This may not be an unusual reaction. When I am hard on the gas and shift at high rpm between 1st and 2nd, the rear end will twitch. This is common to rwd vehicles. Traction controlled cars will minimize this reaction. Last year, I had an AP1 flywheel and an SOS sport clutch installed in my '06 just so I could get the bite between shifts. I love the feel of the rear end wiggle when I am banging through the gears. I just need to be mindful of the weak differential.
T

 

You should probably read the OP - everything will be explained.

 

^^I think the op acknowledged this and didn't meant torque steer in its literal sense.

 

if you have a stock n/a or basic bolt on s2k the differential isn't weak, as long as you don't launch it at every light it suits the s2k perfectly for the power levels produced. But that goes with every car, launch it enough times and any differential will give out, the s2k is notorious for the weak differential on higher than stock power cars.
Now if you are F/I then yea it becomes the weak point.

 

Definitely sounds like tire pressure to me. Mine has done that several times and always had one tire with low pressure.

 

Sooo.... more variables... and unfortunately it was snowing and raining so no road test... One back tire was 32 and the other 30... not crazy different.. except I noticed that one tire is a Conti, and the other another brand... so who knows how close they are even at the same inflation.

I'll see how it acts once the sun is out again... the roads here still have a lot of sand/gravel on them from winter. Other than the acceleration issue, could this cause (or could it already have caused) and wear on the rear diff? I don't plan on driving it hard... and would prefer to leave the tires on for at least this season... they are in decent shape. Though I suppose I could replace the rears and leave the front alone... I am kind of anal and want all 4 to match.

It was just above freezing here, so all I could do was give it a quick wash, detailed with Lucas quick detail... checked all the fluids and lubed all the window trim. Looks 100% better... a few chips I'll take care of once it is warmer...

Thanks for the tips - I'll let you know if new tires are needed after my next drive...

 

opposing tires is 100% your answer. match them

 

 

So... was able to get enough sun to take it for a spin... the air pressure equalization has definitely reduced the effect to almost nothing... so I attribute the remaining effect to the difference in the tires....

Once I get new tires that will answer the final variable.

Thanks for the help!

 

When you get new tires, I'd recommend getting an alignment.

Just put a new set of tires on my S2K and had the alignment checked. I was surprised how off it was, and had even put a few track days on it.