LSD recommendations, LSD reccomendations Options

[Charles Freeborn]

Greetings.
While my engine is out for top end refresh I'm also planning on installing a limited slip diff.
What have people run and why? Obvious choices are Guard (true LSD) Quaif, Wavetrac (Torque bias). Pros / cons of those types? I've heard the TB is easier on the rest of the gearbox. Not too concerned about having to run LSD additive as the fluids get regular service anyway (every event).
Quick rundown of the car:
100% track use (not street legal) Little to no AX - all road course.
2.0L 4 cyl with fairly extensive mods. Estimated hp around 150.
901 side shift with AFKSX gearsets.
Car weighs approx 1700 lbs (18 & change with me in it)
Currently running Toyo RR 225/50 slicks. May step up to Hoosiers if I get more serious about racing. I've got another set of wheels for running in the wet with R888R's. Not great rain tires, but that's what's on those wheels now. When they're done I'll probably switch to RA1's.

Thanks!

[wndsrfr]

I just put in a Guard for my /6 track car--all road course like you're doing.
The AFKaSX is a great choice although you may run out of revs on really long straights with high speed entry...I'm on AFNSZ with 215RWHP but am about 1940lb dry.
I've been on RR's in the past and now Hoosiers as required by SVRA, etc. RR's are actually faster I think--less rolling resistance but find the Hoosiers are nice at the limit, lots of slip with same cornering force, don't suddenly break away.
That said, neither of us are going to break away the rear end in any of the higher gears with a limited slip in there but there's some discussion about how the Guard helps on braking but I'm fuzzy on that count....

[brant]

Hi Charles...

a touchy subject actually
there have been lots of previous arguments over what is best.


when I was trying to make the same decision for myself...
I had a conversation with Paul Guard years ago...
he told me that in a mid engine car the TB could be faster...
this was in response to my pointing out that the clutch LSD was the defacto and widely publicized as the best differential for track use

Paul pointed out that this was absolutely true on a 911 rear weight bias

I went with the Quaif on my vintage racer teener.

Prior to the Quaif about 8 years ago... I previously raced (for about 5 seasons) a 2.0 (AJRS motor) 4cylinder 914 with a welded-locked diff. It was different but ultimately faster than an open diff. Took me a little while to learn how to drive it since it was so different.

[Charles Freeborn]

I just put in a Guard for my /6 track car--all road course like you're doing.
The AFKaSX is a great choice although you may run out of revs on really long straights with high speed entry...I'm on AFNSZ with 215RWHP but am about 1940lb dry.
I've been on RR's in the past and now Hoosiers as required by SVRA, etc. RR's are actually faster I think--less rolling resistance but find the Hoosiers are nice at the limit, lots of slip with same cornering force, don't suddenly break away.
That said, neither of us are going to break away the rear end in any of the higher gears with a limited slip in there but there's some discussion about how the Guard helps on braking but I'm fuzzy on that count....

Yep, runs up against the rev limiter about half way through a long straight. Fortunately 2 of the 3 tracks I run the most are pretty "technical" and straightaway speed is less of an issue. My car is a 4, with way less hp, so breaking loose the rear is less of an issue.

Haven't run Hoosiers yet ($$!!) so can't say. The RR's feel good - especially once their warmed up.

The "tail wag" phenomenon with 911's is a real thing. I've set mine swinging before and it's a pucker inducing feeling.... essentially when lifting off the the throttle from high speed in a straight line the diff is dancing back and forth to whichever wheel is on the "inside" this gets the trailing throttle oversteer excited. When said wheel hooks up it makes the rear dance to the other side and the oscillation occurs. Only recourse is to get back on the throttle.... as with most 911 handling quirks..

[Charles Freeborn]

I'm leaning towards a TB unit too - or just leave the open dif in for this season.. Not enough hp for wheel spin to be an issue.

I've driven a welded dif car once (vintage Alfa), and yep that was an interesting feeling. Had a dog box too. That car didn't like anything less than WOT. Was a blast, but not for the faint of heart or easily distracted..

Thanks for the input. I think I'll look at the Quaif, Guard and Wavetrac TB's. They all swear they're the best, so there's a little wheat / chaff separating to be done.

Cheers!

Hi Charles...

a touchy subject actually
there have been lots of previous arguments over what is best.


when I was trying to make the same decision for myself...
I had a conversation with Paul Guard years ago...
he told me that in a mid engine car the TB could be faster...
this was in response to my pointing out that the clutch LSD was the defacto and widely publicized as the best differential for track use

Paul pointed out that this was absolutely true on a 911 rear weight bias

I went with the Quaif on my vintage racer teener.

