Well, we got our "bouncing" issue fixed. We made 3 changes at the same time, so not exactly sure which one fixed it. We'll see if it comes back once we start changing things around again. . .

Here are some spy photos of a new setup that "someone" will be trying this weekend

 

Got camber???

 

yah i was the fastest sm car but that wasnt saying much... yah the bump class was brutal, it included the red sm2 Z06, berry and grice in that insane white BSP car, and a lot of other guys... i got to about 50-55 mph id say before the 1st turn i have some video that i can prolly put up on youtube, youll have to deal with my moms awesome commentary though.

this weekend was my first trying the 18x10.5 up front 18x10 in the rear. it worked very very well and the car felt awesome. i had 18x10.5 nt03+m's in the front (not sure about the offset, somewhere between +30 and +40) with no spacer, and 18x10 +38 RPF1's in the rear with about a 5 mil spacer for control arm clearence. the tire was a 285/30/18 hoosier. everything fit perfectly. with that offset on the NT03's i didnt have any clearence problems with the bumper and didnt have to cut it at all, so if you want to do a 10.5 i would def reccomend these wheels. let me know if you have more questions.

that sounds way too fun, whered you do that? is andy still driving with you?

also what kind of hood is that? have you gotten a trunk yet? voltex fenders im guessing? let me know how those work, i think there within 10 mm of my garage hrs fenders...

 

Jarrod, the car is getting more awesome by the day--makes my car look like an SM-wanna be!

Great job @ that event. We had a Member's-only event for our club @ Sebring (paddock area) this past weekend. We had a 4 cone 150' spaced (!) slalom--I was in flat in 4th (must have been upper 90s as well), before a crazy slowdown into a large Chicago box--Great course!

FTD & my car was on streeties...

 

some pics....


getting a lil late in the slalom oh no

almost 2 wheelen it

you can see the 10's and 10.5's fit real nice

new trunk, weighs just under 4 lbs



rediculous bsp car. good job grice and berry




sm2 corvette

nice stu cars

jarrod, id have to say his wing is better than yours

 

I am curious about your hunches for the "hopping" issue resolution. Care to elaborate?

BTW love the aero bits.

 

Well, I am beginning to realize it is not just one little problem in and of itself. I think it has to do with the car as a whole "system". I've noticed this in the past - the more you stray away from the "norm", the more little problems can crop up that at first seem to have an easy fix, but often end up being problems that you just can't figure out or explain WHY one car does it but not another one. The hint Marshal gave me about the operation of the ACD helped me finally see the big picture with my problem, kind of an epiphany if you will . . .

To come to this realization I had to make a few assumptions, which may or may not be true (you know what they say happens when you assume - it makes an "***" out of "u" and "me" ). First, I will assume that my car is probably near the top of the horsepower game as far as StreetMod EVOs go, at least of the folks who post on here. Second, I will assume that I am running as stiff or stiffer springs and sway bars as anyone else here. Third, I will assume that my car generates as much or more lat. and long. acceleration as other Street Mod Evos out there. Once again these are just assuptions I used to help explain why the car was having this problem. . .

Ok, now on to my thought process. The bouncing first started after we added the TRE rear diff last year. We figured it was just the diff being too "tight", so we added some LSD additive and it seemed to go away. I noticed that it seemed worse on grippier surfaces but not present at all on real slick asphalt. Fast forward to the middle of this year when we started running in Peru, Toledo, Milwaukee - all pretty grippy surfaces. The bouncing came back. We thought, well, maybe we are bottoming the shocks, maybe our dampning is way off, maybe our rear wheels are compressing up to far and the tire is making contact with the chassis creating some binding, maybe we had changed the rear diff fluid and not added the LSD additive. . . . .

Well, we changed to a narrower wheel in the rear, added LSD fluid, and changed the dampning setting a bit and it is completely gone. This is my theory of what was happening:

The ultimate cause of the bouncing was the ACD locking and unlocking due to inside front wheel speed difference. This was caused in part by:

-- HP - more acceleration G'forces transfering more weight off the front end on corner exit
-- light weight - more acceleration . . .
-- stiff springs - more weight transfer off the front under acceleration
-- improper dampner settings - allowing weight transfer to happen too quickly
-- stiff rear diff "locking" L+R together decreasing total rear end wheel speed relative to total front wheel speed (not allowing inside rear to spin), causing ACD to freak out
-- stiff sway bars and springs together - getting nearly 100% weight transfer to outside tires in cornering
-- 18x10's on all 4 corners - many other cars not having this problem are running wider in the front, thereby reducing the likelihood of front wheel spin relative to rear wheel spin

So, if this IS the cause of the bouncing on corner exit then the way to fix it is to create less/slower weight transfer off the inside front tire, or to increase traction on the front end. How do we do this?

- less power
- stiffer rebound dampning
- softer shocks or sway bars
- more weight on the front end
- more grip in the front (wider wheels)
- less grip in the rear (narrower wheels)
- less lock up in rear diff under accel
- more lock up in front diff under accel
- modify the ACD program to eliminate the surging
- sell your ACD EVO and buy an '03 or '04 with the VCU


Or I could have made all that up and be completely wrong on everything!

EVOlutionary

 

Hey you weren't supposed to figure it out.

 

I really didn't think I would, and actually still don't really know if I did. That's just what my mind came up with the way I understand all the different systems of the car working together. I did read a couple things on suspension setup and tuning recently that finally helped me to visualize WHY making certain changes cause certain reactions. . .

 

the good news is the 'rodeo' doesn't seem to start until you get the car set up well. So obviously you have the car working well.

you did leave off one of the solutions though. You can make it stop by letting off the gas.

 

my friend who sets up evos said that once the evo is pushed to the limit he could never get the ACD to work well, he puts LSD's in all of his cars which he said fixes the problem.

 

That, Sir, is NOT an option!

 

"Pushed to the limit" is a relative term. Buschur and AMS have pushed the limits for drag racing. CyberEVO and HKS and Simon Norris and AMS have pushed the limits for Time Attack/Road Racing.

What limit is he talking about? Traction limits? HP limits? Did he try a fully programmable ACD controller? Perhaps there are other reasons besides those stated that he prefers an aftermarket LSD.

What exactly is the "problem" that he fixes with an aftermarket center diff?

That statement is kind of like saying "once I push the stock turbo to 30psi then I get knock, so I'll just replace it with a 35R" . . .

I'm not knocking anyone - I don't have any background info on the situation you are referring to, but the way you describe it makes me think there's probably more to it.

 

I'll talk to him more about it, i am not knowledgeable enough to even know about this, all i know is that he has raced evos in many areas, including esp before they were moved to bsp (i think he got 2nd at nationals on stock shocks) and now on his world challenge cars and privateer cars, he always dumps the acd for a lsd because of problems he has with the handling of the car which sounded similar to the problems you are having

 

If his name is Bret Norgaard then he did get 2nd in ESP in 2003. Very interesting. . .

I'm sure another reason is weight. Going with a straight clutch style center LSD will save weight over the ACD unit, pump, wiring, controller, etc. . .