Arragonis: Thanks for allying my doubts about diesel. I'm gonna stick with it.
Thanks also for letting me know that the stuff we've worked out for the golf is applicable for the Octavia. It looks like it's gonna be Octavia. I'll search out one that needs a fly wheel and get it done when I buy it.
The other advantage I can see is that taxi drivers should be very interested in any way I can help them save fuel.
To come to that conclusion I also did some calulations in addition to what you say. Took a while to work out but kind of rewarding when you get the final figure. (whew!)
Conclusions:
1) Other people who drive my van must drive a lot less efficient than I do because they look after them just the same.
2) I calculate, very roughly that a high roof delete is only goin to save me 7mpg at best (UK metric). Probably only costs me 4-5mpg. That's a saving of £30(~$48) on a 800 mile ski run. Thus, if I'm going to change vehicles for this reason I better do it properly and get something
really low.
My working out. Other people might find this useful:
Very approximately(measuring with a ruler on screen!) the high top is 23% of the frontal area. The van cda without the high top is quoted as 0.36.
(
1.7 Delivery Program )
I can't just add on 23% to 0.36. I need the frontal area used for the normal roof T4 to get that 0.36 figure.
The german for frontal area according to google translate is "Frontfläche" but could also be "Stirnfläche" (
Google Translate )
...
A search on that turns up nothing:
"vw t4" frontfläche "m²" -volvo - Google Search
Ah! Found the calculator at:
Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com
perhaps I can use that with trial and error to make some estimations...
if a '95 GTI VR6 has a frontal area of 21.66' then my van is going to be just under double that (sadly a very rough estimate... have to get an exact figure when I have the van in front of me). If I use 33' and all other settings on the most optimistic I get 27.91mpg... ah, that's imperial. Check that my figures were calculated as UK... yes they were... should be about 33mpg. (I drive at 60mph)
So!
Minus the 22% gain from high to low roof (~25') gives 39mpg(UK units)
So the grand total saved from hi to low roof is.... (wait for it!)
4mpg!!
- and that's being very generous on the frontal area difference.
I loose being able to stand up in the back for that? hmm... ok, not worth getting a standard roof T4.
What if we go lower, as a control test on these calculations I'm doing...
put 21 back into the calulator for a Golf...
= 45mpg (UK units).
Hmm... sounds a bit high for a diesel golf... lower engine efficiency to 20%
= 40mpg (UK units). Sounds more like it.
Replug the figures in
with engine efficiency at 20%...
29mpg to 36mpg(UK) =
7mpg saving. (metric UK)
and from standard t4 roof to even lower... 44mpg.
edit:: I think I was putting the mpg US/UK converting in the wrong way round on here:
http://www.tdiclub.com/misc/conversions.html
...might need to start again....