Changes to be made to 444
 

So I took 444 out to an autocross a week ago to shake down the new engine and get a feel for the current suspension setup, as it has been very loose in the past.
Current setup is:
Tires- Kumho Ecsta MX, a little old, but as cold as it was it really didnt matter
Wheels- Kosei F3 18x9
Dampers- BC Racing coilovers
Springs- BC 8fnt 6rr
fnt camber- -2.5
caster- approx 4deg , this may be off slightly as we made ride height changes and reset camber/toe but unable to re-check castor accurately
fnt toe- 1/8th OUT
rear toe 1/16 IN
camber- -1.5
ride height- 4 fnt 4.7rr
1deg rake
Stock NA fnt and rear bars
dampers set to full soft settings

Surface was cold, there was literally ice in places, and unfortunately it did not warm up appreciably throughout the day.
Had very little rear grip, reasonable fnt grip although the car would push if really overcooked a corner. almost zero midcorner grip, going to power instantly made car transistion to oversteer and required corrective input. Car was flat through the corners with almost zero roll. No one really had much traction throughout the day, but this has been a running theme with the car, unable to put the power it makes through to the ground. When we see warmer weather will be changing the tires to slicks. For autocross will likely move to a 16" wheel rather than the heavier 17 and 18 wheels.

To find more rear grip, the following seems to be a good starting point-

RR springs changed to 250lb ERS or Hypercoils
add 1/16th toe IN
lower car to lowest legal (SCCA) ride height
Disconnect rear bar (likely will replace fnt and rear bars in near future)

Before you take the rear bar out. I would clock the neg camber up in the rear. something closer to -2.0 that improved our rear grip dramatically with 6k springs. We don't run any rake. I do think adding more toe in, in the rear, will help as well.

Is your front bar a 22mm or 24?

To qualify this, our drivers like manageable oversteer vs a totally neutral or pushy car, they like a very aggressive turn in and manageable oversteer under throttle. We like gaining time with aggressive trail braking.

Curious what your car weighs? I know you have said somewhere else but cant find it.
More weight is coming off of this car as time allows, there is just a lot of weight left in it that needs to go.

The car was set up for 10" wide rears, which seem to like -1.5-ish camber, but cerianly more negative might help. Honestly I really like to stand the rears up as much as possible, on the really wide/sticky tires I have run as low as -3/4 deg of camber, but of course we gain camber as we arc so starting at -3/4 ends up being -2 or 2.5 in roll.

This car also needs to have the bumpsteer set, but before that we need to determine where it will be run so we know what will be legal ride height. Looking like NASA or maybe some for of SCCA IT catch all is where this car will end up. Really thinking more about an EP or GT NA car now, but really cannot justify it at this point. Maybe do an FC up for IT-something? and just run with the SCCA/NASA as an N/A.

Cheers,
Don

Few thoughts:

• 6kg/mm (445lb/in) to 250lb/in is a big drop in rear spring rate
• Would less rake help rear bite?
• Is "almost zero roll" keeping you from seeing any camber gain?
• Will lowering the car that much take away bump travel and make things worse riding on the stops?

No roll with the shocks full soft makes it sound like you've got a go-kart with no suspension...

Good questions!

1- Yes, it is a big drop, but BC sent me the "standard spring" which allows for a full weight car, hence the 6k (445lb) spring rate. I also think thier worksheet is off, because even for a full weight car with a full tank I think 445 is a "lot" of spring.
2- running a little less rake might help, something to try
3- other competitors and photos show that I have virtually no roll through the corners. I am certianly seeing no camber gain.
4- The cars ride height is actually pretty high, as it was set up to run Pikes Peak, where there are large rocks and other hard things to hit. I have a fair amount the car can go down.

It is exactly like a go-kart, which is why I need an actual rear suspension movement. Stiffer is not always better, and the way it feels is the tires are my springs and the suspensio is solid.
A couple of caveats- Autocross speeds are pretty damned low and both the tires and surface contributed to the lack of grip. However, at the Hillclimb we also lacked traction at higher speeds and different surface. Not sure the car will make it out again until the weather improves, and when it does more than likely it will be at La Junta (Drivers School) or HPR (open track/test) and will be on different tires, have the rear wing/front ground plane.

True. The lack of grip can play tricks by making you think you have no body roll when you will when you add grip.

I autocrossed my full weight '87 TII with the MazdaComp suspension on it (which at the time was 400# front, 275# rear) and it worked really well for me. I was actually lifting the inside front wheel with the bolt-in cage (don't ask!) and suspension. IIRC, that was on Toyo RA1s and early in the season in Ottawa so temperatures were cool/chilly. The rear camber was left close to stock with the adjustable dogbone set the same length as stock. The front camber was more than -3.

BTW, I goofed. 8k is 447# and 6k is 335#. I assume the front motion ratio is 1.0 (or very close) being a strut, does anybody know the rear? I think I asked this before and forgot to save it away.

