I am having trouble finding out what the max bore is for the desoto 291 engine. I have one bored .125 over. Will this cause it to run hot in a street car. If I need to rebuild it, in the future, is there any room left to bore it out if I have to? I know .125 is pretty far out. Thanks for your time Jesse
.125 is max on low deck chryslers, haven't heard anything on low deck DeSotos, might be simular situation. A sonic check is in order to find out how much wall you have left. I'd guess there's no room for any more boring.
The engine I bought is a rebuilt short block. I will pick up another block when I get home just incase I need to do a rebuild in the future. I was looking for info on the other engine because I wanted to build mine somewhat like it. Thanks for your help George.
the largest overbore for street is .060, anymore would remove too much meterial between cylinders, thus it will run hot, ( not enough cooling surface ) mopar charlie 727-271-5068 P.S. I do have a standard bore 291 DESOTO HEMI FOR SALE
Thanks for the info Charlie. I already picked up two complete 291s as spares right now so I should be good.
It is not an issue of cooling surface...the surface area exposed to the fluid/coolant does not change. What does change is the amount of thermal mass, e.g. wall thickness, that is a heat sink. With a diminished heat sink the high temp travels right thru the thin walls and essentially boils the coolant. With thicker walls (better heat storing capacity) the temp is more uniformly distributed and more uniformly radiated to the coolant. This is the reason behind the Hemi truck engines that have a 354 block but have only been bored to 331 size...more cylinder wall mass... .
I wouldn't worry too much about a .125" overbore. A lot of guys bored these motors that big. Back then, core shift was an issue and castings were a little on the thick side on these motors just to be sure there were no thin bores anywhere. Have the block sonic tested. I bet you'll be pleasantly surprised. The first slant sixes were made of aluminum and the bores were extra thick to make way for steel sleeves. Later the blocks were iron and Chrysler left the molds alone. That meant they had some really thick cylinder walls. And this is when casting technology was getting better. Bill
Mine is .065 over...runs fine, no overheating ( I don't know how they can run hot, can barely get my hemi to 160 degrees
From everything I have read,the wrist pin and piston heigth are the same on 291 and 341,why wouldn't the 341 pistons fit in the 291 after sonic test and boring.I am thinking a bigger bore,500 cfm carb,late model hei ignition,headers,and reground cam.291 pistons are 7.5 to 1 and 341s are 8.5 to 1 ?
In the old days it was normal and expected for an engine to be rebuilt at least once, possibly several times during its working life. All Chrysler built engines were made to be bored up to .125 in a normal rebuild, if you got a good block, maybe farther. Starting in the mid sixties they reduced this to .060. New casting techniques allowed thinner castings, and they realized engines hardly ever needed to be rebuilt anymore. Some newer engines can only be bored .030. The Chev 400 small block comes to mind. Since the 80s cylinders don't seem to wear at all hardly. I put this down to the low friction, low tension rings that came out at that time. Plus the oils they have now.
I think this was discussed in the Hemi tech index, have you found it yet?. Also the nominal C/Rs may be up to 1 point on the 'optimistic" side.
.125 is generally considered max with sonic check, though you might find some that might go a little bigger. The high decks hemis don't seem to have the wall thickness of the low decks.
Mine is sleeved also, when I get home from afghanland in oct i will check the bore size. I was going by what the seller told me and the tag on the ross pistons I have for it.
I know that sounds odd. I personnally have never seen or heard of it before this time. However, they are in there all right. I will try to get a pic when I'm home also.
The 341 compression ratio is based on 3.800 inch stroke, vs. 3.344 of the low deck. I also have had several 331 blocks that would only go .060 over safely.
For the life of me I don't understand why people are still guessing about this. Have the block sonic checked, it's that simple fellows. Also, pistons can be made in as little as .005" over all the time. Whether it's 4.600" + .005" or it's 4.125" + .005". Yes, it won't be a " shelf " piston I understand that. So you might have to pay for a custom piston in a .005" over size, it's worth it if you have a KNOWN good block. I do this for a living fellows. As opposed to start over with a used block, have it all checked out, blasted, hot tanked, align honed, bored and honed, cam bearings, hone lifter bores, decked and maybe square decked, and on and on and on. No see where the custom pistons are NOT so expensive anymore?
As I mentioned earlier, the OEM C/Rs were often up to a full point high when actually measured. This is a situation where he needs to measure & find out the C/R with this set up, if good then fine. If not, then he needs to order custom pistons that will give him the C/R he wants matched to his measurements.
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