View Full Version : flathead ohv conversions: flow?


revkev6
06-23-2009, 02:15 PM
i have long been intrigued by the "Oddball" ohv conversion of flathead V8's. I have been pondering the Dixon F-head design as a "mental exercise" to design a conversion that would look like a piece made just post war.

somwhere between a Smith Jiggler and a dixon (how many different versions were there of these, I've seen no less than three totally different designs)

questions i had were mainly to do with flow. The dixon F-head that was built on a 37 block that has been posted up with a dyno sheet put out 148 hp with merc spec B&S. The article didn't mention what was done if anything to help intake flow. with an F-head exhaust I could basically make the exhaust flow as much as needed, but that won't do any good if I didn't match it to the intake flow. Without the exhaust port in the way what would be the max flow for an intake port?? bigger valve, porting, head shape, piston shape, etc.??


so, what would a "modern" take on an F-head conversion for a flathead look like??

I've posted three pics with this thread to get the juices going, one is a smith jiggler, the other three are Dixon heads. two different valve in head conversions (one using a stock intake bolted to an intake built for the dixon heads, the other using external twin external intakes (WAY cool IMO)) the third is the F-head that was run on the dyno.

RichFox
06-23-2009, 02:40 PM
If you were to make a head, wouldn't it make sense to go full OHV?

Ole don
06-23-2009, 02:48 PM
If you were to make a new head, why not use both existing valves as exhaust and one big intake right over the cylinder?

revkev6
06-23-2009, 02:53 PM
If you were to make a head, wouldn't it make sense to go full OHV?


yes and no. performance wise yes it would make sense, but you can already go out and buy an ardun conversion for that. I'm not looking for all out performance because without a huge wallet the bottom end of a flatty can't handle all the power from a hot build full ohv.

another reason to go for the F-head is it would be less work. no intake manifold to fabricate.

revkev6
06-23-2009, 02:57 PM
If you were to make a new head, why not use both existing valves as exhaust and one big intake right over the cylinder?


lots of reasons for this one. problems with the intake ports handling the heat of the exhaust and cracking over time, exhaust pulse mismatch, getting the heat out of the block etc.

not to mention I would have to make some sort of SOHC arrangement for the intake valve actuation.

dana barlow
06-23-2009, 02:57 PM
I turly don't see the point at all,now if ya built a 3 or even 4v per cly,ya still got a junky bottom end. Seems to be fun for the look if out of old stuff for a rod,but new stuff may as well, just get a good bottom end if ya want'ta play .

Casey
06-23-2009, 03:01 PM
although those are cool as hell, why bother if you want a hemi buy a hemi
there``s no reason to use a Flathead block if you don`t want a Flathead

revkev6
06-23-2009, 03:04 PM
odd, different, the engineering exercise, the satisfaction of building something yourself?? aren't these the reasons we build hot rods in the first place??

you could just say, why build a hemi if you can get more power out of a small block??

Bruce Lancaster
06-23-2009, 03:27 PM
F head means huge, meandering combustion chambers as well as probably loss of the rather efficient turbulence of the stock chamber...that means hard to get much compression AND much greater sensitivity to knock at low compression numbers. Why not a simple, primitive looking OHV like a Miller Model A head?
There's even the possibility that an F with OHV could be a great improvement for the wrong end of the cycle...look at how much power a flathead can pick up with blower or nitro, which are huge induction helps, even though there is little that can be done to help exhaust flow. If exhaust were as stuffy as many believe, most flathead hopping wouldn't work...the engine would choke to death on the exhaust side.

RichFox
06-23-2009, 03:34 PM
Well I always thought Willys F head motors were cool since I was a Mo Pool mechanic. Never worked on one since then. But I did put a Y block head on a '32 Plymouth. That was not really the best, most efficent thing to do. But if that discribed me I would be working for some German car firm. If you can pull it off, good on you.

revkev6
06-23-2009, 03:38 PM
bruce, I'm a bit confused by a couple things.

an F-head combustion chamber would be smaller than a stock flathead, how could it be more prone to detonation?? I'll try to find a picture of the jiggler combustion chamber.

