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Discussion Starter #1
My engine makes a good amount of vacuum at idle around 20in or so. I have an on3 bov that came with the kit and I think the issue of why I’m not making boost untill way up in the rpms is because the bov spring is to weak. What brand springs can be put in these bov because it looks like on3 does not sell replacements
 

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Google BOV springs. They are all pretty much the same. Find a spring rated for the pressure you want and try it. They are fairly cheap, so you can get a few springs plus or minus your target and go from there. That is what I did.
 

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Ok cool I didn’t know if they where brand specific. Was there a certain brand spring you used? Such as ones for turbo smart or tial because I see that even different tial bov require different springs
 

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Discussion Starter #4
Will a stiffer spring actually help spool time? Like I can drive the car up to 4000 rpm but not putting too much load on it and I am still in vacuum. Or is that normal
 

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Ok cool I didn’t know if they where brand specific. Was there a certain brand spring you used? Such as ones for turbo smart or tial because I see that even different tial bov require different springs


I would use the Tial 50mm blow off valve springs. That’s the one the On3 resembles. I ended up buying another valve off fleabay (knockoff Tial) that came with a few other springs


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Honestly I don't think a bov spring is supposed to affect spool time at all. The valve should be lightly closed at idle so the spring is only supposed to be slightly stronger than the vacuum pressure in the valve dome. In overrun conditions when the valve needs to open, your manifold vacuum will be greater than idle vacuum so it'll pull the valve open to release trapped pressure but the valve will be closed as you normally drive it and as soon as you give it throttle because there will be less vacuum in the manifold, allowing the spring to keep it shut, keeping air from escaping.

Spool time is generally more controllable via wastegate and obviously turbine sizing.

Edit: Just making sure I capture the OP issue here but even if the spring is very weak, it still adds force to the equalized pressure above and below the valve keeping it shut. I think you'd basically have to have no spring in order for this to potentially become a problem.
 

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Discussion Starter #7
Right now I have my wastegate to my manifold because my turbo didn’t have a bung. So if I tap the turbo housing it may help? My hot side is a .96 and I have a 347 I thought that would work good together but it builds boost like a turd
 

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Right now I have my wastegate to my manifold because my turbo didn’t have a bung. So if I tap the turbo housing it may help? My hot side is a .96 and I have a 347 I thought that would work good together but it builds boost like a turd
pressurizing the gate from the turbo housing vs manifold doesn't make *much* of a functional difference on these cars, but can in other cases, which is why the housing is usually chosen for wastegate signal. It shouldn't affect spool time.
 

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many other factors affect spool time aside from housing A/R. what are the rest of the turbocharger specs (impeller sizes, housing sizes, connection type), and what is the diameter of your hot side tubing?
 

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Discussion Starter #10
I’m trying to figure out what to do. The car didn’t make good power and I’m trying to go through everything now and figure it out. I know number are numbers but it was disappointing
 

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I just drilled and tapped my housing because that’s what the precision wastegate instructions recommended to do lol. I don’t know if it will be any better but it did make plumbing easier. I wonder if it has more to do with the .96 AR housing? I’m sure a .81 would make it spool a lot faster


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Edit: nvm, I'd expect a healthy 347 to spool a 7675 pretty easily. I'd also tap the exhaust housing and run that line straight to the lower gate port, then make sure you have no other vacuum leaks in the system.
 
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