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

[ThePaintedMan]

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?

[sixnotfour]

(IMG:style_emoticons/default/confused24.gif) ive called him out before,,,,no pics... (IMG:style_emoticons/default/confused24.gif)
(IMG:style_emoticons/default/thisthreadisworthlesswithoutpics.gif) (IMG:style_emoticons/default/thisthreadisworthlesswithoutpics.gif)

[stownsen914]

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.

[stownsen914]

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:

[jd74914]

- 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.

Very cool! Thanks for sharing pictures and details! (IMG:style_emoticons/default/smile.gif)

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.

[stownsen914]

Very cool! Thanks for sharing pictures and details! (IMG:style_emoticons/default/smile.gif)

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

[jd74914]

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.

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?

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.

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 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.

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 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!

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.

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.

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

[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 ...