331 Hemi heads with a Poly block?,...Hemi Guru's???

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Change the pistons.... and the intake, I believe.

 

check Scooter's Hemi tech index here on the board... some good stuff in there...I'll post the link in a minute or two...

 

scootermcrad's index on Hemis - pop a beer and cancel your evening plans!

http://www.jalopyjournal.com/forum/showthread.php?t=118764

 

We need to back up a couple of steps and ask which poly he is referring to.......


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Hey man! Here's the thread in Hemi Tech section that tells you more. And YES it can be done, assuming you are talking early Poly motors and not the later 318 Poly motors.

http://www.jalopyjournal.com/forum/showthread.php?p=3911032#post3911032

 

Exactly!

 

I know that 241 and 270 Hemi heads will fit on a 259ci Poly block.

 

The Chrysler spitfire Poly block will accept the Hemi heads however the pushrod angle is different between the two. The polyhead block has a shallow angle and the hemi is more radical and clearance will have to be made on the poly block. Hemi pistons will also have to be used. Intake manifold should bolt up as physically the two blocks have the same dimensions. Dodge Hemi heads will work on Dodge and Plymouth poly blocks. Desoto Hemi heads will not work with Dodge or Plymouth blocks, they are slightly longer. Tex Smith's excellent book Hot Rodding the Hemi covers this in detail. Early Bonneville racers would do this with the Chrysler Windsor block (Poly) because they could get the magic 300 C.I. which today would be a D engine size. They were getting truly incredible performances out of this combination. Talking with Neal Thompson about running that engine he said they used a prodigious amount of fuel but they were the engine that could.

 

edit: Dodge Hemi heads work on Dodge, Plymouth & DeSoto Poly blocks. DeSoto hemi heads only work on DeSoto hemi blocks.

 

Thanks for the clearification George.

 

I believe there's a lot of misconceptions about this swap- if you look at the cutaway views of a poly vs. a hemi, you can plainly see the pushrod angle is more severe on the poly- not the hemi

if you look at the decks of the actual blocks (I have owned many of them both types, but never did the hemi head to poly block swap), the poly has elongated figure "8" pushrod guide holes in the block deck- while the hemi guide holes are round because the pushrod angle on the hemi is not as severe

the poly has a VERY drastic exhaust valve pushrod angle, the pushrod seat in the exhaust rocker arm is above the upper row of head bolts on a poly-the exhaust valve pushrod on the poly is radically angled much higher towards the center of the engine, looking at the engine from the front, you can see it plainly in the cutaway view drawings

on a hemi, both intake/exhaust pushrods seat into the rockers between the 2 rows of head bolts

I started another thread asking about this, because whenever a thread is started and the question asked, we get answers from the Hemi books which isn't the whole story- we need to hear from someone who actually swapped the parts and ran them.

I'm not positive, but have a notion the cams are identical in both types, except for the 392 with its higher deck- the cam location and lifter bores are in the exact same location. The cam specs are identical for lift/spring pressure for poly and hemi, except for the solid "C300" hot factory cams.

 

THANK you, George. DeS is just a different animal. Good engines; different animals, right?

 

You just have to remember that a DeSoto hemi is a DeSoto & a DeSoto Poly is a Dodge, either are good!

 

There were no 392 Polys, but you could get creative &....

 

Different animal (except for the exceptions! LOL). This is why I love the HAMB. And the Hemi "gurus know their shit! I just keep learning. Thanks again, George!