DRIVE SHAFT

[DROLDS84]

Doing a 3.8 to Olds 350 swap.Going to use a turbo 350.Probably around 350 horsepower.Will the smaller diameter drive shaft from the v6 be strong enough?I have another v8 drive shaft that is larger but it is an inch shorter from a 8.5 rearend car.The car I'm working on is a 7.5 rearend.

 

[vanrah]

Greetings Drolds & all; I got the OE unit that I removed from the Bronze Brick back in 86. It has about 30,000 miles on it & is 51" long? If you're interested I'll get it out re measure it & take a picture. It's included with the car for the new owner, but it won't fit it's too long (8.5 diff). And I'm sure the new owner will never miss it. So make me an offer ++ shipping from Wisconsin & it will be on the way? Good luck Ole' Bob.

 

[lilbowtie]

Shouldn't be a problem - don't know what RPM your planning on turning so check driveshaft critical RPM.
PST has a nice chart. I have a heavy duty shaft and close to you, 52.75 center to center of universals if needed.

 

[ck80]

I'd suspect the 7.5 driveshaft is plenty strong. I bought a beat to junk 85 regal that had a high revving built up 283 in it that was running the stock v6 driveshaft. It lived for years in that car before I got it for parts.

Plenty of guys with backyard engine swaps - 350s, 403s, 455s run those too, just with new joints.

If a car is going to be raced or driven hard a driveshaft loop is cheap security and worth putting in anyways.

I'd say start with that one, then if you want later get something better, maybe even an aluminum one from an fbody.

I know you said olds 350, but any other details/specs on the engine? Stock? Built high compression/modded? Some type of home brew turbo? A stock olds 350 is a big upgrade from a 3.8, but not exactly crazy horsepower to start worrying too much about exceeding the stock engineering

 

[DROLDS84]

Thanks for the replies.I will just use what I have and see how it works out.

 

[pontiac guy]

my car came with a 301 and it has the small diameter shaft. I shortened it and used it with my T5 swap. I'm not worried about it at all. Ill be running a 3.42 rear end when I get it all wrapped up

 

[Injectedcutty]

Fwiw, my Cutlass had the 7.5" rear when I swapped the 307 out for the healthy 355 pushing north of 400hp. I did an 8.5" swap and just shortened the shaft and had the shop install new u joints. I spun that engine/drive shaft to 7,000rpm plenty of times without a failure.
You should be fine to use what you've got on hand.

 

[lilbowtie]

It's not so much the size or material of the shaft, it's if your operating in the critical speed - I learned the hard way.


Critical Speed Chart

Critical Speed is the RPM at which the driveshaft is computer projected to bend or whip. Exceeding Critical Speed can produce vibrations that can result in driveshaft failure.

The vibrations can also cause damage to the differential gears and bearings. The transmission extension housing, along with the torque converter and planetary gears can also be destroyed.

When you take a small piece of steel and bend it repeatedly, the stress will eventually break the steel. The same effect occurs on your complete driveline when no attention is paid to Critical Speed.

 

[DROLDS84]

Thanks for posting the chart.I'm sure it will be good to.I will replace the u-joints and have it balanced.