Quote:
Originally Posted by roc111672
Rich, What can you tell me about Charlie Stumpp?
|
Not a whole lot. He was kind enough to come over here with some acquaintances to help me with a fuel injector problem and took a look at my tune. I had a leaking fuel injector and at the time didn't have a clue about how to replace the seals. Turns out that it is extremely easy to do.
As for the tune he didn't really do much and was rather noncommittal about it. He knew Jim Smith (who was doing the tuning for Aaron Scott at South Georgia Corvette) and obviously didn't want to step on any toes. Since the car never moved he really couldn't have looked at any of the driveability issues in the tune. But that certainly would have taken a lot more time than was available to him then.
He claimed he could tune my car without the 2 bar MAP sensor I was planning to install for a Speed Density tune, but in retrospect with what I learned about tuning afterwards, I don't believe a MAF based tune is really the best way to go with a boosted engine. The 1 bar MAP sensor that is stock in these cars stops registering at ambient air pressure. The MAF sensor only registers air flow up to a certain point then holds that value no matter how much more air is flowing. So as you can surmise, after the MAP and MAF sensors top out, a tuner can only GUESS at what values are needed for when the engine is in boost. They no longer have ANYTHING to use as a reference. And here is the kicker: You can't even get feedback to tell you what the air/fuel ratios ARE in those cells, because the tuning programs don't have anything to use as a reference. The tables don't have cells for those boosted values. You need a custom operating system to provide the tables needed. You NEED the input from a 2 BAR map sensor or a MAF sensor that is scaled to show higher air flow values. Scaling a MAF sensor then introduces it's own set of problems because you gain higher flow values for a tradeoff of lower resolution all across the spectrum of that sensor. So driveability can suffer as a result of broader jumps from one cell to the next. So what most tuners do in a case like this is to just try to guess at what is a best middle of the road figure for the last values they CAN determine and then use that same value ALL across the range of projected air/fuel needs of the engine while in boost. Depending on how much boost you are using, that can be a lot of ground being covered by a single value for a desired air/fuel ratio. There is just no way that this can be optimal.
Consequently, from all that I have read, EVERY really competent tuner strongly recommends using a 2 or even 3 bar MAP sensor along with Speed Density tuning. What Speed Density tuning is, if you don't already know, is a tune that bases air/fuel mixtures off of a grid based on vacuum/boost in the intake manifold as reported by the MAP sensor, and engine speed. A MAF based tune, on the other hand, is air/fuel ratio tuning based on air flow detected by the MAF sensor related to engine speed. Two different philosophies trying to determine the same thing: How much air is in a cylinder based on the needs of the engine when the PCM commands how much fuel to trigger the injector to deliver.
Oops, sorry, got a bit carried away.....
Anyway, while my car was up on the lift, Charlie looked over the handiwork there from the last two shops (Chris Harwood and Aaron Scott) that worked on my car and expressed shock in what he saw. And in hindsight, he didn't see nearly all of the things that I found later on. He was just looking at trailer hitch wire that Aaron Scott had spliced into one oxygen sensor harness and radio shack wire on the other side, along with the awful fuel system that Chris Harwood had installed. I asked him about fixing the kluge fuel system plumbing, and he said he would figure out a price and get back to me about it.
My issue with Charlie is that he never did get back to me. So I moved on without his help. I presumed that he was just blowing me off, and that was that as far as I was concerned. Your mileage, however, may vary.
Linear Mode
