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Posted by: Racer Chris Jan 20 2004, 09:53 PM

I finished welding the driver's side today.


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Posted by: Racer Chris Jan 20 2004, 09:54 PM

View from the engine comp. side.


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Posted by: Racer Chris Jan 20 2004, 09:57 PM

Yesterday I had the trailing arm attached to line everything up before welding.


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Posted by: ChrisReale Jan 20 2004, 09:59 PM

Nice work, Looks solid

Posted by: Racer Chris Jan 20 2004, 10:00 PM

Pickup points are raised 3". Everything is based on the stock pivot shaft and stock system of alignment.
This pic shows the piece I fabricated to hold the trailing arm, after tack welding in place.


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Posted by: Gint Jan 20 2004, 10:03 PM

914 porn...

Nice work Chris. Thanks for posting the pics.

Posted by: Racer Chris Jan 20 2004, 10:03 PM

This pic shows the ride height of my car. The top of the I-beam is the theoretical ground level.


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Posted by: Racer Chris Jan 20 2004, 10:05 PM

The front A-arms are nice and flat. Note the bolt head that just clears the 3" square tube.


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Posted by: Racer Chris Jan 20 2004, 10:09 PM

I set up the car on my platform and aligned everything with the car suspended on the springs/torsion bars at my planned ride height.


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Posted by: drew365 Jan 20 2004, 10:22 PM

Chris; your workmanship looks great. Please humor me, what are you trying to accomplish by raising the pivot point?

Posted by: Eric_Shea Jan 20 2004, 10:29 PM

Awesome... so, what gauge metal is on a 914?

Posted by: Racer Chris Jan 20 2004, 10:30 PM

A National Championship!!

More to the point, better grip, through improved suspension geometry.
The car is drastically lowered for better CG.

Posted by: URY914 Jan 21 2004, 06:37 AM

Chris,

Will this mean your shock and spring will need to be shorter?

And will the halfshafts be horizonal between the gearbox and the trailing arms?

Paul

Posted by: URY914 Jan 21 2004, 06:40 AM

Is your wheel travel reduced or do you raise the top of the shock too?

Just wondering how everything will change from raising the pivot point.

Paul

Posted by: Racer Chris Jan 21 2004, 07:31 AM

Eric,
The long. frame in that area is a double layer of approx 18ga. The inner layer starts right there and extends forward just past the jack post.
I used both 16ga and 14 ga to box in the 1/8" square tube bracket I made, after welding the bracket fully to the existing metal.

Paul,
I plan to use stock length shocks for the time being. The springs are 10" x 2.5", 250#. The top mount is already raised, using the custom pieces I have shown on my website. I may modify this area again, as I think there is room to go up a little more. I haven't measured the remaining shock travel yet as it sits now. I think the angle of the halfshafts is higher at the wheel end. The front shocks have about 2"" of travel remaining.

Posted by: groot Jan 21 2004, 08:07 AM

Chris,

Excellent fabrication.

We should compare notes. I'm working on a 914 SCCA production racer, too, for a while now. The big difference is you've been racing yours for a while I've been running an ITB car.... and I'm jealous. My 914 has only been to auto-x's.

Here are some of my notes:

I'm been redoing the front suspension on my 914 with the goal of improving geometry. I'm going to toss the control arms and use 2 tubes on either side with rod ends on both ends of each tube. I wrote a little spreadsheet program that calculates roll centers under different conditions and concluded that I need to extend these tubes to the center of the car and make them level at ride height.

The only thing I was doing to the rear was to fabricate some sperical bearing mounts on the chassis and plug the trailing arm with threaded plugs....... and make sure I've got enough travel to align toe and camber.

Now, to my point.... Given that in production we have to stay with the "same type" of suspension that came on the car. In the rear, we're stuck with a trailing arm setup. Everything I read says there's not much one can do to improve it, unless you lengthen it significantly to reduce the wheelbase change with travel. Is that what geometry you're trying to improve? or have I missed something?

Thanks,
Kevin

Posted by: John Kelly Jan 21 2004, 02:08 PM

Hi Chris,

Nice work! Wish I was closer...I would rent your rack when you are done instead of having to make my own.

John www.ghiaspecialties.com

Posted by: Racer Chris Jan 21 2004, 08:11 PM

I welded up the passenger side today. It was a little tougher because I didn't remove the quarter panel.


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Posted by: redshift Jan 21 2004, 08:19 PM

oh my god dood that rocks!




