About 2 weeks ago Vishnu Performance hosted a Dyno Day at TurboTrix in NJ. Prior to the event my Evo was lightly modded... HKS RS Intake, Full Exhaust, BOV, MBC, and Mail-in XFlash ECU from Vishnu. Prior to the event I talked to Shiv about the mods I currently have and what I was adding at the dyno day (cams/gears/headstuds). I told Shiv that I had an RS Intake and he strongly suggested that I put my stock intake back on if I still had it. I had just driven to NC in my Evo, and while I loved the RS's sound driving around town in NJ, after 10 hours each way on the highway, listening to it whistle the whole way, I grew tired of it real quick. That annoyance combined with Shiv's advice led me to take it off and put my stock Airbox back on.

A buddy of mine on this board also had an RS intake and he too was getting tuned by Shiv that weekend. He elected to leave his Intake on his car. Well I headed to TurboTrix and I was the first Evo to spin the rollers, my car made 323HP with a very steady 10:1 A/F mixture. I asked Shiv why he ran the car so rich, and asked if I'd make more power by leaning it to 11:1. He explained (very politely) that it wouldn't make more power, but still took the time to lean out the ECU program for me and run the car again. Not to his surprise, the car made only 1HP more than before. Not worth the lack of a safety net that the 10:1 provided, so we went back to that map. For those that want proof of this:



Those are the three runs with the three different A/F settings...

Now about the HKS Intake. My buddy with the HKS intake was the second Evo to spin the rollers. After a baseline run the car made respectable power, somewhere in the 250 to the wheels area, I don't remember exactly. (The car had full exhaust, the RS intake, BOV, and MBC @ 20lbs) The thing that was scary was the A/F graph... It was VERY erratic. When we asked Shiv about it, he smiled and said he's seen that on every car he's tuned with an intake (notice I didn't say RS intake, I said intake). My hypothesis to this (being an Engineer I always look for reasons) is that the design of the stock airbox makes the airflow over the MAFS very laminar (laminar is smooth non-turbulent). This laminar flow is much more consistent for the MAFS to meter, allowing the ECU to better judge the airflow into the engine. The design of aftermarket intakes that place the filter directly on the MAFS makes for a turbulent flow over the MAFS. This turbulent flow leads to inconsistent A/F reading. While that inconsistency can be improved with tuning, the fact of the matter is that it's still there, and I think tuning over it is putting a bandaid on a wound that needs stitches. My friend decided that he wanted his car tuned for the stock airbox since he didn't want the possibility of a lean spike while on a hard pull.

Well we pulled the airbox off of my car and put it on his for the remainder of the session. With no other changes, just the airbox, the car made 2HP more than with the HKS intake, I know that's not much, could be any number of things causing that change. I'm not trying to say the HKS intake is bad because it takes away power. The point here is the A/F plot. The A/F plot became very stable just like my car with the stock intake. Shiv then did his magic and the car made 300 at the wheels, which was very impressive to me.

I'm not trying to say that the HKS intake is bad and makes you lose power. I don't really think it hurts power output at all. What I do think is potentially dangerous is the erratic A/F readings that result from it's use. While those erratic readings never caused any problems on my car for the 12k miles the intake was on, I'd still like to think that the car is safer now the way it's set up. And maybe someday when I get a bigger turbo I'll be sacrificing a few HP without the intake, but I don't think that's the case where I'm at now. And while on the highway my ears are thanking me, I do miss the sound around town.

In any event, this post is in no way trying to say that one tuners philosophies on tuning are better than any others... what it is doing is informing you of what I've observed. Does this mean intakes are bad? You decide... and to be fair, a number of other Evos getting tuned that weekend all had aftermarket intakes still and all still made good power.

A second point... Oil based filters... All I can say is be VERY careful with the amount of oil you put on your filters. One WRX that was being tuned took a baseline roll on the dyno and ran DANGEROUSLY lean. While looking for leaks on the intake plumbing Shiv pulled the Perrin drop-in air filter that the guy had installed. It was dripping in oil. Shiv then pulled the MAFS out and it was soaked in oil. He cleaned the MAFS and the guy went to the auto parts store around the block and bought a paper filter. They put humpty dumpty back together and took another spin on the dyno. Voila! The A/F problem was fixed and the car made a few more ponies to boot. So make sure your filters aren't dripping in oil before you put them on

Anyways... those are my observations, like anything you see on the internet, take it with a grain of salt.

