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12 bolt or 9" rear??


Guest Anonymous

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Guest Anonymous

I'm definately in the serious planning stages and parts buying of the krazy Z I'm working on. I'm now looking at which rear end I should be looking for. I need a rear end that is removed from the front (third member). I am aware that the Ford 9" is a 3rd member unit but I am concerned at the potential of serious inefficiency due to the pinion placement. I believe that the Chevy 12 bolt is also a third member unit. I have heard that it is much more efficient but I am concerned with how far down it would have to sit in the rear to make the halfshaft angles correct. I need some testimonials and people who have had experience with either of these units to guide me in the right direction. Thanks!!

 

SpencZ

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Guest RON JONES

I,m a little confused(nothing new).Your going to run a 9"or 12bolt with half shafts? I beleve the center section of a R200 is very strong ,the weak link are the half shafts.Mike kelly or one the other guys that have more experience with these rears could tell you for sure.If your going for straight line performance here(drag raceing),wouldn,t you want to run straight axle rear.I don,t think you can run faster than 11.0 w/independent rear ends.If your looking to run IRS, why not make the nesasary changes to beef up the r200(these guys in here know what to do).As far as the 9" goes theres no problems with pinion placement inefficiencys.Also the 12bolt dosn,t have a removable 3rd member.If your going for real big HP here and want to run IRS,and thats why you want to modify a 9" or 12bolt for IRS.I personaly wouldn,t run IRS with big HP.

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Guest Anonymous

Yeah...actually I'm going to make a custom diff case to allow the half shafts. The reason I'm going to go with the 9" with IRS is because 200mm is only 7.8"...that is pretty shabby in the differential world. I'll be using corvette half shafts which are very tough and would be very hard to break. Jim Biondo uses the same setup...and the Dodge Viper uses IRS...even on the 600R. I'm not doing this for the drag qualities but rather for the safety factor. Sure...I could run an R200 with 280ZX CV half shafts, but the margin of safety would be small. I want utmost confidence in my system and that cannot be achieved with Datsun products. Another reason I'm going with the 9" is because of the gear selection. I'm going to run a 3.50 with posi but I could have the choice of having 20 different ratios all the way up to 6.10:1...and the gear sets only cost a couple hundred bucks. Thanks for the info on the 12 bolt.

 

SpencZ

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Spencz,

 

Jim Biondo is using an R200 set up by Jason at Jim Cook Racing with the now-NLA 3.15:1 gear set.

 

Jim is NOT using the Corvette HALFSHAFTS but using C3 Corvette STUB AXLES. He is using 280ZX Turbo halfshafts and custom adapters to the C3 Vette companion flange.

 

That 9" Ford IRS sounds neat. If you never top 11.00, I think it would be a good choice, especially if you want to car to be more than a drag car.

 

BTW, I've seen two people swap the C4 Vette aluminum posi housing into the Z. One used a vette center section that had a mounting arm broke off and fabbed up a mount to use with the Mustache bar mounting points. This guy used the corvette halfshafts at the inner ends in place of the inner U-joint end of the Z halfshaft, and welded it together.

 

The other guy that did this swap used a C4 vette center section that was intact but had the mounting arms cut and rewelded so that the center section mounted to the Mustache bar studs. Then he got some spicer male and female driveshaft slip yokes that mated to make extending halfshafts. He had custom adapters to go from the outboard end of these to the Z stub axle companion flange. The thing I kind of questioned on this setup was that those slip yokes might bind under high torque loads and not let them extend or retract. I don't know if that's a real problem or not. The guy that engineered the car is pretty sharp, so I'm sure he looked into that. BTW, this last guy is Henry Costanzo, Pres. of the Georgia Z club. He described this swap and alot of other V8Z stuff at the Atlanta Z Car convention in 95?

 

 

 

------------------

Pete Paraska - 73 540Z - Marathon Z Project - pparaska@tidalwave.net">pparaska@tidalwave.net -

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Correct me if i am wrong here. Isnt the r200

diff. strong enough to hold around 500 hp.

I have heard that the biggest problem is

the ujounts on each end of the half shaft

binding up and breaking. I thought that i

destroyed my diff. after launching really hard but it turned out to be busted mount and strap causing the nose of the diff to

hit the e-brake mounts... Desktop Dyno

claims my engine to be between 464-513 hp

and over 450lbs of torque. I have HAMMERED

it a bunch and havent heard any complaints

fron the diff and ujoints... just the mounts

I did manage to fry my tranny. AM I AN ACCIDENT WAITING TO HAPPEN BY LEAVING THE

COMPLETELY STOCK REAR END IN THIS THING????

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Guest Anonymous

My bad on Biondo's car...I was under the impression that he had more going on in the rear end. I suppose the R200 would be sufficient for my application...but to have a diff that is safe up to 500hp..and running close to 500hp...doesn't sound like a good idea to me. It would probably hold up, th the posibility of it blowing up would be pretty hugh. Just my opioinon...but I'm going with 9 inches of ring gear.

 

SpencZ

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