Stock WRX intake vs Stock SS

[Splinter]

Looking specifically at the airbox, how do the dimensions stack up?

Im wondering if you took a VF23 and a WRX aftermarket cone filter intake, if it'd bolt up

[BAC5.2]

Unfortunately, they are very different.

Because of how the intake is routed under the manifold, the airbox outlet is facing the front of the car. The MAF is different too (2-bolt, and the housing is actually the airbox lid, ours are 3-bolt, and need the tube).

Unfortunately, it just won't work.

[Splinter]

I'll be switching to MAP sensing

but it physically wont fit?
unfortunate.

[BAC5.2]

Ugh, map? Any reason?

MAP has it's drawbacks, and they are quite significant.

[Subtle]

Splinter

On my list of things to do is the intake. The original box has the panel K & N, so the idea is to have a new top half made with a roomier and less angular
flow out of it.

Upstream, the snorkus has been long gone and the opening through to under the fender will be made bigger.

Autospeed did a test of a typical intake system and IIRR , the total pressure drop was around 37 inches of water and the silencer-thing only amounted to 5 of that.

[Splinter]

Ugh, map? Any reason?

MAP has it's drawbacks, and they are quite significant.

Atmospheric BOV, cone filter

Its going to be on the autronic SMC ecu

[BAC5.2]

You could run a MAF system and set it up as a blow-through with the BOV before the MAF.

MAP tends to have starting issues, and overall tuning issues.

Just something to think about.

[Legacy777]

Also,

MAP systems don't adapt/utilize very well to new modifications without being re-tuned.

[Splinter]

Wouldnt that place the MAF in the hot turbulent post-turbo airstream?

Wouldnt that severely impact the performance and lifespan of the MAF?

[BAC5.2]

That's what an intercooler is for.

We took a turboXS front mount, stuck our Snap-on heat gun at the inlet and let it blow at 1300 degrees (yes, one thousand three hundred degreees) for 30 minutes. The air coming out the other end was, maybe, 90 degrees? And that was without air flowing over it.

A high quality air-air intercooler should be near 100% efficiency.

If you air-water intercool like Vikash did, you can actually exceed 100% cooling efficiency (The "heat exchanger" mounted to the front of the car was colder than ambient air).

You could ask Steve, but IIRC supercharged marine motors have intercoolers that exceed 100% efficiency because they are cooled by the water the boat is on. The air entering the engine is nearly as cold as the water cooling the charge, which is almost always colder than ambient.

[Splinter]

Maybe Ill go to a higher output MAF then

Thanks for the input

[93forestpearl]

Honda ran speed density for a long time, until recently. If you know how to tune your VE table, it shouldn't be a big deal.

Each has it's drawback though. I want to completely eliminate any BS before the turbo. A bent tube with a cone filter, with no restrictions. Using a mass airflow system can get you better fuel economy, but it all comes down to tuning.

Personal preference I guess.

[Splinter]

Alright, I suppose what I could do is set it up for MAP, see how it runs, and if I have problems, put in an MAF

[BAC5.2]

You could do that, yea.

I think the only input difference is an intake air temp sensor. So you could just not use that input, or use it for something else if you switch to MAF.

I'd run blow-through before I ran MAP.

Subaru ran MAP on the Impreza and Forester in like 2001 to 2002. They went back to a MAF.

MAP also has far less... definition... when it comes to trimming fuel. With MAF you know exactly how much air is coming into the engine. With MAP, you know how much pressure is in the manifold. Lots of guess work with MAP.

If you don't want to retune your car for the summer, and then again for the winter, or if you take a road trip to a colder or warmer climate, then I'd highly suggest running MAF.

MAP has absolute pressure. But with knowledge from turbos, pressure doesn't always mean the same volume. And VE changes with the density of the air, right?

[Splinter]

I still dont understand how the same manifold pressure at the same temp at the same volume can mean a different mass of air...
It seems to violate certain laws of physics

[Subtle]

The SDS ecu is map and it has a temp sensor.

Beyond various car installations, they also use it on Subaru engines used in light aircraft.

[93forestpearl]

With a speed density system, you shouldn't need to retune for summer or winter. Thats what the intake air temp sensor is for. You have a table to correct for air temp. You may have to wait untill cold/hot temps to tune for it, but thats part of it. So yeah, your VE will change with temp, but it should be a pretty linear change across the RPM range. So with MAP, VE, and IAT tables, you should have a really good idea of how much air is in the cylinder, at any given RPM and load. True, MAF is prabably easier to tune, since you have less tables to account for.

Some people don't even use VE tables with MAP. They'd rather just tune for it in the base fuel map. Again, just people's personal preference.

I like the idea of speed density because there is no issue with how air is flowing across the MAF sensor. I've always read that MAF's can be really touchy to airflow patterns and turbulence. Since my pre-turbo plumbing will be completely custom, I don't want to deal with those issues.

I believe that MAP can be just as good as MAF, it just comes down to how much tuning you want to do. Speed density is more flexible as far as working with lots of modifications, but requires more tuning. And like Phil said, you have to retune with any modifications that change your engine's VE. MAF systems can just roll with modifications, since it just senses the mass of the air, and doesn't need to take VE into account. You can max out a MAF sensor easier, unless to change to a larger MAF, like one from a Mustang Cobra, or something else. I don't plan on exceeding my MAP sensor's 3.5 bar capability.

How flexible your EM is and your goals for the car are considerations when deciding between speed density or MAF. People do just fine with either, you just need to know where you are going with your project.

This book I bought is extremely informative on tuning and EM. Best $30 I've spent on a book in years.

http://search.barnesandnoble.com/bookse ... 5825&itm=3

It goes over everything you need to know about engine management, how to tune them, and about a dozen projects the author did over the years from a boosted Honda and Focus, to an all out MR2 and other American iron.

[Splinter]

The autronic SMC has the autotune, which supposedly allows it to automatically adjust to those kind of changes

[93forestpearl]

Damn, quick reply. That would be nice. I've heard Autronic makes a nice system. An auto tune feature is nice for getting you close, but shouldn't be relied upon for your perfect tune. I would still tune for high RPM and load manually. Just like high-load closed loop. Do you want to trust your engine to that little computer? Nothing can beat tuning manually with a wideband w/ EGT. But even widebands are not perfect. There is a lag from what is happening in the cylinder to what the O2 is reading, some say about 100rpm.

[Splinter]

The idea would be that I do one good tune when I do my initial build and install the ECU, then let the auto tune handle minor mods as I go along, and take a trip to Rocket Rally's all-wheel dyno for big tunes after major mods (i.e. new valve train, etc)


I probably wont be changing the intake or exhaust after I install the ECU, Ive got a pretty good idea of what I want.

[93forestpearl]

Sounds like you have a good plan. I'm kinda in the same boat. Once I do my intial build, I won't have any changes until something like newer heads.

Rock on.