I have a Chrysler flathead 230 and was curious if its possible to bore it out to a 251. Was the 251 block made differently?
You can't do it. The 201, 218, and 230 flatheads are small block. The 239, 251, and 265 are big blocks. The difference is about 2" in length. You can get about 235" out of a 230 by boring. The best thing you can do is balance the moving parts, pick up free horsepower and rpms this way. If you want inches you have to locate a 251 or 265, tough but not impossible.
I'm far from being a MOPAR expert but my old MoToRs manual indicates that you can't get there from here (at least in terms of an eqivalent engine.). The Dodge 230" engine has a 3.25" bore and a 4.625" stroke. The Chrysler 251 (250.6) is a 3.438" bore x 4.50" stroke. To achieve the same displacement would require an overbore of .141" (even with the longer stroke in the smaller engine.) That sounds like a WHOLE bunch. ( I know; the flathead Ford guys routinely go from .250" to .312"). Only the experienced will know for sure.
My dad and I believe it can be done, we have always wanted to do that very combo but just haven't gotten to it. We have bored a 201 out to .125 +.40 (that would be a .40 over 230cu piston) we had NO problems with boring it etc. The concern with what we did is that the bottom end needs to be good condition because the 230 motors had bigger mains then the 201. The reason I explain all that is it applies to your combo. You will be boring out your 230 .125 if you use a standard 251 piston. Standard piston is a good idea (cheap) because nobody needs a standard piston for their 251 they always what a oversize. The issue is the same for your 230, the Chrysler 251 six had a beefer bottom end. Just make sure your crank etc is in good shape. If you do this you will end up with over 251cu because your 230 has a longer stroke then the 251 Chrysler. It would be one heck of a good running six. Basically its a Chrysler motor without the headaches of trying to make it fit in the smaller dodge/plymouth body and its much easier to get general parts for the smaller dodge/plymouth six at NAPA etc.
If your into spending money, you can have your crank welded up and offset ground into a stroker. You'll need custom pistons to match the longer stroke. If your just looking for speed in general, Hawkeye and I are developing a new amuminum head for the 230.
quick butin question with same motor: who makes custom intakes for duals for this motor? anyone have any pics? Just picked up a 49'
offenhauser makes dual single barrel intakes. you can find them on e-bay aswell every now and then. and a few places are still making split exhausts. Hank at Hanksville Hotrods (an alliance vendor) is making a pair of mandrel bent headers for me, and is using it as a template to make more. they should flow very well and be affordable, as well... as soon as i get the prototypes i'll mock them up and take a picture... bugman- tell me more about the head your making.. i'm very interested!
i built a 230 for my bis coupe full balanced .030 over pulls till the valves float and then some fun to drive tons of lo-end torque
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