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  #1  
Old 03-09-2006, 02:19 AM
ItsPeteReally ItsPeteReally is offline
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Lightbulb Variants, variant reduction and the germ of an idea

I admit to possibly starting to be an obsessive! Perhaps I should go on some kind of medication

Why so many market variants? I can understand that legislation may force market differences, the US headlight design, the US motorised seatbelts, and the JDM speed limiter being prime examples of this. But there are other variants, such as the brakes and transmissions, where some markets appear to have different implementation for reasons that are less obvious.

Looking at this road test page http://www.geocities.com/jamsvx2/autocar5.html ( many thanks to the poster) it is pretty obvious that the gear ratios chosen for the UK market (and any others?) is pretty much optimal, the 3.54 ratio of other markets not letting the engine wind up to anywhere near peak power in top gear, whereas the 4.11 swap-outs that the five speeders are putting in will mean that the car will be over the power peak and sit on the rev-limiter when flat-out.

Question???? is there a manual gearbox option that lets you keep the 3.70 ratio?

As for the brakes, the only reason I can see for the solid unventilated rears is that they may well run at higher temperatures under less than punishing use, and thereby may not glaze up so readily. But then we don't all drive like Nigel Mansell in the UK, I certainly don't, so am I risking less than optimal braking when I really need to throw the anchors out?

Did all these market variants do little more than make the car even more expensive for no good reason?

Finally the germ of an idea.

Has anybody got access to a wind tunnel? The SVX is pretty slippery out of the box, its drag coefficient of 0.29 is pretty damn good, but it could probably be improved. If it could be got down to 0.25 say, my back of fag packet calculations seem to indicate that the car would max-out at 151-152mph, something that would otherwise need another 30-40 horsepower to achieve.

Unfortunately something that looks right, may not necessarily be right, and fiddling with air dams and spoilers may not actually achieve anything. Has anybody looked at underbody wind trays, modified wheel well shapes, radiator air flow management etc?

It seems to me that unless you can find a really significant increase in horsepower, of the order of 30-40 horsepower, then it is not going to make any significant difference to the performance of the vehicle, whereas a reduction in drag would pay off in both performance and economy.

A manual gearbox would be good too!
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  #2  
Old 03-09-2006, 03:21 AM
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b3lha b3lha is offline
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Quote:
Originally Posted by ItsPeteReally
I admit to possibly starting to be an obsessive! Perhaps I should go on some kind of medication
We're all obsessive here. You have to be obsessive to spend all your money on maintaining a 9-14 year old car

Quote:
But there are other variants, such as the brakes and transmissions, where some markets appear to have different implementation for reasons that are less obvious.
I think Subaru were experimenting. With the transmissions for example: They played safe in their biggest market, the USA, and gave them the proven legacy transmission, beefed up a little. In their smaller markets, they fitted the new and unproven VDC transmission. This allowed them to do a long-term comparison study of how well they last in the real world. They undoubted learned that both types explode somewhere between 80 and 100 Kmiles.

Quote:
It seems to me that unless you can find a really significant increase in horsepower, of the order of 30-40 horsepower, then it is not going to make any significant difference to the performance of the vehicle, whereas a reduction in drag would pay off in both performance and economy.
It would certainly be impressive if you could improve upon the work of Subaru's wind tunnel engineers. Even if you can't, it would be a learning experience. You could use this site to document the project, so we can see how you are progressing.

Phil.
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  #3  
Old 03-10-2006, 02:58 AM
ItsPeteReally ItsPeteReally is offline
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Quote:
Originally Posted by b3lha
It would certainly be impressive if you could improve upon the work of Subaru's wind tunnel engineers. Even if you can't, it would be a learning experience. You could use this site to document the project, so we can see how you are progressing.

Phil.
In theory, and almost certainly in practice too, liberating another 40 horsepower by reducing aerodynamic drag should be a doddle

The problem is proving that you have done it!

Let me explain, one horsepower is 550 foot-pounds/second, a velocity of 150 m.p.h. is 220 feet per second; so the force required to expend one horsepower at such speeds is a mere 550/220 pounds, that's 2.5 pounds

If we are looking to liberate another 40 horsepower then we would need to reduce the aerodynamic drag by a mere 40 x 2.5 pounds, only 100 lbs.

I maintain that getting an aerodynamic drag reduction of that order of magnitude should be an easy task - if you don't believe me, try sticking your hand out of the window when driving along at a high velocity and see just how much drag even a small obstacle to smooth airflow generates.

Now look underneath the car. Does it look like anybody spent any time at all worrying about airflow management?

What is all that ironmongery doing under there? You'd be very upset if the upper side of the body design was as lumpy and bumpy as that.

Late model Subarus have had some attention paid to this area, and have an undertray, whose purpose is not merely to annoy people at every oil change!

Unfortunately the changes that we are looking for are so small that attempting to discover whether the drag has actually gone up or gone down by a few pounds is pretty much impossible without access to a wind tunnel. In the example that I quote, of looking for a reduction of 100 lbs in drag, it is less than 3% of the weight of the car. How could we possibly measure that?

One possibility is to wind the car up to maximum speed, slip it into neutral (possibly buggering the gearbox in the process) and measure the decelleration of the car due to the aerodynamic drag.

