|
|
Member
Posts: 16
| Will the 325 Hemi heads fit on a 325 poly engine, Ive got a D500 car with no engine - the parts car has a good running 325 poly head engine Id use if I could change to hemi heads |
|
| |
|
Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
   
Location: bishop, ca | This is from the "My New DeSoto" thread, found elsewhere on this website:
The REAL problem with putting Hemi heads on a Poly engine is that the compression ratio....(owing to the greater volume inside the Hemi c.c.'s......AND, the physically-shorter Poly pistons----will-both combine to give your 'New Hemi' heads a lower c.r. of around 8.0:1)
The OEM c.r. of the Hemi engine is 9.25:1
The OEM c.r. of the Poly engine is 8.50:1 (IIRC)
the HOT-trick trick is to put POLY heads onto a Hemi engine block!!!
The c.r. would go up to something approaching 10.0:1, and the engine would LOOK like a civilian Poly engine....
similar to the 440 B-block Wedge, that can out-run a 426 Hemi!!!
And, the Poly heads can be smiled-upon by a good mechanic, to flow very nicely.
But, due to the mundane appearance of the Poly heads, compared to the eye-candy of the Hemi heads, street
rodders usually go for the easy-score (Hemi) instead of the EFFECTIVE-score (Poly) ...heads.
Edited by d500neil 2015-04-26 4:20 AM
|
|
| |
|
Expert
Posts: 3035
Location: N.W. Fla. | d500neil - 2015-04-26 3:04 AM
The REAL problem with putting Hemi heads on a Poly engine is that the compression ratio....(owing to the greater volume inside the Hemi c.c.'s......AND, the physically-shorter Poly pistons----will-both combine to give your 'New Hemi' heads a lower c.r. of around 8.0:1)
The OEM c.r. of the Hemi engine is 9.25:1
The OEM c.r. of the Poly engine is 8.50:1 (IIRC)
it should be noted that advertised C/Rs can be close to a full point on the optimistic side when actually measured. |
|
| |
|
Expert
Posts: 1730
Location: Michigan | Just for the sake of discussion. If you put hemi pistons in the poly block do you essentially make it a full hemi? At least on the Chrysler side, the blocks, crank and rods are the same. The shape of the piston and the heads should be the only difference between poly and hemi, correct? |
|
| |
|
Expert
Posts: 3035
Location: N.W. Fla. | Beltran - 2015-04-26 3:17 PM
Just for the sake of discussion. If you put hemi pistons in the poly block do you essentially make it a full hemi? At least on the Chrysler side, the blocks, crank and rods are the same. The shape of the piston and the heads should be the only difference between poly and hemi, correct? yes, a poly is just a hemi with different heads on it. Specifically the complete head assembly including push rods, pistons, ex mans. Some debate as to weather you actually need to replace the cam or not. The Hemi came 1st, they just made those changes to create a cheaper to build engine.
|
|
| |
|
Expert 5K+
Posts: 8445
Location: Perth Australia | Ok, to clarify for me, there are 2 types of poly engine, the early poly with the scalloped rocker covers and the later "A" poly with the saw tooth rocker cover, right?
Hemi heads wont fit on a later "A" poly right?
The later "A" poly is more related to the "LA" engine
Just to make it clear for me (and anyone else), am I right or wrong?
|
|
| |
|
Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
Location: bishop, ca | Yes; we are discussing the 'early' A-poly engines, with the rounded, scalloped-shaped lower valve covers.
I should know this, already, but what is the engine-family stamping prefixes for the early Polys?
So, if you came across a bare block, you would recognize it, for what it is/was.
|
|
| |
|
Expert
Posts: 1740
Location: Alaska | Not sure about the stamped marking, but it would include the Dodge: 241, 270, 315, and 325 (also used in the Desoto). The 259 used in the Plymouth and the 301, 331, 354 used in the Chrysler. |
|
| |
|
Member
Posts: 16
| 58coupe - 2015-04-27 10:27 AM
Not sure about the stamped marking, but it would include the Dodge: 241, 270, 315, and 325 (also used in the Desoto). The 259 used in the Plymouth and the 301, 331, 354 used in the Chrysler.
