I want to build this 273 for gas mileage in a truck. I want more power than a 318 and better mileage. Here is my plan: fresh bottom end, Comp Cams #20-210-2...260 dur/.440 lift 110LSA, rated 1200-5200 RPM, dual exhaust maybe headers, 3.23 gears 31 inch tires,Either Edelbrock 500 four barrell or Holley two barrell#2300. Any input is appreciated

My 360 gets bad mileage

Oh I forgot. I know the 273 heads suck. I plan to use 318 small port heads for port velocity #675,#308, or #302

you might get better mileage out of a 360, way more TQ, so your foot doesn't have to be into the pedal as deep as with a 273

I have the 360. It gets 10mpg on a good day if I baby it. It is a 1975 with a Holley four barrel. Plenty of power but I want better mileage. I drove a 273 Barracuda to San Diego and got 25mpg. 360s get terrible mileage. Maybe the fuel injected 5.9 magnums are better but I am building a 70's truck. The 273s were rated at 180 hp. The 318s were rated 235 hp. I am only looking for 240-250 hp. Mileage is my goal. The 273 is 45 cubic inches smaller than the 318. That should help mileage. Anyone try this before??

Slap an overdrive in it and have the best of both worlds.
Seriously,by the time you buld a motor and swap it you have spent more than enough to install an overdrive tranny.Keep your torque and have your mileage too.

when will you get a return on your money buy removing the 360 and installing a rebuilt 273 to gain maybe 5 mpg? i would remove the 4bbl on the 360 and install a 2bbl set up first and see what happens you can probably find someone that will give it to you for free, next thing i would look at is your timing to make sure your running full vacuum advance in the area of 50 deg total at light cruse, make sure you have a clutch fan, my 4.7 03 dakota only gets about 19 mpg highway with the 5 speed auto turning 1,800 rpm at about 60mph. are you sure the barracuda got that milage was the gear stock? tires stock, speedo working right? Not tring to be negative, but i would try to maximize what i have before i undertake all the work and $$$$

The overdrive is a good idea. However it is only a gain at highway speed. My commute is all below 40 mph. I used to have a Dakota wit the V6. It got good mileage but was too small for me. I need the full size truck. I am not worried about the cost of upgrades or the work involved in swapping motors. I just wanted to experiment with Chryslers smallest LA V8. I have a motor lifter on the back of my truck and do this all the time. P.S. the tow truck also has a 360 and gets really bad mileage but LOTS of power. Thanks for the input guys

You can't expect a power wagon to get the same milage with the 273 as the barracuda. Your talking 1500lbs difference at least. Not to mentiuon the rear end ratio. The 360 will get better milage than the 273 will in that truck by a good bit. By the time you build the 273 to get anywhere near enough power to move that truck you've blown the gas milage all to crap.

I dont expect a truck to get the same mileage as a lightweight car. I realize a truck is heavier. However Mopar did build 225 cubic inch trucks. Those sixes did move the trucks and also got better mileage than the V8s. Yes they had less power. But my goal is to make as much power or possibly more than a 318 (which is available in trucks) and try to get better mileage than a 318. Perhaps this is not possible. Thats why I am asking if anyone has had experience with the little 273. Many of you say the 360 will get better mileage. I know for a fact that the 360 get really bad mileage. I have had dozens of them. I have had many 318s also which get better mileage than the 360s. The brown truck is a 1/2 ton two wheel drive. It weighs 3800 lbs. Thats not much more than your average B body. Thanks again for your help

When i had a 360 in my 74 D100 longbed got 16-18 mpg. You won't get that with the 273.The sixes also had a trans and rear end geared for milage and they didn't get all that much better mpg. Put a 2.76 or 2.91 under the truck and you will boost the milage.

[I know for a fact that the 360 get really bad mileage. I have had dozens of them.] well go ahead and build the 273 , I have a 360 about 425hp runs very low 12's, single plane 750 race holley, that gets about 12 mpg with a 3.55 gear in a 3450lbs car. something is not in good working order on your 360, have you tried to tune it up?

I was about to say with my 360 based 408 stroker ,od auto trans and 3.91 gear I get 14-15 on the highway and 12-13 in town. My truck weighs 5000lbs.

i bought an aspen from a guy in colorado who had build a late 70's crew cab. it had a 500 inch motor. the build was designed to make as much torque as possible. he was telling me that he would get around 18mpg on the hwy. torque is the key. your combo with the tall tire and tall gear will eat you up. the slant motor makes more torque than the 273 will.

Put a thermoquad on the 360 along with a wide band A/F meter ($200 for an innovate LC1 with digital gauge) and tune ignition and carb for mileage.

don't bother with a 273. pistons are too expensive to get high compression/0 deck. copy hotroddave's 318 build...

the key to mileage is high compression and little overlap. you'll get neither with a stock bottom end 273 and that cam.

or another option is his short block (KB167 pistons at 0 deck), magnum heads, lunati voodoo 60400. the magnum heads will make significantly more power than the 273 or '302 heads.

or use an '85 up 318 (roller cam motor, 302 heads or magnum heads) with the KB167's, and get the roller cam reground by bullet cams, probably with the HRL256A lobe on the intake and exhaust if using magnums, the HR259/316 on the exhaust if using the 302's...if you're maximizing MPG, use the HR247/306 lobe--similar adv. duration as a stock cam, but about 10 more .050 dur than a stock LA 318 cam, and a lot more lift (almost as much lobe lift as a stock cam's valve lift!) use that lobe for intake and exhaust and you'll have 23 degrees overlap on the stock 112 LSA

my combo is a stock '86 short block, pistons .055 in the hole, magnum heads home ported by me, magnum roller lifters, pushrods, and stock mag rockers, thin head gaskets (9:1 comp measured) RPM air gap, headers, eddie 600, and the roller reground by bullet with the HR259/316 lobe for both intake and exhaust.

on the butt dyno, engine has as much power as my old XE262 equipped 360, but I'm getting 3mpg better (18 vs. 15) in my 3900 lb 5th ave. the great thing with roller cams is the aggressive profiles...my cam has 10 degrees less .050 duration than the old XE262, but only 3 degrees less duration at .2", and more gross lobe lift. area under the lift curve is the same or better than the old cam, but with 13 degrees less overlap.

I predict worse mileage with the 273. A small motor trying to push a big lump equals poor mileage.

You'd be better off buying the LM1 someone mentioned and tuning your current 360. 360's can get good mileage, but not with an off the shelf carb, especially a Holley generic type carb.

I had a 273 in a 67 coronet. So more weight than the barracuda, but not as much as the truck.
got around 11 mpg around town. Just too big to move with that little motor.

these hyper-mileage 273 threads turn up every now and again, but there is never a follow up thread, because building a 273 for mpg does not make sense.

honestly, you drive a truck its only going to get so good with a vintage powertrain under the hood.

i would go along with the TQ swap mentioned above. smaller motor doesn't necessarily mean better mileage - my 78 D100 only got about 9 mpg with the 225 /6 1bbl and a 4 speed. the worn-out 440 in my car was getting 13 at that time. i always wanted to put a 360 or 318 in my truck to get better mileage, thinking the slant 6 made it too under-powered, thus working harder to get moving