MAF-T Blow through pros and cons??

[3literpwr]

I have a maft setup on my 92 talon rally car, which seems to work well.... I was thinkig about installing it in the blow through manner, but am unsure if this will result in problems.... I Have heard that it requires frequent cleaning? I know turbos spit a bit of oil which can fug up the hot wire....

So the question is has anyone run in both forms? If so was there any advanages from one to the next....

Thanks
Larry Parker
#622 scca club rally

 

[nine5raptor]

I have run both. Started drawthrough, went to blowthrough. Added a front mount keeping it in blowthrough. Then went back to drawthrough.

The reason for switching back to drawthrough was I was having trouble with the boundary layer in my couplers causing air steering problems (not sure if that describes it at all). I was getting a non-linear tuning curve. For a given tune, at low rpm, I was running lean and at high rpm, I was running rich. My piping is 2.5" and I am using a 3.5" sensor.

What I figured was happening was at lower airflows (still at wot), air was flowing smoothly through the transitions and through most of the maf and the airflow readings were correct.

At higher airflows though, the air was creating a thicker boundary layer in my expansion/reduction and the majority of the air was staying to the center of the maf where the hotwires are also located. This was giving me an artificially high airflow reading, causing me to run richer.

Switching back to drawthrough cured the problem.

I didn't have any trouble with oil on the maf, but my system is pretty clean - my pipes don't have an oily feel to them at all after the turbo. Others have said that they like to keep the maf clean though and it makes sense as an oily film will definitely change the Specific heat of the wires.

If you have any thoughts of running water injection as well on your rally car, it is not a good idea to run WI before the maf. So if you wanted it just post intercooler, it would be a good idea to stay drawthrough.

Really, you can run either way. It is mostly personal preference and ease of install. At least one person has made over 500 to the wheels in drawthrough and he saw no reason to go blowthrough so it is not a hinderance being drawthrough.

Your choice...

 

[3literpwr]

Thanks for the info!! For the 200 bucks for the new upper IC pipe I dont see a real benifit if any........ Besides a cool sounding BOV......

Cheers
Larry Parker
#622 scca club rally

 

[nine5raptor]

Yeah, there really isn't any benefit unless your setup is such that it is nearly impossible to install the maf in drawthrough.

Seeing how yours is already installed, the only difference would be the ability to vent.

 

[3literpwr]

Some one in the galant VR4 forum did make a good point stating that if I was to blow off a or get a big leak in the intercooler or IC pipe that the car would run much better with the blow through...... This could mean the difference from wining or lose/dq from a rally.....

I guess its something to think about.......

 

[DCJ98GST]

I was looking through Maximum boost by Corkey Bell and he talks about a reduction in throttle response when the air meter is further from the throttle body. So in this case the blow through may have better throttle response because the low pressure air pulse when opening the throttle passes progressively down the intercooler pipes until it hits the air meter.

I dont fully understand how this becaue I have not thought it out yet, and I have no experience with either system but since it is noted in a respectable turbo book it was worth noteing. Any other thoughts on this issue?

 

[Groomz]

The problem that nine5raptor was running into would be reduced or eliminated with proper sized piping. A 2.5 inch tubing with a 3 inch MAFT would reduce that amount of airflow reading problems. If the piping was correctly expanded with enough length, the airflow could travel complete through the MAFT, not hitting the MAFT at a single smaller area.

I like the blowthrough setup because the air intake temp would be read after the intercooler, and allows you to vent also. The airflow readings would be more accurate to what is actually going into the engine versus what is being ingested by the turbo. Getting tons of heat soak? A drawthrough can't measure the air temp different a hot intercooler will play on the intake temps.

 

[nine5raptor]

The airtemp argument is moot as the air temp is never read with a gm maf. The airmass is measured directly as opposed to being calculated from airflow, pressure, and temp like the stock karmann vortex sensor.

Even a 2.5" to 3" will experience some of the effects I saw. Only if you had the piping exactly the same throughout the system would it be eliminated.

The throttle response issue is due to the lag time between the ecu seeing air entering the system and the air actually entering the motor. As quick as the ecu and sensors are, I don't consider it an issue. The difference between pre and post turbo air metering on fueling response time is almost nothing.

The blowing off a pipe is a good point, I had some experience with that when I first put mine in blowthrough. For me, that wasn't a selling point as I wouldn't want to drive the car with unfiltered air and an exposed maf hanging out there. For a dedicated race car, though, it might be worth it.

 

[3literpwr]

Thanks for the input guys.... I think I will stick with the suck form for now.........

Cheers
Larry