'55 270 Hemi top end on a '57 325 Poly ?

Discussion of the Early Dodge / DeSoto HEMIs.

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oldngood
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'55 270 Hemi top end on a '57 325 Poly ?

Post by oldngood » Sat Mar 15, 2008 11:29 am

this is another one of my projects and I'd like to get some opinions on this:

I have a 1957 Dodge 325 Super Red Ram poly engine

I have access to a complete 1955 Dodge 270 Hemi top end

Hemi top end will bolt onto the 325, but valve sizes are smaller on the '55 Hemi heads, than what a "real" 1957 Hemi 325 would have

is the only difference the valve sizes, or did the 1957 D-500 Dodge hemi 325's also have larger PORTS

in other words, is this swap worth doing, or should I just hold out for 1957 Dodge heads with the bigger valves ?

George
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Post by George » Sat Mar 15, 2008 6:16 pm

You'd be best useing 315/325 heads, but check out Doc Fromader's 315 build on www.webrodder.com

oldngood
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Post by oldngood » Sat Mar 15, 2008 8:18 pm

George wrote:You'd be best useing 315/325 heads, but check out Doc Fromader's 315 build on www.webrodder.com

where exactly is that buildup ?

George
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Post by George » Sat Mar 15, 2008 8:22 pm

go to engines & look through the pages till you find it.

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scottm
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Post by scottm » Sat Mar 15, 2008 8:30 pm

Click on this...

http://www.webrodder.com/index.php?sear ... ies&CID=15

Wow, what a wealth of information!
Scott Moseman
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George
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Post by George » Sat Mar 15, 2008 8:53 pm

scottm wrote:Click on this...

http://www.webrodder.com/index.php?sear ... ies&CID=15

Wow, what a wealth of information!
Yeah! But I'd hate to think of what he spent on that cam/crank/rod set up!

oldngood
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Post by oldngood » Sat Mar 15, 2008 9:32 pm

yeh, I'm starting to think spending big bucks on a Dodge 325 hemi may not be worth it- I always had the opinion that the only early hemi worth messing with would be a 392- but could never find one for good price- so I never did a 392- now I'm trying to low-buck it with a Dodge 325 poly with hemi top end, or a 331 Chrysler poly with early 331 hemi top end- it seems like it may very well be a waste of time power-wise, I'm sure I could get the engine assembled and running, but the HP level would be 250-280 HP at best with those stock small port/small valve heads, if that even

those Dodge hemi ports look mighty restricted to me


is there a PORT SIZE difference between 270 Red Ram and 315/325 Red Ram hemi heads ? That's what I really need to know before I proceed.

TrWaters
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Post by TrWaters » Sun Mar 16, 2008 11:36 am

I dont believe there is a significant difference in port size. The slight problem with using 270 heads on a 315-325 block is that due to a casting difference, the heads do not quite cover the keyhole shaped pushrod holes in the 315/325 block. You will need to either add some weld or epoxy onto the heads to completely cover these holes.
Early hemi to late sb Mopar trans adapters. Precision billet parts for early hemis.

oldngood
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Post by oldngood » Sun Mar 16, 2008 3:21 pm

TrWaters wrote:I dont believe there is a significant difference in port size. The slight problem with using 270 heads on a 315-325 block is that due to a casting difference, the heads do not quite cover the keyhole shaped pushrod holes in the 315/325 block. You will need to either add some weld or epoxy onto the heads to completely cover these holes.

why would you want to cover excess pushrod keyhole space ? it only is dead air space between rocker box area and lifter valley area- both areas are open to crankcase pressure- what's the purpose of adding expoxy to make it smaller ? I don't get it, please explain

George
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Post by George » Sun Mar 16, 2008 5:46 pm

On the Webrodder Forum there was a thread were Doc was talking about his 315 build. He was saying that the sealing surface between the head & block @ the top is minimal when useing 270, & espicially 241, heads on the 315/325 blocks. I guess he means you might get oil leaks above the valley pan

oldngood
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Post by oldngood » Mon Mar 17, 2008 7:11 am

ok, looking at picture of bare block in Tex Smith book, I see the row of keyhole pushrod holes across top of block for pushrods to go into heads- if the 241/270 heads have less surface area towards top of head, that area would become a thinner sealing surface- this is similar the problem some Pontiac valley covers have, when bolted down.

the fix is, bolt the heads on, then wipe a layer of black permatex across the top of that area, from front to back- between head and block- then it won't leak oil there

the 270 hemi ports look pretty dismal from a performance standpoint, in that one webrodder thread- it kind of took the wind out of my sails for that project- I'm starting to think the only way to go, is the 315/325 heads on the 315/325 hemi

what grabbed me was they ported them considerably, and they only flowed around 209 cfm, which is only what a wedge head flows out of box, and many like Buick, Olds, Pontiac actually flow more than that- but with the 270 heads, you have to work to get it

a labor of love, for sure

but I'm still attracted to the 325 for a few very good reasons- #1 it has comparable displacement to the most affordable big hemi, the 331 Chrysler- #2 the Dodge is lighter and smaller #3, it's still a Hemi !

George
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Post by George » Mon Mar 17, 2008 9:22 am

Bingo!

TrWaters
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Post by TrWaters » Mon Mar 17, 2008 6:43 pm


the fix is, bolt the heads on, then wipe a layer of black permatex across the top of that area, from front to back- between head and block- then it won't leak oil there
Actually, thats not a fix. Its an oil leak waiting to happen. But to each their own. Good luck with your build.
Early hemi to late sb Mopar trans adapters. Precision billet parts for early hemis.

oldngood
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Post by oldngood » Tue Mar 18, 2008 6:46 am

TrWaters wrote:

the fix is, bolt the heads on, then wipe a layer of black permatex across the top of that area, from front to back- between head and block- then it won't leak oil there
Actually, thats not a fix. Its an oil leak waiting to happen. But to each their own. Good luck with your build.

I totally disagree with you there, because the new liquid sealants are better than gaskets ! Many new OEM engines don't even use gaskets anymore, you get a gasket kit and there's a head gasket, thermostat o-ring, and intake gasket- the rest is sealed- with sealer.

If that head/block interface is wiped and ends up leaking, it can only be due to excessive blowly causing pressure blowing the gasket out- because modern black permatex is good stuff.

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