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Old 12-30-2004, 01:12 PM
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gas milage on a bbc 427

i am in the process of builing a 59 chevy 1-ton pickup. i came across a deal for a motor, but i need some input on this. i have posted some questions on here about running a sbc on 87 octane, but i would rather have the BBC. the problem i am dealing with is that i want to make the truck a daily driver, and i was hoping for 12 mpg out of it (avg. for a tank) on 87 octane.

i will build it with 9-9.5:1 compression and aluminum heads to help run on 87 octane, but what can i do to increase fuel economy? smaller carb and lower duration cam? is it even attainable to acheive an average of 12 mpg on a tnk of gas with a carbureted BBC?

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Old 12-30-2004, 01:29 PM
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I get about 8 with a GMC 4x4 ton truck running a 454, 20/80 highway/city. I had a buddy getting 12-14 out of his 440 in a 1/2 ton shortbed Dodge, mostly highway. I think I can get mine up to 10 with some more tuning.

I'm running a .030 over 454, 8.5 cr, stock peanut port heads, Edelbrock performer cam/manifold and a 650 cfm Holley spread bore.

I'm going to install an O2 sensor in the X pipe and run a rich/lean meter to get the jetting just right in hopes of the extra few mpg.
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Old 12-30-2004, 01:32 PM
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In the 67 model year the 427 was rated at 10 MPG.If mileage is a concern a big block is not the way to go. I would throw the gas mileage issue out the window,install the big block for cool factor and be happy. If you must have that mileage buy a cheap car with a 4 or 6 in it for daily driving duties.Then on Friday night take the BB truck out.
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Old 12-30-2004, 03:49 PM
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gas milage is a concern, but BB's are cool. i have an 03 Lightning for my DD that averages ~12mpg. i was hoping for something similar with this. it wil have O/D, so that should help. i will probably end up with a 350 or 327, but the 427 is a good deal, and the BB in the big truck would be nice too.

i will not drive a 4 cylinder. i do do a lot of short highway runs (10 mi.) at 60-85 mph.
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Old 12-30-2004, 04:08 PM
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I wouldn't expect over 10 with a big block, my 1/2 ton with a mild 454 9.5:1 with fairly lean jetting gets between 6-8mpg and thats with 3.08's as well.
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Old 12-30-2004, 04:12 PM
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?

Why would anybody concerned about gas mileage even toy with the idea of a big block?
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Old 12-30-2004, 05:31 PM
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Gotta Have Some "Cool" Every Day!

Hey, don't give up on the BB! They CAN
be made to run decent on 87 without
acting like there's a hole in the gas tank!

Years ago, I replaced an anemic 318 2bbl 4 speed with a hopped up 440 6 pack and hemi torqueflite in a heavy duty 3/4ton 4x4. The 318 got 12 mpg, and
so did the 425 hp 440, even though it
took premium.

I also had a warmed up 375hp 396 Camaro 4 speed 3:73's that got
mid teens driving it hard.

And I helped tune a couple friends
box stock 1/2t 350 Chevy's with Q Jets that increased their highway mileage
from barely 12 to over 16 AND gave them
a throttle response boost.

Two things - parts combo and tuning.

What type of 427 do you have?
If it's not a truck engine to start with, hopefully it's a hydraulic cammed oval port and not the 425 hp version.

Let us know what the engine is setup like now, and we'll take it from there.
Lots of good low buck oem or aftermarket used parts out there like intakes, heads, carbs, & cams that can make it happen.

In the meantime, here's some calculators that'll help you determine
compression ratio, both static and
dynamic, and the dynamic one really helps you zero in on a good cam for your combo and goals.

http://www.smokemup.com/auto_math/index.php
http://cochise.uia.net/pkelley2/index.html

Stick to your big block idea!

Now, down to practicalities -

To your 427 - if you don't have a truck motor to start
with, you might have the 390 or 385 hp rating? That would
have oval port heads which are great for street - good
port velocity for good street throttle response yet big
enuf to make decent upper mid range power. And they're
NOT mileage killers in themselves.

A good even oem dual plane, like would have been
on a 390 hp 427, or on the 325 or 350 hp 396's would
again make a great street intake, esp. if you can
score an aluminum one. If not, an Edelbrock Performer
(NOT the RPM version) would also make a great match
for those heads, give you great low and mid range
throttle response with decent upper mid range, and
again not kill your mileage.

For cam, all the stock BBC cams are now old tech, so
you'd want to go with a Performer or something similar.
Stay on the mild side on both lift and duration. Probly
somewhere in the 205 to 210 intake duration at 050,
not over 215. Go into Comp Cams, too, and read their
descriptions for their hydraulic flat tappet cams, NOT
the XE ("Extreme") series - a little radical on lift for what
you're looking for, but rather the Hi Energy or Dual Energy.

THEN tackle the tuning - a decent advance curve, tuned
to give max advance without detonation will make an
amazing difference in both throttle response AND mileage.
I've seen it time and time again, on all types of motors.

Same goes for tuning the carb , esp. if it's a Q-Jet.
I worked on one for a friends' box stock 350 1/2 ton and
increased his highway mileage from barely over 12 to
nearly 16. There are (or at least were) several good
Q Jet experts that sold reasonably priced kits that were
mostly tuning instructions but with some small parts to
go with it that really worked well. A lot of it's got to do
with the adjustment of the vacuum lift on the rods out
of the jets. If you're going 4bbl Holley, a good 650 vac
secondary will do well, esp if you tune in the secondary
vacuum tip ins, not hard to do. Then do some research
on jetting and you can have a good responsive carb that'll
give you good mileage. Esp. if you go the spreadbore
650 Holley that's a replacement for a Q Jet - they're even
likely jetted pretty close.

