Theres a short article on David Wood's GTP S2000 in the latest "Fast Fours" magazine. Interesting thing that DW mentions is that they run 2x the stiffness of the springs at the back in order to deal with the 'tail happiness' of the S2000. He hais that now the car is perfectly neutral. It does not mention anything about the front springs, but this is not the 1st time that I've read that the S2000's rear-end is too soft. Motor/Wheels mention that in almost every S2000 write-up ... they always complain about the back-end and suggest that it is too soft. I'm not really sure how a stiffer back would 'help with the tailhapiness' but maybe someone with tuning experience can answer that.

Also, it does mention that despite the GTP S2000 running MoTech, it only produces very minor power gains and that most of the power gains were made from the exhaust. Though, the artcicle lists 138kW at the rear-wheels ... which is not that much. 138kW is 184hp and concidering that the S2000 is ment to have 176kW stock here, that would mean 21.6% power-loss between the engine and the rear-wheels. Also, all the Dyno charts that I see in 'Car talk' have between 195 and 210hp .... that is 146 - 157kW at the rear-wheels for stock cars. It's odd that all the plots here show more power at the rear-wheels than the GTP S2000 - which I would pressume to be tuned to the max. maybe the dyno machines don't work on the same scale, or DW under-quoted the power figure as most race-car drivers do.

 

Don't they spin backwards down under?

Seriously Dyno numbers are only valid to compare with themselves (same dyno). Trying to compare two different dyno results is fruitless. It is only good to compare the relative change numbers on the same dyno.

 

David, I am sure the US dynos measure things in different ways to what Aussie dynos do.

Have you not also noticed that US stop watches read more slowly than Aussie ones?

i.e. all there cars seem to be about half a second quicker than ours in the 1/4 mile

 

Yeah, those were my thoughts on the dyno as well ..... though it's the spring settings that I found to be of most interest.

ps. About the 1/4 mile times - I think that in US they like to do all they can to best their times while here the measurments are usually more 'real world' related. ie. 2 people on boad, all stock, equipment, 1/2 tank, standard pressures and 'cold' tyres.

 

A stiffer rear generally promotes oversteer and counters understeer. This is because of the effect on weight transfer through roll. Whether you stiffen the springs or the anti-roll bar the effect should be noticeable. Most people have stiffened the front of the S2000 to reduce oversteer. At the extreme of this effect is FWD cars with such a stiff back end that they lift the inside rear in tight corners. Imagine the effect than would have on a RWD car My old Celica would do that and it handled very neutrally thanks to a big rear bar.

I think what David Woods was talking about is perhaps a reduction in bump steer? Maybe the car was hard to control over ripple strips or something. Then again maybe they stiffened the front even more. You've got to be careful what you believe when someone is quoted out of context.

138kW on a Dyno Dynamics (most popular dyno used in Aus) is a very healthy number indeed. A stock WRX or 200SX usually won't make more than 100. In the US they use Dynojet inertia type dynos (no electro-mechanical counter force applied) and their calibration gives higher numbers. I think the multiplier used is pretty arbitrary in their case but it's become some kind of standard in America.

 

naishou,

A stock WRX will usually get around the 95kW at the wheels mark, but this is at all 4 wheels. I would have imagined that a stock 200SX would make considerably more than 100kW at the rear wheels however.

 

[QUOTE]Originally posted by Alister
[B]A stock WRX will usually get around the 95kW at the wheels mark, but this is at all 4 wheels.

 

Hi Naishou,
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A stiffer rear generally promotes oversteer and counters understeer. This is because of the effect on weight transfer through roll. Whether you stiffen the springs or the anti-roll bar the effect should be noticeable. Most people have stiffened the front of the S2000 to reduce oversteer.
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Yep, that is how things worked to my knowledge. That's why I posted these comment ... as I said, I've read in a few Motor/Wheels articles a suggestion that the S2000 rear is too soft and that stifening it would tame some of the rear-bias. As far as the "Fast Fours" article goes, the magazine is on the stands and the article is pretyty short so see if you make anymore sence out of it.

ps. 138kW in that content is a pretyy healthy number ... any idea what number the STi's are producing?

 

Maybe 135. It varies with car, day and dyno so it's hard to compare. In any case that S2000 is making amazing power for a 2L NA engine. Must be very close to top level Super Tourer numbers.

 

All this new "hp at the wheel" info that DW and Naishou have provided makes me rething this article:
http://www.autospeed.co.nz/A_0911/P_2/article.html

They claim 152hp at the wheel stock ... that is 114kW which seems to compare to the 95kW WRX and 135kW Sti. Also they claim that just with an "rear exhaust boxes upsized a little and replaced with free-flow designs" the power jumped to 173hp, which is 130kW. That is close to the Sti territory which means close to 200kW at the fly-wheel (ie. ~16kW increase). Now with the addition of MoTec they increased the power to 187hp, which is 140kW .... that puts the engine at somewhere around 210kW at the flywheel.

Now referencing the David Wood "Fast Four" article that claims 138kW at the rear-wheels with exhaust and MoTec seem to agree with the "Bob Romano Performance Motors" findings. Not only that but David Wood did mention that most of the power increase was from the exhaust work and that the Motec gains were minor - right on what the "Bob Romano" article shows.

So this has really go me thinking .... would simpe exhaust work lift the engine power to ~190kW ... I'd be very happy with that and I'd certaily concider changing the exhaust for extra 20kW.