Originally posted by patkeefe
I believe the subject of BOV's and backpressure is certainly interesting, which we should continue as long as Merv doesn't mind the hijack.
My situation is a bit different than the 930 or other higher pressure ratio setup. I have a SC, CIS with an old BAE kit, Rajay T04B. My turbo needs a rebuild anyway, and I'm still shaking the installation out. I have enough rubber and tubing in my system to absorb the pulses, and have been toying with the idea of a bypass back to the inlet side of the compressor for the lift-the-throttle conditions described above. I have something of a modified throttle positioner which came with the CIS, which was evidently an emissions thing to keep the throttle open momentarily, but works pretty well to avoid the pulses...turbo has spooled down by the time the throttle closes.
However, I'm scrapping that throttle positioner when I put in the new IA fuel head and Brian Leask WUR, hence the bypass idea. My concern at my pressure ratio is not blowing anything up, but how can I take advantage of the "pressure pulses" to get spooled up again faster during a shift?
I haven't fully thought this out yet, and I'm open to suggestions and further dialogue.
I don't mind at all... we're all here to learn so please, hijack away
I'm not sure whether you can actually utilise the back pressure pulses to spool you back up again faster during gear shifts. Then again, a lot of pressure is stored in the intake tract and when these reverse spikes are directed back into the compressor inlet, it may aid it to spin up again quicker?
I certainly can understand how not running a BOV would result in these backward spikes reaching the compressor and slowing it down by a sudden surge of air pressure, especially when running high boost.
I think perhaps running low boost with no BOV might actually result in an "anti-lag" kind of scenario, since all the pressure is still stored in the intake tract and once you open the throttle again, Xpsi is available at the throttle body instantaneously. Again, this might be the case for a low boost application, but for high boost, I'd re-think that theory as it could potentially damage your compressor blade with high pressure boost spikes
'89 911 Turbo Cab
Protomotive MAP ECU, Twin Plugged Heads, GT2-EVO CAMs, 3.3L fully finned P&C's, ARP fasteners, C2T head gaskets, Titanium Retainers, Turbo spec valves, springs & guides, 964 splash valves, GT35R BB turbo, GSF Stainless Headers, Magnaflow Exhaust, Full bay Intercooler, TiAL 46mm w/gate, TiAL 50mm BOV, Apexi AVC-R EBC, SPEC Stage3+ Clutch kit, Crane CDI Ignition