Flathead breathing

Deuce Man

Deuce Man

Well-known member
I know you guys will probably say that I have too much time on my hands, but here is what is on my mind. In reading Verns flathead book, and admiring the beautiful metal sculpturing they do with the intake and exhaust ports, I got to thinking that the valve/open area at full lift, is only about one half the open area of the port runners. Is this on purpose or is it a design limitation of our beloved motors? Do a little math and see if you guys come up with the same figures as I do. Thanks Rich
 
Flatheads do have limits in the valve area, but to some extent so will almost any engine. The runners are almost always larger than the valve area. The valve stem alone is going to block flow and decrease area. I think most test have shown that increasing valve size in a flathead does little to improve flow and/or performance until you get into a very highly modified engine.
 
First, use some of that time on your hands to cruise old book stores for books and magazines from the '40's and '50's that described how to modify a flathead. Then search the internet for more recent thinking on the subject. Look for dyno tests and race results, such as Bonneville. Find information on what Harley Davidson did to the heads, ports and valves on their flathead twin race bikes. Pick the brains of any and all flathead experts you can find. Next pour all this data into a big bowl, stir well and ingest. You will now be the world's most knowledgeable authority on flathead power-making, as well as thoroughly confused!
I'm not poking fun, just making the point that flathead airflow has been analyzed and dissected by many people for many years!
 
I think you're right! Any new ideas on what to do about it? This probably explains why flatheads respond well to super charging.
 
maybe some of the guys on here that racedthese engines will have a good idea on porting and valve sizes that worked well????
 
The intake system of the flathead has been modified in one way or another for the past 80 years and the only way to improve the power output isnitro a blower or both. Be interesting to see the comparison of hP output from a stock port to a big valve port. JWL's book had one, didn't do much better.
 
The valve is NOT the major restriction most seem to assume. After performing hundreds of flow tests on nearly as many modification levels I will tell all that after .450 lift the valve can be COMPLETELY REMOVED from a seriously modified port and there is almost NO INCREASE in flow. Big valves(here I mean 1.7 or more) provide the majority of their increase at lifts up to .150 but don't do much after that. If it is a fight for every silly CFM many hours can be spent on a single port aiming to smooth and calm the path. Sad to say Ol'Ron can do a standard port clean-up of all ports in 4 hours and get close results.
 
What I am thinking is that almost one half of the fully opened valve is walled off by the cylinder head. I know that it might lower the compression, but could you grind a relief into the head to let some of the gas flow around the back or top half of the valve? Maybe my math is wrong, but with .400 lift, with one half of a 1.5 inch valve in use, there is only .942 inch of open area to flow the needed gas/air mixture.The ports are roughly 2 square inches of flow area. The harley K motor research dealt mostly with an exotic relief in the deck, didnt say much about the head. I am still stuck on unshrouding the upper half of the valves. Make sense? Rich
 
I have always heard that a flathead cant suck enough air fuel to hurt itself. Hold it wide open and it will run out of air at some point. rbg :>)
 
No, I don't think much flow increase can be had from increasing these areas. Having used a flow bench, it becomes addictive to find the holey Grail of flow and you try anything you can think of to improve it. On a junk block I went into the water jacket and even shaped the port with Bondo, but never found it. I did improve the flow from stock, but not by much. Back when the 4.2 V6 engine was used in NASCAR I was in a shop that was modifying these engines. This was while I was writing my book. I watched one of these engines put out 450 HP and was impressed. I asked what they did to the head to improve the flow? I was told that some of the heads they tested had great flow numbers, but produced less power. I'm not sure why this is, I think there are too many Variables.
 
Deuce Man said:
What I am thinking is that almost one half of the fully opened valve is walled off by the cylinder head. I know that it might lower the compression, but could you grind a relief into the head to let some of the gas flow around the back or top half of the valve? Maybe my math is wrong, but with .400 lift, with one half of a 1.5 inch valve in use, there is only .942 inch of open area to flow the needed gas/air mixture.The ports are roughly 2 square inches of flow area. The harley K motor research dealt mostly with an exotic relief in the deck, didnt say much about the head. I am still stuck on unshrouding the upper half of the valves. Make sense? Rich
Click to expand...

These engines have been modified, dyno'd, flow tested and track tested for over 75 years. It is a fairly easy task to read up on about any aspect of improving breathing. I will bet that any modification you could ever dream up has been tried and tested (and not just once, but repeatedly over the years!).

One note about any engine, what seems like a good idea in your head or on paper often does not pan out with put to the test! Odd but true.
 
The size a flathead chamber has to be to work at all and all the tight twists & turns the flow has to make due to the design are a limiting factor. The limit on cubic inch displacement is also a factor. There aren't many tricks left to make them better that haven't already been tried at one time or another over the years. FoMoCo did a fair job of getting them to work at a horse power range that was quite acceptable for the era.
 
A lot of the Harley KR race guys did do work to the backside area of the head, to radius it to "supposedly" give the air a place to turn and come over the top of the valve at low lift. My neighbor was a big KR builder - he had every dang type of head they made . . . and he claimed that it did work. His engines ran extremely well and he won a lot of races with them. I also have heads, barrels, cam stats, etc..

