Exhaust , Does it affect fuel usage?

[123-jn]

This week I fitted a kawasaki zx6r exhaust can in place of my old back box. Today I completed a journey I do twice every term to pick the kids up from Aberystwyth Uni. On filling up In Aber I thought I had a problem as I could not get much gas in (not as much as I usually use.) I managed to get just 25 litres in. On arrival back home I again went to fill up as by now I was on the fumes of fumes surely? No I could only get 37 litres in and the tank holds 48 litres? So I worked out the fuel usage on the entire journey (having used the same pump on return.) It works out at 24.5 mpg on LPG. Now until today the van has been as regular as clockwork on this trip 18-20 MPG. So my Question is , could the new exhaust make this difference to the fuel usage? It seems quite alot? Any experts out there? (I always get less gas in at Aber as the slope next to the pump causes it to cut off about 5 litres early.)

[itchyfeet]

personally I doubt it
LPG fill ups are very dependent on many factors including slopes, pump cut off pressures and temperature
you would need to do this for a few weeks to be sure.
if is is better it may not all be good if its lean it will run hot.

[ghost123uk]

A before and after test on an exhaust gas analyser would prove it, and as Itchy says, might indicate it's now running lean, but I I too wouldn’t have thought a silencer could make that much difference, but stranger things have happened.

It works out at 24.5 mpg on LPG.

If that turns out to be consistent, I want one !! (17/18mpg average for me)

Oh, and I find outside temperature affects how much I can get back in to my tank by a noticeable amount, and it has been warmer this week.

[ajsimmo]

Somebody tell Rob...

[ghost123uk]

And, somebody ask Ralph...

[123-jn]

It certainly does seem very strange I will compare the next few fills also. As for running lean, I have a lambda and closed loop with a gauge in the cab so am pretty sure that is not the case. I don't think I was wearing my fairy slippers? I will be doing another run next weekend so we will see what that brings.