Hemi-head Fords

keith oh

keith oh

Well-known member
In 1936 ford changed pistons from flat-top to round-top and altered the heads to fit. Question-could this be considered as a hemi-head engine and if so has anybody dino checked to see if there was actually a HP increase. Just wondered.
 
Would not be considered a "hemi" head, as the combustion chamber is not hemispherical. The pistons and chamber only have a slight dome; the radius of curvature is much larger than what a hemi would have.

Now, if you changed the heads to something like an ARDUN, then you'd have a "hemi".
 
Pic is from 2005 { yes thatz mee } when I parted with this car after having it for 18 years . Putting me in that car was like putting 50 # 's of stuff inna 10 # sack . BOSS 429's were the only " hemi " ford made back in the day . The SOHC 427's were not production engines and are less of a hemi than a BOSS 9 . Arduns are " hemi " heads also but again not production items .Had 18 426 hemi powered mopars also . They all turned into farmland . Nowdays many engines are " hemis " but Chrysler has that name trademarked . The old nickname for Boss 9's was " shotgun " motor . The SOHC 427's were called " cammers " or " sock " motors .Had to replace the intake gasket on the BOSS as it had sat in a garage in CA since 1971 & the intake gasket leaked coolant in front once I got it up and running in 1986 . The point of this is that I got to see first hand that the top of a pop can FIT in the intake port :eek: . Most folks don't realize that 10 of Richard Pettys wins came in 1969 driving a " hemi ford powered torino Talladega . Plymouth made the superbird in 1970 so Petty went back to them in 1970 .
 

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David J said:
Pic is from 2005 { yes thatz mee } when I parted with this car after having it for 18 years . Putting me in that car was like putting 50 # 's of stuff inna 10 # sack . BOSS 429's were the only " hemi " ford made back in the day . The SOHC 427's were not production engines and are less of a hemi than a BOSS 9 . Arduns are " hemi " heads also but again not production items .Had 18 426 hemi powered mopars also . They all turned into farmland . Nowdays many engines are " hemis " but Chrysler has that name trademarked . The old nickname for Boss 9's was " shotgun " motor . The SOHC 427's were called " cammers " or " sock " motors .Had to replace the intake gasket on the BOSS as it had sat in a garage in CA since 1971 & the intake gasket leaked coolant in front once I got it up and running in 1986 . The point of this is that I got to see first hand that the top of a pop can FIT in the intake port :eek: . Most folks don't realize that 10 of Richard Pettys wins came in 1969 driving a " hemi ford powered torino Talladega . Plymouth made the superbird in 1970 so Petty went back to them in 1970 .
Click to expand...
Petty also ran "BIG" cranks in most all of his engines Ford , Chev, Pontiac & Mopar ! including the 5/8 crank in the ingine of his last win infront of the President ! I Know !!!!!!!!!!!!!!!!
 
I think the advantage to the Hemi is that you can put bigger valse for a given piston diameter. Valve geometry may also aid in breathing. Harley made hemis for years but in 84 went with a bathtub style combustion chamber. They have never looked back.
 
The torque placed on the crankshaft is determined on the pressure placed on the piston during combustion. As the piston has a surface area determined by the diameter of the cylinder. Now if the area is increased with a dome, more force is placed on the crankshaft. Does it work?? I have no idea, but Ford seemed to think so.
 
Fascinating stuff here . Was this not an attempt to get a little more useable power from the same available force.
Ol' Ron said:
The torque placed on the crankshaft is determined on the pressure placed on the piston during combustion. As the piston has a surface area determined by the diameter of the cylinder. Now if the area is increased with a dome, more force is placed on the crankshaft. Does it work?? I have no idea, but Ford seemed to think so.
Click to expand...
 
Downward force on a flat or dome piston is equal for the same size piston. The dome piston provides some additional side force but it equalizes across the piston so no side thrust. The main reason for domed pistons is strength. Think of an arch in a doorway and the additional load it can carry.
 
I once asked Dad ( A Ford Dealer in the thirties) and he gave me a cynical answer with a wink, " Parts my boy, can't interchange, so we have larger inventory's of parts to sell".
 
I often wondered why other manufactures if Flatheads didn't use domed pistons, if there was an improvement in power or ware considerations. But Henery had his way of doing things.
 
Still no answer as to whether anybody has ever seen any actual dino testing HP comparison of the round top and flat top cylinder engine, 221 cu. in.
 
The technical reason is the dome has more area than a flat top so more energy is transformed to the crank. I doubt you could measure it. You could build two 36 engines exactly the same except for the pistons and heads then test them under identical conditions. When I see Hank, I'll ask him.
 
The Ford theory for domed pistons and near matching heads was probably built around several sound ideas from the engineers. It is true there would be a small increase in surface area. It is also true the dome shape could allow higher strength with less weight, but, flat pistons have proven to be plenty strong before, during, and since Ford used those with domes. So, I seriously doubt that as a reason for the change. Also, the silly theory that the domed piston "blocked flow" in a performance build is rediculous. The most likely technical reason was to increase turbulence which will result in more complete combustion.

Now to the question of testing an engine with and without flat/domed pistons: After having done hundreds and hundreds of dyno tests, of Flathead engines, I can say many of the changes we make have such a tiny, incremental value as to render them almost impossible to measure. And, building any 2 engines which produce exactly the same power is downright hard to do. So, determining why one engine might make 1 or 2 more horsepower would make a serious investigation necessary. As I have said in my book, a 1% power improvement on a stock Flathead engine is well below 1 horsepower. Being able to consistently measure that small change and then being able to assign a specific factor responsible for the 1% change is beyond the capabilities of most shops in this world.
 
Thanks All for your comments. I just felt that with all the tooling it takes to make just a small change there must have been some concrete research and testing made before making such a large one and documented someplace.
 
Also, back-to-back comparison of flat vs domed 1936 engines would br futile, because everything else about the combustion chamber is also different.
Flathead design is full of details that astound, like the pockets to direct flow off of valve seats, the offsets in the shafts, and so on, all of then rooted in some sort of development history and many of them verifiably pretty good. The olde "Elementary textbook of Automobile engineering" from Ford of England (1935) goes heavily (and frequently beyond my math) on the offsets and reasons for them. I'll dig in and see what they were thinking about pistons. It would also be interesting to see if domes come up in Ricardo....I think this period of flathead change in '36-7 is probably when Ford ran into patent infringement issues with Ricardo on the issue of turbulent flathead chambers.
 
And...resistance to knock was VERY important in the '30's, because some very poor gas was out there and because without automatic transmissions, the lazier drivers lugged engines like crazy to avoid the effort of shifting.
 
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