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So my buddy told me something that didnt seem to fit well with me. I told him that I wanted a ITR TB(62mm) to match up with my Skunk2 intake manifold(62mm)... he said why would you want an ITR so bad when you can just get a bigger one? 65-68mm? He said" being the TB bore is larger than the intake bore it will be better overall.... how is that true? I always thought you wanted to have EVERYTHING port matched..... 62mm to 62mm bore.... yanno?
 

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ej1
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Tell your buddy to get his head out of his ass. You don't want to have the air going over a step up against the flow. The other way is good so it can't back up and go the other way as easily. You want the intake the same diameter or larger than the throttle body exit. The same thing goes for the head intake port inlets from the intake mani and the exhaust port outlets to exhaust mani inlets. I'm running the 62mm throttle body on the skunkII.
If you try to run a 65-68mm you'll have issues by the iacv ports when you try to open up the intake mani side. If you daily drive the thing the larger throttle 68mm body may be an issue with low end response on a d-series.
 

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you do want to port match/ or at least blend the opening to create velocity, but just because you have a huge throttle body may not make huge power. There are such things as too big.

You engine can only flow so much so putting a huge TB on it is like putting a 4 inch exhaust on it it can hinder your performance more than gain power.

Depending on your engine, cam, application will determine such things as header exhaust size intake TB ect....
 

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Discussion Starter #5
Tell your buddy to get his head out of his ass. You don't want to have the air going over a step up against the flow. The other way is good so it can't back up and go the other way as easily. You want the intake the same diameter or larger than the throttle body exit. The same thing goes for the head intake port inlets from the intake mani and the exhaust port outlets to exhaust mani inlets. I'm running the 62mm throttle body on the skunkII.
If you try to run a 65-68mm you'll have issues by the iacv ports when you try to open up the intake mani side. If you daily drive the thing the larger throttle 68mm body may be an issue with low end response on a d-series.
thats what I thought... unless I misunderstood him..... I am gonna stick with the 62mm size tb and roll with it! thanks guys!
 

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Yea thats not true at all, If you can picture the air coming out of your intake manifold picture it with a larger tb. It wont do anyhting becasue only X amount of air is exiting your intake manifold so simply having a larger tb wont draw more air in anyway. In fact like someone said the step will probably distort the flow and make things worse than better.
 

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If anything I would think you would want it slightly smaller as there could be some reversion in the plenum. Certainly wouldnt want it bigger.

Tell your buddy he is a ricer.
 

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Air isn't being drawn into his engine, it is being forced.
I beg to differ its being drawn. Force would imply its being pushed in. Whats pushing it in? Why do you think a turbo is called Forced induction, becasue more air is being Forced into the engine.
 

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Air isn't being drawn into his engine, it is being forced.
With piston at the top of the cylinder, the intake valve opens. The piston then moves down in the cylinder, creating a vacuum or lower pressure in the cylinder.

Air (at atmospheric pressure ~ 14psi) outside the carb flows thru the carb, from the atmospheric pressure outside to the low pressure in the cylinder. In the process, the flowing air picks up fuel from the jet and takes it along.

The intake valve closes at the bottom of piston travel and the piston moves back up, compressing the air/fuel mixture. When the piston has reached the top, the spark plug sparks, igniting the fuel/air, generating pressure that pushes the piston down.

The exhaust valve opens when piston is at bottom, and as the piston rises, it pushes the exhaust gases out... then it all starts over again.


So yea the air is drawn in not forced.
 

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I beg to differ its being drawn. Force would imply its being pushed in. Whats pushing it in? Why do you think a turbo is called Forced induction, becasue more air is being Forced into the engine.
You have a lot to learn. It's being pushed!! You have an area of high pressure and an area of low pressure. The high pressure pushes in to the area of low pressure. To put it simply.
 

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So what is the advantage of having the step from the TB to IM? And for that matter the IM to intake ports, etc etc?? Why wouldnt it be profitable performance wise to have them port matched?
 

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The vacum created in the cylinder is what is drawing in the air to begin with, im sticking to my guns
I thought this way for the longest time. Its wrong sadly. It is being pushed in thats why in Denver where you are a mile high and the air is less dense (meaning lower atmospheric pressure) you get less air in the cylinder and make less power than you would at sea level.

Being pushed in makes more sense for when a na motor makes "boost" when it has more than a 100%ve at a very certain and small rpm range.
 

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Sucked or pushed is really semantics. The air flows from high pressure to low pressure to attempt to equalise the pressure.

A throttle body should really be a bit bigger than the down stream flange size as the throttle shaft obstructs flow.

However the throttle body flange should NEVER bolt to a manifold flange with the manifold smaller as airflow hits a blunt shoulder and is severely disrupted.

If the manifold flange is a bit bigger than the throttle flange this disruption to the reverse flow can help, so best deal is bigger throttle body then a tapered adapter to bring it down to a bit less than the manifold flange.

To be frank, 62 sounds big enough, but 65 with a taper down to 60 sounds better or a taper down to 62 with the manifold flange opened up to 65 if there is room.
 

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So what is the advantage of having the step from the TB to IM? And for that matter the IM to intake ports, etc etc?? Why wouldnt it be profitable performance wise to have them port matched?
Port matching is the best way to do things but if you had to have a ledge having it on the trailing edge of the air flow will make less turbulence than if its on the leading edge.
 

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The reason for the step is to reduce reversion.

Reversion is air trying to flow back out of the cylinder. This can be from bounce back as the inlet valve closes or the piston moving up the bore before the inlet valve closes. This is worst at low rpm where the inertia in the column of air is lower. At higher rpm the inertia works against the reversion of back wash in the flow.

In effect the step makes the airflow better in the right direction and worse in the wrong direction.

Simple flow bench tests will not show this and port matched will work best on a flow bench, BUT NOT on a running engine.

A test you can do on a flow bench is to test the port and manifold in both directions. You want the inlet flow maximised and the reverse direction flow minimised without hurting the inlet flow.
 

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With piston at the top of the cylinder, the intake valve opens. The piston then moves down in the cylinder, creating a vacuum or lower pressure in the cylinder.

Air (at atmospheric pressure ~ 14psi) outside the carb flows thru the carb, from the atmospheric pressure outside to the low pressure in the cylinder. In the process, the flowing air picks up fuel from the jet and takes it along.

The intake valve closes at the bottom of piston travel and the piston moves back up, compressing the air/fuel mixture. When the piston has reached the top, the spark plug sparks, igniting the fuel/air, generating pressure that pushes the piston down.

The exhaust valve opens when piston is at bottom, and as the piston rises, it pushes the exhaust gases out... then it all starts over again.


So yea the air is drawn in not forced.
Thanks for explaining that, we would be lost without you :dots:
 
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