What mpg do you get at 70 mph cruise on

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
C

cljcars

Active Member
Posts
328
I just ran up the motorway , flat ish, zeroed mpg at 70 on gas got 23.5 mpg instantainiois result. I get 24.7 on petrol at the same speed. What are yours like.

Mine is a 96 4.6 with a bigas gas conversion. Fresh engine rebuild but on 124k.

My average on a 14 mile round trip is 17 mpg gas/petrol.

Very interested to see what new petrol 4.4 rangies do if any have gas/petrol.
 
Last edited:
Right, most computers must be slightly out then. Mine reads ..23.5mpg thought it was high.
 
cljcars said:
I just ran up the motorway , flat ish, zeroed mpg at 70 on gas got 23.5 mpg instantainiois result. I get 24.7 on petrol at the same speed. What are yours like.

Mine is a 96 4.6 with a bigas gas conversion. Fresh engine rebuild but on 124k.

My average on a 14 mile round trip is 17 mpg gas/petrol.

Very interested to see what new petrol 4.4 rangies do if any have gas/petrol.
Click to expand...


How does the trip computor know how much gas you are using is it psychic?
 
Explain psychic? What am I missing?. Surely they ain't far off (or meant to be resonably accurate).
 
Last edited:
The Wammer is asking how the system knows how much gas (LPG) you are using when it isn't plumbed into that system, it will only measure petrol/diesel usage.

Also the P38, isn't fitted with an instantainous MPG display (that I know of)....it averages the MPG based on fuel used and the mileage run since last reset.
 
Not sure about the science behind how the RR calculates MPG but lets assume it knows how far you have driven and also how much petrol you have used. Divide one into the other and bingo - mgp. With lpg I guess the ecu does not know how much lpg you are using thus any MPG calculation will be skewed. I don't have lpg so don't know much about it.
 
Now I remember from years back that mpg calcs on fuel injected motors where made using fuel used in injectors, and miles travelled (why it needs time to calc). Now if the injector timing Tinj petrol stays the same when you are on gas, ie you have the gas system tuned correctly so the Tinj gas gives the same combustion products as a petrol (read by the lambdas) then the Tinj petrol timing shouldn't be out by that much, and therfore the mpg reading shouldn't in theory be that far out. So therefore in theory the extra little bit you open the throttle should be accounted for.

Thoughts?
 
cljcars said:
Now I remember from years back that mpg calcs on fuel injected motors where made using fuel used in injectors, and miles travelled (why it needs time to calc). Now if the injector timing Tinj petrol stays the same when you are on gas, ie you have the gas system tuned correctly so the Tinj gas gives the same combustion products as a petrol (read by the lambdas) then the Tinj petrol timing shouldn't be out by that much, and therfore the mpg reading shouldn't in theory be that far out. So therefore in theory the extra little bit you open the throttle should be accounted for.

Thoughts?
Click to expand...

Trip computor works as far as i know, on fuel quantity being used at any particular throttle setting set against miles covered. As when on gas there is no recording of fuel being imput, computor can only use last known petrol usage for it's calculations. So basically it is guessing. That's what i think. Unless anyone knows different.
 
Totally agree with how the fuel input is calculated, then used to get mpg. Lpg systems run independantly of engine ecu's, in fact they piggy back them and sense the signals the petrol ecu send to the petrol injetors to control the lpg injectors. So the ecu never stops calculating the mpg and averaging it (in the p38's case). So the lpg mpg is still depending on the petrol ecu for its figures. So what happens is you stick you foot down a wee bit to compensate for the lpg's lower energy content during combustion, and the ecu compensates and increases the Tinj petrol timing to get more oomph. (then need to consider gas volume delivered to the cylinder).
 
Last edited:
My 4.2 doesn't have any mileage computer but me. After doing some rather difficult and intricate mathematical calculations my computer says I get 18 mpg going that speed not stopping for anything.

Starting and starting changes it to 16.5 mpg.
 
70mph for a longish motorway run !?!?

Hang on I'll ask

Ere Ratty, what mpg would you get at a steady 70 with my P38 on the back?
 
Nice, had mine since august, 50% of that time I've been soaked on the bike going to work, whilst fixing it.
 
Hi clj, thank god someone gets about the same as me!! Steady mway cruising about 24mpg petrol/22 gas. These were full to full measurements, not the computer, although the computer only gave me 1.5 mpg more on petrol, didn't ask it on gas cos I've got a single point system which only asks for engine rpm and load, then stuffs gas into the plenum chamber. If you floor it going up a hill and you're in a high gear you get gassed before kickdown!
 
You must log in or register to reply here.

Similar threads

mutsnutz
P38A what mpg do you get out of your 2.5 deisel
Replies
14
Views
1K
mutsnutz
mutsnutz
Awad
Very Low MPG
2
Replies
28
Views
3K
cooltide
cooltide
martys0uth
Do the extras and tyres make that difference to fuel?
Replies
19
Views
2K
300bhp/ton
300bhp/ton
Horse_Apple
Judder at 70 mph
Replies
5
Views
1K
wammers
wammers
S
whine at 60 - 70 mph
Replies
10
Views
2K
sirchatalott
S
Back
Top