I have a BBK Full setup with a Exedy Twin Disk clutch only making around 400whp/400wtq (uncorrected @ 5900ft altitude).

I recently went Speed Density with a VTA Tial Q BOV.

Only when I apply heavy or WOT throttle and shift gears, the RPM quickly spikes and go back down. If I apply light or moderate throttle, it shifts fine.

I have checked for user error by making sure my foot wasn't on the gas. It still goes up. This happens across all gears.

3 Possibilities in my mind:

• Compressor surge from too stiff of spring in BOV
• Clutch Slip
• Sticky trottle

The TD shouldn't slip at that level of power. I put my car in 4th going 30mph and floored the gas. It was sluggish but both my RPM and speed slowly went up.

A side note, when I let off my gas, I almost always get a fluttering sound. No surge DURING accleration, only when I let off gas. If I go WOT, I get a clean cut BOV sound, no fluttering.

 

Sounds like it very well could be compressor surge, I can't remember, does the BBK Full have an anti-surge intake side? Also what spring are you running in the BOV?

 

Thanks for responding.

I don't think its compressor surge because it doesn't flutter as I am accelerating (sometimes it does by rarely). I usually get fluttering only after i let off the gas.

I'm not sure about the anti-surge intake but that sounds interesting. I will have to do some research on it.
Anyone else care to chime in on the anti-surge thing.I think I'm running a heavier spring either 11 or 10 lbs. I have another black one laying around. I think black is at 6 lbs?

I am over mile high from sea level if that makes a difference.

 

Sounds like rev hang, it's also a tuning based issue.. Check out this thread and see if it helps.

https://www.evolutionm.net/forums/ec...-evo-8-9s.html