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Discussion Starter #1 (Edited)
Has anyone ever tried this on a b20 intake?

Now since I have 4 motors lying on my garage floor due to a spun bearing in my b21, a very huge mistake buying a junkyard b21 with 2 dead cylinders, and a rod out the back of a b20a5 and now a good running b20a5 I have an ample supply of interchangeable parts. (yes I'm very abusive to my engines on the track :)
I was wondering if anyone on the board has taken the sec. butterfies and connecting rod completely out and aluminum welded in where the the rod goes through each hole on a b20 intake. Kinda like making a plenum spacer. We use these on our Mustang race cars and they supposedly give slight HP gains. I was wondering if it would be the same concept on these intakes?
If I try it I'll post some pics.
 

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No...nobody here has ever thought of that. Why don't you just pull the vacuum line (and plug it) from the vacuum can. That will open the secondaries and let you see if there are any gains. Remember...long intake runners for low RPM power and short intake runners for high RPM power. The secondaries are not so much for adding EXTRA air as they are for giving the engine an air supply closer to the intake valves. Think of the senondaries as a cheaper version of the dual runner Accura intake manifold.
 

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But who needs more bottom end power when you're racing all the time (if that's what this car is for)? Wouldn't the top end benefit from removing the butterflies totally so that there is nothing impeding air flow? I know H22 owners do this for some top end gains, I'd imagine that it would work for 3g engines too.

I'd follow the same basic principle of companies that modify H series intake manifolds. They remove the butterflies and then port it all w/ flow testing. I'm sure that you'd get some good top end gains with this process...
 

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there was a company that did this.. it was black something.. Also a person on this forum has done it. i beleive but could be wrong that he actually just hollowed out the entire butterfly valve section and removed the seperator from the first and secondaries. basically made it a large chamber right before the last few inches of the IM. From what I have read this would destroy your low end power and when you can't rev to seven for very long without blowing your motor then it seems to me kinda pointless. but do a search for that black something intakes..
 

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Blacktrax probably...

Don't know why it would blow your motor unless it created a need for tuning (which is always good, even if it's a stock setup!)
 

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Daily Interlude said:
Blacktrax probably...

Don't know why it would blow your motor unless it created a need for tuning (which is always good, even if it's a stock setup!)
B20's don't like to rev that high, though. With the intake wide open like that, it probably flows most efficiently above 6k or something. Enough revving like that and you're gonna bvttsechs some bearings.
 

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yes, more then a few people have tried it. and it doesnt do anything but lower your low end power. its no different then the secondary butterflies sticking open. if you remove the entire secondaries PLATE and not just the butterflies and rod, then you are basically shortening the runners. whether it affects peak hp, i dont know. but it will deffinitely bring the hp curve higher up into the rpms as your shortening the runners almost a full inch by removing the entire plate. a few people on this site have also tried doing this, but i dont recall any results being posted
 

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I wanna try leaving them open. Which vacuum hose is it that if unplugged and sealed, would cause them to be left open?
 

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you're wasting your time by trying to leave them open, but if you really want to try, look on the driver's side of the intake manifold. below the plenum is a vacuum line going to a small diaphragm with a small linkage. the linkage is attached to a rod that goes through the center of the intake mani. remove the vacuum line from that diaphragm and plug the rubber line but leave the diaphragm un-plugged.
 

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there is a diaphragm on the front of the intake manifold on the driver side... it has a lever that goes right into that plate with the secondary butterflies. the vacuum tube goes right into the top of the diaphragm housing.. you can't miss it.

it is vacuum that holds the butterflies closed, remove the vacuum, and the spring will force them open.

EDIT: lol.. we posted at the same time..
 
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