which is better for fuel economy bigger engine less gear or smaller engine more gear?

[moturbopar]

Hi all, I am trying to decide on an engine combo for my work van. the old 250 is getting old and has horrible fuel economy now. Anyways I am trying to decide on the best way of getting the best performance and fuel econmy. I basically have 2 choices.
What I am looking at is either using my 400sb or my 283. The engien I will be building will be very mild rebuild with small cam pocket ported heads and performer intake. I will be using 1.5" long tube headers. Which ever one will be run through a 700r4.
The difference will be in gear ratios and converter choice.
The gears planned for the 400sb will be 3.07 and the gears for the 283 would be 4.10s So which is better for fuel economy bigger engine less gear, or smaller engine more gear?
Either way I am sure it will out perform the old 250.
thanks

 

[blazerpro79]

im gonna say the smaller motor would use less fuel, and if calibrated with the right components, could be a litter better. a 283 is a good, old, motor. whats the 283 from anyways? either way, they are both gas guzzling v8s. the torque numbers will be a little lower out of the 283 as opposed to the 400 though. id go with the 283 and lower gears

 

[txfiremank5]

I don't know the "for sure" answer .. But look look at a Toyota for example:
Small engine, usually low gears, w/ good mileage.

 

[350k5]

Personally I would say that the 283 with the 700R4 and the 4.10 would give you the best gas mielage. The higher gears would mostly make the engine run at higher RPMs while cursing at highway speeds. But since you've got an overdrive it would probably give you pretty good results. I'm not sure but 4.10 could be a little high for best mielage and a slighly lower gear ratio may not make it as qucik but will save you mielage on the highway. Thats just my .02 but I'm sure someone else on here would be able to give you some more specific advice.

 

[Greg72]

I'll bet the answer has to do with the throttle position required to create the needed HP....

Assuming that it took 100HP to maintain the vehicle speed (rolling resistance, aerodynamics of a brick, etc), then no matter what engine you choose you still need 100HP. Gearing will help to give some advantage to the engine (less power needs to be generated at the crankshaft) but the deeper gears will require more revs....and every cylinder gets a sip of fuel every time around...so those extra revs are still costing you fuel.

It's a good puzzler... I'll be checking back on this thread to see what people come up with.

 

[dyeager535]

Go check out a model line like the GM trucks. See what the 5.3 gets vs. a 6.0 (those the current 1/2-3/4 ton engines?) in the same truck.

Smaller engines must be more efficient, no matter how well geared or how much torque they make, I have yet to see a V8 equal a 4 cylinder in economy. I wish I had a tach in my car just for curiosity, it sounds like it's screaming at 60MPH, but still puts down 36-38MPG at that speed. I would suspect a K5 with a 4 cylinder would net terrible mileage at slow speeds compared to an engine 4 times the size in the same truck.

Look at all the folks that have changed from 305 to 350 in these trucks and achieved similar or better mileage. All sorts of factors at play here though...rolling resistance, where the motors make power, etc.

Part of it is how enjoyable it is to drive though. No matter what the economy, acceleration and being able to climb hills is infinitely more enjoyable than the alternative.

 

[neverendingproject]

From experience, my smaller motor had to work harder with my truck than a bigger one. The bigger motor gets better mileage. I would say that either way would yield about the same results b/c

1 the samller motor will have to turn at higher rpms and work harder witch means more fuel on both ends.

2 the bigger motor will turn at lower rpms, and have to work less but it is a bigger motor.

So with that, the smaller motor burning more fuel or the bigger one burning less..... its a tough one, but in a van, I think results would be comparable for both.

 

[pauly383]

I'd run the 400/700r4/3.07 in the van with a quadrajet and keep my foot out of it .

I'd buy some speed parts for the 283 , a Nova II body and frame , and hit run what brung nite with those 4.10's

 

[moturbopar]

Yea Im not sure what to do. If I had my choice I would put my 472 I have in and run my 2.73 rear end, but the problem is it just doesnt fit in the van.
I am leaning to the 400 since parts are cheaper and it will make better torque for pulling.
I think the 283 would get slightly better fuel economy on the highway with it higher compression, and less rotating mass, but around town I think the torque/or lack of would hurt the fuel economy.

The cam I have is very mild. 204-214 exhaust with a 112 lobe seperation.
I think this cam would work well in either engine for what I am needing to do. The intake is an old performer EGR and I have a couple quadrajets to use.
So what you guys thnk? Anything else that I could do to help out fuel economy?
Tnaks for the replies!

