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04-04-2007 04:34 PM #1
E34 540iA turbo.... on the cheap?
planning a remote mount turbo for my '95 540i. I want to run 7-8psi boost at first, and more if I can get it. More than that will no doubt require a good intercooler and probably alky injection. However, I don't think just going with a FMU will cut it at much boost. So, my plan is to go with larger injectors (probably in the 36lb/hr range) and make a larger tube for my MAF which has double the cross-sectional area so the stock ECU only reads half of the actual airflow. Since the injectors will be double the stock rating, I would think that the A/F ratios should be about the same as stock. Is my logic flawed with this? I know other guys have done this with other cars and it's worked well. Anyway, the only problem with this is that the ECU advances timing too far at part throttle because it thinks there's much less air going into the engine than there actually is. Since I want less timing at WOT anyway, is there an easy way to trick the computer into running less ignition advance at every point except idle? I suppose I could make a bracket which manually moves the crank sensor clockwise to retard timing, and that would retard the timing by that amount everywhere, right? I could live with that. My plan from there is to get a wideband O2 sensor and fine tune it with fuel pressure. Sound like a plan?
04-04-2007 04:40 PM #2
to clarify a bit...
since the ECU will be trying to over-advance at part throttle with the larger MAF tube, I was thinking that manually moving the crank position sensor would put it back close to where it should be. Then, when I get under throttle and the boost comes up, the MAF will be able to read that air without maxing out and the larger injectors will feed it. The ignition timing will also be retarded 8-10* from stock and that would work perfect while in boost. Sooo, my main two questions are, is there anything seriously flawed with my thinking AND, is there a better affordable option to retard the timing than making a bracket to adjust the crank sensor (such as $100 spark retard ignition box that has a knob on it to dial back the advance by a set number of degrees above a certain rpm point)?
05-18-2007 01:16 AM #3
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05-30-2007 04:54 AM #4
Re: Don't know much about turbo but if you could
well there's some guys on Volkswagen forums that have been experimenting with making larger diameter bodies for their MAF tubes and then using the stock computer/tune with larger injectors. It seems to be working very well for them. The intent is to avoid the cost of custom tuning. In theory (and it seems in practice too) if you double the cross sectional area of the MAF housing, the sensor itself will only "see" half the air that is actually going through the housing. The computer will take that signal and tell the injectors to only feed half the fuel they should be feeding. Now, if the injectors were changed from the stock 18lb/hr to 36lb/hr, they should inject double the fuel for the same pulse duration (assuming same fuel pressure). So if the computer is only seeing half the air coming into the engine and the injectors are squirting double the amount of fuel the computer thinks they are, it should equal out. The advantage to doing this is it gives a lot more head room to push more air through the MAF without "pegging" it (where the MAF sends the highest signal to the computer yet there is more air than even that going into the engine. And the injectors can supply enough fuel to keep up with the extra air that comes with forced induction. Sooo, all one needs to do is the math to figure out the size the MAF housing needs to be compared to the new injector size and that's it. As for retarding the timing, it sounds like the knock sensors will provide enough spark retard under boost until at least 8psi. Above that would be getting iffy. However, if I go above 8psi I'll need to add a methanol injection kit anyway so that'll allow more timing. Right now I have a Garrett 56mm turbo (equivalent to a T04E 57 trim) with built-in wastegate. All I need to do is buy some injectors and run the piping. Of course I also need an electric pump to pump the oil from the turbo to the engine. Since this is somewhat of a redneck build, I'll get a wideband O2 sensor also to make sure it's safe as I go. It's just hard to get around to my 540i project with my '69 mach1 and two Infiniti Q45s that also need work. Hopefully soon though.
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