Runner size for an ITB?

[tyler031734]

I've taken up aluminum casting for a hobby and Im trying my hand at making an ITB setup for an L. Casting small pieces machining them and using tubing available on-line. A friend does AL welding so it works out.

 

My question being; How big do I make the ID of my runner? I had no idea I had four choices between 1.63" and 1.5" and even a 1.25" readily available. Being made from 6061 tubing. I'm just looking for un-restricting a little air for a street car possibly or at the very least adding the ITB rumble they have, just thought it was a cool idea.

 

Hoping I could get an opinion on this from somebody in the know.

 

Thanks

[Lazeum]

I would measure ports in the head, you'll notice they are smaller than the ITB setup you're going to use (Ø 45 ?)

So I would run a design with a taper going from head port diameter to ITB diameter.

 

You should also think about harmonics in the intake to get the best VE possible. That would let you find the length of the runners. It should be based on air horns length also.

Edited March 19, 2012 by Lazeum

[NewZed]

You've probably seen them, and I don't know if he has design specs in them, but if you search "throttle bodies" under the username Derek you'll get three threads that might help.

[Leon]

I would measure ports in the head, you'll notice they are smaller than the ITB setup you're going to use (Ø 45 ?)

So I would run a design with a taper going from head port diameter to ITB diameter.

 

You should also think about harmonics in the intake to get the best VE possible. That would let you find the length of the runners. It should be based on air horns length also.

Exactly. Runner geometry should be based on having as little pressure drop as possible, while having them tuned to your specified rpm range, i.e. "resonance tuning". Tuned rpm depends on intake length, diameter, air temperature, and valve timing. Generally speaking, a longer and/or narrower intake tract will be tuned at lower rpm, and a shorter and/or wider runner will be tuned at high rpm. Holding runner geometry constant, increasing cam duration will shift your tuned rpm range higher and decreasing duration will shift your tuned rpm lower. Temperature plays a more minor role.

 

Keep in mind that frictional losses increase with the square of velocity, which is inversely proportional to the square of the diameter!

 

With that said, these properties would push me to use as wide of a runner as possible, while matching it up to the head port, and varying intake length to get my tuned rpm. Air horns or a taper cast into the intake at the proper location will widen your tuned rpm range and a radiused entrance will decrease entrance losses.

 

That should give you a start!

[Tony D]

ITB as in EFI?

Nominal size for ports was 35mm by FIA Homogolation rules, and if you look most guys with properly ported heads for EFI won't have ports far off from that diameter at the intake/head gasket joint.

 

Work from that point backwards to get what you want/need...

[josh817]

ITB as in EFI?

Nominal size for ports was 35mm by FIA Homogolation rules, and if you look most guys with properly ported heads for EFI won't have ports far off from that diameter at the intake/head gasket joint.

 

Work from that point backwards to get what you want/need...

Mine was ~39mm. Oh well.

 

 

You could go to Kinler or Hilborn and purchase some of their ram tubes. The L series manifold they provide is 1 13/16" but tapered to something like 34-35mm if I remember correctly, after the throttle plates.

 

You may want to check the spacing on a stock EFI manifold. I have a hunch that if it is the same as the Hilborn then perhaps... you take any one of the stock manifolds whether it be for EFI or SU's. Cut the runners off, use the flange. Get yourself some 12" ram tubes of whatever diameter and weld them onto the flange. Since they're straight tubes, the port spacing at the head is the same spacing all the way down the tube, which is the same as the Hilborn manfiold (I think! maybe not though!) which means you can take the 5/16" throttle shaft if Hilborn sells just the shaft, get your throttle plates and screws too. Then line bore/drill wherever you want the throttle plates/shaft to be on the ram tube, and weld on injector bungs. Of course with this idea, there is no taper to the bore so another way could be...

 

Get one of the stock EFI manifolds. If you look, the first 3 or 4 inches appear to be straight (I'm only eyeballing pictures). Cut the runners right where they start bending so now you have the flange and 3 or 4 inches of straight runner. Now, get a ram tube that is of a diameter that will slip over, tightly, the straight bit of runner on your cut manifold. Run small welds around where the edge of the ram tube meets the manifold. At this point, a cut away few should look like this:

 

So from here, the red is the thin ram tube, the black is your stock manifold, the green is the weld, the blue arrows point toward the thick manifold that you have which you can get a hand tool die grinder whatever, make your taper. Of course if you slide your ram tube all the way up to the flange, you would have potentially 3-4" of length to make your taper from the big ram tube to the small port match on the head. If you only slide the tube over 1" of stock manifold runner length then you only have 1" to make a taper which might be detrimental.

