Cannonball89 Posted June 23, 2011 Share Posted June 23, 2011 The Dyno session went pretty good. I got my VE table set for WOT. I learned a lot and the car made more power than I expected, but it also revealed a problem. Here is the chart: AS you can see It made 253 HP and 280 lb ft of torque. But you can also see that it really dropped off around 5000 RPM. At first we thought it was detonation, so I backed the timing off from 21 degrees under boost to 18 degrees to see what would happen. It did the same thing. The AFR's were solid even when it started missing and dropping out so we checked the plug gaps, they were nice and tight. So we were scratching our heads for a few minutes and we decided to check the datalog to see what the battery voltage was like. I believe that is the problem. You can see that right about where the power drops off on the Dyno, the Battery voltage is dropping off to 11.6 volts. We believe this is causing the coil to not make a powerful enough spark and basically the boost was blowing out the spark. It also may have interfered with the injectors slightly by looking at how the Pulsewidth becomes unstable as the voltage drops. Here are a few snapshots of the datalogs of my pulls. The yellow line is the Battery voltage. I have the 105 amp alternator upgrade purchased from the Z man of Washington, and it is less than a year old, so we don't think that the alternator is causing the problem. We believe that the stock white/white with red wire is not up to the task of keeping the battery charged when both of my fuel pumps are at full song and the injectors are at a high duty cycle and the coil is firing rapidly. So what I'm going to do run an 8 or 6 gauge wire from the alternator + directly to the battery + with an 80 amp inline fuse and also change the wire feeding power to my megasquirt power blocks from 10 gauge to 8 gauge, and see if this solves the problem. I think I will also install a relay for the coil + side so that the coil can draw power directly from the battery instead of through the stock ignition switch. Quote Link to comment Share on other sites More sharing options...
NewZed Posted June 30, 2011 Share Posted June 30, 2011 When the engine is running and the alternator turning, the battery is just another load on the alternator. I don't know enough to say what would be drawing all of those amps, enough to pull the battery down, but I think that you should be focused on supplying the loads directly from the alternator, not the battery. The battery circuit can just be a branch circuit off the main line from the alternator, along with fuel pumps, relays, etc. When lines are run from the battery positive terminal, the power is just passing by the battery through the positive terminal and all of its junctions. Many people install a terminal block, fed by the main wire from the alternator, and run their loads from that. Some also run another block for grounds. You should make sure that your alternator is well-grounded also. Just some thoughts. The main reason I'm reading this is I'm browsing dyno graphs to see where the stock 280's power typically drops off. Quote Link to comment Share on other sites More sharing options...
jacob80 Posted July 5, 2011 Share Posted July 5, 2011 This is interesting. I would think if you've got a big alternator, you would see voltage in the mid to upper 13s. Where are you tapping power for your Megasquirt from? Quote Link to comment Share on other sites More sharing options...
bradyzq Posted July 5, 2011 Share Posted July 5, 2011 (edited) Couple of questions: Is your alternator belt tight and not slipping? Why would you want to limit your 105 amp alternator to 80 amps with a fuse? Not that you should need that much current.... 50 amps for 2 fuel pumps MAX 25 amps each, probably more like 15 amps each 12 amps for 6 hi-Z injectors, 10 amps guesstimate for Megasquirt and coil, probably too high. total 70ish amps Do you have an electric rad fan? If so, at what temp does it come on? It's too late now, but really, the dyno is the perfect place to diagnose this type of problem. You can do pulls while measuring voltage at the battery, at the alternator, at the Megasquirt, wherever. My guess and hope for you is that the belt is too loose and/or old and glazed. Maybe the pulley is worn too and the belt bottoms out in the groove, providing less friction. I'm actually surprised this isn't seen more often. These pulleys are 40-ish years old! BTW, what's up with the drop to 28inches of vacuum as you start your run? Edited July 5, 2011 by bradyzq Quote Link to comment Share on other sites More sharing options...
Zmanco Posted July 6, 2011 Share Posted July 6, 2011 Are you running a single coil? If you do the math, at high revs there just isn't a lot of time between spark events to fully build up the field in the coil. For example, at 5k rpm the coil has to fire every 4 ms. You could try a capacitive discharge system such as MSD which will help some. As I tuned above ~1.7 bar I found I was getting erratic spark at higher revs and boost. I eventually went EDIS and haven't had an issue since. Quote Link to comment Share on other sites More sharing options...
NewZed Posted July 6, 2011 Share Posted July 6, 2011 He just ran a bigger wire to the positive post, see Post #14 - http://www.zcar.com/70-83_tech_discussion_forum/dyno_day..._advice_899360.msg2716588.html#msg2716588 Quote Link to comment Share on other sites More sharing options...
