Hi, If you really want to save gaz, change the tranny for an overdrive such as 200r4, 700r4. You will improve gaz mileage and motor will not be affected. If you need more power... transplant to 350 engine.

 

Yes I do understand that, thanks, but that wasn't the question.

 

If built the same, the smaller engine will have better gas mileage....but less power.

 

My thoughts are there is a trade off some where with power vs. fuel. Wouldn't a 305 have an easier time then a 265? In having an easier time, would it get better economy? What about between a 305 and 350?

 

I don't understand what you mean by "easier time". It takes a certain amount of horsepower to push a car down the road at a given speed. It takes a certain amount of fuel to make that horsepower. Either engine can make enough power to do that.

The difference is that a larger engine has more frictional surfaces (rings, pistons, maybe crank), and more pumping losses because it's displacing a higher volume of air. It also has a larger cylinder area to lose heat through, which results in losses. Those losses translate to higher fuel consumption, all else being equal.

 

So to move my car @ 55mph, a 265, 305 or a 350 would have to produce "X" amount of HP using "F" amount of Fuel?

IF:
Using a 265 and "X =55 HP" and "F = 14 MPG", would that be the same for the 305 and 350?

 

would that be the same for the 305 and 350?

No, as I said above, the bigger engine will typically have higher frictional, thermal, and pumping losses. That translates into higher fuel consumption. I can't tell you exactly how much higher, but it's not a huge amount compared to the fuel required to make the car move.

 

Bigger engine = bigger consumption of fuel.

 

265, 305, or 350

CLSSY 56....Believe it or not, I have a 55 in progress and was making the exact same considerations...I finally found a 64 283 engine with a 2 bbl carburator....The 265 woul maybe get a little better gas mileage, but has no provisions for side mounting and the oiling system is another drawback for me...Plan on rebuilding the 283, going with a 200-R4 tranny and already have 3:36 gears installed....Later down the road, I plan to install a Holley Pro Jection system....IMO this combo should do pretty well on gas, power, and reliability....david

 

So would I be better with a v6?

 

almost afraid to get in this one . size matters bigger eng. will use more gas lead foot will burn more gas anyway

 

Just my opinion, but if you're talking about the 3 engines mentioned in stock form, then the 265 would be the way to go, especially just to cruise in since the 265 will make plenty of power to move you down the road and will consume less fuel cruising at a given RPM. On the other hand, if you were planning on upping the breathing ability of that little motor to have the power of a larger engine and the gas milage of a 265 think again. bigger cam, better breathing heads and so on = low efficiency at low rpm, might be better off with a stock 350 which would be perfectly suited for low RPM cruising. All depends on weather or not performance is in the equation.

 

There is one main parameter that drives gas engine efficiency.....compression ratio. The higher the compression ratio, the more efficient the engine. Better breathing heads don't make an engine less efficient. A cam not designed for low RPM operation can significantly degrade gas mileage, as can a mis-matched carb.

Clssy56....you're not listening. Less displacement will usually yield improved gas mileage. Why not go with a 4 cylinder, or even a V-twin?

If you want good gas mileage, pick a smaller dispacement engine, keep the compression ratio up as high as your fuel will allow, use EFI and a good ignition system, keep it tuned up, get an overdrive transmission, and drive slow.

 

Well my 265 gets about 14mpg (as they did new), but I do know mine isn't dialed in right. My carb is too big for my motor (smallest 4bbl edelbrock makes is a 500 cfm). I know getting an OD tranny is the ticket. Just wondering if I should continue to stick money in the 265, or upgrade. I do have a 350, but needs rebuilt. I would like to get a 200-4r, just haven't yet.

 

If your looking for economy, I'd buy the 260 HP 350 Crate Motor for under $1500. If wanted, add a high performance cam, headers, 4 barrel manifold and carb. That would probably be cheaper in the long run then rebuilding a 265, 283, 305 or 350. You can use all the money you saved buying gas.

 

in my opinion, the answer to the question is, it depends on a bunch of factors. i have had all of those engines, and it just depends on how they are built, and the trans, axle, ect. i have also heard people say that the less gear in the axle, the better, but thats only true to a point. my wifes 56 4dr, stock 265, powerglide never got more than 15 mpg. my 56 2dr turns 3100 rpm at 55 mph and has a 420 smallblock with mechanical roller cam, victor jr intake, 750 holley carb, 350 turbo trans. i got a consistant 16.6 mpg on a 900 mile trip. it was just dumb luck, but everything must be at peak effecentcy at that rpm. i would use the 350, and choose my parts carefully, and my timing curve. i dont know how a 336 gear would work with a overdrive trans, may be too much??

 

CLSSY56, what kind of mileage are you looking for?

