318poly to hemi

Discussion of the 331-354-392 HEMIs.

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olkyhippy
Posts: 17
Joined: Fri Jan 16, 2009 9:08 pm

318poly to hemi

Post by olkyhippy » Fri Jan 16, 2009 10:33 pm

ive got a 65 cornet with a 318 poly in it ive also got a 331hemi out of a late 54 newyorker is there any chance the heads will work on the poly motor ? :-?

George
Posts: 646
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Re: 318poly to hemi

Post by George » Sat Jan 17, 2009 6:28 am

No! The A Polys can't be converted using early hemi parts. The Australians swap A & LA heads back n forth & there is someone making hemi heads for LA engines, rather expensive though.

olkyhippy
Posts: 17
Joined: Fri Jan 16, 2009 9:08 pm

Re: 318poly to hemi

Post by olkyhippy » Sat Jan 17, 2009 8:22 pm

i saw another post where some one put 331hemi heads on a 301 poly engine whate are the differances between the 301 and the 65 model 318 poly?

mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: 318poly to hemi

Post by mart » Sat Jan 17, 2009 10:09 pm

[quote="olkyhippy"]i saw another post where some one
put 331hemi heads on a 301 poly engine whate are the
differances between the 301 and the 65 model 318 poly?[/quote
]=======================
The 301 Poly was a Chrysler engine- basicly the same as the 331
and 354 Chrysler hemi, but with a smaller bore and poly heads
instead of hemi heads, so an interchange to hemi heads is fairly
straightforward. (*Note* - Chrysler even produced some 331 and
354 "poly head" engines - mostly used in the Canadian built Chrylser
Windsor cars and also used some in Dodge and Fargo truck
applications). Likewise, the Dodge Poly engines were based on
the Dodge "Red Ram"and "Super Red Ram" hemis, so again, an
interchange and upgrade to *Dodge* hemi heads is posiible on the
Dodge polys. However, the 318 poly is an entirely different duck.
It was originally designed and built by Plymouth, as a
"Plymouth-only" engine - first appearing in the high-performance
'57 and '58 Plymouth Furys and then in later years, detuned and
used across the board as the basic 'bread & butter' engine in both
Dodge cars and trucks and Plymouth cars. Being a Plymouth design,
except for using the basic polyspheric valve layout and
combustion chamber design, it has almost nothing in common
with either the Dodge or Chrysler engines, so a head swap to
either Dodge or Chrysler hemi heads (or even to Dodge or
Chrysler poly heads) is not do-able.

mart
================================================
Last edited by mart on Thu Jan 22, 2009 5:43 pm, edited 1 time in total.

George
Posts: 646
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Location: Fl

Re: 318poly to hemi

Post by George » Sat Jan 17, 2009 10:58 pm

There's also a Plymouth 301 "A" Poly that, being an A block, can't be converted like the '55 301 Chr Poly.

olkyhippy
Posts: 17
Joined: Fri Jan 16, 2009 9:08 pm

Re: 318poly to hemi

Post by olkyhippy » Sun Jan 18, 2009 11:57 am

well george thanx for all the info looks like im gona have to bite the bullet and try to get the 331 built and buy an adapter plate for my 727 in the cornet i was hoping i could use the heads on the old 318poly and have me a hemi without spending too much lol you know i should have known that would be way too simple . :lol:

George
Posts: 646
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Re: 318poly to hemi

Post by George » Sun Jan 18, 2009 3:34 pm

I've had good luck with the 392 adaptor from QEC, other than getting longer bolts than was in the kit.
EDIT: a '63 & up Poly will bolt up to modern small block Mopar trannys, '62 & earlier need the adaptor.
Last edited by George on Wed Oct 14, 2009 4:01 pm, edited 1 time in total.

mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: 318poly to hemi

Post by mart » Mon Jan 19, 2009 12:17 am

olkyhippy wrote:......was hoping i could use the heads on the old 318
poly and have me a hemi without spending too much <lol>
A hemi without spending "too much"??? <double LOL> That's a
good one!!! :D

mart <who firmly believes "that If some is good and more is
better, then too much should be just enough!" and "if it
ain't broke...you're not really trying!" >
====================================================================

oldngood
Posts: 121
Joined: Thu Mar 13, 2008 5:14 pm

Re: 318poly to hemi

Post by oldngood » Thu Oct 01, 2009 5:21 pm

olkyhippy wrote:ive got a 65 cornet with a 318 poly in it ive also got a 331hemi out of a late 54 newyorker is there any chance the heads will work on the poly motor ? :-?

