I have a cheap manual b/c that just screws in and out and stays in place with a locking nut. I turned up my boost today to 12psi and took it for a run. In all my gears the boost spikes up to 12psi then falls to about 9.5-10psi. My EGT's where good and never went over 1500-1525 deg. My question is can or should I turn the boost higher to like 15psi so when it falls it goes down to like 12-13psi. Now I know you should retard timing at 15psi but it would only be there for a sec. I am trying to get my hands on a profec b to replace my mbc so I will end this problem but not for a while. Let me know if this is safe or not. Thanks
Patrick
96 GS
14.14 @ 96.5 mph on 8psi 8 Nov.02
HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

bump ^ come on guys I do not want to damage my motor again like I did last time. I want to get good info and knowlege before I do something dumb.
Patrick
96 GS
14.14 @ 96.5 mph on 8psi 8 Nov.02
HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

IF YOU HAVE A BUILT MOTOR YOU WILL BE FINE LETTING IT SPIKE TO 15 IF YOU RETARD YOUR TIMING A LITTLE. BUT IF YOU REALLY WANT TO BE SAFE ABOUT IT JUST LEAVE IT WHERE IT IS UNTIL YOU GET THE PROFEC B.

if its dropping from 12psi, u might have a vacuum leak. or maybe just a bad mbc.

MBC ALMOST ALWAYS HAVE A LITTLE BIT OF SPIKE TO THEM. ITS JUST BECAUSE OF THEIR DESIGN. YOU GET WHAT YOU PAY FOR.

you should be fine at 15 psi with no timing retard. just use good gas.

yeah, i've heard of people easily going up to 15 psi with no ignition controller (like me with the 1G SMIC). just don't have any correction in the AFC. rumor has it that you can go to 18 psi if you have an decent fuel system and a FMIC with 17-18 degrees of timing at WOT...

EDIT: this is on 93 octane, just to make sure. no california 91 octane "emissions" fuel or whatever the BS reason is for them not having 93 and 94 octane avaiable.

Well I think I will turn it up a little to 13psi to see if that will hold a steady 10psi. I dont think I have a vaccum leak cause I idle at like 19hg on my boost guage. Unfortunately the best gas where I am at now is only 92oct. I think that gas should be good enough to boost 13-14psi. How can I tell if I am having timing issues? Just in case my timing is to advanced for 13-14psi. Thanks
Patrick
96 GS
14.14 @ 96.5 mph on 8psi 8 Nov.02
HRC kit, S20G, FMIC, Howell bottom end 8.6 pistons, S-FMU, Blitz BOV, P&P head, SS valves, lots more little goodies

YOu prob have a boost leak somewhere. MIne did the same thing. I made a leak tester out of PVC piping and a cap. Put a air compressor fitting on the cap, and use a coupler to mate it to the turbo inlet. PRessureize it with the air comrpessor, and listen/feel for where the air is coming out. It will be normal for a little bit to leak from the PCV vlave, and the throltte plate shaft.

I also used a different boost source for the MBC. Instead of using the nipple on the turbo, i went to the brake booster vac line, cut it, and intalled a T fitting. Then from the T, this went to the MBC inlet, then from the MBC to the wastegate. This way, if you have any leaks, or small unfixalbe leaks, the MBC will now see manifold pressure, instead of turbo pressure. If you have pressure leaking out, that affects the pressrue in the intake. Since the MBC Is connected to the intake vac line, it will see this pressure drop, and it will result in steadier boost, with less spiking, and less boost fade. I have done it this way since i had that bosot fade problem, took care of my boost leaks, and now it holds really steady. I have the Hallman MBC by the way..just a simple ball and spring type