I've got a stock 05 Evo. All I have done to it is a Hallman MBC and a Defi D series boost guage. My boost controller is hooked up to the turbo nipple and my boost guage is tapped at the fpr.

In gears 3-4 I register ~21psi for maybe a second and then it settles to 20 all the way through. In 5th gear however, it spikes to around ~22.5, settles to as low as 21 psi or so but keeps fluctuating in between those two figures. Is this ok behavior for 5th gear or should I turn the boost down?

 

I am only comfortable with making changes when I can monitor the results. i.e knock, EGT, AFR's. Without these things you are flying blind.

 

what is one supposed to do on an otherwise stock car? It seems boost controllers are one of the first modifications most people do. Dynoing a stock car seems like a waste but it seems that is the only way.

 

No tuning done? And boosting to 22.5psi.

I had mine Dynoflashed with all my mods and Al told me i should set it to about 21psi and taper down to 20psi. I don't even want to set it to 21psi since i don't really know what my A/F ratios are and egt temps. Good way to slowly kill your engine.

 

Only with race gas run higher than 21 psi

 

i thought 5th gear read higher/inaccurate boost pressures because the wastegate flapper can't open up fast enough.

The other gears are holding steady at 20. I'm a turbo newb so I'm not sure if this is normal or not.

 

overboost fuel cut starts to come into play over 21 psi...

 

haven't hit fuel cut in over 3-4 weeks of driving...maybe my boost guage is off?

 

Yeah your boost gauge might be off. I had an HKS 46mm gauge and now, a Blitz 52mm boost gauge and both seem accurate and hold at the peak boost I'm setting at. Before tuning, I would hit boost/fuel cut at 3rd/4th gears when I was setting my Buschur MBC. Probably had it to over 1.5bar(21psi). After reflash 20-21psi is steady and holding at 4th and 5th gears.

And, just FYI, i don't think I've hit 20psi at 1st, 2nd or 3rd gears. 3rd probably taps/peaks at 1.2bar...around 18psi.

 

There are two things that kill an engine before its time:

1) high rpm
2) detonation

Raising your boost without a tune is the shortest way to #2. I would upgrade just about anything else, before thinking about raising boost. That way you get all the inefficiencies out of the system, and when you do raise boost levels, the resulting gain will be much better too.

 

thanks for the tip, it is appreciated and I will keep this in mind. My intention isn't to raise boost but to get rid of the boost taper that the stock boost lines cause.

I still can't make sense of the 5th gear discrepency. Am I supposed to set my boost controller according to 5th gear readings? If I set it so that it only reads 20-21 psi in 5th gear on my guage, I'm guessing I'll only hit around 18-19 psi in gears 1-4. What is the point of a boost controller if it can't hold the boost steady through the gears.

All I want to do is hold 20psi of boost. Is this bad?

Sorry if I'm coming across as dumb

 

Not dumb at all - getting rid of boost taper was also one of the first problems I tackled - very different from raising boost. The trick is to find a way to change the shape of the boost curve, which is much harder than just changing the peak value. You will find an endless variety of opinions on how to do this, so take the following as one view of many.

Some people will tell you that boost taper cannot be removed due to stock turbo limitations. That's BS. At stock boost levels (20-21 psi), the 05 turbo can hold boost pressure all the way to redline without running out of air. There are two parts to the problem: hardware and software.

Hardware: the lower the pressure behind the turbo, the less the turbo has to work to maintain boost. As your rpm goes up, your are starting to cram more and more air through your exhaust system (the intake side isn't really a restriction at stock boost levels). The more free-flowing your exhaust system, the easier this is. No exhaust would be best, but noise and emission will generally force you to compromise to a larger diameter / straighter exhaust system.

Software as you already know, you need some form of boost control, to tell the waste gate when to open and when to close. In my experience, the only way to truly eliminate boost taper (not just reduce it), is by using Electronic Boost Control (EBC). That being said, the ECU is (among other things) your stock EBC, and if reprogrammed correctly can hold boost just like a standalone EBC. A manual boost controller will always show taper no matter what you do with it. There are a number of vendors that offer reflashes or piggy-backs for the ECU to improve the stock boost control function and do away with taper. There are also endless flame-wars about which is best. I personally had good results with the WORKS P2 flash.

If you plan on raising boost in the future, or switch boost levels for use of race gas, and want no boost taper, you will need a separate EBC, ECU replacement or piggyback. If you want just stock boost levels with no taper, and don't plan on changing you boost levels frequently, a flash can do the job too.

Of course there are other benefits to a software upgrade (tune), like preventing detonation, getting the most power out of the hardware you have, better gas milage, higher redline, etc. Ok, now I'm going to put on the flame-proof suit and wait for the backlash...

 

voidhawk, thanks so much for your explanations.

I did not know that an MBC would not get rid of taper by itself. One more question, sorry for the redundancy: I was told to use 4th gear pulls to set the boost controller. Should I be using 5th gear as I'm experiencing highest boost in that gear?

I think if I do set it so that it only reads ~20 psi in 5th, I'll only be able to hold 18 psi in the lower gears...which sorta sucks. I guess I need to get reflashed.

 

dunno about that one. how would you know really without a true gauge test which no one does.

 

careful careful careful about listening to this. An MBC does indeed get rid of the boost taper. He may have mistaken the boost spike for taper. The stock present taper is a function of the ECU making adjustments over the boost solenoid. A properly installed MBC takes the boost solenoid out of the equation... so no boost taper.

However, you will still see variations in boost stabilization due to the physical characteristics of the intake system. This is why an EBC units have Duty Cycle and Gain settings. For reference I captured a page from another site (when I was doing some research like 2 years ago) here:
http://www.serioussolutions.com/evo/ebc.htm

Most will say an EBC is a waste of money for the Evo8. You don't need to trust me on this opinion... just ask around.

I should add that some systems, like XEDE, tap into already existing ECU boost controls to give you the boost curve ideal for the solution's tune. Won't hurt to talk with Shiv about this.