Hello all,

Just as the title says, can someone explain the difference?

If a turbo spikes to 28 PSI and holds 25-26 then tapers to 18-19, how is that different than a turbo overboosting to 28 PSI? Does overboosting mean that it holds 28 PSI all the way to redline?

If so, is a quick spike under a second (more like .5 sec) bad for your engine/turbo?

From what I understand, over boost is what kills it right? Or are quick spikes just as bad?

 

Or do they mean exactly the same thing?

 

This is my understanding and can be completely wrong...

A boost spike usually happens when you have a MBC. Boost slightly spikes right before reaching you target peak boost and goes down to you target peak boost. Depending on the tuner, I have actuallly seen tuners tune for a boost spike.

Overboost can be cause by changed weather conditions (being alot colder than when you were tuned) or a mechanical error (disconnect vaccuum line, malfuctioning WGA, etc). Overboost usually does not happen like a boost spike. A spike happens during spool up but quickly comes down. Overboost can happen at any rpm or at all rpms (after spool up). Example of overboost having 28psi peak and tapering down to 23 be redline but actual boost is 32psi peak taper down to 30psi. Overboost is going above the targeted psi.

Feel free to correct me or explain this better.

 

You guys have it right at a basic level. To be more general:

Boost spike is a quick spike. It looks like, well, a spike if you are looking at a plot of boost.

Over boost can describe a boost spike, but generally refers to a boost level that stays above safe/desired levels.

Engines *can* survive boost spikes, but they can also blow up because of them. Any boost spike will be greatly exaggerated when it starts getting much colder in your area. Overboost for a long time is bad because the turbo may be over-spun, your FMIC will get heat soaked from hotter air that is generated, you will probably see knock that is more pronounced and continuous, etc etc.

Both are bad when not managed effectively, but having them happen once in a while may not be the end of the world.

 

I see. well the description of my tune map says it's supposed to boost to where the 3 port will allow and there is no set PSI in the description. I think it's supposed to be set to 25 PSI so I was a bit worried. Oh well, if it gets any lower in temp, I will just switch it to the LWG map.

Thanks all.

 

I used to run21psi and had to turn it down in the winter because it would boost cut