Bypass Tube? HP gain?

SC UL8R1990

Registered User
I was reading back in the archives and read something about capping off a "bypass tube"?

anyone have any input on this? where is it and what does it do? is it harmful?
 
I think what you are reffering to is the bypass valve that is open when there is no boost being made and closes to let the boost enter the engine. By disconecting/bypassing the bypass I think the supercharger would be pumping air into the engine at all times. My dad told me that racers in the past used to do this. I am not sure if this is correct but I think that is what you are talking about.

Shane
 
I think you are referring to the "crosstalk" tube. This is about a 3/8" line that runs from the SC inlet plenum to the lower IC to lower manifold adapter. It is there (from the discussions on the boards) is that since the SC came with a very small MAF and restrictive TB. As the SC moves air there is a point that the SC tries to pull more air than what can pass through the inlet system without restriction.

As this happens the creation of low pressure area at the inlet and the high pressure area above the rotors cause a large differential pressure that pushes against the rotors with a downward force. Since the blowers output is not continuous (like a leaf blower) it's pulsed it beats on the bearings(this is also the reason for the distinct howl of a roots blower).
The tube is there to allow a small amount of air to enter the blower and keep it from cavitation.

On a stock car without extensive inlet mods leave it alone. If you have a car with a 75mm TB, high flow inlet plenum, and MAF then go for it.

Jeff



And on the byass valve they leak big time. you could probably pick up about 1psi if it sealed properly. I am trying to figure out how to make one using a valve (like an exhaust valve) for a proper seal. I have a bunch of different bypass valves but haven't really tested them to see how bad they leak.

The Bosch valve used on Saab's and some others (Vortech uses one of these in their kit), I have been told leak at about 8 psi but I haven't verified this. There is a replacment unit that is aluminum instead of plastic. It's made by Forge, don't know if it's much better.
 
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Removing the cross talk hose made my bypass valve too sensitive. Barely touch the throttle and it goes into boost..it was very annoying so I put it back on.

David
 
David Neibert said:
Removing the cross talk hose made my bypass valve too sensitive. Barely touch the throttle and it goes into boost..it was very annoying so I put it back on.

David
Would that make your car any faster though?

Shane
 
bingo , yea thats what im wondering too.....would it cause an increase in power?

also would it wear it out faster?
 
Would that make your car any faster though?

I thought it would.....but on my car there was no measurable difference on the dyno or the track. It just isn't enough air to make much of a difference either way.

David
 
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