Auto Transmission Puzzle

Automatic transmissions have to be designed for a particular engine, A transmission made for a small car is not strong enough for large engines and conversely, A transmission for a large car, won't work with a small engine let alone fit. Also small engines run at a higher speed than a large engine. The transmission has to be designed to work within that speed band.

Economy of manufacture or prohibitive cost per market share...

Back in the sixty's Ford had that little 289 engine. It was no more powerful than Chevy's 283, but because it had so much low end response and torque, it felt much more powerful.

With today's drive by wire and electronic engine controls, throttle movement can be set up to fool us. Think of this. Suppose you had built a car that felt sluggish when driven away from a stop. What if you take that throttle position sensor, and have the first 10 degrees of throttle movement tell the engine computer that you have opened the throttle 50 % the engine will surge with the 50% power. As the throttle is opened further it will just slowly reach 100% at the end of the travel. The end result is a car that feels like it has a lot more power at light throttle settings than it does.

When todays engines drop cylinders when not needed, how do they get the cylinders to cut in and out so smoothly? When the engine suddenly reaches the point where the next two cylinders are going to drop out, the computer will analyze the amount of power it is making on all 8 cylinders, and compute what the throttle setting would need to be on 6 cylinders, and at the time the engine drops the 2 cylinders, it suddenly changes the throttle setting to match the power it had with 8. Smooth as silk.

There is a significant wimp factor designed into most modern automatic transmission shifting modes. The concept is than mommies and kids will spill their happy meals if the auto transmission shift is too crisp. The actual shift is dragged out so it occurs smoothly over a longer time period.

I had the opportunity to modify a stock wimpy automatic with a "performance valve body". Shifts became crisp and driving performance was greatly improved. Needless to say that mommies and kids WOULD spill there happy meals with this modification. Although there is some HP loss in the automatic transmission, I think many drivers would be pleasantly surprised at how much better a performance shift feels even with the smaller engines.

Thanks for that. It seems to explain the paradox.

I had the need to use an auto a couple of years ago after an injury and hired a Smart. even with the tiny engine it was still a very peppy little thing. I now have a 3.2litre auto (which is large by European standards) and I am often disappointed at the lack-lustre performance.

regards

Chas

It was a nice brief about engine control and behavior. I'd just add that you need also to take in account the car size, weight and the travel you are doing. Huge cars with big engines are much heavier and are very nice and comfortable in highways. But it does not mean that they will leave a small, light, and with a reduced transmission car behind in city circuit under traffic. Well, at least untill you reach about 50 km/h, after that is another history, of course....

I have a small ford fiesta (with manual shift of course) with the old CHT 1000 cc 8v block valve cam engine. It builds up speed from the rest in the semaphores very quickly, it has a good torque response in low speed besides the small sized engine. Sure, around 60 km/h any 1600 cc multi-valve double overhead camshaft just keep accelerating as nothing was happening (oh! boy, in this occasions I miss so much my previous VW AP1800 engined one...) while my little boy starts to stall, but you cannot have everything in this life, can you? At least, does well in the city and make a loooooot of km per litre.

BTW, Nice to hear from somebody here some references regarding engines in the 2.0 or 3.0 litre. As good americans, all I hear here is "Dodge RAM" here, "V8" there, "SUV" here again, "5.4", etc. I really feel ashamed about my "small condition" sometimes...

Rgds.

Being one of those one of those "spoiled" 5.4/5.7 types, all I can say is, make the best out of your, "small condition". If you don't let it get you down, maybe no one else will notice.

5.4/5.7 Hell I got pistons as big as a Quaker Oats container. There is no replacement for displacement.

I was used to driving big gas guzzlers here in the U.S. Many years ago, I was on a trip to Italy and I rented a Fiat (128 I think). I was surprised of how swift and responsive that car was, despite only having 4 cylinders. Italians love their cars and the factories that produce them, tune them for performance. In the U.S. cars are usually "de-tuned" for economy and comfort reasons. Our cars are not designed to handle like European cars. Export models are the same as their at home models. The only difference is the export model has been detuned and some smog controls have been changed to satisfy destination standards. These changes are the difference between a peppy, responsive car and a floating-on-a-cloud ride.

GA.

I also did a few transmission shift improver kits. I also had a 400 turbo from a 69 SS396 Chevelle. As changes to cam and intake started to wake up the engine, I discovered that if left in first gear, it would up-shift REALLY hard when it reached about 6500. That was a drink spiller.

It's my guess that the smart car is geared pretty low due to it's small engine. Low gearing will give you the kick in the pants feeling while taking off and driving at lower speeds. If I recall the smart cars max speed is about 80 mph, it's my guess the engine is turning some pretty good rpms at 80 unless it has a serious overdrive on the tranny.

Another thing that might be different is the number of gears the tranny has. Many of the newer cars have up to 6 gears in the auto's which will keep the engine in the max torque curve much easier than just having 3 gears. Not sure what the smart car has so can't be sure that is why the car feels so peppy.