seriously considering selling or trading

[Vendetta]

I was curious about the same items, ex post facto. I do know they were able to read the fuel mappings and determine they were right on the line. Any more boost and we'd need a piggyback ECM, plus an upgraded FPR, injector setup and fuel pump.

When I see him again (and I will), I'll ask him more specifics.

-V

[89Vette]

Thanks V. Here's what I'm going to guess...and it's based on your 2nd-to-last post concerning the parts necessary to make it work.

I'm betting they changed nothing in the ECM. And, by piggy-back ECM, they're saying they reached the limit of boost w/o having greater control of tuning parms -- which probably means spark control.

You can use things like bigger injectors and/or more fuel pressure to deliver more fuel -- in response to the increase of air provided by a supercharger. But a change in fuel pressure or injector size is linear. That means you'd have extra fuel at idle and lower rpms -- where the supercharger isn't really adding air. That's my many/most superchargers come with a fuel management unit (aka FMU). Either yours wasn't initially setup right...or they added one.

http://www.ehow.com/how_12175053_use...rcharging.html

The link above explains an FMU and how it changes the "slope" of fuel delivery. It allows more fuel to be delivered at higher rpm/higher load conditions without flooding the vehicle at idle. I'm better your shop finally got the fuel delivery right with the use of one of these EXTERNAL devices. That means your ECM is still stock and still "thinks" it's pushing a stock engine.

It also means your spark map is still the same as stock. For more boost, they probably need to "hack" into that spark map and start pulling some spark. By that, I mean lower the amount of electronic advance before the piston hits the top of the cylinder. Spark actually STARTS before the piston hits the ideal top of cylinder location because of the amount of time it takes for the fuel to combust/burn. Higher pressures of supercharging, turbocharging, and smaller cylinder chambers make fuel ignite easier. Fuel ignites easier under pressure. (For diesel engines, the pressure itself is enough to create the combustion.)

So, when you say you need a piggy-back ECM to run more boost, I think you're hearing that you've reached the limit of the stock ECM's ability to self-adjust spark advance. Like fuel delivery, modern engines can/do adjust fuel/spark delivery by monitoring sensors that provide feedback. The O2 sensor lets the ECM know when to deliver more/less fuel. The knock sensor tells it to back off timing advance. In both cases, there are pre-programmed limits and pre-programmed tolerances. Once you get outside something like a 15% correction, the ECM can't adjust any further. You end up with the type of problem(s) you saw before the FMU was configured correctly.

89V