Right now I have to spike to 12 psi for it to settle to hold 10 psi above 5.5k rpm. Greddy 15G, stock wastegate, ebay ball and spring MBC. Basically this is an issue of too weak of a wastegate right?
Let's say I want quick spool up and then for it to hit a set psi and hold it strong. What's the surefire way to do it? Don't tell me to use EBC with MS - I've already ruled that out as it's far too finicky.

I've heard amazing reviews about the Greddy Profec-B (not type II).

I've also heard of HKS and similar brand wastegate which are supposed to be stronger..

New ideas? One of the ones above?

-Ryan

EDIT: SOLUTION AND RESULTS ON PAGE 2

 

You are using the fitting on the side of the compressor to feed into your MBC, right? Nix that. Cap the fitting, drill a hole into the cold-side charge pipe (between the intercooler outlet and the throttle body) and install a 1/8" NPT to hose-barb adapter (available from your local ACE hardware store in the plumbing section). Use that to feed your MBC.

The problem is that intercoolers are inherently restrictive. Yes, even ones the size of a Peterbilt truck's front grille. Thus, for any given airflow, the pressure after the intercooler will be lower than the pressure before it. Now, a fundamental tenet of fluid dynamics is that pressure drop across a restriction increases with flow. Assuming a constant load, flow (volume of air per second) increases linearly with RPM. If the engine is passing 100 CFM at 3,000 RPM, then it'll be passing 200 CFM at 6,000 RPM. (made-up numbers.) So, the pressure drop across the intercooler will be roughly double from 3,000 RPM to 6,000 RPM.

(Physics majors, please ignore the fact that I'm pretending all these relationships are precisely linear. It's easier this way.)

So the problem is that since you are feeding your MBC pre-intercooler, it's probably doing a nice job of regulating the pre-IC pressure to a steady state. But since the drop across the IC increases with RPM, MAP decreases with RPM. Move the fitting to a position after the intercooler, and then the MBC will be regulating pressure after the intercooler.

 

I've heard that if you drill a tiny hole in the MBC that it will help smooth out spikes, is this true?

 

Excellent info and thanks Joe. Just one question arises about the suggested change: I've read that it is crucial to keep the vac line to the MBC and from the MBC to wastegate as short as possible to increase response. Obviously a line from my coldside to the wastegate instead of running off the compressor is going to be 5x-6x longer than it currently is. Is this an issue?
-Ryan

 

I've not heard that one before.

The reasoning behind it is understandable, though fallacious. The volume of air inside a length of 3/16" vacuum hose is relatively minuscule- approximately 0.33 square inches per foot. This is going to have next to no effect on the operation of the boost controller or the wastegate canister.

From a practical standpoint, I went down this path myself. Initially, I used the stock compressor nipple on my turbo to feed my MBC, and spent a lot of time troubleshooting boost drop-off. First, I went through a series of "helper springs" on the wastegate arm, but all these did was raise my base pressure. Next, I thought my cheap hardware-store MBC was at fault, so I bought an expensive TurboXS unit and had exactly the same result. (Incidentally, this is the one with both the ball-and-spring as well as the variable bleed- functionally equivalent to drilling a hole into a cheap MBC.) Then I replaced the wastegate canister that came with the Greddy turbo with a big one from Garrett. Nothing helped.

Finally, Abe suggested that I relocate the MBC pickup to a port after the intercooler, and that's when a light went off in my head. Duh! My dropoff was caused by the pressure drop across the intercooler! Moved the line, and problem solved.

As to line length, you should see my setup. The vacuum hose goes from the coldside up pipe, along the radiator, down to a brass "T" fitting mounted behind the headlight, up to the MBC which is mounted on the valve cover, back down to another "T" fitting, and back up to the wastegate canister. (The "T" fittings are mounted to either side of an air solenoid, which disables the MBC as a failsafe if my water injection doesn't come on.) Total line length is probably close to 10 feet.

 

Excellent info. I'll give this a shot and post results as soon as I do.

Got a pic?

 

Since we are talking vacuum/boost sources.

Getting the wastegate signal from the vacuum booster supply line should be safe too? I was going to install BEGi's 3 port vacuum splice at the booster, and run my wastegate, boost gauge, and MAP sensor off it.

 

I have heard that certain death may result from sourcing your wastegate signal from a throttled location (ie brake booster line or manifold) because then the turbo is free to create as much boost as it possibly can when the throttle is only partially open creating a potentially dangerous situation.

 

No.

If you do this, the wastegate will be closed damn near all the time. When you're at part throttle, just tooling along at 3 or 4 PSI up a hill, the wastegate will be closed and the turbo will be spinning like mad, putting as much pressure into the intake piping as it possible can, trying desperately to get to a limit it'll never reach, and making gobs of heat in the process.

