Your springs seem soft to me...

It seems like you could run some stiffer springs and take out some camber to increase braking contact patch... Your definitely rolling a lot :P and you don't really gain any camber by doing so on an FC... especially when you have the car that low.

congrats on the 1st in PAX

 

if you're running a rear bar, the droop limiters arent doing anything. try disconnecting.
otherwise... holy **** never seen an FC pull a rear tire lol. perty killer grip for 225 street tires!

either way, you can probably run a lot stiffer setup in front. The guy who took 4th in SM last year (s14 240sx) just built an s13 for STS for his wife. she's running 600# springs up front, same tires. he runs 700# + roll center correction + fat front bar on his s14

 

Actually the car is a little over-sprung. At my ride height with 430lb front and 300lb rear springs the natural frequencies are 2.3Hz front and 2.1Hz rear. With "street" tires, 2.2/2.0 is probably a better target, or maybe even lower.

That picture was a bit misleading. The corner is off-camber, it was a very high speed entry with heavy trail-braking. So the car is putting a large percentage of its total weight on the left front corner due to combined braking and cornering forces. It doesn't really roll much at all - not enough to lose the measley -2.9* front camber it has (on this surface - different setups for other venues with more grip).

From my testing last year, the car went faster when it was lower. It's not really THAT low - 12 1/2" front and 12 3/4" rear wheel center to fender lip.

It's a compromise and we'll keep testing this year. Make the front stiffer and it loses compliance over bumps, plus you have to run the rear stiffer to keep the car neutral. Make the rear stiffer and it loses compliance, making the car knife-edged. In general I think people tend to run their cars too stiff, but autocross is a weird application. Because AX is so transitional, it's more important to make the car friendly to pitch around and get the damping right.

 

agreed, but i think the present setup would work well road racing too. our initial setup for our old IT car was 320F and 220R springs, it worked well, totally streetable too.

actually speaking of streetable, PKO's car is the old 320/220/AGX setup and it doesn't ride as well as mikeys koni/450/250 setup. THAT car rides and handles AWESOME, and its all the shocks

 

I don't usually see people tuning autocross cars with frequencies just because it is such an weird application...

They mainly just tune to stay off the bump stops and then balance front to back... Have you tested to see if you're on the bump stops at all?

You'd probably hate my corolla haha, I'm running 525/600# springs w/ r-comps

 

The front wheel will make contact with the body before the shock bottoms out, and that hasn't happened yet. Remember also that my car has a lot of caster compared to a typical FC. The roll centers are low, but it isn't bad with regard to front camber.

There are many schools of thought when it comes to autocross cars. I've seen BSP Evos so stiff that they lose contact with the ground over any manner of bumps. I've driven ESP Camaros and mustangs so soft they move around more than my SS Z06 Corvette did.

As it is, with the valving on these dampers I can only get up to about 90% of critical with the front rebound full stiff. Going to a stiffer spring would only make that worse.

 

The car really seems to be progressing nicely John. Good luck this season!!!!

 

did you ever redesign you own custom rear camber adjusters? or are you still using the MMR links?

 

different cars need different setups! we're lucky in the rx7 world that our cars get into "race" trim with such a streetable spring rate.

 

The rear camber adjusters are designed, I just haven't had the time to do the math to see if they'll handle the loads on the rear suspension.

The MMR adjusters are off of the car. I'm tempted to throw them in the trash, but they're in my spares bin.

Thanks, Chike. Given that the car wasn't actually that slow last year at the Pro finale or at nats, I'm confident that if Greg and I drive well this year we have a shot. It's working really well.

 

what's on the car now if the MMR adjusters aren't?

 

Karack's center camber link (similar to Mazdatrix part but with stock bushings).

