Warrtalon, quick question for you. What are you tapering down to at the high elevation track you are running at?

 

i have the same problem on my IX with my forge. k&n drop in tbe, forge mbc. its boosting to 22 around 35-3600rpm, drops to into the 16s by 6500rpm and drops into the 15s above 7k rpm. im assuming the problem is the mbc but i dont want to change it out for no reason.

 

It's not a "problem" and it's certainly not because of the MBC. It's the stock turbo tapering like it always does. The taper is more severe on IXs due to the MIVEC. If you have a MAP sensor log showing that you actually hit a peak of 22 and drop all the way to 15, then that is more severe than normal, and you should do a boost leak test.

 

I hit a peak of 26.5psi in 3rd, and by 7k rpm it's down to 17psi...16psi by 7500. This is even with the Forge WGA. At sea level on the same boost, I would hit 26psi and only drop to 22.5psi at 7k...21psi at 7500. Altitude makes a big difference in the stock turbo's efficiency.

 

Did you have the Forge WGA on when you ran at sea level?

 

Yes, I did and made 341whp/361whp on alky without cams on a Dynojet uncorrected. Now, up here with cams and retune, I make 300whp/337wtq on a Dynojet uncorrected, plus I hit the peak whp at 5300rpm and fall off from there, so you can see how much of an effect the altitude has. It doesn't just kill power, but it gives me nothing above 6000rpm. I now shift at 6200rpm at the drag strip and have to go to 5th before the 1000' mark. That will change with my 5spd conversion, but I still will be sucking wind at the top of 4th.

For clarification, the boost numbers I'm claiming are based off MAP sensor logs during tuning by Dynoflash Al, and we verified my nasty taper at altitude on two separate tuning sessions 6 months apart, so it's a pretty sure deal. All the other stock turbo'd Evos he tunes up here displayed the same characteristics. I also ensured no boost leaks multiple times with my own tester.

 

Killswitch... FTW

 

Thanks for the info. The reason I was asking is that I wanted to know if a Forge WGA would help me from tapering down to 17 PSI at redline on my 03. I understand that our turbos run out of steam at the higher RPM range, but I would like to maintain 19-20 PSI by redline. I would assume that a high perfomance WGA would help. BTW, I leak tested my car to 25 PSI and found no leaks.

 

It's not the WGA causing the taper, so if you force the turbo to spin more than it wants at high rpm, it may have the opposite effect of blowing hot air, causing knock, and pulling timing. If you make a change, monitor the effects closely with your wideband and datalogger.

 

logged with zeitronix. peaked at 22, dropped to 15.4

 

mbc connected to wastegate and turbo outlet, its at around 15 clicks. it could be a boost leak, and that was my initial thought, but if it is a boost leak it was there previously, as i didnt touch anything that would cause a boost leak, but still something to be checked. unless its a leak at the boost gauge line. i know its supposed to taper, but i dont think it should taper to under 17 maybe 16. i was told it was the boost controller thats why i was questioning if i should change it or not.

 

Yeah, nice log. That's too much taper if it's 3rd gear or higher, but the MBC wouldn't cause that. There could have been a boost leak pre-existing - most Evos have them without the owner ever knowing, but I don't see why you think one couldn't have developed when installing the MBC. I had 4 leaks when I installed mine the first time - one at each connection. Leaks can also develop over time at IC connections due to the constant stress of on-boost and off-boost. I'm not convinced, though, that a boost leak would actually cause that much taper.

What is the altitude where you live, and who blamed it on the MBC?

 

yeah im going to do a boost leak test when i get the chance, but i see all these people with IXs tapering like crazy. some said it helped when they changed the boost controller. others no idea what their problem was. i know the IXs tend to taper more because of the mivec but 15lbs is way off. was just wondering if it could be a problem with the boost controller. im also not convinced it is a boost leak but it is worth checking. elevation is around 500 ft above sea level so thats not the problem.

i was told by the guy helping to tune my car, only reason it would taper that much is boost controller is installed wrong or it is messed up. and i said either that or its a boost leak. but he didnt think it was. its not installed wrong i checked twice, and even reziptied the vac lines. so other than a boost leak. i figure it could be mbc.

 

It would only be the MBC if it was broken, though, because that is not typical of a Forge UNOS.

 

I've installed the Forge UNOS boost controller on my buddy's Evo 9 and it held boost just fine. It hit the desired 20 psi and held it there up til redline at which point it tapered to about 17 psi. Keep the Forge. Don't spend more money on boost controllers until you can say for certain its the boost controller that is at fault. I've seen plenty of boost controllers taper, Dejon, HKS EBC, Hallman.... In the end, it comes down to a combination of the modified parts and tune. If you have the proper parts and tune, you should be able to get constant, safe boost levels, regardless of the boost controller used.