Gas Mileage Test 5 speed vs 6 speed - Chevelle Tech
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post #1 of 43 (permalink) Old Oct 21st, 19, 12:51 PM Thread Starter
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Chris
 
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Gas Mileage Test 5 speed vs 6 speed

Over the weekend a buddy of mine and I tested our OD's on the highway to see what kind of fuel economy our cars could do.

Mine is the 71 Chevelle SS454 with T56 Magnum and 3.91 gears.

His is the 68 Chevelle SS396 with LS6 454 crate engine, TKO600, and 4.11 gears.

Both having EFI, similar weight and power, a lot of the comparison came down to the extra overdrive gear since it was highway only.

What kind of mileage do you guys get?


1971 Chevelle SS454, T56 Magnum 6 speed, 3.31 Posi

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post #2 of 43 (permalink) Old Oct 21st, 19, 1:29 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

have no idea its pretty lousy even with a 6 spd
When its empty gotta fill it anyways. At least youre out having fun

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post #3 of 43 (permalink) Old Oct 21st, 19, 1:47 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

LQ4 (364 cu in), T56, 3.73s, big-ish cam, I average mid 18 on highway trips. Normal driving I try not to judge as it's usually giving people rides and burning through a lot.

*Jeff*

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post #4 of 43 (permalink) Old Oct 21st, 19, 2:27 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

18 mpg is fantastic with a big block!
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post #5 of 43 (permalink) Old Oct 21st, 19, 5:04 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

My goal is to get 15 out of mine! We will see if that happens!
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post #6 of 43 (permalink) Old Oct 21st, 19, 5:53 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

I drive a 70 Nomad Sta. Wgn. with a 468 and a 700R along with a 3:07 - 12 bolt. At 75 MPH. the 468 spins 1950 RPMs and 20 MPG.
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post #7 of 43 (permalink) Old Oct 21st, 19, 6:07 PM Thread Starter
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Re: Gas Mileage Test 5 speed vs 6 speed

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Originally Posted by Robinls5 View Post
I drive a 70 Nomad Sta. Wgn. with a 468 and a 700R along with a 3:07 - 12 bolt. At 75 MPH. the 468 spins 1950 RPMs and 20 MPG.
Bob
That's awesome. Now that I hit my goal... curiosity makes me think what I could do to hit 20 mpg.

1971 Chevelle SS454, T56 Magnum 6 speed, 3.31 Posi

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post #8 of 43 (permalink) Old Oct 21st, 19, 6:10 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

1969 350" in 1957 4 door 3650 with driver then add a 20 foot pontoon boat.
Yukon OK to Texoma on Texas side 190 miles.
Averaged 11.5 MPG.
I August of this year with AC on and 1969 350" Ported 601 heads 280H magnum flat tappet RPM intake and 750 Edelbrock 1407. Recurved 1978 HEI.
3.70 gears NO overdrive TH 350.

Yea not a BBC.
Drove a Dually tow truck I stuck a 454 into, had granny 4 speed and 4.11 gears .. pulling a car for 1/2 the trip.. mostly city I tuned it to 12 MPG dropping the APT adjustment on the Quadrajet and Recurved the HEI.
Before APT adjustment and recurve it would get 6 MPG.

I feel the Andrews 68 Chevelle could have got better MPG if he was a little leaner in the cruise.
My part throttle cruise from 2200-3200 rpm cruise is in the 14.5 area and 18 MPG is the normal on highway.

But maybe his car does not like that..I am sure he has thought about that or tried it though.
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post #9 of 43 (permalink) Old Oct 21st, 19, 6:13 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

11 mpg, that's with a 496 cu in, big cam, 850 Holly, 373 rear gears, 5 speed manual. I'm happy with that.
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post #10 of 43 (permalink) Old Oct 21st, 19, 6:54 PM Thread Starter
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Re: Gas Mileage Test 5 speed vs 6 speed

Quote:
Originally Posted by jeff swisher View Post
1969 350" in 1957 4 door 3650 with driver then add a 20 foot pontoon boat.
Yukon OK to Texoma on Texas side 190 miles.
Averaged 11.5 MPG.
I August of this year with AC on and 1969 350" Ported 601 heads 280H magnum flat tappet RPM intake and 750 Edelbrock 1407. Recurved 1978 HEI.
3.70 gears NO overdrive TH 350.

Yea not a BBC.
Drove a Dually tow truck I stuck a 454 into, had granny 4 speed and 4.11 gears .. pulling a car for 1/2 the trip.. mostly city I tuned it to 12 MPG dropping the APT adjustment on the Quadrajet and Recurved the HEI.
Before APT adjustment and recurve it would get 6 MPG.

I feel the Andrews 68 Chevelle could have got better MPG if he was a little leaner in the cruise.
My part throttle cruise from 2200-3200 rpm cruise is in the 14.5 area and 18 MPG is the normal on highway.

But maybe his car does not like that..I am sure he has thought about that or tried it though.
I would love to tweek the tune on his car. I think some small tweeks could get a full MPG gain out of it.
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1971 Chevelle SS454, T56 Magnum 6 speed, 3.31 Posi

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post #11 of 43 (permalink) Old Oct 21st, 19, 7:01 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

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11 mpg, that's with a 496 cu in, big cam, 850 Holly, 373 rear gears, 5 speed manual. I'm happy with that.
That is what I got with my th400 with a 3500 stall and 3.73s. With a carb is was like 7 or 8(but if I leaned it out it would hurt the car somewhere else).
With fuel injection it picked up a bit.
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post #12 of 43 (permalink) Old Oct 22nd, 19, 7:35 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

Recently, I went for a nice little drive for a couple of hours. A total of 72 miles were driven. About 15 miles were interstate. The remainder of the miles were "stop and go city traffic" and some back road driving. Interstate was driven at 70-75 mph (6th gear) and the back roads around 50-ish mph (5th gear). Hammered on it pretty good getting onto the interstate, the rest of the time was pretty normal driving, but not "babying" it. Topped the tank off and it took right at 6 gallons to fill it up to the spout. 12 mpg. I don't think that's too bad considering my combo.......496, 10.5 cr, Brodix rect port heads, solid roller (256/264, .660/.660, 108lsa), Vic Jr, Pro Systems Venom-VX 1050 carb, Tremec 6 speed, 4.56 rear gears with 30" tires. Last year did a short "all interstate" drive and was able to squeak out a little over 15mpg. With this drive I was really watching how I drove and "babied it" quiet abit.
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post #13 of 43 (permalink) Old Oct 22nd, 19, 7:51 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

15.X mpg with 3.31s @ 3100 rpm.
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post #14 of 43 (permalink) Old Oct 22nd, 19, 10:22 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

That's a great test and video, thanks for taking the time to put it together! I got 13 MPG with my '68 last time I actually tested it (carbureted). Now that I have EFI I haven't checked it.
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post #15 of 43 (permalink) Old Oct 22nd, 19, 11:25 AM
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Lightbulb Re: Gas Mileage Test 5 speed vs 6 speed

Are those license plate gas doors lightened by drilling holds? Gosh.

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