Rev hang - a curse or blessing

[aquasurf]

Out of curiosity what cars did they introduce that with? ....

I do not know when rev hang first appeared. My first experience was in February 2003 in Spain where I hired a new Fiat (I think it was a Punto model) and in 7 days I drove it I could not figure out why I could not change gears smoothly.

…Im just curious on your reasoning behind it being an emissions thing?

I am positive about that. The problem car designers try to solve by rev hang is the sudden leaning of mixture when throttle is closed abruptly as it generates a spike in NOx (oxides of nitrogen) emissions. I had car emission lab test results from about 1985 (the voluntary test costing me over $1000 at the time), proving that beyond doubt.

… Unburnt fuel gets sorted by PVC System. Plumbed back into the intake track for a second shot at redemption.

I agree the rev hang is not about removing unburnt gasses. In fact, it works to the opposite effect because it intentionally feeds additional fuel to the engine when throttle pedal is off. This causes the engine (and car) decelerate much slower that would otherwise be the case, bringing on all the nastiness of hanging revs.

… This is my 1st DBW Car and its the only car that I've owned does this. I also know its cos Im shifting like race car when it happens. If just driven Civil, granny shifting in traffic is all good.

People describe their experience with hanging revs in different situations. Some write about revs hanging at fairly low engine speeds, say 3000 rpm, others cannot get idle down to the normal 700-800 rpm without revs first hovering around 1500. My concern and solution deals with the problem of revving my engine high and the revs not dropping fast enough when upshifting. Generally, the rev hang gets worse with increasing revs. I can upshift at low rpm without difficulty but I did not buy my Honda VTEC to "shortshift" when I wish to use all of its 140 kW at 7000 rpm.

… On S & S# there is no hang in my car, behaves like a cable operated throttle & more sensitive pedal & more power.

I understand some cars, like yours, have several programs in their ECU and engine control can be varied by the push of a button.

… Little bit better then module as on I - limited to 60% throttle at max pedal depression. IE throttle plate wont open past 60% even when given the full blow.

I find it interesting that people often refer to the opening of the throttle plate as if it was the determining factor in setting engine revs. Would you believe that in EFI cars it is possible to have the throttle plate fully open (by the ECU, of course, taking cue from the DBW throttle pedal) and yet go nowhere? This happens when the ECU cuts signal to injectors, stopping supply of fuel to the engine.

… I also don't see how it would help upshift don't you want the rev's to drop when upshifting instead of hanging around?

Of course, I want the revs drop fast when upshifting. This was the reason behind my efforts to delete rev hang. If you want to read more about my rev hang investigations, look at my rev hang webpage.