FWD...Locked Diff.

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zracer22

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I race at 1988 GTI in GTS Challenge. Having raced Datsun Z cars and E30 BMWs for the last 10 years, I am somewhat ignorant about FWD racing. I had good success with spooled/locked diffs in RWD cars, but I'm not sure what to do with the GTI. Is anyone running a locked diff in their FWD racecar? What are the pros and cons? My car put 155 HP to the wheels, and weighs in at 2150 with me in the car.
 
Lots of folks run locked diffs--usually welded because that is the least expensive option--with FWD cars in IT.

Lots also run some kind of limited slip.

Locked diffs work extremely well with FWD but can be a bit tricky under hard braking and in the wet, but it is an aquired taste.

I even think someone had a "spool" for sale for a VW application.

Locked diffs require a lot of manuevering room in the paddock since you cannot make low speed tight turns very easily without risk to your CV joints.

Have fun!
 
With that much horsepower, a welded diff is going to be a problem. I'd suggest a Quiafe limited slip. It takes some getting used to with the torque steer, but it's worth that in exchange for the wheel spin. Welding is cheap, quick, and easy. It works great until it doesn't. I've know lots of people that used it, and lots of people that snapped axles inside the gear box. Ferdinand Porsche once said that the car that uses the same wheels to turn that is uses for motion does neither job well. But he also used a swing axle for a rear suspension. In lower powered cars like mine, the Phantom works well, but anything more than 125 hp needs the weight and strength of the Quaife.
 
There are guys running more than 125hp fwd cars with a welded diff. It is not substantially different than our 100-110hp versions. It works fine and never spins the inside wheel or the airborn wheel. It does require special attention in the paddock.

If going with a clutch type diff, I would definitely want to test and ajust for best performance - since this is the only one that provides that option.
 
I'm one of those who's doing the clutch-pack thing and I'm pretty pleased. That said, I think my next 'box might employ an actual spool, since I'm one of those guys who was weaned on a welded diff before we could actually get any "real" LSD options, and I'm totally OK with their behavior. The advantage would be that I could absolutely, totally not worry about it as a service item or potential point of failure in endurance races.

K

EDIT - I think if I were dealing with MORE power, I'd be even more likely to look at the spool...
 
>> The advantage would be that I could absolutely, totally not worry about it as a service item or potential point of failure in endurance races.

But that stress goes the next weak link.. the axles. Better carry a few extra sets for the enduros. I've sold a few axles sets at the track to guys running welded diffs including this forum's biggest VW welded diff fan. ;)

PS - Clutch diffs dont "fail" They were out very slowly unless you burn them up without oil. Same diff design that is in the rear end of many BMWs and other HiPo RWD cars. They last.
 
I have had a welded on my FWD for about 3 races...so kinda new to it still

there is definitely a big learning curve, as it will change everything you ever knew about driving a FWD...

But, once you get it right, it can be pretty damn fast...

But, I dont think it is faster then a good clutch LSD, and much harder on parts...

So, if you can afford it, I would consider an LSD.
 
I've run a welded diff in my FWD Wabbit for over 7 years. I've only lost 1 CV joint on track in all that time, but I do change out the entire 1/2 shafts every year.

It does require a different driving style, but like Kirk said, once you get used to it, it is 2nd nature.

Making 90 degree turns in the paddock does requie Popeye style for arms.

I just didn't like the inside wheel "chirping" while going through turn 10 @ Sears Point. If any of you know that turn, this turn is the LAST place you want to be "searching" for grip.

I also have a 020 close ratio box with a Quaiffe that is installed in a 1975 ITC Scirocco, that's just keeping the trailer on the ground. $1,000 for the entire tranny and you get the car for free.
 
I was planning on putting a LSD in the Geo Prizm GSI over the winter. The last owner said he tried the welded diff but kept breaking the drive shaft.
ANy advise and expected cost on which Diff??

Is the OBX diff OK? you can get it on Ebay for around $400 What other types of diff available and cost? or performance advantage.
Also how easy are they to put in.??

Cheers SteveP
 
I was planning on putting a LSD in the Geo Prizm GSI over the winter. The last owner said he tried the welded diff but kept breaking the drive shaft.
ANy advise and expected cost on which Diff??

Is the OBX diff OK? you can get it on Ebay for around $400 What other types of diff available and cost? or performance advantage.
Also how easy are they to put in.??

Cheers SteveP
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I've never run a welded diff nor do I know anyone who uses one so I can't comment on the broken axle problem other than to say "yes, I've heard that too." ;)

I've had good luck with my OPM diff. The Phantom Grip is an incomplete copy of the OPM diff... OPM's unit uses friction material where the diff and spider gears meet. Additionally, the spider gears are machined so there is additional contact area with the diff for added lock-up. With it's flexible design, I'm pretty sure Tom could get one made for your Prizm.

I don't have any personal experience with the OBX units but know that many people have tried them in different Honda Civic/CRX applications. Most people who've purchased the OBX unit seem to comment on the overall questionable build quality. Many people have commented that some of the nuts/bolts on the OBX unit weren't torqued properly (or sometimes at all). A small percentage of users have run into problems getting one or both axles to pop out of the diff after the intial install. I seem to remember the problem being traced back to the area that engages the circlip not being chamferred so the clip wouldn't allow the axle to come out.

