Fuel economy

[JadeMach1]

I am trying to get a comparison on fuel economy for my 70 Mach1 what are people getting l have just finished doing a tune up my figures are as follows

21 Litres per 100km Highway
26 Litres per 100km City

Engine is a 351 stroker (395) FMX tranny and 3.25 gear set for the diff.

Do these numbers appear normal???

[GEOFF289]

I have to convert those figures to old school mpg for them to mean anything to me. It comes to about 13.5 on the highway and 10.9 in the city.

I'm no expert but I think it could do a bit better than that even with those big cubes and the inherent slippage of an auto. Your diff is fairly modest. Obviously how you drive it is a big factor.

[JadeMach1]

I have to convert those figures to old school mpg for them to mean anything to me. It comes to about 13.5 on the highway and 10.9 in the city.

I'm no expert but I think it could do a bit better than that even with those big cubes and the inherent slippage of an auto. Your diff is fairly modest. Obviously how you drive it is a big factor.

Trying to stop using a lead foot on the accelerator. 
Planning on doing some big km over Christmas break and trying to work out what is normal fuel economy being toying with the idea of moving to fuel injection for better economy and cold start up after the car has sat around in the garage over the working week. Car runs fine when cold if l drive it more then one day in a row. But fuel cost are killing my desire to use it at $1.80 litre premium unleaded🙃

[Bucks]

just a note on fuel, i notice Mobil is trying to make inroads, i got premium 98 in Albury for $1.66, every other station selling 95 was around 1.72 and 98 for $1.77

[barnett468]

that is good mileage an better than many others.

[lukep6470]

I would expect better than that for HW even with the lack of aerodynamics.  You should at least be getting into the teens.

This isn't really a valid comparison but I got 12.5l/100km from my EFI 289 on the HW.  That is with an AOD and 3.55 gears.

[lukep6470]

lol I just noticed it is a stroker so maybe not :-0

[BAC]

that is good mileage an better than many others.

Remember our gallons are bigger than yours...

[barnett468]

Remember our gallons are bigger than yours...

yeah and that's all you guys have that is bigger than ours. 

[barnett468]

You should at least be getting into the teens.

ummm...he is.


21 liters = 5.4761 us gallons

100 kilometers = 60 miles

60 divided by 5.4761 = eleventeen miles per gallon...almost 

This could likely be increased to twelveteen mpg with an annular booster carb. Also, if the ignition timing is not optimal, it will get better mileage if it is adjusted to the optimal setting.

If you are running much less than around 36 psi in your tires, increasing it to that will increase mileage.

[BAC]

yeah and that's all you guys have that is bigger than ours. 

Including asses and stomachs... 

[barnett468]

Including asses and stomachs... 

I sure hope you start an engine build thread someday. 

[lukep6470]

ummm...he is.


21 liters = 5.4761 us gallons

100 kilometers = 60 miles

60 divided by 5.4761 = eleventeen miles per gallon...almost 

This could likely be increased to twelveteen mpg with an annular booster carb. Also, if the ignition timing is not optimal, it will get better mileage if it is adjusted to the optimal setting.

If you are running much less than around 36 psi in your tires, increasing it to that will increase mileage.

Sorry for the misunderstanding I was meaning l/100kms teens.  Damn metric system!!!

[Dwayne]

Ahhh yes, those non-metric countries of Burma, Liberia and the US 

[GEOFF289]

The exact figures are as follows:

A US gallon is 3.78541 litres and an imperial gallon  is 4.54609 litres, so 21 litres is 5.5476080379846 US gallons and 4.61935 imperial ones respectively.

100 kilometres is 62.13 miles so his figure of 21l/100k is 11.2007 mpg US and 13.451479812423 imperial mpg.

His city figure of 26l/100k is 9.04671 mpg US and 10.864645688036 mpg imperial.

As I said, I'm no expert but I still reckon this could be better.

[Reborn67]

Do beg my pardon but l thought that owning a big block or heavily modified engine in a "muscle car" was a unique experience, and that poor fuel economy was always going to be "part of that experience"..,   

[mcarnage59]

Is it really necessary to use 98 fuel? Is it a high compression engine. I once read its only necessary to use high octane fuel in high compression engInes to I dropped back from 98 to 95 in my beat up stock 289 

Can someone explain when premium fuels are really necessary?

[SXTY8]

Do beg my pardon but l thought that owning a big block or heavily modified engine in a "muscle car" was a unique experience, and that poor fuel economy was always going to be "part of that experience"..,   

I agree. I always enjoyed driving my big block with it's lumpy idle and knew that if I was going to drive it for the day, I would have to put 80 to 100 bucks worth of petrol in it. I did take it on a short trip once and the 10mpg or 28l/100km left me a bit underwhelmed.
On the other hand my Corvette returns 9l/100km or 26mpg on the highway and is very comfortable doing it.

[BAC]

Is it really necessary to use 98 fuel? Is it a high compression engine. I once read its only necessary to use high octane fuel in high compression engines to I dropped back from 98 to 95 in my beat up stock 289 

98 isn't necessary unless you're pushing a compression ratio up near 11:1 and/or lots of advance.  While I wouldn't risk 91 in an old tired motor, 95 is a good compromise between cost and performance.

[BAC]

100 kilometres is 62.13 miles so his figure of 21l/100k is 11.2007 mpg US and 13.451479812423 imperial mpg.

If it wasn't a stroker I would think 17 mpg (Aussie) on the highway should be achievable on a properly tuned engine.

[GLENN 70]

Big block engines seem to chew the fuel compared to a Stroker engine . Still comes down to the way you drive it in any case . My 347 Stroker was very good on a hwy run and about the same as a stock 302 . If the carby is tuned correct it should be good in fuel unless your giving it a hard time .

[JadeMach1]

I agree. I always enjoyed driving my big block with it's lumpy idle and knew that if I was going to drive it for the day, I would have to put 80 to 100 bucks worth of petrol in it. I did take it on a short trip once and the 10mpg or 28l/100km left me a bit underwhelmed.
On the other hand my Corvette returns 9l/100km or 26mpg on the highway and is very comfortable doing it.

Thanks for those figures.

I own the car for a number of years and just started tracking fuel usage as felt my carburettor was running rich so have made some adjustments to it. Yes it is a modified motor and cammy your figures line up close to mine.

I think the accelerator pump was adjusted incorrectly for a quick fuel carburettor and is now set at 17”. Planning on doing some kilometres this weekend and will interested in seeing what the difference is if any.

[JadeMach1]

just a note on fuel, i notice Mobil is trying to make inroads, i got premium 98 in Albury for $1.66, every other station selling 95 was around 1.72 and 98 for $1.77

Thanks for the tip.... will be doing a few laps of Deans street over Christmas

[GLENN 70]

What carb are you running ? . A lot of guys are fitting fuel ratio meters now to set the Carbys up ,other wise it's hit and miss .

[Fitzy1980]

I'm getting 0L per 100km, doing my bit for the environment