Subaru tuning guru's, pros, newbs...a question.

[JET02WRX]

I was reading a recent issue of Subiesport and they stuck a rotated Perrin kit in one the project cars... I think it was their Legacy GT. Anyway... they were having an idling / stalling issue with the car after the installation of the turbo. They diagnosed, along with Jeff Perrin, that the size of the turbo was drawing more air across the MAF at idle than was expected. Ok, i can see that. Their solution?... move the maf further away from the turbo. Now, while i realize that is a solution, it still makes for a guessing and trial and error game. Since tweaking is going to be necessary either way, wouldn't the more "professional" approach be to tune the maf table in the low end? Isn't the placement of the maf in their rotated kit somewhat standard?
I know tweaking the maf is tricky...i'm still having issues with mine, but i'm just surprised by the response from Jeff Perrin to just 'move the maf'.
Looking for thoughts / education from some of TSTs DIY tuners and or some of our pros... Ray, Andy, R/T? 1320?

[Honest_Bob]

Interesting question. I wonder why they chose that instead of just going with a perrin big maf.

[04wrbsti]

The best solution would have been to convert to a speed-density system using a map sensor.

If that wasn't a viable solution (mainly due to OBDII checks), then a big maf probably should be the way to go.

Even if you rescaled the stock maf in the stock tube, it would max out and flatline in the upper RPMS.

[RayArroyo]

Originally Posted by JET02WRX

I was reading a recent issue of Subiesport and they stuck a rotated Perrin kit in one the project cars... I think it was their Legacy GT. Anyway... they were having an idling / stalling issue with the car after the installation of the turbo. They diagnosed, along with Jeff Perrin, that the size of the turbo was drawing more air across the MAF at idle than was expected. Ok, i can see that. Their solution?... move the maf further away from the turbo. Now, while i realize that is a solution, it still makes for a guessing and trial and error game. Since tweaking is going to be necessary either way, wouldn't the more "professional" approach be to tune the maf table in the low end? Isn't the placement of the maf in their rotated kit somewhat standard?
I know tweaking the maf is tricky...i'm still having issues with mine, but i'm just surprised by the response from Jeff Perrin to just 'move the maf'.
Looking for thoughts / education from some of TSTs DIY tuners and or some of our pros... Ray, Andy, R/T? 1320?

Hello Jet great question, they are correct larger turbos especially rotated kits do seem to skew with the cars short and longterm fueling especially on cars with front mount intercoolers. you can simply obtain your stock fueling back by tweaking the maf, while the placement of their maf was somewhat standard perrin used a bigmaf intake which requires alot of maf scaling through out the entire maf voltage range. a big maf is used to allow more air around the maf therefore providing you with more fuel and timing resolution since the stock maf size is too small and would get maxed out rather quickly.



what perrin is doing now is converting the maf into a blowthru type, what it does is moves the maf housing after the turbo, it allows people to run atmospheric blow of valves since the air being measured is after the turbo and the blow off valve eliminating stalling issues. Another benefit of running a blowthru setup is that the ecu will see a better temperature reading since its getting an actual charge reading rather than an intake reading which helps prevent the ecu from pulling timing when it sees a higher temperature reading under the hood at idle and you initially start driving.

and last but not least their blow thru setup just like the big maf allows more air around the maf which provides you with more fuel and timing resolution.


The verdict (in my experience)


Either setups are great and stock drive ability could be achieved with some changes to the maf. you can have over 500 whp with out maxing your maf with these setups. sure speed density is a little better but currently there are only 2 options available 1 is a stand alone 2 is a utec which im not a big fan of. Someone in the open ecu community is working on a patch that will allow the stock ecu to be tuned with speed density.

[RyanG]

^^^

Exactly. If you are at the point of needing to go rotated, then you are at the point of needing SD. Or going blow through. ;)

[Vince@R/TTuning]

Blow through is def the way to go, alot more accurate. the only issue with blow through is that usually its alot easier to max the voltage out....

[RayArroyo]

Originally Posted by Vince@R/TTuning

Blow through is def the way to go, alot more accurate. the only issue with blow through is that usually its alot easier to max the voltage out....

vince with perrins blow thru they increase the diameter of the actual pipe where the maf is located therefore it helps with themaxing it out even though i have seen them get maxed out. i have however seem to have more resolution using the big maf. perrin has a philosophy to tune these blow thru setups which im totally against which allows the system to never be maxed out. once again im totally against it, they tune their cars by leaving the injector size stock in the scaler and latency alone. they do all their fuel thru the maf. the problem with this is you dont have much resolution down low for cruise which im totally against off. oh did i mention im against it.

[TROLL]

I know that on the original Perrin kits the design of the intake resulted in inconsistent MAF readings... so its not something that could be tuned out. They basically redesigned the intake design and MAF location moving it farther away to try and get a more consistent and accurate sample of air to work from. Its independent from tuning, which of course would also be necessary. A lot of intakes have this issue, but the Perrin was apparently pretty bad initially and a lot of people were having problems with it on NASIOC and beyond...

[JET02WRX]

I just reread the article. Jeff Perrin sent them an 'additional piece of pipe' to extend the intake down into the fender. So the maf was definately not converted to blow thru. Why they didn't call it the "perrin big maf' i have no idea. The author writes..."Suddenly our rough idle was gone and fueling returned to normal." No mention of tuning anything. I guess its just bad journalism? Are we to assume the retuned everything including the maf?
I don't know if I understand what you mean by being independant from tuning, Brian. I was of the belief that the common rule of thumb is...increase the size or efficiency of the intake you have to rescale the maf to compensate.

