Fuel economy for an I6? What's your gas mileage?

[mahanian]

I'm looking at purchasing a 67 short fleet that has an I6 with a 4 speed manual on the floor and 3.08 gears. I was planning on keeping it a 6 cylinder, mainly for better fuel economy. But the owner told me that the I6 250 and 292 with the monojet carb gets worse gas mileage than a 2 barrel sbc.

I find this hard to believe so I thought I'd do a poll. To the guys still running your 6 cylinder, what kind of gas mileage are you getting and with what gears and tranny?

[Mister laugh]

I have a 250, with a 3speed and 3.73s. the PO told me the engine was slightly worked over, I'm not sure if i believe him or not although im farly sure it has an RV type cam to it, and i can obviously tell it has a dual header on it. My speedo it broken so it's hard to tell accurately what kind of mileage i get, but judging by where i drive/how much i spend on gas i would guess that it is hovering around 13mpg.

[caminokid]

I know I put 10.00 in mine today. I6 with a granny 4 speed. I think 3:73's maybe. In town traffic stop go crap. Also hauling stuff...remains of fox body mustangs....I went about 35 miles on that 2 gallons of gas. So it's not doing bad.

[scrapmetalart]

Stock 250, 3 speed. I am not sure of my rear gear, but it screams @ 60 MPH...
highway is 14ish. I think it is runnin a bit rich. Electronic ignition is coming, so I hope that helps a bit...

[ksjh1316]

I have a 292 with a granny 4 speed with 4:10 posi rear. Average 11-14 mph but I run the snot out of her.

[68gmsee]

Originally Posted by mahanian

I'm looking at purchasing a 67 short fleet that has an I6 with a 4 speed manual on the floor and 3.08 gears. I was planning on keeping it a 6 cylinder, mainly for better fuel economy. But the owner told me that the I6 250 and 292 with the monojet carb gets worse gas mileage than a 2 barrel sbc.

I find this hard to believe so I thought I'd do a poll. To the guys still running your 6 cylinder, what kind of gas mileage are you getting and with what gears and tranny?

A lot depends on the condition of the engine and rear axle ratios, type of transmission, carburation, etc. A well tuned and tight v8 can get as good gas mileage as a six.

My 250 with 3 speed standard and 3:54 axle is getting about 16 mpg average. On the highway I think it's closer to 17 but I drive both city and highway.

I like the fact that the one you're looking at has 4 speed trans with 3:08. I've been kicking the idea of changing mine to 3:08 rear axle and slapping a 700r4 on it with my 250... Maybe.

[6977chev]

my stock 230 with 3 speed, longtube headers, clifford intake and 500 edelbrock gets 15 around town. i do very little highway driving so im not sure what its doin there, id say its a bit better on the highway. 3.08 rear end.

[d10s69c10]

i got a 350 i get 15 if i baby her. but this I-6 isnt a huge issue mpg wise its the driver many times

Copperhead was equipped with a 572. and a feather light foot gave it 12 mpg at 720 hp.

[mahanian]

Thanks for all the good info, looks like the gas mileage of an I6 is on par with that of a sbc.

Can A/C be added to an I6?

[samwise68]

You also have to remember, that yes, I6 and V8s get almost the same mileage, but most of the I6's are on their last leg while being ran. So people will pull them, and slap in a fresh 350, and say "oh, look, just as good as that 6".

I'm getting about 17 with my tired 307. So, I'm not complaining. But theres little doubt in my mind that a fresh 6 could pull as hard and get as good of mileage as the sbc.

Personal opinion backed by little to no research though, so, yeah.

-Sam.

[Willy Prost]

71 Short bed stepside
250 stripper model
the only option listed on the glove box plate is "rear bumper"
weight with 200lb driver and half tank gas 3750lbs
3.73 rear with a Tremec TKO 5 speed (0.68 5th gear OD)
pertronix ignition in the distributor
I drive it daily to work
I get 15mpg without trying
If I pay attention to milage I get 17 in town
Highway is 19-21mpg

[Brad]

Originally Posted by samwise68

You also have to remember, that yes, I6 and V8s get almost the same mileage, but most of the I6's are on their last leg while being ran. So people will pull them, and slap in a fresh 350, and say "oh, look, just as good as that 6".

I'm getting about 17 with my tired 307. So, I'm not complaining. But theres little doubt in my mind that a fresh 6 could pull as hard and get as good of mileage as the sbc.

Personal opinion backed by little to no research though, so, yeah.

-Sam.

My 250 is tired and has about 150,000 miles and with the T-5 I'm getting about 17mpg @ 65mph. I know that a good solid refresh with porting and a bump in compression would seriously increase this.

Oh, and anyone considering going 3.07's with a 250-don't do it! Unless you drive alot of highway miles, your in town economy will decrease and you'll get sick of having to ride the clutch to get it up and rolling from a dead stop. Ask me how I know.

[bad6772]

i run a stock bottom end 250...(85,000 miles) fully re-worked the head (after a over head few years ago)..stock carb. single exhaust with a 40 series flowmaster..3-speed .with 3.73s...i get 12 mpg in town..and 15/16 on the highway.....probably could do better with a tune up(been about 10,000 miles)....,and electronic ignition.....

[N2GMTrux]

I have a 71 Chevy C-10 LWB with a 250 and three speed manual trans, HEI, and 31 tall tires,,,,, unsure of rear end gears at this time... I get 16 MPG in the city and I have never taken the truck on a long highway cruise so unsure of the highway mileage.

I can say it has over 142,000 miles on a non rebuilt engine and now has an HEI distributor which has the truck running smoother and more efficent. With the old points distributor you could always smell gas fumes at the tail pipe and was getting close to 13 MPG in the city, and the engine ran rough.....

[*Dylan]

Does anyone know if my 250 with a 2 spd Powerglide would get better or worse mileage than whats stated above? I was at least hoping for 18.

[PICKMUP]

I used a '69 short stepside PU for a test mule:
1. I ran a stock 250 with 4spd & 4:10 posi (slow & boring).
2. Added a 700-R4 trans. It was a pain to get all that junk hooked up and then... (250 wouldn't pull the OD).
3. Added a stock 292 (now it would pull the OD fine).
4. Added alum intake, 4bbl, headers, HEI (now this was starting to be fun).
5. Blew up the 292!!!
***Gas mileage??? Not a clue. LOL. I never had one setup running long enough to check it.

[Brad]

Originally Posted by 1967 C10 Dylan

Does anyone know if my 250 with a 2 spd Powerglide would get better or worse mileage than whats stated above? I was at least hoping for 18.

My guess is probably worse in a truck, however I get about 18-22 @ 60 in my all stock Camaro depending on whether I'm following a big rig.