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

Posted: Sat Mar 15, 2008 11:29 am
by oldngood
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 ?

Posted: Sat Mar 15, 2008 6:16 pm
by George
You'd be best useing 315/325 heads, but check out Doc Fromader's 315 build on www.webrodder.com

Posted: Sat Mar 15, 2008 8:18 pm
by oldngood
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 ?

Posted: Sat Mar 15, 2008 8:22 pm
by George
go to engines & look through the pages till you find it.

Posted: Sat Mar 15, 2008 8:30 pm
by scottm
Click on this...

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

Wow, what a wealth of information!

Posted: Sat Mar 15, 2008 8:53 pm
by George
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!

Posted: Sat Mar 15, 2008 9:32 pm
by oldngood
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.

Posted: Sun Mar 16, 2008 11:36 am
by TrWaters
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.

Posted: Sun Mar 16, 2008 3:21 pm
by oldngood
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

Posted: Sun Mar 16, 2008 5:46 pm
by George
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

Posted: Mon Mar 17, 2008 7:11 am
by oldngood
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 !

Posted: Mon Mar 17, 2008 9:22 am
by George
Bingo!

Posted: Mon Mar 17, 2008 6:43 pm
by TrWaters

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.

Posted: Tue Mar 18, 2008 6:46 am
by oldngood
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.