I am think of getting some upgrades. My T/c is still good, how much to do the Stage 4 on it plus a Rear diff upgrade?

 

Send Jon at TRE an email, that's usually the best way to get a hold of him: jon@teamrip.com

l8r)

 

Guys,
I don't post all that much around here, but I just recently had Jon upgrade my rear diff and have to say it made the single biggest handling improvement in my car to date. As my car is prepared to SCCA T2 specs we aren't allowed to do many things, but I do have a mega $$$ JRZ suspension. The suspension is cool, but the TRE rear made an instant change.

I just returned from a Double National race at Roebling Road Raceway in Georgia. For those that don't know this track it is very much a handling track. It may come as a shock to some of you, but the Evo in T2 form handles like a dump truck compared to some of the competition like the Solstice GXP and Nissan 350z. I raced against a brand new GXP freshly prep'd by the reigning T2 Champion builder. I was able to drive in to turns and use the throttle to come out... so drive in, start to get mid-corner push (understeer) and go to the throttle and the rear would hook and drive me off (throttle oversteer). It felt great! Good enough to take home wins in both races!

I'd do it again in a heartbeat...only issue I have is kickin myself I didn't do it sooner

 

Nice work

I knew you'd like it once you tried it. Pretty crazy how you can manhandle the EVO at the limit while exiting a turn eh?

 

Jon, or others, I am trying to diagnose and fix a handling problem and would like some input.

Anyone who watched the car come through the finish at the Toledo ProSolo probably saw this - powering out of the last corner and coming through the finish the rear of the car was hopping or bouncing sideways. It also did this accellerating out of corners this past weekend on the concrete at Oscoda.

It seems to happen worst on real grippy concrete, and never did it on fairly slick asphalt. It is only under full accelleration coming out of a corner. It does not do it on braking or decel, or steady state through a corner.

I have 2 main theories as to what's causing it:

1st idea - shock valving is causing it, needs compression and/or rebound adjustment to try to stop the hop.

2nd idea - rear diff is causing it - under accel and cornering rear tires have huge grip and will not slide. Diff is very stiff and acting like a spool, tires need to move at different speeds, so they are forced to break traction every so often so the inside can "catch up" to the outside. Car doesn't do it in steady state corner because inside rear tire has almost no weight/traction . . .

What do you think? Add some LSD additive to the rear diff or start playing with shocks. . . or could it be something else altogether different?

 

is there any change in rpm associated with the hopping as if you're getting wheel spin?

 

from the pic you posted it looks like your car is near the limits of compression travel in the back, have you considered that the extra loading (greater acceleration, both lateral and longitudinal) from the sticky concrete was putting the rear on the bumpstops and thats the cause of your bouncing??

 

my car does it too, coming out of low speed corners only. I think the rear suspension is getting into resonance, just like hop on a RWD car. Shock adjustments may tune it out, but you may sacrifice more time from the adjustment...or not.

Based on my expience with various locks, I think the more the rear is locked the more this will happen. The more work the rear tires do, the more the rear suspension in compressed, changing the resonant or natural frequency of the rear, possibly pushing it into the bad zone.

 

I had this same rear hopping this weekend. Twice I almost took out the timer because of it. On the gas really early on a 90 or so finish curve and all of a sudden it hooks up and hops sending me the other way. I did FTD and PAX though...I need higher overall spring rates as I think my suspension is too soft for the rear diff, aggresive throttle and r comps. Asphalt BTW. I used to get this on my Miata after I supercharged it without replacing the tired stock suspension. Very strange feeling when it happens.

 

Thanks everyone for all the great info. To touch on a couple issues:

- wheel spin - I don't recall hearing the RPM rise or feeling like the car was experiencing wheel spin. . . I've had that before on my silver EVO and I know how that feels. Plus, Toledo has SO much grip, I could barely get the tires to spin launching at 6K rpm . . .

- bump stops - VERY good point. I never even thought about that. Hitting the stops would cause immediate weight transfer to that side. It would also cause the normally "slow" and smooth oscillation of the rear end to be jerky and harsh . . . interesting . . .

- slow corners in the road race world are probably equivalent to high speed corners in autocross, 40-50mph. . . does it feel like you're driving over washboard bumps that are about 10-15' apart and about 2" high??

- I've also had someone suggest it could be the ACD locking and unlocking trying to put the power down, causing an oscillation in the suspension . . . does that sound feasable?

Thanks !!

 

Congrats!! Seeing where you're from, I have to ask, was Daddio there?

 

I also do not remember hearing rpm jump indicating wheelspin. I did datalog some of my runs. I will sift through the data to see if there was wheelspin.

I have no ACD so perhaps the ACD is not the cause.

 

I wish he could say he was, but he wasn't. I have been second to him in raw time which ended up to be about 2 seconds on a 35 second run! I MaxQDataed him and he was getting time on me at almost every point on the run. If I have to estimate, he would be about 1 second faster in my car vs. his awesome car.

 

Is it possible in your case that your damper or dampers might be the cause due to the rear diff causing extra stress on the suspension? I am basing this on your washboard comment. I assume that your spring rates are stiff.

 

Similar to the front of my Neon years back. Rides on the bump stops, which are of course very high rate springs, and it would bounce. I normally dial up rebound on high grip surfaces on pretty much anything I'm driving. Neon solution was extremely high rebound rates.