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My goal in modding my car, a 1990 900 Cab, is basically better spool up, bottom, and midrange response rather than sheer top end boost. To do this I have my own verion of the BCP mod. My other goal is to be able to easily put everything back into stock tune so that I can pass the increasingly stringent California emissions test when I need to, so I'm purposely staying away from directly modding the F and P pots in the APC control.
I have great throttle response everywhere but I'm concerned that I may be getting too much boost for the stock fueling. I take it easy in 1st and 2nd to protect the transmission and when I hit it in 3rd, boost soars to 1/2 to 3/4 of the red zone for the first throttle application. It doesn't seem like overboost because it doesn't surge or drop back dramatically. On subsequent throttle application, the response is only about 1/4 into the red indicating that the apc still has at least some effect. After some time cruising, the high boost is available again. So far I haven't experienced any fuel cuts, probably because of the delayed APC response I've seemed to experience.
Basically, I still use the apc system but have my own way of doing the BCP mod. Rather than adding a washer check valve before the bpc solenoid, to replace the existing restriction on the C or center connection on the solenoid, I add an additional restriction before the C connection, leaving the existing restriction in place. I then use a pressure relief valve between the solenoid W connection and the wastegate. Since my valve doesn't have a bleed, I've removed the teflon tape from the brass fitting on the wastegate side of the valve to add at least some bleed, to maintain throttle response on the next application. The pressure relief valve seems to act like a SMBC to greatly increase spoolup but also creates more boost than I expected.
I understand, in general, what you achieve using an MBC along with a paralled ball spring MBC. What I don't understand is why you need to use two different types of devices. Isn't a ball spring MBC just another way to achieve pressure regulation? If so, one could use two ball and spring devices in parallel or one could use two pressure regulators with different settings.
I know I can just turn down my pressure regulator at any time (for use in wet weather or when my wife needs to drive my car) but I've already gotten addicted to this level of response. I don't think I could use your anticipator type circuit but I see at least two possible solutions, 1) measure my fuel/air ratio under boost and, if I'm going critically lean, do something to increase fueling (injectors, fuel pressure reg., etc., 2) use a hobbs pressure switch and solenoid to set an upper threshold to boost. The later wouuld enable me to stay with stock fueling and feel better about continuing to use my mod. What do you think about what I've done and am trying to accomplish?
posted by 63.207.102...
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