Need some advice 318 POLY vs 318 LA

-
R

RichieDart

Member
Joined
Sep 26, 2018
Messages
22
Reaction score
8
Location
Staten Island NY
I have the opportunity to buy a '66 Belvedere 4dr. (I know it's a B Body but I always get good advice from my A Body friends). It has the 318 Poly engine. I believe that they were built with forged cranks.. Is this true? I don't really plan to modify that engine. Are parts available (water pump, distributors etc) for this motor or is it gonna be a challenge finding stuff? Also are they much heavier than the 318 LA? Any other info or comments regarding the benefits or problems of these polys would be appreciated.
 
Forged crankshaft, weight more than the 318 LA. Actually, a great engine performance parts are hard to come by and expensive. 65'
 
Water, fuel, oil pumps interchange with LA (early iron water pump). Distributor, oil pan also. The cranks were forged, entire assembly is quite a bit heavier due to the heads. As wide as a 440, almost all had mechanical cams that CANNOT be interchanged with an LA engine. Pistons have different valve relief
 
based on everything I've seen on them, can be built into GREAT truck motors with tons of torque with the parts that interchange with LA motors as listed above. Can also be built into high performance motors but you will likely need a lot of custom parts along the way to get you there.
Less availability of parts, larger footprint, more weight... vs LA motors
But IMO, they have some of the coolest valve cover designs out there with the saw blade look
 
Projectile Dart said:
based on everything I've seen on them, can be built into GREAT truck motors with tons of torque with the parts that interchange with LA motors as listed above. Can also be built into high performance motors but you will likely need a lot of custom parts along the way to get you there.
Less availability of parts, larger footprint, more weight... vs LA motors
But IMO, they have some of the coolest valve cover designs out there with the saw blade look
Click to expand...
The first link I posted gives a part number by part number list to build a stroker poly. How much do GOOD FORGED stroker 360 pistons cost? Case closed.
 
Stock vs stock both in good running condition I like the poly much better.

if you get it adjust the valves early on.
 
Projectile Dart said:
based on everything I've seen on them, can be built into GREAT truck motors with tons of torque with the parts that interchange with LA motors as listed above. Can also be built into high performance motors but you will likely need a lot of custom parts along the way to get you there.
Less availability of parts, larger footprint, more weight... vs LA motors
But IMO, they have some of the coolest valve cover designs out there with the saw blade look
Click to expand...
Please define “Larger footprint” please.
 
rumblefish360 said:
Please define “Larger footprint” please.
Click to expand...
I wanna know too, since the A and LA blocks are essentially the same exact size. The only weight differences would be the heads and intake.
 
As far as "larger footprint", I assume he means the physical size- the poly is just shy of 25" across the valve covers, while the LA is right about 20". So the LA is narrower, which makes sense since the LA was initially developed to more easily fit within the confines of the A body engine compartment and reduce the manufacturing costs associated with the poly heads.
Weight is also a factor, Hughes published this list of weights:
1668194433145.png

It gives an approximate difference of 75# between the LA and poly. The majority of that weight difference is in the heads, although a fair amount is in the block itself, with the LA being produced with newer "thinwall" casting methods to further reduce weight. Remember, "LA" is "Light A".
 
Last edited:
Professor Fate said:
As far as "larger footprint", I assume he means the physical size- the poly is just shy of 25" across the valve covers, while the LA is right about 20". So the LA is narrower, which makes sense since the LA was initially developed to more easily fit withing the confines of the A body engine compartment and reduce the manufacturing costs associated with the poly heads.
Weight is also a factor, Hughes published this list of weights:
View attachment 1716009361
It gives an approximate difference of 75# between the LA and poly. The majority of that weight difference is in the heads, although a fair amount is in the block itself, with the LA being produced with newer "thinwall" casting methods to further reduce weight. Remember, "LA" is "Light A".
Click to expand...
Absolutely the difference is the heads. It's not far off from the LA weight at all. Not as far as I thought. I do agree the width can pose some issues especially in a A body for exhaust. It can be done though, because people have put the 331, 354 and 392 in early and late A bodies, and the Poly is norrower. I guess it all depends on how hard you wanna work. lol
 
RustyRatRod said:
Absolutely the difference is the heads. It's not far off from the LA weight at all. Not as far as I thought. I do agree the width can pose some issues especially in a A body for exhaust. It can be done though, because people have put the 331, 354 and 392 in early and late A bodies, and the Poly is norrower. I guess it all depends on how hard you wanna work. lol
Click to expand...
Oh, they fit- it's a squeeze, but they fit even in an early A.
@A56 posted these in another thread. Too cool!
1668195560895.png


1668195600391.png


1668195644119.png


1668195702936.png

AND it's a four speed to boot!
And the recall wheels.
Overall, just a big ol' heapin' helping of awesomeness!
 
Last edited:
They aren't that much heavier than an LA. About 50 lbs. I weighed mine when I removed it earlier in the year for the stroker rebuild - it was 590 lbs with the starter and exhaust manifolds.
I put a 3.58" crank in it and it's now 354 cu in.
Lovely engine, sounds great.
311876154_555566043241546_9148353747614540613_n.jpg
 
66 Sat said:
They aren't that much heavier than an LA. About 50 lbs. I weighed mine when I removed it earlier in the year for the stroker rebuild - it was 590 lbs with the starter and exhaust manifolds.
I put a 3.58" crank in it and it's now 354 cu in.
Lovely engine, sounds great.
View attachment 1716009400
Click to expand...
Just beautiful!
 
One of the few mistakes Mother made...was discontinuing the Poly. In this country they were much sought after for Midget speedway racing.
 
rumblefish360 said:
Please define “Larger footprint” please.
Click to expand...

RustyRatRod said:
I wanna know too, since the A and LA blocks are essentially the same exact size. The only weight differences would be the heads and intake.
Click to expand...

I was referring to the overall width fully assembled. Its already covered in another post above. It's not a HUGE difference, but every inch counts under the hood of an A body. Sorry if that was confusing at all.
 
Projectile Dart said:
I was referring to the overall width fully assembled. Its already covered in another post above. It's not a HUGE difference, but every inch counts under the hood of an A body. Sorry if that was confusing at all.
Click to expand...
Thanks, just looking for a clarification.
 
You must log in or register to reply here.
-

Back
Top