Hey Stownsen914, you've done a lot of work to your car over the years, but I've never seen any pictures of it bigger than your thumbnail. Can we see some details of the car?

x2.. haven't seen this car in decades!

Happy to! I'm away for a few days and can't seem to access some of my pics, so I'll post this week.

I'm looking forward to pics too!

ive called him out before,,,,no pics...

Sorry for the delay guys. I seem to be caught in Apple icloud password reset Hell (it's where I keep most of my pictures), but I just found these from a PCA club race at Monticello ...

Here are some of the car with most or all of the bodywork on. In the first and third pictures, the thing sitting on top of the roll cage is the engine cover that has an integrated headrest fairing.

The rear shot shows the diffuser I made for the car a few years ago. The lighting isn't great, but you can see the outline of the diffuser if you look closely. I had to move a lot of stuff in the rear of the car to make room for the diffuser. The car is flat-bottomed in front of the diffuser with aluminum sheet and a carbon diffuser at the front.


Click to view attachment

Click to view attachment

Click to view attachment

AWESOME!!!!!

Some details about the car:
- Started life as a 74 914 that had the usual rust issues. I stripped the chassis, fixed the rust, and welded in a roll cage and lots of additional tubing to triangulate out to the suspension pickup points.
- The bodywork is mostly custom fiberglass or carbon that I made or modified. I made a mold for the front clip, which is based on a 935 front piece. The doors and rear fenders are modified 914 pieces. I also made a tonneau cover over the passenger area.
- The scoop you see protruding from the engine cover is a modified piece from a formula car. There is a carbon airbox under the engine cover that leads to the intakes.
- I redesigned the front suspension using a suspension modeling program called susprog. Then welded new pickup points to the chassis, and made new A arms and shortened struts according to the new dimensions I came up with using susprog. I modeled the rear suspension as well, but haven't gotten around to building that out yet. For now it has reinforced 914 trailing arms mounted to raised pickup points.
- I moved the pedal box forward about 10 inches and moved the seat forward, lower, and leaned it back to about 45 degrees to put driver's weight where I wanted it. I moved the steering wheel and shifter as well.
- The engine is a 2.7L six that makes estimated 260 hp. I spun a rod bearing at the 2015 Monticello PCA race where these pictures were taken, and haven't rebuilt it yet.
- The trans is a 901 with custom gearing and pressurized lubrication to the gears and R&P, and also an oil cooler. Current gearing is GA-KA-P-S-U, which has been a good compromise for the NE tracks I usually drive on, with 2nd through fifth (and occasionally first) usable on track.

Here are some "naked" pics showing details under the bodywork:


Click to view attachment

Click to view attachment

Click to view attachment

Very cool! Thanks for sharing pictures and details!

What did you do to the front suspension? And what were your goals? Just out of curiousity if you wouldn't mind sharing.

I've been lucky enough to have access to Lotus Shark and modeled the whole suspension. I'm more of a powertrain controls kinda-guy, but it seems like it would be beneficial to move the strut tops inboard, lengthen the control arms, and remove the added camber from the spindle [while raising it] in order to tame the camber gain curve (somewhat) and modify scrub radius. The caveat being that bringing the inner pivots too close messes up bump steer.

My build is "street-ish" and I've been considering narrowing the strut towers and building new front struts from scratch with bolt on spindle (like a 944 of other car) which would allow some independent tweaking of the KPI and wheel camber with inserts. Then adding on threaded perches to remove the torsion bars. Seems like a shame to cut apart 5-lug struts when they are so valuable.

I'm no suspension expert, but I did a bunch of reading and asked opinions while starting to play around on susprog. In short, I wanted to:
- Get more camber gain. Stock is minimal. I wound up getting about .75 degrees additional negative camber per inch of bump travel. I was told that 1 degree would be ideal, but .75 isn't bad for a strut suspension.
- I wanted the roll center to be low but above ground. I think it wound up like 1" above ground.
- I managed to reduce scrub (side to side travel of the tires as the suspension moves up and down) to almost nothing in the normal range of travel. I think it's like a millimeter total scrub.
- I optimized anti-dive as much as I could. I think susprog expressed it as a %. I don't recall the specifics, but I got it to a place I understood to be "good."
- I played with Ackerman a bit for the steering. I followed the advice of Carroll Smith on this, as I didn't have much else to go on, frankly.
- I also widened the front track 3-4 inches.

