I've come up with another crazy question, and I'm hoping I can get some confirmation or deny...-ation(there is no noun form of "to deny") on whether it's a good idea or not.

I found this resource on the BMW m3, and for a time, they came with slide throttle bodies rather than butterfly throttle bodies. For a time, BMW made slide throttle bodies to get better performance out of their engines. They made driveability tough because they're inconsistent. It isn't a linear or even exponential gain in airflow with a linear increase on throttle. Basically, they're good for WOT and nothing else.

Knowing that, I was ready to close that book of thought and move on. However, there are gains to be made in throttle response if the intake runners are shorter, and the air distribution is more even with independent throttle bodies. At WOT slide throttle bodies are more efficient because there's no sideways-butterfly-valve hampering flow and creating turbulence.

To solve the non-progressive problem, why not change the shape of the intake? What I mean is, instead of making round O shaped openings, make them triangular or even square. If they're triangular, like < and the slide moves from right to left, creating a forced progression on air intake levels, wouldn't that solve part of the driveability problem, while giving the same huge gains at WOT? You'd also get much better throttle response from the shortened (possibly 6" or less) intake runners, and lack of a plenum. It would also be really cheap to manufacture, and would require next-to-no maintenance.

Mounting up electronics and vac lines would be identical to the Suzuki ITB setup a lot of people are running now, and mounting injectors would just require some messy holes drilled with oversized rubber gaskets bored out to fit the injectors for a tight fit.

Correct me if I'm wrong, but this sounds like a fun weekend project. Let me know what you guys think.

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wouldnt making the openings square or triangular decrease air flow kinda making them useless?? If i understand correctly the reason they are round is to maximize flow with little resistanse and increase turbulance in the air flow since it will intake in a tornado style air flow giving you better mixture in air and fuel. correct me if im wrong. Blake would deff know about this he has a home made itb project going on.

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Interesting reflexion...

To my mind -tho I'm not specialized in fluid dynamics- as A_White_Gs-R stated it, the round shape is to maximize air flow speed through a kind of swirl effect. Edges brings turbulences, turbulences slow the air column...

PS: Is not the noun form for deny...denial?

Funny this is being thought of on cars. For years to get more performance and throttle response out of our RC car engines we switch to slide carbs rather then the more restrictive butterfly style.

When I switched my T-Maxx to a slide carb the tunability greatly improved as did the top end.

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The shape of the intake tract usually follows the port shape usually. The shape really wouldn't matter much i'd think with respect to flow, but changing shapes wouldn't be a good idea.. especially that close to the port. I didn't do that well in fluids though so I don't know that much about laminar flow or that shit haha.

Making a non linear throttle would actually not be that hard if that's the battle to making the tuning easy. I really don't know what the problem is with slide throttles, just heard that they're a pain to tune at part throttle (have heard the same about ITB's though so who knows).

I actually have a couple designs drawn up that would work better than traditional butterfly throttle bodies but meh, it'll probably never get done.

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nine.five.four.

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I think I'm going to greenlight this on my project list. First step is to get a camera, though. I've got to get pics, if I do it. I imagine it'll sound pretty interesting with pod filters too.

Is there a reason for long runners on the intake side that anybody knows of?

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Resonance. What basically happens is at certain RPM's the runner length will be perfect and create an actual mild positive pressure... that's the best way I can summarize a 274 page book in a sentence but yeah, a lot of science behind optimum runner length.

Excellent book on this subject:
Amazon.com: Scientific Design of Exhaust & Intake Systems (Engineering and Performance): Books: Philip H. Smith,John C. Morrison

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nine.five.four.

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Just ordered a copy. $10.76

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Thats exactly right, Check out AEMPOWER.COM and look at the "How the V2 works" demonstration, it does a pretty good job conceptualizing the air pressure/velocity thing. Wavelengths change as RPMs change. Long runners typically produce better high-rpm performance, whereas shorter runners produce better torque and throttle response. (Almost sure i'm right on all that.)

Other way around, shorter for high rpm.. at least I think so.

There are many engines with variable length runners also that we havn't talked about which is a good idea. I think the e46 BMW's had them and of course the 787B le mans cars did.

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nine.five.four.

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Let's just skip right on past the part where you go more in-depth about that. I'm not competing with any le mans cars here. I'll actually be happy as long as my power doesn't go DOWN. So, 6" runners? Velocity stacks, basically?

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velocity stacks help get the most air in and creat the swirl effect which causes turbulance which you do want inorder to get a maximum air fuel mixture. Short for high rpm power band and long for low rpm power band. You might get away with a 3"runner with the velocity stack since that will ad maybe another inch or two to the total runner length.

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I disagree with that. Velocity stacks do help get the most air in but it's because they allow the smoothest entry possible into the pipe with the least turbulence.

I have no idea what to suggest for runner length, i'd just make sure to make it adjustable because it's very hard to calculate the best runner length with so many variables.

