8RT / 8BA heads
8RT / 8BA heads
Post Fiend
Joined: Mar 2007
Posts: 5,776
Likes: 2
From: springfield il
8Rt has much larger chambers than the 8ba so compression is gonna be lower on that side . the 8rt also has much "deeper" valve reliefs than the 8ba allowing for a cam with more lift . the eab heads have smaller chambers and allow for if i remember .395 or .410 lift on the cam . flatheads seeing as they have the valves in block suffer greatly on flow and while a smaller chamber does increase the compression ratio , they also have a detrimental effect on flow . that being said i am running a stock 239 shortblock with eab heads milled .010 for a compression of 7.8:1 with a merc 4 bolt intake (4 bolt carb pad) a rochester 350cfm 2 jet and a merc 8cm cam . i gave up a little bit of flow for a little more grunt and a little less rpm . my oe 8ba heads would be a better choice for flow allowing the engine to run better at higher rpm's but they do not have the deeper valve reliefs but a competent machinist can fix that and allow for larger cam lift's . in oe form the 8rt heads flow the best ..... So make your decision on what your intended purpose is . oh yeah too much compression can cause a flatty to run really hot which is also detrimental as we all know . my 52 customline had a bone stock 53 8rt in it to replace the worn out oe flatty and it ran super smooth , quite , and was ultra dependable even at modern day highway speeds .
Post Fiend
Joined: Mar 2007
Posts: 5,776
Likes: 2
From: springfield il
Oh and if you have an earlier flathead in it the engine has two different deck heights and as such the right and left heads have different sized chambers to keep the compression the same on both banks .
Fleet Mechanic
Joined: Feb 2015
Posts: 1,668
Likes: 111
From: southwest missouri
in other words ford has not adapted the make is simple like chevy small blocks. I have a flat head that is out of I think a 50 or 51 f-1 but has mercury heads. I am just learning the flat head so where on the motor can I fine some numbers to tell me if it is a ford or merc flatty. I have heard that the merc is the one to have because of the crank or block I really do not know. Thanks for the help.
Post Fiend
Joined: Mar 2007
Posts: 5,776
Likes: 2
From: springfield il
on the back of the block on the lip above the bell housing should be some numbers . van pelts website will have a chart to decipher it if i remember right . it makes little or no difference though as the blocks are identical . the early merc's were the same displacement as the ford , so what your looking for is the crank out of what i believe 49 and newer as they had a longer stroke than the ford . ford was 3.75 merc was 4.00 . they use all the same bearings even piston rings . the pistons will be different in the height due to the longer stroke but that is the only difference .
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