To do all this, I just put the stock coordinates in susprog for starters and then moved things around (within reason) until I was seeing results I was happy with. The front strut tops moved out a bit for the wider track. The A arms are about twice as long as stock - they attach essentially in the middle of the chassis. I also shortened the steering rack and made a bracket that allows the tie rods to attach almost in the middle of the car to keep the bump steer manageable.

I found that everything is a compromise. If I over-optimize for one attribute, others went bad. So I kept playing around with it until I got it where the things I cared about were in the ballpark of where I wanted them. One thing that suffered in my design was the scrub radius (how far the wheel sticks out from the axis defined by the strut). Ideally this would be small, but we're limited with a strut in the first place. Scrub radius wound up being my main compromise.

I like your idea to make new struts. Using newer parts would be good (maybe Boxster?), and being able to bolt to commonly available struts sounds like a good way to do it. For mine I cut 911 spindles off used struts and welded them to new steel tubes, and welded the tops and bottoms off the 911 struts to my new tubes. Spindles are raised, and the struts are an inch or so shorter than stock as you suggested. My way was a lot of work, and I'm not sure I'd want to do it that way again!

I'm really happy with the results of the redesign. I only got to drive at a couple events after finishing the redesign before I blew the motor, but it really transformed the car. Better than any other single mod I've done to the car.

Scott

Nice car! Any shots of the undertray?

Specifically from the engine bulkhead back to and including your diffuser from underneath if you have any?

Thanks
S.Chapman

Sure. I'm out of town for a few days but should be able to snap a pic later this week. The car is on a lift in storage now, but I think I can get one of the underbody while it's up there.

What is that car in your avatar? Am I seeing things, or is that some kind of combo of a 911 and a 914?

Scott

Thanks!

The bodywork is removable and I love messing with people who can't believe it's the same car ;v)

http://www.914world.com/bbs2/index.php?sho...=186361&hl=

Version 2.0 is going to have a splitter, diffuser, and 935 style wing intergrated with a one piece rear clip. I'm having trouble trying to figure out how to keep the engine cool without disrupting the air going to the diffuser though...

S.Chapman

Curious about the rear wing height. Do your class rule say it must be below the roll bar? Just wondering why it's not higher up and into the airflow.

I like it, the rear quarter panels look like they are inspired by the Porsche 936

Cool! Have fun developing the car. I have thought of adding a roof back on my 914. My first iteration had a raked windshield (back and down a couple inches in each direction). I would put that back and have some kind of rear hatch to guide the air back to the rear wing and off the back of the car.

Sorry if I missed this detail in the other thread, but is it a 911 roof? It looks more curved than a 914 roof.



Keeping in mind that all my aero experience is from reading and copying other designs, there seems to be clear evidence that when you have a flat bottom and/or diffuser, that a low rear wing helps draw the air out from under the car. When designed correctly, the increase in downforce from the underbody with this design exceeds the losses from the lower wing position, so overall more downforce. I lowered the rear decklid and put the wing as far back as possible (PCA club racing rules limited) to maximize this. There is a second, smaller wing below the first one to help with this, like the GTP cars used to run back in the 90's. Who knows if I got any of this right, but that's the thinking.



Thank you, sir. I was inspired by the rear fenders from the Audi LMP cars from the early 2000's, sort of similar to the older longtail Porsches. Same idea I would imagine.

Nice machine!!!

Good eye, while I never transferred any of the roof shape directly via a mold from my 911 or 912, I did fab up a lightweight fiberglass roof that I tried to emulate the shape as much as possible by "rolling around" the rear B pillar. Note that I did make the removal sail panels work with both the stock roof and this piece just in case though...

I must say it's not near as good of a job as you did on that front nose clip, you really nailed that shape!

S.Chapman

Same here-I just dabble based on books and other's experience. Thanks for the design goals list.

I've likewise been trying to shoot for ~-1 deg/in. bump as well and an above ground roll center which at extremes never crosses the ground plane.

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?


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.


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.


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.


That's awesome! Nice to like the changes after so much work.

Sorry for all of the questions! It's so rare that people redesign/refine the OEM suspension, you and Kevin Groot are the only people I can remember on this forum, so it's nice to hear your rationale.

Jim

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

To answer some questions:



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.




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 . 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.



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.




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 ...

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?



Yours in Motorsport
S.Chapman

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...

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:

Click to view attachment

...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.