Big block MPG?
Thread Starter
Safety Car
Joined: Nov 2004
Posts: 4,182
Likes: 94
From: going faster miles an hour...with the radio on in browns mills new jersey
Big block MPG?
Has anyone calculated their mileage? Mine seems to be somewhere between bad and poor. What kind of numbers might I expect if I am brave enough to actually figure it out? I'm running a Tri-power 454 and 4 speed. EFI and OD tranny guys feel free to boast.
Melting Slicks
Joined: Dec 1999
Posts: 2,489
Likes: 32
From: New Smyrna Beach FL
Originally Posted by nassau66427
Has anyone calculated their mileage? Mine seems to be somewhere between bad and poor. What kind of numbers might I expect if I am brave enough to actually figure it out? I'm running a Tri-power 454 and 4 speed. EFI and OD tranny guys feel free to boast.
427/435 M21 4:11 gears....what a blast!
Last edited by 67435animal; Jul 15, 2005 at 07:26 PM.
Drifting
Joined: May 2002
Posts: 1,420
Likes: 254
From: Hogansville ga
2021 C2 of the Year Finalist - Modified
My yellow 67 has a mild well tuned 400hp 427 w/a 700R4 trans and 3.55 gears. best ever was 22.1 with AC on top up coming back from carlisle. I caravan with a buddy in a 66 390hp coupe M20 and 3.08 gears. He usualy gets between 17 and 19 depending on how fast we are traveling.
Dennis
Dennis
Melting Slicks
Joined: Jan 2002
Posts: 2,132
Likes: 71
From: SOUTH SHORE Massachusetts
My 390 hp which has a mild comp cam and larger than stock holley, with 336's and 215x75x15's gets 17plus on a highway cruise at about 70mph....i never checked city driving....why bother.
Safety Car
Joined: Feb 2000
Posts: 4,977
Likes: 38
From: Massachusetts , USA,
My 1966 ,427 cu in single 4 bbl "Used to get" 15 MPG on trips when I had the 3.08 rear gears..........now have 3.70 gears & in the 11/12 mpg city MPG range At best ..... 
the double pumper Holley contributes to this, but its the price you pay for the E-Ticket ride.....food for thought>>>> used to drive the 66 , 1,200 miles a season.but with $2.55 high test , no more HWY cruisin.......this may be OK for the NCRS guys who spend all day waxin & shinin & only drive to shows & sayin my Corvette is perfect ,,,,but for me that likes aceleration & drives hard ........WOE, thoughts & 2 cents from the Dog 
the double pumper Holley contributes to this, but its the price you pay for the E-Ticket ride.....food for thought>>>> used to drive the 66 , 1,200 miles a season.but with $2.55 high test , no more HWY cruisin.......this may be OK for the NCRS guys who spend all day waxin & shinin & only drive to shows & sayin my Corvette is perfect ,,,,but for me that likes aceleration & drives hard ........WOE, thoughts & 2 cents from the Dog
Last edited by StrayDog; Jul 15, 2005 at 08:39 AM. Reason: clairification
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Le Mans Master
Joined: Nov 2000
Posts: 7,246
Likes: 21
From: Going too fast over the hill. Iowa
IMO Bunch of optomists on this site 
My experience, 454 (bored .03) BB in suburbia with 4.56 gears 6mpg.
Switched to a 350 SB and 3.36 gears to get 14.5 on the highway (65mph average speed on trips cruising about 73mph using cruise control)
Switched to 3.08 gears for 19mpg. Added an air dam for 20mpg. (same average trip speed )
My experience, 454 (bored .03) BB in suburbia with 4.56 gears 6mpg.
Switched to a 350 SB and 3.36 gears to get 14.5 on the highway (65mph average speed on trips cruising about 73mph using cruise control)
Switched to 3.08 gears for 19mpg. Added an air dam for 20mpg. (same average trip speed )
Last edited by magicv8; Jul 15, 2005 at 09:59 AM.
