Optimal front sway for a 1.7 ? Options

[Literati914]

I believe, if I’m not mistaken, there was a 13mm front sway bar for the 912 cars.. and I was wondering if that wouldn’t be more appropriate for a 1.7L 914 rather than the stock oem 15mm. I’m not sure if anyone bothers with a ARB on a 1.7L, but the 13mm ones are fairly easy to come by, cause everyone upgrades to bigger. So that’s a plus. Thoughts?


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[Literati914]

Anti roll bar size has nothing to do with engine size …. So how many are really trying to increase understeer?

Superhawk, I based my question on (my) understanding that a front bar is basically there to add a bit of understeer which helps counteract the oversteer situation of a given car.. I certainly may have that all wrong, I’m no suspension expert (& thanks for the book recommendation). But if that’s close to being right, then in my mind a smaller bar would be more appropriate for a simple 1.7L street car than the 15mm one used with a 2.0-2.4L type IV power plant (for example - since they weigh the same) - because 1.7L would theoretically produce less oversteer (all other things being equal).

Anyway the car will get a bar while torn down for bodywork, and the 13mm seems logical enough to me, I’ll probably give it a try. BTW, did any of the 1.7L cars come from the factory with sway bars?

Also, @wonkipop (thanks for your input) says the 13mm bars are on all 1.8L cars, but I don’t recall reading that 914-4 used anything but 15mm - perhaps that was a European/Aussie thing? Anyone?

I wonder what Porsche’s thinking was with giving the 912 a 13mm front bar, it being a more tail happy car than a 914.. but the 914-4 getting a 15mm up front?


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[wonkipop]

Anti roll bar size has nothing to do with engine size …. So how many are really trying to increase understeer?

Superhawk, I based my question on (my) understanding that a front bar is basically there to add a bit of understeer which helps counteract the oversteer situation of a given car.. I certainly may have that all wrong, I’m no suspension expert (& thanks for the book recommendation). But if that’s close to being right, then in my mind a smaller bar would be more appropriate for a simple 1.7L street car than the 15mm one used with a 2.0-2.4L type IV power plant (for example - since they weigh the same) - because 1.7L would theoretically produce less oversteer (all other things being equal).

Anyway the car will get a bar while torn down for bodywork, and the 13mm seems logical enough to me, I’ll probably give it a try. BTW, did any of the 1.7L cars come from the factory with sway bars?

Also, @wonkipop (thanks for your input) says the 13mm bars are on all 1.8L cars, but I don’t recall reading that 914-4 used anything but 15mm - perhaps that was a European/Aussie thing? Anyone?

I wonder what Porsche’s thinking was with giving the 912 a 13mm front bar, it being a more tail happy car than a 914.. but the 914-4 getting a 15mm up front?


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not an aussie /uk thing.
914s never sold in australia.
my car came from maryland usa.
never modded.
out of the box with the roll bars.
standard show room stuff.

1.8 has even less horsepower than a 1.7 unless you are unlucky enough to own a 73 cal 1.7. (IMG:style_emoticons/default/stirthepot.gif)

the 74s are interesting - as i understand it this is how porsche-audi north america decided to set the base models up to improve tham. it is during this period that porsche gained marketing control over the joint project. theoretically you could despec a 74 1.8 and get rid of the performance group package but you would have to order it that way.

to clarify - far as i know its 15 front and 16 rear.
i could try and double check that.
i didn't mean it had 13 mm sway bars.
i meant it had front and rear sway bars, not just a front one.

this is what porsche thought they should have for street.

i've driven an earlier car a quarter of a century ago without the bars.
i preferred mine.

but then again i run skinny 165 tyres so most blokes would consider me a retard.
i do run bilsteins, but that is because boges are not available in the modern world.
it runs stiffer than it used to. i'm not complaining about that. its far superior out on second rate old country roads and stays planted with the bills. but the spriings are soft and standard - and comfortable. we don't have smooth tarmac once you get off the main interstate highways in australia.

if you want the evolved set up for the base cars that porsche thought appropriate thats the set up.

but then again you could experiment.
note - they appeared to have the slightly stiffer bar on the rear,
which kind of goes with your idea of a single softer bar on the front.
but that will be more aggressive effect than the factory set up.
depends what you want to do with the car.
you can also get a lot out of setting it up level or a little bit nose down.
or as the factory did, a little (or a lot) nose up. that made them understeer.

