Stock piston question

[earlbrown]

A flat top at the same CR would probably lose a little. Any benefits from what little quench we have would be gone, and it's probably need more ignition advance to get everything lit off at the right time.

 

[GNVAIR]

The benefit on a pump gas car is that it is less likely to spark knock/ping with the tighter clearance and not to necessarily make more power. I have seen this proven on different engines. This theory has been around since the 1920's but it is only within the last 20 years that OEM manufacturers have been incorporating it into their production engines as it works really well on high compression engines as well. The down side is that you need to set the clearance larger on engines with a lot of piston to cylinder wall clearance and/or larger bore sizes as the propensity for the piston to rock and contact the cylinder head become greater.
I set my current engine at .040" with a .020" over bore and iron heads. If you are running race gas then this is probably a non issue for you. But for myself it was a detail I wanted to explore since the squish/deck clearance on a Buick is enormous. If the piston is .060" down in the hole and the head gasket is .050"; you have .110" deck clearance. Ideal is is typically .025" (race) to .045" (street)

 

[bison]

A flat top at the same CR would probably lose a little. Any benefits from what little quench we have would be gone, and it's probably need more ignition advance to get everything lit off at the right time.

Probably or will it? Other things are more important. CR and turbine selection and Cam overlap and position


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[bison]

The benefit on a pump gas car is that it is less likely to spark knock/ping with the tighter clearance and not to necessarily make more power. I have seen this proven on different engines. This theory has been around since the 1920's but it is only within the last 20 years that OEM manufacturers have been incorporating it into their production engines as it works really well on high compression engines as well. The down side is that you need to set the clearance larger on engines with a lot of piston to cylinder wall clearance and/or larger bore sizes as the propensity for the piston to rock and contact the cylinder head become greater.
I set my current engine at .040" with a .020" over bore and iron heads. If you are running race gas then this is probably a non issue for you. But for myself it was a detail I wanted to explore since the squish/deck clearance on a Buick is enormous. If the piston is .060" down in the hole and the head gasket is .050"; you have .110" deck clearance. Ideal is is typically .025" (race) to .045" (street)

.025”? I was getting a little shadow around .030” and low 6000’s. If the engine. .025” would have been a no go. More rpm would have been a problem most likely also


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[captndave737]

Roughly how much is a set of custom pistons?

I paid $771 for Custom Earl Brown Pistons, pins, rings and shipping. Earl even balanced them before shipping!

 

[GNVAIR]

.025”? I was getting a little shadow around .030” and low 6000’s. If the engine. .025” would have been a no go. More rpm would have been a problem most likely also


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I was stating .025" for a strictly race application. At that you have no margin for carbon accumulations and certainly not margin for loose piston to cylinder wall clearance that would cause the piston to rock in the bore. But there are non Buick engine builders that would go that low. Like I said, for a street car .040" to .045" should be entirely safe. My ideal is 0 deck with the piston and use compressed head gasket thickness to set the clearance. Like I said, it really helps prevent spark knock/pinging on pump gas.

 

[Ernie GN]

I paid $771 for Custom Earl Brown Pistons, pins, rings and shipping. Earl even balanced them before shipping!

That’s a great deal!

 

[captndave737]

That’s a great deal!

He was great to deal with.

 

[bison]

I was stating .025" for a strictly race application. At that you have no margin for carbon accumulations and certainly not margin for loose piston to cylinder wall clearance that would cause the piston to rock in the bore. But there are non Buick engine builders that would go that low. Like I said, for a street car .040" to .045" should be entirely safe. My ideal is 0 deck with the piston and use compressed head gasket thickness to set the clearance. Like I said, it really helps prevent spark knock/pinging on pump gas.

Usually the race engines I’ve encountered have larger bores, looser clearances and run more rpm so they need even more clearance


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[No disintegrations]

.025”? I was getting a little shadow around .030” and low 6000’s. If the engine. .025” would have been a no go. More rpm would have been a problem most likely also


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How thick was the head gasket on this setup?