For all you tranny experts... My '75 914 w/3.2 is now ready for it's 901 tranny rebuild, which will include a limited slip of some kind. My first choice is a factory LSD but it seems like it's easier to find a needle in a haystack. So while I look for one, I'm also open to alternate suggestions on the best way to get the most from my 3.2 which I run with the POC at Streets of Willow and "Big" Willow. Thanks.

you can find factory ones.
call car quipt they always have.
you can buy a guard ZF style for about the same price as a factory.

I've been amazed at the difference in driving style between the different diffs out there.
part of the answer depends upon what driving style you want/like

a really high% ZF is going to be similar to a locker
a quaffe is very different.
a locker is more predictable in mid corner but requires more sliding
a quaffe can be felt in mid corner going on and off.

I recently changed to a quaffe
its taking me a bit to get used to
I expect to ultimately be faster, but at this point my lap times are only equal to those of my locker (this after 4 days of events)

I know when I went to the locker it took about 8 days of use to get the hang of it. I expect to improve yet with the quaffe, but just need more time.

I put the car off last week on saturday because the quaffe requires me to apply full throttle before apex or else it feels tail happy. I imagine it is makes the car "feel" much like an early 911. The locker didn't require this style if you messed up. Last week I had messed up my turn in at 110mph and let off of the gas only to have the car walk off of the track

so you have to committ and then floor it to make the corner.
taking me a bit of time to get used to it.

I could ramble on for hours
but the bottom line is that the two diffs require vastly different techniques to get the most out of them.

I switched because my theory is that it takes anywhere from 200-300hp to really be faster with a locker and overcome the drag created... conversely I think (or hope) that a low hp 2.0/6 like mine can eventually be faster due to saving that same drag with the use of a quaffe.

on and on.....

brant

Damn that's some heavy theory.
I am glad to be just a AX hound and occasional track wanna be.

I've looked for ZF style diffs but haven't found any. Can you be more specific about possible sources?

Thanks,

Andrew

Take your car to Otto - which I'm sure you're doing
Give him a blank check - not sure about that one
Say thank you when you pick it up.
You know the routine. Nobody knows more about getting the most out of a 901 than John.
I have a factory LSD, it's all I've ever run so I can't compare it. I've seen them advertised on the bird board from time to time.

I would say, in order of my shop's preference is a GT, then Quaffe and finally a factory limited slip. I would not use a spool or locked set of gears as they really make a car push terribly. I have a trans with a GT and a Quaffe and actually can not tell any difference on a track such as CA Speedway or Willow Springs. The advice about a great trans shop is very true.

I'm almost certain that if you call tom conway at car quipt he will have 1 or more factory diffs already rebuilt in stock.

the thing is the GT clutch pack (ZF) style is no more expensive than a used factory diff and is much more adjustale. the ramps in them can be adjusted to offer different amounts of lock up on both accell and decell. So it would be better to buy a GT brand clutch pack.

The GT brand Torque biasing diff is supposedly 1-2 lbs lighter than the quaffe at the same price. However, these have been on back order for about 1 year now, so you will not likely be able to get one. Thus if you go with a TB style the quaffe is the only thing actually available.

Also for clarification. The spools and lockers don't actually push if you drive the car differently.... VERY differently. Like I said it took me about 8 track days to figure out how to drive around the push.
(in fact you can drive any car around any habit/worn tire/problem, if you learn to change your line and style) Once you figure it out, they don't push anylonger. If you don't believe me go ask the 75% of the SCCA guys who use them on championship cars.

brant

Thanks to everyone for their advice. Yes, Otto will be doing the work. And getting that big check. But I like to get a variety of opinions and info.

Do you have a number for car quipt?

No one has one of those GT units? That's a drag.

I've just received my 915. As soon as my mechanic gets back from holiday it's going to his shop. He's doing a rebuild, LSD install (R&P flip too), and WEVO 915 side shift conversion.

For the LSD I've decided to go with the Guard ZF type (clutch pack like the OEM). I like the way that a ZF LSD operates on trailing throttle (still provides LSD action) and helps a bit with turn in. With the Guard ZF type units you can also select the amount of lockup in each direction so you've got say 40% acceleration locking and 80% decceleration locking. ZF types still function when a wheel lifts as well whereas a TBD (Quaife) doesn't.

Later,
Kevin

I thought that the Quaife diffs could be adjusted by shiming the belville spring washers in the middle to make it "think" that there was still some traction on the unloaded wheel?

just for clarification
you can get GT brand ZF style.
you just cant get GT brand TB style.
he makes (has made actually) both styles.

also, I have never lifted a tire unless I was seriously Fuch'd already.
with the car dialed in you don't have to worry about lifting a tire unless your off road.

I think I've been mis-spelling carquip...

oops...

CARQUIP

brant

There are an excelent pair of articles out there on the quaife TBD and clutch LSDs. Im sure I have them at home. If anyone wants to shoot me an email I can send them out.

Paraphrased:
Quaifes are torque biasing diffs (NOT limited slip). They can only be set up to a max of ~6:1. If the rear is stiff and you unload the inner wheel more than 1/6 the avail torque (or go curb hopping) the inside will spin. Since they dont casue the wheels to try and turn at the same speed, they'll never introduce a push. Avoiding the wheel scrub can make lower hp cars faster (than w/ a LSD). They don't ever "lock up" thus you cant feel them working and they dont suddenly upset the handling - a bonus for the autox crowd. Also a must for FWD cars.

