I have an Evo IX with a Hallman Pro RX MBC, K&N drop in filter and Works Exhale ABE. I had the boost set to max at about 19.5 psi (autometer boost gauge) and noticed about a week and a half ago that max boost was down to about 16 psi.

I tested for boost leaks and found none. Avg. tempature is up about 15 - 20 degrees in Southern Cal (highs almost 100 degrees).

Boost while the engine is warming up at 3/4 WOT is 18psi but after the car has warmed up and been driving for a few minutes (even on the highway), max boost only reaches 16psi.

Heat soak causing 3 to 4 psi drop or something else?

 

I would attribute the heat to power loss more than the boost drop. I just came from the dyno today and had no problem boosting 30PSI but did not make as much power as I expected.

As far is the 16psi of boost, that is very low for the stock Evo 9. I use to get 15.5-16psi boost by rel line but that was on the bone stock Evo 9 and almost to red line. Once I put the MBC(same as your) I had no problem running 19-21psi.



Carlos

 

Thanks....thought I had read that some people had to "turn up their MBC's" during the summer to make same boost. Just don't want to turn mine up if something else is causing the problem.

 

Well....going to turn up the boost a little this morning. Any other possibilities? Anyone..

 

If you are some how running off your wastegate and not your bc, then 16psi is were you should be at. Maybe check your connections and vaacum lines.

 

Eve-slow.


Do you mean a close loop between the nipple of the compressor side of the turbo and the nipple from the waste gate actuator? If that is the case neither the stock electronic boost solenoid or any boost controller of any kind would interfere on the boost.

Carlos

 

Ummm...my MBC is connected from the nipple on the wastegate actuator to a t-fitting between the intake and the BOV.

Still not sure what would cause max boost to go from 20psi when the engine is warming up to a max boost of 16psi when the engine is warm.

 

dude, here in Vegas you have to turn the boost up. we're used to the high temps and will notice about a 2-3 boost drop.

 

did u remove the restricter pill??? that is good for another 2PSI...

 

There is no restrictor pill with an MBC...

 

bump...this is an old thread but I am having the same problem now that it is hot out i noticed a 2-3psi drop and now my vac. is reading 15-18....is it a boost leak or just the heat?

 

Makes sense to me. If you think about it. There are many threads about the need to turn down the boost when ambient air temps drop during the chilly winter months or on especially cold evenings.

So, if boost levels tend to rise due to the colder weather, then it makes sense that the inverse would prove true as well...That boost will drop in the summer season when ambient temps are generally higher.

 

what is a normal/average vac reading?

thanks