block releiving
- Thread starter ken-r-mer
- Start date
Re: block relieving
The problem is the head gasket when laid against the head, there are sizable areas in the transition area (between the bore and valve pocket area) of the head surface that don't align with the gasket perimeter of the combustion area. So in making the cut line on the block, do you use the profile of the gasket or the profile of the machined head area? I looked at both, Edelbrock and Offenhauser heads and multiple gaskets and the misalignment is consistent.
I'm relieving the block to drop the compression a few fractions of 1 psi and maxing the air flow for a blower setup. The relief is only 0.10". There is even misalignment with a few water jacket openings. If you look at a 49-53 after market head, either Edelbrock or Offy, there are 3 large size water jackets openings on the right hand side, the head gasket only as 2 large and one small and the one large is misaligned as seen in the pic.
The problem is the head gasket when laid against the head, there are sizable areas in the transition area (between the bore and valve pocket area) of the head surface that don't align with the gasket perimeter of the combustion area. So in making the cut line on the block, do you use the profile of the gasket or the profile of the machined head area? I looked at both, Edelbrock and Offenhauser heads and multiple gaskets and the misalignment is consistent.
I'm relieving the block to drop the compression a few fractions of 1 psi and maxing the air flow for a blower setup. The relief is only 0.10". There is even misalignment with a few water jacket openings. If you look at a 49-53 after market head, either Edelbrock or Offy, there are 3 large size water jackets openings on the right hand side, the head gasket only as 2 large and one small and the one large is misaligned as seen in the pic.
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petehoovie
Well-known member
Bored&Stroked
Well-known member
Most folks use the outline of the gasket for their relief - though there are different "styles" of reliefs. The Offy heads do have a different shape on the exhaust sides of the chamber which is a bit strange in that even with a stock block, this creates a channel underneath that area. This was probably done to increase compression . . . as I don't see it helping flow.
Notice the chamber shape difference in these Navarro heads (made by Barney):
If you desire more CC's in your chambers (due to a blower), then I would modify the Offy shape to more closely follow the gasket pattern (more like what most other head manufacturer's do) - as noted above. At the very least, radius the sharp edges that are hanging out in the chamber.
If it was my engine and I was putting a supercharger on it, I would modify the chamber to match the gasket and the relief would as well. My relief is usually .125 to .187 deep. I'd probably use a .125 deep relief on your setup.
One thing to note with a blown engine is where is the top ring on the piston? With a deeper relief, the top ring is closer to the bottom of the relief and will take on more heat. On blower pistons I have the manufacturer lower the ring package a bit - to take some heat out of the top ring.
If you're ordering your pistons from Ross, they can move the ring package for you a bit (down). Also, check the shape of your chambers as they relate to your piston crowns. I've not had a set of new/stock Offy heads in years - do they have a consistent radius in the dome (like Ross pistons) or a pointier shape in the middle - which is caused by multiple elliptical shapes converging. There are two basic dome shapes - one tends to follow the stock Ford cast pistons and the other aftermarket pistons like Ross.
If you have the more "pointy" shaped domes and run the consistent radius pistons, then the quench will be inconsistent over the piston crowns . . . something I don't like.
On a custom-built engine (what I do) I make sure I match the head dome shapes to my piston crown shapes to achieve a .040 quench.
To achieve this, it usually requires either custom head work, custom piston compression heights . . . or both.
Notice the chamber shape difference in these Navarro heads (made by Barney):
If you desire more CC's in your chambers (due to a blower), then I would modify the Offy shape to more closely follow the gasket pattern (more like what most other head manufacturer's do) - as noted above. At the very least, radius the sharp edges that are hanging out in the chamber.
If it was my engine and I was putting a supercharger on it, I would modify the chamber to match the gasket and the relief would as well. My relief is usually .125 to .187 deep. I'd probably use a .125 deep relief on your setup.
One thing to note with a blown engine is where is the top ring on the piston? With a deeper relief, the top ring is closer to the bottom of the relief and will take on more heat. On blower pistons I have the manufacturer lower the ring package a bit - to take some heat out of the top ring.
If you're ordering your pistons from Ross, they can move the ring package for you a bit (down). Also, check the shape of your chambers as they relate to your piston crowns. I've not had a set of new/stock Offy heads in years - do they have a consistent radius in the dome (like Ross pistons) or a pointier shape in the middle - which is caused by multiple elliptical shapes converging. There are two basic dome shapes - one tends to follow the stock Ford cast pistons and the other aftermarket pistons like Ross.
If you have the more "pointy" shaped domes and run the consistent radius pistons, then the quench will be inconsistent over the piston crowns . . . something I don't like.
On a custom-built engine (what I do) I make sure I match the head dome shapes to my piston crown shapes to achieve a .040 quench.
To achieve this, it usually requires either custom head work, custom piston compression heights . . . or both.
Last edited:
petehoovie
Well-known member
Thanks for the detailed comment on the block relief.
