Autocrossing the DOHC 88 Fiero

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Series8217
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Autocrossing the DOHC 88 Fiero

Post by Series8217 »

This weekend, I participated in an autocross practice (12 runs) and championship (4 runs) in my DOHC Fiero.

Setup
  • Tires/Wheels
  • Front: 17x7 (42mm offset) Raze R-74, 205/50/17 BF Goodrich gForce KDW 2
  • Rear: 17x8 (48mm offset) Raze R-74, 255/40/17 BF Goodrich gForce KDW 2
  • Alignment
  • Front toe in: 1/4 inch
  • Front camber: -1.6 deg
  • Front caster: Mechanical maximum (I didn't have time to measure)
  • Rear left camber: -1.8 deg (as much as I could get; the wheel is about to hit the knuckle. I need 18s)
  • Rear right camber: -2.5 deg
  • Rear toe in: 1/16 inch
  • Shocks/Springs/Bushings
  • Front springs: Stock with 1 coil removed
  • Front shocks: Koni reds
  • Front swaybar: Stock, with Rodney Dickman's solid endlinks
  • Front bushings: Polyurethane everywhere except the swaybar mounts are stock
  • Rear springs: 350 lb QA1
  • Rear struts: Koni reds, adjusted somewhere in the middle, flipped top hats
  • Rear swaybar: None
  • Rear bushings: Poly on the trailing links, solid rod end lateral links
  • Weight reduction/relocation:
  • Front mounted Miata battery (23 lbs), mounted behind the front crossmember
  • Corbeau A4 seats on original Fiero sliders
  • Removed jack, wrench, spare, and spare tire tray
  • Engine:
  • Balanced and blueprinted 1993 3.4 DOHC V6, custom intake, 220whp on a Dynapack
  • Transmission:
  • Fiero Getrag case with later Getrag 282 internals (slighter shorter 5th gear, larger and stronger diff)
  • Clutchnet kevlar clutch, Luk pressure plate
  • Exhaust:
  • Stock exhaust manifolds and crossover, 2.5" cat, custom 2.5" single inlet, dual outlet muffler
  • Brakes:
  • Slotted/drilled 12" Corvette rotors
  • 88 Fiero calipers
  • Porterfield R4-S pads
  • Factory replacement brake hoses
  • Steering:
  • 2-turns lock-to-lock power steering rack from a C4 Corvette
Initial driving impressions:
* Fiero Getrag gearing is not ideal
* Easy to put power down
* The super fast ratio ZR1 steering rack is awesome
* Brakes could use more rear bias

Power/Gearing:

The gear ratios really break the car for autocross. I can go full throttle in second gear when going straight or mostly straight and not loose traction, nor hit the rev limiter, so it needs to be shorter. First gear is only usable for the launch, and the beginning of the course until it opens up. After shifting into 2nd, there aren't any spots where a downshift (and subsequent upshift back to 2nd) are practical, it scrubs off too much time. I think a Northstar in 2nd gear with a 7k RPM limit would be just right, or a turbocharged 3.4 DOHC with a fast spooling turbo and low boost.

With my motor, the Getrag gears with the shorter 2nd would probably be a lot better. I hated the 2nd to 3rd shift with those gears when I ran them though.

Fortunately (or unfortunately) I can't drive the car well enough to take too much advantage of the extra speed a shorter 2nd would give me, so it's not a limiting factor right now.

Handling:

The fast ratio steering is amazing. It's VERY easy to point the car where it needs to go, on even the tightest hairpins. I didn't have any problems with steering feedback. I can still feel the loss in self-aligning torque when approaching the lockup point during threshold braking.

Speaking of braking, it seems the fronts lock up pretty easily. I feel like the car should be able to stop faster. I think it needs more rear brake bias.

My car tends toward oversteer; if I turn in hard enough it spins out. I can countersteer and recover almost every time, but it scrubs off a LOT of speed when it happens. It's annoying trying to find the traction limit in a turn only to have the rear step out and then lose all your speed. This is the only serious handling problem I experienced.