As always, YMMV.

Christian
 
I've had good luck with my OPM diff. The Phantom Grip is an incomplete copy of the OPM diff... OPM's unit uses friction material where the diff and spider gears meet. Additionally, the spider gears are machined so there is additional contact area with the diff for added lock-up. With it's flexible design, I'm pretty sure Tom could get one made for your Prizm.[/b]
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I have an OPM diff in my Swift. It's a total waste of money... the only time it ever worked was watkin's glen in the rain (but then my problem was spinning BOTH wheels, not just one :D )
 
I have to agree with Roy...my experience with phantom grip was horrible, like there wasnt an LSD there at all.
my car makes about 85 hp to the wheels and I was getting wheelspin in fourth gear corners.

Now, the tranny on a swift is very tiny, so probably is a contributing factor.

But, you get what you pay for, and on a FWD this isnt an area to skimp.
 
This thread got me thinking (something new for me there) and I remembered that I have a spare 4 speed. So now its torn down and the diff is welded. Should be put back together sometime tomorow and in the car monday. I keep reading that driving a welded diff. is different than driving an open diff. What do you differently when driving a FWD car with a welded diff?? Any insights to what to expect would be appriciated.

Jon Schneider
ITC Wabbit #06
NeOhio Region
 
my best way to describe it is if your not on the power your likely understeering around corners. Takes a little getting used to out ont he track, but remember not to turn too hard int he paddock or you will need a new axle as the CV joints get torn apart.
 
your just going to have to try it to see the difference.

As you turn in for the corner, unless there is some pretty heavy trailbraking going on...you need to be on the power. You control the amount of understeer with the throttle.

The throttle basically steers the car. As your going thru the corner the throttle will pull you into the apex! This is a very weird feeling the first time you do it. So, if you find yourself understeering off to the outside of the corner, feed in more power (if arent already...)

Before welded, I had never even driven a FWD with a LSD, only open diff's...so basically everything I had learned from youth about driving a FWD was thrown out the window, and I had to re-learn FWD technique...which is not very easy at 35 yrs of age.

It takes any emphasis that there may have been on the rear tires...and makes your whole world all about the front tires. You will notice the rear becoming more loose. When going in hot on the brakes....release at turn in (for instance), and as you feed in more steering, your throttle should go pretty quickly to the floor. As this happens, the rear will step out a little...but all will be fine....as the rear tires just follow the front tires around the corner. You want full throttle long before the apex...

I have never driven my cars loose before. Always right on the edge of adhesion...10-15% slip angle...whatever...but not "loose" (I've always owned underpowered vehicles...and been more of a momentum racer). With a welded, I have had to change my driving style.

Just believe me when I say the welded can be very fast. You will find that you can pitch it in and drop the throttle to the floor and in most corners the car will scream around the corner...sticking like white on rice
 
This thread got me thinking (something new for me there) and I remembered that I have a spare 4 speed. So now its torn down and the diff is welded. Should be put back together sometime tomorow and in the car monday. I keep reading that driving a welded diff. is different than driving an open diff. What do you differently when driving a FWD car with a welded diff?? Any insights to what to expect would be appriciated.

Jon Schneider
ITC Wabbit #06
NeOhio Region
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Do yourself a favor and get that bad boy checked for cracks by a good machine shop before putting it back together. Stress cracks from the welding process, or from just being a 30 year old part can and have caused dramatic failures of welded differentials.

In the paddock the important thing is to not turn very sharp at all when backing up. Also don't just let the car roll in either direction without holding the wheel securely.
 
Hi Guys,
I'm a Newbie to this forum but I may be able to throw some practical experience into the pot.
I was fortunate enough back in 1988 to purchase from Mugen Japan, and import to New Zealand, a fully Mugen built, ZC DOHC '86 CRX Si.
This was a really cool, fast, little car... and as far as I know, it is still running competitively in New Zealand even now.

The only problem we had was of course the HP induced, massive Honda understeer. To be able to find, let alone afford a LSD for that car back in '89 was pretty much out of the question. So we welded the diff and experimented with wheel sizes to get the best gearing we could for our local track.
Apart from my starting to develop the beginnings of a Swarzenegger like upper body... It worked fine! Knocked about 4 seconds off my lap times. Very hard to drive around the pits, (Ignore the horrible noises)and of course you had to literally pitch the car into corners, then get back on the gas as quickly as possible. You will find that you will start to develop a Rally style driving technique, but generally I found the welded diff to work fine.
Oh by the way ... Wet tracks on a welded Diff, Watch where you are going! If you see a puddle? Avoid it! Or try and get both front wheels to go through together!! Otherwise you will probably very quickly see where you have just been!

I now reside in Southern California where I have the privelage of running Special Projects Motor Sports.
All of our 5 Honda Touring Cars have the luxury of Cusco, KAAZ, Quaife or Stock Type R LSD's and any Final drive ratio we want. But I still have fond memories of racing back in the days of just having to make do with what we had.

Good Luck,

Kiwi
 
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