My friend replaced his driveshaft, I guess one of the u joints was too stiff and not moving correctly. Replaced the driveshaft.. How much difference would this bad drive shaft make on a quarter mile time? Or in other words any idea how much HP the bad driveshaft ate up?

Thanks

 

I really would be suprised if he gains anything from a different drive shaft.

 

Actually driveshafts make a significant difference in the way a car accelerates! If the shaft wasn't spinning freely before then the car wasn't accelerating like it should've. With the new shaft it should remedy that...also remember the lighter the component the better the acceleration (thus you can get a carbon fiber driveshaft) due to less rotational inertia to overcome. Basically if the shaft is bad then not all of the power is going to the wheels (drivetrain loss increases...that's what rwhp is all about, how much is lost through the drivetrain).

 

I totally agree but do you really think its going to make a big difference? Something that the driver can accually fill the difference from before? I tend to think not unless it was really binding before.

 

Most definately, if the driveshaft really wasn't spinning all that great before you WILL notice the difference quite well. Same for the carbon shaft, it's kinda like installing a new lightweight flywheel if you've done that before. You'll see the car revs faster, thus faster acceleration. All of these things are the same, lightweight rotors, driveshafts, and flywheels it's just that most people don't think of things on the darkside of the car (out of sight out of mind). If those things aren't working right then you can pretty much stop spending money on the mods for your car because you'll never get the full potential anyway.

 

It made quite a difference and added almost 5 mph per gear more.


I assume we were losing around 30% to drivetrain loss compared to 15 to 18% from a normal working car.

 

I replaced mine in my n/a 88 SE with one from a TII.

- James

 

Who makes a CF drifeshaft? I really doubt that it could be *that* much lighter than a stock one. I was really suprised at how light the stock driveshaft is...

 

ahhh no you didn't.... doesn't fit

 

Are you sure it was a TII or do you have an automatic because the TII driveshaft is longer than the NA manual driveshaft and the holes dont match up to an NA rear diff.

Youd be surprised how light one is. I dont think there is a company that makes them for distribution, but there are a few companies that make them for racing applications.

Well sort of. A carbon fiber driveshaft weighs less and thus has less rotating mass but, the purpose of a cabonfiber driveshaft is to lessen the twisting force on the driveshaft itself. The carbon fiber driveshaft is designed to give a little thus putting less stress on the u joints and preventing the shaft itself from damage or warping. Youll find alot of import drag racers use them.

-Gabe

 

Well i didnt do it myself, when i bough it he said he had it and he was gonna do it before he sold it so i said go ahead....

- James

 

uhh I guess I could call the guy who did it. The guy I bought the car from got all his work done at MR. MAZDA on camden ave in cambell CA.

- James

 

Rotorific, true it does give a little, but I was just talking about the rotational mass. Thanks though

 

How about a custom light aluminum shaft? What would the weight diff. be from the stocker?

 

Not sure, but the stock one is very light IMO. Its been awhile since Ive handled one, but Id say about 15lbs?? Its been years I may be way off, but it was way lighter than any other driveshaft Ive seen.

 

If you can I would replace the small u joint that come on the stocker. Replace them with a unit with a grease fitting. They are so small its a wonder they hold like they do.


I heard that the original u joints that are a no maintenance joint last longer than the ones you can put grease into and service.


Is this true?

 

You wouldn't want to do that. The whole reassoin for using carbon fiber is because it is aabout as light as fiberglass, but about as strong as steel. Aluminum really is niether, and I would wander how much torque it could handle. You would prolly have to use an alumiinum alloy, then you start adding weight.

 

An RX-7 driveshaft has nonreplaceable u-joints. (atleast the S4 non turbo)
This means you cant reaplace the u-joints you have to replace the whole driveshaft.
It is true that cars with replaceable u-joints tend to go out faster but hey its a 15 dollar fix.

 

Why do you think the hot American cars have a aluminum shaft?

 

Hot American cars...what cars are you talking about, and what in what America do they make "hot cars"?!? Not to bash on American cars (after all...I AM American ), but as far as I'm concerned there really aren't any hot cars made in America (save a few "high dollar" cars).

By the way, I argree the stock driveshaft is pretty darn light to start with.

 

Hot Rod i think he meant

 

I've seen AL drive shafts on American made pickup trucks. Not exactly a hot car but it came that way from the factory. It was about 4" in dia and around 6ft long and could easily be carried in one hand.

The factory Rx-7 shaft isn't all that heavy but it is very short. A lighter one would help but not all that much. Especially at low speeds where the shaft is spinning very slowly. But when it comes to racing every little bit helps.

I replaced my drive shaft that bad u-joints with a new shaft from mazdatrix. Didn't really notice any difference in acceleration (less vibration though). Would need timing equiptment to measure the gains I guess.