Piston ID

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I re measured the dish and it is .300 deep 3.380 at the top and 3.88 at the bottom.
Click to expand...

The dish is clearly bigger at the top.
Did you flip the numbers, or read the caliper wrong?

0FA1783A-AF07-41CC-910F-3A0A54EEA200.jpeg



Assuming the two dimensions are correct, I get right around 51cc’s for the dish.
Same basic result by either averaging the two diameters and calculating the volume, or by calculating the volume for the large dimension, and the small dimension......then averaging the two results.

The other unknown is the chamber volume of the heads.

906 heads with nominal milling and OE type valves are typically in the 88-90cc range.

For a .060 over 440, pistons down the hole .050, steel shim gasket, 51cc dish, 88cc heads.......it’s just about 6.9:1.
With 78cc heads it’s about 7.25:1.

Again, those are assuming the 3.88/3.38 x .300 dish dimensions are correct.

When the CR is that low, a couple of cc’s here or there doesn’t impact the number very much.

Since the OP came up with a dish volume of 43cc, I suspect the dish diameters are probably more like 3.38/3.08.
 
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I'm sorry, but I would simply have to cc that dish. But I'm lucky, my cc setup was free. Clear plastic plate from work, drill a hole, 100cc syringe, used, free from my vet, some grease, and some glass cleaner, done!
 
PRH said:
The dish is clearly bigger at the top.
Did you flip the numbers, or read the caliper wrong?

View attachment 1716133543


Assuming the two dimensions are correct, I get right around 51cc’s for the dish.
Same basic result by either averaging the two diameters and calculating the volume, or by calculating the volume for the large dimension, and the small dimension......then averaging the two results.

The other unknown is the chamber volume of the heads.

906 heads with nominal milling and OE type valves are typically in the 88-90cc range.

For a .060 over 440, pistons down the hole .050, steel shim gasket, 51cc dish, 88cc heads.......it’s just about 6.9:1.
With 78cc heads it’s about 7.25:1.

Again, those are assuming the 3.88/3.38 x .300 dish dimensions are correct.

When the CR is that low, a couple of cc’s here or there doesn’t impact the number very much.

Since the OP came up with a dish volume of 43cc, I suspect the dish diameters are probably more like 3.38/3.08.
Click to expand...
Checked my math and came up with 52cc this time. Dont know what i screwed up last time.
 
33IMP said:
I'm sorry, but I would simply have to cc that dish. But I'm lucky, my cc setup was free. Clear plastic plate from work, drill a hole, 100cc syringe, used, free from my vet, some grease, and some glass cleaner, done!
Click to expand...
Its horrible either way and at this point ill just stick in a small cam and a good intake on it and run it since its already .060 over. I'll build a better one later. Ive enjoyed learning how to calculate the dish volume, compression etc.
 
Checked my math and came up with 52cc this time.
Click to expand...

3.38 + 2.88 = 6.26
6.26/2 = 3.13

The volume of a 3.13 x .300 hole is 37.8cc

Subbing in a 38cc dish instead of the 51cc dish put the CR at 7.4 for 88cc heads, and 7.9 with 78cc heads (still assuming a steel shim gasket and .050 deck clearance).
 
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PRH said:
3.38 + 2.88 = 6.26
6.26/2 = 3.13

The volume of a 3.13 x .300 hole is 37.8cc

Subbing in a 38cc dish instead of the 51cc dish put the CR at 7.4 for 88cc heads, and 7.9 with 78cc heads (still assuming a steel shim gasket and .050 deck i
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I added half the difference between the two and came up with 3.63 when i should have subtracted it to get the 3.13.
 
No matter how you slice it........it’s looooow CR.

By comparison.......
Silvolite 1263 pistons(which are .110” below deck on an uncut block), heads milled to 84cc, steel shim gasket........you end up at almost 9:1.
 
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Yabbut! 7.5 is better than a high 6!
As long as you know the compression ain't much, and you taylor expectations, you can sti get a decent running engine thatll run on garbage regular. It is still a 440, right? (Well, 452)
 
One of the byproducts of low cr that I dislike, especially if you run much of a cam at all.....is the exhaust temps go up.

So, keep the cam on the short side with your low cr combos(leave the ex valve closed as long as practical).
 
PRH said:
One of the byproducts of low cr that I dislike, especially if you run much of a cam at all.....is the exhaust temps go up.

So, keep the cam on the short side with your low cr combos(leave the ex valve closed as long as practical).
Click to expand...
Is 226int and 234ex at .050 alright?
 
Unless you’re building a low buck bracket car, that’s not where I’d go for a cam.
For something that’s primarily going to see street duty, I’d be looking at something more along the lines of an Isky 264 Mega cam.

Many years ago(80’s) I put a MP484 cam in an 8.2:1 400.
It had bowl blended 516 heads, SD intake, Holley 650dp, headers, and was run with a 3500 converter and 4.10’s.
That was probably technically too big of a cam for that engine, but it wasn’t terrible to drive around.
Mid-13’s in a 71 Charger street car.
The emphasis with that combo was placed on getting a decent ET while doing it on the (semi) cheap.
 
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whatsamerc?? said:
I have a 77 motorhome 440 that has dished .060 over pistons in it. The only numbers i can find on them are 1886 inside of the skirt. I cant find any info on them and was someone might know what they are.
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Im not sure what the pistons are but they look like the pistons that belong in the blow through turbo set up that came on some motorhomes.
I have the exhaust manifolds and turbo from one.
Also there were 1.928 pistons factory but I don't know about a 20cc dish
 
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whatsamerc?? said:
Its already .060 over though. The bores are in really good shape but i hate to put new pistons in old holes
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Some decent forged pistons in your already.060 over cylinders with a clean up hone will be perfect as they need a little more clearance than a cast piston.
 
PRH said:
Unless you’re building a low buck bracket car, that’s not where I’d go for a cam.
For something that’s primarily going to see street duty, I’d be looking at something more along the lines of an Isky 264 Mega cam.

Many years ago(80’s) I put a MP484 cam in an 8.2:1 400.
It had bowl blended 516 heads, SD intake, Holley 650dp, headers, and was run with a 3500 converter and 4.10’s.
That was probably technically too big of a cam for that engine, but it wasn’t terrible to drive around.
Mid-13’s in a 71 Charger street car.
The emphasis with that combo was placed on getting a decent ET while doing it on the (semi) cheap.
Click to expand...
I like how isky marketed that 264 "Mega" lol
 
MOPARMAGA said:
Im not sure what the pistons are but they look like the pistons that belong in the blow through turbo set up that came on some motorhomes.
I have the exhaust manifolds and turbo from one.
Also there were 1.928 pistons factory but I don't know about a 20cc dish
Click to expand...
Factory turbo manifolds?
 
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