the 318 poly isn't a bad running engine in its own right, if you soup it up. per previous posts, sorry, the poly 318 is a poly only

interesting sidenote- the earlier Dodge and Chrysler polys are better than most realize, they are much better than early Chrysler and Dodge hemis, actually

early Dodge hemi intake ports- 100 cc's
Dodge 315/325 poly intake ports- 125 cc's

early Chrysler 1951-53 Hemi intake ports- 115 cc's
Chrysler 331/354 poly intake ports- 150 cc's
392 hemi head intake ports- 145 cc's

the only factory early Hemi heads with bigger ports than the poly, are the 1954-55 331 heads with 175 cc intake ports, or aftermarket HotHeads- the 354 and 392 heads actually have the same size, or slightly smaller, intake ports than a Chrysler polysphere

I poured all the above heads myself, and a net contact poured his 392's

put 13:1 to a poly with bigger valves and it's going to make some nice horsepower and for a lot cheaper too, and all the hemi intakes fit it

mart
Posts: 536
Joined: Tue Mar 22, 2005 2:06 pm

Re: 318poly to hemi

Post by mart » Thu Oct 01, 2009 8:09 pm

oldngood wrote:
interesting sidenote-
the earlier Dodge and Chrysler polys are better
than most realize, they are much better than
early Chrysler and Dodge hemis, actually early
Dodge hemi intake ports- 100 cc's
Dodge 315/325 poly intake ports- 125 cc's
early Chrysler 1951-53 Hemi intake ports- 115 cc's
Chrysler 331/354 poly intake ports- 150 cc's
392 hemi head intake ports- 145 cc's
the only factory early Hemi heads with bigger
ports than the poly, are the 1954-55 331 heads
with 175 cc intake ports, or aftermarket HotHeads
- the 354 and 392 heads actually have the same
size, or slightly smaller, intake ports than a
Chrysler polysphere.
I poured all the above heads myself, and a net
contact poured his 392's put 13:1 to a poly with
bigger valves and it's going to make some nice
horsepower and for a lot cheaper too, and all
the hemi intakes fit it
--------------------------
CC's by themselves are not really any indication of the
airflow ability of a port. Port volume only matters when
you're comparing more or less identically shaped and
configured ports. Obviously a 354 hemi port that's been
ported to displace 170 CCs will *potentially at least*,
flow more air than another 354 hemi port that only
displaces 150 CCs. But you can't for example compare
that same 170 cc 354 hemi port with a 170 cc port on
a Chevy, Ford, Polysphere Chrysler or even a Toyota and
then say that because the volume is the same, that the
airflow capability will be similar too. There are too many
variables in port shape and particularly length etc that
affect the total volume in CCs, but don't necessarily
increase or decrease the airflow ability. Another way to
put it is that while you can directly compare 'apples to
apples', you can't likewise directly compare apples to
oranges and/or bananas and coconuts!!! :)

mart
====================================================

George
Posts: 646
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Re: 318poly to hemi

Post by George » Fri Oct 02, 2009 4:28 pm

You can put a 360 crank with the mains cut down into the 318 Poly &, depending on the sonic check, you can have stroke & bore it anywhere from 349 to 402 CID engine.

oldngood
Posts: 121
Joined: Thu Mar 13, 2008 5:14 pm

Re: 318poly to hemi

Post by oldngood » Sat Oct 03, 2009 7:27 am

mart wrote: --------------------------
CC's by themselves are not really any indication of the
airflow ability of a port. Port volume only matters when
you're comparing more or less identically shaped and
configured ports. Obviously a 354 hemi port that's been
ported to displace 170 CCs will *potentially at least*,
flow more air than another 354 hemi port that only
displaces 150 CCs. But you can't for example compare
that same 170 cc 354 hemi port with a 170 cc port on
a Chevy, Ford, Polysphere Chrysler or even a Toyota and
then say that because the volume is the same, that the
airflow capability will be similar too. There are too many
variables in port shape and particularly length etc that
affect the total volume in CCs, but don't necessarily
increase or decrease the airflow ability. Another way to
put it is that while you can directly compare 'apples to
apples', you can't likewise directly compare apples to
oranges and/or bananas and coconuts!!! :)

