Older 276 Desotos versus 291

Discussion of the Early Dodge / DeSoto HEMIs.

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Ol'Hemijunkie
Posts: 2
Joined: Mon Apr 24, 2006 3:58 pm

Older 276 Desotos versus 291

Post by Ol'Hemijunkie »

New to this forum and building a 54 276 wondering what's changed between the 276 and the 291. I was thinking of making a 291 out of it. I see the bore is different but the valve sizes show the same diameter but different part numbers. Anybody that's done this changeover or has any info would really like the help. Thanks in advance.
Gullwing
Posts: 35
Joined: Mon Jul 04, 2005 11:08 pm
Location: aLBANY

Post by Gullwing »

Have you seen the Liberty Tech papers or Panic Papers on the internet? They list quite a bit of information on the Desoto. They also have several pages on modifying your motor. I am unsure but I believe the 276 has smaller valves and ports than the 291. You don't want to use the 291 heads. Use the tall deck 330-341-345 heads. They have the largest ports of them all. Technically you could simply install the largest valves in your 276 head. The ports are what you want though.
Ol'Hemijunkie
Posts: 2
Joined: Mon Apr 24, 2006 3:58 pm

Thanks for the help on my 276

Post by Ol'Hemijunkie »

Thanks for the info I found the papers you recommended at victorylibrary.com. I probably am going to have to stick with the lowdeck setup though as I have a really nice 291 4bbl setup. This motor is getting crammed into a chopped 1951 Plymouth coupe and I am trying to make it look like it belongs there. I may have to give up some power for the look I am going for. Probably punch it out to a 291 anyway and bump the compression on the pistons a bit too, seems like these motors are pretty tight valve to piston.
johnny5
Posts: 128
Joined: Mon Dec 05, 2005 3:52 pm
Location: St Charles, MO

Post by johnny5 »

I'm going to upgrade my 276 to something in the 330cid range using a tall deck crank (when I find one) and over bore accordingly. I'm buying a sonic checker soon so I'll be able to check the wall thickness and make sure this can be done. Shouldn't be a problem but it's always good to check.

As far as the heads go, I'm going to try something different. I think the exhaust valve is a little on the large side in the 330-341-345 in relation to the port size. I'm going to install stock 330 intakes and cut down the exhaust to 1.60-1.65 (not sure of the exact just yet) and use 276/291 heads. There is no real difference between the 2 low deck heads other than final machining. The ports are not that bad and when the throat is opened and blended to put the larger valves in it should flow pretty well. This will be backed up with before and after flow numbers.
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