M

Posted by: TimT Jan 21 2004, 08:34 PM

Chris, scribble me in your appointment book for next fall

Posted by: Racer Chris Jan 21 2004, 08:35 PM

Kevin,
Theoretically what you suggest is correct regarding longer arms both front and rear. In practice it is largely unnecessary. By limiting suspension travel with heavier springs and anti-sway bars the camber change is held within the desirable limits anyway.
One of my primary goals with my project is to keep the budget under control and develop alterations I can do for customers at a reasonable cost, and still get greatly improved performance.
I haven't done any suspension simulations, only real world testing. I get excellent tire wear and high levels of grip already with the changes I've made and the camber settings I use. The most recent changes should help further in this regard.
I think that raising the rear pickup points helps the tire go over a bump more smoothly because the tire isn't trying to move forward as it goes up, as it would with the stock pickups on a seriously lowered car. I guess that's another way of saying I'm trying to reduce the wheelbase change.
Your plan to make long tubular front arms means you will have to use coilovers. I have no desire to go that route. I also am not interested in altering the stock method of pivoting the rear arms, other than beefing up the attachments and using better bushing material. (BTW, I offer delrin bushing installation service with grease fittings for rear trailing arms that equals the needle bearing setup performancewise IMO, and at a lower price. $250 installed.)
I heartily subscribe to the KISS method of performance enhancement. Track time is more important to me for lowering my lap times than having the most trick setup. Fancy sh!t you are constantly playing with gets in the way of track time, therefore is undesirable IMO. Everything I have done so far is working pretty well, based on my results.

Posted by: Racer Chris Jan 21 2004, 08:37 PM

Will do Tim!

Posted by: groot Jan 22 2004, 11:09 AM

I, too, am after what works, not what's the "trickest." That's why I asked the question concerning your reasons for the rear suspension changes.

You're spot on with your statement about track time. I couldn't agree more.

I've been running fwd VWs for enough years to know that it's hard to get the front suspension to work decently with the stock layout on a lowered car. That's why I'm changing the front suspension. BTW... I'm really going after fixing the roll center, not the camber curve. The camber curve will benefit from this setup, too.

Also, I'm not using a needle bearing setup in the rear. I'm using spherical bearings mounted to the chassis with threaded plugs inserted into the trailing arm.

Keep up the good work!!
Kevin

Posted by: andys Jan 22 2004, 01:25 PM

Chris,

With your Delrin bushings for the trailing arms, why do you need grease fittings? Do they squeak? Delrin is a naturally lubricious material commonly used in many kinds of bushing applications.

Andy

Posted by: Mueller Jan 22 2004, 02:16 PM

The friction force can be reduced from ~.35 to .05 with the addition of grease...not a bad idea at all.

Posted by: Thorshammer Jan 22 2004, 07:15 PM

Chris,

Stop Posting and get my car done. LOL, pics look great. I am randy for this mod to my racecar.

All you Suckas will have to wait my car is there and it's next, Drool cup please!

Erik Madsen

Posted by: Racer Chris Jan 22 2004, 07:31 PM

I think there is a relationship with the steering tie rods and the a-arm length that is necessary, to minimize bump steer. Doesn't a long a-arm and a short tie rod have a lot of bumpsteer inherently? Since the stock steering rack is required in FProd, how will you overcome this?

Posted by: groot Jan 23 2004, 06:26 AM

Excellent question, Chris.

I will move the rack up to center it at ride height, but that's about all I can do, given the rules. It's one of those compromises, but for me the improved front geometry under roll is the highest priority.

The ITB car I built had problems with the front geometry, as I mentioned before. We tried, but couldn't lower it too much without throwing away any usefulness of the front suspension. We had to run much higher rates on the front than I'm comfortable with to counter roll. I subscribe to the "run it as soft as you can get away with" school. And I didn't enjoy how skittish the car was over small bumps, it reduced traction and cornering power. It felt real racy, though......

Just my opinion, though.

Posted by: Racer Chris Jan 23 2004, 07:53 AM

Kevin,
I'll be interested to see what your front end looks like (and how it feels on the track) when completed.

When I ran ITB I thought the biggest problem was the lack of hp. I actually ran slower laps on 205 tires than on 195 tires because of the additional rolling resistance.

I believe the front end naturally has too much grip relative to the rear. That's why using big torsion bars and big anti-sway bars is the first upgrade for most people.

Now that you have me thinking about roll centers again, I understand from reading, that the roll center of a macpherson strut suspension is already quite low, especially when the a-arm is flat. It doesn't appear that lengthening the arm changes this substantially.

(BTW, I wasn't trying to be critical of your choices in my first response. I was only describing the reasoning behind my own choices.)

Posted by: groot Jan 23 2004, 07:56 AM

I've been thinking about the bump steer with lengthened control arm issue.

Let me babble on about my thoughts and others can jump in and criticize as they want.

Bump steer occurs because the track changes as the suspension travels. The lower the car, the worse this condition because the ball joint moves in more because of the angle of the control arms. Now if you move the rack up in the vehicle you can reduce this effect by straightening out the tie rods.

If that statement is correct, and I believe it is, then a longer control arm would improve bump steer since the track change is reduced and therefore bump steer would also improve. This assumes that the rack is mounted in the proper position, either by spacers or a complete change in mounting system.

Thoughts?

Posted by: groot Jan 23 2004, 08:00 AM

The problem with McPhearson strut roll centers is that they are too low. You front is truly optimized already, in my opinion, given your wants (maintain torsion bars and stock mounting location).

The roll centers should remain above the ground (for reasonable roll) and below the Cg (to resist jacking), ideally for all conditions. With short A-arms the roll center moves around quite a bit for different conditions.