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-   -   Flathead domed pistons and 21A rods (https://www.fordbarn.com/forum/showthread.php?t=273217)

scicala 11-26-2019 02:26 PM

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

Tim Ayers 11-26-2019 02:35 PM

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.

scicala 11-26-2019 10:15 PM

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.


Sal

Ronnieroadster 11-30-2019 02:20 PM

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.
Ronnieroadster

Ol' Ron 11-30-2019 03:34 PM

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.

JWL 12-01-2019 08:33 AM

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.

Ronnieroadster 12-01-2019 03:27 PM

Re: Flathead domed pistons and 21A rods
 

Quote:

Originally Posted by JWL (Post 1826984)
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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