I will admit that the turbulence is something I'm not very familiar with (hence the post with question)

the Flow listed in the description of the thread is part of the equation I'm looking for. what are the flow rates of a flatty stock, what has been massaged, and what could be possible by moving the exhaust valve out of the way.

Casey
06-23-2009, 03:41 PM
odd, different, the engineering exercise, the satisfaction of building something yourself?? aren't these the reasons we build hot rods in the first place??

you could just say, why build a hemi if you can get more power out of a small block??

well then I will be routing for ya, and watching good luck with it !
I love flatheads.

Sixcarb
06-23-2009, 03:56 PM
Years ago we had a v8-60 Jiggler setup laying under the stairs in the barn for years and sold it off at some point, I always pictured a regular flathead v-8 with a larger build of the Jigglers or some Riley 4 ports on each side. As far as bottom end I would think that would be the easiet part of the equation......girdle, caps and lighten everything to spin and balance perfect. I'm working on just a carbureted motor right now and still think I should lighten the crank a bit to take some rotating mass off. As far as flow goes has there ever been a comparision among overheads, I'm sure some arduns have probly been done but not the Dixons, Jigglers or Cummins......we could go to Speedy Bills with a flow bench and test motor and start yanking heads off those motors :)

revkev6
06-23-2009, 07:14 PM
sixcarb, If I could get some of the heads off of the motors at speedway, I wouldn't be looking to make my own! I'd take the money and run so to speak! and you are correct, that's exactly what I'm picturing. as for my flow testing, I was looking more towards what you could do with a stock ford intake port for flow.

I did find the pics of the V860 smith jiggler setup, I've read they had a big problem overheating (they don't really look like they have much water flow through them) I'm thinking they were a mainly midget setup for methanol (heat wouldn't be an issue)

miller91
06-23-2009, 07:28 PM
I encourage all mental exercises whenever possible. Don't let anyone discourage you. Check out Uncommon Engineering's design. While your idea might provide improvement, note that Uncommon also supercharges in his application, overcoming the inherent weakness of the flathead's intake flow. I love flatheads, and part of their inherent charm is in their quirky inefficiency which contributes greatly to their signature sound.

http://www.uncommonengineering.com/index.html

Ned Ludd
06-24-2009, 10:02 AM
odd, different, the engineering exercise, the satisfaction of building something yourself?? aren't these the reasons we build hot rods in the first place??

you could just say, why build a hemi if you can get more power out of a small block??

I'll third or fourth that.

I'm rather partial to the idea using the intakes as additional exhaust valves. I'd be inclined to rework the porting, block off the exhaust ports just downstream of the valves, break through into the intake ports, and give the rest of the exhaust runners over to the water jackets. The stock intake ports become the exhaust ports. Then the new (ohc) heads would have intake ports on their outboard sides. I'd drive the intake cams by chains from the exhaust cam, which would be in the stock position.

The F-head configuration can work really well on a blown engine, where one is going for a low static CR. If the intake valves are directly over the exhaust valves rather than over the pistons, one could have a compact combustion chamber and yet retain the quench/turbulence characteristics of the flathead. One can have huge flow, lots of turbulence, and good heat retention, just not a lot of compression. I'd put the spark plug at the extreme upper edge of the head, just above the gasket.

The configuration of the engine suggests dual superchargers located low on the sides: perhaps two Eaton M112s, with a 2" SU on the end of each? I still don't know what to do with the bottom end, though.

panic
06-24-2009, 11:34 AM
I'm beginning some comments here: http://victorylibrary.com/mopar/IOE.htm

banjorear
06-24-2009, 11:45 AM
Some of the beauty and fault of the Smith Jigglers is the lack of coolant flow and lubrication. They did use zerks to grease up the rockers, but leaves a lot to be desired. Since they were designed to be used midgets, they didn't care too much as long as they one. I'd assume that heat would kill these things on the street.

I also say go for it. Hell, why not fab up something different, new, use modern design techiques and materials. You may realize some HP or flow gains from just making sure everything is CC'd & matched equally when compaired to sand casting from back in the day.

