Which would give you better gas mileage supposing you could drive the same way every time, a chevy 6 cylinder with a high rise intake and holley carb (or) a chevy 8 cylinder with a high rise intake and a 2 barrel carb? Is there a better combo? Keep in mind that Im on a budget and these are junyard motors that are easily found. Is there something better than this? If I had to summarize a price range I d say that Id be willing to spend around 3 or 4 thousand.
More of a question than an answer, but what rear end do you plan to use and what kind of tranny? To me, that is key to gas mileage.
I'm running a 350 c.i.d., 4-bolt main, 10.0:1 compression, Aluminum dual plane intake manifold with a Holley 4bbl, turbo 350 transmission and a 10 bolt with 3:73 gears. I get 13 mpg on the freeway and 14 in town.
Many Variables TOO many in fact , your driving place and style have much to do with it too but , all else being equal it'd be hard to beat a well tuned 235/261 with two single barrel Cart er YF's and a merged , dual outlet exhaust manifold . You'll have to keep a sharp eye on the tappets and ignition timing , fiddle it by setting full advance to the maximum it'll take and not ping during a Throttle Ping Test... A 185° thermostat is necessary to as the engine is more efficient the closer to boiling you run it . Narrow , high profile _radial_ truck tires of course .
trans and rear axle I plan to run a 700r trans and a guess a 3.? rear axle. Im not sure what rear axle ratio would be the best for highway speeds. Thats a topic for research for the future. michael grove ok.
Final Drive Ratio ..3.72 would be *perfect* but you'll need to always remember to keep it out of overdrive when In Town . Most American driver's cannot remember this simple thing and so lug their engines to death in 30,000 miles and blame the manufacturer .
The two well tuned carbs are a definite plus because an inline six has a terrible intake manifold layout. The air/fuel mix has to make FIVE ninety degree bends: into the side of the air cleaner and a 90 to go through carb (more with an oil bath), out of carb and a 90 into the manifold, a 90 into the cylinder runner, a 90 to go up under the valve, and finally a 90 to pass under the valve and into the cylinder. You can't do much about the design (maybe eliminate one 90 by making a K&N funnel type filter, but by having a carb by #2 and #5 cylinder you distribute the fuel so much more uniformly, eliminating the long travel to #1 and #6 cylinder. A real plus in cold start up. A tri-Y exhaust along with an "H" pipe is the most efficient but a lot of fabbing. Then it gears, gears, gears. I drove a 57 with a 3.08 rear and a Borgwarner OD, thats a final of TWO SIXTEEN (2.16). I drove it about 20 miles back to the guys shop through rolling hills, don't know about wind direction at the time, and it did fine. Had a very sweet running stock 235. I think 65mph with his tires was about 1600 rpm. What this shows is that if the picture doesn't include hauling or towing then this old torquer can handle some really shallow gears which translates to better fuel mileage.
