Searching for the perfect Chassis
 

A new thread for me and this is a natural follow-on to my quest for a strong engine for my hill climb Sti v3.

I have to say a very big thankyou to Power Station for the opportunity to help develop the AST suspension systems for the Impreza.
Out of the blue they have asked to use my roadgoing hill climber to get real-world feedback on their products.

This thread will be a detailed account of how things go over the next few months through the trials of the West Midlands highways and byeways as well as the chase of the precious tenths of a second in full-on hill climbing in the Championships I'm involved in.

So, what is the plan?

1
Remove the nasty AVO coil-overs off the car. They have done 3 years duty (about 8K miles) and look it.
2
Fit new road spec (with stiffer springs) AST units that anyone can buy for their car.
3 Develop the system/alignment to find the very best set-up for the car and it's 'activities' and to let you all know the findings.

I have to admit to enjoying Chassis engineering to engines as a top chassis is paramount over BHP for a dash from A to B (if there are bendy bits). I have a great engine and a good chassis, but there is always scope to move forward.

The first step was taken today at the plush new premises of PowerStation, located very close to the M5/Cheltenham/Tewksbury junction.
After meeting all the guys there it was straight to work for Curtis, the engineer who will follow and develop the progress we make. Curtis is a proven 911 fan so obviously a Good Man.

In pictorial form:

Car goes on the dead level ramps for surgery:
http://tinypic.com/9kuk49.jpg

Off comes the AVO legs. The rear units were buggered, completely shot!
Here is a comparison shot, old and new.
http://tinypic.com/9kulw5.jpg

A general shot of the existing suspension:
http://tinypic.com/9kumhu.jpg
http://tinypic.com/9kumtc.jpg

Curtis was very carefull to ensure all the parts came together well, but kept the existing MRT top mounts. They give excellent caster positioning as will be evident later.
He usually works in a normal position, sorry, what he saw of the old units sent him giddy..
http://tinypic.com/9kuoow.jpg

The detail and engineering of the AST's has to be seen. Precision come to mind as a description, and they are clearly a quality product. The mountings for the strut/hub is a replica of the OEM design, welding is aerospace quality and everything simply went togerther with zero fuss. Well impressed.
http://tinypic.com/9kv2no.jpg
http://tinypic.com/9kuq1t.jpg

Once all together and in place the alignment started:
Installation
http://tinypic.com/9kurv6.jpg
http://tinypic.com/9kus7q.jpg

Curtis looking happy:
http://tinypic.com/9kusn8.jpg

On with the German alignment gauges. This system was newish at PowerStation and is State of the Art. With this the car was aligned to within a handful of minutes of a degree or actually spot-on with no left/right deviation.

A bonus was that the car had no bumpsteer variances when measured under high front end suspension compression/extension.

http://tinypic.com/9kuuxj.jpg
http://tinypic.com/9kuv60.jpg
http://tinypic.com/9kuvdl.jpg

Curtis managed to get the top mounts in a position to maximise the caster (nearly 5 degrees) as there was enough scope in the camber bolts to dial-in the camber of 2.5 degs.
http://tinypic.com/9kuvtd.jpg

Quite a long day's work (for Curtis) and for all the others at PowerStation putting up with me in their way.

The acid test is always in the drive home....(45 miles of it)

Yes, exactly as you expected, a really superb transformation.
The springs Curtis selected were 50Nm front/40 Nm rear and these are slightly softer than what came off the car, and on the road the car is better for it. The provisional damper settings (so easy to adjust) are almost there out of the box. They are quiet, smooth and ride the usual motorway/A roads/B roads and some nasty roadworks locally really well.
I will have a play with the fine tuning over the next week on my 'test tracks' and see if I can tune the last bit in.

This will get me ready to try them in real anger at Loton Park hillclimb (my local) in 2 weeks time when they and I will be under pressure from the Cossie turbo developed by Mr Turbo Dynamics himself!
Why do I get the tough ones all the time?

Finally a big thankyou to Power Station, and I hope you will all enjoy the road to the Perfect Chassis!

Graham :D

Variety is the spice of life:
http://tinypic.com/9kv2wn.jpg

Excellent little write up.

I will be watching this topic for the results, good luck!

Good to chat to you yesterday, good luck with the new setup.

Phil

Good meeting you too. Listening to your 'love' of your Type 25 didn't do me any good!
Graham :D

Graham

when you have your next visit to powerstation, you must have a go in the T25, the grunt is incredible.
Andy

No, don't tempt him! ;)

Graham,
I know the sprinting/hillclimbing is about speed, but have you ever thought about better brakes??

Had a chat with Rich @ PS while I was there.
He will be doing some BIG brakes soon (saw them) and argued the same as you.
Hill climbing is a strange sport.
On my local 1 mile long hill (Loton Park near Shrewsbury) I brake 4 times hard and 2 time as a 'reassuring tap'.
They hardley get hot (as in blue) BUT Rich would say that the smooth retardation gains you those elusive tenths...
I need a set of slicks and a ppg gearbox first....and then the 2.5......

