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Definition / Example
Reversion is most common in engines with very large camshafts operating at low speeds such as close to idle. Situations where MAFs read unreliably due to reversion can generally be greatly improved by moving the MAF further from the throttle body. Increasing the volume of the intake between the MAF and the throttle body is also effective at smoothing out the pulses of air coming from an engine with a radical camshaft. It is normally possible to get a reliable enough MAF signal in most circumstances. Even extremely wild cams that draw 3-4″ of vacuum at idle can be tamed with an appropriately designed intake system.

Another form of reversion that is troublesome to MAF systems happens with poorly designed supercharger bypass valve systems. In most of these systems, the pipe connecting the outlet of the bypass valve connects with the inlet of the supercharger at an angle where recirculated air flows backwards through the intake. This causes any reverse-flowing air to be metered multiple times by the MAF, leading to unreliable operation. This can almost always be remedied by adjusting the angle of the pipe from the bypass so it points at the inlet of the supercharger directing the flow of recirculated air away from the MAF.


I ask this because I installed a new Turbo inlet pipe and It seems that my MAF is experiencing reversion even tho the new inlet pipe is longer than the stock accordion silicone inlet. The disadvantage i guess to installing this new turbo inlet is that it is a smooth surface inside so reversion is getting to the MAF a lot easier than with running the stock accordion tube.

Is there a way to tune for this? The car will sometimes just stall when coming to a stop or slowing down. Doesn't do it with the stock turbo inlet.

Thank You.

Found my answer! Can't tune out the "reversion"

I will go blow through setup now!

Is it best to have the BoV AFTER the maf so in between the TB and MAF or is it best to have it BEFORE so in between MAF and intercooler

User_Name wrote:Found my answer! Can't tune out the "reversion"

I will go blow through setup now!

Is it best to have the BoV AFTER the maf so in between the TB and MAF or is it best to have it BEFORE so in between MAF and intercooler

I cured the same problem on my sr with tune.

When air goes throw MAF it tells injectors to spray fuel while it doesnt need really. So, when revs going down, the engine gets to much fuel. I didnt cared about all range, because you need only to get correct amount of fuel on idle (right before idle). So I leaned out few cells right before engine idle on some load, where you cant get in normal conditions and it worked very sweet.

unex wrote:

User_Name wrote:Found my answer! Can't tune out the "reversion"

I will go blow through setup now!

Is it best to have the BoV AFTER the maf so in between the TB and MAF or is it best to have it BEFORE so in between MAF and intercooler

I cured the same problem on my sr with tune.

When air goes throw MAF it tells injectors to spray fuel while it doesnt need really. So, when revs going down, the engine gets to much fuel. I didnt cared about all range, because you need only to get correct amount of fuel on idle (right before idle). So I leaned out few cells right before engine idle on some load, where you cant get in normal conditions and it worked very sweet.

I may have to give this a shot or at least inform my tuner. He is widely known and does an awesome job so I'm pretty sure he wouldn't have any problem tuning for this.

I honestly may just end up going blow through tho as the advantages seem very worth it.

I appreciate your response.

This stuff can be very tricky and you'll often find that changing the inlet slightly will change things. You're right about increasing volume being good. My usual suggestion is to get the MAF as far as possible from the turbo inlet. For some reasons big turbos seem worst. The little T28's rarely have trouble.

The other thing is the BOV. Particularly when having trouble coming back to idle smoothly - something SR's seem to struggle with more so than other engines. A sensitive BOV is your friend. You want it to open as soon as you even think about closing the throttle. Note that the factory BOV is open at idle. Return path for BOV is also important - plumb it in close to turbo and angled away from MAF. Putting some sort of baffle in the intake to further stop airflow back to MAF is recommended.

I've not tried this but maybe decreasing TTPmax figures in the area where reversion occurs might help? This would theoretically limit the injector pulsewidth to avoid the richness. Worth a try...

PL

PL wrote: I've not tried this but maybe decreasing TTPmax figures in the area where reversion occurs might help? This would theoretically limit the injector pulsewidth to avoid the richness. Worth a try...
PL

Maybe this would help, but it could get some problems to start moving the car, because TTPmax is related only to rpm range, while we need rpm+load (like in fuel map), because we know that when air goes backwards throw MAF there is low rpm + some load condition (and yes, you can see this while logging).
Maybe not very clearly, but I hope you understand But leaning out some cells (I mean doing it 29:1) on fuel map have other issue: fuel map colors changes drastically would be nice to get future, for example with the right mouse click, to ignore these cells...

