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Talking With HSV's Chief Engineer - Part 1

Part One of our interview with HSV's Number One engineer...

By Michael Knowling

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In Part One of our interview with HSV's Chief Engineer - John Clark - we discuss suspension, ride and handling...

How many engineers work at HSV?

Currently we have twelve engineers, with the support of another five CAD designers. Things are going great guns for Holden and HSV at the moment; we've got lots happening. When I started at HSV ten years ago, we were looking at a model every 18 months - and that may have been just a Series 2 upgrade. Now they're doing coupes, long wheelbase and everything else - and they're happening about every 6 months.

We've road tested the SV300, Clubsport R8 and GTO Coupe and been impressed by their ride quality. Is there a specific ride standard that HSV aims for?

One where your fillings don't fall out!

We don't have a list of things to tick off for ride. At this point there's not a good correlation between using accelerometers or G-sensors and the feeling of a certain ride. We go by the feeling - that's what important.

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You can say for a good riding car you have a certain speed of deceleration and acceleration as you go through a bump - but that doesn't take into account what the person feels. What's important is the result of the overall package - the padding of the seat, whether the steering wheel jumps around and so on.

We focus more on different people driving the car and putting some kays on it. We also get a lot of feedback from our previous customers - we have a yearly survey that we do and we get heavily involved in HSV Owner Clubs.

Ride is difficult to quantify. Handling is different; you can go by the time it takes to get around the ride/handling track at the proving ground, you can measure how much body yaw there is and how much compression there is over bumps.

What handling balance does HSV set their cars up for?

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Well, look, you don't want a car that breaks into oversteer straight away because oversteer is harder to control than understeer.

Our cars have a very neutral turn-in, mid corner mild understeer and a neutral exit, with the option for power oversteer if required. With the new multi-link rear suspension, if you get half way through a corner and you back off, the car is extremely safe. The rear end doesn't feel like it's going to come around.

Really, it's great that anyone can get in and drive a 300kW HSV safely - and, look, the traction control obviously helps. The traction control will give you a slight amount of slip before it activates and that's it. What did you think of the traction set-up on the GTO you drove?

We thought the system worked fine, but the accelerator pedal kickback was very crude.

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Well, I think that's a good thing because it gives driver feedback.

There's always this sort of discussion about ABS. ABS doesn't need to give you any feedback, but it's important that the driver knows when they have lost grip. In our cars, the accelerator pushes back to let you know you're going a little bit hard and to back off a bit - and then you can step back onto it.

With ABS, though, it's just a pulse through the pedal - your traction control goes 'bang'!

That's just part of the design of the system - that's how Holden designed it. I don't mind the feedback: if you don't like it you can always switch the traction off. [laughs]

The HSV XU6 uses different criteria for its traction control - it goes through stages of reducing spark, drops off cylinders and applies the brakes. The Gen 3 just relaxes the throttle itself - that's the big round canister you can see under the bonnet. I prefer the throttle relaxer, because it gives better feedback to the driver.

Is stability control coming on the SV300?

Ahhh, that's future model stuff I can't talk about. Sorry.

In a recent road test of the Holden Monaro, AutoSpeed's Editor - Julian Edgar - noticed insufficient damping and suspension travel during rough road cornering. The HSV GTO Coupe doesn't have that characteristic - why?

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Holden set their cars up in a certain way and that's what their customers are wanting. I don't know the valve code Holden did or the suspension style, but the Coupe was - for us - very much a challenge because the torsional rigidity is changed from a sedan. The rear part of the car is also lighter by roughly 50 kilos. Initially we thought it should be quite similar, but it was quite different. Put the sedan suspension in and the rear didn't want to follow the front of the car - the feeling of the torsional rigidity was tighter in the rear. We had to balance the front and rear differently.

What kind of handling characteristics were created?

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It was more turn-in oversteer. Mid corner wasn't too bad - it was the initial turn-in. We also use a different steering rack to the Holden Monaro - they've got 3 turns lock-to-lock, we've gone 2.5 turns lock-to-lock. Our customers want crisp turn-in. With the multi-link rear end it's much less likely to oversteer when you back off for turn-in. On the exit, if you want power oversteer that's your choice - that's fine. With a rear-wheel-drive car, that's something our customers like.

We set our cars up with different criteria to Holden - we're about sports handling while maintaining ride. Our suspension engineer who did the GTO was very focussed on improving handling, but also the ride when compared to a HSV sedan. You want something that's comfortable, but able to go club racing or to a driver training day.

