I thought I'd share a gem I found on Jalopnik.

"Give or take for some variance in pumping losses, if you are getting 200HP out of a 2.0L I4, it’s using as much fuel as a 200HP 5.0L V8"

This was in response to an article about the downsizing of ford engines to the 4 pot turbo (ecoboost) engines.

Oh, America...

Two chestnuts today:

"Such and such has just bought an A7 3.0 V6 diesel. A proper drivers car, absolute weapon."

I concealed my snigger well.

"Just had my car fixed and the needle that goes up and down when you're driving is over 2 a lot more than it used to be. Is it broken again?"

I thought about explaining what a rev counter was and how it related to wheel speed and gearing and how having the EGR replaced could not change this. I then thought better of it and just told her it was fine and not to worry.

but there is an element of fact in there isn't there? Look at the latest litre SBCs in the Corvette; 400/500(ish) horse power and yet able to return mid 30s on a run. Try a 4pot with that power and see their mpgs....

A workmate today came out with a couple of good ones his 54 plate 530d will do a 1000 mile on one tank of fuel when taking it steady apparantly, then when I said my nect car will probs be a mk5 Golf Gti he said I should get the Gt Tdi as it's actually quicker when I said he was talking crap he then came out with "well the mk2 Gti was quicker than the mk5".....the guy is known for telling the odd tall tale but I really can't understand where he gets his info from!

Mitsu FQ400

http://www.autoexpress.co.uk/mitsubishi/evo-x/1749...


I'd also venture to suggest that the V8 would be cheaper to service not mention a lot more reliable....

If he resets his 'miles to empty' while at a gentle cruise it might say 1000 miles with a full tank. My E39 3.0 automatic 5 series will show 500 miles+ in the same conditions. Not achievable though, just like the instant consumption reading 99.9 mpg when going downhill

Also, he probably means the MK4 GTi - there was a 2.0 non turbo version which was/is a dog and I think the MK2 was quicker.

But it won't be producing anywhere near 400bhp whilst delivering 30mpg, and with cylinder deactivation, it will be a 4 cylinder...

Way too many factors to just churn out a ”x l/s of fuel burn = y bhp”

think I'm right in saying that the Vettes don't have cylinder deactivation....

I think that he's referring to an engine with a turbo which is for marine use. Presumably there's some racing class which demands high power but small 4-cylinder engines. I don't know personally, but that's my understanding.

No, but getting back to the original statement of fuel used to generate 200bhp, the energy losses in the I4 and the V8 won't be too far apart by the time they're putting out that sort of power. If we keep to very simple examples, a 2l I4 and a 4l V8 with the same bore will need to be pumping the same (similar, anyway) amount of air to generate 200bhp - and the I4 will need to rev twice as fast as the V8 to do that. Piston ring friction will effectively be the same if the bore is the same, as the stroke is the same for a given time period due to the revs.

If we use a simple V8 like the SBC, a 16 valve V8 with the cam in the block and a 16 valve DOHC will probably not be a million miles apart in terms of losses elsewhere in the engine - as losses due to friction increase exponentially with speed, the I4 is going to losing more energy to friction that the lazy V8 with crankshaft/camshafts turning at twice the speed, etc. This could then be extrapolated to further drivetrain losses (especially as I assumed the original statement said BHP and it actually says HP).

To clarify though, I completely agree with you that there a vast number of factors that would need to be taken into account, but I do believe with equivalencies in each system wherever possible, there wouldn't be a huge amount of difference at the end.

With cylinder deactivation it would be worse than a 4 cylinder, what with the extra friction and mass still to move; however it won't deactivate cylinders if you're asking for it to deliver 200hp.