318 magnum VS 318 roller VS older 318 gas mileage

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rustytoolss

rustytoolss

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I'm looking for gas mileage input ( not my cars faster than your car)
In comparing a 318 Magnum with a carburetor installed gas mileage/ compared to a 318LA Roller with a carb/ compared to an old 318LA with a carb.
I know that all things can not be equal (trans/gears/ DRIVERS RIGHT FOOT/ car weight ETC)
But which of the 3 engine combs above seem to get the best fuel mileage. I'm looking to replace an old worn out 273 SHOT cost to much to fix. And finding the most BANG for the buck best gas mileage combo is were I'm headed. No big lumpy cams. Just high vacuum and just a reliable driver . Doing this on a budget.
 
magnum would be the best, it has the best heads.

but you could probably get comparable mileage from each of them.

LA motors are probably cheapest though.
 
If you're not planning to rebuild, but looking for a lower mileage replacement engine, then I agree with the Magnum choice for gas mileage and longevity. There will be extra initial costs as far as balance/flex plate issues, and front drive pieces, but in the end I still think you'll be money ahead on the overall swap for what you're looking for.
 
Is t this just like your last thread????

Same question re worded?
 
Technically the non roller LA would be the worst.
So Magnum vs roller La both have roller cam (less friction) and closed chambers (better combustion) that leaves head ports, La are smaller and would help with VE%
So the LA roller should be better but in reality the there probably little to no difference in mileage .Saying that I would go with the Magnum better flowing heads will make the most power per mpg.
 
I pulled the 273 in my 65 Cuda about 1 1/2 years ago and swapped in a 2001 Magnum 5.2. Best thing I ever did! I did it for the same reasons you are thinking of it - too much $$ to rebuild the old one.

The block is pretty much identical to the old one. From the old engine I reused the timing case, water pump and pulley assemblies, motor mounts, valve covers, distributor and exhaust manifolds.

The new motor had a mini starter so I used it. Nice added bonus!

I didn't use the old intake manifold. The bolt holes are angled differently and it's somewhat restrictive.

Your old oil pan won't work. The mains are different size on the the Magnum but that's just a minor problem.

I did very little internal work to the engine. I replaced the oil pump and screen, rod bearings and main seals.

Mine is a 4 speed car with 3.90 gears and i get 15-16 mpg around town. I plan on swapping in a set of 3.23s that I have to make it cruise just a bit easier.

I'm not a 'speed' guy but this thing has WAY more power than the 273. It's reliable and runs great.

If you want more details on the swap, I'm happy to help however I can.
 
It's a worthwhile question...I'll just add that the price of a decent LA 318 vs a comparable Magnum 5.2 would ne basically nothing. You could get a clean running version of either one for just a few hundred bucks.

Given that it already won't be original and assuming you're ok with the few small considerations needed to run the Magnum motor, I don't see too many compelling reasons to try to find an LA.
 
MRGTX said:
It's a worthwhile question...I'll just add that the price of a decent LA 318 vs a comparable Magnum 5.2 would ne basically nothing. You could get a clean running version of either one for just a few hundred bucks.

Given that it already won't be original and assuming you're ok with the few small considerations needed to run the Magnum motor, I don't see too many compelling reasons to try to find an LA.
Click to expand...

Agreed. I found prices all over the board when I went looking for an engine.
I ended up paying $350 for it. Came out of a wrecked truck. I think the total job, paint, new intake, clutch and misc parts ended up at $1400 +/-
 
I agree with above - the magnum is the way to go. Roller cam, better pistons and rings, better heads... The net horsepower is 230 on the magnum - the net on the LA roller is about 140. Some of that is the better injection but most of it is better technology in the long block parts.
 
Real numbers. I installed a flat tappet (old LA) 318 in my B-body. The 318 was a real good motor though. With the 2bbl, I got 20 mpg. Its an auto (904). Checked it several times on 55-60 mph cruises. Besides the obvious of final gearing, how rich your carb burns will major in the MPG. If you use the mag, you'll be running a 4bbl intake, then most likely a 4bbl carb. If you use the LA roller, you can keep the 2bbl carb from your 273, and this I believe will give you your best fuel mileage.
 
jameybro said:
Agreed. I found prices all over the board when I went looking for an engine.
I ended up paying $350 for it. Came out of a wrecked truck. I think the total job, paint, new intake, clutch and misc parts ended up at $1400 +/-
Click to expand...
What ever I do, I will change bearings/ rings/ oil pump/ T chain/ get the heads checked. It there a BIG problem going to a Magnum with engine Balance issues ? I've got a 727 since the original engine was internally balanced. I will also need to keep all of my stock alt brackets/ motor mounts and possibly my mechanical fuel pump . Would like to use 91-92 Dakota exhaust manifolds but my current exhaust system is in perfect shape (maybe down the road)
Thanks for the input keep it coming At this point I'll be looking for a 318 magnum/ or 318 LA roller. (and yes this is like my last post/ but better input)
 
using a 318 magnum I had no problems converter / balance wise.
I used the magnum flex plate and it bolted right to my converter.
I run an electric fuel pump on mine.
 
rustytoolss said:
... It there a BIG problem going to a Magnum with engine Balance issues ? I've got a 727 since the original engine was internally balanced. ...
Click to expand...

I have a B&M Magnum/727 flexplate if you need one. It was originally on a 5.9L so I'll have to make sure it's the same as what the 5.2L would need but it would solve the balance question. If you end up going that route, drop me a PM.
 
I can't speak to the auto tranny questions but it sounds like you've already got the info you need in the last couple of posts.

I also put in a new timing chain. I believe I used the harmonic balancer off the Magnum however as my old one was not great

The entire front end of my old 273 bolted right on to the Magnum. Alternator brackets, timing case, water pump - Even the fuel pump. You'll need a cam snout extender for the pump. Hughes Racing is where I got mine.
 
None of them will get appreciably better mileage than the other. Just pick one and run with it. If you keep thinking too much, you'll never get a damn thing done.
 
Mine was free.Magnum 360,horse swapped. Has new heads,and a more aggressive cam now.
 
Mag would probably be the most efficient, considering low friction roller cam, moly rings, 1.6 rockers on modern heads, plus previous life with EFI.
 
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