Could we repeatably measure this?

How accurate would our measurements actually be, could we even get the same measurements repeatably within 3%?

Just a small variation in initial and final velocities, or the windspeed, temperature, relative humidity, etc. may totally invalidate any results.

Put the car in a windtunnel, tethered via a strain-gauge to measure the forces, and such experiments become much more feasible.

I've no doubt that I could cobble something together that might look right, but as I implied earlier, aerodynamics has little to do with aesthetics, and what looks right may actually be worse.

So, has anybody got access to a windtunnel?
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Old 03-10-2006, 03:33 AM
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Quote:
Originally Posted by ItsPeteReally
Late model Subarus have had some attention paid to this area, and have an undertray, whose purpose is not merely to annoy people at every oil change!
Is your car missing the tray under the engine compartment?
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  #5  
Old 03-10-2006, 04:06 AM
m.messenger
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It's a drag

Quote:
Originally Posted by b3lha
Is your car missing the tray under the engine compartment?
Or is the driver missing the point......
Why gerbil about with a shape that's so refined that it is 0.28/29 straight off the production line - a figure most sports cars would love to run with.
On the subject of sticking one's head out the window at speed (!) why not start, say, by electrically folding the wing mirrors on the move? Or looking for a management chip for that lovely 3.3+ litre motor? Or fitting skinnier wheels/tyres to reduce drag?

MM
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  #6  
Old 03-10-2006, 08:50 AM
ItsPeteReally ItsPeteReally is offline
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Quote:
Originally Posted by m.messenger
Or is the driver missing the point......
Why gerbil about with a shape that's so refined that it is 0.28/29 straight off the production line - a figure most sports cars would love to run with.
Well because as the management buzz-word speakers would say it's the 'low hanging fruit'. It seems easy and cheap to prototype, a few sheets of plywood, something that you could find by raiding a local skip (dumpster) is all you would need to start. It's the measurement of the results that's difficult.

Quote:
Originally Posted by m.messenger
On the subject of sticking one's head out the window at speed (!) why not start, say, by electrically folding the wing mirrors on the move?
Cheaper still, take the mirrors off entirely, or manually fold them back. The problem is still measuring how much benefit this actually gives you.

Quote:
Originally Posted by m.messenger
Or looking for a management chip for that lovely 3.3+ litre motor?
What chip will give you another 40hp at the wheels, which probably means more like another 50hp at the flywheel?
Is there a magic chip which will give you another 20% more power? I don't think so. Certainly not without prejudicing the reliability and longevity of the powerplant.
Quote:
Originally Posted by m.messenger
Or fitting skinnier wheels/tyres to reduce drag?
A possibility, but how much would that cost? Several hundred pounds I guess, would it save 100 lbs of drag? How much would it affect the useability of the car?

As I said, it's the germ of an idea. One that might stand a chance of bearing fruit, and may well be totally undetectable from outside the car. If it works then it will give not only better performance but better economy too.

I'm not claiming that it will work, only measurement will prove that.

So, has anybody got access to a wind tunnel?
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  #7  
Old 03-12-2006, 06:58 AM
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Quote:
Originally Posted by ItsPeteReally

So, has anybody got access to a wind tunnel?
http://www.imperialwindtunnel.com/
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  #8  
Old 03-13-2006, 06:26 PM
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Quote:
Originally Posted by ItsPeteReally
Well because as the management buzz-word speakers would say it's the 'low hanging fruit'. It seems easy and cheap to prototype, a few sheets of plywood, something that you could find by raiding a local skip (dumpster) is all you would need to start. It's the measurement of the results that's difficult.


Cheaper still, take the mirrors off entirely, or manually fold them back. The problem is still measuring how much benefit this actually gives you.


What chip will give you another 40hp at the wheels, which probably means more like another 50hp at the flywheel?
Is there a magic chip which will give you another 20% more power? I don't think so. Certainly not without prejudicing the reliability and longevity of the powerplant.

A possibility, but how much would that cost? Several hundred pounds I guess, would it save 100 lbs of drag? How much would it affect the useability of the car?

As I said, it's the germ of an idea. One that might stand a chance of bearing fruit, and may well be totally undetectable from outside the car. If it works then it will give not only better performance but better economy too.

I'm not claiming that it will work, only measurement will prove that.

So, has anybody got access to a wind tunnel?

Interesting thread. Verified success depends very much on the accurate measurement of any changes. Without wind tunnel access, I can't see the point.

I'm also inclined to agree with Michael. It does seem to be gilding the lily to try and improve on an already slippery shape. Also, improvements in CD only give any decent benefit at somewhat illegal speeds. Any changes you make may improve the slipperiness of the car in the wind, possibly at the expense of downforce, and make the handling at very high speed more dangerous.

Closing the mirrors or removing them should make a measurable difference. Measurable say, at an airfield, using a number of top speed runs, with/without or folded/not folded.

Smoothing the airflow under the car should also yield improvement. I still think these type of improvements would only show up under continuous hi-speed track use. The notional gain [or reclaiming] of 50 lost horsepower is only true at banked oval speedtrack velocities.

In real life, I would prefer to improve the power output or torque, something that would genuinely shift the metal a little faster, when you could actually use the benefit.

Roll on supercharger mod

Joe
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