Flathead valves and flow??

R

revkev6

Senior Member
Valve flow!

I know I should just order up a book as I'm sure it's in JWT's but I have a couple questions on valves and angles.

I've read discussions on valve flow in a flathead stating that 30 degree valve jobs flow better than 45 as they push the flow more parallel with the face of the transfer area (vs an OHV engine that you want the flow mostly parallel with the cylinder walls) this makes a lot of sense to me.... now thinking along those lines I have also read that a lot of guys are using SBC manley stainless valves in their motors.. they are undercut and flow better than stock ford valves.... BUT.. in looking at exhaust valves vs intake valves there is a pronounced difference in the radius that leads to the underside of the head of the valve. an exhaust valve needs to absorb more heat and doesn't need to flow as much (in an ohv, this has been somewhat debated in a flathead I believe) so the manley valves which still flow better than a flathead are a cheap easily available performance upgrade. but comparing them to the same SBC intake valve it appears that we could still gain some more...

the manley 11521 1.5" stainless undercut polished etc exhaust valve has a 12 degree under head angle vs the 10 degree under head angle of it's corresponding 11506 1.84" intake valve.. it seems to me that the under head angle would be as helpful to directing flow parallel to the deck as the valve seat angle. I'm guessing that I'm not hitting on anything new here.. but has anyone cut down a 1.84 intake valve to see what the gains are over using the exhaust valve??
 
manley 1.5" exhaust valve:
Exhaust Valves

Type: Exhaust Valve XH-426 Material
Head Diameter: 1.500''
Stem Diameter: 11/32'' / 0.3415''
Installed Height: Stock
Overall Length: 4.911''
Tip Length: 0.250''
Underhead Angle / Radius: Pro Flo 12° x 3/8''
Margin: 0.060''
Seat Width: 0.100''
Top of Head: 7° Dish
Weight / Grams: 89


660-10721-1.jpg


manley 1.84" intake valve:
ntake Valves
Type: Intake Valve NK-842 Material
Head Diameter: 1.840''
Stem Diameter: 11/32'' / 0.3415''
Installed Height: Stock
Overall Length: 4.911''
Tip Length: 0.250''
Underhead Angle / Radius: Pro Flo 10° x 3/8''
Margin: 0.060''
Seat Width: 0.080''
Top of Head: 5° Dish
Weight / Grams: 104


660-10722-1.jpg


they both use a 3/8 radius but the underside angle is 2 degrees different as well as the seat width being larger for the exhaust valve. I'm assuming the seat is ground at 45 degrees anyway so this would be set to whatever you would like when the valves are ground
 
30 degree valve cuts and/or various radius valves are not going to make a noticeable difference in performance. Yes it will help, but you will won't see it.

A professional port & polish will provide the most improvement.
 
rotorwrench said:
This is one of the reasons folks usually recommend you read JWL's book.
Click to expand...

yes... it's in my birthday wish list which my wife has said doesn't exist since I just bought a complete rusted out 46 ford for the driveline... she says that's my birthday present :p

Daryl Middlebrook said:
30 degree valve cuts and/or various radius valves are not going to make a noticeable difference in performance. Yes it will help, but you will won't see it.

A professional port & polish will provide the most improvement.
Click to expand...

the next flathead I build will be a large cube motor and is going to get as many flow improvements as I can manage on my budget. I don't pick and choose... I try to address everything as a system. It will be ported, possibly a larger intake valve with associated machine work required.

before I do anything on it I'm going to do a lot of reading... like JWL's book and fordbarn and the HAMB
 
A good thinking tool: Dave Vizard's "How to Build and Modify Chevrolet Small-Block V-8 Cylinder Heads."
DV might be one of the most sophisticated writers around, and his analysis of results for different sorts of mods to ports, seats, and valves is great transferable theory.
A Chevy port is kind like an upside down flathead port...but of course the relatively huge bowl and the upside-down entry into the cylinder allow a lot more of the curtain to be useful. But...the theory shown, discussed, and tested in this book is certainly transferable.
 
And...remember the Late, Great Flatdog's flow experiments...he developed clear plastic head chambers so he could watch, and did the flowing in his garage with a huge vacuum cleaner and kitty litter!
His 3,000 pound '34 got into the high 12's and was still a smooth, driveable street car. I was privileged to drive it for a hundred miles or so on a trip once, and it was astounding.
There was no curve in the torque curve...simply as much torque as you wanted whenever you wanted it.
 
