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Anyone's Forge MBC do this too
I recently had the forge MBS installed on my MR, mods in sig. On the soft spring it would only boost to about 19.5-20psi and then tapered off to around 16 by redline. We then switched in the stiff spring, which didn't seem to seat completely on the top of the valve assembly, it more just rested on it. The car then spiked immediately to 25psi and we shut it down.
My installer decided to switch back to the soft spring and try to install a small shim to see if we could compress the spring just a lil more than full "+". This worked - sorta... Now the car spikes to 22.X psi @3500which is great, and tapers to about 19 psi, which is fine. But at around 5200 it tapers down again to about 17psi, which was kinda disappointing. It is hooked up to the compressor housing, and mounted under the intake, so maybe 12" of tubing. I know the car previously held 19-19.5psi to redline with a different BC. Could it be the mbc causing the taper, or should i try some other source first? I SOOO wish forge provided an intermediate spring, or atleast a stiffer spring that started out with some overlap on the soft one. Has anyone gone to the hardware store and picked up a middle spring?? Just figured i'd see if there was any consensus on this and give a heads-up since this is a fairly new product Thanks for the help guys...and i still put down 282 @6500 on a mustang with only the 17psi, so i'm not too upset :) |
I'm pretty sure one guy mentioned having the same problem, and it was discussed in the original forge mbc thread. I think the answer was that you need to press the end of the spring down so that it sits flush, not just resting on the assembly like you mentioned. I have the stiff spring in mine and hold a steady 21# all the way to redline - I love it.
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Originally Posted by hardt45
I'm pretty sure one guy mentioned having the same problem, and it was discussed in the original forge mbc thread. I think the answer was that you need to press the end of the spring down so that it sits flush, not just resting on the assembly like you mentioned. I have the stiff spring in mine and hold a steady 21# all the way to redline - I love it.
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Just installed a forge and before what seems an unrelated problem I had the softer spring running peak at 21.5 or so and really holding w/in a pound or two. I was, admittedly, surprised because of what I'd read here. Mine's running to the manifold pressure hose not the turbo outlet, however. I heard that would be much less exact but hell, I've been happy enough.
I am running Buschur's Deluxe FMIC and piping as well as their intake, however, as well as 264/272s untuned. I have a Works P2 flash for my 3"TBE on 93 octane. Those are the key differences I can say about my '03 and your MR I guess ... Have you done a pretty solid boost leak test? |
That's good to know. Maybe I will try playing with it a bit if the weather gets a little warmer one more time hopefully!
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I rechecked my graphs: I get a boost spike to 22psi, then it falls to 21 psi at 3500 and stays pretty flat until 4600 and steadily drops off from there, down to 18psi by 7000.
I haven't done a boost leak test, but since it is holding 21psi for a solid 1000 rpm's (3500-4600) before it drops off, I don't think it is a leak in the system. Could it be BOV related, I am running a 1G bov that came from Buschur on his IC piping? That's the only other thing I could think of, but I don't know why it would hold 21psi at 1 rpm range and not at another. I will hopefully try the stiffer spring seated more completely this weekend and see if that solves things. |
i installed mine last week on the spring that came on it and it's holding boost just fine. it was acutally holding 22-23 psi with a small taper at about 6500rpm. right now im boosting 20 and it holds pretty much to the end. i have mine installed from the wastegate and the turbo outlet
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Damn sirloin, sounds like you got a good one! its seems that 21psi is kind of the bubble for the soft spring, some people are just over it, some are just under it in general. For whatever reason my car decided it wanted to be both :)
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hey try intstalling it to the turbo outlet. since you said it's installed to the intake housing. you might get a better boost flow?
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OK, after reading another thread here, it seems that if you do wish to use the stiffer spring you must make an effort to get it into the base. Otherwise it rests on top and is too stiff.
I noticed this when I put the springs in. Frankly, I think the soft sits on top of this short, cylindrical base as well. Hopefully, it's not much effort to press one end of the stiffer spring in and give it a try. Trojan man - you might try a thorough sit-down-and-search here about boost taper. There's been alot said about it. I'm afraid all I know is my experience with the Forge I have installed. Good luck and let us know what's working or not! |
Perhaps you have a boost leak and your turbo runs out of steam keeping up with this added demand at higher rpms. The Forge MBC from what I read is the best MBC out there and should not do that, I would rule that one out at first and would be affraid to 'shim' it - or 'shimmit'. Hey I just created a new curse word - shimmit.
Or maybe your mechanic hooked it up wrong, but I would say most likely after you hit 25 psi on stock tightened clamps designed to boost at only 19 psi, you blew a leak somewhere. But I could be wrong |
Use the stiff spring, you'll have to work at it to get it to seat right. 15 turns from soft got my boost up to 21 psi and it holds 20 to redline.
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I'll try to clear up a few things.