Instructor
Joined: Jan 2005
Posts: 146
Likes: 5
From: Florida
Hard to say with a non-functioning fuel gauge, and broken odometer.
But I wondered the same thing.
So I kept a log for one tankful.
Went back over all the routes I took with another vehicle, and recorded the mileage.
I've removed the original carb, and replaced it with a newer Holley 750 cfm (that doesn't leak so bad, and is easier to adjust) before this test.
With the 3.36 rear end, my 427/390 seems to get about 8mpg.
(All city, few stop lights, pedal to the floor until the tires spin acceleration at at least a few stops).
After talking to some people who drove these in the '60's and '70's they don't seem to think that's too unusual.
12mpg would be good for these engines.
But I wondered the same thing.
So I kept a log for one tankful.
Went back over all the routes I took with another vehicle, and recorded the mileage.
I've removed the original carb, and replaced it with a newer Holley 750 cfm (that doesn't leak so bad, and is easier to adjust) before this test.
With the 3.36 rear end, my 427/390 seems to get about 8mpg.
(All city, few stop lights, pedal to the floor until the tires spin acceleration at at least a few stops).
After talking to some people who drove these in the '60's and '70's they don't seem to think that's too unusual.
12mpg would be good for these engines.
Heel & Toe
Joined: Jun 2003
Posts: 17
Likes: 0
From: Valencia CA
Originally Posted by magicv8
IMO Bunch of optomists on this site
My experience, 454 (bored .03) BB in suburbia with 4.56 gears 6mpg.
Switched to a 350 SB and 3.36 gears to get 14.5 on the highway (65mph average speed on trips cruising about 73mph using cruise control)
Switched to 3.08 gears for 19mpg. Added an air dam for 20mpg. (same average trip speed )
My experience, 454 (bored .03) BB in suburbia with 4.56 gears 6mpg.
Switched to a 350 SB and 3.36 gears to get 14.5 on the highway (65mph average speed on trips cruising about 73mph using cruise control)
Switched to 3.08 gears for 19mpg. Added an air dam for 20mpg. (same average trip speed )
Safety Car
Joined: Feb 2003
Posts: 4,068
Likes: 26
From: St. Joseph Mo
"Big block MPG?"
Sucks, even with my QJet setup (tiny primaries).
They'r not too good on oil consumption either. Guide seals?
All you have to do is put your foot in it and you forget about economy.
When I had a plain vanilla 327 in my vet I used to get 21-23 mpg on the hiway with a spreadbore.
Sucks, even with my QJet setup (tiny primaries).
They'r not too good on oil consumption either. Guide seals?
All you have to do is put your foot in it and you forget about economy.
When I had a plain vanilla 327 in my vet I used to get 21-23 mpg on the hiway with a spreadbore.
Last edited by 67L36Driver; Jul 15, 2005 at 01:04 PM.
Race Director
Joined: Jan 2003
Posts: 17,632
Likes: 3,648
From: Central Arkansas
66 Coupe with a pieced together, mostly L-88 motor and 4.11:1 rear - I get a pretty much steady 7 mpg running around town and nearby country roads. Worse is my completely stock 1967 440 Plymouth GTX which also gets only 7 mpg with 3.23:1 rear. 
Melting Slicks
Joined: Nov 2004
Posts: 2,302
Likes: 26
From: Cave Creek AZ
Just did a 500 mile check with a combination of freeway & country driving, nothing over 70 mph. My average is 13.6. That's as good as it gets (454/435hp, L71 Tri-Power, 3.70:1 gears, M21 tranny). 
Le Mans Master
Joined: Feb 2001
Posts: 8,017
Likes: 2
From: The problem is all inside your head she said to me.
damn
Originally Posted by Dad's '66
427/425 with 4.11's. Going down the freeway at 70-75, I swear you can see the gauge move........
and see the persian gulf doing the wave. You guys are driving BB corvettes..... what's not to like.