 

i think the whole 'stiff vs compliant" thing boils down to transition response. stiffer sprung cars transition faster, and dont need the excess damping to compensate like softly sprung cars do (excess rebound speeds up load transfer at the expense of grip)
with more spring, you can run softer damping for a given transient response, thereby increasing your grip twofold (less load transfer, no overdamping).
the downside of course is bumps, but with good dampers (cough cough ;-)), the car should work just fine.
MacP cars especially need the higher roll resistance since their geometry sucks ballz.

yes a stiffer sprung car is more 'knife edge,' but that just means it changes direction faster. i would think it would pay off in an autox scenario more than a soft car that can float over really rough **** without much TFV. guess it all depends on where you race? i personally like stiffly sprung softly damped. seems to be the consensus for cars where comfort is a non issue

in regards to natural freqs, ive asked a pile of suspension engineers, and they've all said to just tune the car's balance and forget about ride freq. the prescribed ~.2Hz F/R freq split is supposed to give a flat ride for consumers' comfort in an underdamped car (most production ratios are ~.2 - .3). with racecar damping (L > .6 ish), the damped natural frequency is nowhere near that number anyway. of course, theres always gonna be people on both sides of the fence. i've definately seen a lot of ppl adhering to the 2-2.5 law for non aero race cars. iono.

not trying to tell you what to do John, just throwin stuff out tehre for the masses

 

I hear you. Anyone reading this also has to realize that my car is lighter than most of the FCs that are being autocrossed. And it does have the monster ST front bar, too. So it's really not soft at all. Just softer than some

 

Dyno time this Friday (finally!)

 

people think about it the wrong way. the 2 and 2.5 numbers are the BALLPARK, not the magic everything works number.

we see this in the tuning threads all the time with the AFR numbers tossed out, like as if you tuned the suspension to 2 and 2.5 and the engine to 13:1 and you'd have the fastest FC ever.

people like to get fixated on numbers...

 

Good luck. Hope the hp & torque numbers come back looking solid!

 

Thanks... I'm more interested in the gains I see with different tunes. I have a lot of maps loaded into the ECU right now - baseline stock S5 NA Tune, four fuel maps between 12:1 and 13.5:1 AFR and a pile of timing maps. And I can always do some fine tuning at specific points in the RPM band based on what the dyno tells me.

Ian had his car at the same shop last year for a couple pulls, so I'll have a reference power level as well

 

hey I have been checking this thread out a little, awesome job! Anyways my two cents on the whole rear camber adjusters is to use the adjustable links to get the spacing between the bushings for the correct camber then, either cut and weld the stock links to that length or machine a custom link to accept the stock spherical bushings.
I am building my car for STR and am going to try the whiteline rear upper hub adjusters to take out the negative camber, since I am using solid delrin bushings and delrin sub-frame and diff bushings.

 

Dyno day went well. Did a baseline run with stock fueling and timing (red curve), then ran a few fuel maps which worked out to 13.5:1, 13:1 and 12:5:1 (ish) across the rev range. Decent pickup from 6,000 RPM up, but otherwise not much. Didn't seem sensitive to fuel other than it didn't like the pig-rich stock settings.

Bigger gains came with timing. I ended up adding about 4 degrees advance to the leading from 4,000 RPM up, as well as reducing split (advancing trailing) by about four degrees. I tried even more aggressive than that, but didn't see more gains so I dialed it back.

Last pull (blue): peak of 156rwhp, peak torque of 118. Weird is the dip in the curve at 5,500 RPM. Didn't respond to timing, fuel, or VDI switchover point.

Car has a custom shorty header with 3" collector, a 3" Magnaflow "bullet" cat, 3" Magnaflow air-injection cat, 3" Vibrant resonator into a Dynomax muffler at the axle. Stock intake, stock ports.

 

156 is good with a cat!

 

Two cats!

 

kittens!

 

I imagine you need to run the cat for your class? I can't wait to see some more vids! Good luck this year!

 

Maybe i'll see you in Packwood Washington for the Prosolo. Buddy runs a Mx-5, and hopefully my CSP classed FC will be out and about. Mega bump for the thorough and completely awesome build.