 

[pauly383]

Change your filters , and oil religiously , use synthetic axle lube , and keep your foot out of it

 

[monster man]

It would be hard to compare unless both motors are freshly built, using the same exact carburetor, intake, exhaust, etc. Then you would just compare how much each engine will suck in within a certain time frame, using your gear ratio, speed, weight, etc. But, I'd guess the larger motor would be a better choice. Just because it has a lot of cubes doesn't mean it will suck more gas- put smaller jets on it, lean out the idle circuit, make sure it has a lightwieght dual plane manifold, mild cam, headers, and free breathing filter. With that combo in my '73 I increased MPG over stock by at least 1.5, and it has more power. You can control the fuel flow, but overall it will still pull more torque than a built 283 with those extra 117 cubes.

The 396 in my '78 will pull up a hill with 3.73 gears/38" Boggers at 1000 RPM and no lugging, torque will be a huge factor in motorvating down the road.

 

[diesel4me]

My results...I swapped a V8 in my 6 cyl Van..

On my 81 G-10 Van,that had a 250 six with the 2 bbl "vari-jet" carb,I got 17 mpg when I first got it in 1991..then as it got older,and they switched to "oxogenated" fuel here,it dropped to 13 mpg..it had a 3.08 axle..and a "lockup converter "TH350 trans..

I tired of the sluggish six,and the rear end also wore the diff case out where the side gear goes--so I got another rear axle from a friend who was scrapping a similar van (freebie! )--only bummer was it had 2.73's.. --I thought it would not make much difference!-WRONG!--it was a real dog now,and mileage actually dropped to 11 mpg,adding 235/15 tires didn't help either,in place of the stock 215/75/15's --I could feel the loss of power immediately!..

Then I accuired a 1973 Chevelle,for 150 bucks --it was headed to the crusher--it had a 307 with a 2 bbl. carb..I spent a month of diddling in my shop yanking out the six,and putting the 307 in..took me 4 days to finally invent a passenger side motor mount--could'nt find a bracket for a V8 van anywhere(that bolts to the crossmember),so I made a plate to adapt the chevelle block bracket in it..not a big deal,just wasted lots of time boneyard hunting,and buying brackets that ended up not working on my van....

I used the chevelle's larger radiator too,(it had A/C),it bolted right in.(had to move the brackets to the other set of holes,thats it!).After it was all done,I took it on my first long ride--got 15 mpg!--I was stoked,but the 2GC rochester carb had a "flat spot" and hesitation that no amount of rebuilding or fiddling could cure--so I ditched it for a 2 bbl holley "Economaster" that was originally used on a 78 dodge 318--bolted right on,same choke setup,it worked great..mileage was about the same(15-16 mpg) but much more "drivable"..rather peppy compared to the rochester carb..

I had my 600 CFM Edelbrock performer on it in for awhile with a 2 to 4 barrel adapter--to my suprise it got 14-15 mpg with that carb too--but you could tell it didn't need the secondaries..it slowed down if you floored it!..I removed it as soon as I bought the "Economaster" for 3 bucks at a swap meet!

Looking back,I think it was a waste of time in a way..I wished I could have stuffed my 500 Caddy motor in it instead--I bet it would still get the same mileage with 2.73's!!..but I tried,-- the Caddy motor wont physically fit in an 81 G10 engine bay--not without cutting out where the gas pedal goes.. --other than that I bet it would have been do-able--if you can put one in a 2wd GM pickup,the van is nearly the same identical crossmember,so the mounts are not the problem..its just that the Caddy motor is so W-I-D-E- !..and a chevy van is very narrow in the drivers feet area already!..cant make it any narrower! --(Other years later than 81 might be feasable--I think the floor area was changed,also the steering colum used a U-joint shaft,and the box was relocated-)..

I bet the 400 small block would rival or equal the MPG a 283 with 4.10's would get,if it used 2.73's..you could use 3.42 gears with a 700R4 and still have good mileage and fast acceleration..the 283 would be straining to pull a 4000+ lb van around,even with the lower gears,and it would be winding out on the highway-- (with my 307 you can tell its "working hard"!--its a chore to get it up to 65-75 mph,and passing is suicidal on hills! )..You'd likely be better off with the bigger motor in a heavy work van loaded with tools,etc..only a few mpg less,if that..plus it will live longer than an overworked smaller cube motor..

I got 13 mpg in my 74 K20 that had a 400 SB with a 625 CFM carter carb,and that had 4.10's and weighed 6200 lbs empty!..a van is about 1 ton lighter,so that alone would be an advantage..but I also had a 1967 Impala with a 283 2bbl motor,that got as much as 20 mpg with 3.08 gears,and it was not a light car..but much more areodynamic that a Van is....I say screw the extra 2-5 mpg the 283 might get,and go for the 400!--you only live once..