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Nick if the velocity stacks only help get the most air in the air still comes in straight right? It wouldnt seem like something ide go out of my way for. I honestly figured since its got a circular pattern to it that the air flow starts circulating one its way in to the narrow part of the stack after it gets passed the funnel portion.



As far as the air being turbulent i had always understood and heard that turbulent air was best once it got past the runners.

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It's all about allowing the smoothest possible entry and the quickest possible transition to laminar flow as far as I know.

There are different theories on that and i'm not sure honestly. From a purely flow stance, turbulence is bad. There are many different theories though on turbulence allowing for a more even air/fuel mixture across the cylinder and more complete combustion though. These would really only come into play after the fuel is injected into the mixture though.

It's such a complicated science and there really is more than 1 way to skin a cat so to speak. I was reading not too long ago in one of the engine master's magazines about one of the top guys welding the ports up and making them smaller to increase velocity and fill the cylinder quicker (SBC).

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Yea ive heard about that also and about getting as much air in there as possible to fill the cylinder as much as possible. The whole thing i heard about a regular manifold vs itb's is that in the manifold the air distribution between cylinders is un even and hence why itb's are technically better. In some cylinders there is very little turbulance compared to some of the others Which is why on some engines theres uneven burn and wear through out the cylinders. one cylinder might be darker than the other one. (partially the reason not the entire reason) with itb's and a velocity stack you get the smooth entry and you maximize air ingestion because the entry is smoothed out and rounded but once inside doesnt it become week if theres no turbulance? Its like when you mix chocolate milk. you have a glass of white milk you drop the powder in and you can see some of it mixes but the rest just clumps in there. Once you drop the spoon and mix (causing turbulance so to speak) you get a real good mix (and drink the hell out of it i think im gonna buy some chocolate milk now that i think about it) Or if you have one of those turbo blenders that cause the milk to turn violently as you add the chocolate powder it mixes as its going in. Why wouldnt the same apply to air fuel. though i see where it gets confusing since the fuel isnt actually introduced untill the air is already plowing into the cylinder right before ignition. its fucking weird.

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If you shorten the runners believe it or not you increase turbulance. way to prove it is grab a straw. Blow into it at normal length then cut the straw in half or more and then blow into it again the air escaping on the other end is more violent and you can hurry more air through it faster.

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Turbulence in the intake is another old school thing that should really go away.

Back in the days of carb's, you need that turbulence to properly mix the fuel into the air and get a cleaner burn. Thats why oldschool intakes had that rough texture inside them and the intake ports were rarely POLISHED.

Shorter runners make more horsepower, longer runners make more torque. Thats the simplest way to describe what goes on.

In a modern engine, you can extrude hone the intake manifold and ports and if you have your injectors sized right and the tune is spot on, then the correct mixture will happen anyway. On a honda, with the pent roof design if you extrude honed everything and unshroud the valves slightly, you get a BEAUTIFul tulip entry pattern, and the design of the cylinder head then squeezes the entire mixture up to the spark plug gap. By mirror finishing the entire intake, you would increase the velocity(as long as you didn't open the ports up to large) thereby creating more low end and high end power.

That brings us to runner size. If the runners are to large or the ports opened to much, you lose velocity, and thereby hurt your low end numbers. Lots of R&D goes into making a factory car's intake and exhaust ports JUST right for day to day applications. Just the right port size, shape and finish(rough, polished, mild) to get the best hp/tq numbers for the best price to sell a good reliable around town hill climber with a little bit of pep when you ask for it.

For an all motor build, the thing on a honda you really need to concern yourself with is low lift porting. Honda spent alot of time making B/H/K's flow well at high lift, not so much on the low lift. You can have someone witha flowbench, slowly rework the ports for low lift flow and gain considerable numbers without loosing the velocity you require for that off the line bite. If you are building a track car that launches at 5000+rpm's and never goes below that for the most part or a boost monster then, by all means, hog that @@#$@#$ out

/2 cents.

I got tons of information up here.. and no time to use it =(

Dave

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the tuning aspect really isnt that bad when you have programs like Neptune, eCtune and Crome which have Alpha-N tables (TPS and MAP based).

Having a tuning table that is just MAP based doesnt give the most accurate reading so throttle angle becomes an aid in determining how much air is really coming in at X throttle angle.

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as nick said, and as a general rule

shorter runners - more top end power

longer runners - more low end power

you just need to figure out what is gonna be done to the engine, if the head is going to remain basically stock then i wouldn't spend to much time fooling around with different intake manifold designs and ITB's

slide throttle plate designs flow better

velocity stacks are designed to created less turbulence which in turn creates more uhh.... velocity, which does help create a good air/fuel mixture. turbulence kills an airs velocity and in turn fuel will no longer be suspended and can puddle in the intake tract which will make an engine run like shit

this is all that i know from 3 years of school, 3 of my buddies projects that we made intake manifolds for, and a few books. so i could be wrong

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