You said no mid-corner grip, and I'm assuming that continues through corner exit? When you get on it going straight does it hook up? Pull either side showing something is tweaked or there's thrust in the alignment somehow?

On throttle roll in I have decent grip, but at boost onset there is not traction, the car just spins the tires (again, realize cold surface/mediocre tires) but again this has been an ongoing issue. It IS very predictable and can virtually be steered with the throttle, but this is not the fast way around.
I think a wheel/tire size needs to be decided on before too much more is done, as a 15x7 steel wheel with canti slicks is looking pretty damned good right now as opposed to 17 or 18 inch alloys and DOT's or slicks. Just in ride height and mass alone the small wheels are winning, not to mention the adding to the effectiveness of the stock brakes.

I think you will like what disconnecting the rear swaybar does.

Rear swaybar on the FC seems to lift the inside rear tire and the nice smooth oversteer becomes snappy.

Disconnected rear swaybar my car lifts the inside front a little, but this mild throttle on understeer just aids the racing line.

I also had a problem with JIC FLT-A2 where the rear lowspeed damping was way too high even on the lowest settings and the car was at all times drifty.

I am on the same 7/5 spring rates with JIC FLT-TAR and the car is very settled. Can get on the gas at the apex and more stable under braking.

17x8.5 255/40 NT01/ 17x9.5 275/40 NT01


https://www.rx7club.com/picture.php?...ictureid=17629

great picture with the inside tire lifting.....

Okay, so corner entry is good, mid-corner sucks, tip-in is good, and exit has throttle induced loose. I really would try changing the rake to get a little more bite in the rear... I say this because tip-in is going to put some weight on the rear and that seems to be working for you already. Throttle induced loose seems like you're heading down the right path with softer rear springs to get the sucker to squat and bite.

The rear swaybar doesn't really strike me as the issue, but it's a cheap and easy test. If everything sucked after entry I would look at the swaybar but if tip-in is good you've already got a side load on the car so the swaybar is already doing what it's going to do. Plus you've got a small rear bar on the car already. If anything, I'd look at doing a stiffer front bar -- remember the end opposite the end you stiffen gains traction.

The only other thing worth checking is making sure you're not riding the bump stops... if tip-in is good, but uses the last of your bump travel, once you're on the bump stops all kinds of weird stuff can happen. I do realize you've got some pretty heavy rear springs and this shouldn't be an issue, but a zip tie to check travel is also cheap to test with.

Just thinking outloud...

Corner entry is OK, likely because i am used to being slightly loose on entry (Porsche thing) and may not even notice loose entry. Loose midcorner bothers me, because thats where I am used to the weight transfer tightening up the rear grip and being able to go to throttle harder. Exit is just bad because midcorner sets the tone.
I do have a larger fnt bar, and might try it out just to see what happens.

I will check travel but I really do not think thats much of an issue at this point, but certianly could be an issue once there is grip.

I ran nearly the exact same setup and alignment as you are running. My car was NA though. I have BC coilovers with the same spring rates, I ran the dampers 2 clicks from full soft in front and 6 clicks from full soft in the rear. I was running RB sway bars front and rear and 235/40/17 NT05 tires all around, and the car was nearly perfectly balanced. Very slightly loose on entry, neutral mid corner and neutral to slightly tight on exit.

I think the cold pavement and the old tires were playing tricks on you. If you have a turbo car with more power, running a larger front bar and no rear bar will probably be better.

Hey thanks for the input. How did you like your BC's? I had thought about having them re-valved but decided to wait until the tires and wheels etc are what will actually be used to see how they do.
3R and Leary both have shock dynos and it would be worth it to see how these do, so might do that at some point anyway.

No problem. I am putting an LS1 in the car and the setup is going to change a bit. The tires will be staggered 255/275 and I am going remove the rear sway bar, and probably go up to 500 lb (9k) front springs and see where I am at.

For the price I think these coilovers are great. I have over 2000 track miles on them, and about 10,000 miles total and have no issues to speak of. I have 5 friends that have daily driven on them for literally 60-70 thousand miles with no problems. I've installed about 10 sets of them on various cars, so I knew the quality was good before I put them on my car.

I know they are not the absolute best dampers, but for what they are I have zero complaints. I may get mine revalved as well after I get my car running again with the LS1, especially if I change the spring rates in front.

All I did was have the camber plates machined so I could get more negative camber. I run about -2.75 degrees up front now and can go to -3.1. I could only get -2 degrees as they were stock and it was not enough. If I had a nit pick, it would be that they should be set up to run more negative camber from the manufacturer.

Yes we had to modify the upper mounts as well.
I have also had good experiences with the BC's and have no complaints about the shocks themselves, just the springs they came with.

Yea I will be putting on Hypercoils when I switch them.