Flow VS. Turbulence

[Greaser]

My son and I have been planning a Big Six build up and are working with the head right now. We cut a couple of section profiles of IN/EX ports and noticed that the intake runner tract looks like it would flow alright but the exhaust runner looks like it has one heck of a pinch point in the transition from pocket to runner. Before we just start digging I will set up a flow bench to see what works and what don't.

Well I was reading an article about ignition timing and it stated that once an engine reaches a certain RPM (About 9000 rpm I think) an engine doesn't benefit from more timing advance because the air/gas mixture is so turbulent that it is mixed about as good as it will get.

I know that you don't just want to port as much as possible since large high CFM ports have terrible velocity at low RPM's, low velocity means fuel dropping out of suspension and less turbulence so I need a port that flows it's max at my desire peak RPM which is much lower that most other engines.

So my question is how do I introduce uniform turbulence (is there such a thing) without destroying flow? I have read that leaving the short side radius of the intake port alone or sharpening it creates turbulence. We are planning on using the EFI head because of the fast burn characteristics, but then you have valve shrouding, expecially at low lift. I thought that undercutting the shrouding around the intake valve would help low and moderate lift flow as well as introducing an edge that would cause more turbulence. Transition from modrate to max lift would see not as much benefit though. Also thought of cutting grooves/rings on the back side of the intake valve with the lathe.

Anyone have any comments or ideas? I am a firm believer of there are no stupid ideas, some ideas don't always work but they are good starting points.

[Asa]

well, unless you're setting one up like FrenchTownFlyer did, you really don't need to worry about what happens at 9000 RPMs
how much power are you trying to get? what's the application for the motor? if you're planning a street/strip truck i doubt you'll really need to worry about turbulence other than making sure the head flows well

if you're trying to get every ounce of power for drag strip racing for money? yeah i could see it

[Thad]

One little caveat. When porting don't open the port at the gasket face too much. There is no aftermarket intake manifold that can be opened up to match. Got carried away and my finished port ID was larger than OD of a Clifford manifold.
There is good results in pocket porting including the short radius then blending into port runner. Cleaning up port runners, don't polish but finish with 60 grit hard roll.
The fast burn head was developed more for emissions than power. A carb head will make more flow/ power than what is possible with the fast burn.
Welcome and good luck.

[Greaser]

well, unless you're setting one up like FrenchTownFlyer did, you really don't need to worry about what happens at 9000 RPMs

You miss understand me, I am not shooting for a 9000 rpm engine, I want my peak torque in the 3000 rpm range. I just want as much turbulence as I can at the CFM my engine needs. Just mentioned the 9000 rpm engine to say that it sounds like the turbulent flow is a good thing since it mixes the fuel/air better allowing me to back off the timing advance.

how much power are you trying to get? what's the application for the motor? if you're planning a street/strip truck i doubt you'll really need to worry about turbulence other than making sure the head flows well

I want the motor to run as efficently as possible. Do I want 300 hp. and 450 lbs. torque, you bet, but I am not going to put on power adders to cover up bad design. I will settle for a solid engine that makes 275 hp and 325 lbs torque and gets close to 20 mpg, I think this is very possible.

One little caveat. When porting don't open the port at the gasket face too much. There is no aftermarket intake manifold that can be opened up to match. Got carried away and my finished port ID was larger than OD of a Clifford manifold.

I the past the way I port match is to bolt the intake to the head without the valves in, hook a shop vac up to the intake seat and lightly spray flat black paint into the intake, then reverse the shop vac to the carburetor flange and spray the paint into the valve pocket. Let it dry then tear it down and anywhere the runners are mismatched it is painted black.

The intake manifold will be a custon made twin carb, those stock log style manifolds with the 90 deg. bends are a joke. Ford didn't make them because they made power, they made them because they were cheap and easy to make, deffinetly not very efficent. The Cliffords and the Offenhausers may be alittle better but you can't tell me that the motor likes having some runners 3" long and some 12" long. You can use intake runner length to tune where your torque comes on at, long runner engines make power down low, short runner engines make power up top. So with those single carb set ups you got some cylinders wanting to run strong at low rpm's and some wanting to run strong at high rpm's and the whole time some cylinders dragging the others along, NOT effecient.

Just because Ford built a truck motor that is a legend doesn't mean thay did every thing they could to make it that way. There is alway room for improvement.

[Thad]

My understanding of intake flow dynamics is that laminar flow in the port runner and through the valve is desired then turbulence in the combustion chamber during compression and ignition.

[THE FRENCHTOWN FLYER]

Greaser, You ask some great questions that shows you have given your project a lot of thought. But let me try to talk you out of grooves in the valves as it will introduce both physical and thermal stresses which will lead to a short valve life. Also, opening up the mask around the intake will enhance flow but at the expense of burn rate. The burn rate "flalls off a cliff" if you go past 3mm mask clearance, which unfortunately is way too tight to flow well. A higher lift cam might just be a good compromise instead of increasing mask clearance - I dunno - just speculating here. The fast burn qualities are accomplished more through micro turbulences than by wholesale swirlling of the entire charge. Masking, quench, plug placement, chamber and piston design, and compression ratio all play a part.

Fast burn and good flow are at odds in our engine - helping one generally will hurt the other.

BTW, when this engine was first designed the intake ports were actually bigger and more rectangular. Making them rounder and smaller helped the flow.

