DuncanG

Exactly the problem I had Dave.

Damping or the lack of it is not the only problem though, there is very limited bump travel available with the springs you have and the bump-stops are virtually useless owing to the design of the top spring cup.

Have a close look inside your front wheel-arch and see if you've had tyre-body contact. Increasing the ride-height will reduce this contact but replace it with coil-bind which is even worse. I gained about 20mm of bump travel by throwing out the helpers and using 50mm longer springs. Longer bump-stops will also help.


It doesn't seem to be sinking-in that I tried that Graham. There's no point in upping the spring rate if the dampers cant cope with the rebound. Your point about compressions is quite valid if you're talking about a banked circuit or some other scenario where you have long duration compressions. For most of us compressions are a transient event where the (fast) compression setting of a damper plays a large part.

The bottom line is that with 28N springs and AGX shocks I had less problems with bottoming than I did with the ASTs on 50N springs. My latest suspension uses 45N fronts and is far more resistant to bottoming on compressions than either of the other 2 setups. So its not all about the springs, to paraphrase Gordon Brown 'its the dampers stupid'

Somewhere in the ASTs there's a decent damper trying to get out, but they need work IMHO - but if they work for you as they are thats great.

ZEN Performance

I would second Duncan's comments, he has summed up pretty much what I felt. The high speed damping was certainly low, as the car felt very smooth on the small sharp features of the road.

I am no expert on suspension, but being able to go from 57N/mm on the front to only 40, and finding better comfort (logically) but also better control was impressive. However, how you can get that sort of performance for under £1000 I don't know at the moment, I haven't tried the Tein product range which looks favourable, especially as it has UK centric support.

Paul

911

Perhaps I'm missing the point as I'm looking at a different set of conditions..?

My car has never bottomed out and seems to ride the bends that are changing direction and camber change at the same time.
Those who have seen or preferably driven the 'Pardon' bend at Prescot or the 'Keepers' esses at Loton will be able to understand the corners I'm judging the car on.

In these very tight bends changes happen quickly along with a desparate desire to keep the power on as much as possible to gain a fast hill climb.

I'm not trying to delve into the AST's technicalities, just can I find a setting (springs or dampers) that give me a fast chassis in a space where a tail slide can wrap you round a tree.

Cost is an important part here too, and understanding/accepting that these AST's are road spec units.
Anyone who has bounced around on AVO's at £650 3 years ago cost will find these units a revelation. Squeezing more from fine tuning them is good fun.

Great debate and good to read other views too.

Very interesting subject.

Graham.

Floyd

iTrader: (9)

I've tried Tein around the Ring and it was horrid - don't bother IMO. The price is important Paul and SS Nitron kit is going to be too pricey for many at £1500 and £2100. For the time being AST does well in most road situations and far better than OE on track, so it is priced quite well considering.

The Ring is an extreme track. They bottomed at Foxhole and Karussell but this is not unusual as some exotic cars I've been in do the same there too. The tyres definitely made contact with the arch liners but the bottoming could have been less so. The compression at foxhole didn't unsettle the car but it is an unusual feeling for me.

I have read that it is acceptable to use bumpstops as part of the suspension system - is this true?

F

DuncanG

Modern bump-stops are made from polyurethane foam so you should'nt be able to tell whether your touching the stops or not. In my current setup I probably only have 10mm travel before touching. The important thing is that on full compression the stop should be fully compressed.

The AST design flaw I was referring to is that due to the shape of the top spring cup there is a void inside the cone that is unreachable by the strut but which is big enough to accomodate about 1/2 of the stop uncompressed. The result is that the stop is not fully compressed before metal-metal contact. The other factor I was referring to is that if the ride height is set marginally too high then the springs will bind, again with the stops doing little. The vendor should provide a maximum height for the lower perches to avoid coil-bind on full compression, but of course they don't. The most effective bump-stop you have is probably the tyre contacting the bodywork, like this:



Note the tyre against metal, not just the plastic.

They could be better without costing more, thats the frustrating thing.

