Nir

Hey people.
Mind if I ask what are these dyno figures in this website?
What's that? A new scooby does 240 bhp?
Apparently, the "Drivetrain compensation factor" is too generous.
Therefore, I suggest you to use at-the-wheels figures, where the figures are much closer to reality: about 100 Kw (136 BHP) for a new Scooby (at the 4x4 wheels)!

A Link for at-the-wheels scooby results:

GavinP

A more complete list of figures is given on

AndyMc

Hi

I agree with what you are saying.

I would just like to point out that some of the info on that dyno manufacturers site is misleading.

They say it is wrong to simply add a set percentage to the "at the wheel" figures to obtain flywheel power,which is true.

It also says their chassis dynos can calculate the powertrain loss by measuring the coast-down loss and adding it to the"paw" figures,but this is simply untrue.

The coast-down method only measures the losses while the drivetrain is transmitting NO torque so, for example, the friction between gears when under load is unaccounted for.
This just backs up your point about using "paw" figures

Andy

AndyMc

[This message has been edited by AndyMc (edited 28-05-2000).]

Nir

Still, the scoobies power-at-wheels is very disappointing.

Why do I say disappointing?
My FWD 620 TI measured 166 BHP at-the-wheels on a dyno with a brand new engine.
After the rechipping, it should be now 184 BHP at the wheel.

Nir

The Power-At-Wheel is more important than "estimated flywheel" figures, isn't it?

Nir

But, there's one interesting point:
The Impreza AWD is not constant!
Hence, in most road cases, full power should be applied on front wheels only, and less is lost in drivetrain, isn't it?
Why do they test it 4x4?

Ian Cook

Impreza is constant all wheel drive so MUST be tested on a 4wd rolling road ?

Nir

Well, I thought there will be some disagreements over the fact that any plain TI, or Accord Type-R for that matter, has much more power-at-wheels than a scooby,
but I was proven false.
Is it really noticeable?
If we ignore the wheelspin factor of the FWD drive Type-R, is it really much stronger on the road? (as it has more pAW)

AlexM

Nir,

An Accord type R may have a good peak power at the wheels figure, but compare the areas under torque curve, the peak torque figures, and the revs at which it is delivered for a Scooby and a Type R...

I rest my case

The Type R does have very good traction for a FWD car though - the high peak torque RPM helps here.

Rgds,

Alex




[This message has been edited by AlexM (edited 29-05-2000).]

Lee

its quite funny..people put a lot of importance on bhp just to be told that torque moves cars..bhp sells em so everyone swings onto torque being the all important figure.

but frankly if low down torque was SO important everyone would be changing gear at 4000rpm LOL.

lets face it, a road car needs driveability and low down torque is great for that. But when wringing a car out on the track you spend all the time in the upper ranges. "Power" is a derived figure comprising engine pull, rpm and gearing which gives us the actual oomph on the road. I'm sure if you ran a type-r against a scoob at full chat (given a rolling start to minimise wheelspin issues) there'd be faff all in it.

Nir

The 620ti delivers the peak torque from 2100 rpm, which is better than the Impreza.
But I agree with Lee, that torque is not the issue of this topic.
The issue is this: since we agree that the Type-R has more power-at-wheels than the Impreza, do we also agree, that if both cars drive on the same line, in 60 MPH and, to a sign, they will accelarate... Do we believe that the Type-R will overtake the Impreza?
(this specific example was given to avoid wheelspin)
If the answer is NO, hence, we don't belive the Type-R will win, it puts a shade on all the dyno figures as we know it.
It basically means, that dyno figures worth nothing.

Ian Cook

Dyno figures are only good for bragging down the pub IMHO, they dont mean much as they are, you have to take weight, aerodynamics, rolling resistance etc into the equation when matching one car against another, and not least of all the driver

So in answer to your original question, no i dont believe all these dyno figures !!!

AlexM

Nir,

Power at the wheels figures tell you exactly that. In general terms, how that is translated into effective performance is dependent on gear ratio selection, final drive ratios, vehicle mass etc, and the width of the power band of the vehicles you are comparing.

In terms of the Scooby/Type R comparison, there may not be much in it in all-out acceleration but the Impreza has much faster in-gear acceleration. This is due to the fact that the Impreza's turbo engine generates torque in excess of the Type R's maximum everywhere from 2500rpm to about 6200rpm. As I said, if you're ringing it out in each gear it might be fairly close because the type R remains within it's narrow power band (2000rpm or less?) at each upchage. On the other hand, if you're accelerating from 2000rpm then the in-gear performance is much, much better in the Impreza. Which 'style' of performance delivery is better for you is a matter of preference and driving styles (yes I do chage at 4000rpm Lee - I do it because I can and still accelerate nicely )

I would agree that comparing the chassis dyno outputs of different cars will only give you a gross indication of their relative performance levels if you only consider that one factor.

