Where's my boost spike coming from?

[Billdogg]

I'm getting boost spike. My wastegate is set at 17 psi, and it gets up to 20 right out of the hole when it's spooling up. It will go up to 20, then go back down and stay at 17. What could be the problem?

 

[Billdogg]

bump

 

[wiked87gn]

port the whole on the elbow on your turbo to match the downpipe puck, but dont overbore, just big enough to almost match the puck, i did that and it solved my spiking problem.

 

[Billdogg]

I still have the stock elbow and downpipe. Will that make a difference?

 

[BJM]

How are you controlling boost, chip controlling solenoid, bleeder, etc.

Any chip with a fast spool set up will cause this.

 

[TurboBob]

If you don't get knock during the boost spike, then it's not really a problem, right?

Bob

 

[BJM]

Good point about the knock, if you can get rid of the spike then you can raise your boost some more. Run at 18-19 if there is no knock at 20.

 

[TurboBob]

My point is that the initial spike might not cause knock, but sustained boost at the high pressure might. Since everything (theoretically) is cool before you stand on it.

i.e. the engine is tuned for no knock on a long pull at 18 psi, but will knock at 19 psi. But a 3psi overshoot of boost doesn't cause knock because the intercooler hasn't heated up yet. So let it overshoot to 21 briefly, and then settle at your tuned boost setting.

Extra pressure is not bad if there is no detonation.

Bob

 

[Billdogg]

I got 2.1 degrees of knock on the 17 psi run. I run a 100 octane chip from Red Armstrong. I had 93 + xylene in the tank.

I'm assuming the knock was on the shift, and I could have gone up another pound or two, but that was already my 6th run, and I figured I should quit while I was ahead.

I made this post, because I was worried that if I was to raise the boost up a couple more pounds, it would be spiking at 23 or so, and I might get some bad knock then.