better fuel economy from highstall

[Boonz]

ive recently installed a new high stall converter behind the 5 litre, also 3.45:1 diff gears.Now ive been getting better fuel economy from about 40% town/60% highway driving. i filled my tank ($82) and reset the trip meter and ive done almost 400 k's and its only down to a 1/4 of the tank. It used to be an absolute dog on the gogo juice and i thought the diff gears and highstall would of made it worse but it hasent for some reason.
anyone got any ideas??

[totq]

that doesnt sound logical and hard to believe, i would have thought the extra revs as a result of the stally and diff gears would mean more fuel use.
let us know after a few tanks.....

[Boonz]

it sits on about 2500 revs at 100 km/h when the lockup clutch engages, around town just seems to sit around 2000-2300 revs so it must just be putting it under less load or somethin.
whatever it is i like it

[1991_Vn2nV]

Actually to a certain point 3.45's are a more efficient gear ratio for the 3.8..

Around town, even 3.7's can be better off than the standard ratio...Not on the open road obviously though

[totq]

sounds like thats what YOU WANT to believe....
the stock setup is the most "efficient".
boona - if you're doing 2500rpm at 100km/h with the new diff and stally now then you are definitely not more efficient than stock, which would have been around 1500-1700rpm at 100km/h.
even around town, you ARE doing many more revs than before so you have to be using more fuel.
in a logical business sense, no car manufacturer in the world will spend millions of dollars in research and development to mass produce a car with a setup as "efficient as possible" in order for it to sell.
like i said, record it over a few tanks and see, but i'm willing to bet my left testicle it will go thru more fuel than the stock setup....only need one to survive, LOL!!

[stocky]

maybe the diff gears are making your odometer inaccurate?

[danielsan]

i've heard of many people getting better economy when they switch from 3.08 to 3.45 diff gears, but not 40-60%, 5 - 10% is a more realistic figure.

[Boonz]

this is in the country by the way....so town is just 50 km/h or 80km/h

[1991_Vn2nV]

sounds like thats what YOU WANT to believe....
the stock setup is the most "efficient".
boona - if you're doing 2500rpm at 100km/h with the new diff and stally now then you are definitely not more efficient than stock, which would have been around 1500-1700rpm at 100km/h.
even around town, you ARE doing many more revs than before so you have to be using more fuel.
in a logical business sense, no car manufacturer in the world will spend millions of dollars in research and development to mass produce a car with a setup as "efficient as possible" in order for it to sell.
like i said, record it over a few tanks and see, but i'm willing to bet my left testicle it will go thru more fuel than the stock setup....only need one to survive, LOL!!

Remember he has a 5L too. The 3.08 ratio is most efficient for the V6, but perhaps not the 5L V8. Newer V8 manual models ran a 3.46 ratio STOCK... And the VZ SS manual actually ran a 3.73 ratio.

They do more revs... As all manuals do, but they use less fuel than the 3.08 ratio counterparts.

Even with 6's, the RB30 VL's ran a 3.45 ratio too.

Maybe he uses less fuel because he doesn't have to use as much throttle any more becuase of the diff gears. Cruising speed will involve higher rpm yes, but not necessarily acceleration. On the highway at 100 or 110km/h he would use more fuel, but stop and go or at 50km/h I think he will use less fuel and at 80km/h I think it will be much of a muchness.

They do NOT spend millions of dollars choosing diff gears either, especially back in the VN/VP/VG/VQ days.

[1991_Vn2nV]

i've heard of many people getting better economy when they switch from 3.08 to 3.45 diff gears, but not 40-60%, 5 - 10% is a more realistic figure.

You didnt read his post properly. It says 40% city driving and 60% highway driving. It does not say 40% to 60% improvement.

[totq]

Remember he has a 5L too. The 3.08 ratio is most efficient for the V6, but perhaps not the 5L V8. Newer V8 manual models ran a 3.46 ratio STOCK... And the VZ SS manual actually ran a 3.73 ratio.

They do more revs... As all manuals do, but they use less fuel than the 3.08 ratio counterparts.

Even with 6's, the RB30 VL's ran a 3.45 ratio too.

