I went for another dyno sessions today and got the same strange boost surging results but this time I was using a manual b/c. So I was talking with this guy there and he thinks the actuator is bad. The spring in it is not strong enough to hold 18psi so it lowers it to stock 8psi actuator pressure. When trying to boost the 18psi the actuator arm would move back and forth opening and closing the waste gate causing the boost spike. So I lowered the boost to 10psi and the actuator could handle that and stayed open, the arm did not move back and forth. And my boost stayed constant at 10psi. So the guy thought that I may just need a new higher psi actuator. What do you all think? Have you ever heard of anything like this before? Do you even know what the heck I am talking about? I am really trying to be ready to race on the 24th in NJ so I need to know if I should try and get a new actuator. 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

If the arm is moving under hard boost, that's not good. Either your MBR is fluctuating the actual boost seen by the wastegate, or it is perfectly posible the standard HRC can't hold the 18psi.

(on a side note, hit me up if your racing in NJ. :) I'm in northern NJ)

Think about this for a second..If you are using a MBC, then your wastegate is never seeing 18 psi..The MBC is "letting through" a regulated pressure to your wastegate, that almost matches your wategate spring setting(HRC is either 5 psi, or 9 psi). So when you are at 18 psi, the actual signal going to the wastegate is around 9 psi(9 PSI SPRING). If you would run more than 9 psi to your wastegate, then well, you would not even be able to, since the wastegate is opening and staying open to keep boost at around 9 psi..Make sense? The MBC just "tricks" the wastegate into thinking its only seeing 9 psi, when really, you are running well over that using regulated pressure from the MBC outlet. Look over all your IC piping and couplers, and make SURE you have no boost leaks..Also, I have had good success using a boost source at the intake manifold that goes to the MBC inlet, instead of using the small hose barb on the turbo compressor. Just cap that off..

i have the same problem. might be the boost controller. i have the greddy profec a. i can set it to like 10psi and it will stay. but if i turn it to like 1 bar. then it will sometimes just shoot right to like 30psi and if it does actually stay at 15psi, it will go from 15 to 18 to 14 to 18 and shit like that. i dunno whats causing it.

Yeah it really sucks not beeing able to bost to the cars potential. I dont think it is the b/c because it did it with two different b/c's. Oh well when it stops raining I will go and recheck all my i/c elbows and what not.
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