911

Once onto the bump stops you are in a difficult position as the spring rate suddenly rises (solid rubber stops) and the tyre becomes the sole suspension .
Metal to metal is alarmingly worse in my opinion and experience. The AVO's bottomed out in the first fitting as they were supplied without any bump stops (or brake hose brackets)

So what to make of this?

The purpose of this thread is to help PowerStation develop the AST's into a robust value for money coil-over system. I know they read every entry on this thread and are discussing this with the dutch supplier.

It all improves the breed.

Graham

Aztec Performance Ltd

iTrader: (234)

Graham. Sounds very tempting. Money is tight at the moment (after splashing out on the new box) and is the only thing keeping me from giving it a go. Let me know when your near the Mids or Herts and I'll will try and pop out to see you.

I run Tein Type HAs on mine and find them to work well. In saying that I can only compare to the OE suspension as I done the sus upgrades at the same time (coilovers, drop links, adj ARB, fast road geo). It is on the firm side but takes on my fav backroads very well. Need to be careful for bumps on unknown backroads though.

Bob

911

Bob!
Next hill climb is by Cheltenham, so not that far from you.
About j8 i think off the m5, the one south of the M50 junction.

Sounds like your set-up might be a bit stiff? (for hill climbing).

The 2005 season is nearly over now, but 2006 starts in April so get saving

Graham

911

Back from PowerStation's very busy Open Day...an awful lot of cars there, and the Litchfield Sti's were realy nice, even the wife fancied one (Forrester).

The hill climber went onto the RR there, and this is the second time the poor thing has been run on a RR. The first was at Well Lane in May, a very cold damp day where it cut 360/380/407/392 and 385 on the 5 runs.

Today it cut a solid 368.4 bhp and 402.1 Nm torque (that will please Floyd) and if David Wallis is reading this lot, you were right! This might explain why the gearbox is surviving and why I'm a lot slower than the 450 ish EVO...

From the readout the small dip in the torque is still there (turbo boost falling at 5100 and settling at 6K) but peak torque is at 5090 rpm and peak power at 7505 rpm.
Nervewracking but NICE.

Doubt it was the most powerful there but ran very crisply and suffered initially from tyre slip on the rollers. Curtis and the rest of the PS crew seemed impressed.

The car has the important bits on now, the 60/50 springs, and I wound the damping from 7/12 front to 9/12 and the 5/12 rears to 7/12 to compensate.

The drive home was over the M5/A grade dual carriageway and some of the worst West Mids roads around Stourbridge, so a good first test.

They are much harder than the 50/40 in reaction to the road, but certainly not in a difficult way. Manhole covers and bridge joints are easy, but scooting round islands is sublime.
The stiffness adds to the anti roll bar's effect and the steering is much more alert. I have this kind of set-up on my old hill climb 911 which I drove a lot yesterday, and the sensations are the same.

The NVH is a lot worse, the car 'zings' a bit at speed (ie 90 mph) and chimes-in at 45 mph too. Not too harsh but not as smooth as the 50/40 springs. Remember this car has no rubber anywhere on the chassis.

I think the front needs another click or even two, will have a play over the weekend.

It will be very interesting at Prescot hill climb next weekend to see how it behaves as the hill has a real mix of sweeping curves and super tight bends all in a 1/3 of a mile, and it takes me about 48 seconds to cover it all from a standing start.

First impressions are now:

Compromise of fast road/hill climb = 50/40 springs with 7/12 and 5/12 damping.
Compromise of hill climb/fast road = 60/50 springs with 9/12 and 7/12 damping.

Saw all the other AST units there including the killer race units albeit in Gravel stage spec, the tarmac ones will be another dimension, and grounds for even more debate!

Just a few pics for you:
General views before the crowd decended



I'll have the ones bottom center...if you turn this pic 90 deg clockwise.


And a snap from Shelsley Walsh, the first hill climb car ever in England (1905!)


As ever, many thanks for the support from everyone at PowerStation, lets hope I can chase that EVO next weekend...now, Curtis was on about Race Fuel for the odd weekend bash.........it's illegal in hill climbing!

