MistaX

Originally ran bottom mounts, switched to the top mounts after doing the torsion bars to get the ride height lower, and the added bonus of being able to use their strut tower bar.

They're very close to parallel. I have minor issues with tramlining, but no bump steer at all. Maybe a bumpsteer kit could correct that? Also need to change rack bushings to delrin. It's probably the alignment though, since it felt exactly the same before I lowered it further, swapped mounts and was still running crappy stock bars with crappy worn out rear bushes. Ran the same alignment before all the work. It's nowhere near unbearable or even uncomfortable, it just happens occasionally on highways and it's typically no big deal. If that's the only downside to keeping the car how it is I can live a happy life with that.

924srr27l

Cool, maybe the tramlining also is you neg 3 camber ?


Was the front improved & felt much better when you fitted the top mounted GC mounts and brace bar ?



Due to the spring rates GC spec with their Koni / struts after discussions with them they suggested they were too hard for my application because I was looking at spring rates around 175lbs, and they said the shocks wouldn't work with this low rate.


Due to the big weight losses I only have 555lbs on each corner and I'm currently running 190lbs which does roll a bit cornering but straight line compression is too hard, so I think it's because my wishbones are at such an angle that the roll is excessive (I'm only running 1.5 neg camber) and that the already angled wishbones are levering too much as they are jacked from static.


Also the shock travel I think is lacking, I'm using stock struts with threaded adjustable platform 2.25ID race coils, and Sport Gas inserts.


So I want to tackle this and was thinking I'll sort the wishbone angle issue with either the extension adapters or the weld on type extensions and then Steel boxed arms? (Currently I have new aluminium wishbones) also a bump steer tie rod kit and GC top mounted mounts


But an ideal solution would be like you have with the shortened GC Struts and maybe I try 250 lbs but the current balance has a hint of understeer, no oversteer at all and it would look like I'd need to increase the 27mm hollow Elephant T bars to compensate for stiffer front coils. I could come down the front ARB it's 26.8mm from the 44 turbo but my car is 650lbs lighter! maybe it's too stiff? the rear is 18mm maybe I need this to go up to 20mm


It handles very well, street & track so the above analogy probably sounds a lot worst than it is, only I want more because there is for sure room for improvement.


Mines currently not as low as yours..


It went from this.......











To this...







Here it has 8x16' cups fitted and 205/55/16 & 215/50/16 R888 which I've not tried on a track yet, but it does look more slammed because of the wider tracks







Compared to my road set all four wheels 7x16 & 205/55/16 all round as you can see a fair amount of Roll on a wet and greasy Track day...









R

MistaX

My corner weights are more than 125lbs heavier than yours, and not even. My balance is more toward the rear even with a slight forward rake, 49.1/50.9% Total weight is 2758.

Note that I'm still running the stock M456 swaybars, 23mm front and 14mm rear. I don't think I need bigger bars, but I'm going to get M030 bars and mess with the combinations eventually and see if I like it better or worse.

I'm not really a fan of using swaybars to make the suspension stiffer and I think it's a common technique on these cars to avoid changing the torsion bars. Big torsion bars and high rate springs shouldn't need a big swaybar, at least in my understanding of it. But I haven't run bigger sways so I'll try it.

The strut tower bar did make a difference in how tight the front feels.

Only you can really answer if it's worth changing to stiffer springs and torsions. If my car weighed what yours does I'd probably be rocking 250lb and 28mm bars, with the sways you already have, or smaller.

924srr27l

Ok I've heard of this approach before stiffly sprung and soft ARB's, maybe I've gone for both and hence one area needs more or less resistance?


Yes the considerable losses of sprung and unsprung weight make the handling easier to control and the suspension needs to be tuned accordingly. The 17" wheels & tyres trial proved to make it handle worst (as suspected) as it wouldn't turn in as sweet or settle when taking a set as well, The car was also slower in acceleration which was the deciding factor they were not staying on the car and were sold.







I want to get all the angles and dangles sorted first and the wishbones in a parallel position like this shot below (before the Engine was fitted) is the first goal, then more suspension travel and then the spring rates..







R

Noahs944

Thank you brother. You helped "fill in the gaps" of my knowledge.

Regarding the aluminum A Arms, from my understanding, they can easily handle 1.25" reduced ride height and still be strong enough. Though if anyone has a valid argument for the contrary, please state your claim.

924srr27l

It's an Opinion not firm knowledge !


I'd be interested to learn the 3 different formula's for calculating the front and rear spring rates (balanced car, under or oversteering car)?


You may want to consider regaining the Loss of suspension travel, to put the piston rod position 31.75mm back where it's designed to be , and also the wishbones and tie rods as discussed on here back to their best angles as many examples on this forum have confirmed the changes are a considerable improvement.


