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I am setting up an EP 914-6 for SCCA regionals. I have 22mm front torsion bars and 350# springs in the rear. How low can I set the ride height? I have found the bolts that hold in the front sub frame to be the lowest point of the car and I can adjust the bars till it hits the ground. The rear I use the jack points on the back corners of the tub. I can lower these down to 2" off the ground.

I have a set of the 23mm front bars also and can get heavier rear springs if needed. Any suggestions? I am runing cantilevered slicks from Goodyear.

I will be running tracks like Road Atlanta, Barber, Roebling and CMP. How low can I go?

Thanks,
neilca.

Other more experienced SCCA will chime in, but....
Don't loose all your shock travel!
I have read of successful FP and EP 914s that are 3.5" - 3.75" off the ground at the jack points.....but they also have raised rear suspension pick-ups and raised front spindles to keep some shock travel.
Good luck

Lowering the car won't give any benefits if you don't have good suspension geometry
If you don't have raised spindles I wouldn't go below 5" ride height at the rockers. Much lower than that and raised rear pickups are a real good idea.
You have to be real concerned about shock travel when the car is lowered much more.
350lb springs at the rear are way too stiff for any 914 torsion bar front end IMO.
What front anti-roll bar are you using? I make a 1 1/4" front bar which is larger than any other available 914 front bar and works very well on a EP/FP car.

I ran 350# rear springs and 23mm t-bars with an 1 1/4" .095" Speedway bar in the front on the IT car. It worked good. I plan on using the same rates on it when I switch to EP next year. It might be too much for a car that is loosing nearly 400#.

I believe the concept and creation of cantelevered tires is to allow a larger tire WIDTH to be used on a specified (smaller) rim. It,s deffinately a competative advantage for the user and tire manufacturer. Lowereing the car (any car) can be a tricky business. Primarialy you want to keep the suspension in a range of vertical travel, bounce and compression so the suspension does not "bottom out", meaning has no more travel. Thats when the car gets out of control quickly, and all this usually occurs at the most critical points on the track. A suspension with too stiff springs essentially replicates this situation. A too stiff suspension gets less traction in turns and down the strightaways. Other people on this forum have given some very insiteful reasons why lowering too much is detremental, relative to (ackerman effect) suspension toe changes in movement, both compression and bounce. You may want to consider approaching the ideal ride height, lowering, by having shock travel indicators, sleeves on the shocks to determine actual suspension movement when on the track in practice or a race. getting some real time/ use information. Having a car with a too stiff suspension,and lowered into a range that is determental to the suspension design is easy to do. It may well be the most common reason for a poor performiong car.The best engine, and tires cannot overcome a lousy suspension setup. ...this for your consideration. Murray

Hey Neilca,

From what I've read, you are getting very good feedback on the issue of ride height! I started out lowering my car as low as I could go and the car was a nightmare to drive. I ended up RAISING it back up to 5" because lowering the car SCREWS UP the suspension!!! Please go back to other posts on "suspension setting for V8 cars" (mine is one!) and you will see that I did bump-steer measurements front and rear and found that the car is DESIGNED to run at "about Stock" ride height or we end up in ALL the wrong parts of the suspension arcs. The issues are not only Camber but more importantly TOE CHANGE, especially in the rear. Basically, the suspension is for the STREET and NOT the race track. I have to keep reminding myself that the car was originally designed to run on those tiny 165 radials!

As far as how to set spring & swaybar rates for a 411-motor 914, I can't help...but for data on what the suspension does in compression and droop, I can. if you would like the data I measured, feel free to email me: porschepiloto914@verizon.net. I believe it is important to have a basic understanding what the suspension is designed to do, before we dive into big changes.

Hoping this helps,
Terry

Thanks for all the feedback. My car is far from stock. I have:

Lengthened the lower control arms 2 inches, then changed the strut angle to compensate, which gives me one degree of negative chamber per inch of bounce. This also allowed me to tuck the ball joint into the wheel so I have almost a zero scrub radius. I spent a lot of time fixing the bump steer from all these mods, but I got it down to 0.03 through the entire arc. The inserts are Bilsteins for a Scirocco. These are a lot shorter than the 914 inserts. I made my own sway bar from 0.080 wall 4130 1.25 in diameter. It mounts in the usual place.

The rear upper mount has been raised and I use a set of aluminum Pro shocks. The engine was raised in the chassis in order to improve the driveshaft angle when the car is lowered.

The car weighs about 1800# with the driver.

Any suggestions on spring rates or shock travel?

neil

Keep a close eye on the inner rod of those Bilsteins. I have had wear problems with the stock strut inclination & cantis.....see pic.
The worn off chrome (& base metal) is right where they sit at static ride heights.
For that reason alone, I didn't lengthen the A arm. The top of the tube where the rod passed thru was not properly deburred.....they are now, but I haven't taken it apart to see if the problem has persisted.....no guts.

Edit:
Come to think of it, I was running 10 inch slicks up front when this happened.

Thanks for the heads up JP.

Hopefully, the Scirocco struts wont have the shape edges but I will keep an eye out.

