Pros or Experts Needed, Tuning on a draw through MAF S/C?
10-18-2003, 08:31 PM
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Pros or Experts Needed, Tuning on a draw through MAF S/C? Did a search but couldn't find anything.
Here's the issue. My friend has an 02 Z06 and just installed a Vortech S/C on an otherwise stock car (long tubes are the only other mod). He simply cannot get the LTFT's in the ballpark. When we scaled the IFR for the 42# SVO's that are in the kit, it ended up being only like 160 over stock, which seems very low according to my math. That got them away from the +25% zone, down to around 15%, but the car was smelling rich at idle and part throttle. But, on the dyno with the wideband, the AFR was dead on.
That got me thinking. The MAF is really just wires that heat up and the air cools them down, then the PCM computes how much air was going across them by taking into account the IAT readings how much the wires cooled off, right? So, on a draw through MAF system at part throttle, the supercharger is still pulling all the air it can, it's just not boosting at the manifold because the throttle plates are blocking most of the air and the by-pass valve is open because of the manifold vacuum. So, the air is being drawn though the MAF regardless of the throttle position. The by-pass vents to the intake tube after the MAF, but if it can't get through the throttle plates, it only has one place to go...backwards out of the MAF and filter. So, the MAF does not know which direction the air is running, it only knows that the wires are cooling down, so it thinks more air is going across it than there really is, so it would think it's running lean and dump fuel. Right? This would explain the rich smell and +15% LTFT's, I think. So how do you end up tuning on a draw through system?
As a side question, is there any good way to tune on a draw through on a Z06 since the IAT is in the MAF, which is on the inlet side of the supercharger? This does not give even a remotely accurate reading of actual IAT.
Oh, side note #2. Why did the IFR table end up only being scaled by 160ish % to get the LTFT's in the ballpark? My math shows it should be in the high 170%'s.
Sorry for the long post, I spent all day trying to help him and it was getting frustrating.
Steve
Here's the issue. My friend has an 02 Z06 and just installed a Vortech S/C on an otherwise stock car (long tubes are the only other mod). He simply cannot get the LTFT's in the ballpark. When we scaled the IFR for the 42# SVO's that are in the kit, it ended up being only like 160 over stock, which seems very low according to my math. That got them away from the +25% zone, down to around 15%, but the car was smelling rich at idle and part throttle. But, on the dyno with the wideband, the AFR was dead on.
That got me thinking. The MAF is really just wires that heat up and the air cools them down, then the PCM computes how much air was going across them by taking into account the IAT readings how much the wires cooled off, right? So, on a draw through MAF system at part throttle, the supercharger is still pulling all the air it can, it's just not boosting at the manifold because the throttle plates are blocking most of the air and the by-pass valve is open because of the manifold vacuum. So, the air is being drawn though the MAF regardless of the throttle position. The by-pass vents to the intake tube after the MAF, but if it can't get through the throttle plates, it only has one place to go...backwards out of the MAF and filter. So, the MAF does not know which direction the air is running, it only knows that the wires are cooling down, so it thinks more air is going across it than there really is, so it would think it's running lean and dump fuel. Right? This would explain the rich smell and +15% LTFT's, I think. So how do you end up tuning on a draw through system?
As a side question, is there any good way to tune on a draw through on a Z06 since the IAT is in the MAF, which is on the inlet side of the supercharger? This does not give even a remotely accurate reading of actual IAT.
Oh, side note #2. Why did the IFR table end up only being scaled by 160ish % to get the LTFT's in the ballpark? My math shows it should be in the high 170%'s.
Sorry for the long post, I spent all day trying to help him and it was getting frustrating.
Steve
10-20-2003, 08:03 AM
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Re: Pros or Experts Needed, Tuning on a draw through MAF S/C? On my car with the 42's I netted about 6ish on the ifr table, and I think the calculated value comes out higher. Putting the blower on made me drop it down to the high 4's to maintain the same ltrims. That, I don't quite understand.
As to the air going back out the maf/filter, Think about it like this: the blower is blowing against the closed throttle plate, and in turn goes out the bypass. Now the air coming through the bypass would seem to go out the intake, but since the blower is moving air, it has to get a supply from somewhere(read: bypass outlet). So it in effect makes a loop for the air until the throttle opens. Kind of a nice idea, but I tried it on mine and the benefit(resolving pcv issues) was not worth how it ran worse. For the iat, I know someone makes an adapter to plug the separate sensor wires of fbodies into the combo maf. Maybe there is also a reverse adapter available? Or cut and solder a sensor on the iat wires, but I'd hate to do that.
As to the air going back out the maf/filter, Think about it like this: the blower is blowing against the closed throttle plate, and in turn goes out the bypass. Now the air coming through the bypass would seem to go out the intake, but since the blower is moving air, it has to get a supply from somewhere(read: bypass outlet). So it in effect makes a loop for the air until the throttle opens. Kind of a nice idea, but I tried it on mine and the benefit(resolving pcv issues) was not worth how it ran worse. For the iat, I know someone makes an adapter to plug the separate sensor wires of fbodies into the combo maf. Maybe there is also a reverse adapter available? Or cut and solder a sensor on the iat wires, but I'd hate to do that.
