Stownsen914's car, Let's see some pics Options

[sixnotfour]

(IMG:style_emoticons/default/smilie_pokal.gif) (IMG:style_emoticons/default/beerchug.gif)

[stownsen914]

OK, realized I hadn't responded to the last post ... thanks for the positive comments!

To answer some questions:

I haven't looked into track width change though-good thought. Why did you seek to minimize it? Is it a tire wear or motion ratio change concern with the variable torque arm length change?

Scrub (the track change as the suspension moves through its range) causes undesirable movement as the suspension moves through its range. For example, when going into a lefthand turn, the right front tires take the majority of the load in front. So if the right front tire moves to the right by, say .1", what actually happens is the tire stays planted and the front of the car moves to the left and possibly also forces the left front tire to skid to the left. Basically it's extraneous movement that is a destabilizing factor in the car's handling, so best to minimize it for most applications.

How did you shorten the steering rack? It never occured to me to build a secondary tie rod attachment; very cool idea. That really should help with the bump steer issues resulting from pulling the control arm inboard mounts more towards the center.

I use a machine shop in NJ called Verden Tool. They are experienced with Porsches and racing, and are happy to take small jobs like the ones I come up with (IMG:style_emoticons/default/smile.gif). Basically they shortened the body of the rack by couple inches on each end and also shortened the rack (the rod inside) by a similar amount on each end. I believe they made custom new bushings for each end of the housing. By attaching the tie rods near the middle of the rack, I got the bump steer to near zero in the normal operating range.

Realizing you haven't extensively druven it, are you happy with the scrub compromise? It doesn't seem like it'd be as big deal in a street or track car (excepting parking lots and maybe pulling out the the pits) as it is in an AX car.

I'm very happy with the mods. I didn't notice any issue with heavy steering or quirky handling from the additional scrub radius. It seems like it was a good compromise.

The issue I'm having with Boxster/996 uprights is that they are front steer and have a ton of caster built in so they look non-ideal to turn backwards. I don't really like the idea of moving the rack into the trunk, especially since there is a radiator going in there and having a little cargo space would be nice. They are super cost effective at ~150/set fully built with hubs, bearings, etc. Really a nice clean package. It almost might make sense to plan on using Boxster hubs/bearings and machine a fully custom upright to press the bearing into but that's a ton of effort. The 944 units are a little nicer to turn around and can fit old VW Golf struts.

Ah, I see your point about the Boxster uprights. I wonder if there is a practical way to modify them to either alter the caster or to make them rear steer?

I guess the 944 units are rear steer? Maybe another easy way to get a Porsche 5 lug hub ... If I did this again I'd definitely be looking at options like that instead of modifying old 911 parts.

I believe I also owe a picture of the diffuser. Sorry for the delay on that. Need to get out to the back of the storage garage and snap a picture of that ...

[c/s914]

I never knew I had a bump steer problem until I noticed how much I was sawing on the wheel during some onboard race footage. I was able to dial most of it out with an elephant racing kit, but can't quite get it to zero degree deflection. Maybe someday I'll get to your level of racecraft and find that it is also my scrub or some thing causing it, but for now the best I can do is calculate motion ratios to give to to my shock guy to valve my struts/shocks appropriately.


Meanwhile this winter's project I'm going to take a look at adding some downforce, but I'm stuck on how to keep my 3.6L cool while incorporating some underbody aero. I'm liking what Maltese Falcon posted on another thread below and wondered if your setup was similar?

(IMG:http://www.914world.com/bbs2/uploads/post-2755-1422416664.jpg)

Yours in Motorsport
S.Chapman

[914 Ranch]

Joe Sharp was here...
Sooo much more work to do on AR-14...
Flat bottom is easy, now you have me obsessing over the diffusers.
OK I got this, hold my beer... What the Falcon, now the car is 2 years out.
More goals take more time, I hope the Falcon I have it...
My first goal is to make it running and drive her in an A/X. Should be able to get that done this year.
Thank you for all your inspirations as I think that this will take me to the end of the build. The end, ha, that will never happen...
The pic of the diffuser set me off on the right track...

[c/s914]

Keep in mind that autocross rules prohibit diffusers in most classes, bumping you way up...

Btw I ended up dropping my flying buttress and just adding a splitter and wing:



...and I gotta say this dropped significant time off my lap times!

S.Chapman

[stownsen914]

Btw I ended up dropping my flying buttress and just adding a splitter and wing:

...and I gotta say this dropped significant time off my lap times!

S.Chapman

A wing may have been the best single change I made to my car.