Bruce Lancaster
06-24-2009, 12:00 PM
The operative chamber size in a flathead Ford is the open area, the area above valves and the transfer pocket which extends over maybe 1/3 of the piston. The dome is quench area, functionally like thge flat area rhat makes MOST SBC heads effective. Putting valve over the piston is going to enlarge the open area and eat up much of the quench area that makes the stocker effective...a related prob is the design of the valve area. The stock valves are tilted, then there is a bowl are around ech that is effectively an extension of the valve seat angles, offereing further angular transition for the mixture turning into the chamber. I wish I had a block here in the office...but I don't think you can really seal off just one of the stock valves because of the bowl structure, unlike the situation in the purely flattop Model B block. Those things are what I mean about an F approach enlarging the chamber...
Now if you can use both stockers in your design and put new valve over there, you could retain proper quench and a fairly compact chamber.

Quench are as I understand it: The dome are on a flathead beyonf the transfer bulge, like the flat area in an SBC, is volume that ceases to exist at top of compression/firing time. Proper clearance there is as tight as you can make it without impact...typical desired static cold clearance would be only 040 or so, likely meaning less when running hot.
This are shoots the mixture that fills it out towards the remaining open chamber area and towards the spark, creating turbulence that speeds combustion and makes everything more efficient. Engines with good quench function, like tight SBC's and flathead Fords, require short spark lead and tolerate increases in compression. Engines with poor function there require long spark lead to get the combustion done and typically tolerate compression less well...they are more apt to ping and will do so at lower compression than an efficient chamber.
The SBC's history illustrates this...small SBC heads (typically 55--64 cc types) produce more power and allow more compression and less advance than big chamber heads, even if compression is equalized by piston change.
When GM went to round negative area in piston in early smog years, they killed the quench area, and those engines tended to knock even at really pathetic compression ratios. The aftermarket and later corvette engineers finally figured this out, and went to D shaped piston dishes, leaving quench are intact. This, along about 1985, allowed small blocks to have some compression and decent power again...
So look at chamber design in regard to the squish area above piston.
The use of both ports also needs close study...there is a history of A-B blocks cracking at intake when that is used as exhaust. Lots of thought about water jacketing is needed if you are going to send the hot stuff out an intake port. You'll need some study of that area to form a flying guess about the adequacy of cooling around the valve pocket. Using both as an intake would be pretty hairy on a V-8 and I think would almost require fuel injection to avoid having carbs all over the place.

Bruce Lancaster
06-24-2009, 12:03 PM
PS...Mopar flathead, post 17, allows more trickery I think---block is flat with simple vertical valves if my memory is working, and of course all the ports go to same area, allowing easier mods there. All could be hooked to one intake manifold...or the intake vale used as exhaust could open a few degrees after exhaust valve so it wouldn't deal with the hottest gases.

RileyRacing
06-24-2009, 12:08 PM
Watching with interest, but I'm partial to the Riley OHV conversion myself.
Anyone with one of those seven sets wanna pony up for pattern making?;)

I like out of the box thinking...

JK

RAY With
06-24-2009, 02:19 PM
[
I like out of the box thinking...

JK[/QUOTE]
I am in total agreement in the thinking but the bottom line is there is still the lower end to consider and to me thats always been the weakest link. It would be nice though to see something brand new on the top side.

panic
06-24-2009, 06:16 PM
Putting valve over the piston is going to enlarge the open area and eat up much of the quench area

The area is down, but the critical distance from the plug to the leading edge of the quench area may not be much different since the transfer "scallop" isn't needed to direct intake flow down the hole.


I don't think you can really seal off just one of the stock valves

Th usual method is a conical plug that fits into the guide hole, matches the seat, and pinned in place, then milled flat to the deck surface. Obviously, head gasket to suit. If done well, the plug is also the point of passage of the intake pushrod, and the intake rocker oil drain.

RileyRacing
06-24-2009, 09:09 PM
[
I like out of the box thinking...