Performance:

Hard to say. I don't really have enough driving ability to know how fast the car will run compared to others, and the oversteer problem made it hard to find the limit of the car. My buddy running an AP2 S2000 with lots of suspension mods but stock tire sizes and motor ran about a second faster than me. Both of us are novice autocrossers. Even if I could drive it well, it's hard to compare right now since I have four year old tires, and almost every other cars in my class (with the exception of my friend's S2000) is running RS3s or Z1s. That will change soon if I decide to continue developing this car.

Video
Unfortunately the videos didn't turn out too great. My GoPro's battery ran out before I could get more than a few seconds of useful video of rear suspension motion. I'll try again at the next event.

Photos
Click the images for bigger versions.
Image
DPP_0355 by Borowski.G, on Flickr

Image
DPP_0357 by Borowski.G, on Flickr

Image
DPP_0441 by Borowski.G, on Flickr

I'm running -2.5 deg of camber on the rear right, but you can see it still goes way positive due to body roll. Look at how much the inside is lifting! Note that I am not running a rear swaybar. When I did in the past, it made things even worse.
Last edited by Series8217 on Wed Oct 17, 2012 9:03 am, edited 3 times in total.
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Re: Autocrossing the DOHC 88 Fiero

Post by The Dark Side of Will »

Looks like it's time to raise the rear roll center... I think you've done everything else reasonable.
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

Well, I could still add more rear tire. My silver car had a weight distribution of 42.4%/57.6% and didn't have a trunk. I haven't weighed my 88 but it has a full trunk and the battery is more in the middle than up front. I imagine my red car is still around 42/58 or worse.

My current tire width distribution is 44.5/55.5. I would need 275s in the rear to match the weight distribution if I keep running 205s up front. I would really like to have a bit more tire up front if possible to improve braking. A 215/285 stagger would be 43/57. Either way, I need wider/bigger wheels in the back to fit anything larger than a 255. I would like to be able to widen my current ones to save money, but then I would need to run 1" thick spacers. The rim hits the knuckle before I can max out camber. If I got 18s it would clear the knuckle... and give more room to lower the outer link pivots.

Somehow I forgot to include my tires sizes in the original post. I guess I was tired. I added them at the beginning.
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Re: Autocrossing the DOHC 88 Fiero

Post by The Dark Side of Will »

Raising the roll center would make better use of your tires, as the lower moment arm on which the rear weight acts would result in less weight transfer at a given lateral g.

I agree that having matched tire sizes and weight dist is the best place from which to start, however.
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Re: Autocrossing the DOHC 88 Fiero

Post by FieroWanaBe1 »

I think if you took the car to a road course track day or an autocross set-up for more for pro-touring cars, you might feel a little different about the ratios; The 2-3 shift would become more imperative for the corner-exit points. You may even feel different about the camber change characteristics since you will spend more time accelerating and braking. The level of trail braking could affect your thoughts on rear bias as well. But, if you want to limit your motorsports use to Auto-X, you may even have the wrong drive train, since it's moving your rear cg height even higher, and cause the rear roll rate to exceed the front even more.

I'm not saying your impressions are wrong; they are based off performance under one specific application. I'm just suggesting trying a faster course as well as to evaluate the performance in a full road race session.

I can definitely see rear roll rate is higher than front, explaining the oversteer sensation, and agreeing with the lower roll-center relative to the front. I also agree with the absence of a rear anti-roll bar, especially with a standard differential.
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Re: Autocrossing the DOHC 88 Fiero

Post by The Dark Side of Will »

Yeah, the top-heavy engine doesn't help, even though it may deliver great power and have a wide powerband.
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

FieroWanaBe1 wrote:I think if you took the car to a road course track day or an autocross set-up for more for pro-touring cars, you might feel a little different about the ratios; The 2-3 shift would become more imperative for the corner-exit points. You may even feel different about the camber change characteristics since you will spend more time accelerating and braking. The level of trail braking could affect your thoughts on rear bias as well. But, if you want to limit your motorsports use to Auto-X, you may even have the wrong drive train, since it's moving your rear cg height even higher, and cause the rear roll rate to exceed the front even more.

