Bob_H Posted October 26, 2006 Share Posted October 26, 2006 So I'm doing all this reseach and I come across a few setups which have the MAF AFTER the turbo - seeing pressurized air. As I understand, the downside is you take the chance of the MAF being susceptible to shock waves and reversion pulses. However, putting it on the other side of the intercooler will dampen some of those waves, etc.. The only reason this intrigued me was because of the hard time I am having finding good room to fit the two MAF's and intake tubing in addition to the turbo tubing. In the end I think I'll go with a fender mounted intake, but this was intriguing.... Anyone have any experience with this? -Bob Quote Link to comment Share on other sites More sharing options...
skillet Posted October 26, 2006 Share Posted October 26, 2006 im using a blow-through setup on my 240sx right now. been using it for over a year with no problems. i have a good sized turbo and once i started hitting 1bar of boost i was blowing the I/C pipes apart. nothing we did would hold the silicone couplers on there so we ended up welding a piece of aluminum accross the MAFS. Quote Link to comment Share on other sites More sharing options...
Guest Aguyandaredhead Posted October 26, 2006 Share Posted October 26, 2006 BE sure to place the MAF in a straight piece of pipe as far from any bends as posible or you will exp. a bunch of turbulance that will give false readings. Just my 2cents.. Jeff Quote Link to comment Share on other sites More sharing options...
skillet Posted October 26, 2006 Share Posted October 26, 2006 ive heard the same. i have about 4" on the t-body side, and 6" on the IC side and it seems ok. very nice throttle response. Quote Link to comment Share on other sites More sharing options...
blueovalz Posted October 26, 2006 Share Posted October 26, 2006 Interesting. I have a ram-air set-up on my SX, and it was very sensitive to the resultant turbulance until I baffled the area just ahead of the MAF. I thought it was just something I did not design well (which I guess is the correct conclusion). Quote Link to comment Share on other sites More sharing options...
Tombarace14 Posted October 27, 2006 Share Posted October 27, 2006 That is why you see alum. honeycombs before some MAFs to help combat turbulance. I work with Mitsu's alot and kids will take the baffle out thinking more power will result, but makes the cars run very loopy. I wasnt aware that this setup was possible. One might think the pressure would blow the MAF to bits. Quote Link to comment Share on other sites More sharing options...
skillet Posted October 28, 2006 Share Posted October 28, 2006 i have heard of that happening since the Z32 MAFS i use is all platic. i wrapped a few zip ties around it for a little extra support. i know i already posted this pic in another post, but you can see the blow through setup in it. MAFS is now on the left side of the pic on the cold pipe right before the T body. notice the aluminum brace we had to weld in to keep the pipes together. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted November 14, 2006 Share Posted November 14, 2006 The reason you don't see people running MAF on the pressure side is because they can't measure pressure. Thery measure flow. If you're running 1 bar of boost (all efficiencies given at 100%), the air entering the turbo is twice the volumetric flow of the engine. Once the air is compressed to 1 bar (after the turbo), the flow is that of the engine, but it's twice as dense. The AFM can't see density changes. Therefore, the ECU adds the same anount of fuel whether you're on the boost or not for any given rpm. It's actually worse, because the heated air under boost actually causes the ECU to lean the fuel. If you have the tune set for WOT on boost at, say, 5000 rpm, it won't run very well at 5000rpm when there's no boost yet and you're at WOT on a hard transient. At lower boost levels, it just makes for a poor tune that will ususally run without misfire. The higher the boost level, the larger the gap. Basically, you can tune it for WOT on the boost, and make it run OK, but you can't have the best of both worlds. Quote Link to comment Share on other sites More sharing options...
mjfawke Posted November 17, 2006 Share Posted November 17, 2006 "MAF" stands for "Mass Airflow", with the emphasis on "Mass" - not "Airflow". It works regardless of air density & temperature. Go read up on hotwire and thin-film resistor MAF sensors. Note : This does not apply to the flap-style airflow meter. Quote Link to comment Share on other sites More sharing options...