[Superhawk996]

note - they appeared to have the slightly stiffer bar on the rear,
which kind of goes with your idea of a single softer bar on the front.

Can't judge bar stiffness just by diameter. Although the rear bar appears larger (by 1mm) it is a far less effective geometry than the front bar. I'm sure the overall rate of the rear bar is less than the front based on experience though I haven't done the math to calculate the rates.

The 15mm OEM front bar is basically a stright bar with two very short lever arms down to the LCA's. That aspect makes it highly effective.
However, the drop links are long, thin and probably flex substantially reducing effectiveness some.

The 16mm OEM rear bar has very long lever arms. But then the rear drop links are very short and probably don't flex much at all. But on the whole, the stiffness lost to the long lever arms won't be made up by the short, effective drop links.

Bottom line, I don't know the engineering rates (wish I did - next time I'm bored, I'll do it) but don't judge an ARB just by it's diameter.

[wonkipop]

note - they appeared to have the slightly stiffer bar on the rear,
which kind of goes with your idea of a single softer bar on the front.

Can't judge bar stiffness just by diameter. Although the rear bar appears larger (by 1mm) it is a far less effective geometry than the front bar. I'm sure the overall rate of the rear bar is less than the front based on experience though I haven't done the math to calculate the rates.

The 15mm OEM front bar is basically a stright bar with two very short lever arms down to the LCA's. That aspect makes it highly effective.
However, the drop links are long, thin and probably flex substantially reducing effectiveness some.

The 16mm OEM rear bar has very long lever arms. But then the rear drop links are very short and probably don't flex much at all. But on the whole, the stiffness lost to the long lever arms won't be made up by the short, effective drop links.

Bottom line, I don't know the engineering rates (wish I did - next time I'm bored, I'll do it) but don't judge an ARB just by it's diameter.

very good point. quite a different affair that rear bar.

[914_teener]

note - they appeared to have the slightly stiffer bar on the rear,
which kind of goes with your idea of a single softer bar on the front.

Can't judge bar stiffness just by diameter. Although the rear bar appears larger (by 1mm) it is a far less effective geometry than the front bar. I'm sure the overall rate of the rear bar is less than the front based on experience though I haven't done the math to calculate the rates.

The 15mm OEM front bar is basically a stright bar with two very short lever arms down to the LCA's. That aspect makes it highly effective.
However, the drop links are long, thin and probably flex substantially reducing effectiveness some.

The 16mm OEM rear bar has very long lever arms. But then the rear drop links are very short and probably don't flex much at all. But on the whole, the stiffness lost to the long lever arms won't be made up by the short, effective drop links.

Bottom line, I don't know the engineering rates (wish I did - next time I'm bored, I'll do it) but don't judge an ARB just by it's diameter.

very good point. quite a different affair that rear bar.

I spent a lot of time playing around with different things when I did my 914 suspension. Mostly in IMHO this is where you should throw your money and time in the car and not so much on the engine other that have a good running one.

For street and ocasional twisties I ran Billies Sports on all four corners ''progressive" valving set up. Ajustable perches with #140 SR in the rear.

NO rear bar.

In the front the car was ever to slight biased down in the front by torsion adjustment.
Rack spacer to take out any bump steer with a solid steering coupler. Turbo tie rods and stock ball joints....all new.

I found the stock drop links length for this junk and threw them away and used Tarret adjustable links for the bar.

Corner balanced and aligned to sock specs less a little more camber in the front, that car drove like it was on rails......forget the size of the engine it had a 1.7.

I could take 911's ....downhill of course in the corners.

I ran 205's BTW for rubber all the way around not a staggered set up on stock 2.0 fuch's. The fenders were already rolled when I got the car.

Mostly I think the car didn't really need one but Porsche...and still to this day...and I know cause I normally never buy a P car that isn't optioned up makes money by selling options....my Cayman was the only exception. The car is just so fun to drive who needs Nav.

My. 02 without all the technical explanation of why.