The Ford Barn

hardtimes · 04-17-2013, 10:58 AM

Anyone using CP pistons in their A/B build? If so, what p/n are you using and what attributes made you select this model, i.e. - wt ?

J Franklin · 04-17-2013, 07:53 PM

What are CP pistons?

hardtimes · 04-19-2013, 02:35 PM

Quote:

Originally Posted by J Franklin

What are CP pistons?

Hey J,
google cp pistons for information

J Franklin · 04-19-2013, 08:27 PM

OK I thought they were some sort of style or design.

PC/SR · 04-19-2013, 09:08 PM

No experience and have not heard anything about them. INteresting website. I would like to know what material they use or have available.

MikeK · 04-19-2013, 09:14 PM

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CP pistons are forged. Any forged piston would be last on my list for an A/B build. The only advantage a forged slug has is extreme strength. A really hot A/B build, even an OHV, won't put much more horsepower load on a piston than grandma's grocery-getter.

In a Model A/B the thermal swings of the block and pistons are not as well controlled, nor are they monitored by a computer with a shut-down mode like modern iron. There are three types of aluminum pistons- Cast Aluminum/silicon alloy, cast hypereutectic Al/Si alloy, and forged Aluminum alloy. Each has a different coefficient of thermal expansion. Forged has the worst (greatest) expansion rate, near double that of hypereutectic pistons. You will need near double the fit clearance with forged. The result is clacking piston-slap rattle until you get up to temp, which needs to be fairly high. Cruising at low throttle will cool the pistons and they will then wobble and rattle, wearing the rings. Forged are best suited for engines that constantly run at high output loads, not varied throttle street driving.

The best piston (IMHO) for a 'hot' A/B is a hypereutectic with narrow ring lands to fit modern rings. If you spec a moly filled top ring they will fully seat in less than an hour of driving and last 70K+ miles with good compression seal.

For way-too-much info, google 'hypereutectic vs. forged'.

PC/SR · 04-19-2013, 11:17 PM

The primary consideration for custom pistons is what alloy they are made of, not whether they are forged. There are two commonly available alloys for custom pistons, each with different characteristics.
Because of a machinist screwup, 2 screwups actually, I needed a set of custom pistons. It was an expensive mistake and lesson. First I got a set of forged Ross with 2618 alloy, recommending .008 clearance and they rattled like.... They never did heat enough to expand to take up that clearance. Did some more research and next got forged JE with 4032 alloy, with .003 clearance. They work fine.
I agree with MIkeK that for less than all out racing an A does not need these types of pistons. The JE's have a shorter skirt but weigh about the same as the replacement pistons from Snyders (which I cannot use anymore, anyone want an ashtray?) so there is no advantage there. They are stronger so can take more detonation I suppose, but you should not be doing that anyway. You can specify ring and pin size, but is it worth it? Nah.
BTW, if anyone wants or needs these things, do the research and get the specs right. They have no clue what a Model A is or what it needs, but they can build it if you tell them. Do not rely on their expertise.

hardtimes · 04-19-2013, 11:20 PM

Hey MikeK,
Off to google with a sponge like attitude, thanks!

hardtimes · 04-19-2013, 11:32 PM

Hey PC/SR,
Thanks for sharing your experience and advice! Ashtray ?....don't smoke, and don't want my engine to either. That's why doing research for right the first time. Can't afford ashtrays,eh

Seem to remember a great piston make/model/weight piston tech thread here in the past...but couldn't find my wallet , but for the lanyard.

04-17-2013, 10:58 AM	#1
hardtimes Senior Member Join Date: May 2010 Location: South California Posts: 6,190	CP pistons Q... Anyone using CP pistons in their A/B build? If so, what p/n are you using and what attributes made you select this model, i.e. - wt ?

04-17-2013, 07:53 PM	#2
J Franklin Senior Member Join Date: May 2010 Location: Oregon Posts: 6,370	Re: CP pistons Q... What are CP pistons?

04-19-2013, 08:27 PM	#4
J Franklin Senior Member Join Date: May 2010 Location: Oregon Posts: 6,370	Re: CP pistons Q... OK I thought they were some sort of style or design.

04-19-2013, 09:08 PM	#5
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,285	Re: CP pistons Q... No experience and have not heard anything about them. INteresting website. I would like to know what material they use or have available.

04-19-2013, 09:14 PM	#6
MikeK Senior Member Join Date: May 2010 Location: Windy City Posts: 2,919	Re: CP pistons Q... Sponsored Links (Register now to hide all advertisements) CP pistons are forged. Any forged piston would be last on my list for an A/B build. The only advantage a forged slug has is extreme strength. A really hot A/B build, even an OHV, won't put much more horsepower load on a piston than grandma's grocery-getter. In a Model A/B the thermal swings of the block and pistons are not as well controlled, nor are they monitored by a computer with a shut-down mode like modern iron. There are three types of aluminum pistons- Cast Aluminum/silicon alloy, cast hypereutectic Al/Si alloy, and forged Aluminum alloy. Each has a different coefficient of thermal expansion. Forged has the worst (greatest) expansion rate, near double that of hypereutectic pistons. You will need near double the fit clearance with forged. The result is clacking piston-slap rattle until you get up to temp, which needs to be fairly high. Cruising at low throttle will cool the pistons and they will then wobble and rattle, wearing the rings. Forged are best suited for engines that constantly run at high output loads, not varied throttle street driving. The best piston (IMHO) for a 'hot' A/B is a hypereutectic with narrow ring lands to fit modern rings. If you spec a moly filled top ring they will fully seat in less than an hour of driving and last 70K+ miles with good compression seal. For way-too-much info, google 'hypereutectic vs. forged'.

04-19-2013, 11:17 PM	#7
PC/SR Senior Member Join Date: May 2010 Location: Santa Rosa, CA Posts: 1,285	Re: CP pistons Q... The primary consideration for custom pistons is what alloy they are made of, not whether they are forged. There are two commonly available alloys for custom pistons, each with different characteristics. Because of a machinist screwup, 2 screwups actually, I needed a set of custom pistons. It was an expensive mistake and lesson. First I got a set of forged Ross with 2618 alloy, recommending .008 clearance and they rattled like.... They never did heat enough to expand to take up that clearance. Did some more research and next got forged JE with 4032 alloy, with .003 clearance. They work fine. I agree with MIkeK that for less than all out racing an A does not need these types of pistons. The JE's have a shorter skirt but weigh about the same as the replacement pistons from Snyders (which I cannot use anymore, anyone want an ashtray?) so there is no advantage there. They are stronger so can take more detonation I suppose, but you should not be doing that anyway. You can specify ring and pin size, but is it worth it? Nah. BTW, if anyone wants or needs these things, do the research and get the specs right. They have no clue what a Model A is or what it needs, but they can build it if you tell them. Do not rely on their expertise.

04-19-2013, 11:20 PM	#8
hardtimes Senior Member Join Date: May 2010 Location: South California Posts: 6,190	Re: CP pistons Q... Hey MikeK, Off to google with a sponge like attitude, thanks!

04-19-2013, 11:32 PM	#9
hardtimes Senior Member Join Date: May 2010 Location: South California Posts: 6,190	Re: CP pistons Q... Hey PC/SR, Thanks for sharing your experience and advice! Ashtray ?....don't smoke, and don't want my engine to either. That's why doing research for right the first time. Can't afford ashtrays,eh Seem to remember a great piston make/model/weight piston tech thread here in the past...but couldn't find my wallet , but for the lanyard.