Trying to decide which pistons for 440 build

[Bigsbetter]

I’m rebuilding a 1973 440. It is a very low mileage engine from an R/V. I have Aluminum heads with 75cc chambers. My question is about pistons. I want my compression to be between 10.0-10.5-1. I’m looking at the Icon 9947 which has a compression height of 1.991 but also a +5.6 cc dome. I’m the pictures of the piston, it doesn’t look like the pistons have any dome. So when I do the compression calculators, I’m not sure weather to add the 5.6cc or not? It makes a difference. This is a stock 4.32 bore and I’m assuming about a .040 head gasket. Or maybe someone else has a good recommendation for a piston that will get me close to 10.5 without going over? Thankyou.

 

[BSB67]

Icon IC836

 

[70rrclone]

I did basically the same thing, I have a 77 440 out of a motorhome. I used wiseco pistons std bore. Trickflow 240 heads 74cc. With a .039 headgasket. I ended up with a pump gas friendly 9.84:1. The wiesco have a 2.05 ch.

Wiseco 5531AS

 

[BSB67]

I’m looking at the Icon 9947 which has a compression height of 1.991 but also a +5.6 cc dome. I’m the pictures of the piston, it doesn’t look like the pistons have any dome. So when I do the compression calculators, I’m not sure weather to add the 5.6cc or not? It makes a difference.

9947 - Not a dome, it’s the volume of the valve relief.

Maybe the Speed Pro 2266 would work for you

 

[Iroc78]

You would need to add the 5.6cc in the calculator. Based on the picture of the Icon 9947 the +5.6cc dome is positioned to provide valve clearance. If the +5.6 cc spec I am seeing on Summits website is indeed correct it would still be considered a dome while not looking like a traditional dome whereas a -5.6 cc would be considered a dish.

 

[threewood]

If you want to save a bit of money, look at the KB237 hyperutectic pistons. 2.067" compression height. I've been beating mine up for about 10 years and they are great. Stealth aluminum heads, runs on 88 clear gas.

 

[BSB67]

You would need to add the 5.6cc in the calculator. Based on the picture of the Icon 9947 the +5.6cc dome is positioned to provide valve clearance. If the +5.6 cc spec I am seeing on Summits website is indeed correct it would still be considered a dome while not looking like a traditional dome whereas a -5.6 cc would be considered a dish.

The piston is a flat top with valve reliefs. No dome. The combustion volume is increased by 5.6cc. The compression ratio will be lower.

 

[BSB67]

If you want to save a bit of money, look at the KB237 hyperutectic pistons. 2.067" compression height. I've been beating mine up for about 10 years and they are great. Stealth aluminum heads, runs on 88 clear gas.

The OP has 75cc heads. Is that what you are using?

 

[threewood]

The OP has 75cc heads. Is that what you are using?

Stealth heads are 80cc

 

[Bigsbetter]

As of right now, I’m leaning toward the Speed Pro 2355. Get me somewhere in the 10.2, -10.4 or so

 

[RR Fan Dan]

I just went through this exercise a couple of hours ago, as I am ordering a 440 source stroker motor. They have some handy charts for the pistons they sell. The kit we got is around 9.7 according to their chart. But we are going to make up the difference to achieve 10.3 by using MLS head gaskets. So my point is. If you can’t find the exact piston you can make up the difference by changing the thickness of the head gasket.

Here is their chart just for a visual on how different bore sizes pistons affect CR.

 

[Iroc78]

" Piston Dome refers to the amount of added volume on top of the piston compared to a flat top piston." Quoted from the second sentence of link below among others.

https://www.performancetrends.com/Definitions/Piston-Dome.htm

By definition +5.6cc piston head volume is a domed piston.

While some may look at this piston the original poster was asking about and see a flat top with valve reliefs, I (as well as the piston manufacturer who labeled it +5.6cc) see a flat top piston with a 5.6cc dome added in an area where valve to piston clearance won't be an issue (circled on the upper RH side of pictured piston).

 

[RemCharger]

9947 - Not a dome, it’s the volume of the valve relief.

The piston is a flat top with valve reliefs. No dome. The combustion volume is increased by 5.6cc. The compression ratio will be lower.

Agreed they're flat tops. Which means of course , there's nothing on top but flat. It's easy to understand when you're from saskatchewan.