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Underbody braces, turbos and more!

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PostPosted: Sun Jun 28, 2015 4:51 am 
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Let me first say I'm not posting this willy nilly. I have read every post I could find regarding blow off valves,waste gate,boost level ect and still find it necessary to as questions.
I know it has been asked a million times but So I figure one more won't hurt.
Question -1 What is a safe boost pressure with out a wideband? I have a dyno jet wideband
commander with LCD but dyno jet screwed me royally so for now I do not have a wideband installed.
Question -2 what is a safe boost pressure WITH a wideband installed?
Question -3 what is the relationship between boost, blow off and waste gate pressures?

If I'm running 10lbs of boost at what Psi should my wast gate start to open?
If I'm running 10lbs of boost at what psi should my blow off valve open?
If I adjust the boost in the future will I need to adjust the blow off pressure as well? IE electronic boost controller

I have a small low pressure hand held pump for setting up Jet Ski carburetor pop off pressures which I can attach to the waste gate and the blowoff valve to set the initial pressures
I'm sure this is basic to most of you but would appreciate you're time on this. Promise I'll never ask again.

Edd

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PostPosted: Sun Jun 28, 2015 10:16 am 
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Joined: Fri Jan 07, 2005 2:46 pm
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Location: Arizona
You are over thinking this
Q 1 & 2 : Safe boost pressure is one that does not overwhelm the fuel system. As long as your air-fuel mixture is slightly rich , at full boost, you are safe. O2 narrow or wide band just helps you know when you are about to blow up your engine because you are running 18:1 air-fuel
Q3 waste gate pressure is same as boost if it is factory set up. If you have boost controller you are effectively bleeding the pressure from the waste gate to achieve higher boost then factory intended. Blow off valve should not open at all until there is vacuum in your intake manifold ( meaning you shut the throttle ), it doesn't matter what the boost pressure you are running.


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PostPosted: Sun Jun 28, 2015 1:12 pm 
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Ok. I think I'm getting it. I was under the assumption the BOV operated when boost was too high in the system I didn't realize it operated off of vacuume. So I guess the vacuume present in the line is what opens it? So simple but I just misunderstood it.
I understand about the wide band and air fuel ratios I just don't know what I can safely set the boost at with out monitoring it. I have a K03 Audi turbo. Should I just set it at the factory setting of 5lbs to be safe or can I go up a little?
Thank you for responding to both posts I do appreciate it.
Edd

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PostPosted: Sun Jun 28, 2015 1:50 pm 
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I've been doing 10-12lbs of boost on my Mk1 for years. With 91 octane and all ignition components in good working order its been a hoot :D For couple of pounds more then that you have to switch to bigger injectors but after that factory engine management is just done.


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PostPosted: Sun Jun 28, 2015 2:11 pm 
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That's about what I was thinking 12lbs max from what I've seen in other posts. May start at 10lbs. I'm not looking to have to upgrade fuel system or engine management. Not looking to make huge HP numbers. just want what I can get with out sacrificing reliability. Waiting to get my cam back from Superfly and I think between that and the added boost I should be good.
Back to the BOV. If I vent to the atmosphere is there a chance it could ingest air along with dust or would it close before that could happen? Is there a reason why I shouldn't recirculate it or is it just not necessary? Again sorry for being so basic I just want to understand why I'm doing what I am doing.
I want to learn not just fix it.
I've already learned way more than I knew when I posted this. Thank you
Edd

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PostPosted: Sun Jun 28, 2015 6:35 pm 
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There is no way any dust can make it into intake system through BOV. You have 10 psi blowing out and as soon as you step on the gas the spring inside it will slam it shut.
There is no reason why you should not make it closed loop system . There are reasons why you should. When the BOV is open and 10psi of air is dumped to intake side of turbo compressor it keeps it spinning and the whole mass of air keeps moving in the direction of the throttle plate in the whole system (thats why its important to have BOV as close to throttle as possible. To minimize amount of air moving in opposite direction, away from the throttle) . Opening the throttle, that whole moving mass of air will be moving toward cylinders now and the turbo will be back to full boost instantly. Lets not forget the fuel that was injected for the air thats metered , if you dump the air to atmosphere the fuel cant burn (it is the fuel that makes power ) and it cools the turbo in the process. As we know the turbo works on heat and pressure of exhaust gasses. Cooler the gasses less power for it to spin and make boost.
I had closed loop system on my Conquest ESiR and it made huge difference after the gear shifts. The fall in boost pressure was almost imperceptible during shifts.
In your case with CVT I'm not sure how much of a difference it will make, but you will find out for us :mrgreen:


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