alexideways Posted November 17, 2006 Share Posted November 17, 2006 Once the air is compressed to 1 bar (after the turbo), the flow is that of the engine, but it's twice as dense. Witch in turn provides twice the amount of air molecules available to snatch away heat from that heated wire wich in turn will cool down more and need more voltage to keep it at it's target temp.. The ecu will add the correct amount of fuel accordingly, without knowing if the voltage signal increase was due to flow or density augmentation. Maybe the name mass airflow is missleading, maybe it should read more like "mass and airflow sensor". Quote Link to comment Share on other sites More sharing options...
cheftrd Posted November 17, 2006 Share Posted November 17, 2006 "MAF" stands for "Mass Airflow", with the emphasis on "Mass" - not "Airflow". It works regardless of air density & temperature. Go read up on hotwire and thin-film resistor MAF sensors. Note : This does not apply to the flap-style airflow meter. So, are you saying that air, flowing at the same speed, but twice the density across a surface will cool the surface twice as much? You would be wrong. It cools a little more due to the additional molecules, but not even close to being a large enough differential to tune accurately. The major cooling delta T comes from the air speed through the sensor. MAS has to do mostly with changes in temperature; cooler air is more dense and the sensor can read this because the air is...cooler, which in turn, cools the wire. Barometric pressure changes, but this is minor, not 20 and 30 psi increases. If what you're saying is true, and flow isn't really a factor, we could use a 200mm pipe with the sensor in it in fromt of the turbo, eliminating any restriction. Air resistance increases at the square of the speed, but not even linear to the density because it's a compressable medium. Why do 99.9% of tuners scrap the MAF in favor of speed density with high power applications if you can just put it in the pipe and eliminate the restriction? Why don't the manufacturers do it? BS in mechanical engineering+physics major+ASE Master tech says I don't need to read up on it; I already have. Instead of me looking up "anecdotal information" from some internet forum, or believing crap spewed by some tuner that defends something just because that's the way they do it and are too dumb to know different, why don't you pick up a physics book and read up. Just wondering, but do either one of you guys actually build and tune engnies for a living? I do. almost 20 years experience with EFI. MAF in the pipe works for a crappy tune compared to leaving it in front of the turbo, or better yet, speed density. Based on actual R&D and not stuff I gathered from Wikipedia, Zilvia, 240SX.com, etc. Now we know where my info comes from, let's hear yours. Quote Link to comment Share on other sites More sharing options...
skillet Posted November 17, 2006 Share Posted November 17, 2006 were you talking to me? if so i wasnt the one disagreeing with you. i only built it this way because i have a 4" turbo inlet, not for any imaginary gains in efficiency. and not to doubt your high and mighty degrees in basket weaving or whatever, i run this setup every day. runs like a factory car under WOT or part throttle. rock solid AFRs, and its pretty quick. Quote Link to comment Share on other sites More sharing options...
cheftrd Posted November 17, 2006 Share Posted November 17, 2006 were you talking to me? if so i wasnt the one disagreeing with you. i only built it this way because i have a 4" turbo inlet, not for any imaginary gains in efficiency. and not to doubt your high and mighty degrees in basket weaving or whatever, i run this setup every day. runs like a factory car under WOT or part throttle. rock solid AFRs, and its pretty quick. No, I wasn't talking to you. If you're going to build engines for customers and give them they're money's worth, you need to study the stuff to be a better basket weaver. If not, you're just a hack selling something you don't understand. I'm glad your afr's are rock solid. Ask Stony about the engine he bought running high boost and 280 cams with an inline MAFS, big single throttle with aftermarket surge tank making 600hp vs. my engines with 270 cams, only 1.3 bar of boost, stock ITB's and speed density making 600hp on the same dyno... Nice looking SR. I have a customer running speed density making 700hp in a daily driver. It makes 450WHP at 1bar. Same chasis dyno as the other two engines. I know a little about tuning SR's too. Quote Link to comment Share on other sites More sharing options...
mjfawke Posted November 17, 2006 Share Posted November 17, 2006 Neither the Bosch automotive handbook, the Bosch Technical specifications or the SAE paper on thin-film airflow meter design which I read ~ 10 years made any mention of limitations due to air pressure. The fact that skillet has a working setup with correct AFR's after the turbo indicates that the MAF is working correctly under pressure. And here's a link to a pic of the Koenigsegg CCR engine - look where the MAF is located here. Quote Link to comment Share on other sites More sharing options...
