34 replies to this topic

[TRJ3]

Just found out last weekend that my SM has an stock open diff ) ;  So we are looking at a torsen replacement. Does anyone have any knowledge of lap time differences between the two? I know it will handle better without spinning the inside wheel and probably braking as well. I was running summit last weekend for the first time in the car and just wonder what effect on lap times I can expect to see.

 

Thanks in advance!

 

 

[Johnny D]

Use the search box upper right for tons of threads. Not sure what year you are with no info TRJ3

Torsens are bullet proof but heavier, 1.8's and 99+ don't seem to mind.

1.6 can use the LSD, torsen to be reliable, there's a new LSD not by Mazda out as well.

Make sure you have a 4:30.

J~

[TRJ3]

Thanks Johnny. My car is a 1.6 and has the mazda open diff. Open for suggestions....

[Mike Collins]

TRJ3  At Summit it can be worth .5 + or nothing.  I drove a customer car with an open diff from 45 to 4th.  You do need to drive a little different.  It never changed my braking just the carousel and turn 8.

[Ron Alan]

That would be 4.3 ratio...not time of day To answer your question directly...at the top level I cant imagine the 1.6 guys see more than tenths difference in lap times. The Mazdacomp is lighter(rotating mass)but fragile. Easier to find a torsen than a used Mazdacomp. BTW...how did you determine you had an open? Wheel spin can occur in the original oem VLSD especially when they get tired.

[TRJ3]

Good question. We took the diff apart and determined that it was a stock non lsd diff. 

 

So the lap times between open and lsd are only tenths of seconds?

[Johnny D]

Depends on the nut behind the wheel and budget.

New to everything including track, leave it and have fun.

Turns out or you are your pretty quick, step up to one.

J~

[Bench Racer]

Here is a wonderful article on differentials.

http://www.miata.net/garage/diffguide/

[RacerX]

Here is a wonderful article on differentials.

http://www.miata.net/garage/diffguide/

 

Great article, thanks for posting.  R1chy

[Glenn Davis]

Don't know who you are from your username.  I was at Summit last weekend as well.  My diff story includes two broken comp diffs @ 1k apiece.  They are becoming even more expensive now.  I went with a Torsen conversion and have never looked back.

 

One time I broke a comp diff and drove an LSD on Sunday.  I agree with Meathead that the only real difference at SP was in the carousel; I found that rounding it out and keeping the inner wheel off of the gaiter was the way to go.

 

One of my race buddies blew his comp diff on Saturday this last weekend.  He replaced with a really old LSD and he ended up turning a faster lap in Sunday Qual (Dry) and having an easier time in the Sunday race (Rain).

 

I still look back fondly at the feel I would get from the positive engagement of the Comp diff.  However, my lap times and pocketbook tell me that the Torsen diff is plenty good for me.

[Ron Alan]

To clarify my first post i thought you were asking the difference in lap times between a Mazdacomp and a Torsen since those are your 2 options!

[TRJ3]

Hey Glenn, we met at the track. I had the silver/black opm car 31 that raced in SM. My diff is a total stock open diff, not an LSD. I enjoyed meeting and running with you guys. My home track is VIR which I would guess favors an LSD even more..... Looking for options today.

[Bench Racer]

This is funny no matter where it came from.

 

Recently got a Traqmate and the wife is started to get pissed at me for comparing her time to/from the market compared to mine... need to get out on the track soon!!!

 

If she's quicker. maybe she dosen't lift the inside wheel.      

[davew]

There are actually more than 2 options. 

 

Let's start with the small diff as installed on a 90-93 car. All are 4.3:1 ratio. These will break. A few people have been able to make them survive, but they are few and far between.

Available from the factory as an open diff. Has 2 stub axle shafts of the same length.

Available from the factory as a Viscous limited Slip (VLSD). Pretty much an open diff for our purposes, but the parking lot guys love them. Has 2 different length stub axles, one shorter and one longer than the open.

Original aftermarket (from Mazdaspeed) diff unit. Basicly a shrunk down posi-unit out of a 69 Chevelle. Requires special tools and knowledge to properly adjust on installation. Uses the open diff stub axles. Approx cost $1000 parts and labor.

New style after market (from Mazdaspeed) diff unit. I have no personal knowledge

 

The larger diff came in all 1.8 cars from 94-2005. NA cars (94-97) used a 4.1:1 ratio ring and pinion. 99+ used the 4.3:1 ratio. These are almost in-destructable. I have seen 1 break. For SCCA the 4.3 ratio is required. All accessory parts (axles, driveshaft etc) are interchangable within all years of the big rear end. Nothing from the small rear end is interchangable with the big one.

Available from the factory as an open diff.

Available from the factory with various versions of the Torsen (TORque SENsing) diff, depending upon model year. Most of us can not tell the difference. I know some have tested back and forth and found slight advatages, but not much.

The early cars had stub axles, while the newer ones have one piece axles. The one piecers give better exhaust clearance.

 

It is very common to purchase both a 4.1 ratio Torsen (fairly easy to find) and transfer to a 4.3 open rear end (again easy to find) since finding a 4.3 Torsen is getting harder and more expensive.

 

Not a whole lotta SPEC in our rear ends

 

Dave

[TRJ3]

Im sure we will get it fixed this week.  Cant wait to go racing again!

[Adax]

Anyone have any experience with the TOCHIGI FUJI SUPER LSD?  Are friction modifiers needed?

[RacerX]

This is funny no matter where it came from.

 

Recently got a Traqmate and the wife is started to get pissed at me for comparing her time to/from the market compared to mine... need to get out on the track soon!!!

 

If she's quicker. maybe she dosen't lift the inside wheel.      

 

I've been told I tend to push my luck and should have stopped after getting "The Look" when I started wearing my helmet while watching the Speed channel, but I really had to lay low when she caught me with our desk chair tipped over trying to figure out how to attach my 5 point harness for iRacing. 

 

I'm really going to have look into moving farther south to limit my off season withdrawals.  Good thing I'm back on the track now.

[AW33COM]

Since we're talking about diffs, let me post a picture what happened to mine the first time I went racing.  This is not the best pic, but you can see the diff arm broke in half.  I have to read on the diffs, because I have no idea what caused this.  The bolt that holds the diff from the bottom of the diff through the long membrame did come out,  and I missed few gears, but I'm not sure if that would cause this. 

The only good news is it happened after the checkered flag and I was able to roll down to the garage. 

 

 

[MPR22]

Did you clean the underside of your car with a tooth brush?

 

The break is usually caused by a bump crash or just plain hard impact from behind.  The diff housing is scored there to shear.  Have a shop weld it up and you are good to go to the next race. 

[Brandon]

Ouch!  Sorry to see that Andre!

 

I'd speculate that with the bolt coming out/loose you may have had enough of a repositioning in conjunction with the missed shifts to cause the housing to shear as MPR22 notes.

 

And MPR22 - this was literally a 'clean sheet' build for him.  He started early last year I believe (his first post was early 2012?) so he's paid his dues in getting the car prepped, built, & finally out on track.

It was great meeting him last weekend and I hope to see him at the track again soon.

 

Brandon