Many go for the Look with lowering cars and do not maximise the performance benefits, so references about only consider shorter length shock absorbers if you do Jumps are quite wide of the mark !


As you'll not get any lower than neg 2 degrees on the rear camber??


My car is quite lowered (see photos on the above posts) I didn't measure it before or after because the race team choose the corner weights and heights after I'd told them not to go too mad.


The rear Camber is .5 degrees negative both well under 2.


The wheel size may be an issue here for Morg as he likes the low slammed big rim wide tyre look for "looks" and not performance...also are they Steel Trailing arms on the 931 or not?


I'm using aluminium arms, and so far so good (except the wrong angles)but there's a lot less weight and load on the ball joints when you compare them fitted to a 2300lb 924S and a stock near 3000lbs 944 turbo 220 and less unsprung weight (Wheels / tyres / Brakes)


And "what you can expect from any shop is they have no idea" well this is of course dependant where you live, I can see many times how Lucky I am to live in the Uk (Where we have so many Motorsport & Engineering / Geometry specialists.)


R

morghen

Its only an opinion based on my personal experience and observations on my own cars...nothing more...this does not make it correct for your car, just like Roger said.

when I chose the springs front and rears I used the information on the page below.
Since the cars are 50/50 weight distributed and I planed to use identical tires front and rears I went for equal effective spring rates front and rear as I was looking for a neutral behavior and more cornering speed capability..but you may want to choose differently for your application.
https://www.paragon-products.com/kb_results.asp?ID=58

Suspension travel is an issue if you really use the suspension system close to its limits..otherwise not really. That's applicable both for shock rod length and front arms position.
If you know you're using the suspension fully then you should get shorter shocks and keep the wishbones parallel to the ground.
I for one am not using it fully and by using stiffer springs and larger sway bars limits the suspension travel and so far I've been ok...about 10 years I guess.

Strangely enough my wide track (951S) suspension on the red GTS wannabe keeps the Carrera GT alignment specs even with 225 tires on 9" x 17" wheels(same diameter as original) but that car is not lowered that much compared to factory(front a-arms are still parallel to the ground)
However, my other 924, the 931 is lowered more and as I said, if you exaggerate the lowering you will get more negative camber in the rears that you cant dial out.




I'll list the suspension modifications on both my cars and my personal opinion on how they work and feel compared to the factory ones, perhaps it helps you.


My 931(ROW 924 turbo S1) (street driven sports car - fast road driven)
steel rear arms
steel front arms
factory 23mm front sway bar
factory 14mm(?) rear sway bar
250rate front springs (significant amount lowering springs)
no coilovers on the rears, just reindexed torsion bars.
205/60/15 Dunlop SP Sport tires on all 4 wheels.
track width front and rear are equal, so the rears are no sitting in any more than the fronts.

This car can only get 2.5 degrees of negative camber on the rears, no less is possible. It uses factory wheels and factory size wheels and tires.
It is lowered a hefty amount, a bit too much to be honest as on some rare occasions on some slight jumps I can feel the rear suspension (lower spring rate than the front) bottom out and seat on the safety suspension travel stoppers (big rubber dampers).
Compared to a factory 931/944 this car offers a bit higher cornering speed capability while still retaining a neutral to safe (slight under-steering) behavior. It feels planted and corners great but still has a good amount of body roll. The ride is still comfortable(compared to the factory setup) but the car is almost too low to use on the road.







My GTS wannabe (ROW 924 turbo S2) (street driven sports car - fast road driven)

steel front arms
late offset aluminum rear arms
29mm front sway bar
14mm rear sway bar (I have a 19mm one but I get less grip with that one)
280 rate front springs on coilovers using factory shocks.
200 rate rear coilovers added to the 21mm factory torsion bars.
225/45/17 Conti Sport Contact 5 tires on all 4 9" wheels.
Rear track is a tiny bit wider than the front (GTS rear panels)
This car can keep the 924 Carrera GT/S alignment specifications.
It rides a lot harsher than the factory setup and feels a huge lot stiffer, its almost too harsh to use on the street but still acceptable.
It corners a lot faster than the factory setup(of any 924 or 944) and has a perfect neutral behavior regardless of the situation.

I'm happy with the mods on both cars but I'm not racing or rallying either of the cars. I'm driving them fast on the twisties but that's about it.

924srr27l

Interesting,

Front
What make shock absorber Inserts are you using in the stock legs?
Also 250 Lbs 2.25ID or 2.5ID race coils ? on adjustable platforms?

Rear
The additional Coilsprings added to the stock 21mm T bars which are approx 95Lbs totals a combined rate pf approx 295Lbs compared to the front which is approx 17% less at 250Lbs.