mjfawke Posted November 18, 2006 Share Posted November 18, 2006 While cheftrd may have departed, the original question could still do with some additional info. here is a company which manufactures hot-film air-mass meters which operate at up to 8 bar pressure @ 4,800 kg/h (the 200mm tube version). They only have an operating temp of up to 80C, however, despite the sensor being mounted in an aluminium tube. As for cheftrd's question about why people ditch the MAF's - I don't know, it's not my field. I tune mainframe computers for a living, not cars. Neither did I try and claim that I was an expert in the field - I just had an issue with the statement "The AFM can't see density changes. ", which appears to have been incorrect based on available info. Quote Link to comment Share on other sites More sharing options...
Bob_H Posted January 25, 2008 Author Share Posted January 25, 2008 I had a question recently about this thread - some more input since i posted this - the main reason many people have issues with the MAF after the turbo has to do with turbulent flow, reversion - i.e. reverse flow, etc.. It leads to times when the MAF see's less than is actually going by, and it can lean out the motor. The opposite is true as well - it sees too much, and tells the car to go rich. People have killed motors with the lean issue - when you put the MAF on the suction side of the turbo, it sees a constant pull - vs. a changing pull on the pressure side. Think of BOV's - when you close the throttle - it sends a pressure wave back to the turbo - which the BOV is supposed to help reduce/eliminate. If the MAF is in that tubing - it can actually see a reversion/reduction in flow and lean out the motor. Over time, this beats up the pistions/etc.. and can kill the motor. Food for thought. -Bob Quote Link to comment Share on other sites More sharing options...
jerryb Posted January 25, 2008 Share Posted January 25, 2008 I run a blow through on my RB20. Before this setup my install would always stall or caugh whenever there was a sudden airflow change...ie my bad ass electric rad fan turned on OR off. So I switch the MAF position and all my problems went away. In fact the car runs smoother, seems to be quicker onto power, idles better....it does just about everything better. Nothing worse! It seemed that most of the folks that told me it couldnt be done...had never tried it. The few that told me it could be done...were running a blow through setup successfuly. So I tried and the rest is history. Yes ...it is in a straight section of pipe, ...it is a Z32 MAF upgrade ...yes it did run a bit rich upon conversion...the PowerFC took care of that. ...Still running stock boost, will run higher this year. ...no Im not a master tuner.....and I cant argue the physics of density vs cooling rate...but I can say that ...with a little effort....it works real well Cheers! Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted January 25, 2008 Share Posted January 25, 2008 I had a question recently about this thread - some more input since i posted this - the main reason many people have issues with the MAF after the turbo has to do with turbulent flow, reversion - i.e. reverse flow, etc.. It leads to times when the MAF see's less than is actually going by, and it can lean out the motor. The opposite is true as well - it sees too much, and tells the car to go rich. People have killed motors with the lean issue - when you put the MAF on the suction side of the turbo, it sees a constant pull - vs. a changing pull on the pressure side. Think of BOV's - when you close the throttle - it sends a pressure wave back to the turbo - which the BOV is supposed to help reduce/eliminate. If the MAF is in that tubing - it can actually see a reversion/reduction in flow and lean out the motor. Over time, this beats up the pistions/etc.. and can kill the motor. Food for thought. -Bob Bob, you need more sleep. 2:30 am! Jeez I somewhat agree with what you are saying here. I have had a blow through setup for a couple years now. My main gripe is making sure air flow is not turbulent. It makes the car run TERRIBLE and puts you in a different part of the map. I saw this on my power FC. I am contemplating going back to a draw-thru setup. BUT I probabally won't since its already "done" this way. I can, however log my a/f's when I hit the track and reynolds so we can see what happens to my air fuel ratio when I lift off the throttle to shift at high boost. I can also cap the BOV opening off completely and see what happens (this will create surge obviously, but I am curious to see what happens to the air/fuel mix). Evan Quote Link to comment Share on other sites More sharing options...
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