The Ford Barn

Yoyodyne · 04-09-2012, 01:20 PM

I'm building a 221 for my 36 PU. If you have the corresponding correct heads, and have the same static compression ratio when assembled, will domed pistons make more HP in otherwise identical engines? I haven't seen this discussed. As far as I can tell, the difference between a 85 HP engine and a 90 HP engine are the pistons and heads, and maybe the ignition curve in the distributor. If it doesn't, why did Ford make the change? Which one would make more turbulence in the chamber?

I already have a set of .100 over flat top pistons, but I can get a set of replacement heads for 36 waterpumps that have domed chambers, and I thought that if there is a significant advantage I should use the domed heads and get another set of pistons. I'm using an L-100 cam, might go to Don Orosco's Eddie Meyer heads which can be had either way. Opinions?

phartman · 04-09-2012, 03:34 PM

I can strongly recommend that you get the heads cc'd by a reliable machinist so that you'll know what you are working with, domed or not. Here is a thread that may help you in the variety of 21-stud heads that I encountered in my 36LB motor rebuild:

https://www.fordbarn.com/forum/showthread.php?t=42266

I have a set of the Don Orosco heads, and he will provide them to you either way, that is correct. As of this past summer, however, he was troubled by bad castings and didn't have any available in either configuration. Don't know if he ever got good castings from the foundry and finished up my his machinist.

But from my research, the configuration boiled down to a personal preference. Opinions were strong for both camps. Take your pick.

Pete
Richmond, VA

Yoyodyne · 04-09-2012, 04:45 PM

I have several sets of heads, I've CC'd them myself and they match up with what they are supposed to measure per the casting numbers. I only have cast iron heads, if I want 8-1 CR I'll have to mill something heavily or get the Don Orosco heads. The flattops should be easier to deal with because I won't have to recut the chamber domes.

richard crow · 04-09-2012, 06:34 PM

i would not boar a 36 221 eng .100 over the walls on these engs are not as thick as the 37 up engs your going to need a radator from a peterbuilt truck.

phartman · 04-09-2012, 06:44 PM

Quote:

Originally Posted by Yoyodyne

I have several sets of heads, I've CC'd them myself and they match up with what they are supposed to measure per the casting numbers. I only have cast iron heads, if I want 8-1 CR I'll have to mill something heavily or get the Don Orosco heads. The flattops should be easier to deal with because I won't have to recut the chamber domes.

I believe that is correct, you will need to mill them. But the iron heads seem to lend themselves to milling. You can cut them down quite a bit. And many guys that I know prefer the cast iron-to-cast iron nature of the head to block arrangement rather than cast iron-on-alloy. I have a set of the milled iron heads on my '36 LB and they've done quite well. Kind of hate to disturb the set up.

But I just got a call from the polisher that the ribs on my Don Orosco repops are now bright and shiny, and I can come pick them up at his shop.

Decisions, decisions.

Bruce Lancaster · 04-09-2012, 06:45 PM

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The dome type heads are essentially Ricardo type chambers, causing high turbulence and allowing better combustion and better advance tolerance. I think they are very likely a performance inprovement over the flats. The 9o HP designation was just really a parts book thing. Ford kept the 85 advertised on several changes to the engine with different compressions, hotter cam on pre 1937 engines, several different curves.
On the things you mention, I would choose domed chambers and if using the helmet distributo use the '37-41 type with 1941 11A stamped advance mechanism.

Yoyodyne · 04-09-2012, 08:50 PM

I'm using a 37 block, but thanks for the warning.

I have 37-41 guts in my 36 distributor, but I don't have the 11A advance. How important is that?

Bruce Lancaster · 04-09-2012, 08:55 PM

It is a quicker and longer curve that should give a little extra pep. Rear of shaft will have the 11. Helmet distributor cores are dirt cheap, and few people charge more for the '41 or even know that it's different, a development of Ford noticing gas getting a bit better. It can be pretty close to a free upgrade.

phartman · 04-10-2012, 07:27 AM

Don't you just love these little 21-stud motors? I'm nuts about them, but many people aren't fans. My buddies call it, "A more expensive way to go slower...." That's pretty funny, and maybe just a little true. Good luck with your motor.

Pete

Yoyodyne · 04-10-2012, 09:09 AM

Thanks guys. This is going in a real original 36 pickup and I don't want to change motors, plus I think the 21 studs are neat now that I know a little about them. The truck was certified HPOF at Hershey, then the babbitt went out. I'm plotting how I can put the grease and dirt back on after I reinstall the engine...

Anyone have pressure test plates for a 21 stud?

Bruce Lancaster · 04-10-2012, 09:19 AM

Oddly, I have never actually lined up a 24 stud head and a 21 stud one...I'm sure lots of people here have and can comment.
I believe that all the stud holes will be in same place except for the bottom row so that if you drill the holes for the studs that are at the lower/outer edge of each cylinder, 24 stud test plates would go on, and at most you might have to thread and plug any of the paired 24 stud lower holes that overlap with a water hole...if no one on here has actually matched up heads to see, unlikely, I think I can find one of each tonight and see.

