FFR Drive Shaft Power rating???

[BigB]

Any body know what it is? I plan on being in the 700hp range. Thanks.

[mikeinatlanta]

Didn't realize there was such a thing. Don't see how you could even begin to accurately rate horsepower a drive shaft could take without knowing torque, flywheel weight, gear ratio, axle ratio, type and size of tire, car weight, and so on.

That said, it's a featherweight car and there is a long history of roadsters with big power successfully using a T-5 tranny and 8.8 rear end, just not on drag slicks.

[NAZ]

According to the replay I received from The Driveshaft Shop (the folks that make FFR driveshafts) the shafts supplied with the 33HR kit are rated for 500HP and the critical speed is 12,000 RPM. My build goal is 700HP / 700 plus torque and I scrapped the idea of using that lightweight driveshaft and even lighter duty u-joints. I had an aluminum shaft made that will handle more than my power goals and went to Spicer non-drilled 1350 u-joints (rated >1,200 ft lbs) front and rear. Beside the torque rating you also should look at the critical speed rating if you're using overdrive and want to go fast (think Texas Mile type go fast).

[mikeinatlanta]

Been forever since I ran the numbers but I'm thinking that 200mph with a 3.73 rear will still give a shaft speed less than 10,000rpm. 3.55 gives closer to 9,500rpm shaft speed. I'm thinking 12,000 rpm will be closer to 240mph. All depending on tire choice of course.

Also keep in mind that if a shaft is going to fail, it sees the most torque at launch. Each gear raises rpm but lowers the torque it sees. My general theory is run light and upgrade if you break it.

[TDSapp]

Mike,


Considering where the drive shaft is and how little protected you would be from a failure I would not want to wait until it breaks. You might not get a chance to replace it yourself.

[BigB]

I am by no means an expert on how they rate the driveshafts, all I know is what the interweb says, driveshaft companies tout their products by HP rating.

[mikeinatlanta]

Mike,


Considering where the drive shaft is and how little protected you would be from a failure I would not want to wait until it breaks. You might not get a chance to replace it yourself.

Appreciate the sentiment, but have custom built close fit driveshaft and half shaft safety hoops. No doubt I'm in the minority there and your point is quite valid.

[NAZ]

I've exploded two driveshafts now and can testify that they do major damage and create a significant pucker factor. Both have been in vehicles that the driveshaft ran below the floorboards not right next to my seat like the 33HR does. NHRA requires me to run a front hoop but based on experience I've added a mid hoop and a 1/8" heat treated cover the full length of the driveshaft in the cockpit. And I spec'd an aluminum shaft as if it lets go the pieces have less kinetic energy and the softer metal is less likely to penetrate my shield than a chrome moly driveshaft would. So I'm a bit more conservative now -- stronger than necessary is more better when it comes to my safety.

[mikeinatlanta]

I've exploded two driveshafts now and can testify that they do major damage and create a significant pucker factor. Both have been in vehicles that the driveshaft ran below the floorboards not right next to my seat like the 33HR does. NHRA requires me to run a front hoop but based on experience I've added a mid hoop and a 1/8" heat treated cover the full length of the driveshaft in the cockpit. And I spec'd an aluminum shaft as if it lets go the pieces have less kinetic energy and the softer metal is less likely to penetrate my shield than a chrome moly driveshaft would. So I'm a bit more conservative now -- stronger than necessary is more better when it comes to my safety.

Kinetic energy differences between a smaller diameter chromolly race shaft vs a larger diameter aluminum shaft can make for a fun internet debate. Maybe another day.

[1932]

I built in more safety, makes me feel better.