boost tapering

criptballer · Nov 1, 2009, 09:09 PM

ok, so i'm trying to keep my psi through the rpm bands somewhere in the 21-22 all the way to red line but apparently i'm having some issues figuring out why I can't do this. I have a Hall man pro Rx MBC and from the sounds of it i don't need a boost pill when running a MBC. Is this correct? and if so, then why am i still tapering down all the way to 16 by red line? has anyone figured this out yet? this is really frustrating, i tried doing some research but i didn't find anything on how to fix this problem. Help and advice is greatly appreciated.

criptballer · Nov 2, 2009, 07:23 AM

Bump for some answers. I've been reading about the new plug and play Grimmspeed 3 port bcs, is this the answer?

rogue · Nov 2, 2009, 07:47 AM

You don't need a boost pill.

When you installed your MBC did you use new lines to attach it to compressor housing, intake and wastegate? Those lines cannot have pills in them.

You can use a 3-port boost solenoid and control boost through the ECU, you will not need a MBC if you do this.

criptballer · Nov 2, 2009, 08:06 AM

Yes I used new lines when I installed my mbc but I'm still tapering about 8-10 psi to redline. Are u running solid till redline? If so, what are u using?

Also, I don't have a line going into the intake. My mbc only had a boost inlet (coming from the nipple of the top intercooler pipe) and a boost outlet (going straight to the wastegate).

buchnerj · Nov 2, 2009, 08:08 AM

Well, it will usually taper back a little by redline, however 12psi taper is too much. Did you do a boost leak test to check for any problems in the system? It is good you got the pills out of the lines, but something isn't right setup wise if you are losing that much pressure every time.

rogue · Nov 2, 2009, 08:09 AM

Well with my 3 port I am able to hit 27 psi and then I taper to 20 or so by redline. You will see some who hold 19-21 until redline and no more. This is because of the flow characteristics of the turbo.

Clark_Kent · Nov 2, 2009, 08:18 AM

^This. There is nothing more you can do to sustain higher pressure that far in the powerband.

criptballer · Nov 2, 2009, 08:21 AM

So no matter what I do I will always be tapering down that much? What would happen if I install a boost pill on the line going to the wastegate? Also, I set my mbc correct right? Thanks for all the input guys

rogue · Nov 2, 2009, 08:22 AM

I do think that if you are using a MBC you should not be going so low into the boost range...

All your lines are hooked up correctly? (Yes, a dumb question, but I have made mistakes before)...

right Clark =)

rogue · Nov 2, 2009, 08:24 AM

Quote:

Originally Posted by criptballer

So no matter what I do I will always be tapering down that much? What would happen if I install a boost pill on the line going to the wastegate? Also, I set my mbc correct right? Thanks for all the input guys

1. The boost pill would be used with the stock BCS, not ever with the MBC.

2. You will always taper at the far end of the rev range, you cannot do much about that at this time.

criptballer · Nov 2, 2009, 08:38 AM

Can anyone verify I have installed this right. I have a hallman pro rx, I have a line going from the uicp nipple into the top nipple of the mbc(inlet) and the outlet line coming from the mbc going into the wastegate. Right or wrong?

criptballer · Nov 2, 2009, 11:01 AM

bump for some much needed help

buchnerj · Nov 2, 2009, 11:06 AM

that sounds right, the setup is a little different for my 9 like i PMed you, but if you think about it, the outlet (bottom nipple) on mine goes to the wastegate, same as yours, and the other nipple goes to the boost source. Mine is on the hotside pipe right after the turbo, yours is on the UICP, same thing, just different pipe after the air is charged...

rogue · Nov 2, 2009, 11:29 AM

Yea I think yours should be going to the compressor outlet and the other to the wastegate...

I do not think you should have it hooked up to your intake as that on sees vacuum.

You are probably running boost of the waste gate at this point, which is why you are not seeing the boost stay at a higher level.

UT_EvoX · Nov 2, 2009, 12:14 PM

It's because you are at altitude and you haven't adjusted your boost/vacuum data logging item in EvoScan. I have mine calibrated to about -12.65 rather than -14.5. That will show the actual positive pressure up here (it will show higher once adjusted). Also, you'll never see as much boost up top at 4500 ft as you do at sea level. I saw 21 psi at redline at sea level, and only 19.5 up here. Be VERY wary of turning your boost up beyond 25 psi here, I've lost my turbo in the last 10k miles because I've been running 28+ psi at altitude. The pressure ratio becomes higher with the less dense base air given the same boost pressure (the compressor has to spin faster to achieve the same amount of boost). Anyway, if you need any help tuning, I can drop you some tips.