Hey everyone!
Im sure as some you know, the autox season is rapidly approaching. Up here in Winnipeg it starts in just about a month.
I have been preparing an '85 GS I bought last fall and now am prety near completion of the body/rust work it needed done to pass safety.
Once its road legal I am going to be looking at the finer aspects of the suspension, though I have already decided to stick with most of the parts from an old rx-7 that got rear ended last year. I had installed new struts/rb springs, new balljoints and all new steering componants in the front, end links, sway bar bushings, poly control arm bushings all the way up to new strut mounts.

In the back it had new shocks/rb springs, watts link mod with poly bushings, custom low durometer urethane bushings for the 4 link, new sway bar endlinks...the works.

This held in place a completely rebuilt rear end with the most insane clutchpack(mazda racing oversize discs and thrust washers??? hah), and 4.88 gears. With some 15" rims and BF goodrich g-force t/a kdws it was quite lively for a little 100 hp car.
Then I was hit with the autox bug. A friend took me out and I was instantly hooked, so I told myself this was the year.

Now that youve heard my rant heres the problem:
The damn GS has an open diff and drum brakes and I would really like to get rid of it in favour of something with discs and a LSD.
I was thinking about just swapping back the old diff, but I think it might be a problem for me in the autox due to the 4.88 gearing.

Speed at 7000 rpm in second gear becomes 43 mph or 68 km/h, where as with stock gearing you could acheive 50mph, or 80 km/h. I know you will spend 90% of the time in second so I dont want it to hold me back.
I dont know what to do because Id rather not tear into the 4.88 rear end at all.
What do you guys think I should do, try the 4.88 or look for a stock rear with lsd?
Thanks!

 

Since you already have the 4.88 gear, try it out. If you are hitting too high RPM for 2nd, use 3rd.
The extra acceleration you can acheive with the 4.88's can shave more time off a run, than you would be wasting going between 2nd and 3rd 2-3 times each run.

 

Shifting from 2-3 and 3-2 would waste a lot of time. It could be the difference between you and the other driver, if your competition is really close. If you have to shift to 3rd, you need to be really smooth with the heel-toe downshifting.

 

Where I run, I have to hit 3rd at least once every run. They alway add a long almost straight section, to even the odds against the 20B Miata running a GM powerglide, with high gear removed....... That car brought home the EML National trophy a few months back.

 

Depending on tire size, your effective gear ratio may be more near 4.44 with the 15" wheels due to the difference in rolling diameter from stock. With my 15s, I would need a 4.44 gear to return the speedo to a near correct reading.

 

One of the fastest cars I've raced against (I think his screen name is Bruceman) used 13" race wheels with really low profile tires. This gave him really low gearing, and he runs most autocrosses in 3rd/4th gears. He does a lot more shifting than me, but he's always in the powerband. Very fast car/driver!