Blake,

Looks like we both have about the same set up. How low where you running the car at the ARRC? I will not be able to run EP because of my right hand drive config but rather SPU. Are you going to stick with the 4 cylinder in EP?

Good luck,
neil

In IT you have a min. ride height of 5". That is what my car was at. I will be running a 4 cylinder.

Hey Neil,

Wow, a lot of work and a lot of mods on your car....so we have a whole new story on the ride height issue. While the REAR, with the moved pick-up points, may be lowered quite a bit....you will still be limited to lowering the front NO more than the range that keeps the lower arm parallel to the ground. Of course, it's your call here.

I am interested in the extension of the front suspension arms what the gains you.
However, in so doing you have SOFTENED the torsion bar & swaybar rates. Please review my attached Excel spreadsheet that calculates Front torsion bar rates, swaybar rates, rear coil spring rates and the resultant WHEEL RATES.

Of note is that the FRONT 22mm torsion bar with STOCK arms yields as Wheel Rate of 153.75 lb/in while lengthening the arms (assuming the same swaybar load point) REDUCES the Wheel Rate to 117.72 lb/in.

The input from the other EP racer is very interesting and helps you to have a "starting point", but my sense is that you may want to go Softer in the REAR or choose a STIFFER torsion bar rate. As recommended, the softer you can go, the better....so I would suggest the lower cost approach of balancing the car by SOFTENING the rear springs. Summit Racing sells them at $37.88 ea. in 25 lb intervals.....what is not to like?

If the attachment doesn't come through, just email me: porshepiloto914@verizon.net.

BTW: My apology from my last email, I've am use to thinking of the 411 engined 914s as EP and meant no "slight" about your 6 cyl car. I would choose the 911 engine over the VW every time........if I din't gitClick to view attachment me some Chivy!!

BTW2: I have made BOTH of my swaybars the same way and have found them to work great: low cost and easy to mod as needed....way to go!! FYI: for my rear bar I was able to use SUMMIT RACING poly-bushing swaybar brackets (With Zerk fittings) for only $17/set....to easy!

Best,
Terry

Terry,

Thanks for the spread sheet. You are correct the bars have to work harder with the longer arm. I need to spend a little time with your sheet. Is the effective wheel rate the same as the spring constant of a coil over?

Truth is I lengthened the lower arms because I didn't want to spend the money for wheel spacers. I am an engineer so, I am very cheap. Once I did that my camber went way out of wack. I always planned to make my own struts so I went with the radical angle. I was shocked, pardon the pun, to find I was now gaining negative camber. Plus I had the zero scrub radius.

When i worked on a national GT4 car we used plastic ties on the shock shafts to moniter travel. I think I will do this before I start changing springs.

Since Blake was restricted to 5 inches I guess anything lower is goodness. As for having the lower arms parallel to the ground I understand the reasoning however does a lower CG offset the low roll center?

Neil,
you mentioned raising the rear shock mounts but did you move the TA pivot mounts as well?
I'm curious as to what the angle of your pivot shafts is relative to the ground when your camber is set for the slicks.

One (of several) spread sheets I've seen give an effective spring rate of 176in/lb for a 21mm T bar at the rotor .......which is a couple inches off he centerline of the wheel. I'm not sure it's right either.

I ran a 21mm/275 set up at AX (I needed compliance) and it put the front AR bar half hard....and produced a mild ovesteer condition.

Bounce your butt on the front fender then come tell me about a 117in/lb effective rate of a 22mm T bar.
I ain't real scientific, but I ain't dumb.

If you have a chance, I would really like to see a picture of the lengthened control arms and the custom spindle set-up you did on your car to get zero scrub.

-Britain

Click to view attachment

Here is a picture of the front arm and strut. You can see the ball joint is inside the wheel and it has caused some scrapping and wheel weight removal. I originally set this up with a three piece spun aluminum wheel. The forged/cast wheels are a bit thicker. It's a delicate dance between the rotor and the wheel.

Click to view attachmentClick to view attachment

Here are some shots of the rear. I have had to add about 3/8 inch of spacers on the outboard adjuster to get the chamber out. I do need to add a bump stop to the shock so the arm will not hit the chassis. The shock has about 2 inches of travel left in this picture and the tub is about 3 inches off the floor.

Kind of hard to call that an EP car with the amount of original chassis metal missing.
Raising the rear pickups would solve multiple problems:
Shock travel would increase;
Trailing arm would have more clearance to the underside of the chassis;
Less spacers needed to get desired camber;
Lower rear roll center.

Hi Neil,

I built the spreadsheet when I was working out what my car needed. I started with the basic spring rate calculations and then modified to the 914 application.

1) To answer you question: NO, the actual WHEEL RATE of the rear suspension is HIGHER than the Spring Rate!!! Due to the fact that the spring is mounted on a LONGER moment arm than the axle moment arm. The SHORT conversion is to multiply the SPRING RATE by 1.17 to get the WHEEL RATE.

