Matt Cramer, a longtime regular on the GRM message board, is also an engineer for DIYAutoTune.com, a supplier of MegaSquirt ECUs and other engine management solutions. He has also written “Performance Fuel Injection Systems” for HP Books.
Admit it: If you were a kid in the ’80s, you wanted to be like Michael Knight when you grew up. …
An additional tip for this topic: If you think that the car is cutting out because the overboost protection in megasquirt is activating when it shouldn't, you might consider being not me and checking the vacuum source line to the wastegate and/or the boost controller. Don't just turn off overboost. Engines run rather poorly when a rod is attempting an Andy Dufresne style escape through the wall of the block. Talk about your school of hard knocks.
Pffft...cars run great on too much boost! For a very short period of time.
No such thing as too much boost, just too weak of an engine.
NickD said:No such thing as too much boost, just too weak of an engine.
I came here to say this...if you are overboosting...you either didn't build the engine right, need a bigger wastegate, or have the wrong size turbo, either way...boost isn't the problem lol!
Last turbo engine I built I had programmed to have a limiter for the boost - when you hit the limit, the fuel was cut - completely . Pretty eerie when it activated (which it would only do on a long straight with floor to the floor acceleration) - all the noise just stopped happening - until the engine slowed enough to reduce boost below the danger level. First time I hit it, I figured I'd blown something vital but wondered why no noise of parts hitting the pavement. Second thought was wait - lean burn = disaster, but then immediately afterward - ah - NO fuel = NO burn.
I guess today you'd more likely implement over-boost protection via an ignition that omitted every other spark until the boost backed off - it would just flatten out until boost dropped, or a solenoid on the wastegate triggered by the ECM.
In reply to wspohn :
Cutting fuel will do a handy job of cutting boost. Exhaust gases have much more pressure and volume than the same approximate mass of raw air. (That is rather how engines work in the first place!)
I assume (ASSUME) that if you use EAE type acceleration enrichment, the first injection pulse for each cylinder after cut will have an additional blorf of fuel to compensate for the fuel that normally would be condensed out on the runner walls that continually gets removed/refreshed, that would have been completely depleted during fuel cut. Otherwise, the first cycle after cut will be quite lean, as it would be for less comprehensive acceleration enrichment methods. I suspect people get away with it because the chamber will also have been cooled significantly, so running lean once or twice won't hurt.
wae said:An additional tip for this topic: If you think that the car is cutting out because the overboost protection in megasquirt is activating when it shouldn't, you might consider being not me and checking the vacuum source line to the wastegate and/or the boost controller. Don't just turn off overboost. Engines run rather poorly when a rod is attempting an Andy Dufresne style escape through the wall of the block. Talk about your school of hard knocks.
I know this is an old thread, but I'd like to stress the importance of what you touched on here Wae. The guy who built my engine used nylon vacuum line for the wastegate pressure signal line. Wanna guess what nylon does in the vicinity of hot, glowing exhaust bits? Yeahhhhh... it melts.
I found this out one day, when said line melted, I was accelerating, and the MS3 Pro ecu I was running cut the ignition right at peak boost. Took a moment for me to react, but when I let off the pedal and eased back into it, I got a nice, large BOOM and fireball out the exhaust. Turns out, the overboost protection setup in my car only cuts the ignition, but *not* the fuel. Unburned fuel keeps the chambers nice and cool, I suppose, but it does tend to flash ignite inside the super hot housing of the turbine... and when you feed it plenty of fresh air combined with that fuel, because your foot is still on the throttle and that compressor is happily spinning away, you create quite the amusing side effect of a malfunctioning wastegate line.
It was fun for a few spool up and BOOM giggles once I caught on to what had failed, and I was impressed by the reaction speed of a modern ecu to protect the engine, but I didn't wanna push my luck. Said vacuum line has since been replaced with the same silicone that's used on Caterpillar engines.
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