all race
> >a very similar 1961 Midget Mk1 for three years. You could
> >go to the 948 engine and run in an under one litre class,
> >you could punch out the 1100...
>
>
>Hey, Brian,
>Is there a big performance difference between a 948 & 1100?
>
>My 948 is already .040 over and am considering options when
>it's racing days are over. I was wondering what an 1100
>would do for me...
>
>Friends have told me that going from a 948 to a 1275 is like
>going from a small block to a big block performance-wise :-)
>
>I do have a rusted out 74 Midget with a rebuildable 1275 in it
>but they'd kick me into the Cheatin Dog class with that setup
>:-(
>
>Greg
>VSCDA
>Team Thicko Bugeye #517
>Cedarburg, WI
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