weight of 8 3/4" vs. 8.8" rear? Also 4 link/ladder bar ?'s

[gnx7]

I'm going to put a solid rear end out back in my GN powered '87 RX-7 over winter and can find the Ford 8.8" rear in abundance but the Mopar 8 3/4" setup is a little tougher to find. I plan to run 9's and I'm doing this not only for reliability but to meet NHRA rules. I am having my engine built with all the SFI spec parts currently.

Does anyone know what each of them weigh? I know a 9" is a portly beast and weight is what I'm trying to shave off of my car so that isn't an option plus they are too costly. My car should weigh around 2600-2700lbs.... closer to 2600lbs without driver.

Engine at full tilt should make a little over 700hp and obviously more torque with our hairdryer V6 monsters. I plan on 31 spline axles and an Eaton posi with 3:07 gearing. Most likely 26x10.5" tire or a 27" tall tire. Any taller I believe requires tubbing in my RX-7.

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2nd question:
I will be driving this on the street 70% of the time and want to do a ladder bar setup for simplicity.... but wouldn't a 4 link allow me to raise/lower the rear end and allow for a slightly taller tire and more tuning adjustments? Can a ladder bar setup do this?

Which would be better on the street and not squeak like crazy? Any recommended manufacturers to go with?

My goal is a few passes running 9.50's@145mph on full tilt..... but mainly 22-24psi on 20* timing running some low 10's with a T-70BB and 100 octane unleaded or 91/alchy. My mods are in my sig.

-GNX7

 

[WFO]

can't help ya on the weight,but here's a couple things to think about:

-as far as i know 8.75" rears jump from 2.96 to 3.23.aftermarket gear vendors usually only offer replacement stock ratios.hell,they just finally started offering 3.73's

-you should be using coilovers with ladder bars or a 4-link and they are what you change your ride height and spring rate with...

 

[gnx7]

WFO- thanks for the info.... I plan to do some more research and most likely on going with an 8.8".....

........... and if I can somehow get a C4 IRS with pumpkin to pass the NHRA guidelines that is another option as I do want it streetable and safe on the highway at speed. Scottie GNZ runs this setup in his GN powered 240Z.

Anyone else have any suggestions or comments?

A friend suggested getting some adjustable upper and lower control arms and then mocking up a factory style 4 link suspension with HD boxed ends like the Stangs offer. This may be an idea!

-GNX7

 

[Sleeper]

Hey Mark,
FWIW
I run a Ford 9" with a coil spring four link setup. It is the Toyota factory 4 link, so I do not have adjustable rod ends, but after copying the mounting points from the original rear axle with a jig, making a few mods and transferring them onto the chopped Ford axle it bolted right in, (Properly phased of course.) I do have some adjustment with some of the geometry, but I pretty well left it close to stock.
I went with the Ford at the time, because it had the bullet proof reputation,( I only wanted to do this once) liked the idea of being able to pull out the pumpkin with relative ease, (easier to do service or ratio changes) and found the cost, availability of parts and gear ratio's, fit well into my plan. They were also easy to get at the time, and were found under many cars/trucks.
I also didn't want the extra cost of having to do the "C clip" eliminators on the 12 bolt.
I have heard the 8.8's are pretty strong and a bit lighter. For me the extra weight didn't really matter, since this isn't a full time race car.

Paul

 

[gnx7]

Thanks for the info Paul. What are you running for gearing and LSD/Posi out back?

I lifted a 9" constructed to fit in a Regal and a GN 10 bolt and the difference was at least 40-50lbs. Both had drum brakes etc. However the 9" made the 10 bolt look wimpy in comparison.

Maybe copying the Fbody/Gbody or Stang factory 4 link setup with aftermarket beefy boxes and adj control arms would keep the ride nice and not require a competition shop to get the damn thing to go straight vs. doing the 4 link pro-street setup.

-GNX7

 

[Sleeper]

Mark,
I run a 3.25 gear with a 24.7" 245/50/15 " tire.
It's a Trac Lok posi.
I run a custom disc brake setup, so I lost a bunch of weight from the drum setup. You also can get a 356-T6 aluminum case to save some weight.
Not a bad idea about making a copy of the F/G body/stang 4 link stuff. There are a bunch of books out there that lay out all the geometry stuff, to make it simple.

Paul