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Old 07-10-2007, 11:40 PM
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Making the chevy 350 v8 more fuel efficient?

What have you guys done to make your 350 more fuel efficient (or any small block chevy)? im aiming for 300hp that gets atleast 25 mpg highway. Fuel injection conversion is one. any recommendations would be great. as well as books

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Old 07-11-2007, 12:11 AM
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Vortec Block Cylinders honed with deck plates, block decked .010, KB 12cc D Dish pistons, GM head gasket .028 thickness for quench of around .045, Comp hydraulic roller cam, specs of 206 duration @ .050, .500 lift, Cloyes vortec timing chain, Vortec heads set up with springs to match the cam, Edelbrock performer intake, Q-jet carb, small tube headers, dual exhaust with exhaust crossover or X pipe, turbo mufflers, HEI with pertronix flame thrower coil and module, Spiral core spark plug wires routed correctly, High quality cap and rotor. K&N air filter, with cold air induction, serpentine belt system, run on synthetic oil after 5,000 mile break in period, front wheel bearings packed with synthetic grease, rear end with royal purple synthetic lube, keep it waxed and clean. While this is a heck of alot of work, it`s what I did to my cutlass, and it paid off in mileage and had killer torque, problem was it sounded like a diesel, machinist honed the cylinders out to .009, way too big, and dummy me didn`t check them trusting his work. after about 2000 miles, I never went to synthetic motor oil, cause when it got around 2000 miles on it, it started to smoke and use oil. Another way is to install a vacuum gauge in the vehicle, keep it at it`s highest vaccuum that you can, keep a constant check on the tires air pressure, and you`ll see a mileage increase for your rewards. I`m sure there`s several other ways as well without going through this expense as I did only to have to start back over, but the roller cam and springs I`ll soon be selling, my next build with this block will be a 327, and it`ll be more performance minded so I won`t need the cam anymore.
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Old 07-11-2007, 06:46 AM
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Best thing to do is be sure to use a Q-jet it will definately help with mileage.
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Old 07-11-2007, 06:49 AM
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Park it






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Old 07-11-2007, 07:23 AM
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small cam (200/205 degree duration at 0.050")
later model Q-jet (171..... serial number) or efi (q-jet is much cheaper)
small tube headers
manual trans with OD
OD overal gear ratio of 2.20:1 (od gear x diff gear)
skinny tires
light weight car
drive slow
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Old 07-11-2007, 07:34 AM
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Chevy's Performance crate small blocks approach that in street rods. We have several club members who routinely rack up 23-24 MPG on rod runs with their GM Performance Parts crate engines.

My son's 405hp 2003 ZO6 Vette with get 24 MPG highway if driven properly.

Vince
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Old 07-11-2007, 08:01 AM
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Quote:
Park it
That's what I did

It's more about aerodynamics and weight, rather that diddling around with the motor.

I've got 2 mid 60s chevy trucks; a suburban & pickup, and I've tried all different cubes, trans, gearing,carbs,etc. They are land barges and I can't run them as dailys anymore.

I learned a lesson on aerodynamics back in the early 80s when cars stated to go with aerodynamic bodies, tiny cubes, big overdrives with lock-ups. A new Pontiac 6000 with the iron duke 2.5 4cyl, 2.39 gear w/lockup. The car had enough zip & gas mileage, but one day we had to carry something bulky in the trunk and the lid stayed up. I got on the highway and thought something was wrong because I could barely do 60.
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Old 07-11-2007, 08:07 AM
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Quote:
Originally Posted by 454C10
small cam (200/205 degree duration at 0.050")
If you have a roller cam block the GM '395 Marine roller cam is an excellent choice. 196*/206* @ .050", .431"/.451" Lift.

I have most of the pieces to build a 355 very similar to DV's only using this cam. It's going into an '89 C1500 Sportside with a 5 speed manual and 3.42 gears. Final drive ratio in 5th (OD) will be 2.46 to 1. I also plan to lower the truck to get it down out of the wind and will be running 235/70 tires to maintain a balance between load capacity, handling and rolling resistance. I'll be running a 1400 Performer 600 cfm 4 Bbl. on a Performer intake to start but may eventually adapt the TBI. From what I have collected by talking to people running similar combos in full size trucks 20-21 MPG should be a piece of cake and with the addition of the TBI, some tuning and other work I might squeeze a bit more out of it.

