Help with possible vac leak after TB swap

[brian b]

Changed out my stock TB and plenum for a 70mm TB and ported plenum, when testing out at 16lbs of boost I got 2 then 4 knock on the ESC on my FAST. A/F was at 11.2. Tried adding fuel then ran it again still got knock with A/F at 10.7. Changed back to my old TB and plenum then ran it and still knock at anytime over 15lbs of boost. I was able to run 22lbs with no knock before I did the change. I think it could be a vacuum leak but I can't figure out where. I didnt use any kind of gasket sealer on the vac block or the plenum gasket could this be causing vac leak? Also what are those two ports on the bottom of the TB for when I pulled my old TB off I noticed one was plugged and the other open.

 

[DailyDrifter]

Make sure the upper plenum has a flat mating surface. I like to use a little RTV to seal up the T/B and Plenum. Those two nipples are for the coolant, most people dont use them anymore to heat the T/B. On your hard heater hoses you will see two nipples, they should have a hose going from one to the other to bypass the T/B.

 

[brian b]

Thanks

I took it all apart then put it back together using RTV on all gaskets that are on the plenum I am going to let it dry for 24hrs then give it another test drive. By the was if the head was lifting under boost would this also trip knock sensor.

 

[Chuck Leeper]

XFI... what does your datalog look like??
Map reading B4 and after the swap?
IAC change?

 

[brian b]

My MAP did'nt seem to change that I can tell and IAC was a slight change. All data seems the same at 16psi on my log before change and after change.

 

[brian b]

Same

Well let RTV set for 24 hours then test drove.... ya same as before knocking at anything over 15/16lbs of boost, any ideas????