With the reference taken before the throttle plate, the turbo will never make any more than the set pressure in the pipes. (Minus loss across the intercooler.)

 

Here's the best one I can find at the moment.

The hose coming off the top of the throttle body goes to the BOV, which is just to the left of the circular saw blade on the crank pulley. (You can't really see it.)

The hose stretched across the top of the radiator fans goes down to a brass nipple installed in the side of the coldside pipe. The nipple itself is hidden behind the upper radiator hose in this pic.

The pneumatic solenoid with the brass T fittings on it is mostly obscured behind the power steering fluid bottle. If you look hard, you can see the big brass Tees on either side.

The hose goes from the radiator fan, loops around the long way, and goes into the brass tee on the right. The fat blue goes go to and from the MBC (bolted to the front of the valve cover) and then the skinny blue hose on the left tee goes to the wastegate can.




Also, since we're in a picturey mood, here is a tray of sliced pork uteruses:

 

Joe, are you on the garrett wastegate or did you go back to the Greddy one? I have always read about the Greddy one being crappy, is this also the case, or could I just relocate the nipple to after the intercooler, run a MBC and get 14-15psi with the Greddy wastegate? Or would I need to upgrade to a better one/use a helper spring? (yes...I have bigger injectors, fuel pump, MS, etc. I am focusing on the wastegate)

 

um joe i have run with my **** hooked to a manifold vac line for a long time with no issues man the manifold boost is overall your most reliable source. And the vacuum from time to time will not hurt the diagphram either.

 

That doesn't mean it's ideal, does it?

 

Why wouldnt be ideal? It is the endall be all pressure pre combustion chamber barring leaks whats your problem? The further i had my mbc from the boost source the more reliable of a pressure i could maintain up top, or idle once i went with a vented unit.

 

I don't have a problem man, chill, it's just a discussion.

I'm just saying, Joe has laid out an argument against sourcing boost signal from the IM, and all you've said is that you run it that way. That doesn't make it right in and of itself, so I'd be interested to hear more specifics from you about this.

 

Lol no worrys koto u know i respect u and joe. Ok i will do an indepth analzyes and get it to you guys.

 

Ok joe i take particular exception to this the turbo wastegate is always closed until u reach a boost lvl capable of moving the diaphram and opening it. So no matter where u source ur WG line from it will stay closed at 3-4 psi until ur desired psi even at part throttle. The reason we run ebc and mbc etc is to make sure this happens at a pressure higher than WG and or that we can garner a better spool from what our wg gives us becouse sometimes the valve will flutter everso slightly on the way up to maximum boost and this will cause an inconsistant climb in boost and with it tourque and hp. Also u know as well as i do turbos are laod driven. They make boost determined via the restriction of the intake tract and the output of the exhaust, the more laod your motor is under the more exhaust gasses it will expell thus making the turbo spool. By sourcing from the intake vaccuum sources u eliminate the gues work on pressure loss from all the stuff u stick between your compressor and your motor. This rather large chamber of final waiting for our intake tract is the ideal place to take readings on what goes in our motor.
One could also argue that since it is post the cooling process either IC or WI etc the density of the intake charge and its pressure would also bemore reliably measured in the intake manifold. As anyone familiar with the ideal gas laws knows volume is variant given pressure and relative temperature since we have a fixed volume then our pressure and temp work inversly and quite readily in the way that the lower the temperature the more density and relative pressure. Where as when we measure at the outlet of the compressor and the air is at its thinest and hottest our pressure readings will be much lower than that of the cooled charge. Assuming the compressor has the capacity to fill the entire intake tract at a rate to keep the pressure and heat up. If your turbo was going out of its effeciency range then your compressor wheel spinning at maxx rpm would simply be recompressing the same air results in less movement and intake velocity overall and the same or less pressure than when u where in your effeciency range. This ultimatly generates exponentialy more heat than flow and even when cooled u are facing a loosing equation in terms of performance.
I hope that wasnt to horrib man i havent done it like this in a while.
If some of the sciency stuff went over your head the wiki can help u understand it abit better http://en.wikipedia.org/wiki/Ideal_gas sadly im not as good as my highschool chem teacher.

 

Oh god, Magna is going to do an in-depth -----zyes. Everyone pucker up!

 

lol is oficialy back oh and a ebay or home depot made mbc will do u as well as anything else man

 

Quite the story there! I'll keep it in mind for future plumbing. Looks like in the pic you use the factory barb that is for cruise control, or capped if you dont have it. Sounds good. Where is your vacuum source for your boost reading?