Jorge T

iTrader: (18)

Boost still tapers down in upper rpms even when boost tables are at 100% duty cycle.

Is it because boost solenoid is not able to bleed boost fast enough and the wastegate still opens?

Jorge T

iTrader: (18)

ne1?

MalibuJack

iTrader: (5)

The stock boost solenoid is a bleed system.. There are two things that I found cause it to taper, the amount of bleed is inconsistent, or falls off a bit as RPM's climb.. And if you have a stock Blowoff Valve, it begins to leak at 18-19psi (approx)

I've been working on a mod for the UTEC that converts the bleed system to a restrictor system, it should make for more consistent boost.. This is one of those mods that should work on the XEDE also (or anything that uses the stock solenoid)

dude

iTrader: (12)

I'm no expert but I'll take a stab at it. I think there are several reasons boost tapers, namely margin of safety on the manufacturers part. The other reason is that at higher rpm's the turbo is simply running out of puff. The Xede does very well at counteracting wastegate creep, that's why it's lowest load point is at 100% duty cycle, for faster boost response. An MBC can theoretically hold constant boost to higher revs, but I think it will bleed disproportionately more wastegate pressure and thus be less likely to hold that boost pressure reliably. Also, MBC's don't take into account changes in temperature and pressure (humidity) as well as altitude which can vary boost pressures over a couple PSI. Hope that helps you out a little.

MalibuJack

iTrader: (5)

Good points.. I'm familiar enough with how the stock bleed system works to know that it builds pressure faster than it can be bled, especially at higher RPM which will cause the boost to taper.. Partly the reason the restrictor mod is done with the XEDE it raises the amount of air bled slightly so you can get slightly higher boost levels until the pressure going into the system, outpaces the rate that its bled then it tapers..

Jorge T

iTrader: (18)

That is what I thought. Is there another restrictor pill going to the wastegate? If not would this help the bleed rate?

VWs boost solenoid is plumbed differently and with a big turbo can control boost at 22 psi across the rev range. That is with the correct ECU tuning.

MalibuJack

iTrader: (5)

Actually removing the other restrictor will drastically DROP your boost, there's no way the stock solenoid could bleed off the additional pressure.. If you want to raise it more, you need to add another bleed valve so more air can get out. Just remember that your lowest level of boost will also be raised..

Jorge T

iTrader: (18)

I was thinking of adding a restrictor pill to the line that goes to the wastegate, you know if there is one there?

Another thing would see if the the bleed hole on the solenoid can be "bored out", something that can be done on the VWs boost solenoid (just did not work right on that setup cause it bled to fast and opened the wastegate too soon.)

MalibuJack

iTrader: (5)

I don't know that its a good idea, you would really need to determine what the flow rate, and the actuation pressure is if you want to try that.


The restrictors are in the line from the vacuum source (discharge pipe or whatnot) and the other restrictor is near the boost control solenoid.

The boost control solenoid, and the T connector both add a little restriction and contribute to the puzzle slightly.

Hope this helps.

MalibuJack

iTrader: (5)

This is where the old "Fish tank pump valve mod" comes in handy..

Jorge T

iTrader: (18)

My car since new never "put out" the boost levels everyone claimed Evos have 19>>16 psi mine did ~1.22 bar (17.8psi) tapering to a bit over 1 bar. with Xede everything moved up a click, but never over 1.3-1.35 only sometimes with A/C on it would spike to 1.4 bar

Saturday AM Project:
Replaced 3.5mm id hose from T to solenoid with 4mm id hose and 2.5 mm id hose from solenoid to intake tube also w/ 4mm id hose.

What a difference! 1-3 gear I get upto 1.4 and tapers a to 1.3 Bar and 4-5 gear pegs 1.5 bar inching off to 1.4 bar. This is what I wanted!

David@Vishnu

iTrader: (2)

Good points by everyone. We include a bleed coupler if you got a stubborn turbo or miscasting ect. Also since we are talking about less than 2 psi discrepancy I suggest hooking up another more accurate boost gauge just for confirmation before trying to squeeze out more boost.

Jorge T

iTrader: (18)

I went back and put a 3.5id mm hose from the solenoid out to the intake hose and things toned down about .5-.75 bar, so max I see is 1.4 bar. I don't want to stress anything out!
David, still send me the bleed coupler...I got a better boost guage on my next to buy list

A418t81

iTrader: (5)

Sounds good, Jorge. I will have to try that also as I see about 1.35 bar dropping to 1.2 w/ the exede controlling boost. Had no problem running 1.4 dropping to 1.3 bar w/ the profec in the car.

David@Vishnu

iTrader: (2)

I will but I was suggesting just a borrowing of another boost gauge to confirm if your gauge is pretty close also guys lets be aware we are only talking about fractions of a PSI here lets not all jump to conclusions as environment has a ton to do with it