Welded Diff's on road courses
03-26-2009, 12:58 PM
#1
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Thread Starter
Join Date: Feb 2005
Posts: 35
Looking for feedback on this from others who race.
I race a first gen in SCCA improved touring and have been using a welded diff for a while now.
I'm looking for the next investment to cut my lap times, and I'm trying to decide if going with a proper LSD should be my next focus.
I have previously used LSD rears, but they were generally out of a stock car and I always had pretty substantial wheelspin on corner exit. I switched to welded only because I found a used 5.12 unit that was welded up.
I'm pretty hooked on all the traction and control I have coming out of corners with the welded diff. But my car has crap turn in characteristics entering a corner - lazy turn in generally, lots of understeer on tight corners with a tendency to snap oversteer if I trail brake much.
So let's hear your experience/opinions, when is a welded diff a liability?
In all corners or only tight, low speed stuff?
Does it affect turn in only when you're accelerating or also when you are "coasting" or engine braking in a turn?
Does it contribute to oversteer under trail braking?
Will a race prepped LSD be able to put the power down on corner exit? Or will wheelspin still be an issue?
On a related note, Can you safely swap the LSD section of a diff (bolt a new LSD assembly onto the existing ring gear) and only have to re-set the backlash or do you have to re-set the pinion gear too. I'd rather not mess with the pinion depth and crush washer, etc. if I don't have to.
Thanks,
Neil
I race a first gen in SCCA improved touring and have been using a welded diff for a while now.
I'm looking for the next investment to cut my lap times, and I'm trying to decide if going with a proper LSD should be my next focus.
I have previously used LSD rears, but they were generally out of a stock car and I always had pretty substantial wheelspin on corner exit. I switched to welded only because I found a used 5.12 unit that was welded up.
I'm pretty hooked on all the traction and control I have coming out of corners with the welded diff. But my car has crap turn in characteristics entering a corner - lazy turn in generally, lots of understeer on tight corners with a tendency to snap oversteer if I trail brake much.
So let's hear your experience/opinions, when is a welded diff a liability?
In all corners or only tight, low speed stuff?
Does it affect turn in only when you're accelerating or also when you are "coasting" or engine braking in a turn?
Does it contribute to oversteer under trail braking?
Will a race prepped LSD be able to put the power down on corner exit? Or will wheelspin still be an issue?
On a related note, Can you safely swap the LSD section of a diff (bolt a new LSD assembly onto the existing ring gear) and only have to re-set the backlash or do you have to re-set the pinion gear too. I'd rather not mess with the pinion depth and crush washer, etc. if I don't have to.
Thanks,
Neil
03-26-2009, 05:16 PM
#2
Senior Member
Join Date: May 2003
Location: watertown wisconsin
Posts: 1,331
a proper way to go is a 2 way lsd like a kazz or similar. i know alot of guys use welded diffs in 240 and 260z cars and old alfas aswell. we use kazz 2 way on ower 4.30 gear for road america in ower EP rx7 and a stock lsd out of a gtus with a 5.13 for the small tracks.
we have never had an issue with wheel spin as far as the diff was concernd though we where having some snap over steer due to a improper suspention set ups and springs but it was not due to the diff.
i should mention ower car is a second gen rx7 E Production car that i built from an ITS car . we have 3 freinds who run there first gens in EP and GT3 aswell as DP and all of there cars run 2 ways. we have another group of freinds who run there first gens in DP and IT with welded diffs but thoughs guys are usualy at the back of the pack.
randy
we have never had an issue with wheel spin as far as the diff was concernd though we where having some snap over steer due to a improper suspention set ups and springs but it was not due to the diff.
i should mention ower car is a second gen rx7 E Production car that i built from an ITS car . we have 3 freinds who run there first gens in EP and GT3 aswell as DP and all of there cars run 2 ways. we have another group of freinds who run there first gens in DP and IT with welded diffs but thoughs guys are usualy at the back of the pack.
randy
03-26-2009, 05:31 PM
#3
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Thread Starter
Join Date: Feb 2005
Posts: 35
Originally Posted by fc3sboy1' post='919210' date='Mar 26 2009, 06:16 PM
a proper way to go is a 2 way lsd like a kazz or similar. i know alot of guys use welded diffs in 240 and 260z cars and old alfas aswell. we use kazz 2 way on ower 4.30 gear for road america in ower EP rx7 and a stock lsd out of a gtus with a 5.13 for the small tracks.