Thats crazy that perrin would try to do all the tuning through the maf and leave injector size and latency alone, if what you are saying is true Ray. That just seems like insanity to me...but what do I know...I'm still a student of tuning at this stage. It would seem you'd be chasing your tail trying to do that.

[RayArroyo]

Originally Posted by JET02WRX

I just reread the article. Jeff Perrin sent them an 'additional piece of pipe' to extend the intake down into the fender. So the maf was definately not converted to blow thru. Why they didn't call it the "perrin big maf' i have no idea. The author writes..."Suddenly our rough idle was gone and fueling returned to normal." No mention of tuning anything. I guess its just bad journalism? Are we to assume the retuned everything including the maf?
I don't know if I understand what you mean by being independant from tuning, Brian. I was of the belief that the common rule of thumb is...increase the size or efficiency of the intake you have to rescale the maf to compensate.

Thats crazy that perrin would try to do all the tuning through the maf and leave injector size and latency alone, if what you are saying is true Ray. That just seems like insanity to me...but what do I know...I'm still a student of tuning at this stage. It would seem you'd be chasing your tail trying to do that.

yep thats the way they do it, i know this because i had issues with my blow thru maf and asked jeff what he thought the deal was. can you show me where i can see this article, im curious to read this.

[JET02WRX]

Its June/July issue of Subiesport. Pgs 35-42. Not sure if you can read it online or not. Unfortunately I don't have a scanner. Its just a very....vague...article.

[TROLL]

Its two seperate things... lets see if I can try to explain better.

The way the MAF works is it takes a small sample from the center of the intake of the air passing by, which represents the total air entering the car. It doesn't measure all the air, it just takes that sample and calculates what the total should be based on that. This assumes that the air flowing through the intake is smooth and evenly distributed, which it does when you use the stock intake.
If you change the intake design, often times the air wont be smooth and evenly distributed as it flows through the pipe. This is the turbulence I was talking about and can mean less air in the middle and more around the outside, or vice versa, and this is what leads to the inconsistency in the MAF readings. If the air is turbulent it will be bouncing all over the place, sometimes more and sometimes less, and the ECU will have a very difficult time responding to it. This is purely a mechanical problem and cannot be solved by tuning. You NEED to make sure that you do not have turbulent airflow before you do anything else.
Perrin's original intake design was very turbulent and they found that they were able to improve it by extending it (basically redesigning it). Again, the turbulence is purely mechanical and not having to do with the tune.
This is also a common problem with blow through setups, again because of turbulence. Its just very finnicky unfortunately, so its a good idea to go with an intake (or blow through) that has been well tested and proven.

Once you have a proper intake on the car which helps the MAF get consistent readings, then you can tune it through the ECU. Without smooth and consistent airflow tuning it would not be possible. It would be like a ruler where the numbers change all the time... its not possible to measure anything with it.
To explain further, the reason that you have to scale for a new intake is that even a very slightly different design than stock means that the calculation used when the ECU converts the MAF sample area into the total amount of air entering the engine will be incorrect. You need to adjust the scaling so that you can get it back into the proper range, whether you're using a 65mm or 70mm intake or whatever it may be... and they're all slightly different and require custom tunes to get right.

[TROLL]

I just found an old pic I remembered... this was before Perrin released a fix, other guys were doing things like this and finding that they worked. Its just basically tweaking the design before and after the MAF to help ensure a consistent reading...

[JET02WRX]

Right...... yes i agree. Turbulence is bad for the maf, i wasn't sure if thats what you were getting at or not. I already understand the other points you are highlighting..so i'm cool there..which leads me back to my original question...you'd think this all would have been figured upon and planned for by a magazine doing a build on a car. I'm beginning to think subiesport is a bunch of hacks that document the free mods they get via advertising. I should have known something was up when they do a feature article on some girls STi that is basically stock with a body kit, yet has 2...yes 2 fuel pumps and 850cc injectors feeding a STOCK TURBO, and talk up her 300whp result like its some great feat. Heres a quote..."With the basic bolt ons and the UTEC, the car is pushing AROUND 300hp; fast enough to blast past 2JZGTE powered Lexus' and C5 Corvettes." BLAST PAST? come on. Its 300 horse power....not 500.

[TROLL]

Thats in a recent article? Thats strange, I thought this issue was figured out and dealt with a year or two ago. I would have expected the info to be out there, especially if they were working with Jeff Perrin on it in the first place... I guess it depends how long they spent troubleshooting... if they realized the problem quickly or got hung up on it.
And the Big MAF and why it is used is another element completely from anything I have explained, haha. It was touched on above so I'm not even going to get into it.

[RayArroyo]

Originally Posted by TROLL

Thats in a recent article? Thats strange, I thought this issue was figured out and dealt with a year or two ago. I would have expected the info to be out there, especially if they were working with Jeff Perrin on it in the first place... I guess it depends how long they spent troubleshooting... if they realized the problem quickly or got hung up on it.
And the Big MAF and why it is used is another element completely from anything I have explained, haha. It was touched on above so I'm not even going to get into it.

yeah this is so weird especially since all their new rotated kits all come setup for blow thru. i do not know why they are talking about this now.

[TROLL]

agreed...