Clutch types are LSDs. They try to turn the wheels at the same speed. That will cause the car to try and push (the inside tire wants to turn the same as the outside - trying to drive the car straight ahead). On accel, that can be helpfull if the car is loose due to high hp (plus, some cars like the 911 dont like to turn when accelerating hard anyway so its not a problem;). They can also be set to lock up on decel - one of their greatest advantages over TBDs. Makes the car more stable (push) under braking and turn in (which is an excuse to set the rear sway even tighter so the car will turn better mid corner). Since lock is independant of each wheel, you can curb hop w/ LSDs and not loose forward traction. LSDs can really help cars that, when everything else is setup right, are too loose on corner entry (like some 911s - esp when trail braking). LSDs can cause handling changes as they go from slip to lock - dependant on setup, but that can cause problems.

The modes of operation are the same no matter the car. Pros and cons of both types. And, what works well in a 911 might not work as well in a 914 due to the initial handling differences. You need to figure out what properties YOUR car and driving style needs to go faster.

SMD

I guess I have a somewhat expanded sense of where width of the track ends...

Actually, I was thinking more of situations were you are running over curbing as part of the line or even dropping a tire off the track occasionally (it does happen ). Actually lifting a tire as in flat cornering tire lift would probably be rare in a dialed car except when curb hopping.

I guess I've become addicted to the all situations hookup with the ZF. I didn't experience any big problems with my driving style when I first installed it but that might mean that I always should have had one.

I can't wait to see the response with the '14.

Later,
Kevin

I guess I need to clarify my statement.
If I hit a curb hard enough to lift a tire....
Or if I put a wheel off the track hard enough to lift a tire...

then I've blown the lap time that I was shooting for by my mistake.
thus the extra tenth of a second I could of gained from the diff is completely irrelevant because I Fuch'd up the lap at that point.

once I go off track or lift a tire I switch from qualifying and lap goals to the goal of damage control..

thus I could care less about the lap time and I just want to get the car back on track safely without hitting anyone.

some cars will lift front tires I agree.
but lifting a rear tire is largely indicative of an unperfect lap or not perfect set up.

there is a bid debate about wether a TB or ZF style is faster in a 914 on a road course. the 911 guys are clear that the ZF is faster. but very reputable sources can show proof that this may NOT be true on a 914 chassis. The source that I place the most credibility in showed testing to support and help me make my decision.

like everything in racing...
each person my find differences due to equiptment, style, track layout, car design... etc.

brant

Brant, That may very well be true in your case. It also depends on the track. Im from the east coast and what you said is true about Summit Point "main". Summit Pt Shenandoah has one good spot (and another where you're completely airborne but you better be on the brakes there) The lower esses @ VIR has a classic curb hop pair that is used by almost all to carry more speed and straighten out the remaining esses. There was one in the north course configuration at the top of the hill into hog pen, where you could COMPLETELY eliminate a turn. So much so, that they gave up, paved the inside, removed the gators, and completely eliminated the turn a few years back;) So, in the end - it still all depends...

SMD

Ok..
I can concede to "it all depends"
are you hard on the throttle during those described spots?

If I blow it locally and lift a tire, I've lost a full second already (due to my screw up.)

I haven't run a track yet locally where there is any tire slip or loss of traction from the quaffe. But then I haven't run nearly as many tracks as I'd like/dream to.

another qualifying statement that I probably should account for is that I'm only running 147hp to the rear wheels (at 5200ft altitude)

If I was running 300hp to the rear wheels then I suppose I could notice more loss of traction, and possibly loss of traction from both wheels at the same time. of course I'd definitely run a locked diff If I had over 250hp available so it wouldn't be the same arguement anyways.

brant

Brant, I'd love to run more tracks than I have too;)

Heres a map of VIR full (for scale, T12 to T14 is almost 1 mile)
Click to view attachment

The corners in question are T5a & T6. You want to be hard on the gas from T4 to T7 (or until T11 for low hp cars). T5a & T6 get in the way from making it a nice sweeper. It takes a little lift in most cars to hit the apex in T5a. If you actually "apex" T6, T6a gets in the way. To go fast, you lift somewhere between T5 and T5a, turn the car over the berm in T5a and really go over the T6 berm whole hog (wheel has to be straight or you can spin). Literally makes it a straight shot from T5/5a to T7. If you have to brake/lift/scrub/turn to make T6a, you're screwed;) There will be a freight train of folks going by. Since they are relatively slow and tight corners leading onto a good straight, it pays real dividends to be able to get on the gas super early and do whatever is necessary to keep accelerating.

Running VIR South, the T4/5/6 is downhill. You TOTALLY jump the curbs in T5/6 (on the gas across 5 (darn near 4 off), trail braking as you get back on pavement and kind jump 6.) Compared to someone who stays "ontrack" its a 4+ carlength advantage you can make on them.

A LSD might buy you a 1/4-1/2sec of extra traction in either case? Maybe a tenth second lap improvement on full course? You'd have to weigh that against the pros/cons in other areas. You'll be jumping those curbs no matter what diff you have.

~150rwhp isn't "low";) The E30 racecar only makes that and is 2750# (the "spec")

SMD