Replacing my Poly for 318 for a LA 318...

[1966Coronet]

After throughout the year gathering parts to build my 318 on my Coronet, came to find out by 66CORONET, that I had a POLY engine and my parts would not fit:angryfire:. I decided to swap out the engine for a "la" series and slowly rebuild the POLY for a muscle application since my Coronet is a 4 door cruiser.

Dilema:
I found a 1973 318 paired with a 727 off a motor home. What should I take into consideration when looking for another 318 as far as swap and motor mount is concern. I dont wanna go with a too big of an engine b/c of gas mileage... its gonna be a cruiser and its gonna be on the highway a lot.:blob1:

 

[66 coronet]

I don't see any advantage swapping a 318 for a 318, the poly has more performance potential.

 

[gregpurcell]

It's an easy swap. I have done that swap in a 65.
The newer 318 will bolt to your poly's transmission (one bolt is different and is left out) and your poly's motor mounts will work on the LA motor. If you decide NOT to use the poly trans, the other 727 will go in on the same mounts and linkage. Your poly's trans is probably a 727 also. If so, even the driveshaft will work. The exhaust will be different from the poly to the LA, but some of the pullies and brackets may work. If it came in a motor home, the new 318 may have a rear sump oil pan. good news! You poly's pan and pickup will work on the new 318 too. With all due respect to what's been posted above, in my opinion, a new 318 is lighter than a poly with cheaper parts performance parts available, so dollar for dollar you build the LA for less than a poly.
As for OTHER swaps, the 66 Coronet V8 k frame will accept any V8 motor up to a 440 (except hemi) with the correct motor mount brackets. You do not have to change the K frame.

 

[Dako]

gregpurcell is right...Your Poly motor mounts can be used on the LA motor, as with a lot of the other parts. Below is a great site listing all interchangable parts between the two versions of small block.
http://www.1962to1965mopar.ornocar.com/poly318_1.html

I don't know that you will find a great deal in cost difference between the two when it comes to rebuilding though...just more selection in parts. I did extensive work on mine...bored, larger valves, ported, balanced, etc., and was in it for a little over $2K in parts and another $2K in machine work. There is about a 50lb weight difference (Poly heads are heavier), but its head design gives it a higher torque output, and that's where the 'seat-of-the-pants' power is felt.

Doing a search on this site for 'Poly' or 'Poly 318' will also give you a bit more insight on these old, higher torque motors.

 

[1966Coronet]

Thanks for the input guys. I have researched it throughly and discovered that the poly is a nice piece to keep around. But given that i have already bought so many addons for my engine thinking that it was a LA series engine. I will keep the poly and slowly work on it hopefuly this wont be my last Mopar project.
My question is since the 318 and 360 are so similar and the cams carb intake fuel pump gears etc etc are interchageable, should i go 360?

 

[Dako]

Depends...

Depends on what you already have for the RV 318 and what you still plan on replacing. Not everything that is beneficial to a 318 is beneficial to a 360, and vice-versa. Starting from the same square one on each motor, you will get more out of the 360. But to aquire a 360 core you could be looking at a couple $$$.

The question for you is how much more would you spend if you went to the 360 compared to what you already have for a 318? Are you okay with spending that much more? How cheap do you wish to keep this? The good news is any of the three are a straight bolt-in on your car. Good luck!

 

[1966Coronet]

Found a 5.2L 318 magnum, off of a 1999 RAM, will this work carburated?

 

[1966Coronet]

Better yet look what i found baby!!!! 1973 Dodge 360 5.9L on craigslist website. for $350.00

:hello2::headbang::hello2::headbang::hello2::headbang::hello2::blob1::hello2::headbang::blob1::blob1::headbang::hello2::jerk::blob1::jerk::hello2::headbang:

 

[gregpurcell]

More cubes are always better. The 360 has a longer stroke, making it a much more "torquey" engine which is great on the street. Here's the 318/360 interchange problems you will have: They are small, but if you don't know about them, it's a PITA (first letter "pain)

The 360 uses a different oil pan than the 318s. If you get a truck motor, you will have to find a center sump 360 CAR oil pan and pickup. There are plenty around, but remember your 318 pans won't work.

The left mount tabs on a 360 are narrower. You can use a B/E body 340 mount or you can shim the 1/4 inch difference and use the 318 mounts.

This is the most inportant: the 360 is EXTERNALLY balanced! It will bolt directly to the poly transmission, but it requires a weight on the torque converter. Without it, the motor will vibrate badly. B&M makes a really cool adapter flexplate which is balanced for the 360 (sold at Summit racing) or you can weld weights on the old converter, or you can use the newer transmission that comes on the 360 which will have the weights. (the 66 Coronet transmission mount will accept either the 727 or the 360 trans. If you use a 904, it's shorter and you need a longer driveshaft). Dont try just swapping the torque converter. Many newer converters won't interchange.

 

[1966Coronet]

Quick question though, do i need to balance the torqe converter aswell eventhough the front is balanced?

 

[rolling_Thunder]

B&M makes a balanced flexplate for the 360 auto application - a LOT better than having to balance the torque converter.

to answer your question yes - the balancer and TC / flexplate need to be balanced

 

[66 coronet]

buy a torque conveter for a 360 engine it will have the balance weight in the correct position, also i can't remember the specs for the cam you bought but you may want to get a convertor with a little higher stall speed

 

[gregpurcell]

To repeat what's been said already: The 360 is balanced at the front and back. It has a special thicker balancer up front and YES it has be balanced at the rear. The B&M balanced flexplate is by far the cheapest and easiest hassle free way to solve the problem. You will be very happy with a 360 Coronet.