Shop Made EFI Manifold.

Here we go, design time.
Have made a couple of 4 and 6 manifolds both carb and for efi.

Have a rule of thumb for runner length that is close but my work is mostly what looks good is good. I know that is not scientific.

So it is question time.
Have noticed that fabricated sheetmetal manifold runners from plenum to flange have a taper, a decrease in cross sectional area. This will cause an constantly increasing flow velocity from plenum to port to valve.
For power and torque this velocity is important, to increase velocity with out increasing turbulance increase ram effect and cylinder filling.

Does anyone have anything that give this rate of taper / decrease in cross sectional area?

Would appreciate a "WHY and HOW TO" article, but if I have to will extrapolate from pictures.

Remember first rule. The ideal port area for maximum perfromance is the one which gives greater than 250 feet per second at maximum power rpm. So there is a calc you do, which is based on max rpm at full power, and then you work out the air speed using the given minimum port size. So if , up stream of the narrowest port area, your the area is much bigger, you still use the smallest one.


Second rule. You can start with a huge port on port carb size of, say, 3.14 sq in mm, and then use a 2.2 sq in diameter port if it is tapered.

I'll use the geotechnical foundation term, called a flow net. Number of pressure drops must equal number of flow paths. As the cross sectional area tapers off, you get a pressure increase (ideal taper is 16%).

This is found in old motorbike manuals, such as Tuning For Speed by the late Aussie Phil Irving.

In bikes, most of the port angles are pretty good, so the focus has always been on how much inertial ram you can get by bringing the port area down near the valve.

Which brings to mind the next question. How does this effect the optimum port length?

How does this effect plenum volume?

The formulas I have seen use port diameter as part of the equation for optimum port length.

In a properly designed system doesn't the port become part of the plenum? Doesn't the plenum become part of the port?

I have often wondered about this and also the effect on plenum volume.
It seems to me that the tapered port combined with a radiused port entry would effectively tie the port and plenum together and also become part of the plenum.
I have always thought that is the idea, to create a seemless transition thru the plenum and ports with a smooth acceleration helping to keep the fuel in suspension.

After I win the Lotto, (it will take awhile since I only spend about 5.00 dollars a year) I will have the time and money to properly experiment with area. Every time I start playing with the numbers I hit these small areas and usualy end up guestimating and feeling like it's close, but could be better.

I know you guys don't want bunkum, but you've gotta see how many viariables influence the final runner volume and allowable profile of the intakeport. It is a result of 9 items for a carb, and 12 items for EFI or Mech FI.


My narative.

With respect to all the people who have worked hard on getting the design and machinists to make mock ups, and then with zeal, vim, and vigor, spend hours testing them....

Like exhast headers, first you find ones that

1) fit and
2) can be built

Then

3) Dyno test.

4) then report the rests in terms of x, y, and z, the length, width and breadth of the pipe configueration. You have to make some assessment of the angluar bends, which influences the amount of turbulent flow.

All the formulae you see published are in response to simple length, width and breadth calculations, with some input into what the relative engine to plenumb volume is. Resonant flow, the ninth variable, has many presure wave influences, but they are insignificant becasue there are other issues of packaging and build-ability which conspire against such purist and elitist persuits

Hence plenumb volume is at the very least resposnive to 9 variables listed above.

If you think you can just come up with a great envelope or'admirals hat' which gets you close, then don't start with the theory. Its a blind alley.

The only thing which is really productive is Webers ancient venturi size chart, which allows you to determine ideal port on port carb size for independent runner systems. Thats venturi size, not throttle size.

That gives you the right max power rpm rate to suit your engine. Then you see how small you can reduce the port size downstream and still get 250 feet per second at maximum power rpm. Then measure the volume. In practice, the ideal runner length from intake valve to venturi can be anything from 5 to 10 inches, and the ideal length influences mid range torque and high end power.


For Electronic or Mechanical FI, then you have to decide on the packaging restraints, which are much more difficult. The injector rail, or the throttle body placement, or if you decide to run one throttle body, rather than a isolated runner set-up... these escalate the total variables to about 12 items of influence.


All indicated volumes are as a result primarily of buildability issues, so build it first, then test it, Thad. Your the guy with the Tools, and you rule. The theory is largely bunk.

my opinion is tha tyou can put in 50% effort for the IDEAL setup and reach 90% or so of that.....that last 10% gain takes ALOT of work and research. is it worth it if you are only gaining a few hp? I think with packaging and making it a manifold that you can service somehwat easily (who want sone where you have to pull the intake off and apart to get the rocker cover off?) that the optimal design will be compromised anyways. unless you are going to sink alot of research and dyno time into an intake then your efforts are best spent producing a manifold that can be produced easily and cheaply.

OK! the 16% taper number looks good. Have a stack of magazine pics did a little measuring and made some guesstimations, seem to be very close to 16%.

Port size as is at head, dictates flow area on that end of the runner. Plenum end is then port area plus 16 %. Just as the effective length of a curved runner is the long side plus the short side divided by 2, then diameter for calculation purposes is average of the big end and small end. (Got a better idea?)

We all would love to design and build at 100% effeciency. But in truth just doing it and having it work well is good.. And 90% in my book is 100%.

Working with inline engines simplify a lot. Runners can be straight from head to plenum. In some cases there is an angle, usualy upward, of the port runner itself this can be duplicated and continued by the manifold runner.

have you thought about packaging constraints? if you are oging ot sink the money in an intake it better fit most applications to get the most buyers. what are you thinking of for a TB? Cable routing for throttle? Fuel rail and regulator?....all other good questions that need answered.

Looking at building two. One is for the Mercruiser 4 banger in a street rod no limitation to fit ment.

The second is for the 300. Don't like the one I made, going for a do over.
The packaging is a bit tighter due to the shock tower.

I havent posted here in a long time but I do lurk around a bunch. I went though the same deal with intake for my GM 6. I found a book on Honda performance with a great anount of intake building ideas. Everything from fourmulas to basic construction. EFI to carbs on all inlines and it may be a Honda book it really gave me a direction to go. I'm not sure what happen to the book so I cant tell you the low down. Just look around for Honda Performance books.

STEVEN

Hey Mighty6, welcome back what about postin the video of your truck over here? I saw it on Inliners that thing is awesome P.S. sorry didn't mean to hijack the thread. Rich

Thanks guys, I have been a machinist too long. I have spent many years dealing in exact numbers. It sometimes gets in the way of progress.

I guess I just needed someone who's opinion I respect and trust to tell me to, just do it.

Here is a link to my site for everyone. A few pics and vids and some intake photos at the bottom.

http://www.mighty6.com/news.htm

The manifold was designed for turbo charging. Due to time and funds we though a NOS kit on it and went racing.

Steven