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.