2) After seeing your pics on your suspension: 1st: NICE WORK!!. Secondly, please take time to understand the values in my SWAYBAR Rate calculator: I made the ASSUMPTION that while you lengthened the lower arm 2" to 16"length,
I left the STOCK swaybar to suspension input at a distance of 7". It appears the right number would be something like 9".

I'm a business major, but SCOTTISH and "CHEAP" is my way of life!! So we are on the same page there. I lengthened my front arms by 1/2" so I could get the camber adjustment range I wanted. Having done so, I've REDUCED the static front camber as the car got stiffer and believe 3/8" would be a better number.
My current setup is -2.0 degrees camber all around.

-I'm thinking that the 1 degree camber GAIN could work to your advantage: This will allow you to set your static camber at a low 1 - 1.5 degree number and when the car rolls into the corner, it will gain the camber it needs. However, as I learned the HARD WAY, the ONLY way to know what is going on is to buy a TIRE PYROMETER!!! I got one from eBay and THEN the true chassis tuning started.

As far as the Zero-scrub radius, while it has benefits, it does not appear to be a major focus in chassis tuning.....but get a 2nd opinion!

Checking the suspension travel in the corners with spot ties is a great idea....engineers and others, also with a brain, KNOW there is nothing like hard data!!! From the photo, I can already see that in the rear, you suffer from "burning paint" on the wheel arch sheetmetal. So it appears you are already as LOW as you can go...unless you RAISE the sheetmetal arches.

CG vs. Roll Center: THE GREAT QUESTION, from what I have experienced, the Roll Center is the more important issue and the LOW roll center will continue to give you handling problems.....but I would recommend getting a 2nd opinion. Sorry, as a Business Major, I DON'T have THE KNACK!

Hey ANDYZ, would you like to voice an opinion here?

Best,
Terry

Chris,

You are correct, my car is way beyond EP prep. I used EP in the title because it could be recognized. I will be running a special regional class in the SE called Special Production Under 2.4 liters (SPU). Basically, the only rules are it has to be under 2.4 liter and not fit another class.

I have not heard of raising the pivot point of the trailing arms. I would guess that would have been a good thing to do when the car was on the rotesserie. Could you elaborate on what you have done? I have followed, with great interest, your work with horizontal fans. I originally set up my chassis for a 4 cylinder. I found a deal on a 6. That is why my engine mount plates have spacers in them. If I could run a horizontal fan I could loose the spacers and move the weight forward.

Terry,

Thanks for the kind words. I think I enjoy building cars more than driving them. When I retire that is my plan is to tinker on race cars.

The burn marks are from tires I used last year that where 3 inches too tall. At least they were free! They gave me something to ride on while I sorted out the car. This year we use free slicks from some friends in the National circuit.

I hadn't heard of lengthening the arms to get more negative camber, but that is a great idea. If you run radials that would really pay off.

Our local SCCA region is planning on having more Time Trials this year associated with Nationals and Regionals. I will take advantage of this to get some track time, tire temps and travel data.

Based on what I have read so far I should set my ride height in the front such that my lower control arm is parallel to the ground and the rear I am thinking should be about 3.5 inches off the ground.

In the northeast most of the SPU cars are 7/8ths pro-stocks or Baby Grands.

Raising the rear pickups can be done several ways. Starting with a chassis jig is nearly essential when doing it from scratch. Some people have moved the stock mounts but the amount one can raise them is limited. Others have developed complex spherical bearing mounting arrangements that are expensive and time consuming to implement. I developed an economical kit that makes it a pretty straightforward procedure to go up as much as 3", retaining the stock trailing arms. It can be done with the chassis set level up on jackstands. The instructions are on my website and are linked on the chassis page.

As I mentioned, there are many benefits to rasing the rear pickups. In conjunction with altered trailing arms it is possible to lower the car drastically and obtain very good rear suspension geometry. On thing I didn't mention earlier is the benefit to the toe curve.
With your current setup the toe changes pretty quickly in both bump (toe-in) and droop (toe-out). On my car the toe hardly changes through a 6" range of 3" up and 3" down.

I keep saying I will finish development of the horizontal fan, then putting it off again. All that is holding me back is that I don't like the shroud design that was provided to me. So I just need to create a shroud I like and the rest will be cake.
I actually have all the primary parts to build one more just like the two I have on my race engines.

I have set the ride height. I decided the rules dictate how low to set the car. I put a rim on the LF corner with no tire, simulating a flat tire condition. Lowered the car to the ground and set the ride height such that the lowest point was 1/2" off the ground. Put the regular tire back on and measured 2 3/4" from the jack nub ( this is the boss on the bottom of the tub in the four corners). I then set the rear to 3 3/4" in the rear to give the car some wedge for down force.

Now on to corner balancing, see post on the subject.

Chris - from some playing I've done using the susprog suspension design tool, raising the rear pickup points raises rear roll center. You have found differently? Of course, you get other benefits by raising pickup points by bringing the arm closer to its intended range of motion ...




Usually a low roll center is considered desirable. You still have to balance it with other parameters of course. Have you had positive experience in aiming for high roll centers?


Neil - great looking car. I remember seeing the spread over on Pelican a while back.

Scott