The hemi heads off all those engines will work on the 1957 325 block ?? |
|
| |
|
Expert
Posts: 3035
Location: N.W. Fla. | d500neil - 2015-04-26 8:44 PM
Yes; we are discussing the 'early' A-poly engines, with the rounded, scalloped-shaped lower valve covers.
I should know this, already, but what is the engine-family stamping prefixes for the early Polys?
So, if you came across a bare block, you would recognize it, for what it is/was.
The "A" Poly is the late poly of the 318 family, he has a 325 Poly witch is an early Hemi based Poly, not an "A". |
|
| |
|
Expert
Posts: 3035
Location: N.W. Fla. | big sky 57s - 2015-04-27 7:17 PM
58coupe - 2015-04-27 10:27 AM
Not sure about the stamped marking, but it would include the Dodge: 241, 270, 315, and 325 (also used in the Desoto). The 259 used in the Plymouth and the 301, 331, 354 used in the Chrysler.
The hemi heads off all those engines will work on the 1957 325 block ?? |
|
| |
|
Expert
Posts: 1819
Location: Vancouver, BC |
Little bit late with this, but the first generation Mopar hemi engines were Chrysler (1951-1958), DeSoto (1952-1957), and Dodge (1953-1958). Nothing will interchange between the three as they have different bore centre sizes and thus differing lengths of cylinder blocks. Each also had a raised block (longer stroke) versions to gain cid.
With the poly engines, Chrysler and Dodge had poly versions starting in 1955. DeSoto never had a poly verson of their hemi. The 1957 DeSoto Firesweep poly is actually a Dodge poly engine.
Plymouth used Dodge poly engines in 1955 and came out with the A block poly for 1956. The A block poly has no hemi version and nothing from the Chrysler, DeSoto or Dodge hemi/poly engines will interchange with the A block poly. Again, different bore centre size and thus different block length. The Dodge hemi/poly has the smallest bore centres and thus had the shortest block length. Next was DeSoto followed by the A block and the longest, Chrysler. Dodge used the A block in 1959 for the Coronet 326-cid V8 engine.
The original hemi blocks were maxed out as far engine size by 1957-58. Thus Chrysler designed and tooled the B block engines as corporate engines to replace the first generation V8 trio. The 350/361 B block engines appeared for 1958 in Plymouth, Dodge and DeSoto models. and the B block 383 for 1959. The RB engines (Raised B block) with longer stroke appeared for 1959 in Chryslers and Imperials (413 and the 1959-60 383 RB small bore). With the arrival of the B block, all engines were now built by Chrysler Corp's Automotive Manufacturing Group. The car divisions were responsible only for sales and not manufacturing.
|
|
| |
|
Expert
Posts: 1740
Location: Alaska | I didn't mean to confuse you big sky 57s, what I was listing was all the polys that could be made into hemis, but only in each family, Dodge, Desoto, and Chrysler as others have listed.
|
|
| |
|
Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
Location: bishop, ca | Actually, the Dodge engine blocks were NOT...max'ed out, in their bore, in the 1957 325 c.i. engine blocks.
Viz: my own 325 c.i. Hemi engine was bored-out 40-over, to 330/331 c.i. back around 1980+, and its
camshaft was re-ground to the "3/4 race" category.
Since then, NO overheating or 'performance' related problems have ever occurred or existed with that engine,
from its over-boring (and other 'hidden' mods, like its hot-rodded distributor/timing systems).
But, again, merely installing Hemi heads on a Poly-head engine will result in a drastic DECREASE in compression
ratio, like: from 9.25:1, to 8.00-ish:1.....because the Poly has shorter pistons, to start with (8.5:1 c.r.), and
adding the larger Hemi heads increases the combustion chamber volume.
