924Board.org

[aussie931]

Would people give their opinions on the following set-up:

Car is a 1980 931 Euro spec currently with the 23mm front and 14mm rear anti roll bars.

Upgrade to:

250lb lowered springs in front
Bilstein gas shocks
Replace all bushings (polyerethene?)
Retain existing front bar
I need to upgrade the rear bar to match rate

SHOULD I BE LOOKING FOR A 22mm or '19mm' 944 cup bar for best balance????

Car is driven hard on street and used for track days. Email me offline - THANKS

[924RACR]

Depends on how loose you want the car, but I'll bet you'll want the larger of the two rear bars. OTOH, given that you're talking about doing suspension bushings, you could consider replacing the torsion bars while you're in there - unless you do not plan on replacing the torsion bar/spring plate bushings.

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[aussie931]

Thanks mate,

I probably will replace all the bushings whilst it is being done - some look real worn.

Im just trying to keep costs reasonable so I wasnt thinking of replacing the torsion bars at this stage, thought it might be cheaper to just do the rear bar replacement - get one from a parted 944?

What would you suggest for torsion bar 'size' if I were to retain the existing rear bar?

[Peter_in_AU]

wow Pete (aussie931) two posts in one day

Didn't even think to mention when you were over, I have a full set of poly bushings in a box under the house - they're not for sale but if you'd like to borrow them to compare with generic bushings or to get some made up you're welcome.

[924RACR]

Well, yes, I'd say the 23.5mm rear bars from a 944 would be fine and the cheapest option, but if your car came with the 14mm rear bar, it probably already has 23.5mm bars in it! Therefore you'd be talking new bars like 25mm. I'm not sure, though, as I have not set up this combination. However, going back to your original statements, you will probably not want to then spend the money on bars.

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[TroyDest]

I basically have the setup you're gonna upgrade to on my '82 931 daily driver right now, except the bushings. It has the original 23mm front bar and 14mm rear bar. Original 23.5mm torsion bars. I recently installed rear bilsteins, front 944 bilsteins (AK 47115), and 285# 10" springs on adjustable perches. The rear shocks actually lifted my car so I lowered it all the way at the spring plate adjustment. I lowered the front accordingly and it sits a little lower than a stock 931. Now I need to adjust my front and rear camber; front and rear are cambered in at the top too much. So far I've noticed that the front end is great on the street. I don't smack the wastegate pipe on speed bumps any more, I don't have to crawl over RR tracks, the ride is not harsh at all, and the steering is more responsive. It hugs the road pretty well except when jumping into a corner real hard. The rear end seems to lift and oversteers a bit. I have a Weltmeister rear bar which I intend to try to solve the oversteer.

[924RACR]

Sorry, you need less rear bar if you've got too much oversteer. First thing try removing the rear end links for the rear swaybar.

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[924RACR]

Actually, now that I think about it, you need less front camber. Ride height adjustment has more impact on front camber than rear, and the inequality here (more neg camber added up front than rear) is what's causing your oversteer.

Get you car aligned before you do anything else.

_________________
Vaughan Scott
Webmeister
'79 924 #77 SCCA H Prod racecar
'82 931 Plat. Silver
#25 Hidari Firefly P2 sports prototype

[aussie931]

Thanks all,

So let me get this right - does that mean I should be fine with just upgrading the springs to 250lbs & new shocks all round and retaining what the car has now (23mm F 14mm R and 23.5 torsions)? Would have thought I needed the rear a bit tighter hence the question.

The GT had a 16mm rear bar with harder springs (rate anyone - ??) so Im just following down that path - dont think the rate would have been 250lb so thought I would need more bar on rear?

Im looking for a well balanced package.

Thanks,
Peter

[-nick]

aussie931-

i'll share my setup with you which i've been very happy with on the street and a/x.

i'm using 200# front springs (effective rate ~180#) and 25.5mm torsion bars from an M030 951 (~175# effective rate).

23mm front swaybar and 19mm adjustable rear on the softest setting.

the car feels very well balanced in terms of brake dive and throttle lift. it took me a while to get the shocks dialed in right, but the bilsteins would probably give you a perfect match with spring rates between stock and ~250# (i'm guessing a little here). it's not too harsh, although i do take speed bumps slow.

i feel like i have a little understeer that i'm going to try and dial out by stiffening the rear swaybar to the middle setting. this should also help in removing what i feel like is a little too much body lean around turns (albeit only _very_ fast turns). the lean isn't really even noticeable in street driving, playing with the swaybar is mostly to get the oversteer/understeer balance right.

i'm also running about -.5 degrees in the front and -1.5 degrees in the rear of camber. this is where some of the understeer comes from. anymore front camber and you really start to notice the car hunting around while driving down convex-ly paved highways.

the whole car is also about an inch lower. the front springs were preset at the lower height and i had to reindex the torsion bars to match (pre ~'78 cars had no adjustable rear ride height). the rear axles sit pretty level at this ride height and the front looks fine too.

i personally think that poly bushings are not worth it for the street. they do transmit more noise and i had big issues with their longevity (i might have just gotten a bad batch). you won't likely notice the handling difference anyway.

you can get used 25.5mm torsion bars at a reasonable price. i think i paid ~$125USD for the pair off a low mileage 951. putting lots of spring in the front is going to give you understeer. i think 250# may be a little much on the street, just by thinking about how my 200# springs handle. i definately think it's too much if you're not going to increase the torsion bar rate, even if you do increase the rear swaybar.

if you want a little extra stiffness try a strut bar. that's really about the limit i'd use for a street suspension. i've had several people comment at races at how flat the car corners with this setup.

this is just to give you an idea, everybody uses something a little different. talk to any suspension tuner they'll tell you that setups are 20% know-how and 80% black magic. for instance your 931 is a little heavier than my early NA. especially in the nose where i don't have 100#s of AC parts and ## from a turbocharger. the extra weight in your nose will give you even more understeer!

i hope this helps your tuning. i really enjoy trying different settings to try and keep a nice street ride and get 'oh my god' cornering.

good luck,
-nick

[Richard]

Do only one major change at a time or you will never know what is really working for you. Unlike opening up an engine, you can always go back and stick a fatter sway bar on. Maybe the car will be perfect with new shocks and springs. Bigger isn't always better!

[aussie931]

Richard,

Your absolutely right - however if Im considering doing I may as well 'up' the rear torsions because of being such a large job later on. Wasnt planning that way but certainly looks the go if I want 250 up front.

250+lbs front/25.5mm rear torsions/Bilstein shocks and we'll see about changing the rear sway bar later when I get a feel for what I want/what it feels like.

Cheers,

[Vince Ponz]

77.5 924 79 931
23mm f 23mm f
22r Welts. middle setting 18mm r stock bar
Torsion stock torsion stock
bilstein HD 4 bilstein Hd 4

The 77 handles better than the 931. The Na does not have air, lighter bumpers, and carbs which make it lighter in the front. I find it neutral.
On the other hand the 79 931 is bone stock without air and on turns seems to want the rear to come around. It is a heavier car in the front and has the lighter bumpers.
Love them both.