[FordJim]

I don't have any personal experience with porting the stock 300 head, so I am just asking a question here. Is it realistic to hope for 9000 RPM with the stock head? The casting, especially the runners, are pretty thin walled. Can the stock head even be ported enough to support 9000 RPM?

[Buddy Rawls]

...Is it realistic to hope for 9000 RPM with the stock head? The casting, especially the runners, are pretty thin walled. Can the stock head even be ported enough to support 9000 RPM?...

For a 50 cid/cyl to be able to achieve a proper cylinder fill and port velocities at 9000 rpm, requires about 320 cfm (28") to even begin getting close.

The factory head appears to really begin maxing out between 230 and 250 cfm, which will get you pretty near 7000 rpm. Not inertia revving, but actual power making and cylinder fill, which requires correct valve events.

throw that well worked 230-250 cfm on a 240 cid and you have some very nice capability, up near 9000

These have nothing to do with the structural integrity of the block and rotating assembly actual being able to run this, or the valve train capable of accepting the components needed. For example, they cant take a lot of spring load because there is no core support inside the head.

the tried and true build is to take advantage of the motor's geometry and build to that, taking advantage of what it has to offer.

1) high port velocity makes for good cylinder fill potential and awesome torque. The deal is, it needs to happen in the 2000-5000 region. this means it has the potential to be very flat and powerful from idle onward
2) correctly addressing the inlet and exhaust capability to the cylinder and its flow demand (cid and rpm)
3) correct valve events to make it all tick
4) static compression to compensate for the valve events and provide some supplemental help within the limits of the ignition and chamber design.

treating the 5000rpm set-up as a 9000 rpm set-up (with its own requirements) is 100% valid. the problem comes in how to apply the 9000 rpm situations, in the meaningful sense. Taking things verbatim are not going to work. Applying the trends (the correct trends) are what will allow it to work. The same things that happen at 9000 rpm can happen with different combinations at different rpms. It's all cross-sections and displaced volumes. there is no magic at 9000. there was magic at 9000 with the engine being studied, within which the claim was made.

[FordJim]

Buddy,

Thanks for the information. Very interesting and informative. Can you clarify one point for me? When you say that the factory head maxes out between 230 and 250 cfm, I assume you are talking about a factory head that has been ported to its practical limit, is that correct?

Any idea what the flow numbers are for a box stock factory head right off the assembly line?

Thanks,
Jim

[Buddy Rawls]

...Can you clarify one point for me? When you say that the factory head maxes out between 230 and 250 cfm, I assume you are talking about a factory head that has been ported to its practical limit, is that correct?...

Yes, that should be a nicely ported head utilizing the port wall thickness constraints, and proper contouring and shaping, and possibly even "putty filled" in places.

the stock head data typically ranges for the mid 150's to mid 160's (at 28"), depending on the bench, casting, etc.

I am very green on these particular engines when it comes to specifics of the chamber design and port capabilities. It could be that more than 250 cfm is obtainable, but port work increasing the flow potential beyond 60% is pretty sporty. It could be that (250 cfm) may not be all that workable, and 240's may be more realistic.

[THE FRENCHTOWN FLYER]

You can get past 250 cfm (well past it), but that requires cutting into the walls of the ports, filling the water jackets, and otherwise rendering the head useless for sustained opreation.

[Buddy Rawls]

You can get past 250 cfm (well past it), but that requires cutting into the walls of the ports, filling the water jackets, and otherwise rendering the head useless for sustained opreation.

FTF, what is the "typical" maximum capability of the as-cast constraints?
and what level of work is that? Is that performed with a select casting, by a person intimately familar with the 240/300 head, etc etc. (Essentially a $2K+ superstock type work over), or is that typical proper porting techniques and proper care and textbook mods.

From what i have researched, it appears that 230ish is pretty much the most I have noticed, but I wanted to atleast conceptualize that a 250 cfm inlet port might be obtainable out of the stock casting constraints, maybe its not. Or maybe a real 240/300 head guru can obtain 250+, or maybe 250 is even stretching it.

[THE FRENCHTOWN FLYER]

I would prefer not to discuss it in further detail as it would be betraying the confidence of some of the top racers in the country - some of whom even race against each other in the same class(es). If they were to learn that I was giving away info they worked hard to obtain / create they might be less than willing to share their insight with me. And I do rely on them for much valuable info.

Things I have discovered on my own or info that is of generally known technical theory I willingly share on this forum but some boundaries I do not feel comfortable crossing. Since some of the work done to my crossflow head was done on these guys shops and flow benches that includes specifics on that also.

[Buddy Rawls]

...If they were to learn that I was giving away info they worked hard to obtain / create they might be less than willing to share their insight with me. And I do rely on them for much valuable info...Things I have discovered on my own or info that is of generally known technical theory I willingly share on this forum but some boundaries I do not feel comfortable crossing. ...

No problems with any of that. I do the same thing with the valve event stuff. Some stuff is fair game, but other stuff is not. I am not into these motors any where as specialized as you and the other racers, and really no plans to be. I just use the data for the valve event calcs, and my assumptions that come from capabilities of all sorts of other castings likely get me close enough. Knowledge of the 240/300 just gives me another data point (warm fuzzy) on my own calc processes.

['68falconohio]

Buddy,
Here's a link to a thread on speedtalk, a member's posted inlet flow around 245cfm.
http://speedtalk.com/forum/viewtopic.php?f=1&t=22619