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I did a search and found this information on the LT4 bypass valve and adjustment. So I checked and found that my bypass valve was not fully closing. I made the adjustment and got a needle width more boost. Here are several videos on it. It appears now that the max boost is also coming in sooner.
From: 2007 Nat'l Corvette Challenge 11.50 index Champ. New Jersey
Maybe it was set up like that on purpose (to allow a slight amount of air to leak through)?
Does that lean the motor out though, like the bearded guy said in 1 of the Camaro videos?
Is this safe to do to a stock, untuned motor?
During assembly they just bolt the supercharger on as It comes already assembled. The ECM is already programmed for the tune. These are canned tunes, as not every engine is dyno tuned as with a custom tune. One would think when GM did the tune it would be with the bypass valve fully closed. Leaving it "partly opened" would have the tuners going wacko, one would think, as max boost would never be the same.
If the bypass valve wasn't correctly set (as Mary was having a bad hair day) the engine won't be making the correct power. On mine, it was at least a full turn open to much. I did see the boost increase after the adjustment.
Knowing the factory tune is slightly "fat" and the O2 sensors send info to the ECM and the ECM then adjust's the pulse it sends to the injectors for the programed AFR tune am not concerned about it being "lean".
Yes, in one video the tuner said to be careful about it being lean, but that may be just a shop owner looking again for "tuner corvette tax bucks".
Just so we are on the same page about the correct adjustment, all these should be installed with the bolt slightly touching then tightened 1/8 to 1/4 of a turn more? Why not back it all the way out add blue Ioctite then thread it back in
From: 2007 Nat'l Corvette Challenge 11.50 index Champ. New Jersey
Originally Posted by Pacembellum
Just so we are on the same page about the correct adjustment, all these should be installed with the bolt slightly touching then tightened 1/8 to 1/4 of a turn more? Why not back it all the way out add blue Ioctite then thread it back in
This is mine! WTF??? I measured mine and it's 3/8" open!
You want to be careful when doing something like this. That video is showing you how to make a blind trust me adjustment (HOLD MY BEER). However, checking for movement of the bypass valve lever arm isn't the way to check to see if the bypass is closed all the way.
The superchargers come from Eaton already to bolt on the engine and that screw is preset. I have had two S/Cs apart in the last 3 days with the screw set like that and the bypass valve inside the S/C was closed in both of them. Yes, it is tilted just a shade but it is still closed. I removed the snout from one of the superchargers and that required unscrewing the bypass valve blade and removing it from the shaft before I could disconnect the snout from the base of the S/C. What I noticed when unscrewing the blade is there is very little clearance. Once the screws were out the blade could move a few 10 thousandths and stick against the wall preventing movement either way. Open your valve too far so it is flat in the opening and you could run into a problem.
Here is a picture I took of the unit that is still together showing the closed valve sitting at a slight angle with a machinists rule lying beside the lever arm and the adjustment screw mount. A quick estimate with the eye ball shows the adjustment is set to about 3/16 inch.
If you think yours isn't closing all the way make sure you take the lid off before adjusting that screw.
Bill
Last edited by Bill Dearborn; May 22, 2020 at 04:19 PM.
From: 2007 Nat'l Corvette Challenge 11.50 index Champ. New Jersey
UPDATE:
I backed the screw out some and that piece did not move any. So then what's the point to that set up? I ended up just reapplying locktite & putting the screw back to just touching the plate it touches.
Can anyone else confirm the same?
From: 2007 Nat'l Corvette Challenge 11.50 index Champ. New Jersey
So different than on the Camaros some how.
When I backed my screw off the blade, the blade did not move. I even tried to move it further towards the screw but it did not move at all.
When I first saw where my screw was I thought I just found some boost and free HP! : (
I did a search and found this information on the LT4 bypass valve and adjustment. So I checked and found that my bypass valve was not fully closing. I made the adjustment and got a needle width more boost. Here are several videos on it. It appears now that the max boost is also coming in sooner.
close enough If your playing a game of horse shoes. —This adjustment technology looks like it was derived from a 1970’s Rochester quadrajet carburetor.
You want enough load on the set screw so the blade doesn't get stuck in the closed position. That's the reason for the screw.
Correct sir. This is the most important fact here.
The adjustment is meant to prevent the valve sticking closed from spring pressure and metal to metal contact when fully closed.
The book method works well and is technically correct.
However for those of us out here in the real world what you want to achieve regardless of distance measurement of the set screw is this:
You want the valve closed but barley closed. In other words you want the set screw set to a position that ensures the valve completely seals the airgap yet only allows the spring load to create the slightest bit of pressure at the first point of metal to metal contact at the fully closed position.
This amount of preload allows the valve to operate freely and not get wedged stuck from metal to metal contact.
This adjustment also stops a wear groove from forming around the outer diameter of the valve opening after thousand of closures.
If allowed to do this the valve would start to stick. The set screw is there to actually limit travel AND to ensure the valve is fully closed.
As stated originally the reason for the check is to ensure the valve is actually fully closed and the set screw doesn't leave an airgap at all.
This adjustment is set by Eaton at their factory and should be correct. However no manufacturing and QC process is 100 perfect.
So we check it to verify. Most will find it correct.
Last edited by dar02081961; May 22, 2020 at 10:35 PM.
From: 2007 Nat'l Corvette Challenge 11.50 index Champ. New Jersey
Not speaking against anything mentioned above, but on my car at least, when I backed the screw away from the plate it the plate did NOT move at all. Even when I pushed on the plate it would not go any further.
Boost bypass adjustment
