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2 Inch Restrictor Vs 3.5 intake pipe

 
Old 07-18-2017, 08:57 AM
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Default 2 Inch Restrictor Vs 3.5 intake pipe

So I was recently on the Dyno with the K24 swap and I needed to cut the HP back for a different class. I made 3 restrictor tubes. These were 2 inch thick tubes of plastic with and outside diameter of 3.5 inches that I hole sawwed a hole in to make a restrictor. I made a 2inch, 2.25 inch and 2.5 inch one. So on the dyno we got done doing runs for the higher hp class and swapped the 2 inch restrictor into the tube. It was about 8 inches in front of the Throttle body which is a 74mm throttle body. The Before and After are shown below. See if you can tell the difference. I'll give ya a hint. The higher one is the one with the 2 inch restrictor.


I kinda get in my head why it did absolutely nothing. But at the same time myself and the tuner looked at each other baffled by it.
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Old 07-18-2017, 10:44 AM
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Wow that seems pretty crazy, do you have a picture of the restrictor?
Not sure I understand the construction, it's just a small 2" hole inside a 3.5" intake tube?
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Old 07-18-2017, 11:30 AM
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This
Attached Thumbnails 2 Inch Restrictor Vs 3.5 intake pipe-a9cbcc14f9bf4edf9d9a1576686ef26a.jpeg  
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Old 07-18-2017, 12:41 PM
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Originally Posted by s2000ellier View Post
This
IIRC that was my 2.25 one. But same shape.
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Old 07-18-2017, 10:33 PM
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Only thing that pops into my head that makes any kind of potential sense of this, is you effectively sped up the velocity of the incoming air due to your placement of the restrictor, canceling out any effect of restriction. My guess is a full 2" or .2.5" intake would do the trick, not a staggered stack such as what you have done here if im understanding what you did correctly.
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Old 07-18-2017, 11:04 PM
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^^^^ I'm thinking the same thing. My guess is the step that you introduced into the intake caused an increase in air velocity which negated/benefited the efficiency
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Old 07-19-2017, 12:27 PM
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Originally Posted by liquid_helix136 View Post
^^^^ I'm thinking the same thing. My guess is the step that you introduced into the intake caused an increase in air velocity which negated/benefited the efficiency
yup, I think if it was behind the throttle body it would have negative effects.
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Old 07-21-2017, 09:40 AM
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Either before or after the t/b would have a negative effect on power (if) the restriction causes less air to get to the engine than what the engine can handle. Look to nascar and the restrictor plate between the intake and carb. Then in sprint car racing they use go/no go balls in the injector stacks. They limit hp by the size of the injector stack so if you have a 410ci(makes 900 hp) that runs 2 1/4" i.d. stacks and change to 1 3/4" stacks you will lose close to 150 hp.

It would be fun to see some pulls with different size inserts to see what if any difference you would see from your 3 1/2" going down 1/2" at a time to see where the hp starts to really drop off. I would think a intake made in the size of tubing where you got the best hp/tq would not get you real world numbers you want. I think that intake would not be the best because of friction all along the intake, I've seen so many intakes that would feed 1 1/2 to 2 of the engines that were in the car. But they made a smooth transition(some were 12" long) from the larger tube to the final tube before the t/b and that set up made the best hp at the track.
You just have to find the right size pipe to run right before the t/b.

ROD

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Old 07-21-2017, 09:55 AM
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Simply putting a small restrictive filter on the end could be enough depending on how much your trying to cut power. I've pulled vacuum with several off the shelf name brand filters when building an intake for the S recently, which surprised me. That's not what you normally want, but in the OP case it is.
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Old 07-21-2017, 12:15 PM
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I wonder if he was overly lean and with the smaller insert he got the AFR up a little so he gained power?

Rod
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