engine parts choices

[austinsailor]

I'm beginning to collect parts and make choices on my 25" motor rebuild. I'm looking for feedback.

motor is a 251 truck motor. crank was ground to .030 mains and .020 rods. both are in good shape but need cleanup and will be .040 and .030. stroke is 4 1/2.

I also have a 48 desoto motor, probably STD, not sure, but stroke is 4 1/4 for 236 ci.

I thought going under more than .030 was a problem with shortened life, but my old time machine shop guy says that was a bearing problem, not the crank. he says they used to just put on more Babbitt, now the build up the base and it is no longer an issue thoughts?

choices? shorter stroke, higher reves or more cubes? any thoughts?

plan is to get the cam ground with a more aggressive curve, shave the head, add multiple carbs and headers. goal is not a racer, but reasonable power for the highway and to sound mean. oh, and to last a long time.

piston choices? stock? are there better aftermarket ones, like lighter or?

[MarkAubuchon]

Longer stroke, deck the block, cut the head, port it. With the 25 you have room for 3 carbs, Electronic ignition. These are the improvements I made to my 218 (.60 over on pistons) cam is 380 lift vs 240. Only problem is its tought to get it to idle, really has to warm up and then set the idle speed higher. On the sound part, be carefull what you ask for, I changed my exhaust, muffler 3 times to get ones that wouldn't make me go deaf.

[austinsailor]

I'm thinking George asche 3 carb setup.

can you go to that much lift without worrying about hitting the head, or is some relief needed?

I've never done any sort of porting. is there a beginners write up somewhere? I assume you just use a die grinder, smooth and open thing up. am I at oll on the right track?

I guess I should have posted this on the car side, but I spend most of my time here. but then, I am starting with a truck motor!

[Dave72dt]

I know there's some books available on porting. Die grinder works along with deburr bits, stones. Where and how much removed or added in some cases makes a difference. Getting them the same in each runner is important. Polishing the rough casting finish will help. Deburring the inside of the manifolds themselves will also help. They're not all that slick inside either.

[David Muma]

Have a look here to see how to port a mopar flathead

http://www.jalopyjournal.com/forum/showthread.php?t=315555&page=6

[austinsailor]

I wondered if making the ports completely smooth would hurt the mixing of the fuel, and reading these threads it seems others wonder about that as well. I do see that opening the ports to match the gaskets and manifolds would be good. I'll probably do at least that much.

I was reading through that thread and noticed that at the end he painted the inside of his motor. Looks bad to me. Any flaking paint could be a disaster. I'm not sure why it would be done. Not something I've ever considered, but it makes me wonder.

Also, his last post was 2009. Wonder what happened?

Another question. All the compression ratios are about the same, but displacement is not. For example, the 48 Desoto 236 I have is about the same, so I wonder if the head of the desoto, put on the 251 block would give a boost in compression? I suppose I need to measure the volume of both and I'd have my answer.

To take it to another level, I also have a 51 Fargo which has a 25" block, but a smaller motor. I wonder how the head from that would work?

Edited January 16, 2011 by austinsailor

[David Muma]

Glyptol is a paint commonly used inside performance engines. Painting the inside smooths and promotes better oil flow.

[Dodgeb4ya]

The big dodge "Moly Block" engines are painted with the red Gyptol paint on the inside of the block from the factory. All mine are.

Bob

[austinsailor]

I guess I learn something new every day!

[greg g]

Last thing I saw of that rebuild on the HAMB was the stuff for sale in the classifieds.