Hello all, does anyone have data for the chamber size for Edmonds 8BA style aluminum heads? I am helping a fellow flathead enthusiast put a supercharger on his .100 over 239 (stock stroke) flathead. The heads are already on. I saw a post from Ol’Ron from 2011 that said 8:1 on a 239 engine and 8.5:1 on a 255. That data is probably close enough for me but thought I’d ask. Thanks in advance for your help.
Edmonds 8BA Heads Chamber Volume
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tubman
Well-known member
To get a decent number, you'll probably have to measure them yourself. It's not that difficult; just get a burette and some other miscellaneous bits. The problem is that those Edmunds heads are at least 60 years old and the chances that they have not been milled or altered in some way is slim to none. Even if someone can supply the numbers you need, the heads would have to be NOS for them to be useful.
Even then, you can't really be sure, since Edmunds made 2 series of 8BA heads plain "Edmunds" and "Edmunds Custom". Are they the same? I don't know; do you? Also I believe Edmunds used several different foundries during their production life, and they may be different as well. I am a proponent of Edmunds heads (because of the spark plug location), and I wouldn't guarantee that the chambers are the same in an individual head,
This is your chance to play "engine builder" and make sure your numbers are right on. If need be, you can even make sure the 8 chambers are all equal.
Even then, you can't really be sure, since Edmunds made 2 series of 8BA heads plain "Edmunds" and "Edmunds Custom". Are they the same? I don't know; do you? Also I believe Edmunds used several different foundries during their production life, and they may be different as well. I am a proponent of Edmunds heads (because of the spark plug location), and I wouldn't guarantee that the chambers are the same in an individual head,
This is your chance to play "engine builder" and make sure your numbers are right on. If need be, you can even make sure the 8 chambers are all equal.
All great points. I could certainly CC them if they were off and it may come to that. The heads are bolted on currently. If I knew what they were stock I could probably make some reasonable assumptions on milling etc to get in the ballpark. I appreciate you taking the time to reply. Steve
tubman
Well-known member
Before I forget it, the reason I like Edmunds heads is that they have the spark plug moved just enough so it is not over the exhaust valve. This allows me to run extended tip plugs in the engine, which has resulted in better all-around performance. I am still running the plugs I installed when I dropped in the current '51 Merc engine in 2016. I have checked the plugs every couple of years (last summer was one), and the plugs still look and work perfect. I drive the car between 2000-3000 miles a years, so the mileage is getting up there. I strongly recommend using extended tip plugs in these heads. The plugs I run are Champion "L82YC". With a supercharger, you will probably need a different heat range, but these would be a good place to start.
In Champion nomenclature, "L" means 14mm, 1/2" reach. while "82" is the heat range. "Y" means .060-.090" projected tip and "C" means a copper ground electrode. I would imagine equivalent plugs would be available from other manufacturers. Note that stock 8BA's use "Champion "H" series plugs, which have a 7/16" reach. The Edmunds heads have a longer reach, and the "L" series fit them perfectly.
I am running Edmunds heads on two 8BA's and have 2 extra pair currently undergoing refurbishment. These plugs fit and work perfectly in these heads.
In Champion nomenclature, "L" means 14mm, 1/2" reach. while "82" is the heat range. "Y" means .060-.090" projected tip and "C" means a copper ground electrode. I would imagine equivalent plugs would be available from other manufacturers. Note that stock 8BA's use "Champion "H" series plugs, which have a 7/16" reach. The Edmunds heads have a longer reach, and the "L" series fit them perfectly.
I am running Edmunds heads on two 8BA's and have 2 extra pair currently undergoing refurbishment. These plugs fit and work perfectly in these heads.
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Ronnieroadster
Well-known member
For a supercharged application its best to check the CC volume. Your looking for a volume that's at least 71 CC's. The type of blower being used is also important when it comes to this type of modification. If you find the volume is below the 71 you could add a set of good quality copper big bore big valve head gaskets which would help a bit to reduce the static compression ratio. In a perfect world you would hope the heads have never been resurfaced.
Since the heads are already on the engine at the least they should be removed to verify if they have been resurfaced. Measuring the dome diameter on the head's would give you a good idea if they are under size thus pointing to being resurfaced in their lifetime. You could use the head gaskets to compare the fire ring radius to the head dome radius as a visual tool. To much compression on a supercharged flathead will push a head gasket out quickly once the load pedal is used and the boost gets up to 5 pounds and higher.
Ask me how I know
Ronnieroadster
Since the heads are already on the engine at the least they should be removed to verify if they have been resurfaced. Measuring the dome diameter on the head's would give you a good idea if they are under size thus pointing to being resurfaced in their lifetime. You could use the head gaskets to compare the fire ring radius to the head dome radius as a visual tool. To much compression on a supercharged flathead will push a head gasket out quickly once the load pedal is used and the boost gets up to 5 pounds and higher.
Ask me how I know
Ronnieroadster
