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Re: R U using a APR or a pressure reflief valve?
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Posted by Dexter J (more from Dexter J) on Sun, 15 May 2005 15:53:11 Share Post by Email
In Reply to: R U using a APR or a pressure reflief valve?, Jeff in ATL, Sun, 15 May 2005 10:06:32
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Salutations:

I'm using a standard 0-50psi relief type regulator directly between the turbo and the wastegate lines with 1/4 inch barbs - I have removed the BPC from the air-circuit.

I dial it up to 12psi and at 12psi it opens it's internal diaphragm to bleed off excess pressure so the wastegate never sees anything other than 0 through 12psi pressure. It relies on the wastegate spring to hold against the pressure being feed through it until it reaches 12psi (or anything else I would dial to it).

Basically - it sort of replicates what the BPC does - but not as finely of course. I think this might have a lot to do with the smaller air channels in the BPC - but I'm not sure.

It's a touchy thing to set-up. Get into the range where it does anything adjustable - then 1/4 to the right and it runs base boost - 1/4 to the left and it runs overboost. I have it somewhere in between. My BPV (which is an Audi unit for what I think is a 1.8 engine) may be lifting early as I get a sort of hiss as I get into the upper pressure range. Could simply be a helpful leak at this point somewhere too. It is not the regulator as it was there when it was running wide open to the wastegate through the flipped BPC.

When the regulator is cold - boost runs a little lower. When it warms up - boost runs a little higher. I put this down to the diaphragm getting warm. It is set-up next to the BPC near the rad - which is not a really good place for it given it's specified temp ranges.

Like I said, for performance builds - I think your MBC+A is a better thing.

But all I'm trying to do is get my boost back under control having reversed the shorted BPC to overboost rather than base boost. Flipping the BPC would be an interesting mod for folks trying to sneek in under street stock racing rules though.

Anyway - while it is not a great replacement for the BPC on the aero - it has the two 'advantages' over just running unrestricted pressure to the wastegate or default base boost. I get good boost in all forward gears rather than to the mapped restrictions for 1st and 2nd. It doesn't over pressurize the wastegate because unless I set the regulator to release pressure on the wastegate at too high a level.

If I were to continue with the system instead of saving up for a new BPC which I will modify - I would put a second failsafe on the main pipe between the turbo and the Intercooler in the body of a good quality adjustable full release pop-off valve. Potentially not good for the turbo (could then see some occasions where it might be over spun to destruction) - but then - better than overboosting and pushing a gasket out of the head if the MBC goes sour when no-one is paying attention.

Individually - neither the regulator/bleeder nor the pop-off as I have it would be a good way to protect the engine from overshoots - but together they might good enough for jazz.

At the end of the day, I think that the only thing I will want to look at after getting and modifying a factory BPC so it doesn't eat itself - will be a way to get boost back in first and second. Not sure exactly how to pull this off as yet without remaking the APC.

How exactly does it know it's in first or second on a five speed? Is there a wire somewhere on the shift linkage or tranny?

Dexter J

posted by 24.222....

http://www.dexterdyne.org

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