How should I tune around a compressor surge?

robert presti

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I don't recall seeing the problem with the ba3000 and a screen, but I might not have done the same thing. Now I have a ba5000 in a 3 inch housing and the MAF add counts fluctuate by 100 when letting off or holding a steady rpm at least into the 2000 rpm range. This seems to richen the engine, I'm sure by reading air that isn't going into the engine. Why was trying to do things right with the BA5000 in a 3" housing seem to be making things worse? I know the best way is to get a bigger valve to allow more compressed air from getting to the maf, but I don't get why it is worse now, or how one should tune around it. The pulley I believe should make 17 psi of boost. In the past you could hear air recirculating when letting off while driving and this car is loud. So far this car is only in the idle free rev state as of now with the new parts.
 

01yellercobra

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What's your full set up? Are you running blow through? Did you increase the boost level? I ran a BA5000 in a blow through set up and never had an issue. I was vented to atmosphere as well.
 

robert presti

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The car was blow through both times and in the same (not so ideal spot) in the wheel well. The car has never been vented to the atmosphere so to say, it recirculates back to the front of the supercharger. I believe this is this way because at one time it was draw through. No changes were made to the pulleys. I can watch the AD counts fluctuate by as much as 100 when the rpm is over 1200 and the throttle is nearly closed. I could be wrong but it seemed with the past MAF it was something like 20. Seemed much more stable on afr than now, but hysteresis coasting fuel cutoffs might have been set much higher. I'm going to bump the rpm limit there and try to get a screen before the MAF, to see if I get back to where I started. I might move the MAF closer to the engine in a better spot as well, but I'd rather not see it.
 

01yellercobra

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That's weird. I wonder if you got a bad MAF? If the BPV was fine with the old MAF it should be fine now since you didn't change the boost level. I had my sensor in a 3.5" pipe in basically the same place as stock. With all the pipes in place it wasn't visible. The pipe in my set up came through a hole in the wheel well though. I had a pretty straight shot before the sensor.
 

robert presti

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Yeah the thing of it is, it is fine when the throttle is opened and demand is increasing for air. When letting off it goes wacko, like the BPV isn't big enough or maybe it went bad. One thing different too is that is now a 3 inch tube vs a 3.5 tube. I went with the 3 inch because all the other pipes and throttle body are 3 inch.
 

robert presti

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Yeah the thing of it is, it is fine when the throttle is opened and demand is increasing for air. When letting off it goes wacko, like the BPV isn't big enough or maybe it went bad. One thing different too is that is now a 3 inch tube vs a 3.5 tube. I went with the 3 inch because all the other pipes and throttle body are 3 inch.
Today I thought maybe the bypass is not in a good spot. The bypass is in front of the intercooler which I would think is the worst place. I would think as close to the maf as possible to avoid the spring effect, but maybe it doesn't matter when the bypass valve is just to small any way. I checked and the bypass is working as it should. Even with the bypass working the way the supercharger is set up there is a lot of pressure around 2000 rpm. This was causing idle issues that I think are gone now. Set the isc and dashpot to near nothing. The IAC Is fed through the pipes subject to surge rather than the atmosphere. which is not ideal either. Engine is set to idle with no IAC flow and TPS voltage set to base reading.


This wasn't the answer. Not enough air flow for cold starts, but is great when warm. I don't know how many times I'll try to get the numbers right to prevent the hanging idle issue. All I know is there is no issue when I feed the IAC to atmosphere, rather than the intake tube. Might try a one way check valve to prevent air being forced through the IAC.
 
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robert presti

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I thought I would just do a follow up on this subject. I moved the MAF and did a better job of having less bends in the pipe. I removed the screen and just running it. I'm shocked at how stable the fluctuation has become. Less than 20 add counts . The 20 is likely compressor surge reduced as much as possible...down from 100 add count swing with a better setup from the start. Had I not fixed the fluctuation I would have gone to the "back flow entry" in the tune. That is where you can tune around compressor surge that is not manageable. I could have just set the car up and tuned it, but I want mine as right as can be from the start.
 
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decipha

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the bov should be nowhere near the maf, it ahould be as close to the discharge of the blower as possible and if borderline capacity it should be dumped to atmosphere
 

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