we have never had an issue with wheel spin as far as the diff was concernd though we where having some snap over steer due to a improper suspention set ups and springs but it was not due to the diff.
i should mention ower car is a second gen rx7 E Production car that i built from an ITS car . we have 3 freinds who run there first gens in EP and GT3 aswell as DP and all of there cars run 2 ways. we have another group of freinds who run there first gens in DP and IT with welded diffs but thoughs guys are usualy at the back of the pack.
randy
we have never had an issue with wheel spin as far as the diff was concernd though we where having some snap over steer due to a improper suspention set ups and springs but it was not due to the diff.
i should mention ower car is a second gen rx7 E Production car that i built from an ITS car . we have 3 freinds who run there first gens in EP and GT3 aswell as DP and all of there cars run 2 ways. we have another group of freinds who run there first gens in DP and IT with welded diffs but thoughs guys are usualy at the back of the pack.
randy
Thanks for the reply. I didn't think the KAAZ was an option for a 1st gen.
I think I am limited to a stock clutch type, welded or a torsen out of a miata.
I'm actually pretty competitive in my region with the welded setup, but i am looking to improve. Plus it's a major PITA to push the car around the garage or pits!
03-27-2009, 11:16 AM
#5
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Join Date: Nov 2006
Posts: 19
In a recent article in Grassroots Motorsports, they did a diff test with an S2000 and found that the OS Giken diff was the fastest of the stock Torsen (same as the 2nd gen Miatas) and the Kazz. It's not cheap, but I gather its very, very good, and much better than a rebuilt stock RX-7 clutch type unit according to a Miata autocrosser who's tried both. If you can use a Miata Torsen, then you can use it.
When I swapped the Miata Torsen into my diff housing, I didn't have to re-set anything, I just put it back together as it came apart and it checked out fine (mark the position of the pinion nut if you take it off to change the front seal, which is a good idea to do).
When I swapped the Miata Torsen into my diff housing, I didn't have to re-set anything, I just put it back together as it came apart and it checked out fine (mark the position of the pinion nut if you take it off to change the front seal, which is a good idea to do).
03-30-2009, 11:46 AM
#6
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Join Date: Feb 2005
Posts: 35
Originally Posted by Black91n/a' post='919274' date='Mar 27 2009, 12:16 PM
In a recent article in Grassroots Motorsports, they did a diff test with an S2000 and found that the OS Giken diff was the fastest of the stock Torsen (same as the 2nd gen Miatas) and the Kazz. It's not cheap, but I gather its very, very good, and much better than a rebuilt stock RX-7 clutch type unit according to a Miata autocrosser who's tried both. If you can use a Miata Torsen, then you can use it.
When I swapped the Miata Torsen into my diff housing, I didn't have to re-set anything, I just put it back together as it came apart and it checked out fine (mark the position of the pinion nut if you take it off to change the front seal, which is a good idea to do).
When I swapped the Miata Torsen into my diff housing, I didn't have to re-set anything, I just put it back together as it came apart and it checked out fine (mark the position of the pinion nut if you take it off to change the front seal, which is a good idea to do).
Thanks, I'm not sure I can spring for the higher dollar diffs - My only option for now is to get a stock clutch type and rebuild it for tighter lockup. I have a few of those lying around - just need to take one apart and see what I've got.
All this is probably on hold for now any way - I popped the motor during qualifying this weekend at Carolina Motorsports Park. So my limited time and money will be put towards a new motor.
-Neil
04-01-2009, 12:22 AM
#7
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Join Date: Nov 2006
Posts: 19
I would hazard a guess that a stock clutch type in good condition is faster than a welded diff. It'll make it so much easier to move around the paddock too (I know, I've pushed around a race car that had at different times a welded and clutch type diff).
04-16-2009, 10:41 AM
#8
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Join Date: Jan 2004
Location: Central Ohio (Hebron) Zephyrhills Fla.
Posts: 1,322
Originally Posted by sevenracer' post='919182' date='Mar 26 2009, 10:58 AM
Looking for feedback on this from others who race.
I race a first gen in SCCA improved touring and have been using a welded diff for a while now.
I'm looking for the next investment to cut my lap times, and I'm trying to decide if going with a proper LSD should be my next focus.
