TD42 - Dented exhaust = Poor Fuel economy??

[of4x4]

Been having problems with crap fuel economy and lower than normal power on GQ NA TD42. (320 Kms)

Done all the usual things - replaced filters, checked injector pump timing, valve timing, and the little filter in the injector pump. Looked for leaks - none that I can see. It's not blowing heaps of black smoke, so don't think it's injectors.

I crawled under it and discovered a small ding in my exhaust at the front end, under the passenger's feet. Sufficient to reduce the flow through the exhaust by about 10% I reckon. Would this be sufficient to cause my drama's? (simple equation maybe: 10% reduced flow = 10% increase in fuel = 10% reduction in performance ????)

The poor economy started after a recent rocky trip, so I'm thinking the exhaust ding and bad performance may not be a co-incidence. I did hang up on a rock during the trip (on the gearbox mount), so the dent possibly occured then.

My question: is a small dent in a standard exhaust enough to cause problems?

[GRINCH]

it probly would be, when you think that going half an inch bigger in pipe makes a big improvment in most cases

[cooter]

if it causes enough restricion to flow it will mean your cyliders will not scavenge properly leaving spent gas in your combustion chanber which takes up space that should be filled by clean air so more fuel is needed to get the same power so yes but it would have to be a fair dent

[of4x4]

...but it would have to be a fair dent

That's the thing... how much is a "fair dent". IMO, the dent I have is small at about 10% blockage, but I used to average 11.5L / 100 before the trip away, and immediately after the trip it's more like 14L/100 with noticable power loss. I've done nearly 3,500 k's since the trip, so it's not the fuel, tyres etc. As stated, all filters have been changed and the tyre pressures are the same as before (40psi).

I guess if people are experiencing noticable performance gains by going slightly bigger, then the tolerances on the standard must be pretty tight.

Maybe i should just go the bigger exhaust...

Thanks for the replies.

[fnqcairns]

I don't think it would make much of a difference, there would be around or greater than 10% difference naturally between standard exhaust systems once fitted I would assume, 1/3 crush and I would be taking notice although I am new to these beasts.

Short while ago I got 11.08L/100km, 2 people not much gear, 800km round trip, not an economy run, filled at same pump nozzle on return, I think If I suddenly saw the same decrease in economy as you did I would first look at what I have done different or an error somewhere like a pump that counted badly although the lack of power is a problem.

Your air filter and/or gauze 'in pump' fuel filter might be just about due??

good luck with it for such a big and capable do everything car the economy is one of the best bit's about them.

cheers fnq