JK
I am in total agreement in the thinking but the bottom line is there is still the lower end to consider and to me thats always been the weakest link. It would be nice though to see something brand new on the top side.[/QUOTE]

So, put in a bottom end such as "Flatfire" did, and what would the outcome be?
Everybody is so concerned with bottom end issues, but, I ask, did it bother the Ardun brothers? Wayne? George Riley?

In 21st century thinking, of course, 3 mains will never work. We get flow but can't spin RPM's... or can we? Improved oils VS bearing area?
Asked in the context of the original poster, think in 1937 terms?
Chevrolets were still using dipper rods... Wayne conversion... consider a 216 at 2 HP per cubic inch on nitromethane, would an F head really be that much worse overall?

If you take away the 21st century mentality and stick with what would have a guy have done in 1937... would this idea work? I bet it would.

Just the rant after a few too many Red Snapper ales, but the question stands...


JK

Henry Floored
06-24-2009, 11:47 PM
To put this in perspective the Novi V8 that raced at Indy had three main bearings. Additionall the Flathead Ford has a ton of bearing area and hefty main webs. Maybe some sturdier main caps and high end fasteners would be good insurance.

Don't have much to add about doing a modern version of an "F" head. Only that I'd try it first by cutting up a readily available aftermarket cyl. At least in the mock up stage.

revkev6
06-25-2009, 08:26 AM
To put this in perspective the Novi V8 that raced at Indy had three main bearings. Additionall the Flathead Ford has a ton of bearing area and hefty main webs. Maybe some sturdier main caps and high end fasteners would be good insurance.

Don't have much to add about doing a modern version of an "F" head. Only that I'd try it first by cutting up a readily available aftermarket cyl. At least in the mock up stage.


lots of good thinking and ideas coming in guys, bruce, I gotta think some more on the explanation you gave about the combustion chamber. I really like henry's idea of starting with an aftermarket cylinder.

I wonder if companies like offy or edelbrock ever get seconds or bad castings that would need repair work. Not like I wouldn't be welding up the head a ton already to cover up the old exhaust valve and starting with clean better quality aluminum would be a plus.....

one thing I'm thinking about the lower end is stroke. If we are talking about significantly increasing flow I think stroke is going to come into play as a limiting factor to RPM with the three mains. what if we destroked a stock ford crank to 3 5/8"?? go out to 3 3/8 or 3 7/16 on the bore (iffy I know) but you would still get more cubes than a merc (259 on the 3 3/8ths bore). lighten and balance the rotating assembly up as much as possible


one other thing I want to mention. if I go with intake in block and exhaust overhead, what do you guys think about increasing the intake valve size?? Could you get enough flow through the port to justify the valve size?? I found the thread last night that had a cutaway of the intake and exhaust ports. Things looked awfully tight through there....

banjorear
06-25-2009, 08:32 AM
Offy use to sell unmachined head cores. Not even the combustion chamber was machined. Not sure if they still do. Keep us posted.


lots of good thinking and ideas coming in guys, bruce, I gotta think some more on the explanation you gave about the combustion chamber. I really like henry's idea of starting with an aftermarket cylinder.

I wonder if companies like offy or edelbrock ever get seconds or bad castings that would need repair work. Not like I wouldn't be welding up the head a ton already to cover up the old exhaust valve and starting with clean better quality aluminum would be a plus.....

one thing I'm thinking about the lower end is stroke. If we are talking about significantly increasing flow I think stroke is going to come into play as a limiting factor to RPM with the three mains. what if we destroked a stock ford crank to 3 5/8"?? go out to 3 3/8 or 3 7/16 on the bore (iffy I know) but you would still get more cubes than a merc (259 on the 3 3/8ths bore). lighten and balance the rotating assembly up as much as possible


one other thing I want to mention. if I go with intake in block and exhaust overhead, what do you guys think about increasing the intake valve size?? Could you get enough flow through the port to justify the valve size?? I found the thread last night that had a cutaway of the intake and exhaust ports. Things looked awfully tight through there....

