The biggest factor in MIVEC tuning at high load is the backpressure produced by the turbo. As back pressure goes up, overlap (high MIVEC values) become less effective or even detrimental. The stock turbo is a good example because people push it well beyond its optimum operating envelope. As load passes 240 and rpms go up (especially rpms), back pressure gets really high on the stock turbo, and best power is produced by reduced MIVEC values.

 

Pretty much what I've seen on the X

Wanna talk about the exhaust mivec then ??

 

Would John / MRFred / NJ / Shameless / others, please repost you current MIVEC setups (it has been quite a while and I imagine things have changed )....

For a stock turbo being pushed hard on Methanol and 91, should the high load MIVEC values be 0 for 6000 rpm + ? Thanks

 

Here is my current "work-in progress" MIVEC map. I'm running 26 psi at 3300 rpm, tapering to 25 psi at 5000 rpm, and then crossing 22.5 psi at 6000 rpm and 20 psi at 7000 rpm. It got me 10 whp over the MIVEC map below it. With some more more tuning, perhaps I can get another 5 whp.

"work in progress"


old map

 

Wonder how much normal pump gas maps would be affected by using the same methods of reduction.

 

This is the MIVEC map I used on the dyno below (boost is plotted). Evo Green, 30psi tapering to 26psi. 407whp, 375lb-ft with stock cams.

 

MrFred / Recompile -- Thanks for the updates!

MrFred / others -- So it appears that advancing cam timing helps ramp boost and that folks have been using 28.8 or 30 as the peak. What I don't understand is why in the 160+ loads you pulled the advance back to 22.8 vs 28.8? Was there too much back-pressure in those areas and reducing to 22.8 helped? If so, how did you determine (testing wise) that you had a problem and then how did you determine a value of 22.8 fixed the problem? (Sorry I am just trying to learn a bit.)

Thanks a lot!

 

it would probley make a good chuck less of power

 

As the exhaust pressure that drives the turbo rises, it can become higher than the inlet charge pressure (boost level on your boost gauge), and cam overlap causes the inlet charge flow to either stop or reverse. This tends to happen at high boost (high load) and high flow (high rpm) where the stock turbo is way out of its efficiency range. I think CH3CH3 posted some nice results on back pressure vs boost pressure measurements showing that its easily possible for the back pressure to surpass the boost pressure. The issue is exacerbated by any restrictions in the exhaust flow after the turbo, e.g. an HFC.

Once the boost starts getting pushed to its limit for the stock turbo, adding MIVEC only causes power loss rather than power gain. Less MIVEC gives less overlap and more power.

EDIT: I think I mentioned in my original post that the upper map is a work-in-progress. Its probably still a ways away from optimum.

 

Very informative, thank you.

 

guys i need help on my evo9 . im going for tuning tommorow and i need help ajusting my exaust cam pulley. the cams i have are brian crower 272. has enyone ever put the correct decrease on the exaust pulley?

 

yes take the brian crower cams out and put others in. They are crap on the 9's.

 

Was the increase in power due to more airflow (at same boost pressure) or the new mivec map allowed you to run more timing at the same load??


Tks

PS: any updates on the map ?

 

This is basically MrFred's map with some tweaks. After thinking about the back pressure of the stock turbo that was discussed, I thought maybe try lowering it even more as the Rpm's go up. This map has helped immensely with boost taper (using a MBC). I now have my boost set to 26 psi and it only falls to 24 by 7K. Since I started running E85, all I wanted to do was crank the boost. I realized that may not be the best situation for the stock turbo. I was running really high boost, but with excessive taper and it was kinda dead up top. After lowering the boost, raising timing, leaning fuel, and MIVEC changes, the car has never been stronger.

 

It's not really possible to hold 24psi @ 7000RPM on the stock turbo. 20-21 if you're lucky, but more likely is 18-19.

Are you going by a visual check of your boost gauge? Unfortunately that's not good enough. Logging via a 3 BAR MAP sensor will reveal the bad news to you.