04-09-2012, 01:20 PM	#1
Yoyodyne Senior Member Join Date: Nov 2010 Location: Lancaster PA Posts: 535	Flat top VS domed pistons for HP I'm building a 221 for my 36 PU. If you have the corresponding correct heads, and have the same static compression ratio when assembled, will domed pistons make more HP in otherwise identical engines? I haven't seen this discussed. As far as I can tell, the difference between a 85 HP engine and a 90 HP engine are the pistons and heads, and maybe the ignition curve in the distributor. If it doesn't, why did Ford make the change? Which one would make more turbulence in the chamber? I already have a set of .100 over flat top pistons, but I can get a set of replacement heads for 36 waterpumps that have domed chambers, and I thought that if there is a significant advantage I should use the domed heads and get another set of pistons. I'm using an L-100 cam, might go to Don Orosco's Eddie Meyer heads which can be had either way. Opinions?

04-09-2012, 03:34 PM	#2
phartman Senior Member Join Date: May 2010 Location: Richmond, VA Posts: 339	Re: Flat top VS domed pistons for HP I can strongly recommend that you get the heads cc'd by a reliable machinist so that you'll know what you are working with, domed or not. Here is a thread that may help you in the variety of 21-stud heads that I encountered in my 36LB motor rebuild: https://www.fordbarn.com/forum/showthread.php?t=42266 I have a set of the Don Orosco heads, and he will provide them to you either way, that is correct. As of this past summer, however, he was troubled by bad castings and didn't have any available in either configuration. Don't know if he ever got good castings from the foundry and finished up my his machinist. But from my research, the configuration boiled down to a personal preference. Opinions were strong for both camps. Take your pick. Pete Richmond, VA

04-09-2012, 04:45 PM	#3
Yoyodyne Senior Member Join Date: Nov 2010 Location: Lancaster PA Posts: 535	Re: Flat top VS domed pistons for HP I have several sets of heads, I've CC'd them myself and they match up with what they are supposed to measure per the casting numbers. I only have cast iron heads, if I want 8-1 CR I'll have to mill something heavily or get the Don Orosco heads. The flattops should be easier to deal with because I won't have to recut the chamber domes.

04-09-2012, 06:34 PM	#4
richard crow Senior Member Join Date: May 2010 Posts: 1,770	Re: Flat top VS domed pistons for HP i would not boar a 36 221 eng .100 over the walls on these engs are not as thick as the 37 up engs your going to need a radator from a peterbuilt truck.

04-09-2012, 06:45 PM	#6
Bruce Lancaster Member Emeritus Join Date: May 2010 Location: Madison, NJ Posts: 5,230	Re: Flat top VS domed pistons for HP Sponsored Links (Register now to hide all advertisements) The dome type heads are essentially Ricardo type chambers, causing high turbulence and allowing better combustion and better advance tolerance. I think they are very likely a performance inprovement over the flats. The 9o HP designation was just really a parts book thing. Ford kept the 85 advertised on several changes to the engine with different compressions, hotter cam on pre 1937 engines, several different curves. On the things you mention, I would choose domed chambers and if using the helmet distributo use the '37-41 type with 1941 11A stamped advance mechanism.

04-09-2012, 08:50 PM	#7
Yoyodyne Senior Member Join Date: Nov 2010 Location: Lancaster PA Posts: 535	Re: Flat top VS domed pistons for HP I'm using a 37 block, but thanks for the warning. I have 37-41 guts in my 36 distributor, but I don't have the 11A advance. How important is that?

04-09-2012, 08:55 PM	#8
Bruce Lancaster Member Emeritus Join Date: May 2010 Location: Madison, NJ Posts: 5,230	Re: Flat top VS domed pistons for HP It is a quicker and longer curve that should give a little extra pep. Rear of shaft will have the 11. Helmet distributor cores are dirt cheap, and few people charge more for the '41 or even know that it's different, a development of Ford noticing gas getting a bit better. It can be pretty close to a free upgrade.

04-10-2012, 07:27 AM	#9
phartman Senior Member Join Date: May 2010 Location: Richmond, VA Posts: 339	Re: Flat top VS domed pistons for HP Don't you just love these little 21-stud motors? I'm nuts about them, but many people aren't fans. My buddies call it, "A more expensive way to go slower...." That's pretty funny, and maybe just a little true. Good luck with your motor. Pete

04-10-2012, 09:09 AM	#10
Yoyodyne Senior Member Join Date: Nov 2010 Location: Lancaster PA Posts: 535	Re: Flat top VS domed pistons for HP Thanks guys. This is going in a real original 36 pickup and I don't want to change motors, plus I think the 21 studs are neat now that I know a little about them. The truck was certified HPOF at Hershey, then the babbitt went out. I'm plotting how I can put the grease and dirt back on after I reinstall the engine... Anyone have pressure test plates for a 21 stud?

04-10-2012, 09:19 AM	#11
Bruce Lancaster Member Emeritus Join Date: May 2010 Location: Madison, NJ Posts: 5,230	Re: Flat top VS domed pistons for HP Oddly, I have never actually lined up a 24 stud head and a 21 stud one...I'm sure lots of people here have and can comment. I believe that all the stud holes will be in same place except for the bottom row so that if you drill the holes for the studs that are at the lower/outer edge of each cylinder, 24 stud test plates would go on, and at most you might have to thread and plug any of the paired 24 stud lower holes that overlap with a water hole...if no one on here has actually matched up heads to see, unlikely, I think I can find one of each tonight and see.