The Ford Barn

SoCalCoupe · 09-01-2022, 12:53 AM

Will Edelbrock 1125 cylinder heads with a 65 cc combustion chamber work on a stock 1941 flathead without modifications and will it run well on 87 octane pump gas?

I have a stock 221 cid 1941 V8, possibly with a 0.030 overbore. It’s a driver car that’s typically not pushed hard but snappier performance at less than 3000 rpm is more fun. I’ve read a lot about heads on our V8’s and concluded that raising the compression ratio improves performance somewhat. Sounds like milled stock heads essentially do the same trick as after-market heads with smaller combustion chambers. However, in my opinion, the after-market aluminum heads look cool and I’m willing to pay the price to look cool even if it costs more than milling my stock heads.

The numbers roughly are 6.2 stock compression ratio for the 1941 Ford and 6.6 for the 1941 Mercury 239 cid which I believe has the same heads, a difference of 0.4. Edelbrock advertises 8.5 compression ratio with these heads using a 3/16” relief. My calculation is that a 3/16” relief reduces compression by about 0.2, and therefore 8.7 without relief. So, roughly, I could install these heads on my car and end up with a compression ratio of about 8.7 – 0.4 or 8.3.

Again, the question is, do you think these heads will work without modification and allow me to use 87 octane pump gas? The numbers seem close but am I way off?

deuce lover · 09-01-2022, 01:34 AM

In 2007 I put a set of vintage Weiand heads on a bone stock 39 Merc flathead and that sure woke it up. The only thing about the Edelbrocks is make sure your studs are long enough.

flatjack9 · 09-01-2022, 11:10 AM

Doing the calculations, you should end up at about 7.5:1

Bored&Stroked · 09-01-2022, 01:42 PM

Edelbrock heads use a piston crown shape that uses a consistent radius profile. Some flatheads had pistons with dual radius profiles (more like an ellipse). You can tell when you have these pistons as they're a bit more "pointed" in the centers than a piston with a consistent radius.

The only reason I bring this up is that I have seen situations where the center "point" of these types of pistons will hit the center of the dome area on the Edelbrock heads (and many others). So, make sure you CLAY the tops of the pistons and check this clearance before you bolt the heads down and whack them with your pistons (potentially).

Bored&Stroked · 09-01-2022, 01:50 PM

Sponsored Links (Register now to hide all advertisements)

Here is a 3D solid model view of the TWO shapes I'm talking about. I created a CAD model to use for CNC programming to "fix" the chambers on some heads for the more pointed crowned pistons:

3DSectionView-Ford-Egge-Dome.jpg

3DSectionView-RossEdelbrock-Dome.jpg

09-01-2022, 12:53 AM	#1
SoCalCoupe Senior Member Join Date: Sep 2021 Location: Point Loma, San Diego, CA Posts: 424	Edelbrock head question Will Edelbrock 1125 cylinder heads with a 65 cc combustion chamber work on a stock 1941 flathead without modifications and will it run well on 87 octane pump gas? I have a stock 221 cid 1941 V8, possibly with a 0.030 overbore. It’s a driver car that’s typically not pushed hard but snappier performance at less than 3000 rpm is more fun. I’ve read a lot about heads on our V8’s and concluded that raising the compression ratio improves performance somewhat. Sounds like milled stock heads essentially do the same trick as after-market heads with smaller combustion chambers. However, in my opinion, the after-market aluminum heads look cool and I’m willing to pay the price to look cool even if it costs more than milling my stock heads. The numbers roughly are 6.2 stock compression ratio for the 1941 Ford and 6.6 for the 1941 Mercury 239 cid which I believe has the same heads, a difference of 0.4. Edelbrock advertises 8.5 compression ratio with these heads using a 3/16” relief. My calculation is that a 3/16” relief reduces compression by about 0.2, and therefore 8.7 without relief. So, roughly, I could install these heads on my car and end up with a compression ratio of about 8.7 – 0.4 or 8.3. Again, the question is, do you think these heads will work without modification and allow me to use 87 octane pump gas? The numbers seem close but am I way off?

09-01-2022, 01:34 AM	#2
deuce lover Senior Member Join Date: May 2010 Location: Southern France Posts: 5,306	Re: Edelbrock head question In 2007 I put a set of vintage Weiand heads on a bone stock 39 Merc flathead and that sure woke it up. The only thing about the Edelbrocks is make sure your studs are long enough.

09-01-2022, 11:10 AM	#3
flatjack9 Senior Member Join Date: May 2010 Location: Oshkosh, Wi Posts: 4,526	Re: Edelbrock head question Doing the calculations, you should end up at about 7.5:1

09-01-2022, 01:42 PM	#4
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,064	Re: Edelbrock head question Edelbrock heads use a piston crown shape that uses a consistent radius profile. Some flatheads had pistons with dual radius profiles (more like an ellipse). You can tell when you have these pistons as they're a bit more "pointed" in the centers than a piston with a consistent radius. The only reason I bring this up is that I have seen situations where the center "point" of these types of pistons will hit the center of the dome area on the Edelbrock heads (and many others). So, make sure you CLAY the tops of the pistons and check this clearance before you bolt the heads down and whack them with your pistons (potentially).

09-01-2022, 01:50 PM	#5
Bored&Stroked Senior Member Join Date: Jan 2011 Location: Central Ohio Posts: 5,064	Re: Edelbrock head question Sponsored Links (Register now to hide all advertisements) Here is a 3D solid model view of the TWO shapes I'm talking about. I created a CAD model to use for CNC programming to "fix" the chambers on some heads for the more pointed crowned pistons: 3DSectionView-Ford-Egge-Dome.jpg 3DSectionView-RossEdelbrock-Dome.jpg