Maybe he uses less fuel because he doesn't have to use as much throttle any more becuase of the diff gears. Cruising speed will involve higher rpm yes, but not necessarily acceleration. On the highway at 100 or 110km/h he would use more fuel, but stop and go or at 50km/h I think he will use less fuel and at 80km/h I think it will be much of a muchness.

They do NOT spend millions of dollars choosing diff gears either, especially back in the VN/VP/VG/VQ days.

LOL!
dudes, i'm not arguing for the sake of arguing, but i think it is a misconception if anyone thinks a stally and higher ratio diff gear will be better on fuel than the stock setup!
no i did not they spend millions on choosing diff gears alone....read my post again - they spend millions on the whole development of the vehicle.
how on earth can a v6 be more efficient than a 5L on 3.08 diff gears?? its not a "apple to apple" comparison is it?
i mean, the 5L has a lot more torque than the v6 so it doesn't need "as much effort" than the v6, but regardless of this, every time the 5L turns one revolution, its gonna be using more fuel than the v6....
the newer models use a higher ratio diff to IMPROVE PERFORMANCE to compete with other cars manufacturers....to sell!

[1991_Vn2nV]

LOL!
dudes, i'm not arguing for the sake of arguing, but i think it is a misconception if anyone thinks a stally and higher ratio diff gear will be better on fuel than the stock setup!
no i did not they spend millions on choosing diff gears alone....read my post again - they spend millions on the whole development of the vehicle.
how on earth can a v6 be more efficient than a 5L on 3.08 diff gears?? its not a "apple to apple" comparison is it?
i mean, the 5L has a lot more torque than the v6 so it doesn't need "as much effort" than the v6, but regardless of this, every time the 5L turns one revolution, its gonna be using more fuel than the v6....
the newer models use a higher ratio diff to IMPROVE PERFORMANCE to compete with other cars manufacturers....to sell!

Exactly... Diff gears are chosen not just for fuel economy but for performance etc. as well.

Older model 8's had higher diff gears as well... So its not solely about performance and its not solely about economy.

A 3.08 ratio provides better cruising economy. But around town in 60km/h and 50km/h zones a 3.45 ratio can be just as efficent if not MORE efficent than a 3.08 ratio. Its a careful balance, if it was all just about cruising efficiency, we would see more ratios like the 2.87 ratio in the SV6.

[SweetWagon]

Exactly... Diff gears are chosen not just for fuel economy but for performance etc. as well.

Older model 8's had higher diff gears as well... So its not solely about performance and its not solely about economy.

A 3.08 ratio provides better cruising economy. But around town in 60km/h and 50km/h zones a 3.45 ratio can be just as efficent if not MORE efficent than a 3.08 ratio. Its a careful balance, if it was all just about cruising efficiency, we would see more ratios like the 2.87 ratio in the SV6.

I agree, I cant see the 3.45's getting better economy cruising on the motorway etc. but yes, they should be much better for around town. I was watching some sort of car show when testing the SV6 and they said it was an absolute slug in performance because of the diff ratio.

[totq]

thanks for the feedback vn6pwr, i'll sure find out soon - i'm going to replace the stock 3.08 on me vr v6 soon to 3.45 LSD....

[Hairy Eater]

few years back after doing some reading and research .... best fuel economy was attained driving at the revs that gave maxium torque ..... with some cars that was 80 kph on the highway .... so i would think 3.08 would give better economy than 3.45 if you didnt change the convertor or it was over loading the engine ... but should't over load a V8 ....

[greenfoam]

I don't think there would be any difference on the highway because vaccum will be better at the slightly higher revs so the VE map will about the same as it was before and that's what decides how much fuel is going in. Around town will use less because it's easier on the engine, less load = less fuel

[Boonz]

thankyou jason. that was the logical answer i was hoping for lol. ok the utes been out over the last 2 weekends. waited till the gauge was under empty. filled the tank with 62 litres of petrol so there was probably about 65 in the tank TOTAL. Have travelled a total of 513 km's in 2 weekends mostly cruisin round town and 3 40km round trips to another town.
thats bloody good compared what i used to get for doing the same amount of driving.
considering the last cruise i went on i used 1/2 a tank in 45 minutes up in the hills