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LS400 MAF housing with high impedence 550cc injectors

 
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MikeOffline
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PostPosted: Mon Apr 11, 2005 1:11 am    Post subject: LS400 MAF housing with high impedence 550cc injectors Reply with quote

I've been hitting fuel cut at about 13 psi with the upgraded ct26 using the stock MAF housing, so it was time to upgrade.

For those not familiar with this, there is a lot of info out there on it but the gist is that the 7mgte ecu bases fuel cut on the frequency from the vortex shedding air flow meter - once it gets too high the computer says OK the engine is going to blow up if we keep this up so it stops delivering fuel. The frequency that the vortices oscilate at is proportional to the velocity of the air across the probe - not the bulk volume flow rate - so if you run a larger housing, for a given velocity (and in turn frequency) there is more air going into the engine. The very desirable end result is increased boost level when fuel cut is encountered. The idea of increasing the injector size at the same time is that the net change to the overall fuel mapping will be minimal.

The injectors that i was running were mazda rx7 high impedence ones. High impedence injectors are generally not as desirable as low impedence ones because the response time is a little slower. In order to make them work with the 7mgte ecu, the injector resistor must be bypassed.

Now going into this I was pretty curious about whether it was safe to run the stock 440cc injectors with the LS400 housing. I've heard that the 7m runs rich to begin with, so would it be such a bad thing to lean it out a little bit? In addition, the feedback from the oxygen sensor is used to modify the fuel curve anyway, so perhaps after that was done the mixture would be just right anyway. The main concern I had was that at some point the 440cc injectors just wouldn't be able to deliver enough fuel - at 6000 rpm and xx psi boost. I was too lazy to calculate what this boost level was, and because I don't have the equipment to monitor air fuel ratios all the time, it's not something that I'm willing to run permanently at this point. But I did some testing.

I borrowed a wideband oxygen sensor from the school engine lab over the weekend and compared three setups:

-Stock 440cc injectors with stock MAF housing, 11psi boost

-Stock 440cc injectors with LS400 housing, 11psi boost

-High impedence 550cc injectors, LS400 housing, 17psi boost

Data logging was done with each setup, I'll see if I can post up some of the graphs.

A general observation was that for a given boost level, as RPM increased, the mixture became richer. I'm guessing the ECU is just programmed that way to keep things as safe as possible. (stoichiometric AFR is 14.7 or lambda = 1)

The stock setup running 11psi was rich all over. Idle was about 0.85 lambda. At steady cruising speeds the air fuel ratio was about 14.4 / lambda 0.98, but as boost increased it got richer and richer. In third gear, 11psi boost, and 6000rpm, it would drop all the way to 9.8 AFR / 0.67 lambda Surprised While this is good because it is safe, it is far from the typical peak power values of 12-13 AFR.

The LS400 housing installed with the stock 440cc injectors and 11psi boost, was leaner than stock as expected. Idle was consistently lean, about 16.2 AFR / lambda 1.1. Driving at constant speed it was slightly lean. Under boost it stayed on the rich side, but only going as rich as about 0.8 lambda / 11.75 AFR at 6000rpm and 11psi. Basically it was right in the area that a person would tune for, though still perhaps a little rich. The concern with this setup was not knowing what boost level would cause the 440cc injectors to saturate and create a very lean condition. Increased boost was not attempted for that reason.

The computer had a tough time adjusting to the 550cc injectors. Idle was very rough and surprisingly very lean for a long time, even with the injector resistor removed. It wouldn't idle at all with the injector resistor in the circuit. The boost was now increased to somewhere between 16 and 18 psi. I honestly never really saw the gauge at peak, but that's what my friend told me Smile Idle and constant speed mixture remained a little on the lean side. However, under boost it was always rich and in fact it was richer than stock fuel and MAF housing at 11psi was. I believe it dropped all the way down to lambda 0.64 / 9.4 AFR! Needless to say, there is huge potential for increased power with tuning; I need to get an SAFC!

The new pressure plate is awesome! I can't really get the clutch to slip at all, and I actually need to get used to launching with it. We ran the quarter mile using the GTECH, and on one of my launches I revved to high and just lit the tires up and hit about 6500 instantly - Oops Very Happy

Here's a very dark video:

http://www.webpages.uidaho.edu/~simm8647/4Runner/vids/410050~1.AVI [9.1MB, DIVX codec required]
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MikeOffline
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PostPosted: Mon Apr 11, 2005 1:13 am    Post subject: Reply with quote

OK sorry that went on for so long. All in all I have to say that I am a little disappointed with the results so far. The larger compressor wheel on the turbo along with the big intercooler definitely make the lag more noticable. And I figured 18psi would just knock my socks off, but it didn't. Mostly I think because it is runing so rich - I wouldn't be surprised if I could gain 50hp with tuning based on it being that rich at this point. Anyway, I'm probably being too negative here, because it is a blast to drive. And it really is hard to give a good before and after comparison of the recent mods because it was down for about 7 months. However it did run the quarter mile SLOWER than before according to the GTECH. That makes absolutely no sense to me. I'm wondering if the GTECH was not quite level the first time we did it or something, because the speeds that it gave were also much higher than what my speedo said, but this time they seemed pretty right on. On the last GTECH runs I would complete the quarter mile in third gear, and supposedly at 99MPH, which my 4runner can't do in third gear. I basically barely have to shift into fourth now to finish the quarter.
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PostPosted: Mon Apr 11, 2005 10:46 am    Post subject: Reply with quote

nice, you'll work the bugs out. As usually your smarts on alll this stuff blows me away.
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PostPosted: Mon Apr 25, 2005 3:35 am    Post subject: Reply with quote

so mike are you saying fuel economy is better with the ls400 air flo meter?if so what model and where can i buy one and how much?did it improve power noticably from the stock one useing stock ct26 and stock injectors? my 7mgte seems to run way too rich as well and thought maybe it was somthing to do with my setup..what are you doing on the quarter mile now and what tyres and diff ratio are you running?ive got mine absolutely low flying,i broke traction the other day at 60mph just after going over a slight rise,my passenger damn near shit himself,great fun..
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PostPosted: Sun Jun 05, 2005 12:10 pm    Post subject: Reply with quote

Yeah, fuel economy is better with the LS400 housing, but you have to be careful about using it. If you get too much boost at too high of an RPM, the stock 440's won't be able to deliver enough fuel and you'll go lean at a very bad time. However, from what I've seen, that doesn't happen at 11psi, at any rpm. You can find them on ebay or supraforums,and they typically go for about $150 but if you watch a while you can find one for less. It's just the stock setup used in the Lexus LS400 car (don't know whether they have those in Australia though), and all you need is the housing. You can use either the lexus sensor or the supra one.
Yes, it did seem to improve power noticably.

I don't know what it's doing the quarter mile in now. I'm running 32x11.50x15's, with stock 4.10 gearing.
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