Susepsion Setup questions - help me balance spring rates, 75 914 with Suby swap Options

[jpnovak]

So, my "now former" GRM Challenge car went under the wrench this weekend for some suspension work. All of my suspension setup is based on 911s. I have a highly developed formula that works well to produce fast, easy to drive and planted cars.

Background: I built a Suby powered Ej20R (TT) 75 914 for the GRM $2010 Challenge. I went in 2011 and managed to blow up the motor at the event. I fixed the car and had plans to go back this year. Budget and time management will not allow for a long tow to FL and back from TX. So, I spent the entry fees on new suspension components.

The car had original bushings that were completely shot. So here is my "new" setup based on used parts buying with the caveat the the car would be for AX use in the challenge. All parts were purchased and I am still under budget for the event should I choose to go.

Weight: car previously weighted 1920# on scales after the swap. Tires are Kumho Victoracers (V700) ; 205 50-15 on 15x6 Rivearas.

Front:
used 911 Boge shock inserts. Good damping. Bolt on.
used 22mm Front 914 torsion bars.
polygraphite/urethane bushings - Turned on a lathe and fit properly. No slop. No friction. No ER budget. (IMG:style_emoticons/default/smile.gif)
NO FRONT SWAY bar. Car did not have one.

Rear:
Used Koni orange adjustable. Set 3 out of 5 turns from soft. I like extra rebound damping for bigger springs. Compression not adjustable.
used 180# Weltmeister progressive springs.
polygraphite/ urethane bushings. Turned on a lathe and then reamed. No slop. No friction. No ER budget. (IMG:style_emoticons/default/smile.gif)
NO Rear sway bar.

Last night I took the car for an initial drive. The car rides so much better than it did with stock 17mm torsion bars and stock rear springs. The new bushings and removal of a-arm, trailing arm friction really helps these cars.

I have not had the car on the track but I have few "test and tune" curves near my house. The car seems to turn in easily. Neutral maintenance throttle mid-corner makes the car tend to oversteer. Otherwise the car felt balanced.

I chose the initial spring rates based on calculated corner weights on the car and the weight distribution. I gained a little weight in front due to the radiator and cooling system. I lost a little weight in the rear since I had to cut the rear trunk to clear the turbo and intercooler setup. The lack of sway bars also factored in.

I think I need to stiffen up the front a bit to dial out a little of the oversteer. I have not yet played with tire pressures.

Here are some of my options.

1. add a front sway bar. I think this might be too much.
2. drop a few PSI in the tires and help balance.
3. 140# rear springs - would this be too much of a drop in spring rate?
4. Balance with tire size. not much room under a stock body car.

Just want to hear your thoughts and experience. I expect that I will have different ideas after I spend a few days behind the wheel and get used to the new setup. I know, I know. There is no substitute for seat time.

[Chris Pincetich]

You're pretty good right now (IMG:style_emoticons/default/beerchug.gif)
I prefer a slight oversteer tendency for the 914 in AX racin. If you are using stock spring perches, finding stiffer rear springs beyond 180 may be tough, which is why I spent the $$$ to get the 2.5" adjustable sleeves that accept Eibach springs.

Front anti-roll bars are an excellent addition as they help limit body roll. Once those AX turns start coming faster back and forth (slalom), you'll be glad you have one.

[Matt Romanowski]

You're setup with a front swaybar is tried and true. I would personally ditch the progressive springs for a regular pair of 180 pound springs. The progressive give you a weird feeling on turn in as the softer rate gets squashed.

[Eric_Shea]

The only 914 I will own without a front bar is the off-road car I'm building.

That's about all I can add given your useage and motor etc.

A front bar is a must have in my book.

[jpnovak]

Thanks for the help. I am a fan of the "let the spring do the work camp" rather than the "oversized sway bar camp". To me sway bars are for tuning body roll and transitions in and out of braking/steering/ throttle.

I guess its time to go shopping for an adjustable front bar. I think I would like something smaller. A full 22mm sway bar I think would be too much. I was thinking a 15mm front through body bar would be close to what I need. I have an early 19 in the parts stash but that is reserved for my upcoming 911 project.

The car will see quite a bit of backroad driving. More than the track probably. At least in the TX Hill Country we have some incredible roads.

I guess its time to drain the tank and drill some holes. (IMG:style_emoticons/default/smile.gif)

[brant]

914s like a lot of front bar. We runs huge smart bar along with 22torsions. I don't remember the size but 28 or bigger and it helped a lot compared to the 22welt we took off

[mittelmotor]

Thanks for the help. I am a fan of the "let the spring do the work camp" rather than the "oversized sway bar camp". To me sway bars are for tuning body roll and transitions in and out of braking/steering/ throttle.

I guess its time to go shopping for an adjustable front bar. I think I would like something smaller. A full 22mm sway bar I think would be too much. I was thinking a 15mm front through body bar would be close to what I need. I have an early 19 in the parts stash but that is reserved for my upcoming 911 project.

The car will see quite a bit of backroad driving. More than the track probably. At least in the TX Hill Country we have some incredible roads.

I guess its time to drain the tank and drill some holes. (IMG:style_emoticons/default/smile.gif)

Ah, the Hill Country. I've lived in SoCal all my life, but we'd take our summer vacation to visit my grandparents in Fredericksburg. I first drove a car on a gravel road near Enchanted Rock...many, many moons ago.

Good luck with your suspension setup!

[914forme]

If your not a big fan of bars, you could also add more meat out back in your tires. Might have to pull the rear fenders a little bit, just giving you options. And you still have tire pressures.