I need/want a 2.5.

Graham

ZEN Performance

As I keep telling you. race fuel which complies with the British standard is not illegal unless specifically forbidden (by a may RON/MON rating).

Does tesco 99ron count as race fuel?

Do your research, run the best fuel you are allowed.

Paul

jasonius

iTrader: (1)

Hi Graham, what time were you at PS today (early by the look of your pics) and what time did you get on the rollers..?

I got there at 9am and was 7th on at ~10am, hung around till 12 noon (bought an ARB) but didn't see your car there, not that I'd have know your face. Suppose there were a few off SN, I probably spoke to some without knowing. I saw Shaun's car there, can't miss it really..!

Good day and very nice setup they have there. The 06 looks a lot better in the flesh..!

911

I am Paul. For the Championships the Blue Book says the fuel used must be commercially accessible pump fuel, thus Optimax etc. Any other fuel is from a 50 gallon drum.
I've checked this with a C of C and he agrees. The race fuel I refer to is a real 'petrol blue' in colour and is not allowed in the Class in the Championship.

Graham.

911

Jason: Got there about 11.30. My car was on 'display' on one of the ramps. Managed to jump the RR line-up and got on the rollers at 2.30.

Any idea what was the highest bhp?

The little red Honda Civic pulled 330 bhp!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!

Great day. Bit dissapointed with the torque of the car @ 295 Lbft (402 Nm), but 370 bhp was better than I had hoped.
You are right about the 06 model, better when you see it, but still a bit of a 'blob-eye' imho.

Trying to chat the wife into a 2.5/Zen gearbox...

Graham.

ZEN Performance

Perhaps you just need to intepret the rules differently.

Commercially accessible = Anyone can buy it.
Pump fuel = comes from a pump, somewhere.

You know you can get come "race fuels" from permanent pumps in some places.

Paul

911

That's how it is done Paul, but the facts are is is not allowed, just badly written in the Blue Book. Still beat the guy who runs it though
Graham.

DuncanG

Bumpstops:
Graham - does anyone still use hard rubber?
Floyd - I came across this writeup on foam bumpstops

911

Old Porsche's!

The AST stops in foam are very compliant, but as I have said, never got that far down in any condition including the alarming 'off' at Loton Park the other weekend. (bouncing off the deer park terrane.)

Graham.

Floyd

iTrader: (9)

Well done Duncan, this must have been similar to what I have stored in my brain

'The bumpstop has been replaced by a supplemental, active foam rubber spring, which is one of the essential components in the suspension.'

F

911

Bumpstops are there to stop metal to metal impact, not to be part of the working suspension system!
My AVO's came with nothing which is no surprise, and the 911's were 75 mm long....

Graham.

Floyd

iTrader: (9)

I think we'll have to disagree on this one until someone can convince me otherwise.

F

DaveW

The bump stop is an integral part of suspension these days. My brother (who develops damper seals) recommended;

1. Raise the ride height - Done, need to test it.
2. Fit harder springs - Don't really want to go down this route as it feels hard enough already.
3. Try longer bump stops

Not sure I'm willing to go through the same stages as Duncan to get to the same result. So I think I'll live with them as they are for now.

As an aside, I had to take the fronts off to fit new top mounts and they cleaned up really well apart from the springs (paint flaked off). Not bad I thought for being on just over a year with minimal attention.

Dave.

911

That is part of the AST offering that people do forget. The build quality is really good; my old AVO's were bare metal from NEW, and all the collar threads were rusted making ride adjustment after a month near impossible (galvanic corrosion between bare aluminium and bare steel)

Taking the bump stop thing a bit further:

The springs on the units take the normal dynamics of the car over hill and dale in a smooth progressive 'linear' manner.
When the bump stop is contacted the cellular material starts to compress and will dramatically increase in resisting compression.
If the bump stop material compresion rate is greater than the spring (hard to believe it is) then it will add to the overall spring rate at the last 10mm or so of movement.
I don't think it is wise to use this characteristic as part of the package for good cornering.

If the stop was solid rubber then the effect of bottoming out is truely startling mid-way through a fast bend

Graham.