The sneaky-pete/hot-ticket is to install POLY heads onto a Hemi engine!
The c.r. will be something around 10:1 !
|
|
| |
|
Member
Posts: 16
|
Building the 325 Poly out of thr Royal into a hemi shouldnt be a big deal ,I'll have to at least find a Hemi upper end. I dont mind changing to Hemi pistons during the rebuild. Being new to these older engines, I was surprised the blocks are the same. 426 Hemis are a modified RB engine, Ive had plenty of experience with them .
Thanks guys for all the information ! |
|
| |
|
Expert
Posts: 1740
Location: Alaska | Neil, if going to the expense of making a hemi out of a poly, it is just one more step in the build to put the hemi pistons in. Also, it is probably much easier to find new hemi pistons because of the continuing popularity of these old hemis. I plan on doing the same thing. I have a 55 331 hemi that I could rebuild but one cylinder needs to be sleeved because of rust, (already .040 over) and I have a 57 354 poly that appears to never have been apart, so a 354 hemi it will be. |
|
| |
|
Expert
Posts: 1819
Location: Vancouver, BC |
Neil, when you increased the bore on your 325 by .040 over you went to 331 cid - an increase of SIX cubic inches. In the grand scheme of things, that is not much.
But, by replacing the Dodge V8 with the B block, Dodge went from 325 cid to 350 cid and 361 cid in 1958 - increases of 25 and 36 cid, respectively. And then went to 383 for 1959 and eventually 400 with the B block. With the raised B block (RB) Dodge was able to get 413, 426 and 440 cid. All sizes the Dodge block just could not provide.
As I said, the Dodge block was maxed out by 1957. But the B block and the related RB carried Dodge through for the next twenty or so years.
|
|
| |
|
Member
Posts: 17
Location: ocala, fl | Best thing to do is get the Tex Smith Hemi book available anywhere lots of good info and technical data. Thats how I turned a 331 poly into my current 336 (30 overbore) 340:). |
|
| |
|
Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
Location: bishop, ca | Thanks, Bill, for that.
But, as I state, above...from my own multi-decade experience:
The 1957 Dodge engine block was NOT "maxed-out by 1957".
I increased the OEM 325 c.i. displacement....to 331 c.i., by virtue of a 40-over re-boring, back in the mid-80's.
To date, the engine has never over-heated, and, coincidentally, right now (after a few years, after re-coring
the radiator with another row of cooling fins on it...) its Temperature gauge is 'reading' a little bit TOO Cool (engines
like to run on the 'hot' side, for better thermal efficiency!
So, a well built 325 can definitely handle a 40-over re-bore (to 331 C.I.D.) without cylinder deformation or over-heating
problems resulting therefrom.
|
|
| |
|
Exner Expert 19,174 posts. Neil passed away 18 Sep 2015. You will be missed, Neil!
Posts: 19146
Location: bishop, ca | COMPLETELY coincidentally....as I am presently re-reading my collection of Mopar magazines, from the 1980's
and 1990's....
discovered this article from "High Performance MoPar" , from its 11/94 issue.
Actually. have discovered relatively MANY useful, informative articles in these semi-vintage magazines!!
Edited by d500neil 2015-07-21 7:56 PM
 (PICT5227.JPG)
 (PICT5229.JPG)
Attachments
----------------
 PICT5227.JPG (153KB - 154 downloads)
PICT5229.JPG (146KB - 134 downloads)
|
|
| |
|
Expert
Posts: 3035
Location: N.W. Fla. | The hemi & hemi based Polys were dropped for the A & B engines to save money. Reportedly Don Gatlitz said the savings were $30-35 per engine. |
|
| |
|
Elite Veteran
Posts: 888
Location: Peoples Republic of Oregon | ...the bean counters would require major drivetrain changes if they saw a 5ยข savings....
|
|
| |
hemi heads on poly block
