Learn me some limited slip...

[boywonder]

As a disclaimer, this is mostly bench race learning as I don't have the money to put one in my car right now anyway, surprising how much having a baby costs..., but just in case my money tree takes root I'd like to be able to make an educated decision.

So just how much time am I leaving on the track running an open diff? Is it negligible due to having so few ponies to work with (70hp if I'm lucky).

I don't really know much about them so I've been reading online and such and there seem to be very divided opinions on which to use. So what say you...clutch or geared and why? And why would anyone run a welded diff, seems like it would make turning a real chore.

How much does it change the handling characteristics and/or necessitate changes to one's driving style when going from an open diff to a limited slip?

Thanks for your input!

[CRallo]

that answer will depend a bit on the tracks that you run but... at that power level I'd think it would not by you much. That said, how much do you spin your tires? That is a good indicator...

[JLawton]

As Chris said it depends on the track. Fast sweepers? Not so important. Tight turns, you're leaving time on the table.

I would weld it........ like right NOW before the next race. LOL You WILL feel a difference. It does take a different driving style but it's not that different. You just need to stay on the power. If you don't, it will push like a mother.

Of course, welded does suck when trying to drive around the paddock

[Knestis]

What Jeff said. I let the siren call of clutches, gears, and other doo-dads distract me when i came back to the game a few years ago. Cameron Conover built me a gearbox with a spool (over the counter welded diff, essentially - very old school muscle car) last year and i LOVE IT.

K

[joeg]

Ryan--Think turn 13 at Nelson for wheel slippage.

Talk to Carl and Jim in the Renaults about welded diffs--they work well but they are an acquired taste.

I prefer the Quaife over the clutch type, but that is more about reliability--Quaife' don't wear out.

Lots of choices, but the bottom line is you should have something--even a Phantom Grip is better than nothing.

An open is only good for braking on a wet track (and obviously, the welded can be diabolical in such a situatuion).

[Knestis]

Ryan--Think turn 13 at Nelson for wheel slippage.

Talk to Carl and Jim in the Renaults about welded diffs--they work well but they are an acquired taste.

I prefer the Quaife over the clutch type, but that is more about reliability--Quaife' don't wear out.

Lots of choices, but the bottom line is you should have something--even a Phantom Grip is better than nothing.

An open is only good for braking on a wet track (and obviously, the welded can be diabolical in such a situatuion).

Quaife also doesn't actually work if one tire is in the air or on grass. And the spool rocked the rain at Summit two weeks ago. The only diabolical aspect of that is if you are at speed and hit a puddle with one wheel, at which point the car will move laterally. Just let it go and it will keep going straight once it gets the physics figured out.

But to be clear - you CANNOT pussy-foot a welded diff in a FWD car. Like Jeff said, you have to stay on the throttle and not let it boss you around.

K

[shwah]

+1 on welding it.

Quiaffe and Wavetrack stuff is not ideal for road racing. If you want a "real" diff, spend real money on a clutch based, tuneable unit. We have not tested those for budget reasons, but have found a spool faster than the others.

I would say you are looking at 1-2 seconds per lap gains.

[callard]

I go back and forth between a rear engine RWD welded dif Porsche, a front engine RWD welded dif Benz and a FWD Quaif dif Acura. I also had a couple front engine RWD BMWs with a welded dif and a Quaif. I love the Quaif in the Acura but didn't like it in the BMW. I love the welded difs in the Porsche, BMW and Benz. In spite of what others say, they work well in the rain. And I love the price.
Chuck

[Chip42]

one major plus outside of driveability is the lower weight a welded diff has vs. a cluth type or more so a torsen or quaiffe. get a spool and its even lighter. less stuff to accelerate with your 70hp.

[Knestis]

Peloquin - 17 pounds and $800

http://www.pap-parts.com/images/pel020.jpg


KAAZ clutch-type - 17 pounds and $1000

http://d5otzd52uv6zz.cloudfront.net/group-22aa0ddb-417e-4792-8728-2658cf9f0ed1-350.jpg


Quaife - 17 pounds and $720

http://www.usrallyteam.com/images/quaife_QDF1R.jpg


Spool - lots lighter and I think around $400 (although my Google skilz are failing me)

http://www.puredieselpower.com/store/images/thumbnails/6/120/Dana-60-35-spline-%28sm%29.jpg


Last I asked around, I think the going rate for welding up a stock diff was $200-300.

K

[boywonder]

Ryan--Think turn 13 at Nelson for wheel slippage.
Ahh! Great example. I get major wheel slippage there and have tried and tried to find a way to get the car settled and more level there to put the power down. Maybe I've been doing it right and just suffering from the open diff.


I would say you are looking at 1-2 seconds per lap gains.
That's a huge amount of time, but I reckon that's only on a real tight track? NL is flat to the floor, save for three and a half turns, and I can only think of two turns I have slippage at Mid-Ohio.



But to be clear - you CANNOT pussy-foot a welded diff in a FWD car. Like Jeff said, you have to stay on the throttle and not let it boss you around.
My car has a 86.4" wheelbase, I already have to stay on the throttle to keep it from coming around. :)

[Ron Earp]

I'm not a FWD guy but with 70hp I'd go with what Kirk says. Weld it or use the spool. The spool has the added advantage of getting rid of a bunch of weight.

