Studiogeek

iTrader: (6)

NA/T SC300 445hp or so, late model R154, Torsen LSD. The car pulls to the left during a hard pull. The car snaps back to the right if I let off hard. When not pulling, car tracks straight when driving or breaking. This will not be fun in the rain.

What might cause this?

EDIT: IT WAS A LOOSE REAR LOWER CONTROL ARM!

HiPSI

iTrader: (2)

I would honestly start looking at different tires at this point. With my stock open diff the 275 width Toyo r888 completely solved all traction issues. The downside is the treadwear and the noise of the tire.

Other places to check would be your alignment, suspension settings.

Is this your daily driver? As long as you aren't going into boost in the rain you will be fine. The LSD / NA-T setup will not make driving it in the rain harder or more dangerous unless you are pushing the car hard which would be stupid in the rain regardless of the setup.

Studiogeek

iTrader: (6)

HIPSI,
It really does not feel like i'm loosing traction at all (still could be). It feels like the car is being steered with full traction, left, then right.
With regard to rain, you are correct. I will never see boost in the rain except on a track or in a parking lot. I drive like the oldest of Grandma when it's wet out. I spun out my first year driving (many, many, many years ago). Fixed me good for life in the rain. My question about this pitching is as a result of my rain paranoia ,

t2d2

iTrader: (8)

If it's pulling both directions, I'd have to agree that it's alignment and/or tires. (Pulling just one direction would indicate torque steer, but that shouldn't be an issue on RWD.) The first time I drove my SC in standing water on the highway, it was a terrifying experience. I've never had trouble managing hydroplaning before, but I was seriously scared for my life in this instance. It was pulling hard to either direction, feeling like it could go into a complete spin at a moment's notice. I finally had to move over into the slow lane and tuck in behind semis until the rain calmed down.

I was on moderately bald tires, but I later discovered that the P.O. had completely jacked the alignment settings. It pulled straight in dry conditions, so I didn't suspect the alignment was off. It's like they just kept tweaking things by hand until it drove straight, with no rhyme or reason to the settings. In wet weather, it became an untameable monster. Since putting on better rubber and getting it aligned, I've had no such issues.

Ali SC3

iTrader: (10)

Could be some play in the LCA bushings and or the balljoints, maybe have a mechanic use a pry bar on the lca's to see if there is any movement side to side, yours does have low miles but age also plays a factor sometimes. the other place there can be some play is in the rack bushings, but you would feel that play all the time.
It could be something in the diff possibly or even normal to some extent, not really sure on that side of things.

Studiogeek

iTrader: (6)

All new front end bushings and loads of new parts. Feels like torque steer as I have traction. It FEELS like it's coming from the rear.

Almost like a minor version of this video (at 00:33). This guy told me he has a TRD, LSD and makes 500.

KahnBB6

iTrader: (5)

Studio, one thing that stands out to me as a red flag in the video is that the guy with the red SC is on factory narrow rear wheels and tires but has a 500hp engine and a TRD LSD.

That alone would account for not quite having enough contact patch with the road for so much power. You need at *least* a 9-10" wide rim and some 255-275's, plus a good performance summer tire design.

I am sure you are running wide enough rims and tires already on yours. What tire compound do you have and what alignment settings do you have?

The other thing may be that it's a quirk of how the Torsen reacts under that much power. I know Supra guys tend to cite 500hp as the upper limit of what they consider a safe power range with their stock LSD. Goes for the 6-speed and Auto versions. I've never experienced what you're describing in the dry, however, but I am sure that is because I'm not able to.

The example video, even with a TRD clutch LSD, seems more like a case of too narrow and inadequate tread but also inadequate choice of tire compound for this kind of car. It is supposed to be a much more reliable/predictable LSD above 500hp.

In the rain, as I've said in my posts in the other thread, we have to drastically tone down how our pedal and steering inputs affect the power delivery of these cars. When I finally have a boosted engine I'm interested in wiring in not only a "TTC" on/off switch for the twin turbos but if possible an "extreme low boost / zero boost" on/off switch for rain emergencies. Maybe that's impossible to do but I haven't looked into it yet.

Or... as Ali suggested, bushings. Specifically the bushings for the differential carrier (pumpkin). They may be worn. The replacements for them are a set of poly ear bushings from Aliga and rear cover bushings from Figs Engineering. Maybe Figs sells an entire kit. Unsure.

KahnBB6

iTrader: (5)

This is somewhat interesting. It's only informative for the first minute or two during which the technician talks about how heavily modified BMW M3's of this generation also tend to benefit from switching to an aftermarket LSD. Not sure what WHP levels he is basing this on but what he's describing is a similar instability issue with the factory LSD's in the Bimmers. To my knowledge, however, these are not Torsens. Not the T-1 type in this thread or the later T-2 type but some kind of factory clutch style LSD or VLSD. I am not all that familiar the technical specs of M3's, apologies.

Anyway, they're discussing the install of an OS Giken LSD to use under high horsepower applications which is supposed to cure the sidestepping issues they encounter if still using their stock diffs. OSG does make LSD's for our cars (MKIV TT Automatics on their website) but they cost even more than a TRD LSD.

Now I have seen the sister thread to this one on SF and I do agree that the bushings should be looked into before considering that the Torsen is actually the main culprit at 450whp.

For what it's worth, even though I am pretty sure this generation of M3 still doesn't use a Torsen from the factory:

HiPSI

iTrader: (2)

The way the torsen delivers the power to both wheels isn't as reliable / repeatable as the TRD is.

For it to twist and then snap back after releasing throttle tells me you are losing traction and can't hear it due to the open wastegate (which is exactly whats happening in the video above).

If the car isn't a daily driver, consider some Nitto 555r's or Toyo R888's and this will 100% completely solve the problem till you are in the 700-800whp range.

Studiogeek

iTrader: (6)

Thanks for the input guys, i'm going through it all. It does not feel like traction. It feels like someone steered the car with full traction. My tires are 275 I think on a 10 or 10.5. A guy on FB SC group had the exact issue. His control arm was loose.

eknine9

iTrader: (8)

You said you did bushings but did you check the ball joints on the LCA's? As they start to go out the car can start having variable camber and toe issues, and it can make the car more unstable in low traction conditions.

Studiogeek

iTrader: (6)

I'll add this to the check list!

Thank You

Studiogeek

iTrader: (6)

edit: It was a loose rear lower control arm!

KahnBB6

iTrader: (5)

Congratulations on finding an answer, Studio! And good to hear you got the control arm fixed. That really could have been dangerous.

So how does the car track now? No issues with the Torsen after all, then?

Studiogeek

iTrader: (6)

Kahn,
I only got 10 min in traffic after the fix. Cant wait to push it a bit more today. This likely means no Torsen weirdness yet. Yesterday, a couple times it felt like the body was pivoting on the chassis. That was a STRANGE sensation. That sent me to the lift yesterday.

Ill report back after hitting it harder today.

Thanks