Cheers,

Alex

Nir

Alex, Lee, Ian,
We're still in the same place we were at the beginning of the discussion.
The Impreza aerodynamics, so it seems, aren't that special - as it's a basic family sedan structure.
Also, gear ratios, and other factors -
should be negligible, when they come against major differences in horse power.
My car weights 1355 kg and has 184 bhp at the wheels (FWD).
I never drove a scooby but I let a scooby owner drive my car, he said it's slower than a scooby (I believe him and it's seems reasonable)
The point is, according to my bhp to weight ratio my car should perform like Impreza STI.
But it doesn't.
Why?
Probably they have some problem measuring 4x4 cars.

Nir

R19KET

I find rolling road figures a complete nightmare, whether they by at the wheels, or at the fly.

You only have to look at one of the dyno days to see how inconsistant, even the "wheels" figures are. I've had two runs done recently, at different places. First place gave me 206.5bhp @ the RW's, the second, 240.4bhp !!!!.

Now I believe it's somewhere in between, but who knows ?. RR's are only good for same day comparisons, and as a tuning tool, outside of that, it's all BS.

Mark.

Nir

Did it ever occur that 2 tests on the same day of the same car would yield 2 different results?

Nir

R19KET

Nir,

Yes, I'm very aware of how the results can differ. They will differ if the car does a couple of runs, back to back, but this is due to temp' build up, in both the engine, transmission, and inlet.

Our cars (imports anyway) consistantly lose circa 30% in transmission losses. So a 34bhp difference "atw" is worth about 50bhp "atf".

I also gained 93ftlbs on the second RR. The Possum Link map was the same for both, as was the temp on the day. Mb was slightly down, but this would make little difference. Anyway, each of the RR's claim temp/Mb compensation.

It would be great to think my car was producing the figures from the second RR, but I suspect that if I quoted them, I'd be labled a Bullsh*ting lunatic :-).

Mark.

Dukas

Nir,
What kind of car you are driving?
When you say 620 TI you mean the Rover 620 TI?
I don't know were you live but the few ones we have in Israel never had 166BHP at the wheels when standard so maybe here start the problem (and it's heavier in about 150Kg than the Scooby).
Eran.

Nir

Hi Eran
Well Nir is a Hebrew name so yes I live in Israel.
Not only my TI has measured 166 BHP at the
wheel at Computest, but it was on very small
milage (800) when the engine was still "fresh".
Plus add the fact that usually Computests
results tend to show weaker power than in
reality.
The TI weights 1355 kg - that is only 120 kg heavier, not 150.
If you take a quite precise Impreza dynorun -

AlexM

Nir,

It is a mistake to compare any figures between runs on different dynos - too many sources of error (barometric pressure, air temperature, measurement errors) etc.

If you want to see a lot of Imprezas making a fair bit more than 136bhp at the wheels, take a look at

carl

I am confused by all this. I can't see how a Scoob can produce about 130 bhp at the wheels, which is the same as the Group N RWD Corollas they use at Drive-it-all near Oxford (rally tuition that is mentioned in the SIDC FAQ). I've done this course, and those cars have got much less grunt than a Scoob.

Nir

Alex,

We can make an average.
On PE page, the highest value is 154 a.t.w,
and usually the average is about 145.
In Australia, they have measured 136 a.t.w

Dukas

Hi Nir,

I guess you are right about the "Power on the Flywheel is just a number" but power at the wheels is also just a number that say nothing beside the number itself.

What is important is acceleration / barking figures, handling and feelings.
The Power At the Wheels is just one (small) figure in the whole picture so why trying to make it THE most important?

Regarding some other Scooby / TI facts:
I just weight my car in Dynamometer Hetzelia and it's 1180Kg so it's 175Kg lighter than your car. Second I can not figure how a car that produce 185BHP at the flywheel (according to UMI brochure) can produce 165 at the wheels.

Anyway have fun with your car and drive safely,
Eran.

Craig H

Dyno figurse are b0llox. On the same day, we put my Sti 5 on a rolling road with a 22b. The 22b had 30 hp more and 50lb ft more. I overtook him in a straight line. On another occasion, a supposedly dyno proven wrx (between 305 & 320hp, with 300ish lb ft - mine 280ish, 260sh - apparently) - I am still quicker in a straight line. I don't care what the dyno says, as long as my car perform well. It does and is proven. That's the only real issue. Dyno power means nothing except in a pub.

Nir

Craig:
The 22B has heavier engine!
The other WRX - have you both dyno'ed on the same day?