 

A more predictable method of tapering, when you don't have all the right tools or supplies would be to a set of large bore bits for your drill press or whatever fancy bore machine you may have. Bits from 1-2" in size. Then you get your welded manifold and from the ram tube side of the manifold, bore a small hole, say 8" into the runner. Now get a slightly larger bit and run it only 7.5" or maybe 7.75" in, and repeat this until you get almost as large as the ram tube size. Do it in equal increments of length so 8" deep, 7.75", 7.5", etc. Now you go in with your die grinder and smooth out the steps you made. This should hopefully make a more uniform taper instead of eyeballing it. Illustration:

 

Perhaps if the taper angle is how you want it, and you can get the right diameter bit, this would be a much faster method:

 

With using this manifold idea you can utilize the stock port injection setup.

 

What if you don't like the taper idea? Well, the point of it was that with runner spacing the same as port spacing you could utilize the throttle shaft that Hilborn or Kinsler provides as well as the injector location. Another idea, to skip the taper hassle, is to get a triple carb manifold since the taper is in the manifold... I think, you would have to double check!

 

Hilborn and Kinsler offers a 2 bolt flange ram tube which with some luck you may be able to find the same spacing as a Weber. If not then maybe you weld your own tabs onto the tube, and drill the hole in them to match the manifold. If you still aren't complacent with that idea then simply weld the tubes onto the manifold. Now from this point, I would run a tube size that is the same diameter as a Weber throttle plate. So 40mm, 45mm, 50mm, whatever, because you will line bore/drill through the ram tubes, not the manifold. This means your throttle plate spacing should be the same as that of a Weber DCOE of whatever size. You will use Weber throttle shafts and throttle plates. Then you have weld injector bungs onto the manifold and you should be good to go. If it were me I would drill for my throttle shaft in the same location as the Weber throttle shaft if there were a Weber installed. This way the linkage dimensions shouldn't get all messed up.

 

Hilborn catalog and price list location for you to shop:

http://www.hilborninjection.com/product.asp?Id=444&CatId=254

 

Kinsler catalog:

http://kinsler.com/handbookFullIndex.cgi

 

 

 

After typing all this, I realize I didn't even answer the initial question however I refuse to delete all of this.

Edited March 20, 2012 by josh817

[tyler031734]

There's a ton of info there. I didn't think Id get this kind of a response.

 

I wouldn't know the first thing about figuring out harmonics for the best VE. Not that I wouldn't like to learn.

I have a limited grasp of what air does going from idle to red-line at this time.

 

I did find the stock diameter for a late E88 was roughly 1.25" and there's 6061 tubing 1.25 ID with .25" wall.

Should be plenty of good meat for tapering. Im going to ask a buddy in the tool and die room if he could taper these with 1.25" to get it close enough to the head for port matching and 1.50"/1.57" depending on the diameter of the throttle body I use.

 

There's alot of choices on Ebay for motorcycle ITB's. I wish I could make my own TB but I only have a Mini-lathe, no mill.

 

Nothing is set in stone. Still need to cast the flange that bolts to the head. Find with TB's I want to use and select the tubing.

 

 

This is a Inch/mm conversion chart I have bookmarked. Comes in handy for quick reference.

http://mdmetric.com/tech/cvtcht.htm

[josh817]

I think what TonyD said is how you should approach the problem, work backwards.

 

With this knowledge, you should take the port size on your head and then apply the taper TO THE LENGTH you are looking for. If the optimal taper is .2" diameter for ever inch in length and your tuned runner length is 8 inches, then you take your port diameter, lets say its 1 inch. 1 inch + (.2)(8) = 2.6 inch inside diameter runner.

 

How do you find the optimal length? Information can be found on the internet for that but think along the lines of air temperature, air density, cam duration/valve timing, runner diameter, etc. Anything that can effect an air pressure wave.

 

You've seen photos like this right?

 

And the reasoning behind this method is right to do with what you are trying to solve, best diameter and length of runner for performance. Skip the BS and jump to 4:03 for what I'm talking about:

http://www.youtube.com/watch?v=Ul0NzRy7sIA&feature=youtu.be

 

When you find calculators online, they will refer to the number of induction waves. As the video shows, there is a pressure wave that resonates within the runner. This wave is going to crash into the back of the intake valve if it is closed. The first crash is obviously "number of induction waves = 1", then it bounces off the valve, eventually cycles back and crashes again. Each crash is less in magnitude so the first wave will be the strongest, second a little less, third a little less, etc. By changing your runner length, you can tune for which wave you want. Now you're probably thinking you want the strongest, first wave. However, tuning for this first wave requires a freakishly long runner. As Leon said, the longer the runner generally means lower end power, shorter runners are for high RPM peak power. Even at 7000 RPM peak power, the first wave runner length is freakishly long. You're trying to time it so that wave is right at the back of the valve when it opens. You don't want it to crash into the valve and then open; you want it to go right into the cylinder.