PL wrote:This stuff can be very tricky and you'll often find that changing the inlet slightly will change things. You're right about increasing volume being good. My usual suggestion is to get the MAF as far as possible from the turbo inlet. For some reasons big turbos seem worst. The little T28's rarely have trouble.

The other thing is the BOV. Particularly when having trouble coming back to idle smoothly - something SR's seem to struggle with more so than other engines. A sensitive BOV is your friend. You want it to open as soon as you even think about closing the throttle. Note that the factory BOV is open at idle. Return path for BOV is also important - plumb it in close to turbo and angled away from MAF. Putting some sort of baffle in the intake to further stop airflow back to MAF is recommended.

I've not tried this but maybe decreasing TTPmax figures in the area where reversion occurs might help? This would theoretically limit the injector pulsewidth to avoid the richness. Worth a try...

PL

Can you elaborate on this "baffle" you speak of? Maybe a picture because this may cure my reversion im experiencing with my current setup. The new 3" pipe i added for the turbo inlet is in fact longer than the stock silicone pipe however it's causing reversion and the stock silicone isn't.

Thanks for this thread guys I am trying to diagnose if I have reversion from a large camshaft on my EJ25. I have a factory type draw through MAF setup with the MAF and intake filter roughly 30cm from the turbo inlet with a single 90 deg bend. My idle is not very smooth but the biggest problem is hesitation and general roughness just off idle. As soon as I am above say 2500rpm its great, super smooth and makes good power. I have put together the following plots, any advice much appreciated!

I hate reversion too, so I made this, it works great !

louiswun does your dump valve work correctly when its installed that way round?

s200rat wrote:louiswun does your dump valve work correctly when its installed that way round?

Yes, it works.
The stock dump valve also installed that way, but the piping is plastic.

The stock dump valve also installed that way

you sure??? inlet to dump valve tends to act on piston face to open them, not against the back

http://kuddy.net/200sx/removing_dump_valve.html

the way your lined up is high pressure acting on the back of the piston. so vacuum is fighting this pressure and the spring when trying to open hence why i ask is it actually opening correctly at high boost or only opening after the boost has been depleted by reversion.

s200rat wrote:

The stock dump valve also installed that way

you sure??? inlet to dump valve tends to act on piston face to open them, not against the back

I have test many BOV, Blitz, HKS, Greddy, RB20/25 stock bov...etc, all piston facing to the pressure side and the piston opening movement same as air release direction,
most of them leaking, leaking from the adjustable screw, leaking from the piston sealing surface, or the mounting surface. especially when over 1.5 bar. Can't hold the pressure, testing was done on a both end sealed intercooler pipe at 1 to 2 bar fully submerged.
And yes, high pressure acting on the back of the piston, this is exactlly the same as plastic bosch dump valve on Audi and VW, and the boost pressure help sealing the piston, more boost pressure , more sealing force, and it still works fine to blow off at high boost.
And this is the only BOV that have zero bubble when testing under the water, ( a good genuine HKS SQV still have zero bubble in the water but it blow off when positive pressure is droping, still positive pressure but not vaccume, I have also see an old genuine HKS SQV leaking seriously on all small bolts surrounding the valve body)
You won't belief, a small plastic bosch dump valve can hold pressure tight at 2.5 bar, when high pressure acting on the back of the piston, but it still leak when high pressure acting on the front of the piston.

And I have made a paper gasket to seal the BOV cover, teflon tape to seal the hose joint, it is a threaded tube to screw into the BOV body, after that, zero leaking.
It works fine.

Testing photos
http://www.facebook.com/photo.php?fbid= ... =3&theater

http://www.facebook.com/photo.php?fbid= ... =960%2C540

http://www.facebook.com/photo.php?fbid= ... =960%2C540

Good work Louis. Most people don't realise the importance of having a recirc BOV that functions correctly. Most stalling issues come back to BOV (and/or AFM placement). BOV must be responsive AND hold boost. It must open as soon as the throttle starts to close in order to avoid reversion. Get this right and your stalling will disappear.

I like the extra effort you've gone to in order to get the AFM further from the turbo too.

PL