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Posted by clueless [201.202.29.210] on Tuesday, February 07, 2012 at 18:02:40 :
In Reply to: Re: bottom line posted by Kaegi [24.16.253.154] on Tuesday, February 07, 2012 at 12:06:14 :
does your head actually say "Spitfire"?
If so, you have the "long block" chrysler flatty. Mopar made two versions of the flathead inline. One was 23" long (as measured by the length of the head) and the other was 25" long. The "short" engine had a 3.375" bore with some earlier versions being 3.250. The "long" blocks were 3.438" bores.
The short blocks were usually in Plymouth cars and Dodge trucks up to 1 ton. The "long" blocks were in chrysler and desoto cars in the "top of the line" models.
For the "long" blocks, the Spitfire is as good as it gets as far as heads go. That was the maximum effort head mopar produced for it. I really haven't devoted alot of time researching long block heads to know if some obscure application actually had a better chamber than the "Spitfire". There isn't many variations in long block heads, other than a lower compression "no name" head and the slightly higher compression "spitfire" head.
The little flatties, different story. I think I have 5 different head castings - and not two of them are alike. One is 33 vintage (yes, the little flatty goes back that far!) - and its cavernous. The '58 truck head on the other hand, is pretty tight with a dang generous transfer slot between the valve pocket and cylinder. I can run down the casting #s if somebody wants them.
If your engine has the Spitfire head, I'm pretty sure its a 251 flathead rather than a 231. If it is a 231 - that's pretty rare and you immediately need to seek out a 251 or a 265 crank. The reason being, that's a longer rod than deeper stroked engines - but has the exact same journal diameter. If memory serves me correctly, you can use a slant six piston with the long rod/longer stroke setup. Slant six pistons have a slight wristpin offset and can be lightly decked in a lathe to suit your deck height - the wrist pin diameters are the same.
The other difference in the long and short engines are the rods. The rod journal diameter in the short engines is 2.00", the long is 2.125". Rod lengths differ according to stroke, the longer the stroke - the shorter the rod. All mopar flatty pistons had the same compression height at 2.00". A quick and nasty hop up is to offset grind a 265 crank back to the 2.00 rod journal of the short engine - netting you an easy .125" stroke.
so, the maximum bolt together mopar flatty - without getting very complicated would be:
Long mopar flathead block @ 3.438" stock bore. Use a 226 slant six piston with .060 overbore netting you a finished Bore of 3.460". 226 slant piston has a compression height of 1.750 and the wristpin offset - you want the offset in the direction of crank rotation.
Long mopar "Crown Marine" crankshaft (265 CID) @4.750" stock stroke. Offset grind the journals .125" to get the stroke out to 4.875" and use the rods from a 217CID "short" block mopar.
End result, poked and stroked flatty mopar on the cheap - off the shelf slant six pistons and very light custom machine work around the block deck/piston head. Everything is off the shelf and you get a whopping 3.460" bore x 4.875" stroke = 275 CID of bone wrenching torque.
Crown Marine cranks are not junk either - forged steel and can take lotsa punishment.
Whenever Don Coatney shows up on the scene, and I'm sure he'll chime in here shortly. He can fill you in on Edgy Cams and Edgy Finned aluminum heads, as well as aftermarket intakes for the long blocks. There is more available every day for the flatty mopar - short or long.
Most agricultural engines were the "short" engines. Some higher capacity combines (Oliver) used the "long" engines. Make sure you measure the head and know what engine you are considering buying. 90% of the ag/industrial applications I've seen were the "short" engines. Airport tow tractors and some heavy payloaders had the long. Moral of the story - always measure the head!
Stick with the ol' flatty - she'll do you right.
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