Author Topic: Stock rear diff strength? (Read 8168 times)

Beans · « **on:** September 25, 2007, 01:01:03 PM »

I'm starting to get some information together for my V8 E30 swap, and am pondering the strength of the rear diff. I have no clue about the various E30 diffs(big case, small case

??), and plan on running either a 225/50/15 or a 235/60/15 MT E/T Street Radial at the drag strip. My VERY conservative estimate 60' time for the car's gonna be in the 1.7-1.8 second range, and I'd like to keep the rear diff intact as much as possible. With a projected ~300+ wh/tq hitting the pavement, and my driving style, I can already tell it's not going to be good for the rear diff. If anyone has any information on the size, strength and swappability for the rear diff, it'd help greatly. If everything seems to weak to handle the repeated abuse, I may do the heretic and run a Ford 9".... I really don't want to do that though. The car's primary purpose will be the drag strip, and will be pretty gutted out, but I still want to keep good street manners considering I'm going to have to drive 200+ miles just to get to the dragstrip and plan on taking it on the HOT ROD Power Tour in '09.

Febi Guibo · « **Reply #1 on:** September 25, 2007, 01:13:11 PM »

um, I think the stock rear diff on our cars (small case) is good for a little over 200 hp... I would check out http://diffsonline.com/ or call those guys, they can tell you.

silverblades181 · « **Reply #2 on:** September 25, 2007, 05:17:04 PM »

it's not the horsepower that matters it's the torque it can handle. I'd go with a medium or large case if you don't want to overheat your diff.

gearheadE30 · « **Reply #3 on:** September 25, 2007, 06:51:40 PM »

Definitely go with a medium case diff. The small ones are only good for about 250 ft-lbs iirc.

sheepdog · « **Reply #4 on:** September 25, 2007, 07:36:47 PM »

200 pounds torque, 200 hp is about the most it will handle on a repeated basis. Even that is pushing it.
Swap to a 32 it will take around 300.

Beans · « **Reply #5 on:** September 26, 2007, 12:18:15 AM »

Wow, looks like I'm SOL then. How much power can the M3/M Coupe-Convertible handle? Anyone know what the guys with big power in an E30 are using?

D. Clay · « **Reply #6 on:** September 26, 2007, 11:21:45 AM »

I've read articles about high horsepower turbos (600-800HP) that were using a E28 5 series differential, axles, and driveshaft. One even had the entire rear subframe fit into the car, possibly an easier solution as all components would match up except the front of the driveshaft which I think also has a guibo. Not sure if the subframe is a bolt in or if it would require some fab work.
Check out some of the european E30's that claim upwards of 1000HP.

tjts1 · « **Reply #7 on:** September 26, 2007, 11:36:29 AM »

MM pdf
http://www.metricmechanic.com/pdfs/Differentials.pdf

St�ck · « **Reply #8 on:** September 26, 2007, 11:44:33 AM »

A good condition medium case diff will handle anything you throw at it, outside of just nasty abuse like high rpm clutch drops with gobs of tq. The stock half shafts will start to break on dumps long before the diff will.

Beans · « **Reply #9 on:** September 26, 2007, 02:00:59 PM »

Quote from: tjts1;34388

MM pdf
http://www.metricmechanic.com/pdfs/Differentials.pdf

I am not worthy!!!! That's exactly what I needed!!!! Thank you!

badboypolar · « **Reply #10 on:** September 26, 2007, 11:30:05 PM »

Use a diff from a E39 M5. It'll hold 400 ft lbs of torque easy.