Boost spike during shift

[Oclk Dlux]

After I put my 3" exhaust on my stock Garrett T1, I ended up with the dreaded boost creep. Hard to believe with a Garrett, but it did happen. I pulled off the turbine housing and opened the wastegate port from 7/8" to 1". The swing valve barely covers the hole, but it spools up fine and now the boost creep is gone. However, I still have a 2# boost spike whenever I shift at WOT. The RPM doesn't spike as I set both my A413 clutch packs to minimum clearance and raised the line pressure. I'm wondering if this is just inherent to the design. Anyone else seen this or have any ideas?

[kermit]

Would a BOV help??

[detobias]

I am guessing that this 'spike' is due to the RPM drop of the engine immediately after the shift when the air flow that the engine is pulling in suddenly drops and the inertia of the air charge in the plumbing is causing the spike

most likely it is more than 2#, but that is all U R seeing after the real spike has been dampened out by the volume in your boost gauge lines

a BOV would help if you were able to set it *just* above your desired boost level, that way any "overboost" above the desired level would be vented by the BOV

unless the brief overboost is causing an 'overboost shutdown' then I wouldnt worry about an extra few psi just after the shift ...

[Oclk Dlux]

No, I don't have a BOV as I'm still running a T1 with a log intake. The T2 conversion will come this summer.

The shift spike irritates me as I have to lower the boost level to accomodate. With the boost creep, it was worse. I could only run 6# without trouble (91 octane). Now I can turn the wick up a bit as the creep has been eliminated, but still have to watch out for the 2# spike. My non-IC set-up is finicky as far as detonation goes.

[85daytona]

Well I'm running log setup with an a413 and I noticed the slight boost spike also though the shifts. I recently got a new trans and haven't been paying attention to the boost gauge at shifts but I know it is at 14psi of boost and I don't hit cut out. Next time I stomp on it I'll watch and let you know but I do know with the old trans I def saw a 1-2psi increase at shifts. Always wondered why lol...