Larger bore = larger valves. I'm sure there are other tweaks as well. One of fastest Spridget owners told me they wer getting 111hp at the wheels. I've seen 1380 Minis quoting 120 at the wheels. One 1380 Mini owner told me he was rebuilding the engine every other race whereas the couple of Spridget guys I've talked to are getting 8-10hrs between rebuilds.
The BMC A-series engine has been developed to phenomenal level. By comparison the 15 year newer design Datsun A-series (5 main bearing crank and better port arrangement) in 1388cc trim is capable of 140-145 at the wheels. Keep in mind the A14 engine is revving to over 9000 rpm.
I'm not sure what kind of weights race Minis and Spridgets come in at but I'm think they may be identical in weight or damn close.
Haven't owned a Spridget. Had a Mini 850. With only 37.5 HP you didn't want to use the brakes. Fortunately you rarely had to; just flick the thing in the direction you want to go and mat the accelerator. 
The Mini costs more to buy and is much more difficult to work on mostly do to the compact packaging. The seating position is reportedly intentionally uncomfortable as Issigonis considered it a safety feature as you weren't likely to fall asleep while driving it.
It was a fun, 'happy' car and I enjoyed my time with it. It just wasn't enough of a passion for me to endure the impending bodywork and respray it needed.
Stock class Minis shared attributes with Formula V. When you have little power, you damnwell have to really learn to drive well or you won't get anywhere.
I know of several drivers that started out in things like Corvettes and are sloppy drivers to this day, while the guys that started out where it all depended on technique and then moved up to more powerful cars usually do much better.
wspohn said:Stock class Minis shared attributes with Formula V. When you have little power, you damnwell have to really learn to drive well or you won't get anywhere.
I know of several drivers that started out in things like Corvettes and are sloppy drivers to this day, while the guys that started out where it all depended on technique and then moved up to more powerful cars usually do much better.
I was that sloppy beat 'em with horsepower driver until I started racing my MGTD with all of 54 horsepower hauling around 2000 pounds. Racing similar cars taught me the rewards of momentum and positioning.
racing low powered cars makes you feel like a looser until you race identical cars. Then technique and patience gives you such great rewards.
The happiest pits at the track are Vintage MGT series, And HP pits. The rest is all bragging and excuses.
Totally agree. I started autocrossing in a V8 mustang. Went to running a STS Miata and became a MUCH better driver over the years I ran that.
Smallbore cars are just a much better learning tool.
In reply to Apexcarver :
Can't agree more. Walk around the pits at the race track and the guys sharing laughter patting each other on the back etc are all the guys with similar performance cars.
The big bore guys with the ego cars are either complaining about cheating, making excuses or bragging because they won. Nobody is thinking "Good for Charlie. He's had it rough up to now and finishing third is a job well done."
I also see a lot more parts lending helping out or sharing of techniques in the communities where things are more equal and it's more about the driver than the car.
You'll see Spridget drivers lending stuff to mini drivers, heck even complete motors since you can hoist one out on a 2x4.
I do need to admit the pleasure of storming past a fellow racer on the straight though. my Corvette and Black Jack were just such cars. I knew a Formula Ford would beat me any day. But blasting past a slower car(s) on the straights is always good for a giggle.
frenchyd said:In reply to Apexcarver :
I do need to admit the pleasure of storming past a fellow racer on the straight though. my Corvette and Black Jack were just such cars. I knew a Formula Ford would beat me any day. But blasting past a slower car(s) on the straights is always good for a giggle.
I used to get just as much fun out of out braking the heck out of the big cars - my MG has 4 wheel discs and can go in deeper than most production based cars. One of the most fun races I aver had was against a 57 fuel injected Corvette. Of course he would smoke me every time we got on the straights, but then at the next corner I'd drive right by him into the braking zone. I actually turned slightly faster laps than he did, but could only have beaten him in the race if they'd moved the start finish into the last turn before the straight. he even had a sense of humour - every time we went into the braking area he'd point for me to pass, so I did the same for him coming back on the straight.
Of course I also enjoyed passing stuff on the straights when they didn't think I should be able to, like Jag XK150S.
Small bore cars are just so much fun. I've driven lots of exhilarating cars on track; GT-3RS, Venom Viper, single seaters but the most fun have been things like the Mini and the Sprite. You just drive them like a total animal..........it's the closet you'll ever get to being Yosemite Sam or The Tazmanian Devil.
I've never driven a Mini or a Spridget, but this is a great thread regardless of my own shortcomings. However, I tend to like Spridgets slightly more than Minis. Couple pics from the UK:
This is a current CL listing in Western MA. Converted to B Series engine and Datsun 5-speed gearbox:
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