However the motion ratio of the T Bars (0.6?) is different to the coil springs (?) which will give you the Wheel motion ratio but it would seem the rear rate is harder than the front in general and this could be why anything stiffer than the 14mm sway is to stiff and traction suffers?


I've currently got approx wheel rate of 170 front / 135 rear and hence I have a hint of understeer, so I need to stiffen the rear, or stiffen both with different ratio's.

R

morghen

I use 280 springs on the fronts of the red car not 250.
I use 250 springs on the other car(silver over blue), the 931.

My red 924 came with 23.5mm torsion bars, that means 70Lbs effective spring rate...so I use 280Lbs front springs which on a McPherson is the effective rate and 270Lbs rear effective rate of the torsion bars + coilovers.
So 280 fronts, 270 rears. The rear shocks are adjustable so I tuned them to a balance between ride quality and grip in the conditions I usually use them.
That's spot on in my mind with the 51/49 weight distribution.

Like I said, I don't need a thicker sway bar, especially with this engine's torque output style which is a bit explosive due to the massive K27 pumping it. Grip is just perfect the way it is and there isn't any significant body roll, as visible in the above picture while I'm cornering on the Silverstone Porsche experience center circuit.

For the fronts I use the OEM rebuilt shocks, the ones that come from the factory that are serviceable. You can rebuild them as you wish, use thicker oil, revalve or whatever. I just had the oil changed as everything else was in check.
On the factory strut I use adjustable platforms and 2.25" coils, I need those to clear the 9" rim and 225 tire.

If your car is very light 170 /135 is probably very good but you could use some stiffer ones on the rears as well.

924srr27l

Ok I wrote 250 instead of 280 front coils, so your using the stock Sachs? struts but with springs twice the standard 931 rate of (140Lbs) I would of thought they would not of coped so well but you would be better with a Gas Sport insert like Bilstein or Koni, unyet for sure the photo at the Porsche Centre Silverstone suggests a flat body control.

I think or thought the Motion ratio's differ for the 924 and later 944 because the wishbones were longer and also because of the strut angle and wishbone length the actual Wheel ratio is like .8 and .6 on rear T bars of the actual spring rate?

Clarkes Garage list the 23.5mm bar at 126 Lbs unless your 70 lbs is already the calculated actual rate due to the trailing arm leverage.?

I'm not 100% sure a Coil spring wrapped around the rear telescopic damper is also a direct poundage rate? or if this also has a percentage like .8 ? etc...

It would be good to know and clarify this (Anyone ?) So the OP, and I and anyone else looking at lowering and changing spring rates can use this info..

This is why I didn't go too stiff on the rear and a 27mm Hollow T bar @ 220Lbs less then ratio of .6? would be a wheel rate of 132Lbs ? which also gives my rear end good compliance for great traction although I have the beauty of Normal aspiration and no sudden surge of power like a turbo engine.

Combined with a Mechanical Biasing Wavetrac LSD. These 3 features allow me to run a lightweight wheel & Tyre 205/55/16 which does not have any wheelspin or loss of traction issues.

R

morghen

Well I don't do a lot of miles with that car but still it has some decent mileage with the current setup and the shocks seem to be fine. I plan to replace them with more modern cartridges as soon as they start to fail.

When I did the rear coilover upgrade I also looked into the fact that the shock mount position affects the effective spring rate of coil over the shock but eventually lacking measurements and time to do them I gave up the calculation and ignored that aspect.
I approximated that in the worst case scenario I'm getting a 10-15% lower effective spring rate and really worst what could happen is the need to replace the rear coils for stiffer ones...which would cost me lunch money and 30 minutes of wrenching.

I always try to be aware of what is the level of detail that's worth going into for a specific modification before investing too much time and money.
First get a feel of the situation, do some research, some calculation if capable, some tests if mods are risky and then take a step back and see how serious I have to be about the subject before fully commiting.

Like I said, I'm quite happy with the result. The car feels fresh, brisk but not jumping around....it feels somewhat comparable to a new sports car(except heavy steering).
This is obviously a brag but the Porsche instructor that was sitting in the passenger seat that day at Silverstone said the car handles great, stays flat and feels fresh.

Here it is again sporting that sexy GTS ***...I miss driving and looking at that car...will be visiting the garage this week for sure

Noahs944

Sounds like a well engineeredlightweight package!

Noahs944

Big M,

Thanks for the cool pics. Red car does look flat in the corner.

This makes me wonder about the 7mm spacers I see advertised. What affect do they have on the car?

Noahs944

WOW! C,B & J... such an inspirational thread!
http://straightpipe.ca/forums/showthread.php?t=2454

Brockoli

You forgot E for Erik