Big Block VS Small Block gas mileage [Archive] - Chevelle Tech

: Big Block VS Small Block gas mileage

Feb 3rd, 04, 3:54 PM
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?

Feb 3rd, 04, 4:09 PM
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.

Feb 3rd, 04, 4:18 PM
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 tongue.gif

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

Feb 3rd, 04, 6:09 PM
We don't build big blocks to get better economy
in my part of town. :D

Feb 3rd, 04, 7:00 PM
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?) graemlins/clonk.gif 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 :D ) if it wasn't for the gas mileage? Getting about 35-40mpg! I like that for commutting. graemlins/thumbsup.gif

Feb 3rd, 04, 7:43 PM
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 :D

Feb 3rd, 04, 8:00 PM
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.

Feb 3rd, 04, 10:10 PM
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" graemlins/beers.gif

Bob West
Feb 3rd, 04, 10:26 PM
I don't know too many people that buy a big block hoping to get good fuel mileage :D I might get 10-11 light footing it graemlins/thumbsup.gif

Feb 3rd, 04, 11:21 PM
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!


Feb 4th, 04, 12:05 AM
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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Feb 4th, 04, 12:16 AM
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. graemlins/hurray.gif

Feb 4th, 04, 12:45 AM
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. :D

Feb 4th, 04, 12:46 AM

Feb 4th, 04, 12:54 AM
I didn't think my car was getting bad gas milage,I just thought I needed a bigger tank! smile.gif

Bob West
Feb 4th, 04, 8:44 AM may get excellent fuel mileage,but I'd hate to be in a wreck in your GEO vs. my 98 peekup or a tractor trailer for that matter. I'll gladly take the 15-19 mpg and safety vs. 50 mpg. graemlins/thumbsup.gif heck,at 6'3" 285 I don't think I'd fit in a GEO :D

Feb 4th, 04, 8:56 AM
We have five vehicles:
'69 Vette 427
'72 Chevelle 350
'93 Vette 350
'95 Jimmy 6 cylinder whatever engine
'98 Jimmy with same whatever engine
No-one ever believes that a Corvette gets the best gas mileage but the '93 gets between 23-24 highway and the next closest one is the '98 Jimmy with 19 highway. The '69 Vette is 15-16. The other two are right around 14 mpg highway. I really thought the Chevelle would have done better than that. ( and no, it doesn't seem to drive like it needs a tuneup smile.gif )

Feb 4th, 04, 10:08 AM
I agree with pegleg. My daily driver is a 1999 Honda Acoord V6 that gets pretty good gas mileage. It also has 200 hp and is a kick to drive in the Houston traffic down Westheimer every morning and evening. On weekends I will not worry about gas mileage (when my chevelle is finished). Fill the fuel cell and when it's empty, fill it again :D

BTW, a big block automatically has more power than a small block...... graemlins/clonk.gif tongue.gif lol

Feb 4th, 04, 10:14 AM
WTF are we talking about 1200cc motors here???

Oh and BTW, if I whomp on my big block at all, its 10-11 mpg.

Now John 71350SS has an excellent thought. According to my ROUGH equation, a 406 bbc and a 406 SBC would have identical gas milage given identical DCR's temps, gears, chassis, etc.

Wonder if the smaller intake runners of the sbc help here???? That would effect the "throttle opening %" of the equation.
But I really don't give a rats arse about Geo's. I had a Spectrum, it got 35, SO WHAT!

I beleive this is in PERFORMANCE!

Feb 4th, 04, 10:54 AM
more power = more fuel

I bet if you had a mild 396 or 402 BB that was not making much power and compaired it to a really built 350 making tons of power, the BB would get better fuel milage. But why have a BB if it is going to be so de-tuned? Muscle cars are not for fuel milage. build it to go fast, big or small block depending on which you like and forget the fuel milage.

About geo metros: I don't really like them, but my friend had a brand new one and we were riding in it just a few days after he got it. Some cell phone wielding soccer mom in a minivan ran a stop sign and t-boned us in the pass side (where I was sitting), which in turn turned the metro to be skidding sideways in the lane of oncoming traffic where another van, this time full size, t-boned us in the drivers side. the van was going about 50mph and were were doing about the same. THis all happened in a matter of seconds. The impact from the second van actually threw the little metro about 15 yards back before the intersection that the first van ran. My friend and I basically walked away. We both had concussions, glass cuts and such, and he had a broken rib. the car was a mess. So, although I still don't think they are as safe as a bigger car, they are safer than they look, othewise I wouldn't be here today.

mr 4 speed
Feb 4th, 04, 11:10 AM
My daily driver 67 Caddy Sedan DeVille gets 9 mpg and I don't care graemlins/thumbsup.gif
..and you wouldn't want to get into a fender bender w/me ;)

