361 to poly 318.

[jmbass98]

I have the opportunity to grab a running poly 318 for around 300~ USD. Is it worth swapping my 361 out? Thanks.

 

[Curiousyellow71]

No. Poly is a small block...Transmission is a different pattern.
Swap a 383,400 or a 440. They are all bolt in swaps.

 

[Frank Mopar]

Nope. Not even for free. Poly is 100 lbs heavier to start.

 

[slimt]

Keep the 361.

 

[33 IMP]

If you want to improve your small big block, going to a small antique small block with very hard to find parts, and needs a different trans, is so far in the wrong direction, i dont know what to say.

 

[oldkimmer]

Nope. Not even for free. Poly is 100 lbs heavier to start.

So your saying a poly is one hundred pounds heavier than a 361 big block? Wow, I would of thought it was the other way around. Kim

 

[Purepony]

A friend of mine has two polys abd brags about it being the best thing and even calls it a mini hemi but I don’t know hard to believe since at the end of the day it’s a 318

 

[Cranky]

Nope. Not even for free. Poly is 100 lbs heavier to start.

I know the heads on a Poly are a bit heavier than LA heads but where is all the rest of the weight coming from that makes it heavier than the 361? The block alone on a 361 is around 200-215 lbs and the crank is around 70 lbs if it's forged. Been awhile since checking the weights on the B engines but I know a 400 block is around 215. The LA engines are around 520 and the B engines are a bit shy of 700.....

So your saying a poly is one hundred pounds heavier than a 361 big block? Wow, I would of thought it was the other way around. Kim

 

[F4R/T]

I know the new thin wall castings were used on the LA engine hence the name light A engine but wow where it the tonnage?

 

[33 IMP]

I dont know about the 318 poly being 100lbs heavier than a 361 (i have never weighed, or owned, either) but ill bet that a 383/400 (stroker or standard stroke) with easily acquired aluminum parts, heads, intake, water pump and housing, valve covers, etc, can be substantially lighter than an iron head, iron intake, 318 poly with iron exhaust manifolds...... and up to almost 200 cubes bigger!

 

[barbee6043]

That poly 318 is called a wide block, and yep it is a heavy casting (A motor). The LA 318 is the Light casting! Not sure on weight, but I alsways heard it weighs in like a big block.

 

[66 Sat]

Hughes Engines website lists the Poly at 600 lbs (estimate).
In a book I have an article on the 273 when it was first released says a 40 lbs saving on the block and 12 lbs on the heads over the A engine. Another says 55 lbs saving overall.
If the 55 lbs is correct plus the 525 lbs for the 273-340 = 580 lbs. The poly block is the same dimensions as the LA, just a heavier casting.

Putting all that aside, the first question is what is wrong with your current 361 and what do you want your car to do? If the 361 is toast, money is tight, you can get the transmission too, and all you want is a reliable car with good gas mileage that will serve you for the next 20 years then maybe it is a good choice. If that's all you want though, then why not rebuild the 361?

If you want a 500 hp street racer then it's not the right choice.

A bit more info is needed before meaningful advice can be given.

 

[Cranky]

That poly 318 is called a wide block, and yep it is a heavy casting (A motor). The LA 318 is the Light casting! Not sure on weight, but I alsways heard it weighs in like a big block.

You can sit an LA block next to a poly head block and they look pretty close to the same. The heads on the Poly are of course bigger with wider valve covers which makes the Poly look wider.... which is probably the reason why so many call it a wide block

 

[barbee6043]

Lots of parts interchange between the A and LA blocks, and some similarites with the A and 1 st gen hemi block. ^^^^LIke Cranky said th A and LA block look much the same> Chrysler Power with Bruce Toth have and continue to do lots of new stuff for the poly. It is not cheap though!

 

[35desoto]

The Poly 318 is cast on a 90 degree block (ie the cylinders are spaced 90 degrees apart) while the LA 318 is cast on a 60 degree block. This accounts for a fair percentage of the weight saving along with the thin wall casting techniques and lighter heads used in the LA casting. The 361 big block is cast on a 90 degree casting block so sitting a 318 Poly beside one will look similar in size. I will never ever knock a poly 318 - they were one of the most underrated and underdeveloped engines from the Chrysler fold yet if you have a 361 in place the upgrades to 383/400/413/426/440 is so wide for any Chrysler enthusiast.

 

[66 Sat]

The Poly 318 is cast on a 90 degree block (ie the cylinders are spaced 90 degrees apart) while the LA 318 is cast on a 60 degree block. This accounts for a fair percentage of the weight saving along with the thin wall casting techniques and lighter heads used in the LA casting. The 361 big block is cast on a 90 degree casting block so sitting a 318 Poly beside one will look similar in size. I will never ever knock a poly 318 - they were one of the most underrated and underdeveloped engines from the Chrysler fold yet if you have a 361 in place the upgrades to 383/400/413/426/440 is so wide for any Chrysler enthusiast.

I'm pretty sure you're wrong on the 90 degree/60 degree. Happy to stand corrected but I believe both are 90 degree.

 

[Ron H]

My poly has been rebuilt costing a lot of cash. Put in a medium cam, solid lifters, bored .60, some 340 internals, heads redone…etc. and etc. It’s peppy and it was before too after a few adds. To make it more peppy more needed doing. These motors can be bored out considerably more yet. Yeah the poly’s were reliable as all get out and mine runs like a clock – but – it is a 318. A do-over would be my choice; but too damn old now to redo. Nice cruiser. If I had a decent running 361 I’d keep it or rebuild it before going 318, IMO.

 

[35desoto]

I'm pretty sure you're wrong on the 90 degree/60 degree. Happy to stand corrected but I believe both are 90 degree.

And I'd be happy to be proved wrong
BUT
the engine mounts for a LA block are located differently onto the K frame in comparison to the Poly 318
If the blocks were the same you could swap the rubber mounts and bolt out / bolt in without any change however thats not the case
Schumacher makes a conversion kit to swap the later LA engines into Poly frames because of this very issue. The block ear tags are the same so thats not the change plus if I get my act together this difference is recorded in a MOPAR publication buried in my library.

 

[Runcharger]

Keep the 361. Extra inches, external oil pump, dry intake manifold, front mounted distributor. Easiest, best designed engine series of the era to work on and Hot Rod IMO.

 

[old guys rule]

361 period unless you're looking for 400HP PERIOD!