I'm not saying your impressions are wrong; they are based off performance under one specific application. I'm just suggesting trying a faster course as well as to evaluate the performance in a full road race session.
I've already taken it to a track day on a road course. I ran half a dozen sessions of about 15 or 20 minutes each. It was back in '05. Similar setup, just smaller tires and no Konis. That's where I learned to disconnect the rear swaybar to avoid horrific oversteer characteristics. I think there are some videos or photos in an old thread here of my Fiero driving on Streets of Willow. You could see the nasty camber change on the rear in those photos as well, and it was definitely limiting my cornering speeds. Spinning out on a road course is much much worse than spinning out in autocross. I do love the gear ratios and powerband on a road course. Obviously no need for 1st gear in that situation, so the terrible RPM drop going into 2nd isn't a problem. The wide powerband and long 2nd gear make low- and mid-speed sweepers very fun. I had the Isuzu at the time, so 2nd was the same but the final drive makes it even longer.

This thread is specifically about my impressions with autocross use. Most people don't build cars for both autocross and road courses, because they require different handling characteristics and gearing (not to mention the rules). I think it's useful to share my setup and driving impressions for those interested in autocrossing a Fiero. Let's limit the discussion in this thread to autocross. I'll start another thread to discuss road courses when I take my current setup to a track day (if the car isn't sold before then).

EDIT: I found the one of the old threads, but my pics no longer work. http://realfierotech.com/phpBB/viewtopic.php?f=7&t=1921
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Re: Autocrossing the DOHC 88 Fiero

Post by FieroWanaBe1 »

Series8217 wrote: This thread is specifically about my impressions with autocross use. Most people don't build cars for both autocross and road courses, because they require different handling characteristics and gearing (not to mention the rules). I think it's useful to share my setup and driving impressions for those interested in autocrossing a Fiero. Let's limit the discussion in this thread to autocross.
This.

So no one takes what you find as shortcomings, as shortcoming concerning all conditions.

Some one will.
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Re: Autocrossing the DOHC 88 Fiero

Post by FieroWanaBe1 »

Koni's Reds are only rebound adjustable correct?
Perhaps lowering the rebound rate will help keep you inner tire in contact with the tarmac in transisions, reducing turn-in oversteer if that is an issue.
A little more anti-squat may help on turn-exit oversteer as well, and might help make the rear brakes feel more effective with a greater veritcal brake force from the trailing arm. Again maybe not, since load transfer is load transfer.
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Re: Autocrossing the DOHC 88 Fiero

Post by AkursedX »

I wish I lived closer to you. I would really like to see how that power steering setup changes the car. It has to make Autocross so much enjoyable. I was never a fan on my Fiero's in lower-speed, tight-turns as you just had to turn the steering-wheel so far.

I really hope you decide to keep this Fiero and dial it in.
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

FieroWanaBe1 wrote:Koni's Reds are only rebound adjustable correct?
Correct.
Perhaps lowering the rebound rate will help keep you inner tire in contact with the tarmac in transisions, reducing turn-in oversteer if that is an issue.
I haven't experienced turn-in oversteer, but I may not be turning it in hard enough to reach the traction limit of either end.
A little more anti-squat may help on turn-exit oversteer as well, and might help make the rear brakes feel more effective with a greater veritcal brake force from the trailing arm. Again maybe not, since load transfer is load transfer.
That's a good suggestion. More anti-squat should allow me to put the power on a little bit sooner because it won't cause power application to push the rear outside tire further into positive camber.
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Re: Autocrossing the DOHC 88 Fiero

Post by The Dark Side of Will »

FieroWanaBe1 wrote: A little more anti-squat may help on turn-exit oversteer as well, and might help make the rear brakes feel more effective with a greater veritcal brake force from the trailing arm. Again maybe not, since load transfer is load transfer.
Anti-squat geometry uses forward tractive loads to extend the suspension. That means that rearward tractive loads would try to compress the suspension. I don't see that more anti-squat would increase rear brake effectiveness... I think it would be the other way around.
Series8217 wrote:That's a good suggestion. More anti-squat should allow me to put the power on a little bit sooner because it won't cause power application to push the rear outside tire further into positive camber.
What's your reasoning behind that?
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Re: Autocrossing the DOHC 88 Fiero

Post by Aaron »

I auto-crossed mine. I of course can't speak on handling (Stock suspension, stock wheels, crappy tires). It oversteered into the corners, understeered through them, and then did 50/50 out of them depending on the engine.