- Steve

 

Nice analysis... seems to also be the reason many people are selling their intakes.

As a side note, what BOV are you using?

 

I am using a Greddy Type-S. With both springs it surged, with a single spring it leaked, with the spring I picked up at Home Depot, it was juuuuust right And yes, I did do a boost test to verify the leaking or not. With this custom spring it will hold 25lbs without leaking, and doesn't surge at all.

- Steve

 

People tend not to realize that a MAS is a very finely tuned piece of equipment, and is electronically calibrated together with the factory intake setup as a single unit. Because a MAS is very sensitive to changes in airflow quality, if an aftermarket intake assembly alters characteristics that upset the accuracy of the MAS, performance will likely suffer. In other words, just because something looks trick doesn't necessarily guarantee that it will work to your expectations.

 

This has been my theory on intakes also (I am an Engineer too).

He speaks the truth.

 

I wonder if the differences are even greater than meets the eye. The stock air box is designed to force outside air into the box which it cannot do effectively on a dyno. I wonder what the graph would look like if you set up a fan blowing into the intake for the stock airbox to simulate actual driving conditions. I am seriously considering going back to stock from the RMR unit I have now.

 

Very nice writeup. This information has been around for a while now. It is no surprise that intakes make
the MAF read erratic.
Most tuners have learned what it takes to compensate for this, including Mark (TT).
Shiv seems to be one of the "hold-outs", for lack of a better term, although he also can tune around it
if the customer insists.

Most folks get an intake for other reasons like looks or sound, including me.

OT - if you want to sell that RS, I may be interested

 

In regards to the pulling the airbox off...u just removed the top part (leaving the filter exposed ) and it made more HP with a smoother A/F reading?? Is that correct??

 

No...

When I said "Well we pulled the airbox off of my car and put it on his for the remainder of the session. With no other changes, just the airbox, the car made 2HP more than with the HKS intake....."

I meant that we took the stock intake off of my car, took the HKS intake off of his car, and put my stock intake on his car. The intake was completely stock, including the factory air filter, no modifications to any part of the intake whatsoever.

Sorry for not being more clear

- Steve

P.S. I've been revieving a lot of PMs about the spring in my Greddy Type-S and the mods that I currently have...

For the people that want to know my mods... go here.

About the spring... I picked it up at Home Depot. I threw away the package for it as well... I don't remember what it was called, but the next time I go to Home Depot I'll get the part number and post it for everyone.

 

I previously had a k&n typhoon intake on my EVO and I initially loved it! It sounded like I was pulling in a ton of air and the blow off valve was 10 times louder, unfortunatley I did feel a big power dip in the upper rev range. I guess theis intake just flows way too much air and compensates by dumping too much fuel (and/or pulls timing?). About six months ago and a few modifications later, I went back to stock (I had to trade the k&n for stock because I broke the stock air box when removing the MAS) and noticed a nice little power gain and the power curve felt sooo linear and smooth. I guess after-market intakes are good for EVO's without the MAS and stock is good with them. My $0.02.

 

What about just using a hardpipe post-MAS and keeping the OE airbox?

 

Can you use the HKS MAF Pipe in conjuction with the stock airbox?

 

The difference wasn't because it flowed too much air - which makes no difference because the MAS measures as much air as the motor can use and meters fuel accordingly. The difference is that the aftermarket intake caused some turbulence in the MAS that prevented the MAS from metering the air accurately.

 

Hmmmm....thats really interesting, so the safest thing might be just to add a drop in filter to the stock intake setup? Or maybe modifying the intake box itself to allow it to fit over an aftermarket intake? (similar air flow patern...just more airflow)

 

Ok, now go see what Al , dynoflash has to say about the HKS RS intake. He loves it and gets the most hp out of this unit.

Maybe he can show you some GOOD A/F ratios......Im sure that he dosnt tune or use an unsafe intake.

Just to shake things up a bit I guess...

LOL