Big Block VS Small Block gas mileage - Chevelle Tech
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post #1 of 35 (permalink) Old Feb 3rd, 04, 2:54 PM Thread Starter
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I've been wanting to rebuild an engine for sometime (and if I work enough this summer and get the money for it I intend to), but have been told to stick with small blocks as you can still get a great amount of power from them and still have better gas mileage compared to big blocks. Now, I know it would seem obvious, but I want to check and make sure there aren't any little loopholes that I don't know about or anything, but do big blocks really get 'worse' gas mileage just due to their size?
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post #2 of 35 (permalink) Old Feb 3rd, 04, 3:09 PM
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All I can tell you for sure is my 70 SS with a MILD 427, "272" cam, headers, rpm intake, 750 vac secondary carb, 4 speed 331 gears gets about 13mpg on the highway at 65 mph.
My 66 Nova SS 327 L79 clone with 4 speed and 3.08 gears gets 18mpg at 70mph.
I know, apples and oranges but the best I can give you.

70 Chevelle SS396 (496) Straub roller, M21
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post #3 of 35 (permalink) Old Feb 3rd, 04, 3:18 PM
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If you are concerned about getting good gas mileage, buy a compact car with a 4 cyl. If you want a Chevelle with some muscle, put in a big block [img]tongue.gif[/img]

Honestly, I would think that a 350 with a comparable combo would get better gas mileage than a 396 or 454...

John Austin
Katy, Texas
'70 SS454 Chevelle "clone" project
My combo:496 BBC (454 +.060), Muncie 4 spd, Centerforce dual fric clutch, "781" heads 2.19/1.88, 12-bolt 3.73 Eaton posi, Scat forged rot assm (21cc Wiseco slugs for 10.4:1 CR), Lunati Voodoo billet 60213 hyd roller, Lunati hyd roller lifters, Scorpion 1.7 #SCP1014 roller rockers, Edelbrock Performer RPM, Holly 850 Dbl Pmpr (1" spa), Carter 172 GPH mech fuel pump, MSD R2R dist. #8360, O'reilly Master Pro coil, Weiand high volume mech water pump, 772 stock 7 blade fan, Hayden clutch, fan shroud & Hi-flow 160 deg T-stat, Doug's 2" x 3 1/2" headers
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post #4 of 35 (permalink) Old Feb 3rd, 04, 5:09 PM
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We don't build big blocks to get better economy
in my part of town.

1996 SS Camaro. 565 on a 28" x 10.5" tire. All motor.
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post #5 of 35 (permalink) Old Feb 3rd, 04, 6:00 PM
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Seems to me that that should be a simple answer. Just depends on how much fuel you are running. You can't really say that a SB or a BB gets worse gas mileage. I personally favor small blocks because I don't need to get more than 500-600hp out of my engine (in my opinion BB are only a good idea if you plan on producing more than that), i like high reving engines, they are lighter, and parts are cheaper. Just my .02.

Like Texas70 said, if you are concerned about gas mileage get a compact car. Fuel economy shouldn't be a factor when working on building serious power. (unless it's for cruising?) [img]graemlins/clonk.gif[/img] Again...just my opinion.

Why else would I drive a 95 civic (did an engine swap on her so she's faster than she seems wha haaa but still slow as dirt ) if it wasn't for the gas mileage? Getting about 35-40mpg! I like that for commutting. [img]graemlins/thumbsup.gif[/img]

wanna run em?
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post #6 of 35 (permalink) Old Feb 3rd, 04, 6:43 PM
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with my setup

sb 406 with 3.90 gears and a th350 and a 295/50 r15 on the highway with a 3000 stall cruising at 65

i got 14mpg. thats pretty good in my book for a car that runs a mid 12 and no overdrive.

sb=economy gas guzzler
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post #7 of 35 (permalink) Old Feb 3rd, 04, 7:00 PM
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Simple physics man. take ( rpms) X (displacement )X( throttle opening %) at a given rpm and you get a fuel consumption number. This isnt a real empirical formula, but you know what I mean.

So, of course, a 355 will consume less at 2800 rpms than a 454, all else being equal.

You want a rat that doesnt eat much gas at cruise. Use a 3X2 intake. Otherwise you'll be in the 13-14 range , and that isn't bad. 3X2 will get you 15-18. Non overdrive 3000 rpm numbers.

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post #8 of 35 (permalink) Old Feb 3rd, 04, 9:10 PM
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Originally posted by Texas70:
If you want a Chevelle with some muscle, put in a big block
Now that's what i'm talking about !! "Big Block's Rule" [img]graemlins/beers.gif[/img]

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post #9 of 35 (permalink) Old Feb 3rd, 04, 9:26 PM
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I don't know too many people that buy a big block hoping to get good fuel mileage I might get 10-11 light footing it [img]graemlins/thumbsup.gif[/img]
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post #10 of 35 (permalink) Old Feb 3rd, 04, 10:21 PM
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Whats Gas Mileage???? Chevy,... HUH?

1985 350 Small Block/Monte Carlo SS
$60 Per Week Daily Driver

1971 Chevelle SS 396 Big Block
Last Summer Daily - $80

Welcome to my world !!!!! And as sad as this is compared to my girl friends 4 banger,... that costs her $10 Per week,... I still love both these cars and can't seem to make myself believe that I need a 4 cylinder,... Drowning!

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post #11 of 35 (permalink) Old Feb 3rd, 04, 11:05 PM
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Heck, buy yourself a Metro three-door hatch, 3-banger, corn-popper car to commute with AND play with shear hp on the weekend!

You will love the 40 to 50 mpg!! Depending on the way you drive b/c I can hit 50 pretty regular in my 2000 Metro!!


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post #12 of 35 (permalink) Old Feb 3rd, 04, 11:16 PM
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It would be interesting to put a 402BB up against a 406 SB.That would be apples to apples.Doesn,t really matter because with lower fuel mileage usually comes lower ET's. [img]graemlins/hurray.gif[/img]

71 El Camino SS
406 SBC M21 3.31 12 bolt
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post #13 of 35 (permalink) Old Feb 3rd, 04, 11:45 PM
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He's an unusual deal.....when i was driving my chevelle on the day i got it i got 22mpg. lol NICEEE (usually got 15mpg) I had a 1979 delta 88 back in the day that got 8mpg. Kinda funny when you upgrade to a muscle car that gets better gas mileage than your daily driver.

wanna run em?
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post #14 of 35 (permalink) Old Feb 3rd, 04, 11:46 PM
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wanna run em?
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post #15 of 35 (permalink) Old Feb 3rd, 04, 11:54 PM
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I didn't think my car was getting bad gas milage,I just thought I needed a bigger tank! [img]smile.gif[/img]

70LS5 461,10.7 288/296F10,posi 3.73 gears, 5speed. My Chevelle
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