The gearing is even worse on my turbo motor, where it really doesn't come on hard until 4500rpm, and once there it's like a light switch turning on. I tried to downshift into 1st, but that was impractical, so I drove most the course turbo-lagging, waiting for the 2 good straight-aways. But the engine/trans combo are really bad for AutoX. A smaller turbo, and a motor setup for mid-range would be a lot more beneficial. Smaller header primaries, log manifolds as opposed to full length headers, the 1st gen intake manifolds, and a smaller turbo. MIne was built completely the opposite.
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Re: Autocrossing the DOHC 88 Fiero

Post by FieroWanaBe1 »

The Dark Side of Will wrote:Anti-squat geometry uses forward tractive loads to extend the suspension. That means that rearward tractive loads would try to compress the suspension. I don't see that more anti-squat would increase rear brake effectiveness... I think it would be the other way around.
Yes, by attempting to "compress" the suspension under braking, combined with a forward load transfer, the motion would further unload the rear tires dynamically, making the rear feel "looser" when trail braking on corner entry. At least that’s what the flawed kinematic computer in my head keeps trying to convince my brain. I wasn’t real clear in my explanation, by vertical brake force I meant increasing the force pulling up on the wheel/tire from the factory configuration.
Anti squat will lower the suspension movements under forward acceleration load transfer, it wont go into positive camber though, the camber gain is still negative, just not negative enough to counteract body roll. So, the tire will be more normal to the driving surface with less suspension movement.

My point was, if there isn’t enough rear brake bias, and there is too much exit oversteer, more anti-squat may help change both those behaviors.

edit: thought=brake wrote=weight.
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

The Dark Side of Will wrote:
Series8217 wrote:That's a good suggestion. More anti-squat should allow me to put the power on a little bit sooner because it won't cause power application to push the rear outside tire further into positive camber.
What's your reasoning behind that?
I don't agree about the braking, but increased anti-squat would reduce suspension compression at the rear under acceleration, so it would keep the tire more flat (since there's less suspension movement).
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

Just to clarify, I never experienced anything I recognized to be transient handling problems. The oversteer problem I ran into occurs when slowly tightening a turn after the chassis has reached steady-state. I think it's limited to tire contact pressures and the camber curve.
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

I'm signed up for another autocross weekend (Nov 3-4).

I won't have time to fix the rear suspension geometry before the event, but I picked up some front 400 lb-in springs from WCF today and will be running these in place of the cut stockers that I ran before. Hopefully increasing the front roll stiffness a bit will shift the balance more toward understeer. I'll find out on Sat.
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Re: Autocrossing the DOHC 88 Fiero

Post by crzyone »

I'm jealous. We have about 4" of snow, car season is over. I wish I put as much time and effort into the Fiero's suspension. Maybe I woldn't have sold it.
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Re: Autocrossing the DOHC 88 Fiero

Post by Series8217 »

Ugh... took my front suspension apart to swap the springs and found my front left Koni Red shock covered in oil.

I actuated it by hand and it still provides similar damping to the right side, but it ain't gonna last long.

I don't remember when I installed the Konis, but I think it was less than 10,000 miles ago.
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Re: Autocrossing the DOHC 88 Fiero

Post by FieroWanaBe1 »

Series8217 wrote:Ugh... took my front suspension apart to swap the springs and found my front left Koni Red shock covered in oil.

I actuated it by hand and it still provides similar damping to the right side, but it ain't gonna last long.

I don't remember when I installed the Konis, but I think it was less than 10,000 miles ago.
At least they have a warranty, if you are the original buyer.
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