8ba/Merc heads ??

M

mfirth

Well-known member
Ok guys, just got the heads off of what i hoped was a Merc 255. Alas it is a 239 with std domed pistons & Merc heads. This engine pulled good & was peppy. Started getting noisy & using lots of oil so time to rebuild. Aren't Merc heads lower compression? Is there any reason to make a change? This thing ran really good...so any advice/info will be greatly appreciated. THANKS in advance!!! mike
 
those chasing every last horsepower will tell you to find some EAB or aftermarket heads and cut them for .045-.050 clearance over the pistons. Is this a street engine? I suspect if you do the same with your Merc heads you won't know the difference without a dyno.
 
Biggest bang for the buck improvement you can make is higher compression heads and milling to get the clearance down. And I do believe you will be able to tell the difference without a dyno!!
 
I gotta agree with "JSeery". I've done three flatheads from the ground up so far. The first was a 276" Merc about 20 years ago. It had a MAX-1 cam, a 390 Holley, and an MSD ignition. I didn't know then what I know now, so I just bolted a set of Offenhauser finned heads on. That engine ran OK, but I was never real happy with it. Last summer I did a 255" Merc for my '51. This one had a stock cam (heavy car) a 2GC, and a Mallory dual point. This one has a set of Edmunds heads. I have been paying attention to what the guys are saying here, so I spent a lot of time getting the heads to a uniform .050" squish". I don't know what the compression ratio is, but I have a healthy 170 lbs all around (stock is 110). I love the way this car performs; the engine has a crispness that was missing in the first one. I remember being disappointed in the performance of the first engine (it was in a '36 3-window). While this one won't blow your doors off, the torque is amazing; I don't have to downshift much driving around town if I don't want to. I just finished a 258" with a MAX-1 for the Hot Rod I'm building. This one has Edmunds heads on it as well, and I spent a bunch of time on this set too getting them just right. I only have test stand time on this one, but it has been great so far; it also has that crispness that was lacking in the first one.

With all this, I don't know if you can mill a set of Mercury iron heads and work them over to get the proper characteristics. You probably can, but with the time I had to spend grinding the aluminum ones, I wouldn't look forward to doing it to a set of iron heads.
 
The Merc heads have a bigger combustion chamber. Back in the day, some guys put Merc heads on their Ford engines thinking they'd get more power The merc ajd 8RT heads are not very good for econmy either.
 
Thanks SO much for the info from each of you guys. The car is a 52 Vicky & did seem to use a lot of gas....looks like a new or different set of heads is in order, maybe eab's ??
I don't have the skill or equipment to do the mill work, so........ THANKS AGAIN, mike
 
What you want to do is find the heads you are wanting to use, then check them on the engine. You can use rolled up aluminum balls or clay. Determine what needs to be milled off to archive around .050 minimum clearance. Then have a machine shop mill the heads for you. Custom fitting the head is in the every last oz. of HP category, but just doing the milling will work wonders.
 
The Mercury heads gave the 255 CID engine very near the same compression ratio as the 239 CID engine with 8BA heads. These engines were built for torque and reliability more than performance. Using an EAB (1952/53 Ford) cam and heads on a 255 CID engine gives both torque and performance since it increases compression ratio for the 255. Further mods for compression such as milling heads for a specific squish dimension in the chamber will improve performance even more. This stuff works well on the street.
 
Ol' Ron said:
The Merc heads have a bigger combustion chamber. Back in the day, some guys put Merc heads on their Ford engines thinking they'd get more power The merc ajd 8RT heads are not very good for econmy either.
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My friend told me the pickup and truck engines came with Mercury heads to lower the compression. His parents had a new 50 Mercury and later a new
52 Ford pickup.
 
EAB heads are higher compression. Went to install only to find block had been decked during machining. Had to revert to Merc heads as slight interference with valves.
 
Boy, what cam were you running? I can't believe there is any stock cam that wouldn't have lots of clearances with any stock heads.
 
Isn't the difference in chamber size in the depth rather than the lateral dimensions?

From the tenor of this thread, I don't think we're dealing with extreme cams or over-sized valves here, but I could be wrong.:rolleyes:
 
In order to run the L-100 cam (.360 net lift) you have to remove a small amt of material from the top of the valve pockets. I use a 5 deg angle and a shell mill. I don't think more than a few CC's material is removed. This should be done after the piston to head clearance is complete.
 
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