Prior to the Quaif about 8 years ago... I previously raced (for about 5 seasons) a 2.0 (AJRS motor) 4cylinder 914 with a welded-locked diff. It was different but ultimately faster than an open diff. Took me a little while to learn how to drive it since it was so different.

[Charles Freeborn]

Forgot to mention engine and trans built by AJRS roughly 15 years ago. Car was campaigned as a PCA racer in GT5S class. I'm more interested in vintage so some of the aero and other racer bits will come off, but the core driveline is solid and will stay.

Hi Charles...

a touchy subject actually
there have been lots of previous arguments over what is best.


when I was trying to make the same decision for myself...
I had a conversation with Paul Guard years ago...
he told me that in a mid engine car the TB could be faster...
this was in response to my pointing out that the clutch LSD was the defacto and widely publicized as the best differential for track use

Paul pointed out that this was absolutely true on a 911 rear weight bias

I went with the Quaif on my vintage racer teener.

Prior to the Quaif about 8 years ago... I previously raced (for about 5 seasons) a 2.0 (AJRS motor) 4cylinder 914 with a welded-locked diff. It was different but ultimately faster than an open diff. Took me a little while to learn how to drive it since it was so different.

[campbellcj]

I went with a Quaife TBD many years ago for same reasons Brant cites, probably after speaking with some of the same people LOL. My car does have enough power for corner-exit traction to be an issue. Especially as I favor and was set-up for tighter technical tracks the conventional LSD's impact on low-speed turn-in /rotation would have sucked. Although I would've liked the decel lockup for sure, decel stability not being a strong suit of the 914.

My trans is about to be opened up and trying to decide what to do - I may ultimately have another one built w/ longer gears and a different diff, as this one is extremely short-geared (AGaKQV IIRC) though the car does rev to 7800 so top speed not an issue. Don't really wanna go more than about 135 in this car w/ no aero... But the car is quasi-streetable again now and cruising 4500rpms on the freeway is no fun.

I do have an LSD in my 911 and can really feel that; it was added after I bought the car after a rebuild with Guard internal bits so I experienced the before & after. In that car it's a huge plus, a lifesaver really, with the massive torque and rear engine.

[stownsen914]

Two disadvantages of the TB differentials:
1. No lockup on decel. Maybe not as big a deal as on a 911, but I wouldn't say it doesn't matter.
2. The biasing only works when both wheels are on the ground. If you lift a wheel, your freewheeling just like with an open diff.

Certainly better than an open diff. I'd never heard that TB differentials were faster in mid engine applications. I'm sure driving style is a factor too, so for some I'm sure a TB is faster, but maybe not for all.

I wonder what pros are running in modern mid engine cars. I'd guess LSDs, but I don't know.

[yeahmag]

The Wavetrac is unique in the TB LSD world. Check the "How It's Different" tab:

http://www.wavetrac.net/technical.htm

I'm currently shopping for one for my car...

[jd74914]

The Wavetrac is unique in the TB LSD world. Check the "How It's Different" tab:

http://www.wavetrac.net/technical.htm

I'm currently shopping for one for my car...

It is a pretty neat piece-they basically added a Salisbury action to a TB so you remove requirement for wheel loading without needing clutches.

How much do they run?

[jd74914]

...the conventional LSD's impact on low-speed turn-in /rotation would have sucked. Although I would've liked the decel lockup for sure, decel stability not being a strong suit of the 914.

I don't really understand the low-speed rotation impacts? Could someone explain?

Most higher end clutch LSDs are Salisbury (ramping) type AFAIK. Certainly you'll get something similar to a locker if you have excessive preload. Belleville washers were used to hold everything together in original Salisbury iterations (40+ years ago). These have issues with high preloads due to their limited "travel" range. Some newer versions have springs holding the ramps together. This means quite limited preloads are needed (obv. can add to personal preference) which to me implies more "open diff-like" turn in behavior when traction is good. The ramp angles can then be set on both the accel and decel sides to tune for the car. I know its a PITA to do this when you have to disassemble the gearbox.

[yeahmag]

The Wavetrac is unique in the TB LSD world. Check the "How It's Different" tab:

http://www.wavetrac.net/technical.htm

I'm currently shopping for one for my car...

It is a pretty neat piece-they basically added a Salisbury action to a TB so you remove requirement for wheel loading without needing clutches.

How much do they run?

Right around $1300

[stownsen914]

I've been wondering who was going to come up with a hybrid TBD/LSD diff. I didn't realize it had already been done. I'm curious to hear racer feedback on who good the Wavetrac is for hard core track use.