 

Keep this in mind. While Chevynut is right about the pumping loss, friction, and thermal losses, the fact that you are comparing Chevy V8s means that the thermal losses are the same for all practical purposes. The friction varies ever so slightly based on stroke. Pumping loss is roughly the same at part throttle because the throttle opening controls it (you shouldn't need to open the throttle quite as far with the bigger engine). So, .... if your 350 is geared to run slightly slower than your 265 (not too big a stretch to be the right thing to do, all else equal), and you can run it at the same road speed with the throttle closed a bit more, then the pumping loss and friction cancel out.

So.., I say work on what you have.

 

Okay, Rick, then why is it that you say I can't get 20 mpg with my 502?

Why doesn't friction depend on bore as well as stroke? The swept area of the rings is a lot larger with a larger piston. As well, the thermal losses would be proportional to the cylinder wall area, I would think. Your comment about pumping losses makes sense though.

If what you say is true, then displacement should have no influence on gas mileage.

 

Bore size makes a tiny difference on both the friction and thermal loss. I don't think it matters in the big picture. On the other hand, I'm not sure the difference in stroke makes a big friction difference either, especially at overdrive engine speeds.

I think the thermal loss is more of a function of the cylinder heads and overall engine configuration - not much difference there as long as it's SBC.

Just my speculative opinion. In other words, while these things might matter, and all the details add up, you have to make bigger changes than the difference between a 265 and a 350 (or in between) to make a significant difference, or to offset the cost of a different engine.

A V6 should have a small advantage at low rpm's I'd think. Less parts, less surfaces.

Again, as a practical matter, work on what you have. After all, the question is about a DIY economy project. Using the parts already on hand is a good strategy for minimizing the overall cost.

 

travis, go in between all of them and run a 327

 

Man I wish I would of kept my 1966 327 PowerPak.... had bought it for my first 56, sold it to pay bills.

 

Travis....

I'll sell ya a rebuilt 265!

 

My 265 now is relatively low miles. It is leaking again, think it's the timing cover.

My 265:
1956 Powerpak motor (factory replacement motor 1960)
305 heads
stock exhaust manifolds
Offy single plane intake 360º
Edelbrock 500cfm 4bbl carb #1404
1968 distributor w/ Crane XRi pointless ignition system

Rear End Gearing:
3.55 Stock

I would like to get some respectable mileage out of it, not happy with 13-14mpg.

I also have a 2-bolt 350 on an engine stand that needs rebuilt due to low oil pressure (from what I was told).

 

Just to confuse yall more, put in a differant ratio ring and pinion. 272 would give better mileage than the 325. Great on the highway, but forget the acceleration. Even going to a larger rear tire would help.

 

I am running a 327 with 2004R trans, 3.55 rear end. I had 3:08s but they were too tall. If you are running a lopy cam, they don't like high rear ends. Mark

 

you could always try to set up a 4.3 fuel injected witha 6 speed, double over drive and some 4.56 gears in the rear end. good take off and good freeway. bu that's the best of some worlds, not so much drag racing

 

i thought amount of torque would move you, not horsepower. hence a 105 horsepower 3.9 cummins diesel with 320 ft.lbs of torque. the same amount of torque as a stock 350, would get you about 18 mph. or so i've heard. setting up a 4.3 v6 could possibly get you 18-22mph but i wouldn't throw revs at any one. 305 is a small bore 283. 350 is just a stroked 327 307 is a small bore 327, and a 302 is big bore 283. now i'm confused. so here goes a 350 ,327,302 have a 4 inch bore the strokes are 1/4 inch difference. a 307and a 327 have the same stroke, 283and a 302 have the same stroke, a 305 has a smaller bore larger stroke than a 283. so all in all a 327 would give you the best all around performance and a 302 would give you rpms, gearing being a big consideration.

 

a 105 horsepower 3.9 cummins diesel with 320 ft.lbs of torque. the same amount of torque as a stock 350, would get you about 18 mph. or so i've heard.

I have a 3/4 ton Chevy Silverado with a 6.6L Duramax diesel, and I get 23+ mpg highway mileage. I recently took a trip to WY and with 4 people, an ATV, and a bunch of luggage in the truck I got 22+ MPG. I get around 19-21 mpg all-around driving in town and to/from work. That's with 605 ft-lb of torque off of an idle. I can't believe that a 3.9 Cummins wouldn't do a LOT better than 18 mpg.

 

The first thing you need to do is chunk that single plane intake.

Next thing is look around for a 3.36 or 3.08 3rd member.

The manifold will pay for itself quickly.

The rear gear will too if you drive on the highway a significant amount. Otherwise the payback won't be quick but it should still be there.

 

i have a single plane intake on mine why are they bad?