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Old 11-26-2019, 02:26 PM   #1
scicala
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Default Flathead domed pistons and 21A rods

I found this on EBAY, and was wondering, can a flathead V8 actually used pistons with that big of a dome ?


Sal


https://www.ebay.com/itm/Ford-Flathe...UAAOSwfVtd2Bkm
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Old 11-26-2019, 02:35 PM   #2
Tim Ayers
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Default Re: Flathead domed pistons and 21A rods

Others would know for sure, Ronnie Roadster, etc., but they look like Ardun pistons to me. Take a look at the notches for hemi-type valves.

Last edited by Tim Ayers; 11-26-2019 at 02:40 PM.
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Old 11-26-2019, 10:15 PM   #3
scicala
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Default Re: Flathead domed pistons and 21A rods

Tim, thank you. That would explain it. I forgot about the Ardun OHV heads. That would explain the high price too.


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Old 11-30-2019, 02:20 PM   #4
Ronnieroadster
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Default Re: Flathead domed pistons and 21A rods

Yes they are for the ARDUN heads. The price for a set of Ross ARDUN pistons is usually about $80.00 per piston including the pin and rings. The stock Ford flathead rods included in the deal would be the weak link with the compression those domes will end up giving in the combination. However im sure economy can be gained using them.
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Old 11-30-2019, 03:34 PM   #5
Ol' Ron
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Default Re: Flathead domed pistons and 21A rods

Compression, is on part of the internal combustion cycle that add torque to the crankshaft. Compression and displacement is the key to a great street engine. When the L-100 can became the go to cam for a street engine. It did so at the cost of low speed torque. So I and others, added displacement to the brew anr revived most of the low speed torque. After 2500 rpm the cam improves the torque curve with better breathing. But it was the sound that sold it. So when building an engine for the street, compression is your best friend.
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Old 12-01-2019, 08:33 AM   #6
JWL
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Default Re: Flathead domed pistons and 21A rods

Adding compression has nothing to do with exposing the weakness of the 21A connecting rod. The 21A rod will fail at high RPM, on the exhaust stroke, at the pin end, just below the pin bushing. New 21A rods will usually withstand 3 drag strip runs at 6800 RPM in the lights when used with maximum lightened pistons and pins. However, if anything, ANYTHING, happens in the driveline and the engine buzzes to 7000 RPM, for only one second, they will do serious damage to the engine.

As OlRon says, the best first step for improving your Flathead is to bump up the compression ratio. Adding compression or displacement are the only methods for improving power and efficiency at nearly all RPM levels.
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Old 12-01-2019, 03:27 PM   #7
Ronnieroadster
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Default Re: Flathead domed pistons and 21A rods

Quote:
Originally Posted by JWL View Post
Adding compression has nothing to do with exposing the weakness of the 21A connecting rod. The 21A rod will fail at high RPM, on the exhaust stroke, at the pin end, just below the pin bushing. New 21A rods will usually withstand 3 drag strip runs at 6800 RPM in the lights when used with maximum lightened pistons and pins. However, if anything, ANYTHING, happens in the driveline and the engine buzzes to 7000 RPM, for only one second, they will do serious damage to the engine.

As OlRon says, the best first step for improving your Flathead is to bump up the compression ratio. Adding compression or displacement are the only methods for improving power and efficiency at nearly all RPM levels.
We learn something new every day sure glad Im reading all this so i can learn how to do this high performance stuff with the Flathead!
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I use the F word a lot no not that word these words Flathead , Focus and Finish.
"Life Member of the Bonneville 200 MPH Club using a Ford Flathead block"
Owner , Builder and Driver of the First Ford Flathead bodied roadster to run 200 MPH Record run July 13, 2018 LTA timing association 200.921 from a standing start in one and a half miles burning gasoline.
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