Given that the Harley KR was/is the most advanced flathead probably ever built - and these guys had only 2 cylinders to work with, I tend to believe him. With that said - the whole KR combination was purpose built, had tons of hours of flow and dyno testing on the COMPLETE package . . . heads, pistons, ports, cams, intake, carb, etc.. In my mind, one would have to work with a specific combination to really maximize flow characteristics - with a ton of dyno work to boot.

JWL has probably done the most dyno work in recent years . . . and yet I'm also sure there are a lot of things that have yet to be figured out (by he or anybody else). Good luck - keep experimenting, keep trying new things and never give up . . . I sure as Hell haven't! :)
 
If I was chasing every last ounce of power I could get from one of these (normally-aspirated) Flatties, I would definitely consider some .312" valve stems (or smaller), maybe a 1.550" valve, and possibly have the block extrude-honed (if possible) after hand-porting as much as possible. This would take care of much of the porting through 100% of the passageways. Not sure if Extrude-Hone could pull it off, never inquired, but this would help.

Thanks, Gary in N.Y.

P.S. If it could be done I think it would require some "very-deep-pockets" without a doubt!
 
Thanks for all the input guys. After reading about all the finer points of porting the beloved flathead and finding this drastic reduction of flow area at the valve I was just wondering if all the port work is worth it? Maybe the combustion chamber in the head deserves another look? It seems like there is not much that can be done with this area to maintain the square inches of flow that we have through the manifold and intake/exhaust ports. This valve/combustion chamber area seems like the old washer in the water hose situation. I am sure that our motors have the potential to put out quite a bit more horsepower today than what was possible in the old days. A good friend who happens to be a major speed equipment manufacturer, raced vintage sportcars. My pal told me that these old cars are turning much faster times today with amature drivers than they did with the pros 50 to 60 years ago. He credited it mostly up to modern technology {more horsepower} and better tires. We have the same things available to us for our engines today! Thanks Rich ps. maybe the turbulence at the restricted valve area makes up for the small area of flow.
 
I've spent considerable time studying the Ford Flathead engine blueprints while creating my computer model as accurately as I could following the print, 8 months of concentrated effort in fact.

I found it surprising that the intake port shape as represented in the prints is not exactly the same as the actual block I have. What is in the factory print is a shape that will produce a higher maximum horsepower number while the actual production port seems to be adjusted to produce a better torque characteristic within normal operating RPM ranges.

The Ford engineers knew, in my opinion, exactly what they were doing and , again in my opinion, did a damned good job of it on the intake side of it. They apparently had no need to fine tune the exhaust side. Simply put there is little to no advantage in modifying the exhaust when the engine is operated in any street driven manner.

The port shape in the prints has a shape characteristic that is favorable to higher RPM HP. I have accumulated a few books on the performance of internal combustion engines and one by David Vizzard gives insights on how important shape of the port and runner is the primary consideration for optimizing performance at whatever RPM range you choose for your particular combination of parts.

I have done a fair amount of flow bench testing primarily aimed at combustion chamber shapes and spent a couple months or more in intensely focused effort to achieve certain performance goals. I set goals, achieved them and each time set a higher goal.

I managed to achieve a 13.3+ second quarter mile dragstrip time for a street driven daily driver hot rod normally aspirated Flathead on pump gas.

I'd be curious to know if anyone currently is doing better or interested in taking on the challenge. My age and physical condition is such that I'm not going to pursue the next logical goal of getting into the 12 second e.t. range and over 100 mph.

I did achieve 25 mpg when shooting for a max number there and a 115 mph when going for that goal, somewhat limited by safety considerations and certainly limited by aerodynamics of a full fendered 1932 3 window stock bodied coupe.

My engine has a Merc crank 4" stroke and 3.268" bore, 83mm actually. Cam is a street friendly grind, not a rumpity rump.

I did get chassis dyno testing done between modifications, but the dyno guy refused to charge so I don't abuse that. I didn't get one for my latest modification. The test results are relative to my engine only and only reveal if I have made progress.

At one point in time a few years ago my engine was on JWL's dyno, believe me, he does not fudge, nothing but the facts is his deadly serious approach, and as I remember I got near to 150 hp.

JWL has been my inspiration all along and I would like to publicly thank him for that.

Flat32:cool:
 
Another man I have a great respect for, He's honest and does what he says. I had the honor of driving his 32 back in 02 when John and I went to Bville
 
Being only partially aware of the enormous, technically detailed, work Flat32 has accomplished I am honored that he would even remember my name. No other person I know would be willing to make a total commitment to become a master of Solidworks 3D and Mastercam so as to transform original Ford drawings plus his personal ideas and concepts into finished parts he uses to improve his car.

Too, I want to thank O'Ron for his thoughtful suggestions.

Thanks for the mention,
JWL
 
Damn!!
I'd love to be sat at that table next time you guys get together!
The stuff to be learnt from you three is huge, just listening would be awesome. I do ask a lot of questions though, I'll never be done learning.
Martin.
 
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