Does an MBC increase spool?

[sweet97]

There seems to be comtroversy over this perhaps brought on by midleading advertising. However does a good MBC help the turbo spool quicker? Anyone experienced it? How much quicker? No quicker? Opinions? Thanks, mark

 

[tstkl]

the only possible way is if the bad mbc (or whatever is controlling boost) starts to prematurely open the wastegate... and youll only notice it if your anal retentive and think that the spool time from your 70% full boost to 100% full boost time is too long for some reason...

 

[sweet97]

Well I needed a new MBC so I ordered the Forge UNOS MBC. Right now my actuator is T'ed into the BOV line so the actuator/wastegate sees boost the same time as the intake and spool is very slow. I was thinking if the MBC was restricting the amount of the boost signal the actuator gets it would increase the spool. Guess I'll see in a few days! How about EBC's, quicker? Thanks, mark

 

[tstkl]

i dont think any ebc's cut off the flow completely, i think most use a ball and spring type check valve just like an mbc... someone can correct me if im wrong tho...

 

[K_Hill]

A MBC doesn't increase spool at all that i am sure of.. Someone correct me if I am wrong.

 

[turbo2086]

I don't think they do. My friend got a hallman boost controller. Instead of T in the BOV line, he hooked it up to the the little hole in the turbo outlet elbow. He blew his engine, but before he blew it, he said it spooled very quickly. I don't know, one of these days im going to try it.

Check for boost leaks, that helps out with spool time. Also I believe the shorter the vacuum hose length is, the quicker the spool time??...

 

[tstkl]

vacum hose length.. unimportant... compressor outlet difference....psi..
any intercooler will "lose" psi, you put in 10 psi, you get out 9 or so... i had a line go straight from the compressor outlet to the wastegate, and my car ran at 9.2 ish psi.. because the stock intercooler loses about .8 psi... so if i had a mbc, i would have to turn it up an additional .8 psi if i wanted to get 10 psi, but if i had the line go straight from the upper intercooler pipe or the manifold, i wouldnt...

 

[oldman]

vacum hose length.. unimportant... compressor outlet difference....psi..
any intercooler will "lose" psi, you put in 10 psi, you get out 9 or so... i had a line go straight from the compressor outlet to the wastegate, and my car ran at 9.2 ish psi.. because the stock intercooler loses about .8 psi... so if i had a mbc, i would have to turn it up an additional .8 psi if i wanted to get 10 psi, but if i had the line go straight from the upper intercooler pipe or the manifold, i wouldnt...

The difference you see only matters to you, not to the turbo because the boost gauge is tapped to the manifold no matter what. In other words, turbo will still spin at the same speed to achieve the boost level you see on your gauge, whether this is done through slightly lower pressure source from the BOV line causing the actuator to open a little later or through slightly higher adjustment on the mbc when tapping from the compressor housing.

There are however some real advantages when tapping from the compressor housing.

1. Greatly reduces the chance of boost spike and boost leak due to short route pipping.

2. In the case of serious boost leak, it will help prevent overboosting the turbo due to the leaks.

As for the sweet97's question, a mbc should not make a difference if the mbc and the rest of the system are functioning properly, unless you're comparing a ball/spring to a bleeder type mbc.

 

[sweet97]

Well Bruce like I said I simply have a line t'ed into the BOV line from the actuator, no MBC right now. KEYDIVER from DSMchips believes a ball/spring MBC should increase spool as he says the ball should stay seated for a while before lifting and sending a signal to the asctuator. I will do some testing when I get my MBC in the next couple of days. Turbo spools like a mother with no line on the actuator but then the boost goes too high as only the boost pressure on the flapper opens it against the actuator spring.
Someone should have designed a boost controller, MBC or EBC, that would allow the actuator not to see a signal until the desired boost is reached or close to it, that would be boss! mark

 

[pkieley]

Someone should have designed a boost controller, MBC or EBC, that would allow the actuator not to see a signal until the desired boost is reached or close to it, that would be boss! mark

Turbosmart's eBoost has a user defined "Wastegate Pressure", Which won't reduce the point the turbo begins to spool, but claims to reduce the time to full boost.

I'm not logging boost so I can't prove/disprove it, but it seems to work.

 

[Defiant]

There seems to be comtroversy over this perhaps brought on by midleading advertising. However does a good MBC help the turbo spool quicker?