 

From what I have heard, to get a nice balance between length and wave magnitude, third order waves are used. With our large engine bays you may be able to pull off second order but that's iffy. Remember the length these calculators will ask for is from the entrance of the runner to the back of the valve, not just your pipe length. A properly tuned intake ramming air in, and a tuned header sucking air through the cylinder, will lead to lovely results in volumetric efficiency.

 

I don't know enough to even touch on what a taper will do to this pressure wave. I can only make an assumption that the wave will speed up as it tapers, or maybe the calculator takes that into account. Calculators online are sometimes sketchy though. Some taking certain things into account that others do not.

 

 

This source has been referred to once before for its technical articles on cooling systems. There are articles over other things, one being induction systems. It will provide definitions, descriptions, and formulas to solve your questions on intake tuning.

http://mysite.verizon.net/vzezeqah/sitebuildercontent/sitebuilderfiles/inductionsystems.pdf

 

 

Edit:

After reading through the article for the first time in a long while, this should really help you. It will tell you that a 2.5% taper can be applied before airflow starts to get choked, as well as provide reasoning behind length and runner area (get your diameter from this). Quickly regurgitating what I see, runner length will tune peak power over a narrow RPM range, runner area will effect the power across the entire RPM range. I used this source rather than iffy online calculators.

[Leon]

There's a ton of info there. I didn't think Id get this kind of a response.

 

I wouldn't know the first thing about figuring out harmonics for the best VE. Not that I wouldn't like to learn.

I have a limited grasp of what air does going from idle to red-line at this time.

 

I did find the stock diameter for a late E88 was roughly 1.25" and there's 6061 tubing 1.25 ID with .25" wall.

Should be plenty of good meat for tapering. Im going to ask a buddy in the tool and die room if he could taper these with 1.25" to get it close enough to the head for port matching and 1.50"/1.57" depending on the diameter of the throttle body I use.

 

There's alot of choices on Ebay for motorcycle ITB's. I wish I could make my own TB but I only have a Mini-lathe, no mill.

 

Nothing is set in stone. Still need to cast the flange that bolts to the head. Find with TB's I want to use and select the tubing.

 

 

This is a Inch/mm conversion chart I have bookmarked. Comes in handy for quick reference.

http://mdmetric.com/tech/cvtcht.htm

Maybe the long post I just made in another ITB thread will help! It probably would've gone here anyway, if I saw this post first.

 

http://forums.hybridz.org/index.php/topic/105783-ideal-intake-runner-taper/page__view__findpost__p__989770

 

I guess I might as well copy/paste some of it over here...

 

 

So, why taper the runners? It's all about resonance tuning. Well what the hell is resonance tuning, you may ask!

 

When your intake valve opens, the mixture begins to flow into the cylinder. This propogates an expansion wave up the intake tract. Think of it this way: the intake runner is a 4-lane highway, the valve is a traffic signal, and the cylinder is a mall parking lot after the signal. The cars on the highway waiting for the light represent the air-fuel molecules. When the traffic signal turns green (valve opens), cars begin to flow into the parking lot (cylinder). Looking down at the highway (intake runner) with a bird's-eye view, you can see the front-most cars moving first and creating a gap between themselves and the cars behind them. Keep looking down and you'll see that this gap travels down the line of cars on the highway until it reaches the last car and the last car begins to move. This is your expansion wave propogating up your intake tract!

 

Wave dynamics state that if a wave travels through a pipe and hits a discontinuity (a change in diameter, like the end of a pipe) then it is reflected back down that pipe with the opposite effect (negative to positive - an expansion wave gets reflected/inverted as a compression wave). Let's get back to our traffic analogy where we left off, imagine that the reflection happens when the wave hits the last car in line on the highway and it begins to move. The line of cars has now expanded after the light turned green, so the last car in line will work to compress it. So, the last car in line gasses it and rams the car in front! They now go down the line, ramming each car in front of them until they've compressed themselves into a big hunk of metal upon reaching the parking lot (cylinder). This is the compression wave reflecting down the runner and squeezing back into your cylinder! This compression wave increases intake pressure, which fills more of the cylinder (an increase in "volumetric efficiency"), which is what ultimately increases engine torque.

 

Silly analogies aside, those are the fundamentals.

 

Back to our intake and cylinder, we can see that it takes time for the expansion wave to travel up the intake, reflect, and travel back down as a compression wave. In order for our intake to be "tuned", the compression wave must reach the valve just before it closes so that we can squeeze in that last extra bit of air-fuel mixture without reversion of the mixture back into the intake. You can see now, the connection of intake tuning to valve timing and intake length. The longer the intake runner, the longer it takes for the compression wave to travel back to the valve. This means that when you increase runner length, your tuned rpm drops to a slower engine speed, where the wave has enough time to get back to the valve. If you change your valve timing, e.g. closig the intake valve later, then you raise your tuned rpm to a higher engine speed since the wave now has extra time to get back to the valve before closing.