I had two differentials for the Z that were not differenting, i.e. were welded (one was a packed up too tight clutch pak >275 ft lbs), and I learned to drive it it. In fact, other drivers drove the car and I suspect that some couldn't tell you if the diff was welded or not. If the car is setup well you'll just be on the gas and be fast.

[boywonder]

OK, at the risk of sounding stupid...a related driving technique question:
Keep in mind that I race a C car that by definition has little power. I purposefully bought a C car to force myself to learn how to drive efficiently and maintain momentum, rather than having a high hp car where I might be able to compensate for driving mistakes by stomping on the loud pedal. In my quest to become a good race car driver it's important to me that I develop good habits. That said…

Does a limited-slip promote poor technique?

Example:
1) Currently w/ the open diff I have to enter a tight corner with the car balanced and tidy (read: slow) to keep the weight balanced over the front wheels and avoid wheel slippage so that I can get decent power out of the turn. It's challenging to find the line between being too slow and meandering around a corner and coming into too hot and spinning the inside wheel.

2) My other option is to come through the turn fast and at the very limit of available grip, but then I'm unable to put the power down coming out of the turn because everything is rolled over and weight is off the one drive wheel and with the open diff I'm essentially coasting.

When performed correctly with my current setup #1 is faster. It may feel/look slower, but ultimately the lap times are lower because I'm able to put down power sooner coming out of the corner and into the subsequent straight. With a limited-slip and my current skill level #2 would be obviously faster (provided you're aren't coming in so hot you're scrubbing speed laterally) as I'm now able to carry more speed into and through the corner knowing that even with massive body roll at the exit I will still be able to put down the power via the loaded front wheel and squirt out of the corner.

But…

Theoretically shouldn't it be faster to come through with the car settled nicely and putting the power down smoothly? I don't think it is now, with me, but that could be because I need way more practice to do it repeatedly - but by someone proficient shouldn't it be the fastest way around the track? Or am I overanalyzing and should just weld the diff and be done with it?

Obviously I want to go as fast as possible, I just don't want to use a diff (or anything) as a crutch if it's going to negatively impact my growth as a driver (resulting in potentially lazier/sloppier corner approach because it doesn't penalize mistakes as much as an open diff does).

[JLawton]

You're WAY over thinking it............ just get in it an DRIVE!!! LOL

Do you want to be fast??? Weld the thing and move on to the next project!


The only think I liked better than a welded was the diff that Steve Ekerich built for me. It had all the good charactoristics of a welded but none of the bad. I had first suggested welded because you had mentioned expense. Although, Steve's is less expensive than all the others except for welding.

The only way to figure out how to drive it........... is to drive it. The only place I had to really change my style were long sweepers. I'm on and off the gas to keep it from pushing yet not pick up too much speed until I'm coming out of the sweeper.

[Z3_GoCar]

First, no cars classed in IT are power cars, not even in "R." Now if you had a 400hp 2000lb car, that's less than twice the hp/wt of an "R" car.

Second, the only reason to run an open diff is if the rules limit you to an open diff. Think about this: If you started in Karts, you'd be driving a vehicle with a solid axle, esentially a spool. The only way the wheels travel at different speeds is if the camber and weight transfer lifts the wheel, or one scrubs.

[shwah]

That's a huge amount of time, but I reckon that's only on a real tight track? NL is flat to the floor, save for three and a half turns, and I can only think of two turns I have slippage at Mid-Ohio.

When do you mat the pedal in a corner? If you are doing it right with a locker, it is pretty much at turn in. The locker also gives more options when track space becomes scarce. The car drives just fine with the unloaded tire 3 feet into the grass should you get pushed there.

When I went down to Memphis - which is a huge straight, with a long fast sweeper and some zig-zags - I ran day one with an open diff, and installed the trans with the locker for day 2. It was over a 1 second improvement in a 95whp ITB car (I was still running a stock motor with header and tuning at that time).

EDIT - Jeff, try some light left foot braking on those sweepers if it starts to push. But of course increase the rear roll stiffness first so that it is less likely to push first... (all assuming fwd)

[R2 Racing]

The only think I liked better than a welded was the diff that Steve Ekerich built for me.
That's what I'd do - send Steve a stock diff and have him build you one of his LSD's (clutch type with spring packs). That's what I have in all of my IT cars. I like the feel, they work amazingly well, they never disengage like a gear type, and I have yet to ever have to rebuild one. In my ITC '85 Civic days, I tried both a clutch type LSD and a welded diff, and I prefered the clutch type LSD a whole lot more. I actually still have that other tranny sitting around, with the welded diff and a Si 4.4FD.

[JeffYoung]

Have had an open, a Quaife and a Gripper clutch/plate style LSD in my car, and have driven a Quaife, a NISMO clutch pack and a locker in Ron's.

Can't tell much difference (to me) between the locker and the two clutch plates, and they both appear to be faster than the Quaife. Quaife is a bit easier to drive but at least on the TR8, it was fairly easy to get both rear wheels spinning.