Boy, I love this thread. In my book I have some pics of the valves we used in the stock cars. Many hours on a flow bench proved the value of this to increase flow. When building an intake valve O use a 3/4" round carbide incert to cut the underside of a stock 2 piece Chevy valve. I feel these are much better than The SS valves made by the aftermarket, except for the chrome stem unites. Along with the 30 deg seat angle. Unfortunately, the real problem with intake flow is the shape of the port, especially the bowl. For a stree engine, reliability is more important than high power. In Richards engine we used unmodified SBC valves and no port modifications. Just a tight combustion chamber and hi compression. (8.5) The heavy 53 HT Ford had all the low end power you needed. For a mild street engine mods to the ports just remove material from the top of the port. Use a micrometer to measure the thickness of the casting through the water jacket. I bring this down to .100"and radius the output. On the flow bench this increases flow quite abit compaired to other areas. Also filling the bottom of the port also improved flow. Yes Flat Dog was on the right track and gave me allot of Ideas. The biggest problem with flow benches is::: They are addictive, once you start, you can't stop. I do believe the "Holy Grail" of the port will be found, I keep looking for it but?? The stock flathead is a 4L engine in to days automotive world. Most of them make double the power. Increasing the displacement of the flathead, only makes the ports work harder. Blowers do work.
 
revkev6 said:
Valve flow!

I know I should just order up a book as I'm sure it's in JWT's but I have a couple questions on valves and angles.

I've read discussions on valve flow in a flathead stating that 30 degree valve jobs flow better than 45 as they push the flow more parallel with the face of the transfer area (vs an OHV engine that you want the flow mostly parallel with the cylinder walls) this makes a lot of sense to me.... now thinking along those lines I have also read that a lot of guys are using SBC manley stainless valves in their motors.. they are undercut and flow better than stock ford valves.... BUT.. in looking at exhaust valves vs intake valves there is a pronounced difference in the radius that leads to the underside of the head of the valve. an exhaust valve needs to absorb more heat and doesn't need to flow as much (in an ohv, this has been somewhat debated in a flathead I believe) so the manley valves which still flow better than a flathead are a cheap easily available performance upgrade. but comparing them to the same SBC intake valve it appears that we could still gain some more...

the manley 11521 1.5" stainless undercut polished etc exhaust valve has a 12 degree under head angle vs the 10 degree under head angle of it's corresponding 11506 1.84" intake valve.. it seems to me that the under head angle would be as helpful to directing flow parallel to the deck as the valve seat angle. I'm guessing that I'm not hitting on anything new here.. but has anyone cut down a 1.84 intake valve to see what the gains are over using the exhaust valve??
Click to expand...
Before you go buying valves you better decide if your going to change the cam,different base circles affect valve length and valve seat affects valve length
So if your rebuilding and updating the cam have someone cut the valve seats first than get the cam so you can get the proper valve length .
Your adjustments are limited with the lifters and also the gain in flow in 30 degree seats are so small and the longevity of the seat is less because of the shaper edge
And you ask how does he know this well after 45 years of building engines I decided to build a little simple Flathead Wrong there is more hidden secrets in these engines than building a Duesenberg
Good luck
 
Something to consider when doing mental port work before you get to sleep: Air is pushed into the cylinders, not pulled. It makes a difference. We sometimes think the air/fuel mixture is pulled into the engine by vacuum, but it's not. Atmospheric pressure pushes it in. So wherever there is a narrowing of the intake tract or sharp turn, the air "piles up", slows down and fuel drops out of suspension. The resulting turbulence also impedes air flow into the cylinders.
It's easy to visualize the piston pushing exhaust gases out, but maybe harder to visualize atmospheric pressure acting like a giant piston pushing air through the intake tract.
 
Ol' Ron said:
Boy, I love this thread. In my book I have some pics of the valves we used in the stock cars. Many hours on a flow bench proved the value of this to increase flow. When building an intake valve O use a 3/4" round carbide incert to cut the underside of a stock 2 piece Chevy valve. I feel these are much better than The SS valves made by the aftermarket, except for the chrome stem unites. Along with the 30 deg seat angle. Unfortunately, the real problem with intake flow is the shape of the port, especially the bowl. For a stree engine, reliability is more important than high power. In Richards engine we used unmodified SBC valves and no port modifications. Just a tight combustion chamber and hi compression. (8.5) The heavy 53 HT Ford had all the low end power you needed. For a mild street engine mods to the ports just remove material from the top of the port. Use a micrometer to measure the thickness of the casting through the water jacket. I bring this down to .100"and radius the output. On the flow bench this increases flow quite abit compaired to other areas. Also filling the bottom of the port also improved flow. Yes Flat Dog was on the right track and gave me allot of Ideas. The biggest problem with flow benches is::: They are addictive, once you start, you can't stop. I do believe the "Holy Grail" of the port will be found, I keep looking for it but?? The stock flathead is a 4L engine in to days automotive world. Most of them make double the power. Increasing the displacement of the flathead, only makes the ports work harder. Blowers do work.
Click to expand...