What are you calling "spool"? The turbo's driven by exhaust heat, and gas flow. An open wastegate lets the exhaust energy escape without going through the tubine. The rate at which the turbo speeds up is a function of the turbo design- the T-25 is meant to come up to speed at low revs, where most street driving is done. It runs out of efficiency around 5500 rpm, but you've usually upshifted before that, and the "worthless" T-25 is back in its operating range.
Unless you have an issue with a wastegate opening too soon, a boost controller won't affect where the turbo starts operating- it only determines at what pressure the wastegate starts opening and reduces boost. If the controller is adjusted so that the wastegate doesn't open soon enough, damage is inflicted, usually starting with piston melting.

 

[oldman]

Someone should have designed a boost controller, MBC or EBC, that would allow the actuator not to see a signal until the desired boost is reached or close to it, that would be boss! mark

Mark (old man) , a well designed and functioning mbc is suppose to do just that, block off the pressure source completely until the spring tension is overcome and the ball is pushed far enough to expose the actuator path. For this to work properly, the housing ID and the ball OD should be nearly identical (what I consider well designed) so little to no air would get around the ball before the desired boost level is reached. This does not apply to bleeder type mbc like Turbo XS for obvious reasons.

With that said, if you're able to see spool up difference when the actuator nipple is left open (not just the butt dyno playing a trick on you ), let's do a simple test that will help pin point where the problem is.

1. Make sure the actuator is doing it's job by applying compressed air and observe that it holds the pressure completely until the psi rating of the actuator is reached.

2. Apply pressure air through the inlet of the mbc and record what happens at what psi.

 

[sweet97]

Defiant by "spool" I mean will the MBC restrict the positive pressure signal to the actuator to a set point so that the turbo will reach let's say 20PSI 1000rpm's quicker than the way I have mine set now with the actuator simply T'ed into the BOV line. The way I have it now the actuator begins to see the signal immediatly. I am hoiping like oldman said that a properly designed MBC will keep the actuator from seeing the pressure until a "set" point so that boost increases faster.
When the TurboXs MBC's first came out they claimed full boost 800rpm's quicker. I have run my actuator without a hose and let the boost againsat the flapper force it open over the actuator's spring pressure, great spool but no control and near 30psi. Too much boost for my comfort. 25 psi is OK.
Then is there an EBC that will withhold the positive pressure iuntil a set point allowing the turbo to spool quicker and then release the signal opening the wastegate so to keep the boost at the level I set it at? Sorry if this was a long winded way to try to get my questions across!! Mark

 

[oldman]

Mark, I was not aware you had the Turbo XS mbc. IMO a bleeder type valve mbc is the only possibility that a mbc will slow spool because it basically creates a boost leak in order to bleed off pressure. An EBC uses bleeder solenoids just like stock bcs and the Turbo XS so I don't see it being more precise than a well design ball and spring tapping off the compressor housing (instead of BOV) and mounted near the turbo with the shortest hose route possible.

Switch pressure source from the BOV to the compressor running straight to the actuator and see if spool improves.

 

[sweet97]

The Xs was on another car so not relevant. I am getting a Forge but not sure what type it is, just that it is hot and has great reviews. I do expect it to help the spool.
I'll know in a couple of days. mark

 

[Spyydie98]

Like Defiant said, boost controllers do not impact the spool rate itself (only the point at which the wastegate will open). When you punch the throttle, the turbo will spool at a rate depending on how quickly exhaust can be expelled. More throttle=quicker rise in rpm=quicker exhaust=quicker spool up (the gear you're in plays a part due to resistance and airflow speed is reduced if you're in 4th gear at 25 mph for example). The quicker you can expel exhaust will mean the quicker the little exhaust wheel inside will spin=the quicker the intake wheel will spin and the turbo will spool up. The T25 begins spooling at a less rpm due to the size of the wheels inside relative to its own airflow rate. Less exhaust pressure is required to get the smaller wheels spinning, so you can begin spooling up at a lower rpm. As long as the wastegate stays closed (and you have no leaks in the system) the turbo will spool up as quick as it can based on the parameters above. A better boost controller will only impact how quickly (and at what pressure) the wastegate opens or closes based on the boost that is impacting the actuator.

 

[sweet97]

Well I checked with GREperformance.com and indeed the MBC will allow the turbo to spool quicker. The ball stays seated until the set pressure is reached and then it opens to allow the pressure signal to the actuator. I will however do the test oldman suggested as that makes sense. The longer the wastegate flapper stays closed the quicker the turbo will boost. I agree that the rate at which the wastegate flapper opens will change the spool time. That's the point of keeping it FULLY closed as long as possible. thanks, Mark