BLOZ UP Posted July 6, 2011 Share Posted July 6, 2011 What are your MS settings for: Battery voltage correction Coil dwell, spark time, etc. And where are you getting MS's power from? Quote Link to comment Share on other sites More sharing options...
Cannonball89 Posted July 6, 2011 Author Share Posted July 6, 2011 Well this thread blew up unexpectedly... Couple of questions: Is your alternator belt tight and not slipping? Why would you want to limit your 105 amp alternator to 80 amps with a fuse? Not that you should need that much current.... 50 amps for 2 fuel pumps MAX 25 amps each, probably more like 15 amps each 12 amps for 6 hi-Z injectors, 10 amps guesstimate for Megasquirt and coil, probably too high. total 70ish amps Do you have an electric rad fan? If so, at what temp does it come on? It's too late now, but really, the dyno is the perfect place to diagnose this type of problem. You can do pulls while measuring voltage at the battery, at the alternator, at the Megasquirt, wherever. My guess and hope for you is that the belt is too loose and/or old and glazed. Maybe the pulley is worn too and the belt bottoms out in the groove, providing less friction. I'm actually surprised this isn't seen more often. These pulleys are 40-ish years old! BTW, what's up with the drop to 28inches of vacuum as you start your run? Question 1: Alternator belt is as tight as I can get it (at the end of the adjustment range on the top bracket and less than 0.5" deflection on the belt at it's longest stretch). Question 2: 80 amp fuse is installed because as you figured out, I don't need all 105 amps, any more draw than 80 amps that would be indicative of a problem and I would like a fuse to blow well before anything melts. Question 3: No I have the mechanical fan still, and have managed to fit intercooler piping behind it (yes it is possible!) Question 4: I have no idea why the vacuum drops low as you floor the throttle, it is something that has shown up in all of my datalogs but has had no effect on driveability or performance to my knowledge so I am not worried at all about it. Are you running a single coil? If you do the math, at high revs there just isn't a lot of time between spark events to fully build up the field in the coil. For example, at 5k rpm the coil has to fire every 4 ms. You could try a capacitive discharge system such as MSD which will help some. As I tuned above ~1.7 bar I found I was getting erratic spark at higher revs and boost. I eventually went EDIS and haven't had an issue since. Yes, I have done the math and I realized that. My spark duration settings were too high and that was the problem. My Spark Duration settings were at 3.5ms and my dwell time at 3.0ms, so basically it was reducing dwell time WAYYYYYYYY too much. The solution to the spark blowout problem was to reduce Spark Duration settings to 1.5ms and my dwell time was raised to 3.5ms. It now seems to pull hard without spark blowout all the way to 6500RPM which is where the spark cut rev limiter is set. As far as MSD, I have always tried to shy away from there boxes simply because my Dad has been through two MSD boxes in less than 10,000 miles on his mustang, and if you look at NASCAR racecars, you will see that they have two MSD boxes mounted on the dash that they can swtitch between, because it is the most likely component to fail on the entire car. Enough said. He just ran a bigger wire to the positive post, see Post #14 - http://www.zcar.com/70-83_tech_discussion_forum/dyno_day..._advice_899360.msg2716588.html#msg2716588 Yes, The much more detailed solution to all of my current problems can be found in that thread. The dramatic voltage increase at every point in the car is documented in post 14, and the solution to the spark blowout problem is VERY well documented on page 2 of that thread, discussing how Max Coil Dwell and Max Spark Duration settings affect the coil at high RPM. I would recommend you all read that thread for the detailed discussion between me and Tony D rather than make me retype all of that info. What are your MS settings for: Battery voltage correction Coil dwell, spark time, etc. And where are you getting MS's power from? I am using the + terminal stud of the starter motor as my main power point. Four wires intersect at the starter motor + terminal stud: The Battery +, Stock alternator + wire (which now only provides juice to the headlights, accesories, and coil), My new heavy gauge jumper wire form the alternator +, and I have a 10 gauge wire that give juice to all of the EFI components besides the coil (2 fuel pumps, 6 injectors, Megasquirt, Wideband 02, Crank angle sensor) So basically the problem has been solved. That is the synopsis. Read my zcar.com thread for the detailed discussion. Quote Link to comment Share on other sites More sharing options...
Tony D Posted July 6, 2011 Share Posted July 6, 2011 Egads, I've succeeded in pushing hits to ZCar.com by rendering competent technical assistance....SHITE! Quote Link to comment Share on other sites More sharing options...
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