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Automatic vs. Manual Transmission

13K views 18 replies 13 participants last post by  BillyGman 
#1 ·
I know that:

- Auto transmissions suck up a lot of power.
- Due to "slippage" in an auto trans, not all the power gets to the wheels,
- All other things equal, cars with manual transmissions are usually rated with about 10% more horsepower.

What I don't understand is that if all this power is lost by using an auto trans, why don't all cars at the strip have manual transmissions? People cut-and-gut their cars and spend thousands to get that extra "tenth", but still keep their auto transmissions.

I've read about "torque multiplication", but am still foggy on the concept. What exactly is it, and does it compensate for the shortcomings of an auto trans? If not, why even use an auto?
 
#4 ·
I think this guys down right scary with a 4spd..:D This run was in the low tens but if you follow the other youtube post " scroll left at bottom of window, after you watch this one you can see this car has gone 9.43@ 139mph.. Now thats rowing gears!!!

 
#7 ·
That pretty much sums it up you cannot miss a shift or be late in an automatic.... Also in racing Automatic's they only lose about 7% hp so the consistency more than makes up for the slight loss in power, and don't be surprised if in the near future they get that number down to 5% or less.
 
#9 ·
Automatic transmissions are generally less expensive and yes, more consistent than a comparably durable manual transmission. One thing the autos have over the manuals is they have a planetary gear design, meaning there's more surface area for the gears to contact each other, making them stronger. A manual transmission only has 3 gear teeth contacting each other at any given time, so breakage issues are more of a risk but that also helps with frictional losses....plus it doesn't have an internal pump.

Having said that, a manual transmission is more fun and more challenging IMO. Also, having the right clutch setup and shifter for drag racing is the key to being consistent(and not breaking parts) as well as knowing how to shift it. There's a reason Pro-Stock cars use manual transmissions....:yes:
 
#14 · (Edited)
There's a reason Pro-Stock cars use manual transmissions....:yes:
I thought that reason IS that it has to do with class rules. Atleast as far as I know, the rules in that race class dictate that manual transmissions be used, just as they also dictate that carburetors are used too, instead of fuel injection. I didn't think that all the drivers/owners prefer carberators over fuel injection, just as I don't think that they prefer manual transmissions over automatics. I believe that it's only due to the rules in that class that they use those things.

Just as Nascar vehicles MUST use mechanical fuel pumps rather than electric fuel pumps.These types of rules in those certain race classes were originally implemented in an effort to keep the playing field somewhat level. Another example would be the engine displacement limit of 500 cubic inches in top fuel dragsters.
 
#10 ·
If you want reliability and consistancy at the track, you go automatic. People won't admit it, but very few know how drive a stick car any way. i prefer a stick car because it is fun on the street, takes a bit of skill to drive, and it keeps you humble. Just show off once and I can pretty well be sure that I will miss a shift and look like an idiot. To me, it is a real pleasure to watch a stick car go down the track when the driver knows how to shift. Lenco's don't really count as stick because they are basically an automatic with shift levers for each planetary gear set. What the guys above said about having a good shifter is so true. I had two cars back in the day with Muncie shifters. They were the quick road to engine and or transmission destruction if you beat on them. They were the first things thrown away. When I see one of these shifters in a car, I can be pretty sure that the owner isn't interested in pounding the gears. Not that you want to be pounding on these old car all the time. It is fun to do once in a while. Just the way I see it.....for what it's worth.
 
#16 ·
If you want reliability and consistancy at the track, you go automatic. People won't admit it, but very few know how drive a stick car any way. i prefer a stick car because it is fun on the street, takes a bit of skill to drive, and it keeps you humble. Just show off once and I can pretty well be sure that I will miss a shift and look like an idiot. To me, it is a real pleasure to watch a stick car go down the track when the driver knows how to shift. Lenco's don't really count as stick because they are basically an automatic with shift levers for each planetary gear set. What the guys above said about having a good shifter is so true. I had two cars back in the day with Muncie shifters. They were the quick road to engine and or transmission destruction if you beat on them. They were the first things thrown away. When I see one of these shifters in a car, I can be pretty sure that the owner isn't interested in pounding the gears. Not that you want to be pounding on these old car all the time. It is fun to do once in a while. Just the way I see it.....for what it's worth.
What he said.

I don't think I will ever be able to power shift. But I've done some speed shifting. It's not that hard once you get the hang of it. The biggest thing is to balnce your throttle as you are coming off the clutch. Rev it too high and you will break the tires loose, don't give it enough throttle and you will bog the engine. I can't wait to get a four speed in my car so I can really practice taking off.

I try to avoid doing too much with the '70 since it's my car.

I have always said it, but when a guy really knows how to drive a stick car the difference in shift times are damn near nill. With a proper speed shift you can hear the only drop in RPM is from the next gear dragging the engine down.

Once I was attempting to hot dog a little bit with a friend of mine in the car. I took off in first and went to nail second. Completely missed the shift. I let the clutch out and then got back on the throttle, instead of having the right balance. The car made a pretty noticeable jerk and continued accelerating. All he said to me was, "We didn't notice." I laughed even though my ego was bruised.
 
#11 · (Edited)
I believe the biggest reasons are that automatics, for the same money, are stronger, more reliable and are easier on the rest of the drivetrain than a manual trans. They don't shock the drivetrain like sidestepping a clutch will and the only way around that with a manual is to have a certain amount of controlled slippage on launch. This requires the right type of clutch, which is more expensive and will require adjustment to dial in as well as maintenance. Using an automatic generally results in less parts breakage and more convenience.

That being said, I can't wait to do the auto > manual swap in my 66. I guess I'm just a glutton for punishment. :)
 
#17 ·
Wow! I'm amazed nobody brought up the reason why for higher horsepower ratings from a auto to stick. The auto has lower hp ratings because of the torque converter. You lose about 10-15 percent of available power from one "fan" pushing fluid against the other trying to get it to turn at the same speed. This is factory configuration everything equal except trans type.
 
#18 ·
Wow! I'm amazed nobody brought up the reason why for higher horsepower ratings from a auto to stick. The auto has lower hp ratings because of the torque converter.
Some Oldsmobile 400 and 455 motors had different cams with manual trans applications which changed the HP rating.
 
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