The brake Group Buy will be a bargain, but I'll let Rich do the deal!

No one will be dissapointed with the product.

Vulnax...I'm just a poor Sti v3 owner! But they do look great.

Graham :D

Powerstation don't fancy developing a kit for the Cav Turbo do they? :norty: :D

Noticed the brakes myself, susprised there wasn't even a mild upgrade there? Surely a test-the-water £300-400 upgrade could be squeezed in before the slicks?

<thread notification on>

Glad you got this job Graham, I'll be watching with interest.

<thread notification on> too :D

Hey: I'm just the test dummy! (probably an apt description as those who know me will agree)
Carl: Now I've met Rich, I am sure he can adapt the brakes to ANYTHING with a bit of thinking!
The only mods I have to my brakes are vented rear discs and Green Stuff pads which do absolutly nothing IMHO to the brake performance.
Anyway, to go fast on a hill climb you leave the brakes alone (yeh, right) I'm told.

From those who have done it, the slicks on a 60 second hill climb can give about 2 seconds if you use them (ie go faster into the bends). I am about 2 seconds behind the EVO, and at £800 a set it must be the next set for next year.
My beloved Kumho's are getting almost bald now, so are nearly slicks anyway. :D
Even the wife thinks this is the next step, but asked today at Silverstone what a 'ppg gearset is'.
I must be talking in my sleep...:norty:

Graham.

LOL @ PPG comment :D

Good to see you are back on the improvement trail ;)

(knew it wouldn't be long! :cool: )

also noticed the brakes at this end and was very suprised

lol @ nthe reasuring "tap"

do you every wonder if you really need it?
and did you see many gains going from the 16" wheels to the 17" ones on the stages?

I went to the 17's from my stock gold 16's and Kumho medium grade 2 years ago, and all was well.
However, I wanted some super-soft Kumho's and you can only get these in 16's or smaller.
I did that and really noticed that the lighter 16's were much better, and the tyres didn't offer that much more grip, but the dynamics were much improved.
I've swopped about several times and get the same feeling.

The 16's are very dark grey and look better than the bling (nowadays) gold rims.

This is the issue with the brakes of course, the PowerStation Big Brakes only fit under 17's or bigger.
Only notice the poor brakes on the road, not the hill climbs, but lost them totally once at a double-lapper sprint when the discs turned blue...:norty:

Real hill climbers don't need Brakes (but a tap or 3 helps a lot :D )

Graham.

I must admit, I had assumed you were running AP's Graham.

As I've said before, if you need BIG brakes you're using them too much before a corner :D

How do you find the pedal feel on the Subaru OE brakes? Mine have always been a little soft although they've always stopped the car perfectly even after some serious thrashing :)

I fitted stainless braded lines ages ago and the feel is very good, locking of the brakes is never an issue although the ALBS is strange at times.
I'm not that fussed about the brakes as I don't blast on the roads, only on the hill climbs, except when 'testing' :D

Graham.

Graham,

What ride height front and rear are you running with the AST's?

Dave.

Dave:

Rolling diameter on my car = 595mm front /rear, tyre pressures @ 30 psi

Front height from road to apex of wheelarch = 615mm
Rear '' '' '' '' '' '' '' = 600mm

Note! Car has 1/2 tank full and nothing in the boot (inc spare tyre)

hope that helps.

Graham.

Graham,

:) Not really :) I only asked as my car needs its ride height sorted out (also running AST's but on a road car).

I was told to run the ride height 5mm higher on the rear (wheel to arch 45mm on the front and 50mm on the rear). Are those the settings that Powerstation set it at or did you specify what settings you wanted?

Dave.

Curtis set thm on the bench prior to fitting on the car.
I have the spring rates (50/40) off a V7/V8 Impreza (heavier car) so on my Classic, the spring rate is a little stiffer for the Hillclimbs.
I wanted the ride height to be as before which Curtis measured before the swop.
I have it at this height as i feel there is enough travel in the drive shafts/CV's on full suspension deflection, and i can get my jack under the engine subframe for easy wheel changing!
Graham.

50/40 Nm spring rates are near as dammit 275/225lb, the same as the original Leda B kit, which was later upped to 325/225...

Mine is a little over done now at 350/275 :rolleyes: However I've now raised my ride height by around 15mm all round giving me 340mm from the wheel centre to wheel arch on the front and 345mm for the same measurement on the rear. I was also advised that to make an Impreza turn in better and quell understeer aiming for 5mm greater ride height at the rear to give positive rake would be of benefit.

Cheers, makes more sense now.

Dave.

This is the point of the exercise with PowerStation; to develop the units to be a good compromise for the application stage by stage.
Too stiff on the road can be slower and also too soft so to find the sweet spot will take a number of iterations as I originally found on my AVO's.
The 'nosedown' rake is also in the car, but where to measure it?
Any ideas.
the 911 must have a 1 deg nose down rake, and the measure point is along the sill itself so very easy to do, but not sure about the Impreza.