Quote:
Originally Posted by F&J
It's more about aerodynamics and weight, rather that diddling around with the motor.
Yeah, having a light aerodynamic vehicle to start with is probably the biggest factor. Even a small air dam in front to keep air off the underside can make a difference. On my '76 Monte Carlo I easily lose 2-3 MPG by popping the T-tops out and when you're only pulling 16 to start with........ It doesn't stop me from pulling them out on a nice day though.

Last edited by Hippie; 07-11-2007 at 08:16 AM.
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Old 07-11-2007, 08:52 AM
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How heavy is it?

I get an honest 20mpg average on regular gas with a stock 88 Corvette tuned port injection in a 3700 lb car. Possibly a little more could be squeezed out it I used headers and roller components. It is a five speed manual with 3.36 gears. I don't think 25 is possible in my case.
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Old 07-11-2007, 01:22 PM
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Quote:
Originally Posted by k3werra
What have you guys done to make your 350 more fuel efficient (or any small block chevy)? im aiming for 300hp that gets atleast 25 mpg highway. Fuel injection conversion is one. any recommendations would be great. as well as books
My 89 S-15 has a SMOG legal 95 LT-1 in it with injection, headers and duals; 4L60E with lock up and OD; 3.08 posi; Z-28 wheels and tires. It's 2 wheel drive and slammed a little. Driven daily in 30 mile each way freeway commute, it's never seen the high side of 20. Mileage goes away pretty fast over 70 (about 1800 RPM), but then the old S-10/15 body has the aerodynamics of a cement block. Stop and go on city streets is 14-15 if you don't get on it between lights. Seattle area is hilly to mountainous, traffic is ugly.

Bogie
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Old 07-11-2007, 06:59 PM
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thanks for your replys. im doing research right now on how Im going to build up my 350 small block for my datsun 240z. weight shouldnt be an issue since it only weighs about 2300 lbs stock. with the conversion (engine,tranny,lsd,etc) probably around 2700 lbs. could i get 300 hp w/ 25mpg using another small black engine (maybe will a super charger)?
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Old 07-11-2007, 07:14 PM
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Quote:
Originally Posted by Rob Keller
Park it






R

well said and has allot of meaning to it, I am happy at 10 -15 mpg, but that is 383 @ 424HP fun ride HOTROD!!!
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Old 07-11-2007, 09:41 PM
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'72 Nova, 3.08's, 4-speed, 350, 8.5:1, OEM Q-jet, L-82 camshaft pn3896962, points ignition w/40* mechanical advance @ ~2500rpm + 15* vacuum advance, factory dual exhaust, pretty much stock ride height, 235-60-14 radials w/~36psi.

Years ago when the motor was fairly fresh, it got a best of 23.25mpg (highway), but would consistently get 21 or 22 if I kept my foot out of the gas. Around town, more like 15-16.
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Old 07-12-2007, 05:51 AM
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I've got a similar project in the works, 86 chevy short box. Planning on building a very mild 454 grunt motor, th350, 29inch tall tires, and hope to find some 2.50ish gears for the 8.5inch 10 bolt rearend. I figure if it stays on the idle circuit at 65 it just might pull some decent mileage?
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Old 07-12-2007, 06:37 AM
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Quote:
I've got a similar project in the works, 86 chevy short box. Planning on building a very mild 454 grunt motor, th350, 29inch tall tires, and hope to find some 2.50ish gears for the 8.5inch 10 bolt rearend. I figure if it stays on the idle circuit at 65 it just might pull some decent mileage?
Good luck with that ....

My 63 Suburban: stock 400 SBC w/Quadrajet, Th350, 2.76 gear with same tire dia, does not "idle" at 65. It still needs much more gear IMO or a Th350C with lockup converter. This one is real bad around town mileage too, compared to my other truck:

A 66 camper special 4wd, stock 350 w/edelbrock afb on aftermarket dual plane, Th400, 3.21 8-lug full floater, with the tall skinny radial tires. This heavy 4wd beats the suburban on around town driving, and may even beat it on highway miles. I think it's cubic inches more than gearing, etc. IMO....just common sense; 16 to 1 air fuel mixture X cubic inch volume X RPM per mile.
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