Feb 4th, 04, 11:40 AM
Originally posted by mr 4 speed:
My daily driver 67 Caddy Sedan DeVille gets 9 mpg and I don't care graemlins/thumbsup.gif
..and you wouldn't want to get into a fender bender w/me ;) You win! graemlins/thumbsup.gif

Feb 4th, 04, 12:05 PM
Originally posted by mr 4 speed:
My daily driver 67 Caddy Sedan DeVille gets 9 mpg and I don't care graemlins/thumbsup.gif
..and you wouldn't want to get into a fender bender w/me ;) "Pimp Daddy" !!What size motor?

young gun '71
Feb 4th, 04, 12:09 PM
My Dad's 51 chevy 1/2 ton has the original 216 and we get 9 mpg. It has real low gears.
My chevelle gets 16-18 when I drive my dad might be able to get 19-20.
Dad's 80 corvette has a 350 th350 and he gets 20-21
Mom's truck gets about 25 and it is a 02 gmc 4.8 1/2 ton
my 28 chevy roadster gets 0 mpg, there's also nowhere to put the gas. :D
Zac graemlins/thumbsup.gif

Feb 4th, 04, 12:22 PM
cost to fix up a BB engine: $6,000

cost of gas you spend in a day: $20

cost of all the thumb's up and the looks from chicks you get while driving in your fixed up pavement pounding chevelle: priceless

mr 4 speed
Feb 4th, 04, 12:25 PM
Scott,its a 429

Feb 4th, 04, 12:38 PM
The chevelle, with its sickly small block gets gas footage, not milage, and the Olds gets about 8 around town. I think it would be better if it wasn't for the piece of trash transmission in it. Funky slim jim.... JUNK! I borrow other cars from the family whenever possible, and always fill the tank, its still cheaper than driving mine, but not near as cool!

Feb 4th, 04, 1:07 PM
71350ss, I don't think your 406sb to 402bb will work. I say that because 1fast69chevy has a 406sb and he gets 14mpg with 3.90 rear gears. my 402 bb gets 8-10 when really in good tune with 3.73 gears. And, mine as a 700R-4 od trans.


Feb 4th, 04, 1:43 PM
my 86 ford truck is in great has the 302 fuel injected rollor cam factory BS stuff........and even with it 4 speed over drive gets 12 mpg.......thats 80 z28 with a bbc 414ci gets over 17 mpg...........and my 81 camaro i would guess around 5 mpg but never figured just sucks the gas around town........

honestly i dont think there is a huge difference i think personally you could build a bbc to get better gas mileage campared to a sbc....

bbc can use less needs less stall...and in most cases it needs less foot throttle for given mph say to run 70 mph down the highway.

im just saying if there was two engine one sbc and one bbc........both putting down 400 hp.........we all know the bbc can do this with a fairly stock style cam....and wouldn't require much of a stall less then 2500 return wouldnt take much gear either to move it down the track..........compared to the small will rev higher in the rpm range...stall would be 3000 plus ...take more gear for the car .....just so it could keep up with the bbc........

i think in a case like this the bbc would get better gas milage......

how many of you run say 98 mph in a 1/4 mile with a small block chevy and still honestly pull down over 17 mpg......well thats what my bbc does.......

Feb 4th, 04, 1:58 PM
Originally posted by ddeennis:

how many of you run say 98 mph in a 1/4 mile with a small block chevy and still honestly pull down over 17 mpg......well thats what my bbc does....... My 95 Z28 Convertible runs 105 in the 1/4 and gets 28mpg on the highway with 4.10 rear gears, also a 6 speed. Its all in the combination.

Feb 4th, 04, 2:03 PM
I pulled 99 mph in the 1/4 with my 327. I got an honest 16 mpg on a highway trip. Probably could have gotten better, it was in the mountains, and i didn't drive it that easy.


Feb 4th, 04, 2:57 PM
How about 118+mph and 15+ was 16+ with the old cam at a 114 lsa, but I'll take the added power and -1 mpg loss...

I mean since you guys are friggin' braggin' here...usually not my style.....but beat that one N/A

and other than the modern UD cam and MSD ( which I dont think adds much), its all 1969 tech???!!

mr 4 speed
Feb 4th, 04, 3:14 PM 4000# 454 powered 2.73 geared slug runs high 12's and get 12-15 MPG for what its worth..probably better now with the 3310 ET wise and gas mileage ;)

Feb 4th, 04, 8:27 PM
Originally posted by mr 4 speed:
Scott,its a 429 Sweet!! graemlins/thumbsup.gif

Feb 5th, 04, 8:02 AM
You know, I'm not betting that I'm gonna get killed in my Metro driving ta work so I don't even think about it b/c if I did, I wouldn't get out of bed in the morning!!

I drive aggressively defensive which really helps me avoid the dick-bones out there with their cellphones and 2-1/2 to 3 ton gas guzzlers and all....


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