Outer Limits 4x4 Board

Hi All,

I have a GQ lpg/petrol carby wagon and recently fitted pertronix electronic ignition and 33x12.5x15's Cooper ST's.

Before the electronic ignition and 33's (I had 31x10x15's) I was getting an average of 340kms from 80 litres of LPG. Now I am lucky to get 250kms to 80litres. Is this normal ?

They guys who fitted the electronic iginition said they did a tune up but they are not gas specialists so probably did not have the right gear or qualifications to play with the gas side of things. I am thinking of taking it to my gas guy to check the gas side. The last time I took it to my gas guy he mentioned I may need to replace the gas mixer (IMPCO) could this be causing the Gaspig to be so greedy if the mixer is stuffed?

Any comments/suggestions and comparisons of Ks would be helpful.

Cheers

gday,
I have 33's on my Auto shorty have definitely lost some economy on gas as a consequence, dont forget you are trying to turn a larger mass (wheel tyre combo).
I did some calculations the other day just out of interest:
31" tyre = 2.48m rolling diameter
33" tyre = 2.633m rolling diameter
your speedo is calibrated for 31's so if you say you are getting 340kms per tank thats 340 000 meters, devide this by 2.48m you get
137096.77 revolutions of your axle per tank of fuel but remember you are turning a larger diameter tyre. So 137096.77 x 33"tyre circumference(2.633m) = 360.98km per tank. This is what you are really getting. This sort of mileage is typical for a car this size, I get 380kms on the speedo driving like a fairy till the gas tank is bone dry, works out to be about 20lt per 100kms. From asking other guys on this forum it seems those who run a dual fuel set up are getting similar economy. Could be worse, could be still paying for ULP.
cheers Brunsy

If your speedo is calibrated for 31s, and you are driving on 33s, then an indicated 250km of travel is an actual 266km -> 33 divided by 31 times 250.

This is still crap fuel mileage imho.

Are you in a position to whack the 31s back on and drive around for a while and see how the fuel mileage changes? If it jumps back up to 340km per tank then you know it's the tyres. If it stays shitty then you have to assume it's the new work you've done on the ignition.

Jason

sorry didnt realise that now you are only getting 250km to a tank, yeah that is crap, speedo error or not!
cheers brunsy

I get approx the same with my 31's but mine is a REAL pig on 33's.It's not good with 66hp at the back wheels with 31's on using 3.9 ratio diffs,BUT when i put 33 muddies on TOYOTA's go past me.
My setup is S..T