An engine question.

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Ok, my friend had this bad habit of sitting in his driveway and revving his engine when his parents pissed him off. It lead to him destroying his car basically. But he overdid it, he would play "Redline Game" and hold his car at redline. Stupid, I know.

As for me, here's my question. I'm well aware that putting your pedal to the floor in neutral is a BAD idea. The occasional engine rev though, in an automatic car, if it's in neutral/park, does that damage the engine? We're talking small rev here. Nothing big.

I know, weird question, but I just wanted to know.

posted by  Diomedes

revving the car isnt harmfull, as long as u dont overdo it like redline boy. u can just rev it up to around 3k rpms softly n the car will be just fine. it doesnt matter wether its auto or manual, same results for both.

posted by  Inygknok

Cool, thanks. I wouldn't over rev it. But, I just wanted to make sure it's safe. Incase I ever rev it a bit.

posted by  Diomedes

Many newer cars engines have rev limiters to where the pcm will start failing to pulse the fuel injectors beyond a certain rpm range and no load, no gear engaged. This would prohibit an over-rev condition.

I know you know this, but your friend is a MORON...MOM pisses you off so you sit there and trash a car????? STUUUUUUPID. Smack the sh*t outta him for me. If you just gun the engine below red line a few times you're fine, but NEVER rev a COLD engine at ALL nor rev anything at high rpm.

posted by  cmeseadoin

With regards to the reving issue, I know that when you hit the gas really hard in a car with an automatic transmission it sownshifts to a passing gear. depending on how long you hold that gear it could rev the engine really high. How bad is doing that every once in a while?

posted by  wizzyb82

Passing gear is basically coined as such because when you "kick-down" the accelerator pedal more and more, you are going to sequentially knock the transmission down to the next lowest gear. Now, the pcm and tcm will not allow you to go all the way back to first gear because, say, you are rolling 70 and you need to pass a big rig on the interstate, if you mash it to the floor and the transmission went into first, you blow the engine. Therefore, safety is built in and you'll only get so many gear drow downs based on speed thus equating to rpms. EXAMPLE: My 1996 Pontiac Grand AM @ 50mph

This car is equipped with a 4 speed automatic transmission with a lock-up torque converter. So once I am cruising 50 mph, the transmission is in 4th gear and the torque converter is locked creating a 1:1 final drive. If I slightly give the car gas at 50 and with the TC locked, the first thing she'll do in response to my increase throttle pressure is to come out of lock-up. This increased rpm slightly and give me a little more pulling power. Then if I knock the tac the pedal a little more, she'll come out of 4th gear and down into third. More power. Then with MORE throttle, she'll drop down into 2nd gear and that is as low as she'll go for 50mph. First gear would not work, it would over-rev the engine. The trans. controller and pcm in newer cars work together to ensure the proper shift points at the proper times and also that the over-rev condition does not occur. Back in the old school days you had manual linkage running from the throttle cabling down to the transmission called the kick down linkage. This was back when everything was done manually.

As for how "bad" this is based off your question, you are fine to use kickdown if you need it. The system is designed to work that way. I would not make a habbit of doing it for kicks as obviously, the more high rpms you spin the engine at for a longer duration, you are wearing it more and stressing it more. But using kickdown is not a bad thing within a normal set of constraints.

posted by  cmeseadoin

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