Ford flathead milling

[hondo383]

8BA flathead ford heads.Anyone know how many thousandths per CC approximately?
I swear i saw it once somewhere but i cant find it (now that i have some heads on the bench of course)

[ProPower engines]

Most aftermarket heads are .006 per cc.
You could just machine off .006 and recheck the volume. I know it seems like a bunch of work but there is from memory a couple different heads. How many studs hold the heads on?

[hondo383]

8BA=24 studs 1950 ford
I will pour them on monday,I figured I would have to cut and try but just thought i would pick the speedtalk minds first....

had customer take one home this weekend to clay his current piston to head and valve to head clearance to calculate the max amount i could thoretically cut off and still have clearance... he says it should have 6.8~comp factory and he wants 9:1..i dont think thats possible via milling or a good idea with a flathead..
thanks!

[DaveMcLain]

Remember that the more you cut off of the head the smaller the transfer area becomes and the more restricted the breathing. Best bet on a flathead engine is to run the largest chamber you can, compression ratio be dammed.....

[hondo383]

I.was doing some reading on that last night on flathead airflow..I am going to try to talk him out of milling the.crap out of these things for just that reason .thanks all!

[FEnut]

Remember that the more you cut off of the head the smaller the transfer area becomes and the more restricted the breathing. Best bet on a flathead engine is to run the largest chamber you can, compression ratio be dammed.....DaveMcLain


Bingo! You are right Dave. The aftermarket "in the day" increased the compression and reduced the transfer section on the flathead to do so. On a flowbench, the direct impact this has on airflow is apparent. In fact, many aftermarket "race" heads actually flow less everywhere than the factory heads. The aftermarket heads did have extra room for increased valve lift, but cutting valve clearance into the factory head was relatively easy to do, and power followed. The trick is, in my opinion, to balance compression ratio with transfer section area. As with any internal combustion engine, the engine needs sufficient airspeed and air mass flow and a manageable (within the constraints of the combustion chamber design)compression ratio to develop efficient power for the desired engine operating range. So the sizing and shaping of this transfer area is of utmost importance.
Another "trick-of-the-week" or "weak" is block relieving. It was the cats ass then and is still considered the thing to do in the old boy circles of flathead-dom. WRONG. This may indeed open up the area at the transfer section, but the air tends to take the high road after the valve and adding area above and around the valve relief and going a step farther and increasing area at the head transfer section( either increasing in height or width or both)is where the efficiencies are found. Get the piston up close and comfortable with the head (thus increasing the squish ratio), increase flow area at the head transfer area and valve relief pockets, size the valves and bowls for the job, and increase the flow path efficiency .This will achieve a balance of compression and flow area. Just rambling.... Any thoughts?

[DaveMcLain]

I tend to believe that there is probably a certain amount of cross over area cross section that's needed for a given amount of port flow in a flat head engine and that having any more than that amount is probably just reducing the compression ratio. But I'm not sure where that point is and my flat head flow bench experience is pretty limited.

I can say that work in the crossover area really helped on a flat head engine that I worked on for a customer even though it without question reduced the compression ratio. It was a single cylinder engine so it was very easy to try all sorts of different things.

[hondo383]

The way I am seeing it is the transfer area is like having another "choke" in your port,only after the valve so obviously if you make this smaller than your min port csa /get into turbulence you will hurt power.
as far as block.relieving I.do agree it may be counterproductive. It seems to me lowering the area on the piston side of the valve would take away from the top cuts effectiveness and mak
es a harder turn from/to the valves, like going from a good modern type combustion chamber to an older flat bathtub design..I think if you need more transition area it should be included in the cylinder head not the block..

[SMITHBERGRACING]

I have limited experience with flat heads but I will say airflow wins over compression on these things any day. We proved this theory with a single cylinder on a dyno and bolted on three different heads of various designs and sizes, even played with head gasket thickness (more area = more power). I asked similar questions a year or two ago and people were tight lipped. I'm sure there is a sweet spot for a given combo. My experience is to take molds of everything, section it up, and measure/plot it out on paper. I think of the transfer area as an extension to the port really since it acts as another choke point. I'm sure you need a certain window size here otherwise performance will suffer. As far as relieving the block goes my opinion is you need that area somehow so unless you design a new head or grind away on what you have it may help make more power - you have limitations. I'm all ears to learn something new here if people care to share experiences to the young bucks!

[DCal]

I worked on a friends '41 ford and thought I could improve it but after looking up the cam specs I realized it had zero overlap and fairly good cranking compression for it's time, so we left it at 7:1, obviously it could be improved but it would involve camshaft and compession both and a good understanding of air flow. Bet the Briggs gang could shed a lot of light on this configuration.

[ProPower engines]

What about angle milling the heads?
The section over the valves would be less affected by this. Even if the cross section over the valves was reduced slightly is could be returned to the same amoumt after the angle cut was done. The chamber reduction would be greater then the section over the valves thus even if that area required some work you would still gain comp. and retain the flow into the chamber.
Pistons with domes on the other hand would be the best way to go all around

[jsgarage]

This is going back to the middle of the last century, but relieved blocks seemed to crack between the seats & bores more readily than those that were left intact. Or maybe its just that we ran the h... outa the relieved blocks and they overheated.

[DCal]

This is going back to the middle of the last century, but relieved blocks seemed to crack between the seats & bores more readily than those that were left intact. Or maybe its just that we ran the h... outa the relieved blocks and they overheated.

I remember we always looked for Denver motors, thicker blocks and higher compression.

[Kahuna]

Hondo
If those are stock 8BA cast iron heads, the best you are going to be able to do is this:
You or the customer, if he's capable, clay (a better method is to use aluminum foil and make small 1/4" balls with grease), and set the piston quench/squish to .040-.050" . Mill what ever you need to get that clearance. Then check the valve clearance. That's as good as it's ever going to get with those heads. Forget the compression ratio. Whatever the compression ends up to be is going to be OK.
Most all flathead gaskets compress to .045-.050". You can use that as a good guide.
Jim

[hondo383]

yep thats the "homework" i gave him for this weekend, and we will see what the current clearances come up to be....guy also want$ me to build a whole other engine now too so time for more research should be interesting .. thanks againfor all the info guys!