TheRealLefty

Project boost control coming along nicely. Have working mechanical boost gauge installed and all the plumbing in place for the af ratio meter except for the tap-in to the O2 sensor. New boost meter, tapped off the manifold vacuum line to the FPR, shows a very different story than the creative factory sweeper.

At modest accel, with Lindsey MBC in place the new gauge shows about 9 psi rolling off to 5-7. Nice and safe so far. But at full throttle in 2nd, I spiked it a 15 psi.

Does this mean that's the current upper limit of the MPC setting? How many turns from lowest to highest in the MPC? Roughly how much change occurs with each 360 degree turn of adjustment ****?

So many questions, so little bandwidth. So much fun! Still-new-to-me Turbo S is running like a rocket, just want to make sure as best I can that I don't send parts into orbit gaining control over boost and fuel mixture.

Brent951

Here's what I experienced with the in-car Manual Boost Controller:

That seems odd that you're able to spike to 15psi but your car will roll off to 5-7, that doesn't sound right. If I were to set my manual boost controller to maintain around 15psi in the say 3rd and 4th gear it would spike to 18psi in 2nd and 3rd gear. I asked a few people about this and they claimed it was because I was running these long vacuum lines into my car from the engine compartment to be able to control my boost. 15PSI for me was about 3 1/2 to 4 turns if I remember correctly. Just be careful you're not running lean at the upper end. If you don't have a Wide Band it kind of difficult to tell, I'd probably recommened going to a dyno shop and having them check your car pulling to redline in 4th gear just to make sure.

Brent

zerMATT951

The MBC has only *one* limit, so adjusting and testing at moderate boost levels really really isn't a good idea.

When adjusting the MBC, always take your readings where you expect a spike. In other words, if your car spikes somewhere in 2nd or 3rd gear, then that's where you need to be testing it before making furture adjustments. Adjust for the spike so you won't be surprised when it happens. Any other boost level achieved during every-day-driving will be relative as compared to the "maximum" that you dialed the MBC to.

The MBC should be able to adjust your boost anywhere between 7-8psi and the maximum that your car can achive with no restrictions (20+ psi).

HansB

The LR MBC is a bit aquard: It does seem to do nothing for quit some time, but when it is in the area that it controls, it does 3 psi per turn IIRC.

TheRealLefty

Good info, all. Point is well taken that less than full throttle observations are not particularly useful in determining the boost control's actual setting.

A friend of mine is really honing in on the theory of WG management...and he is reaching the same theoretical conclusion that Hans shares from real life. Much of the adjustment range in the Lindsey MBC is not relevant to the job at hand and the boost controller will impact WG operation only around the range of .6 or .7 bar in line pressure. Too much below that and the WG will simply work on its own spring, too much above that and the MBC will be no different than direct pressure from the IC pipe, we reckon. If this is true, it does not in any way reflect poorly on the value or function of the MBC, it just explains the basic principle by which it is able function for a such low cost.

zerMATT951

In a nutshell, you can control the boost level between about 7psi to maximum boost in .5 to 1psi increments. I think it does it's intended job just fine. I wanted to dial in a little more boost than the factory computer would allow, so this worked out fine.

If you need better control than that, you'll need to go with an electronic boost controller.