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218/230 cylinder head difference


40plyguy

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Wondering if there is any difference between a 218 and a 230 cylinder head. I have 3 engines in pieces. 2-218s and one 230. I want to rebuild the 230 for my 40 Ply. I want get the crank ground and the head milled for now. Just not sure if it matters which head to use.   The 218's are both 1948 Plymouth engines and the 230 is a 49 Dodge. I plan on taking .010 off the top of the block and a conservative .040 off the head.

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The only way to now the difference in the combustion chambers is to measure them.  Who knows whether they have ever been milled in their prior life.  There is also the casting difference for the internal and external coolant bypass setups.  Generally later engines had higher compression so one might think that latter heads would have smaller chambers, but can you be sure that any of your alternate heads were original to that engineand unmolested? 

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Thinking about this off and on for a couple of years, I would like to try, or at least mock up a 230 crank and 218 rods, then measure for custom pistons with any CR I like (within reason).  Couple of reasons:

1. I've heard the pistons on either engine don't go to the top of the deck, so either grinding the deck or custom pistons anyway

2. benefits of a longer rod

3. benefits of a shorter, lighter piston, higher piston pin

4. custom pistons aren't that expensive now and are light years ahead of the stock 4 ring pistons, especially with the higher piston speeds of a long stroke engine

If building a little more power is what you have in mind and are rebuilding one anyhow, why not?  

If you squeeze the head down too far trying to raise compression, you will kill what little flow these engines have...

 

Oh, and the 49 Dodge PROBABLY won't have the internal bypass, so either head should work.

Edited by Adam H P15 D30
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i figured out which head belongs to the 230 I'm rebuilding. I compared it with a 218 head and they look identical. Even took some rough measurements of the combustion chambers and found no difference. the first 3 or 4 casting numbers are the same too.

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3 hours ago, Adam H P15 D30 said:

Thinking about this off and on for a couple of years, I would like to try, or at least mock up a 230 crank and 218 rods, then measure for custom pistons with any CR I like (within reason).  Couple of reasons:

1. I've heard the pistons on either engine don't go to the top of the deck, so either grinding the deck or custom pistons anyway

2. benefits of a longer rod

3. benefits of a shorter, lighter piston, higher piston pin

4. custom pistons aren't that expensive now and are light years ahead of the stock 4 ring pistons, especially with the higher piston speeds of a long stroke engine

If building a little more power is what you have in mind and are rebuilding one anyhow, why not?  

If you squeeze the head down too far trying to raise compression, you will kill what little flow these engines have...

 

Oh, and the 49 Dodge PROBABLY won't have the internal bypass, so either head should work.

I thought 218 rods were shorter, not longer.   ???

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16 hours ago, 40plyguy said:

i figured out which head belongs to the 230 I'm rebuilding. I compared it with a 218 head and they look identical. Even took some rough measurements of the combustion chambers and found no difference. the first 3 or 4 casting numbers are the same too.

The only way to know for sure is to "cc" the head.  Easily done on a flathead because you don't have to put valves back in the head.   Smear a bit of transgel around the bread slice and stick a plexi plate with a hole to it. Have the hole at the edge of the chamber.  Fill it up starting from a known volume in a pipette or use a syringe and keep track of volume.  

image.jpeg

Edited by thebeebe5
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1 hour ago, thebeebe5 said:

The only way to know for sure is to "cc" the head.  Easily done. Flathead because you donr even have to put valves back in the head.   Smear a bit of transgel around the bread slice and stick a plexi plate with a hole to it. Hve the hole at the edge of the chamber.  Fill it up starting from a known volume in a pipette or use a syringe and keep track of volume.  

image.jpeg

I had to read that several times, but it finally made sense. The plexiglass prevents surface tension from allowing you to overfill the cylinder. Neat idea. 

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I read some place the 218 rods are longer than the 230s. Part of the reason is the pistons are the same for both motors....think about it. Makes sense...cranks and rods change from motor to motor. Long throw shorter rod on 230 than 218 which has longer rod and shorter throw on the crank...

can you mix and match ? Maybe...balancing would be off more than standard amount.

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4 hours ago, Adam H P15 D30 said:

Being that the 218 has a shorter stroke, I would think the rods are longer

You and Dartgame are correct! My thinking was turned around backwards. I hate it when that happens. 

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4 hours ago, 40plyguy said:

Once hot tanked, I found the head for the Dodge engine has a "D" on it. How many CC's in a stock combustion chamber?

I'll be CCing my '37 201cid when it comes back from its vatting.   Will add the value i find here. 

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There are some references to late 57-59 end of production for cars, were the "best head for combustion efficiency".  These may be the ones from the engine with numbers beginning with "M".  The truck engines that continued to the early 70's probably didn't get these.

138 HP in the 57 dodge 135 for Plymouth, both at 8 to 1 car.

Edited by greg g
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