Dukas:
Yes p.a.w figure is important to show a potential of a car.
I lose a lot of speed on wheelspin, I will maybe
change tyres, weight balance or put anti-slip
system.
Such mod to a Ti, can make the whole difference.
At least now I know that an Impreza is basically weaker
than my car.
Regarding weight: I suggest we both take the
manufacturer's word for this one, usually these
test facilities weigh the front of your car and
multiply it by 2.
This is not the most accurate thing to do.
My sister's Mazda 323 ('94) weighted 1350 Kg in Computest.
Now this is very reasonable...(ha!)
Regarding your UMI brochure - FWD cars do not lose
that much energy like AWD cars.
(though 11% seems a bit generous, they usually lose 17%)

Nir

Craig H

Nir,
you're telling me that the 22b engine is so much heavier than an STi V that, not only does it negate a 30hp & 50lb ft advantage (dynoed on the same day) but also that it makes it slower. Would have to be looking at, what, around 100kg for that, if not more. Sorry, don't buy that. I'm sure 22bs are roughly the same weight as all other Imprezas.
The WRX wasn't dynoed on the same date - but it's figures are consistent, as are mine. Dynos prove nothing on the road.

pat

I think the one thing that is being missed here is that a BHP and/or torque peak figure tells you absolutley nothing about how a car behaves in the real world; it's a pub bragging figure nothing more. What is important, however, is the shape of the torque curve (forget about the power curve, it's just too convoluted... acceleration is directly related to torque, but it's related to power by dividing by speed first... go figure what's easier to work with)

Once the torque curve has been measured, and you know the gear ratios, it will be possible to calculate change-up point. This is where the falling torque at the top of the rev range outweighs the penalty of changing up a gear and losing torque at wheels, ie (current torque @ flywheel X current gear ratio) is less than (new torque at flywheel X new gear ratio). There is, after all, little point in continuing to rev an engine if more thrust could be imparted to the car by changing up a gear! If this point is beyond the redline, you're pretty much onto a winner, though :-)

With regard to comparing power runs on different rolling roads... forget it, it's completely pointless. There are just far too many variables. Comparisons between two different engine dynos are perhaps more meaningful because the conditions can be more precisely controlled, but I for one don't want to take my engine out of the car just for a power run! :-) Rolling roads are useful for comparisons between two setups on the same car, within a reasonable time of eachother (short enough not to allow atmospheric conditions to change).

What a car does on the rollers isn't necessarily related to how it will behave on the road. Hence my theory on tuning ("tune it where you'll use it"). But of course, the rollers allow you to check that what feels right on the road "looks" right as far as torque curve goes. Having said that, cars can run a bit rich on the rollers, probably due to the lower relative charge density while doing 130MPH standing still :-)

The comparison between different cars (22B and tuned WRX) are pretty meaningless, because any car is only as good as its driver... for a meaningful comparison, apply one good driver to each car, one after the other, covering the same ground and time it. Make it a straight line if you want to avoid the influence of suspension etc. Even then it's not perfect, but it's beginning to get meaningful.

With regard to the Scoob vs 620ti / Type R, go grab a set of turque curves for each, overlay them and it should become immediately apparent why a Scoob is faster on the road (basically, Scooby torque is pretty flat for a large portion of RPM range....)

Cheers,

Pat.

steve McCulloch

I thought it was interesting to point out that my sti 5 has been run twice within the last few months at Powerstation. The first time it produced 272hp (253lbs) and 205 hp at the wheels. Then I added a VF22 turbo, Blitz and Dump valve - remapped it - and boy does it pull stronger.

Went and had it done again, recently and the power at wheels was down to something like 187bhp (with 277 hp and 263lbs of torque)

I had to laugh. Ah well I guess only a track outing will tell a true difference.

I agree with C Hughes - The difference between the 22b and the sti5 is minimal if any difference at all (I thought it was supposed to be slightly lighter?)

Anway, the 22b at Powerstation, running totally standard was detting above 5000 revs - and detting very badly!

RoyC

I have been up against a Honda Integra Type R and I just pulled away. This happened on a motorway, in light traffic, with my then fairly standard MY99 (induction and back box). The Type R caught me due to my having to slow down for traffic but I was able to out accelerate him by a good margin. This happened about 4 or 5 times before we went our seperate ways - with a defeated wave from him I may add. There was 2 people in each car so passenger weight was not an issue.

Nir

Pat,
Sorry your Torque theory is not what makes the Impreza faster.
The reason is simple - the Ti's torque is superior to that of the Impreza.
A mod Ti (boost=1 bar) gives 273 NM at rev range 2100-6000.
A reg Ti (boost=0.4 bar) gives 230 NM at rev range 2100-6000.
The Ti engine gives better torque and power with less noise.
The difference (if any) is more likely to be in 120kg overweight, and fwd wheelspin.

Nir