How much mpg????
Discussion
Didn't JC get about 40mpg out of a V8 diesel Audi once? And similar numbers from a Jag V6 diesel.
So if you took that Audi 4.2 Tdi V8 and got rid of the awd. Got rid of the auto gearbox and put the engine in a vehicle with curb weight of around 950-1000kg added some sensible final drive gearing and a regular 5 speed manual box in a car that's fairly aerodynamic. (something TR6 - TVR Chim sized). No air con, no big electrical items. Just a stereo and maybe PAS.
What sort of theoretical mpg do you think it'd be capable of?
So if you took that Audi 4.2 Tdi V8 and got rid of the awd. Got rid of the auto gearbox and put the engine in a vehicle with curb weight of around 950-1000kg added some sensible final drive gearing and a regular 5 speed manual box in a car that's fairly aerodynamic. (something TR6 - TVR Chim sized). No air con, no big electrical items. Just a stereo and maybe PAS.
What sort of theoretical mpg do you think it'd be capable of?
fatboy b said:
Why get rid of the auto box? Probably better than a manual these days (at economy that is).
As I understand it, this is only because they "cheat" at the test, which forces manuals to be in particular gears but lets an auto do what it wants. I think manuals still give better results on the road if driven well. Assuming we're talking about torque converter autos, that is; I assume clutched automatics are the same as manuals. 
trickywoo said:
A quick google suggests that a TR6 has a drag coefficient of 0.44 and a new Audi A8 0.26. The lower the figure the better BTW.
Whilst I'm sure you're right, CD isn't particularly relevant. It's CDa that matters (which I suspect is about the same between the two cars, as it happens).I think he was referring specifically to the size, not the design. Say a mk1 Honda Insight if you like.
ks, it'll be more like 60.1kambites said:
What do you mean by "capable of"? Do you mean if driven normally or if driven optimally?
Both really. As in what could the mean or median average be, but also what is possible.
Reason for thinking is, I've been a bit low on funds this week and have been doing 180+ miles a day for work. Without really trying my car will do an easy 52mpg. In the past I've had a high of 58mpg. However the last couple of days I've been really trying while still being sensible on roads and not annoying other cars. I don't know what it's doing yet, but the gauge seems to be moving slower. I'm hoping over 60mpg. But this is from. 698cc car weighing 790kg.
So I was thinking. If that 4.2 V8 Tdi could muster up 40mpg in a near 2000kg car with auto and awd. What would it manage in a lightweight car with less drivetrain loss. Would it be only a tad better, or could we be talking 70mpg capability?
I find this quite intriguing, even more so when you consider this engine makes 320hp+
When cruising at a constant speed I don't think the weight of the car makes much difference. The removal of drivetrain loss and removing a/c and other electrical items might gain you a few mpg, but I doubt you'd see 70mpg.
The weight of the car only makes a difference when accelerating and climbing hills. Constant speed on the straight and level you won't see much difference.
I think the weight of a 4.2 V8 would ruin the handling of a small sports car anyway. You'd be better looking at the 2.0 twin turbo from the 123d.
The weight of the car only makes a difference when accelerating and climbing hills. Constant speed on the straight and level you won't see much difference.
I think the weight of a 4.2 V8 would ruin the handling of a small sports car anyway. You'd be better looking at the 2.0 twin turbo from the 123d.
Well if you halve the weight and frontal area (while maintaining the CD) then you'll roughly halve the energy losses. Of course you wont get twice the economy because engines are less efficient at lower loads, but I could easily imagine that you'd see 50% more miles per gallon than the Audi.
In reality I suspect the Audi gives under 30mpg in normal driving? So you might see 40mpg from you're theoretical car; and I suppose up to 60mpg if you drive at a constant 45mph with all the electrics switched off.
In reality I suspect the Audi gives under 30mpg in normal driving? So you might see 40mpg from you're theoretical car; and I suppose up to 60mpg if you drive at a constant 45mph with all the electrics switched off.
Edited by kambites on Wednesday 16th March 11:06
kambites said:
trickywoo said:
A quick google suggests that a TR6 has a drag coefficient of 0.44 and a new Audi A8 0.26. The lower the figure the better BTW.
Whilst I'm sure you're right, CD isn't particularly relevant. It's CDa that matters (which I suspect is about the same between the two cars, as it happens).I think he was referring specifically to the size, not the design. Say a mk1 Honda Insight if you like.
2 seats, front engine, rwd type of thing. Short, narrow and not too tall.
trickywoo said:
300bhp/ton said:
in a car that's fairly aerodynamic. (something TR6 sized).
A quick google suggests that a TR6 has a drag coefficient of 0.44 and a new Audi A8 0.26. The lower the figure the better BTW.mnkiboy said:
When cruising at a constant speed I don't think the weight of the car makes much difference. The removal of drivetrain loss and removing a/c and other electrical items might gain you a few mpg, but I doubt you'd see 70mpg.
The weight of the car only makes a difference when accelerating and climbing hills. Constant speed on the straight and level you won't see much difference.
I think the weight of a 4.2 V8 would ruin the handling of a small sports car anyway. You'd be better looking at the 2.0 twin turbo from the 123d.
Never seen a road that is completely straight and level, not even in the USA The weight of the car only makes a difference when accelerating and climbing hills. Constant speed on the straight and level you won't see much difference.
I think the weight of a 4.2 V8 would ruin the handling of a small sports car anyway. You'd be better looking at the 2.0 twin turbo from the 123d.
Weight of engine isnt really what I'm asking about. And plenty of kit car makers get V8 big blocked cars to handle well enough.
Do you really think shedding about 50% of a vehicles weight wouldn't have any bearing on mpg?
Or put it this way. If it doesn't, then adding weight should make no difference either then? So if I took a Land Rover pickup and loaded it with say 1500-2000kgs of sand in the back. Would you expect it to return the same mpg still?
300bhp/ton said:
Or put it this way. If it doesn't, then adding weight should make no difference either then? So if I took a Land Rover pickup and loaded it with say 1500-2000kgs of sand in the back. Would you expect it to return the same mpg still?
On a flat road at constant speed, I doubt you'd notice a huge amount of difference as long as the sand wasn't changing the air-flow and you increased the tyre pressures to give the same deformation at the contact point. As you say though, few roads are flat.Gassing Station | General Gassing | Top of Page | What's New | My Stuff