mart
====================================================


Mart- it's debateable- take a look at the 331 poly factory horsepower ratings, they made more horsepower than the early 1951-53 331 hemis, due to the larger ports on the polyspheres- 150 cc for poly, vs. 115 cc for the hemi

it really does all boil down to intake port volume, cubic inches being the same- especially when such a large amount is added, in this case the poly heads are 35 cc's larger, which is about 30% larger than the early hemi heads

it is so important, that in NHRA SuperStock racing classes, they have intake port volume CC rules, you are limited to a certain intake port volume and going over that is cheating and you're DQ'd- every engine is listed in the rule book with port volume in cc's

the early Dodge hemi ports for the 241 and 270 are downright laughable and tiny, they only have 100 cc's- choking off the airflow. The 325 Dodge poly heads have 125 cc's and are therefore 25% bigger right off the reel, without even touching them with a grinder yet. It's like free porting going to a poly head

another issue is this- the hemi has a centrally located spark plug, but zero swirl effect from the valve locations- the poly has canted valves off-axis to each other, like the later big block chevy, ford- this swirls the mixture, something all modern heads have now

those poly heads were way ahead of their time for the 1950's, they just weren't developed because the hemi had more image and sold better- but I'd wager an all-out naturally aspirated polysphere could run with a hemi, cubic inches/port volume/compression/valve sizes being the same-

I state this because the fastest cars today in NHRA Pro Stock have canted valve heads, not hemis- the canted valve heads make more power in naturally aspirated form

the hemi makes more power supercharged in T/F and F/C classes, and in SuperStock where they are limited to factory produced engines and replacement castings, i.e. SS/A and SS/AA

polyspheric
Posts: 57
Joined: Wed Apr 09, 2008 1:03 pm

Re: 318poly to hemi

Post by polyspheric » Wed Oct 14, 2009 12:25 pm

it really does all boil down to intake port volume

Not at all.
The head's port volume is a small percentage of the volume available to the intake valve, which is the entire passage between the valve seat and the throttle plate. It includes the full length of the manifold runner, and (in single plane manifolds) the entire plenum volume.
35cc (2.1") is hardly a substantial change, when the total volume is larger than the cylinder volume (354 is 725cc).
In any event, a long, convoluted small port simply does not flow as well as a short, wide large radius port with equal volume.

oldngood
Posts: 121
Joined: Thu Mar 13, 2008 5:14 pm

Re: 318poly to hemi

Post by oldngood » Sat Oct 17, 2009 3:46 pm

look what the Chrysler engineers did to make more HP

early Chrysler hemi heads had 115 cc intake ports

1954-55 heads had 175 cc intake ports

they "grew" the heads 60 cc's

in this case, the original heads were 115 cc's, the improved heads were 175 cc's- they enlarged the intake ports in the head castings, by over 50%

that's how they got it to go from 180 HP, to 300 HP

that's not a small amount, it's a huge change- this is so critical that in NHRA Super Stock/Stock classes, they measure intake ports, and if you're over the stock spec, you're DQ'd- NHRA is checking that volume for a reason, a bigger volume makes more top end power

George
Posts: 646
Joined: Wed Aug 25, 2004 4:12 pm
Location: Fl

Re: 318poly to hemi

Post by George » Sat Oct 17, 2009 5:39 pm

oldngood wrote:look what the Chrysler engineers did to make more HP

early Chrysler hemi heads had 115 cc intake ports

1954-55 heads had 175 cc intake ports

they "grew" the heads 60 cc's

in this case, the original heads were 115 cc's, the improved heads were 175 cc's- they enlarged the intake ports in the head castings, by over 50%

that's how they got it to go from 180 HP, to 300 HP
51-3 331s were rated @180 HP, but they were reportedly @ 200HP & they didn't want to scare the elderly folks that were typical Chrysler buyers, 200 HP was huge in '51. in '54 they increased the ports AND added a 4 bl carb & rated it @ 235, so you have to split the improvement between increased port size & the new 4 bl carb. In '55 they increased compression & increased valve size & upped the HP to 250. They got to 300 HP by going to dual quad carbs & a solid lifter cam. Can't attribute big credit to the port volume by itself.

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