What problems will i run into changing from a 318 to a 273 in my 66 pickup? Thanks

I wouldn't think there would be any problems, everything should hook up OK.

Only thing I can think of would be water pump inlet, and pulley alignment. Use the timing cover,pullies and water pump from the 318 and that should eliminate that problem. If you swap timing covers,put a new timing set on the 273 while it's off.

less hp and torque

Good catch! I forgot about that one.

Why are you going to a smaller engine? You won't be getting any better milage and your hauling and towing ability will go way down.

Mabey he has a bad 318 in his truck and happens to have a good 273 sitting around. Mabey he just wants better MPG and don't mind the performance hit, it could be lots of reasons.

He will get better miledge and it will take longer to get an equal sized load going. My 239 in my dakota gets way better miledge than my 318 dakota even towing a 67 cuda on a flat bed but it was working a lot harder going up mountain passes. As a matter of fact the little motor truck only got one MPG less loaded than the V8 did un loaded.

As for the converter you can get one made with the small hub and regular 904 guts. You could also swap cranks.

the 273 will have to work harder and therfore get worse milage in that truck. You can't compare the newer motors with the oldies.

It will get better MPG, been there done that.

It does not work harder, the same amount of work or less (if you accelerate slower)actually gets done. Also it has less pumping loss and less friction loss. At the same power output say about 75HP (about what his truck would require to hit 70mph and maintain it) the 273 will have lower intake vaccume that fights the pistons going down added to the friction reduction it WILL get better MPG as long as the tunes are right for both motors. If bigger is better than he should be able to build a 605 hemi and get 50 mpg because it does not have to work as hard

Isn't a 66 318 still a Poly??

This truck was a slant 6 when i got it. I put a 318 out of a van and now it is tired and needs rebuilt. The 273 comes complete with a transmission and will do until i get the 318 redone. I only drive the truck on weekends fuel milage is not an issue.

Come on and get real instead of going off on a wild trip. The stock 273 will not move that truck as well as the the stock 318 running the same carb etc and will get worse milage. I have owned A bodies with 273 and the same car with a 318 and the 318 got noticably better milage. Hotroddave the problem with your statement is that the 273 has less hp stock then the stock 318 which makes your scenerio moot. Plus the vacuum thing was discussed before and wasn't proved to be correct then.

Obviously you never tried the experiment I sugested before, the vaccume thing is a proven fact. Low vaccume is part of why a diesel gets so much better MPG and why an atkins cycle engine gets good MPG. Now... Go get in your car go to the top of a really big hill, close the throttle shut the engine off and coast, this is simulateing high vaccume low compression, then hit the gas and you can feel the vehicle coast much easier now even though compression is much higher but vaccume is now gone, this will prove beyond a shadow of doubt that vaccume robs more power than high compression. It is true that you want to build your engine to produce high vaccume but that is only because it means your engine is produceing the most HP from a given amount of fuel, what you need to do is to maximize it is gear it really high so it actually runs at a lower vaccume, any HP you produce above what is needed to maintain your speed is wasteing fuel.

Also WOT HP has nothing to do with MPG at a cruise or even mild acceleration, it only takes a certain amount of HP to keep a vehicle going at a certain speed no matter how big the engine is, in his case it probably takes around 75 HP or less around 70 mph and the 273 is more than capable of that and at less than WOT also. Anything more is WASTED FUEL.

My 66 cuda with a 273 got much better MPG than my 68 318 cuda in stock form both motors were completly stock and had 2.76 rear gears. No the 273 was not fast but MPG was un-questionably better till I built the super duper MPG 318 and I am 100% convinced that a 273 built the same way would have got even better MPG.

We went through this before and I still think you are wrong because we don't drive at 70 with the engine shut off or the carb closed. I won't ever agree with you and vice versa so there is no use in continuing this discussion again.

so..you both agree that you both disagree.. correct?

Yes.