This weekend, I was driving my 914 for the first time in a few years and I noticed that in first (old 2nd) gear, the right rear tire would light up as long as I kept my foot in it. While it was fun to leave black stripes across the local intersections, an LSD has got to be a better way of hooking up the power that I've got on tap.

For a car that will spend most of it's time on the street, but some time on the track (Willow Springs, Pahrump, etc.) what's the appropriate type of LSD? Let's assume that the torque and HP are around 300....

Thanks,
Eric

There are several threads about this decision but first I'll say what you might hear a few times in this discussion. Lighting up the tires in first gear in a 914 will lead to heartbreak eventually. Especially after installing one of these diffs.

First is the weakest gear because it's only supported by one bearing. The other end of the shaft is 'in the air" and not supported by anything. So laying scratch in that gear will eventually break the mainshaft if you use tires that actually grip the pavement. Now, on to your question. The two main types of limited slip diffs for us are torque-biased and clutch-type (sometimes referred to as ZF-type).

TBD (Torque-biased Diff):
- gear-operated
- Operates under acceleration only and acts like an open diff (like you have now) under deceleration.
- Generally better for AX
- Install it and generally forget it

LSD (Limited Slip Diff)
- Clutch plates under tension transfer power to both wheels
- Operates under both acceleration and deceleration.
- Generally better for track use
- On slippery surfaces the LSD can get you in trouble if you aren't practiced in driving in "tail-happy" situations under deceleration.
- Occasional replacement of the clutch plates.

Both allow you to get more power down to the pavement under acceleration. The TBD is usually less expensive than the LSD's both at the time of purchase and over the life of the car since the clutch plates in the LSD need to be replaced now and then.

I've run both in my car and prefer the LSD's smoothness. The TBD has a varying application of torque that changes during sweeping turns and under increasing acceleration. I can feel it and it bugs me. That said the TBD allows you to turn better on an AX course.

Have fun deciding!

he is using 2nd gear as his "1st" gear!

"I see" said the blind man!

Here's some good reading:
http://www.914world.com/bbs2/index.php?showtopic=106271

You probably just need more tire. What size are you running? If you get the clutch out and push down smoothly with good 205/60x15 tires you shouldn't have much wheel spin.
Tromping on it to much will take out the do an number on the ring and pinion. I drove mine in the mountains for years and never had a problem with the V8 until I side stepped the clutch a few times.

My 265 width tires will break it loose only slightly in a straight line. I am sure 205 would still have traction issues. Depends on rubber type and engine torque curve.

I'm running 205/50/15s right now. With the car rolling and the clutch engaged at about 1200rpm in 1st (old 2nd), the right tire breaks loose if I press with my right foot only.

I'm switching over to a 915 with 3:10 gears, and going to 265/45/16s on the back. The final gearing including tires will match my current Renegade 901 4 speed (1st gear removed) almost exactly through the first 4 gears and 5th will be a massive overdrive.

I figure that if I'm going to add an LSD, then doing it before the tranny is installed is the prudent thing to do.

I'll keep reading....

If your car is stiff in the rear you could consider softening the rear suspension.

When we put an LSD in the race car we found out how easy it was to spin both rear tires, even with a 4-cylinder.

I tend to agree your ultimate solution is more rubber. Trying to put that much torque to the ground through 205's (especially if street compound) is an exercise in frustration...and smoke.

What "kind" of SBC are you running?
Bore
Stroke
Heads
Cam
Pipes
The car is so light that limiting the torque is important. Longer headers with no crossover and a mid range to higher RPM cam work better than short headers and an RV cam.

I've got a .030 over 327 with a 4 bolt bottom and the nice flowing 1.94 intakes in the heads. The cam is a ince untit from Comp Cams that is about the most you'd want to go with 9:1 compression and hydrolic lifters. Not much bottom end, but once you're above about 1800 hang on to your shorts it will go to 6500 in no time.
I do get considerably more wheel spin now that I changed the 600 holley out for a 750 Edelbrock with manual secondaries and lost several MPG. The Edel floods in tight corners and the holley was probably a better fit.

Renegade did the gear swap in the 901, 3,4 and 5 are taller, I don't use first and it is a delight to drive.

I'm running a 327 built by Wild Bill's purchased through Renegade. I'm still looking for the original paperwork, IIRC it's a 4 bolt main with Dart aluminum heads and about 9.5:1 compression. Nice cam timed for higher HP and lower torque. I'm swapping out the Holley for a Mass-Flo FI, that's a mass air system rather than a speed density FI system. I figure that the MAS FI won't flood on corners and will handle altitude changes without missing a beat.

The headers are standard Renegade issue and I've got the same 901 that you've got with the flipped "H" 5th and 1st gear removed. The new 915 will give the same gearing as yours through the 4 gears that you use with an "extra" 5th to get 70 mph down around 2000 rpm.

I've owned my 914 since 1988 and this will be my third iteration of the V8 conversion. And I agree, the V8 is a delight to drive.

Rand,

Thanks for the link. I had read a number of threads about LSD and TBD here, but had not seen that one yet. I'm leaning towards what Brant and Matt said about what a 914 needs.

Eric

Here are two japanese LS. Since you have a 915 they have one that will fit.

http://www.kaazusa.com/products_lsd.html

http://www.osgiken.net/dealers.html
Rennsport Systems
6416 SW 33rd Pl
Portland, OR 97239
TEL: (503) 244-0990
FAX: (503) 244-0797
www.rennsportsystems.com
Technical Shop: Y
Specialty: European Cars

Here's the latest. I just got off the phone with Matt at Guard Transmission and he reiterated his thoughts about TBDs in a high HP 914 that doesn't do long distance track races. His only warning is that the gears in the TB diffs can be succeptable to heat damage if running high torque for extended periods, just like the rest of the 915 innards. If that is your planned usage, a clutch style LSD is more appropriate.

As far as the handling differences between LSD and TBD in a 914, it is starting to make sense to me. Because the 914 is mid-engine, it doesn't gain as much benefit from the LSD decel lockup as a tail heavy 911. There can still be some improvement on decel, just not as dramatic as the handling change in the tail-draggers.

I want to thank everyone who weighed in on this topic. This is another costly decision and I now feel that I'm going to put my money towards the right set up for me.

Thanks again.

Purple Microdot.

I agree. When I had my timing advanced quite a bit I really didnt break the tires loose much. but when I retarted the timing it just spun them with ease.