Ned Ludd
06-25-2009, 08:37 AM
...
one other thing I want to mention. if I go with intake in block and exhaust overhead, what do you guys think about increasing the intake valve size?? Could you get enough flow through the port to justify the valve size?? I found the thread last night that had a cutaway of the intake and exhaust ports. Things looked awfully tight through there....

Do you have a link? I'd like to take a look at that myself. I'd thought of exhaust-over-inlet myself; it's worth a look. It'd really free up plug position.

Bruce Lancaster
06-25-2009, 08:43 AM
Intake size increase is meant to increase the curtain area of the section where high flow exists in a flathead, basically the edge of valve towards cylinder. Total area isn't the issue. Back to my secret hinged valve tech...

"Everybody is so concerned with bottom end issues, but, I ask, did it bother the Ardun brothers? "

Actually, according to an ancient interview the bottom end was the genesis of the idea!
Right after WWII, Duntov was a smuggler, running heavily taxed goods and gold from areas of supply to areas of shortage where the borders of France, Germany, and the low countries met; Method was late-night runs in his '37 Ford.
He noted that the stock flathead was totally beyond its range at 5,000 R's, but when he went over a hill with the car loaded to the windows with smuggled goodies, it happily ran up to 7,000 on the downhill run flat out.
At the time, he was runnin a French race car in road races, one of the minor Bugatti-like cars(Delage??), and the 7,000 RPM the flatty was surviving was WAY past the bursting point for the DOHC race motor. Duntov realized that the Ford wanted more air...
Remember the the Flathead was probably the first common engine that could be souped to the gills, used or new, WITHOUT need for flogging the bottom end...just exactly like low buck SBC's nowadays. Oiling system was identical to SBC* and needed no mods, mains were adequate, rods were the best on the planet. When OHV engines first began revving past rod survival, racers transplanted 1942 Ford rods into Small block Chevies!
The locked rods on modern engines had to be rather crudely improved in two areas to survive at high RPM, while the old floaters were almost proof against "throwing" by inherent design.

*If you examine a Flathead and a 350 side by side, you will inescapably conclude that Henry stole the oiling system design from the SBC, deleting only the hydraulic lifter galleries.

miller91
06-25-2009, 08:49 AM
I think RileyRacing has the right idea...think in "1937" terms. While useful, applying modern perspective here will only convince you to abandon the project. And while the 3 main bearings are always a worry in a built flathead, the realistic horsepower gains from an F-head probably won't contribute enough power to compromise this. The core idea is to come up with an early looking (and performing) unique flathead that fits within the pre-war to just post-war period. My take on these early OHV designs is that they lean heavily on some of the ideas of the brass era racing engines with exposed valvetrain, and then enclose the valvetrain against total loss and provide pressurized lubrication. The "jiggler" in particular reflects this I believe. While Riley did make OHV conversions for the V8, a possible way to do this would be to take the general design of the Riley 4-banger OHV's, and apply it to the 8. In fact, that would be a neat way to do it, using similar valve plugs and valvetrain covers. Riley's drawings are out there regardless for brain food. You would be the only guy out there with one, unless it really works and you sell them. There is some demand to stand out from the flathead crowd which amazingly is probably as big, if not bigger than it ever was.

revkev6
06-25-2009, 09:41 AM
well, there's nothing modern about an F head design, thats for sure!, the only "modern" thinking i want to encorporate is to match the flow as closely as possible. We know a bit more about chamber design and getting a flathead to breath than we did 40 years ago and I wouldn't want to lose chamber effiencey or make the exahaust ports so large that they lose velocity.

miller91
06-25-2009, 09:58 AM
Yes, challenging with a pushrod F-head placing a valve right over the piston crown. Some guys with obvious expertise have already posted, so calculating volumes and port sizes shouldn't be an issue. That valve placement is problematic, but the stock exhaust valve pocket would be eliminated in your chamber design I would think? And where to place the plug...A fun problem to puzzle over.

revkev6
06-25-2009, 10:39 AM
ned, here is the pic of the intake port cutaway curtesy of vergil on the hamb. he's done an exhaust port cutaway as well. both of these are very enlightening!:

http://www.jalopyjournal.com/forum/picture.php?albumid=4136&pictureid=48257