I have previously used LSD rears, but they were generally out of a stock car and I always had pretty substantial wheelspin on corner exit. I switched to welded only because I found a used 5.12 unit that was welded up.
I'm pretty hooked on all the traction and control I have coming out of corners with the welded diff. But my car has crap turn in characteristics entering a corner - lazy turn in generally, lots of understeer on tight corners with a tendency to snap oversteer if I trail brake much.
So let's hear your experience/opinions, when is a welded diff a liability?
In all corners or only tight, low speed stuff?
Does it affect turn in only when you're accelerating or also when you are "coasting" or engine braking in a turn?
Does it contribute to oversteer under trail braking?
Will a race prepped LSD be able to put the power down on corner exit? Or will wheelspin still be an issue?
On a related note, Can you safely swap the LSD section of a diff (bolt a new LSD assembly onto the existing ring gear) and only have to re-set the backlash or do you have to re-set the pinion gear too. I'd rather not mess with the pinion depth and crush washer, etc. if I don't have to.
Thanks,
Neil
I race a first gen in SCCA improved touring and have been using a welded diff for a while now.
I'm looking for the next investment to cut my lap times, and I'm trying to decide if going with a proper LSD should be my next focus.
I have previously used LSD rears, but they were generally out of a stock car and I always had pretty substantial wheelspin on corner exit. I switched to welded only because I found a used 5.12 unit that was welded up.
I'm pretty hooked on all the traction and control I have coming out of corners with the welded diff. But my car has crap turn in characteristics entering a corner - lazy turn in generally, lots of understeer on tight corners with a tendency to snap oversteer if I trail brake much.
So let's hear your experience/opinions, when is a welded diff a liability?
In all corners or only tight, low speed stuff?
Does it affect turn in only when you're accelerating or also when you are "coasting" or engine braking in a turn?
Does it contribute to oversteer under trail braking?
Will a race prepped LSD be able to put the power down on corner exit? Or will wheelspin still be an issue?
On a related note, Can you safely swap the LSD section of a diff (bolt a new LSD assembly onto the existing ring gear) and only have to re-set the backlash or do you have to re-set the pinion gear too. I'd rather not mess with the pinion depth and crush washer, etc. if I don't have to.
Thanks,
Neil
The locked diff has been a standard in racing for years. I anneal the spider gears and TIG just two tooth throats closed on each side of each gear. Do not re-harden the gears. Everything else remains stock, and another set of spiders returns the diff to stock.
Poor turn-in can be helped with a bit ot toe out at the front end. Almost like power steering. More air in the outside tire, less air in the inside tire.
Sudden oversteer can also be caused by high rear roll stifness. Too much spring. Too tight a jounce setting. A shock dying.
Binding in suspension parts.
Try more air in the outside tire. Less on the inside tire. Very soft rear springs. Soft bushings if allowed. Turn further into the corner then romp on the power harder coming out. Keep after it until the outside tire falls off the track, then back off just a hint.
You may want to run asymetrical tire pressures for each track. Record everything.
A hand full of sand on the floor under a rear tire makes pushing easy in the shop.
Change the ring gear and check the pattern. Pinion depth is controlled by shims between the pinion and the bearing. The crush sleeve is used to save time during production. If I didn't change any bearings, I used the old sleeve over again. Never a problem. The preload on the bearings is checked as a function of rotational torque. In a iron pumpkin very little is required, as the sizes don't change much with heat. Of course the smaller the amount of torque required to turn the pinion bearings
=== less total drag=????
Lynn E. Hanover
04-28-2009, 06:05 PM
#9
Senior Member
Join Date: May 2002
Location: California
Posts: 22,465
Originally Posted by Lynn E. Hanover' post='920560' date='Apr 16 2009, 08:41 AM
You may want to run asymetrical tire pressures for each track. Record everything.
Lynn E. Hanover
Lynn E. Hanover
that is good advise right there!
do not assume you will remember ANYTHING
05-12-2009, 01:20 AM
#10
Junior Member
Join Date: May 2009
Posts: 1
Save your money and get a stock LSD. Your wheel spin is probably from suspension set up. We use a stock lsd on both of our GT cars and only have had an issue with the RX3 which we cured by adjusting the rear sway bar and bumping the rear spring rate.(don't run a rear sway bar on the 7.)
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