 

What does this have to do with intake taper?

 

Think back to the expansion wave hitting a discontinuity in the pipe. A discontinuity causes an inverted reflection of the wave. If your intake is straight from air filter to valve, you get one big, fat reflection but only at one discrete engine rpm. At other engine speeds, the timing of the reflection will be off. This gives your torque curve a pronounced peak but no benefit from intake tuning off that peak. What a taper in the pipe does, is introduce a bunch of tiny, little discontinuities along its length. Meaning, as the wave travels through the taper, the diameter is continuously changing. This allows some of the wave to be reflected back down the intake, while the rest of it keeps moving out. What you have now is a series of smaller reflections but at a broader range of engine speeds. This results in a less peaky but more flat and robust torque curve.

 

From what we've discussed here, it can be seen that a short, agressive taper will make the reflection stronger but last for a shorter span of rpm. The opposite goes for a shallower, longer taper (broader tuned range, but with a smaller bump in performance).

 

Taper location also plays a role, once you think about it. Since the wave takes time to travel up and down the intake runner, the further you space the taper away from the valve, the longer it will take for the expansion wave to reach the discontinuity. This allows you to "activate" your taper at different rpm. If you start the taper further out from the valve, then you delay relfection, which then shifts your torque curve down. At higher rpm, the compression wave simply won't have the time to reach the valve before it closes.

 

In conclusion, there is no ideal intake taper! You must figure out your design intent (peaky or flat torque curve; low, mid or high end torque) from which ideal runner size can be found.

 

Sorry for the long post, but I felt compelled to give a more thorough answer. Hopefully, you can get some benefit out of it!

Edited March 21, 2012 by Leon

[Leon]

I think what TonyD said is how you should approach the problem, work backwards.

 

With this knowledge, you should take the port size on your head and then apply the taper TO THE LENGTH you are looking for. If the optimal taper is .2" diameter for ever inch in length and your tuned runner length is 8 inches, then you take your port diameter, lets say its 1 inch. 1 inch + (.2)(8) = 2.6 inch inside diameter runner.

 

How do you find the optimal length? Information can be found on the internet for that but think along the lines of air temperature, air density, cam duration/valve timing, runner diameter, etc. Anything that can effect an air pressure wave.

 

You've seen photos like this right?

 

And the reasoning behind this method is right to do with what you are trying to solve, best diameter and length of runner for performance. Skip the BS and jump to 4:03 for what I'm talking about:

video removed

 

When you find calculators online, they will refer to the number of induction waves. As the video shows, there is a pressure wave that resonates within the runner. This wave is going to crash into the back of the intake valve if it is closed. The first crash is obviously "number of induction waves = 1", then it bounces off the valve, eventually cycles back and crashes again. Each crash is less in magnitude so the first wave will be the strongest, second a little less, third a little less, etc. By changing your runner length, you can tune for which wave you want. Now you're probably thinking you want the strongest, first wave. However, tuning for this first wave requires a freakishly long runner. As Leon said, the longer the runner generally means lower end power, shorter runners are for high RPM peak power. Even at 7000 RPM peak power, the first wave runner length is freakishly long. You're trying to time it so that wave is right at the back of the valve when it opens. You don't want it to crash into the valve and then open; you want it to go right into the cylinder.

 

From what I have heard, to get a nice balance between length and wave magnitude, third order waves are used. With our large engine bays you may be able to pull off second order but that's iffy. Remember the length these calculators will ask for is from the entrance of the runner to the back of the valve, not just your pipe length. A properly tuned intake ramming air in, and a tuned header sucking air through the cylinder, will lead to lovely results in volumetric efficiency.

 

I don't know enough to even touch on what a taper will do to this pressure wave. I can only make an assumption that the wave will speed up as it tapers, or maybe the calculator takes that into account. Calculators online are sometimes sketchy though. Some taking certain things into account that others do not.

 

 

This source has been referred to once before for its technical articles on cooling systems. There are articles over other things, one being induction systems. It will provide definitions, descriptions, and formulas to solve your questions on intake tuning.

http://mysite.verizon.net/vzezeqah/sitebuildercontent/sitebuilderfiles/inductionsystems.pdf

 

 

Edit:

After reading through the article for the first time in a long while, this should really help you. It will tell you that a 2.5% taper can be applied before airflow starts to get choked, as well as provide reasoning behind length and runner area (get your diameter from this). Quickly regurgitating what I see, runner length will tune peak power over a narrow RPM range, runner area will effect the power across the entire RPM range. I used this source rather than iffy online calculators.

Your post adds some info that I purposefully left out of my post in the other thread I linked above. Otherwise, I'd start to approach dissertation status. I didn't go into harmonics, and yes, the third harmonic is the one we usually go for without having bosuzoku intake pipes. Our posts make for a good match, a nice combo of theory and application!