-------------------------------------------------------------------------------------------------------- As for which spring to use, you need to first consider the base spring pressure of whatever wastegate actuator or external wastegare you are using. If you are still using the stock actuator, your base spring pressure is about 12 PSI or so, so you will be adjusting from that point. Our softer MBC spring will only allow about 22 PSI to be had from the stock actuator. This is about a 10 PSI increase. The stiffer MBC spring will allow a much higher range of adjustment. If you are using our actuator, for instance, it can have a spring pressure of 14-18 PSI or 19-24 PSI depending upon which spring is requested to be installed. Considering that the softer MBC spring allows for about a 10 PSI increase in pressure, you will see 24-28 PSI with the 14-18 PSI actuator spring or you will see 29-34 PSI with the 19-24 PSI actuator spring. The stiffer MBC spring will provide a higher range of adjustment for a given base actuator spring pressure. -------------------------------------------------------------------------------------------------------- When installing the stiffer spring into the MBC, you need to be sure that the spring is stretched around the base of the adjuster of the unit. Failure to do so can result in inconsistent movement of the spring and check-ball. This is easily accomplished by carefully stretching the terminating end of the spring around the base and "wrapping" the first coil of the spring around it as well to seat it properly. -------------------------------------------------------------------------------------------------------- When installing the MBC, we HIGHLY recommend using the pressure source directly from the turbo outlet or from the intercooler piping BEFORE the throttle body. Sourcing the pressure line for the MBC from after the throttle body (intake manifold) or by tapping the BOV line will result in a decrease in responsiveness of the unit and can also cause hesitation and other issues with the BOV. Below is a quote taken directly from page 10 of the original UNOS MBC thread:
Originally Posted by Mike@Forge
For anyone concerned over the best way to install a boost controller......
........Al/Dynoflash and I spent about an hour on the phone yesterday and part of our conversation was concerning the best way to setup/install a manual boost controller of the lock-ball and spring type. (Like our new Unos.) Here are the results: -------------------------------------------------------------------------------------------------------- Turbo Outlet This is the standard method of connecting a boost controller and arguably the safest. If there were no boost controller at all being used in the system, this is the method REQUIRED to be used. Without a boost controller, you ONLY want positive pressure acting on the diaphragm of the actuator. NOT pressure and vaccum as would occur when connecting the source to the inake manifold. The vacuum can pull on the diaphragm of the actuator pulling it into the unit's vacuum nipple and potentially tear it. When a boost controller is used, this is not an issue as the vacuum is pulling on the ball of the boost controller instead of the diaphragm of the actuator. (this is only the case for a lock-ball and spring type manual controller) This also allows the boost controller and blow-off/bypass valve to have their own references improving the response of each individually. -------------------------------------------------------------------------------------------------------- Intake Manifold/Sharing with BOV Sourcing the reference from here MAY provide a very slight improvement in repeatability of boost, however, this is a less safe method of installing the boost controller and actually leads to another issue that can hinder the performance of the car. First and foremost, the Bypass/Blow-off valve must always have a intake manifold reference. NEVER reference the valve from the turbo outlet. Please don't confuse that with what I am refering to here. If the boost controller and BOV share that same reference from the intake manifold, they are essentially sharing the same volume of air (pressure/vacuum). When the boost controller (lock-ball-and-spring type) actuates, meaning when the spring allows the ball to come off of it's seat and send the pressure signal to the actuator, some of the "shared" pressure helping to hold the bypass/blow-off valve closed under boost is now momentarily diverted to the wastegate actuator potentially causing a "flutter" in the seal of the bypass valve and a slight loss of boost pressure altogether within the system. If the boost controller and BOV each have their own individual reference from the intake manifold, the possibility for this flutter is greatly decreased, however, it may still exsist to some extent because both references are sharing the intake manifold pressure. Al and I have seen this issue on mutiple vehicles and sourcing the boost controller directly from the turbo eliminates it completely. -------------------------------------------------------------------------------------------------------- In short, the best method will be connecting the boost controller directly off of the turbo outlet or anywhere on the intercooler piping BEFORE the throttle body. Boost Controller Positive Pressure Only (Turbo Outlet) Bypass/Blow-Off Valve Positive Pressure AND Vacuum (Intake Manifold) |
Originally Posted by Mike@Forge
When installing the MBC, we HIGHLY recommend using the pressure source directly from the turbo outlet or from the intercooler piping BEFORE the throttle body. Sourcing the pressure line for the MBC from after the throttle body (intake manifold) or by tapping the BOV line will result in a decrease in responsiveness of the unit and can also cause hesitation and other issues with the BOV.
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Originally Posted by Warrtalon
Hmm, interesting. I'm going to keep this handy, because I often get asked this question. I personally use the turbo nipple like you suggest here, but I don't have the Forge. For anyone who gets the Forge UNOS, I will be sure to recommend this installation method.
I do not know what will happen when/if a separate source is taken from the intake manifold for the MBC and the BOV line is not tapped, but a similar result will likely occur. Consider that both the BOV and MBC are sharing a given amount of pressure from the intake manifold. That pressure is keeping the BOV closed under boost but also eventually reaching a level of which the MBC will actuate and send the pressure signal to the wastegate actuator to open it. When that occurs, some of the pressure holding the BOV closed is then diverted to the wastegate actuator through the MBC. This can cause a momentary flutter in the BOV and a deviation in the boost pressure of the vehicle. Using a pressure reference only (turbo outlet), this is no longer an issue! |
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