Real World Gas Mileage Numbers Please

[Road_Runner]

Lowering the cruising rpm won't necessarily give a huge jump in mileage because it could put your cruise rpm below a usable torque value.

Remember, the torque peak is exactly the same as the volumetric efficiency peak.

I agree and that's why I'm curious when I read in magazine articles where people have a Gear Splitter with something like a 3.54 gear that when engaged makes something around a 2.66 final drive.  Maybe on perfectly flat highways that would work OK, but it seems like even moderate hills would cause the engine to lug.  That's why the 3.91 / 4.10 range plus the OD seems the best for me.   Great acceleration and still decent road gas mileage.

Later, Jim

[QuartermileCuda]

I have a gear splitter (gearvendors under/overdrive) on my 904 with 3:91 at the back. It does help with the mpg. When I last checked I was getting 9 city. Don't do a lot of highway so I was never able to figure it out. You would think that I should be able to get better gas mileage. If I was to take one guess why my mileage was so low I would say it is because of me. I like to carry out full throttle demands way way more than I should. And thats because the power is always there even when the OD is on. That was one of the best things I have ever bought.

[HP2]

Is that like not being on the cam HP? I find the motor seems to free up when everything is in sync. RPM, speed, and load.

Yes, that is one way of looking at it.

I noticed this with my truck and experimented with it over a 1000 miles journey one fall. My engine/cam/drive train combo reaches peak torque around 3200 rpm.This rpm also coincides with an 80 mph cruise speed. At this point, I can get mileage in the high teens, typically around 18. Running at lower rpm and road speeds, also saw a corresponding drop in mileage until at 55, I was getting 12. Huge differences, no, but effective enough on a segment to notice a difference.

[70burntorangeT/A]

well i have 3.23's and 65mph is about 2700 rpm for me and thats when i get around 18 or so

[thecarkid1970]

In 1989 I bought a stone stock 70 Fury III with a T code 440 and 79840 on the odometer and drove from Springfield IL. to Chapel Hill NC and averaged 15 mpg.  This was mostly interstate driving.  I used this car as a daily driver for almost 6 years before recking it.  I was fairly impressed with the highway fuel economy and the car had plenty of power to boot.

[BP23G0B]

My mild 340 averages 15MPG.  That's with a 600cfm carb, headers, 727, and 8.75 w/3.23s.  I do quite a bit of highway driving (65-75MPH).

[Rare_T_A]

I have no idea what my T/A gets. Not very good I think. It has 12.5 comp, 600 lift solid lifter cam and 4000 stall converter and 4:89 gears. The gas I just got for it was $6.99 per gallon. It's just fun.      If I wanted mileage I'd get a Honda instead.

[72bluNblu]

My '72 has a 318/904 with power steering, no AC. Not sure what the specs on it are since it was supposedly rebuilt before I got it, but its a safe bet that its a stock or very close to stock rebuild with fairly low compression (its an '83 318 block with stock '72 heads). I also have a carter 625cfm AFB, edelbrock streetmaster 318, hooker headers (1 3/4") and currently have 2.76 gears in an open rear (soon to be 3.23).

Anyway, I get 16-17 mpg on the freeway at around 70mph and usually 12-13 mpg around town, I don't exactly drive it for mpg's or I could probably do better. It's definitely no powerhouse, but its not gutless either and I still have plenty of fun with it.

[shadango]

My fish has a 76 318 , jheads (915 I believe), eddie performer intake, eddie performer 600 cfm carb, dougs headers, PS, no AC, 2.76 gears. Its got a purple "something" cam that I suspect is pretty steep.

I get around 10 mpg around town, and I hot foot it a lot..

My 318 Dakota and 360 Durango get 10-12, and they are fuel injected......so I figure I am doing OK.  Of course they also have 3.91 gears....so....