Stop me from glueing my rear end together (Nissan Z31 content)

Ok, so I have this 1986 Nissan 300zx that is mostly a rallycross car. It has, like all of the 1984 thru early 1987 Z31s, an open diff.

It was originally a naturally aspirated (VG30) model with 235k hard miles. At the autocrosses it would on occasion spin the inside tire a bit on corner exits.

Well, now it has a much healthier 80k mile engine from a 1985 Turbo 300zx (VG30ET), and it converts much of it's new found power into tire smoke on the exits.

I'm having thoughts of welding up the rear diff, and I'm sure it would make a huge difference in the dirt at the rallycrosses. But, I do autocross the car, AND I'm planning on entering the $2013 Challenge, so my fear is that the welded diff will ruin the turn-in on pavement.

Please talk some sense into me before I whip out the welding rods. Is anybody else out there autocrossing with a welded diff? If so, how has it changed the handling of the car and/or your driving style? Thanks for any info.

I have nothing to add. I just wanted to see where you were going with that title...

Following

They kinda talked about it in this thread a week or so ago. Something to start with, at least.

http://grassrootsmotorsports.com/forum/grm/a-question-for-those-who-drove-the-grm-crapcan-mar/63544/page1/

I'm assuming that you will be over budget for the 2013 challenge if you get a real LSD? Because that is definitely your best option.

Lesley wrote: I have nothing to add. I just wanted to see where you were going with that title...

Me too! I've heard of a hunger strike but it takes a brave soul to stop function on the other end!

I haven't autocrossed at all, but I think the tight course would be tough with a welded rear end. On a road course it's brilliant, but autocross is a lot tighter.

The_Jed wrote:

Lesley wrote: I have nothing to add. I just wanted to see where you were going with that title...

Me too! I've heard of a hunger strike but it takes a brave soul to stop function on the other end!

Bwahahahahaha!!

A welded rear is awful on a road course or parking lot unless you have a soft enough chassis to lift a rear wheel on corner entry like a kart. Don't do it. Watch ebay for a torsen LSD to install in there.

I've driven plenty of spool-equipped cars on the street. Think 12-18" cheater slicks/drag radials on the back, 145-195 width tires on the front. The steering feels a bit "rubbery" at low speeds but the world has so far failed to end. Have never seen a breakage happen due to it. IMO that's mainly a front-driver problem.

When using up lots of cornering forces, the diff almost doesn't matter since the tires are sliding around anyway. The 5-10% slip where a tire makes peak traction easily picks up the slack. The problem you WILL run into is when you're not at max lat. Turn in will suck more.

IMO it will suck at a rallycross. You can put the power down but if you have courses where you have to do things like turn, you may find that you can't turn and accelerate at the same time without getting immensely sideways, which is slow and an easy way to loop the car when you hit a bump with the inside front tire.

Giant Purple Snorklewacker wrote: A welded rear is awful on a road course or parking lot unless you have a soft enough chassis to lift a rear wheel on corner entry like a kart. Don't do it. Watch ebay for a torsen LSD to install in there.

This was/is my hope for the Lincoln, even though for some odd reason it doesn't seem to flop onto the outside front and unload the inside rear the way a Foxstang does. Maybe it's the RSB that actually looks functional.

Technically not a "Fox", but it is:

Like Knurled said, though, this is at full boogie.

Never experienced this myself, but I think the LuK team lunched a welded diff during the 2006 Challenge autocross. Of course, that was in a firebird with a Buick 455, and AFAIK, a stock 10 bolt, so your case may be a bit different.

The_Jed wrote:

Giant Purple Snorklewacker wrote: A welded rear is awful on a road course or parking lot unless you have a soft enough chassis to lift a rear wheel on corner entry like a kart. Don't do it. Watch ebay for a torsen LSD to install in there.

This was/is my hope for the Lincoln, even though for some odd reason it doesn't seem to flop onto the outside front and unload the inside rear the way a Foxstang does. Maybe it's the RSB that actually looks functional.

