Hoping up a Desoto/chrysler flathead 6

[austinsailor]

Down the road I plan to put a big six in my B1B. Got a Desoto six yesterday, have another located. Should have plenty of good core parts.

7 to one is standard compression. What I see needed is higher compression, hotter cam and better breathing. Compression is what I'l like to find more about now. All the Chrysler and Desoto motors seem to be the same, except stroke. Same bore, same crank dimensions, bearings, etc.

First idea is to find higher compression pistons. Anything off the shelf, or was there at one time? Another method is to have new ones made, cost around $125 ea.

Any increase in compression, whether using custom pistons or otherwise, would seem to need the piston dome to go into the compression chamber of the head. All Mopar flatheads I've seen have pistons that go flush with the block deck. Just brainstorming, it would look like I could take a crank out of a 4 1/2 inch stroke Chrysler motor, put it into the 4 1/4 inch Desoto motor, using standard pistons, leaving the pistons to go 1/8" into the the combustion chamber, increasing the compression. Is this just a completely insane idea? Wilder would be to use a 4 3/4 inch stroke crank out of a 261 Chrysler, going 1/4" above the deck.

Any of you guys ever heard of anything like this, or should I just trash the thoughts?

I don't think it will be be much of a challenge to have a cam reground, or build headers, but the guts will take some thought.

[austinsailor]

Didn't see my typo until too late!

[Don Coatney]

What are your plans for this souped up engine? A full scale racer or a dependable driver? Installing pistons that extend above the block would be difficult as this would require machining the head as the head is flat above the pistons. In my opinion you would be better off by simpling milling the head. You can remove as much as one hundred thousands depending on how radical you want to go. Or you could order a new aluminum head from Earl Edgerton. There is an old thread on the HAMB about a guy who was trying to DYNO 200 HP with a Mopar flathead.

http://www.jalopyjournal.com/forum/showthread.php?t=298125&highlight=dyno

[austinsailor]

Looking for a fun truck that surprises people, sound good and is dependable. Not a racer, more street rod.

Been too long since I saw a head off, stopped by to see an old machine shop guy and realized the piston to head interference problem.

Got some leads from him, probably all outdated.

Another idea I'd had was to weld up the piston top on the correct side. I thought it was too outlandish to mention here, but I found that another machinist here has done it often.

I'll keep looking and asking until I figure out something or drive everyone nuts!

Oh, how much would milling the head .1 increase the compression over the standard 7 to 1? What should be my goal, about 9 to 1 or so?

Edited October 26, 2009 by austinsailor

[Don Coatney]

[desoto1939]

I have a factory Aluminum big 6 head for the Chrysler/Desoto 6. The head has been milled and has the factory DPCD logo and the correct partnumber onthe head. This head will fit from 1938 and up.

I can send pictures if you want to see it. The Al head will increase the HP from 92 to 100 HP.

Rich HArtung

desoto1939@aol.com

[greg g]

I took .010 of my block and .040 off the head. CR with the ,030 over bore was calculated by the guy in the machine shop at about 8.25 to 1. Runs great on regular gas, with 5 degress of initial timing. Lots of folks say you need to relieve the block for better breating but that would negate any increase in CR from the milling.

Sombody said that some work on the area between the valve chamber and the area over the piston will increase swirl and give a better mixed fuel air charge.

If you look at the picture of the Chrylser head Don posted and the interior of the Edmunds head below, you can see there is a big difference with the Edmunds in that the area above the piston is near flat rather than domed. So there is a lot of room to work with as long as you leave space for the valves to open. Instead of build up the piston, filling and remachining the area in the heads might work better and not increase rotating mass. these heads supposedly took the cr to 9 to 1.

The 56 plumouth option of the 2 bbl carb raised HP from 125 to 132. Other than the carb and manifold the published specs don't suggest anything else is different. And it you look at the spec chart on Carnut, you can watch the HP for the MOPAR flat 6's go up over time with the higher CR through the years.

in 50 the 230 6 had a 7 to 1 and 103 hp, in 54 with 7.25 they wnet to 110, in 58 it was 8.to 1 and rated at 138 horse.

So more compression seems to be the key, althoug cams might have been deifferent also.

So I would think 150 HP from a nicely set up 265 wold be within reason.