hello guys!!! I have an Evo with the Evo 9 turbo (10.5T). I ran with 23 psi, but I made some modifications and I want to run with 25 psi, but when the boost charge 25 psi begins to fall until 18 psi at redline...
What could be??? I made boost leak test and nothing!

 

That is just the standard taper of the 9 turbo. If you want the turbo to go above 18 psi at redline, you are likely starting to get out of its efficiency range. You can force the turbo to push more air (hot air) by adjusting the WGA or using an EBC or the stock ECU to control boost. Either way, you will need a really good FMIC to cool the air (as it will start getting really hot) and good fuel (knock resistant).

Running more boost does not always equate to more power...

 

^This.

Its normal for the turbo's to taper down once you get to redline. Your not going to have full boost from 3500-10 000rpm.

 

Thanx for your answer... Well, My car have a FMIC AMS (for 650 whp), I use methanol/water (50/50), and I have external wastegate (Tiall 38 mm). I was use a MBC turbosmart, yesterday I changed for EBC (AEM tru boost), but the same results... 25 psi donw to 17 psi ...

 

But, I think that it´s not normal if you lost 7 psi... (25 psi to 18 psi redline)... I know it´s normal 25 psi to 23 psi at redline...

 

Yea the 9 turbo does things like that. But trash the EBC that's not the way to go.MBC's are simple and the best way to balance the boost.it seems like there's a deffantly a issue going on if its falling off so much like that. My guess is that the car could use a better tune.

 

i pmed u

 

100 % WRONG. The factory 9 turbo using an MBC to hit 25 psi peak will taper to ~18 psi at redline.

 

That is true if the turbo is utilizing an internal gate still... the OP is saying he has an EWGA - Tial 38mm. Given that info, OP - what's your WGA spring pressure? Sounds to me like you may be coming up short on pressure to hold boost (granted whether or not holding 25psi to 7+k is good is another discussion). I'm betting you have around a 9psi spring in there if you're tapering to 18 and trying to hold more. To confirm w/o disassembly, just run straight WGA pressure and see?

 

the spring pressure of the EWGA is 9 psi...

 

that is another issue, you're trying to run almost 3 times the spring pressure, never go above 2x.

what's probably happening is you are operating the turbo well out of the efficiency range and causing a ton of back pressure - forcing the wastegate open. or you are just out of compressor wheel

 

That's why you're tapering. As a rule of thumb you can only typically hold ~2x spring pressure whenever you're trying to run something at higher RPMs. If you can get a 10-11psi spring and you should be safely holding 25psi and tapering down to 20-22psi. Just keep in mind that with an EWGA you need to factor in tapering if that's what you want it to do...

 

Ok, thank you very much... Only one question, if I find a spring pressure for example 16 psi. hold more pressure of boost??? but If i can, today I put the new spring pressure!! one more thing, why if I ran my evo with 23 psi without problem at red line 23 psi too, with the same spring pressure (9psi) why the boost not down?

 

I'm not 100% sure I'm following you here, but I believe what you're asking is what if you go to a 16psi spring (probably a double spring w/the current 9psi one). Well, the only issue with that is that there is likely to be no tapering occurring at all. Generally speaking, once you have gotten below the ~2x spring pressure whatever your MBC/EBC requests the car will do. As Tial said above, it can vary depending on the actual amount of backpressure at the wastegate flapper, but I'd figure if you put a 16psi spring in you will no longer taper (unless you run 32psi with the MBC/EBC).

Now, with that said, sometimes running 22psi constant makes more power than running a 25psi spike tapering to 22psi. Just depends on how much torque you need/want really.

You're saying that on the same setup you were running a 9psi spring and the car used to always hold 23psi? And then just recently it's been tapering down? Have you made any changes at all to the setup or just have noticed a decrease in boost levels? What were the outside air temps when you used to run 23psi constantly vs current?

 

if you wanna hold all that psi by red line just get a big frame turbo or a fp turbo.