You could try removing/smaller rear bar and using a piece of aircraft cable thru the spring to limit droop so when it rolls up on it's side like a beeched whale the tire comes off the road.

I'd assume the amount of suck on the street would be inversely proportionate to the power/weight ratio of the car in question. Your car probably weighs 1,000lbs less than mine but I probably have quite a torque advantage even though our horsepower levels are probably embarrassingly similar. Then there's solid axle vs. IRS and weight distribution...

Which of us will take the plunge first?

In reply to Giant Purple Snorklewacker:

How about no sways and rear droop limiter straps for the lulz?

If I ever do autocross the thing I could aim right for the cones and they'd pass under the rear tire that's hovering about 2 feet in the air!

mr2peak wrote: I'm assuming that you will be over budget for the 2013 challenge if you get a real LSD? Because that is definitely your best option.

Yep, an LSD would put it over budget unless I could luck up and find a cheap, cheap, CHEAP '87.5 through '89 turbo parts car. They had lsd diffs as standard equipment, but you basically have to swap the entire rear k member and everything. I've been looking for one locally for 2 years, and I'm not holding my breath

i had a welded rear in a 300zx and it was not what i expected.... dont do it. chances of finding a LSD is next to impossible at anyprice below $400.00. i have a VLSD and a CLSD for them. it matters who you talk to on which is better. i have one by this company in my S12 200sx with the 200 diff http://www.precisiongear.com/powerbrute.htm which i like better there either nissan LSD's

The_Jed wrote: I'd assume the amount of suck on the street would be inversely proportionate to the power/weight ratio of the car in question.

It's more complicated than that. I think wheelbase vs. track width plays more of a factor.

I don't have a spool or welded diff in the RX-7, but I do have a heavily shimmed clutch style diff. If it is raining, trying to turn and accelerate from a stop is hilarious. Understeer like a 3-wheel ATV with a fat guy leaning back. Have to accelerate first, then let off the throttle and turn.

When it's dry out, it turns okay, but all of the tires complain a little.

Don't do it, absolutely sucks for anything but hooning. Stay open diff and spend your time sorting the suspension to work around the open diff.

I'm still against a spool, but I had a thought. The same team I talked about above may have brought an entire spare open rear end to the event. How cheap would a spare open diff be, and how hard is it to swap in a parking lot?

Knurled wrote: IMO it will suck at a rallycross. You can put the power down but if you have courses where you have to do things like turn, you may find that you can't turn and accelerate at the same time without getting immensely sideways, which is slow and an easy way to loop the car when you hit a bump with the inside front tire.

Was thinking about this. There's a lot more sand in the soil down that way. A spool may be more effective on looser surfaces like that than what we deal with in the great lakes/midwest area.

A guy tries to autocross a RWD rally car with a welded diff by me, it's fun and it would make a good drift car, I'll give it that...

I remember reading somewhere in one of Carroll Smith's books about racing and a locked diff.

He said because of the high slip angles it can work.

I ran one on my 1800 lbs RX-3 autocross car and felt fine.

There some info here on the subject on page 150 of this document.

http://users.telenet.be/AudiR8/Carroll%20Smith%20-%20Tune%20to%20win%20OCR.pdf

can't you find a LSD for these cars in a pick a part?

You probably won't like it anywhere but the dirt. My father welded the rear in his Monte Carlo that he ran on an oval in a street car class. On a small oval with a lot of stagger it was great. After a couple days he started riding his bicycle to work. As a kid I loved it though. When my mom's car was getting a new tranny she was stuck taking us to school in it. There was a lot of noise and a bit of smoke on every turn.

i had a spool equipped ex drag fox body mustang. i will NEVER own ANYTHNG with a spool again. that being said, i used a lincoln locker in the back of my 4 wheeling ram back in the day. it worked for what i was doing (serious off road. were talking winch mandatory and floorboard damage common kind of wheeling) when i drove that truck on the street, it sucked like the vacuum of space.