The Stovebolt Site Forums The Shop Area Engine Shop Domed pistons?

Can someone provide a list of the years that stovebolt engines ran domed pistons? Also was there a different cylinder head for those engines, and how much compression loss could I expect if cast iron domed pistons were replaced with flat topped aluminum ones? I'm planning to "resto-mod" a few 216's by boring them out and installing 235 aluminum pistons. Should a 60 overbore compensate for the loss of the piston dome on the older engines? Also, did the spray-oiler 235's have domed pistons?
Thanks!
Jerry

Only 1937-40 216's used dome pistons. 235's started in 1941.
The head was designed different for those engines.
I don't think 235 pistons will help enough with the compression.

I would be willing to test out one of those engines... if you need a vehicle to put one in. 😇

Chris

None of the 216's I've stockpiled are that old- - - -mostly 1946-up. I've also got a couple of late-40's/early 50's 235's in the pipeline, and a 41 year model 235 on the way. Chris, that's a good possibility, after I get some dyno run time on one!
Jerry

Jerry I'm surprised that you have not already figured out the loss of compression ratio, you only need to know the c.c. displacement of the dome and then crunch the numbers.

Just keep me in mind! I can compare it to the current 216 in it.

Since I don't have early pistons or a head to measure, asking the part number crunchers is the next best option!
LOL!
Jerry

Take a look, the dome looks really low, with shallow taper

http://tinyurl.com/y9oexgzg

Could a guy shave a 216 block and relieve some material around the piston circumference to make pop-up pistons? I suspect you couldn’t gain enough to make a hill-of-beans difference. Just a random thought.

Any stovebolt engine, 216 or 235, can have more compression by shaving the head, with maybe the exception of those early domed-piston engines. However, there's a problem. Unless the intake valves are sunk deep into the head the same distance the head is shaved, the valves will hit the pistons. Then the geometry of the pushrods and rocker arms is wrong, and lots of monkey motion is involved in getting it back close to right. A 1954-56 head that was used prior to the 848 can be milled .090" to get the same compression ratio as an 848, but the valve depth must be altered to prevent crashing them into the pistons. I assume an 848 head could also be milled to raise the C.R. as long as the valve interference was corrected at the same time.
Jerry

This is just a comment for interest. In Canada it appears that they kept the dome piston style until after the war.

I tried to machine one of those domed pistons flat to replace a piston someone dropped and broke during a rebuild. It only managed a few minutes of run time before burning a hole in the middle. Those cast iron pistons are very thin under the dome.
Jerry

This is an interesting thread. I have both a 1939 and a 40 216 with domed pistons. I would like to bore one of those engines to use aluminum 235 pistons. Can one swap a later ('41 and later) head that would work well with the flat top piston? I imagine finding an aluminum 216 or 235 piston would be almost impossible,

Thank you Jerry for your information on the earlier 216 engines.


Harmon

Actually, there are bunches of new aluminum 235 pistons on ebay, in all oversizes, at pretty reasonable prices. A standard bore 235 piston will work in a 216, just bore it 1/16" oversize (.0625"). The wrist pin diameter and compression height are the same. As Panic mentioned, the dome is pretty shallow, so the overbore will compensate for the lack of a dome, somewhat. A bored-out 216 with 235 pistons comes out at 224 cubic inches.
Jerry

A 1941-53 216 head will fit fine on a 1937-40 engine if flat top pistons are used.

Thank you Jerry. I was a little concerned I had an issue.

Harmon

That is good to know. I guess the newer head flows better as the horsepower increased a bit.

Thank you.

Harmon

There's probably only two ways to describe gas flow through a stovebolt cylinder head- - - -"Bad" and "Worse"! Somebody posted photos of a 235 head that had been cut apart on a bandsaw some time ago, and the port shapes are just horrendous. There's lots of 90 degree turns and other restrictive features that cause choke points. These engines were obviously built for low end torque with no thought for high RPM operation. That's one reason multiple carbs are such a waste of time.
Jerry

I would imagine the 216 head is probably just as twisted as a 235?

As a follow up on the heads, I am assuming the early 216 head had a larger combustion chamber thus the domed piston increases the squish area. The later head had a smaller combustion chamber allowing the use of the flat top piston. Just curious as I don’t know.

Thanks

Harmon

I have a 46 model 216 and a 235 of the same year. I've never even seen the inside of a pre-1940 stovebolt, so anything I would say about the combustion chamber shape or volume would just be a wild guess.
Jerry

I will snap a couple of photos of my 39 head and pistons the next time I am at Nabors Automotive. I have the block and head there to be vatted and some machine work to be done at a later date.

Thank you.

Harmon

A little more information. I talked to Egge on the domed pistons. The make aluminum domed pistons for the early 216 (37-40). For stock standard to .060 oversize. Cost would be $332.00 for the set. eBay sells aluminum 235 pistons anywhere from about $125 to $175 per set for flat top in all sizes.

Domed steel pistons of all sizes are all o er eBay.

Harmon

Jesse James had to use a gun to rob people! The logical approach would be to do a CC test on both styles of head, and if there's a noticeable difference in compression, just put a later model head and flat top pistons on the early engine. I seriously doubt that running flat tops with a domed piston head would make a performance change that would be noticeable without using a dyno. That would be especially true if 235 pistons were used in a bored-out 216. Buy a big jar of Vaseline before doing business with Egge- - - - -you're going to need it!
Jerry

Thanks Jerry. I was looking at all of the avenues. I was futzing around last night to see what was out there. I know nothing of Egge and your revue of them is well taken. The price difference made me cringe. CCing is the best answer. I was looking to see if there was head CC information for the early vs the later head but came up with nothing.

Harmon

I can't tell what part of the 216 head is a quench surface - that's the only place where dome size & shape really matters. Small compression loss: NBD.

The earlier head combustion chamber looks a little different from the newer one. I tried to memorize the difference in look when I was searching for another early head and it was difficult. The area around the intake valve is recessed a little and probably the whole chamber is deeper.

Egge: Egge does make new pistons and the design requires their style of ring. The compression rings are quite a bit thinner than the original style.