273 Commando Piston Dome Volume

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perfacar said:
the dome volume is 16 cc. this is from TRW and ross and other dealers. NHRA specs show the dome volume. it's in engine specs on their website.
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I would not take NHRA numbers as gospel as they allow a certain level of mods. (Like chamber volumes, where they allow so much milling of the heads.)

I don't actually see a dome volume on the NHRA pages:
http://board.moparts.org/ubbthreads/upload2/5544049-NHRAAcceptedProducts.pdf

So I suspect the pistons made to meet the NHRA specs have been optimized for max dome volume above the compression height per the rules to maximize compression ratio. That can be different from stock parts.
 
the specs in NHRA are supplied by mopar. they head volumes are same as listed by mopar from way back. the 273 has always been 57.3 cc. my 1966 spec sheet shows that volume. the dome volume was taken from a stock piston. NHRA does insure these things are correct. the chamber volume is for the closed chamber head 235/273. also, same for the 180/273 1964 to 1967. the dome volume does measure at 16 CC. BTW, the dome volume is in the engine blueprint section.
 
Roger.... I would not argue that the mfr's don't supply the numbers, but measurements show that production closed chamber 273 heads are larger than 57 cc, so the NHRA numbers are not actual production numbers but an idealized factory minimum, to which all heads can be milled as needed to reach that number and equalize that aspect of the engines in competition.

So I kinda think the piston numbers may be the same. I also wonder if the 16 cc dome volume reflects the dome only, and the 11.5 volume includes the eyebrow volume; a 4.5 cc eyebrow volume would be make sense for what the op shows in pix.
 
Bottom line, the op needs to assemble one cylinder and measure what he has going on. There isn't any cookie cutter specs that will get close enough..
 
yep both the head cc's and dome can be way off from published specs plush is deck cut
and stock gasket was a .015 shim or thereabouts (which I do not think would work with a 360 head anyway) test fit everything
 
Thanks for the information guys.

Dummy assembly is taking place either next week or the week after. Waiting on my NOS closed chamber heads to arrive and for my components to be balanced then the. Will let you know what final numbers are.

Looking forward to it, another early 273 saved from the scrap yard!!

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Wyrmrider said:
yep both the head cc's and dome can be way off from published specs plush is deck cut
and stock gasket was a .015 shim or thereabouts (which I do not think would work with a 360 head anyway) test fit everything
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And they don't make the steel shim gaskets any more. Without actually measuring, you are just playing number games.
 
Alpine White said:
Thanks for the information guys.

Dummy assembly is taking place either next week or the week after. Waiting on my NOS closed chamber heads to arrive and for my components to be balanced then the. Will let you know what final numbers are.

Looking forward to it, another early 273 saved from the scrap yard!!

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I'm a long ways away from having all the answers but there's a link to my 273 build about a decade ago.
273 Build
 
when the factories manufactured their engines,, they have a set spec for all measurements. most blocks are cut above the min deck hgts. same with chambers , all are usually bigger. this way you can cut to the min specs called for by the manufactur. I know they are larger, the min numbers are the blueprint of the engine. in a perfect world, they should be better, they are not! called tolerances. all engines are built this way back then. the numbers are not bogus.
 
Richard Sweet said:
Alpine, Where did you get nos 273 heads? What casting numbers? How much were they?
Richard
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Hey Richard,

Sorry for the delay in response,

I purchased them though a company here in Australia called Hemi Performance. They are from a 318 truck motor apparently, but the 273/318 heads are exactly the same so will bolt up without issue. If you zoom in on the photo I posted you can see the cast number but I have researched those numbers and they aren’t listed anywhere. All good, I’m happy with the purchase!! I had them delivered for $700aud for the pair. With the exchange rate from aud to usd you would get them a lot cheaper, probably enough to cover the freight.

Here’s the link:

N.O.S. Bare Head (Head Shell) : suit Small Block LA 273/318/340ci (Closed Chamber, Small Ports)

Cheers man,

Luke
 
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Luke,
I see they have a pretty good web site with nos and new parts, shells and assembled.
Looks like a good source for Australians. Best wishes on your assembly.
Thanks, Richard
 
Hemi site says:
Will fit all Chrysler Small Block LA engines.
They are an EXCELLENT CHOICE for standard through to mild 360ci engines.
(Note: big valves do not make any more power on a standard to mild engines.)
end quote start rant

They got that right 2.02 valves can hurt
1.94 can raise sunken seats and give fresh valve job but that's it
thanks HEMI
 
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