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What is everyone's take on a tapered runner compared to a straight runner on an intake manifold?

I know each setup is different , but lets say for an All motor setup.

Some manifolds use straight runners, while some use tapered. I understand the concept behind a tapered runner , but in a race ported head does it really matter?

Are velocity stacks at the end of each runner just to increase runner length within a given space or do they actually help straighten the air in each individual runner? Like a velocity stack at the end of an intake arm is suppose to do ?
For example if you have a manifold with a 6 inch runner on it and you dyno it. Then you cut an inch off the runner and add an inch high V stack ( just an example) in each runner. The length really wouldnt have changed, but will performance be affected positively or negatively?

Just trying to gain a little knowledge of the inner manifold mechanics. . .
 

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iam not sure of the difference but i think the velocity stack in the runners would create a vortex within each runner.

http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466

iam sure you have seen this article it basically sums up what changes in runner length and plenum volume will do to your power band.

longer runners = more torq, and moves peak power band lower.
shorter runners = less torq but more power up top.


there are calculators online that could tell you what size runner you "should" have based on where you want your peak torq or peak hp to be.
 

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iam not sure of the difference but i think the velocity stack in the runners would create a vortex within each runner.

http://www.team-integra.net/sections/articles/showArticle.asp?ArticleID=466

iam sure you have seen this article it basically sums up what changes in runner length and plenum volume will do to your power band.

longer runners = more torq, and moves peak power band lower.
shorter runners = less torq but more power up top.


there are calculators online that could tell you what size runner you "should" have based on where you want your peak torq or peak hp to be.
Velocity stacks are not used to create vortices. If you want to create vortices, there are proven methods, most of which involve irregular protrustions, like the bumps you sometimes see on the upper section of a wing (on a plane) or the protrusions on the roof of some EVOs, etc. The barge boards (the curved plates in front of the radiator ducts) on F1 cars are use to create vortices from boundary layer seperation at the edges...these vortices are fed into the car's undertray...but that's another topic entirely. You get the idea though.

All pipe entrances (or runner entrances) can pose some restriction to the flow going into them. This will vary based on the geometry of the opening. More abrupt openings= more restriction. The velocity stack (or generous fillets in the case of an intake manifold) is used to lower this restriction. Saying the height of the velocity stack can be fully added to the runner length is somewhat inaccurate. The effective length the velocity stack adds to a runner can really only be found through testing, but even then it would be difficult to know exactly what the number is. In the end it's a moot point, because the effective length is worthless. The runner lengths can simply be tuned through real world testing to accommodate whatever effective length the velocity stack adds.

Runners are tapered to accelerate the airflow as it moves down the runner. While your immediate reaction would be to say there is no acceleration in a runner that is not tapered, this is not true. A boundary layer forms along the walls of a non-tapered runner as air flows through it. This boundary layer's thickness increases as the airflow gets closer to the exit of the runner. This effectively increases the velocity of the air down the runner. The longer the runner is, the more this is noticeable, and the less taper is required to get the same increase in velocity as a shorter runner. Getting the airflow's speed up increases the fluid's inertia and can benefit both scavenging and the effect of Helmholtz' resonance.

That's it in a nutshell. :up:

peace,
russ
 

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Discussion Starter #5
Wow, that was one of the most informative posts i have ever read haha.

Thank you very much, Russ !
 

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yes russ nice putting everything into perspective:up:
 

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The boundry layer acts like a lubricant for the airmass, it reduces surface friction. That is one reason why you do not polish the intake runners for a NA engine.

Basically it is the same principle used for the surface of a golf ball. The dimples create a boundry layer around the golf ball allowing it to travel much further than a smooth surfaced golf ball.
 

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The boundry layer acts like a lubricant for the airmass, it reduces surface friction. That is one reason why you do not polish the intake runners for a NA engine.

Basically it is the same principle used for the surface of a golf ball. The dimples create a boundry layer around the golf ball allowing it to travel much further than a smooth surfaced golf ball.
the boundary layer acts like a lubricant for air? the velocity of the air is zero at the surface and increases as it moves away from the surface until it reaches the free stream velocity. shear stresses are greatest at the surface because of friction. this is one reason why air planes stretch after repeated takeoffs and landings.
 

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If you use a smoke generator you can see the air that contacts the surface looking like small breaking waves. This turbulence isolates the main body of the air mass and this decreases the friction between the runners and the air mass allowing for a greater velocity for the airmass.

I was being far to non-technical with the lubrication point. The point being lubrication reduces friction as well.

I have an A&P and I have yet to hear or see a correlation between an aircrafts airframe stretching from repeated takeoffs and landings and boundry layer air turbulence.
 

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good topic
 

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I know this is on IM, but for someone with a stock TB, or for that matter an aftermarket, though I think most aftermarkets have this done already...How would tapering the outside part of the TB, boring it as much as possible down to stock size just at the butterflies v leaving it alone v boring a lil tapering to butterflies? How will this help on velocity in the IM? Would it be too much velocity for NA? Boost? Nitrous? Is there such thing as too much velocity there?
 

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I know this is on IM, but for someone with a stock TB, or for that matter an aftermarket, though I think most aftermarkets have this done already...How would tapering the outside part of the TB, boring it as much as possible down to stock size just at the butterflies v leaving it alone v boring a lil tapering to butterflies? How will this help on velocity in the IM? Would it be too much velocity for NA? Boost? Nitrous? Is there such thing as too much velocity there?
The 6 degree taper they introduce on a TB or any pipe for that matter will increase the flow rate, hence more top end power without affecting air flow velocity therefore maintaining good low end power as well.
 

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I never heard that...good knowledge, where did you get the 6* from? Also, on our 62mm TB, though I think that is what they are stock, what would the outside bore need to be to taper down to 6*? I dont know how to figure that math, or making it harder than it really is.
 

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can anyone explain how a velocity stack work in a exhaust manifold.

I've been told its not possible.
 

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can anyone explain how a velocity stack work in a exhaust manifold.

I've been told its not possible.
I cannot see how a velocity stack is beneficial to an exhaust manifold; but a reverse taper would. i think it was called "anti-reverse".
But again, science is weird. it would be interesting if it actually made significant advantage in power.

where would the stack/taper be placed? in the collector?
 

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can anyone explain how a velocity stack work in a exhaust manifold.

I've been told its not possible.
To increase the signal strength I guess, I have seen it on cars here on this board. Never saw a concrete before/after dyno with that being the only change. Interested to know what the dB change in sound would be as well. Or the O-scope read out :)
 
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