wish you were just a tiny bit closer ron! I'm in the springfield mass area and would love to be able to pick your brain in person as I went through a build. with a first time port job I'm going to be nervous about water...
 
If your building a street engine, don't bother. ANY Porting is only beneficial at higher RPM's. The forum here is discussing methods for improving flow, and we compare notes for better ideas. Over the past 80 or so years, some of us have tried to get better volumetric efficancy from these engines. And as one person has said, air is pushed in amd bloweres do just that. Porting a street engine is a basic waste of time. If Roller cams with 450 lift and re placing the present ports can't do it, then why bother.
 
Kev
If you place an angle finder or straight edge at the same angle as the valve face area (30 or 45 degrees) and make a measurement to the combustion chamber on "most stock or after market heads", you will readily see that the 45 degree is closest to being correct to direct the charge to "bounce" off the chamber and into the cylinder.
Next, it's probably impossible to put a 1.84" valve into a flathead, but easy to use a 1.72" valve, which are available.
If you accept that as a possible improvement, then the next step is to provide as much net lift as possible. The lift is probably much more important than the valve size.

Also agree with OlRon re porting. Unless you are building a real power house (like Dale B&S)
who has tremendous patience, just cleaning up the stock ports will be just fine.
If you have the time, look up some of B&S's posts re porting. He's done a magnificent job.
Wish I had the skill
JMO
Jim
 
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bother because it's fun! this will be going into a 32 ford with a 39 box and a banjo with 3.78 gears. my 28 has a basically stock 8ba in it with heads and intake... runs like a top although she's long in the tooth at 25 years since we built it. that one I'm tearing down and checking it out and just putting it back together. gaskets paint and valves adjusted... maybe a valvejob and a cam if the leakdown is excessive.
 
I am currently building a turbocharged flathead to race at Bonneville. 1.8 intakes and 1.625 exhaust. Those are cut down from the 1.84's you described. Waiting for my block to come back from the machine shop. 3.268 bore with really small metric rings.
 
saltracer said:
I am currently building a turbocharged flathead to race at Bonneville. 1.8 intakes and 1.625 exhaust. Those are cut down from the 1.84's you described. Waiting for my block to come back from the machine shop. 3.268 bore with really small metric rings.
Click to expand...

What are the rules for your class? Not really clear on rules but thought they limited most flathead classes to superchargers
 
we are running our current flathead in a 1985 Mustang body, which is not considered Vintage.......so as such we are allowed to do must anything to the engine, like supercharge, turbocharge, centrifugal, electrical fuel injection, move the ports around. Pretty much the same as a streamliner I guess. XF/BGALT flathead blown gas altered
 
As everyone knows, searching for the maximum potential flow involves much more than seat angle and stem design. In addition to port and bowl shaping the cylinder head must also be considered.

The better seat angle after major port and bowl modifications are done is around 37 degrees. However, custom machined valve underhead designs can closely reach the same potential with 45 degree seats.

Actually, net valve lift is NOT as important as valve size. The REAL truth is the stock valve can be COMPLETELY REMOVED and flow changes little after around .350 lift and from .400 to .500 the measurements are only necessary to help the operator believe what he is seeing. If porting work is successful a bigger valve and larger diameter bowl, with a good shape, can be used and will step up the low lift flows to almost double the stock valve. But, even this begins tapering off at around .400 lift.

With all that said, there is the "quality" of the flow to be considered. Maintaining a completely homogenous mixture gulp into the cylinder can outweigh the maximum flow system when searching for power.
 
saltracer said:
we are running our current flathead in a 1985 Mustang body, which is not considered Vintage.......so as such we are allowed to do must anything to the engine, like supercharge, turbocharge, centrifugal, electrical fuel injection, move the ports around. Pretty much the same as a streamliner I guess. XF/BGALT flathead blown gas altered
Click to expand...

Sounds fun. How small of a ring pack will you run with that turbo? Psi? Anymore specs you would like to share on the motor?
 
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