SO - bottom line, if you have a 390 hp for instance, check
out the stock compression ratio (from what I've seen, 10-1/4, too high for 87, you'd likely want later heads with bigger chambers) and the distance from the top of the pistons to the top of the deck, hopefully it's not too far down in the hole. You need to utilize any
quench area that's built into the heads to prevent
detonation and allow a reasonable amount of advance
while still running 87. If you're a little high on stock
compression ratio and don't have the pistons too far
down in the hole, you can drop compression a little
by using thicker head gaskets. If you can maintain
a quench distance from any flat area on the head alongside
the comb chamber to the piston top of not over .045,
you can make the quench work for you to fight detonation
with a little more advance which helps your mileage.

Or, an alternative would be to look around for other heads,
likely some stockers out there like oval ports from other
BBC's of some type, that would have comb chambers
dropping compression some without using a thicker
head gasket which might spoil your quench efficiency.

Yeah, lots of little things to consider, but a fuel efficient
engine, running on 87 octane, CAN be built in just about
any type or size of engine IF you put the right combo
together and tune it right.

I'll keep digging and see what I can find.

Last edited by macx; 12-30-2004 at 05:31 PM.
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Old 12-30-2004, 08:24 PM
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Re: ?

Quote:
Originally posted by bracketeer
Why would anybody concerned about gas mileage even toy with the idea of a big block?
Agreed.

Cant have the best of both worlds...

However, u can get close.. 9:1 compression and a 114LSA and small lift with a 650-750cfm carb, not ever giving it full throttle and leaving it in OD all the time should get you some decent MPG. But performance just went out the window..
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Old 12-31-2004, 07:20 AM
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thanks macx!

i have at least one supporter here.

i don't have the motor yet, i want to see if what i want to do is even possible before i buy it. about the engine, according to the ad:

427 BBC BARE BIG OVAL PORT HEADS W/SS VALVES,STRIP DOMINATOR INTAKE, 280H COMP CAM FORGED TRW PISTONS,STEEL CRANK NOT SURE ABOUT RODS.

i obviously will have to get a new cam and intake. but it looks like it comes with oval port heads (they just need to be assembled) i will inquire further to the seller about the heads, pistons, and block.
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Old 12-31-2004, 07:48 AM
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Quote:
i have at least one supporter here.

Man,you have thousands of supporters here.We are just saying that gas mileage and a BB do not go hand in hand. I say build it and drive it.The fun will outweigh the stops a t the gas station.
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Old 12-31-2004, 07:54 AM
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Quote:
Originally posted by RCastle
Man,you have thousands of supporters here.We are just saying that gas mileage and a BB do not go hand in hand. I say build it and drive it.The fun will outweigh the stops a t the gas station.
but i want my cake and be able to eat it too!

i am not hoping for amazing gas milage out of this thing, i just want to know if i can do it with reasonable milage (double digits)
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Old 12-31-2004, 08:01 AM
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Re: Re: ?

Quote:
Originally posted by arch
Agreed.

Cant have the best of both worlds...

Actualy you can! you might want to look into a gearvendor under/overdrive? It is possable to save up to %20 on fuel cost! www.gearvendors.com they are pricey but they are bolt on units that can be transfered to another vehicle with the same or different adapter? I installed one on my 700R4 4 yrs ago to get my fuel mileage back after installing a higher stall converter(see attachment) this way I get of the line fast when needed and gas savings in double over!
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Last edited by ronb; 12-31-2004 at 08:14 AM.
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Old 12-31-2004, 08:10 AM
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Just watch your gas gage...

and fill it up every time it gets to 1/4 tank is all....you'll never run out of gas!!! BBC do not = good gas mileage in any way shape or form...does not compute.....don't buy it if your concerned with the mileage you'll get...just forget it!!!


Tazz


Rat Rods Rule!
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Old 12-31-2004, 08:17 AM
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Gearing

You've got a good start - now you need to find out what
is in there for pistons and then what cc heads it would
take to get it around 9-1 cr, then what cc those heads
are.

You're right on the money that you need a diff intake
and cam - you could probly sell those to partly offset
the cost, and likely even find a decent used intake
fairly reasonable.

I totally agree with the above, basically that gearing
will be the other big factor. The 1 ton is likely to have
somewhat deep gears, so your other gearing choice is
in the trans. Gear vendors is great, but quite spendy.

Also, a lockup converter trans helps on the highway.
So, you might want to look at a well beefed 4L60E or even
7004R, although the 700 has a way deep 1st gear, but
again, that might be what you want with a heavy rig even with fairly deep rear gears.

Look around tranny sites like TCI - the 700 is a well known
trans with lots of stuff developed for it.

If you can get your overall gearing up there with an OD,
and use a lockup, you really shouldn't have a problem
getting double digit mileage, if you can set your motor
up right. Cam timing and comb chamber size & quench
utilitzation will be key there.

Keep us posted - sounds like fun!
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Old 12-31-2004, 08:35 AM
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it is going to be a manual, not an auto. i think the factory rear gears are like a 5.14:1. those will most likely br replaced with a 3.08 posi of somethink like that.
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