What about the difference in sizes between the gasket head and gasket water jacket openings? It seems the head gasket is restricting the water flow between the block and the heads.
Bored&Stroked
Well-known member
The head gaskets are designed by the various manufacturers to purposefully interact with water flow. I've seen all kinds of different hole patterns - especially in the middle water jackets. Some guys hog out the middle area for more water flow in the middle area - I've never found it necessary. BUT I have high volume water pumps with improved impellers (39-48 style pumps - with Skip's impellers) - they flow a lot more water than stock pumps (which is what you want!)
In later years (49-53) Ford obviously wanted to move more water to the BACK of the block (where it is usually the hottest) - they enlarged the water galley holes at the back the gaskets have much larger holes in those areas than the gaskets used prior to 49.
In later years (49-53) Ford obviously wanted to move more water to the BACK of the block (where it is usually the hottest) - they enlarged the water galley holes at the back the gaskets have much larger holes in those areas than the gaskets used prior to 49.
Dale,
Interesting that you leave them. I also use high volume pumps. I can only speak to Best copper gaskets, but one of the center water holes was so small, I don't think a 8d nail would pass through the hole. That seems like quite a restriction keeping water around one of the hottest parts of the block with the shared center exhaust port and two cylinders.
You have me thinking though. I opened my gaskets and had to take off my fan due to not being able to get it to over 180 with it on.
Personally, I still think it makes sense to open them up to match the heads, but like many things flathead, people have their own tricks and ways of doing things and it's all good.
Even on the back side in the 49-53 block and heads, there are 3 large kidney bean sized water passage holes yet the gasket has 2 and the 3rd is very small and round. You would think the gasket would at least match the block holes. That 2 big and 1 small opening is also the same in the BEST Gaskets non-copper gasket set. The only thing i can think of is to keep the water in the block longer, where it is the hottest.
Which is what you don't want. You want the hot water out of the block and circulating back to the radiator.
tubman
Well-known member
I don't think it's a good idea to start enlarging holes and otherwise modifying head gaskets without a good, proven reason. The openings in the block are probably configured for the most efficient casting when originally made. What works best for cores and boxes and removing sand might not be the best for distribution of coolant within the engine. They configure the gaskets specifically to do that.
I run 180 degree thermostats on the motor
If you can find a set of old, aftermarket gaskets from the late ‘40’s/50’s, they were made with the proper sized holes. For some reason, a change was made. This suggestion to make the holes the same size as the heads came from a well known builder/member who has many, many miles on high performance motors and record setting speed runs to back up his recommendation.
tubman
Well-known member
There has been a lot of advances in the design of engines and gaskets since the 40's/50's (when they used predominantly alcohol-based antifreeze). There may be a bit of truth to what you are saying in special circumstances, but the Ford (and gasket company) engineers originally designed the COOLING SYSTEM to function best in day to day use. What works "for high performance motors and record breaking runs" is usually impractical for regular street use, which is what the vast majority of of the members here are concerned with. Bottom line? If you are having cooling problems with your flathead, it's best to check out the "usual suspects" first, and refrain from cutting up a good set of head gaskets (which are starting to get quite expensive lately).
I guess it all boils down to do what you think is best. Since original and older replacement gaskets from the '40's/'50's had the correct sized holes stamped in, I'm really curious as to why Best and I'd assume Felpro don't do it like that.
Since these two gasket companies make gaskets for literally hundreds of different motors, I would be surprised if they product test things such as head gaskets on all of the motors they produce them for.
My thought is you want the coolant system to cool and getting the water to flow is paramount to making that happen. Anything besides a thermostat that keeps that from happening is just adding stress to the system and negates the way it is designed to operate.
Your mileage may vary.....
Bored&Stroked
Well-known member
I look at it as a question of WHERE do you want the flow to go. I'm sure there is MORE than enough holes/passages in any of the head gaskets to flow a lot more volume than any of our pumps put out . . . so, to me it comes down to trying to direct the flow to certain parts of the block.
Without a lot of testing and a very controlled test environment, there is no way to know if opening up the middle water ports is a good thing or not. My 284 cube flatty keeps cool without a pressurized radiator - even in stop n go traffic (for over an hour!) on a 95 degree day.
I'm fine with it, though I'm sure the system could be configured in a variety of ways and still perform just fine.
Without a lot of testing and a very controlled test environment, there is no way to know if opening up the middle water ports is a good thing or not. My 284 cube flatty keeps cool without a pressurized radiator - even in stop n go traffic (for over an hour!) on a 95 degree day.
I'm fine with it, though I'm sure the system could be configured in a variety of ways and still perform just fine.
tubman
Well-known member
As I see it, the only reason that head gasket design was changed from the 49's/50's is the change to Glycol-based coolant from plain water or water/alcohol. Alcohol boils at 173 F, which is substantially below today's witches brews, which would be a big factor. I'm no automotive engineer, but that's about the only thing I can think of. Who knows what all is involved? I'm pretty sure that the move to pressurized systems and Glycol-based coolant has something to do with it.