ZEN Performance

I have always read that the bumpstop is a crucial and integral part of the springing.

911

Paul, I think it would be when the suspension is that far compressed, as metal to metal contact changes the spring rate from, say, 250 lb/inch to infinity in less than a hairs breadth of additional suspension compression. A modern progressive (ie substantially compressable) bump stop cussions the transition by adding to the spring rate before metal to metal contact of the piston in the tube.

I ran my old 911 with the suspension very very low, ground clearance was 40mm at rest.
Around some bends (on track) the suspension would meet the solid bump stops and the change in the car mid-bend sent me into a spin and very nearly into the tyre wall at a local sprint.
Car never did it again when I cut the bump stop length in half and cross drilled the rubber section in the rear dampers and raised the ride by 15mm all round, the way the car is today.

I learn't the hard way.

Graham.

Chavsrus

Am I right in thnking there are actually two types of bumpstop

Grahams. Stops internal damage to damper rods and valving by ensuring the damper assembly is not compressed sufficiently to cause the above, and as Graham correctly says, plays no part in the springing of the vehicle.

Zens/ Floyds A progressive bumpstop can be anything up to 4-5" long and does the same as above, but as Floyd and Zen correctly surmised, is also used to provide a progressive increase in spring rate towards the latter parts of it's (the springs) compression

You're both right.......... sort of

Any jobs going at the UN

911

LOL @ Chav!

Get over there and sort this bloody world out!

Nice summary, and and interesting one too.
The debate is good and healthy...but I think I'm right

Good job I'm not looking to be a diplomat...

Graham.

Chavsrus

Graham

Agree with me or sanctions will be imposed.
(Supplies of NF will be rationed forthwith)

Back on topic, are you going to be at Prescott on Saturday and Sunday ?

911

Yes.
Sat is practice day, Sun race day.
I'm the only Impreza competing...
Graham.

911

What a day!
Practice today, 3 runs and the track cool and dry...nice.
Car went fabulously, the stiffer springs were surprisingly good, much better than I had hoped for, and gave a lot of confidence on this very twisty but fast hill climb.

I took the front damping up another click (10/12 from soft) with the rears still at 7/12.
This stopped the bobble sensation on the front while the rears stayed still, and the car steers again so much better.

This combination is a Track Setting for sure, but drove really well this morning as I drove straight past the front door of Powerstation !

As for the times:

First run was a solid 49.05 secs and a start of 2.15 secs to the 64 foot line.
Second run was a cracking 48.4 @ 2.14 start and the 3rd run a stunning (for me) 47.74 secs @ 2.12 start.

The same car at the same track in the 'same' weather this year was 2 seconds SLOWER with the dreaded AVO's on!
This is the difference this package has delivered this year. The car is confidence building. No hero sideways driving, no 'last of the late braker' and boy racer antics, just solid flowing runs, leaving you with the feeling there is more to come!

Racing tomorrow, so for real and racing for points.

The EVO is still ahead of me with a lurid 46.2 sec @ 1.95 start but i am actually faster than him in some sections of the track.
The Nissan GTiR is stuck in the 50's thank god, but may change tomorrow. We will see.

I do realy need the points from a win, but I cannot see me doing a very low 46.
If I'm second, then the class will be his (EVO) in the Championship and I can't catch him.
However I have now clinched the Class win in the Leaders Championship!

During lunch we went to see and try the Litchfield Type C, the actual car in this month's EVO magazine. I was given a chance of a drive , and (sorry Ian) gave it a bit of a run (still in hill climb mode) what a fab car.

The steering just is fantastic, the ride nice and 'robust' but the engine....

The response, the pick-up, the howl and the pace (4 of us in the car) was really impressive.
Great car, I hope my friend buys one!

Hope it doesn't rain tomorrow as my Kumhos are bald on the front...

Graham

LitchfieldImports

Nice to seem the improvement in times Powerstations work has helped with

Glad you liked the Spec C, ypu will have to call back in a couple of weeks and try it with the Milltek and other tweeks

Iain