I have to agree. Half a second is too easy to get wrong, especially over a 7 second period, I dont care how many times you do it, you wll not be consistently wrong. You will be wrong different every time. Your also claiming the 0-60 is up there in the realms of more modern, much more powerful cars, which your 16v is never going to be hitting.

I appreciate your enthusiasm and that your approaching modification from a different point of view, but your claims are a little wild and totally unscientific. As Guy has said, there are far too many factors to be accounted for (though how much each individual one will have is likely to be minimal) that you haven't controlled. Keep up the work, but I should feed back when you have some authentic proof of your achievements if your going to make such bold claims.

Don't confuse inertia and mass.

Rotational inertia and mass are quite heavily linked

Being heavily linked depends on distance and the mass... chortles.

insert engineering joke here.

They're not heavily linked. Infact distance from its axis is far more important.

There's no way, even with all the will in the world that you'll get 7mpg from an undertray. Especially some random home made one.

Please, please think about this because this could end up very dangerous if poorly executed. Bolt a piece of metal under your car and it'l probably act as a wind break rather than some sort of streamlining affair.

Be engineers spend months in wind tonnels with smoke to see the effect any slight change has. If you do this your never get the costs back.

Your car was designed to be as economical as the aesthetic design would allow. If vw could have got 7mpg more and turn it into a market beater with abit of plate steel, don't you think they would have?

I admire your enthusiasm but if your method for 0-60 is anything to go.by then your calculations are useless.

You want better mpg.... Have longer ratios. Less revs same speed = mpg. You want to go faster. Shorter ratios. Though again, vs chose an ideal offset of the two. You won't beat millions of pounds worth of engineering.

insert engineering joke here.

How many engineers does it take to change a light bulb?

Edited 26 June, 201214 yr by Mclovin

A1: None. They are all too busy trying to design the perfect light bulb.

A2: Only the one with the instruction manual.

A3: One. But she would insist that the way she did it was distinctive.

A4: Three. One to hold the ladder, one to hold the light bulb, and the third to interpret the Japanese text.

A5: Five. One to design a nuclear-powered light bulb that never needs changing, one to figure out how to power the rest of the country using that nuked light bulb, two to install it, and one to write the computer program that controls the wall switch.

A6: None. "According to my calculations, the problem doesn't exist."

Edited 26 June, 201214 yr by Leon

none, they pay someone else to do it haha.

there are far too many variables in this whole thread, just try it and see. a lot of undertrays are more for controlling noise and water in wade tests than streamlined heroism for mpg.s and 0-60 times

None, that's what the retarded piece of shit labourer is for

Edited 26 June, 201214 yr by Mclovin

I have access to CFD, I just CBA to model a whole car to use it.

desk fan at front of car.

pieces of paper taped to rear bumper

tape measure to measure paper deflection?

judging by the other accuracy in this thread, this will be more than accurate enough? hahahaha

Indeed. Infact I left the under try off my passat and its no different in any way. Other than the power steering fails in very very big puddles!!!

They're not heavily linked. Infact distance from its axis is far more important.

There's no way, even with all the will in the world that you'll get 7mpg from an undertray. Especially some random home made one.

Please, please think about this because this could end up very dangerous if poorly executed. Bolt a piece of metal under your car and it'l probably act as a wind break rather than some sort of streamlining affair.

Be engineers spend months in wind tonnels with smoke to see the effect any slight change has. If you do this your never get the costs back.

Your car was designed to be as economical as the aesthetic design would allow. If vw could have got 7mpg more and turn it into a market beater with abit of plate steel, don't you think they would have?

I admire your enthusiasm but if your method for 0-60 is anything to go.by then your calculations are useless.

You want better mpg.... Have longer ratios. Less revs same speed = mpg. You want to go faster. Shorter ratios. Though again, vs chose an ideal offset of the two. You won't beat millions of pounds worth of engineering.

I think my geeky joke may have been lost through the internet...

I agree, except they also spend a fair amount of effort (£) powertrain matching. Less rpm does not equal better MPG as a rule of thumb.

I dunno.... I get nearly 70mpg out of a 1.9tdi passat doing 30 in 5th, so its held true for me atleast. I spose it also helps I coast everywhere like a bitch

yeah you go too long and have to work the engine harder to pull it under accel and lose the gained mpg to an extent

Ah see I just drop to 4th when I need to move.... Tank lasts longer now anyway. Well it did. I'll be scrapping the thi.g next week or two.... The bonnet would make a good floor tray

Don't confuse inertia and mass.

Rotational inertia and mass are quite heavily linked

Being heavily linked depends on distance and the mass... chortles.

Definitely should have chosen my words more wisely!

They're not heavily linked. Infact distance from its axis is far more important.

Given that you're referring to a masses distance from the axis of an object I'd say they were (think of a better word..... nope, can't) linked. I'm not saying they're replaceable i.e inertia instead of mass but you can't have one without the other.

reducing 0.1 CD is equivalent to approx 100kg.

What is the equation for this? In what way can you link the equation for CD to mass?

If you really want to achieve better mpg you should be aiming to create positive lift not downforce. By doing this you will actually reduce the force in the Z axis on the wheels when at speed.

This however is not really advisable as you might end up taking off in gusty conditions!! LOL

Ah see I just drop to 4th when I need to move.... Tank lasts longer now anyway. Well it did. I'll be scrapping the thi.g next week or two.... The bonnet would make a good floor tray

I had some spare time this morning, so have knocked this up to explain. Engine is a small gasoline (boosted) which has a good specific output but does run off lambda 1 at what, which isn’t un-common for a boosted motor with component protection on the fuelling.

To explain the graph a little further, this is a brake specific fuel consumption map, with BMEP (brake mean effective pressure) and speed. BMEP is a measure of torque for a given engine capacity, a good theoretical comparison for many different capacity/torque outputs.

However, back in the real world, we don’t drive with torque, we need power, so a quick data fiddle:

Now we have something that’s a little more real world. So you can see there’s clear peak efficiency in the island for 250g/kWh and below. Take a worst case, we’re sitting at a constant speed (thus constant power) requiring 30kW, I’m happy at 3500rpm in 3rd. But I decide to try 5th, dropping engine speed to 2000rpm and having to increase engine load to maintain my cruising power requirement of 30kW. All of a sudden I’ve gone from <250g/kWh consumption to 374g/kWh! All I’ve done is change gear and drop rpm...

That said, every engine has a different BSFC map, and a different set of gear ratios. OEMs do hours of simulations (much more complex than my noddy example above) to give efficiency figures and emissions figures which are favourable for drive cycles which sell the cars – these don’t always translate into real world figures, as no one drives the NEDC every morning on the way to work. Powertrain matching for drivability, emissions, efficiency and a whole host of other characteristics (NVH etc) really is a complex task, especially as the regulated cycles are so far off what the squishy thing behind the wheel can do.

So, your diesel may be more efficient in 5th than 3rd at a given speed, without gear ratios and a BSFC map I can’t tell, but a “drop in rpm = an increase in efficiency” isn’t always the case.

Yoof

^^ Excellent example there. Good Man!!