At the last hill climb I dropped the nose of the Sti by 6mm as I felt the rear had dropped and the car was awful. At just 6 mm i can't imagine that the toe would be changed too much, but the car was bad in high speed corners.
Took it back up and all was well. Just shows how sensitive the car is to a small change, borne out by talking to Curtis at PowerStation.

Weekend after this one will be a full-on hill climb that I know well and usually do well at, especially if dry or streaming wet.
I don't change the car's settings for weather changes as many do (softer in the wet) so can't wait to see how the times are.

Graham.

good job curtis

Curtis was pleased with the whole chassis set-up really as it came off the ramp.
The car looks 'square' on the road and drives arrow straight.
Going home on B and A roads the ride was very good, but must add that the boot was full of tools and all the hil climb stuff I take.
Obviously the boot is empty inc the spare in race trim and the rear will rise slightly.

I will give the car a good run over the weekend and give more detail to the settings and the impressions overall on the country lanes.

Any ideas on the rake angle and where to measure?

Graham.

Re Wheels & brakes - hillclimbers normally have relatively small wheels to allow the tryes to build up heat quicker and get the chassis as low as possible. As 911 has said, you don't really need brakes as a) you only use them rarely and b) you're going uphill. People tend to crash when they use their brakes!
PS. I believe Hoosier do slicks especially for hillclimbing & sprinting that don't need warming up much.

Indeed they do. So do AVON.
Both work straight out the box and are super soft.

Pity they cost about £200 a corner.
The demon compounds are not available in 17's or above. Another reason for 16's or less.
My Kumho's are a rolling dia of 590mm new, and the stock radials are about 620. Improves gearing/weight and accelleration/brakes.

Lot to be said for 16's.

Graham.

with a good sunny day I took the Sti into (almost) Wales and to my Club's hill climb track close to Shrewsbury.
This takes in a motorway, A roads and a B road or three so a good run to check-out the new AST's.
Curtis set the car the way he thought was right, and these settings are very close to the Whiteline specs I've run now for 3 years. A little experimentation is a Good Thing.

The settings are:

AST's with 50 front and 40 rear spring rates
Rear spec:
Camber, negative 2.25' deg
Toe, Zero

Front:
Camber: negative 2.30' deg
Caster: 5 deg @ 20 deg turn
Toe: Zero
Bump steer: Zero!

The damping setting was 5 clicks/12 from Soft on the front and 5 in the rear as we were not too sure when we set it up how to match the spring rate and the weight of the car.
The front seemed a little 'bobby' to me, just a bit bouncy on all roads at the front.
Rear seemed just right.
Chatting with a few friends at the track today (had to replace a piece of Armco flattened by a single seater last weekend) we thought a softer damping rate would do the trick, so changed both ends by 2 clicks from max soft.
Now this is 3 clicks into the 12 clicks available, but the difference was very noticeable, and better for it.
Embracing a few demanding 180 rights was a revelation (right on the outskirts of Telford); the car ran so true and so flat compared to the cr@p AVO's ....
Scared the hell out of the Cavallier (sorry Carl) as I over took around him at quite a speed without any drama; no skidding, no over/understeer just went straight round..sooooo good! :D
Took the car for a little drive through the Hill climb track also and it felt good, but couldn't take any speed as the Deer were out in force (!)

Tomorrow I will take the car to around Shelsley Walsh and see what the lanes are like there. I've wound the damping to 7/12 from soft so to see what that does.

The only issue I can see so far is a real vibration at 100 ish mph (indicated) where the roll cage in the car goes into a frenzy :norty: This is rather like a wheel or two well out of balance, and wasn't there (to such an extent) before the change.
This might be a result of the damping/springing, so tomorrow will be interesting to see what 7/12 does to the vibration.
I'm not at all sure if this is the suspension or going back to the 17's and old Kumho's which are past their sell by date.(by about 3000 miles)

I have to say the car is Ballistic. Just so bloody fast in the straights and the bends (now) and I wish I was on slicks for next weekend, but a holiday to Nice is just booked and a visit to a French fortified town in early September....with Porsche RSR's and Bugatti and such like racing round the Ramparts ! Wow!!

Bet this STi would catch'em! :D

Graham.

Graham, just had a run in mine and I've wound the front down a click to 4 with 4 on rear as well. The car is less choppy on the front but could do with removing a few clicks on the rear as well. The car feels so flat in the corners, like a go kart and so chuckable - real fun :D

I'll try full soft to see how comfy it gets for the kids but at the moment i'm exited and having fun.

I'll be with the old timer cars at the Ring soon too! Snap!

Have fun Graham.
F

:D

Nice to see how you're actually going about setting up the suspension Graham. :cool: Adjustable dampers are something that's completely new to me (i got as far as H&R's and geometry on the fridge) and i've always wondered how and when to tweak them. It'd be interesting to see if an even more 'sorted' chassis creates a step change in sprint times?