You touched on the fact that the Monaro has a relatively slow steering ratio - why is that?

I suppose that's a question for Holden. They've gone in a direction to give the car a particular feel - our aim was to give a sporty turn-in. The difference is between the Monaro and Coupe is definitely noticeable. As I said, the GTO Coupe - and the HSV sedans - are around 2.5 turns lock-to-lock, where the Monaro's about 3.

How much of the suspension design is done on paper or computer?

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I'd say about 30 percent would be done on paper. Once you've got the initial settings you've got somewhere to go. That's when the suspension engineers get out and test it. Somebody commented that one of our suspension engineers had a calibrated bum. But I'm not too sure how we calibrate that - I don't want to get involved...!

How does HSV 'match' its springs and dampers?

The guys we have here use a lot of the shock dyn facilities at the proving ground and we use potentiometers and that to analyse what the car is doing. We also have pull-apart dampers that can be unscrewed the top and you can change the valve codes inside.

We do tests where we do high-speed lane changes. You might do 180 kays on the proving ground and do a very hard pull on the wheel to get in the next lane, and you see how much correction you have to do to keep it in that lane. The proving ground also has a lot of different roads set up to match certain roads in Australia. On the ride and handling track there are tramlines that run across, off-camber corners, different courses of bitumen. They'll even go out and mould potholes - one that used to damage a wheel, or a hubcap used to come off or whatever.

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It comes down to evaluation. In our product group we have about seven or eight members, one being Mark Skaife. We have a driving program, which includes the proving ground and on-road scenarios. The proving ground is good for setting up, but it's very important to get it out in traffic.

After testing, once we're happy, we supply the settings to Monroe and they build the shockers for us.

And what sort of spring and damper rates do you use on certain models?

The full details I wouldn't want to go into.

Later Supplied Information...

The HSV Coupe GTS in comparison to VX2 'Performance' (standard suspension on the SV300):

Front spring - same (linear)
Rear spring - softer
Front struts - steeper compression curve
Rear shocks - reduced compression

Coupe GTO in comparison to VX2 'Touring 2' (standard suspension on Clubsport R8):

Front spring - same (variable rate)
Rear spring - softer
Front strut - increased compression
Rear shock - tighter bleed, firmer rebound

Does HSV change any of the standard Holden suspension bushes?

No we don't. We have looked in the past at doing bushes, but what we find is there's a lot more harshness that gets borne into the cabin. We have looked at changing the exterior trailing bush, but the harshness is increased more than the handling characteristic [improved]. A lot of our customers are business people who, as I said, want the car for weekend track work but still drive it on the road. We don't want it to be harsh.

What about even swaybar bushes?

Even on the models we run a larger diameter swaybar than the Holden, we still use the same specific bush material that they use. The thing is, we know it will pass durability - that some Northern Territory dust won't get in and deteriorate the bush. Then, some need lubrication as well.

How important is it to run the HSV-specified tyres?

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We do a lot of work with both Bridgestone and Pirelli and our suspension package comes tuned for a given size and type of tyre. Our criteria for tyres include wet weather performance, noise, durability and serviceability in Australia. You can be in the back of Bourke or wherever and, if you need to get a new tyre in a very short time, you can. Noise is very important. You don't want a natural frequency from the tyre that runs through the strut into the car, so you get a humming at 100 - 110 km/h. We do on-road wear tests over a specific course, and we also measure wear on the proving ground.

How many kilometres do typical owners get out of the original tyres?

One important thing is to check tyre pressure regularly - it's critical. That's why all our cars get a tyre pressure gauge in the console compartment. With proper rotation and checking - depending how you drive it - you can get 20-35,000 kays out of a tyre. We do have customers that get 45,000 kilometres. The wheel alignment is critical too - and a full four wheel alignment, with the new link in the rear suspension. The first thing to ask anyone doing an alignment is "how often do you get the machine calibrated?"

How does rear tyre wear compare to before the fitment of the extra rear suspension link?

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Ah, look it's a hard comparison to do. At that time we used Bridgestone S-01 and S-02s - now we're at the S-03, so you can't do any direct comparisons. They're a different compound.

Does HSV change any of the front or rear alignment angles from Holden's settings?

We run all the same toe, camber and castor across our whole range - regardless whether it's got a 17,18 or 19-inch tyre. You could increase camber to increase grip, but there's a trade-off - you want a tyre that's durable and even wearing.

In Part 2 of our interview, we quiz John on HSV's engines and ask about those Gen 3 engine failures...

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