I drove my friend’s austin healey (forget model year, it has twin carburetors, 4 cylinder motor). The gears had a lot of torgue - all the way up to the top gear. It had a overdrive stretch perhaps telescoping the top gear to two more higher order gears. Question: Is that normal for sports cars to have such high order torque gearing. I thought sports cars gears stretched from a high order lowest gear to very low torque higher gears. Explain please?
Correction: I meant to say overdrive switch (not stretch) to telescope the top gear to two more higher order gears.
I’m not exactly sure what you mean. Usually race cars are geared so that they go faster than a normal car for the same engine rpm. Did you ever hear that comedy routine by Bill Cosby, where his agent bought him a Mustang Shelby, and he thought it was ver cool until he tried to drive it around his neighborhood! It’s very funny. And the description is sort of what you are saying.
Yes I remember the Cosby episode. Its the engine drag due to torque that I am talking about. I am driving this car around ups and downs of san francisco and even on the top gear its climbing hills and slowing on downhills. I thought a sports car on the top gear would cruise.
The Austin Healy had a LONG STROKE engine that is very torqueky! The rear end ratio is probably around 4.11 or so, ands this gives lot of low speed troque. The overdrive is essential to get quiet high speed touring and decent gas milege, as well as lowering engine wear. Remember, these cars needed a ring job at anywhere from 50,000 to 80,000 miles!!
Why a ring job? Explain please. Too much pressure on the piston, loss of compression ratio or what?
I understand from wikipedia Long stroke to be when the stroke length is greater than diameter of bore and also to produce high torque at lower speeds. Wikipedia also mentions that British cars used this to dodge the road tax system of taxing on bore than stroke. Interesting use of economics to design engines. Any comments?
Hmmm…I thought the British road tax system was on ‘rated’ hp, which resulted in some very low ratings!
Also wikipedia states shortstroke engines or undersquare engines are more common on racing cars to get more speed and not long stroke engines which have higher torque. I am confused.
That’s correct, if you look at the bore/stroke ratio, engines with it significantly less than 1.0 are more likely to produce more torque at low rpms, and have a relatively low ‘red line’ (maximum safe engine rpms). The higher torque is related to the long stroke resulting in a longer lever arm (the distance from crank pin to crankshaft center) combined with necessarily small intake and exhaust valves, which limit the high-rpm ‘breathing’ of the engine. The red line rpms are low because that is proportional to maximum piston speed, which is higher for a long stroke engine than a short stroke engine of equal displacement at any given rpm.
Racing engines today are very ‘oversquare’ (not 'undersquare, that’s the long stroke engine), with bore:stroke ratios much more than 1.0, some near 2.0, I think. This increases maximum rpm and increases valve size, all improving maximum hp (hp = torque x rpm x constant).
@ramikumi The long stroke causes higher average piston speeds and more wear. But he real reason is that popular British cars form the 50s had very poor quality engines. And modern multigrade oils were just being introduced. I burned the valves out on a 1958 Morris Minor in 20,000 miles of normal driving!!
Any 50s British car that made it to 100,000 miles without valve or ring repairs was an exception.
I don’t know how old you are but 50s and 60s imported cars, except for Volvo, Mercedes and VW bugs were constant repair projects. I have a friend who bought an E Type Jaguar and by 90,000 miles everything moving except the engine and gearbox had been replaced TWICE!!!
@texases The 50 and 60 British tax system was based partly on the engine’s BORE!!!, with the result of all these small bore engines. The small bore also made it hard to put big valves in, causing additional valve wear as well.
I can understand earth moving equipment (caterpillar), farm tractors regularly using long stroke engines. But it does not explain why aircraft engines were routinely long stroke. They require speed for liftoff, and after liftoff not much friction for torque.
@Docnick - learn something new every day! There’s no limit to the weird tax schemes concocted by governments…
MGs and Austin Healeys were running at about 4,000 rpm at 60 mph. They sometimes passed the 100,000 mile mark continuing to run well but usually not. Often one or both carburetors would run rich and wash out the cylinders. They were lots of fun if you could handle the nit picking maintenance. The Bug-eyed Sprite was the best of them all for drivers young enough and skinny enough to get in and out.
I don’t think the Bugeye Sprite and its successors, the MKII, MKIII and MKIV were fitted with overdrive from the factory. I could be wrong, as I was never a fan of the Spridgit line. My feet are too big. I think what you may have been driving is an Austin Healey 100-4. Those had overdrive as the OP described. Is THIS the car?
http://www.automobile-catalog.com/car/1955/258575/austin-healey_100_overdrive.html They were FAR more car than the Sprite.
Thats the car
I preferred the A-H 3000s and 100s to all roadsters of that time and although I drove a few they were well beyond my pocket book. I owned a Midget and 2 MG-Bs when I was young enough to jump over the doors and sit down. A friend raced the Bugeyes and bought a yard full for parts with one kept street legal. They were about as high tech as today’s go karts.
I looked over that spec sheet @MG-M. And I saw that the A-H 100 had a 160 ci 4 cylinder. I believe that’s larger than a Model A Ford.
It’s a shame that the Brits let their high performance automobile industry decline from the days of the D & E-Types, the 3000 Mk IV and the DB-5.
Racing engines today are very ‘oversquare’ (not 'undersquare, that’s the long stroke engine), with bore:stroke ratios much more than 1.0, some near 2.0, I think.
I’m sure that’s generally true, but an exception that comes to mind is IHRA Pro Stock motors with 4.75" bores X 5.75" strokes, displacing 815 cubic inches. Sonny’s Racing Engines makes a 1000 CID motor as well.
No substitute for cubic inches as they say!
@auto-owner - very true about racers using US big block V-8s. Formula 1 on the other hand has bore:stroke at 2.5, redline limited by rules to 18,000 rpm, over 700 hp from 144 cid.