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Old 03-04-2010, 02:54 PM
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Revving an engine in neutral / park

Just thought I'd ask this to see what the concensus of opinion is. I've always been wary of revving an engine too high with the car stationary in park/neutral, but I couldn't articulate exactly why. An engineer once told me it's a bad idea because the engine is 'unloaded'. However, I've asked the question of others and they've said it's fine and no different to revving an engine under load. It's not purely an academic question because, for example, if you have a new exhaust installed, you might want to 'demo' the exhaust to a buddy by revving the nuts off the engine for maximum effect. Alternatively, on an engine that's really sweet-sounding at high revs (eg. Ferrari V8s), it's tempting to rev them up if asked.

What say you guys? Harmful to rev an engine (potentially, to maximum RPM) in neutral, or no problem?

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Old 03-04-2010, 05:56 PM
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I would be willing to bet that out of all the rodders on here that. If they have ever raced or even owned what they would consider a rod, They will tell you that they have revved it in neutral/ park and all the drive gears going down the road If something is going to happen it don't care what gear you are in JMO. Someone might say different but i don't think it really matters. I mean i wouldn't make a habit of it or anything. But i am sure there are some that wouldn't do it.


Cole
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Old 03-04-2010, 06:17 PM
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Just my thoughts on this.

I believe that it is possible to rev a motor down the strip past the point of no return and have itself destruct. This would obviously happen while the motor was under a load since it was busy pulling the car along with it. One crosses the point where valves may float & kiss the pistons, or the large and small ends of the rods may decide to get a divorce, so they part ways and go their separate ways.

I would think that if one were to rev the motor with no load, that this "Magical point of no return" would be reached faster... much faster if one wasnot very careful.

Some people never let fear nor common sense get in their way.

Just a thought.
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Old 03-04-2010, 06:49 PM
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True story. My mom had a gorgeous little '72 Pinto with the venerable German-design 2.0 4-banger and a 4-speed.

The choke began hanging up and rather than calling me to fix it, she had one of the neighbor men come over to take a look. Well, he revved the snot out of the motor in the driveway and it must have cracked every ring in the motor. At least that's what I thinkin' happened. No doubt there was a ridge at the top of the bore and when this idiot stood on the loud pedal, the rods and crank journals stretched enough to bring the rings up against the ridge and crack them. He turned a perfectly good motor into a mosquito fogger and mom abandoned the car. What a damned shame. Of course, the idiot denied all responsibility.

I don't rev motors up in neutral.
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Old 03-04-2010, 07:15 PM
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How high are you planning on revving it?

Just don't let it hit the rev limiter. Sure it keeps the engine from spinning to a zillion RPM, but it sounds stupid with the spark/fuel injection cutting out.

Also, don't put it into any drive gears with the engine revved. Unless you want to destroy it.

It seems to me that revving under load would mean higher cylinder pressures since its at WOT a lot longer (you really don't need WOT to hit redline and beyond when the engine is not under load) and an increased risk for catastrophic failure. Even not under load there is still a risk, just like in the case of said Pinto turned mosquito fogger.
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Old 03-04-2010, 07:40 PM
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Quote:
Originally Posted by techinspector1
True story. My mom had a gorgeous little '72 Pinto with the venerable German-design 2.0 4-banger and a 4-speed.

The choke began hanging up and rather than calling me to fix it, she had one of the neighbor men come over to take a look. Well, he revved the snot out of the motor in the driveway and it must have cracked every ring in the motor. At least that's what I thinkin' happened. No doubt there was a ridge at the top of the bore and when this idiot stood on the loud pedal, the rods and crank journals stretched enough to bring the rings up against the ridge and crack them. He turned a perfectly good motor into a mosquito fogger and mom abandoned the car. What a damned shame. Of course, the idiot denied all responsibility.

I don't rev motors up in neutral.
I love this site, Oh and for the record to the OP i don't rev to the limits either when in park or neutral. Richard you made me remember back when my older brother was sitting in my dads 64 ford, Dad just got new pipes put on it and i mean he was revving the crap out of it and then a big "BOOM" I thought he scattered the engine all over the place, Long story short it blew a big hole in the ground as the clutch came apart. Man was my dad made at him for a bit.


Cole
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Old 03-04-2010, 08:30 PM
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He's lucky it didn't take both feet off. I've seen a bunch of clutches blow in the 50 years I've been around drag strips. The last one was just a couple of years ago at Firebird. '65 Mustang was nearly cut in half on the starting line.

Here's an old-timer I keep in my photo gallery...
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Old 03-04-2010, 09:52 PM
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GREAT way to get the heater warm...FAST!! Right or worng...good or bad...I don't like to sit and rev the ******* out of an engine,without some kind of load on it and only after the oil warms alittle.
6sally6
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Old 03-05-2010, 06:41 AM
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holy **** that pic is crazy... i never would have imagined a clutch can do that.
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Old 03-05-2010, 07:32 AM
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There is a guy that races in the modified classes at our local mud bogs with a pretty ****ty 565 and that dude will sit on the line bouncing that thing off of about a 7500 chip just to make some noise. I can't wait till it lets loose one day so I can have a good laugh. Dont make much sense to me. My opinion is free rev is way different than being under load.
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Old 03-05-2010, 07:42 AM
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Quote:
for example, if you have a new exhaust installed, you might want to 'demo' the exhaust to a buddy by revving the nuts off the engine for maximum effect. Alternatively, on an engine that's really sweet-sounding at high revs (eg. Ferrari V8s), it's tempting to rev them up if asked.
Ayuh,... IMHOpinion,...
When I hear that, it just Confirms there's a Moron behind the wheel...
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Old 03-05-2010, 07:52 AM
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Quote:
Originally Posted by techinspector1
True story. My mom had a gorgeous little '72 Pinto with the venerable German-design 2.0 4-banger and a 4-speed.

The choke began hanging up and rather than calling me to fix it, she had one of the neighbor men come over to take a look. Well, he revved the snot out of the motor in the driveway and it must have cracked every ring in the motor. At least that's what I thinkin' happened. No doubt there was a ridge at the top of the bore and when this idiot stood on the loud pedal, the rods and crank journals stretched enough to bring the rings up against the ridge and crack them. He turned a perfectly good motor into a mosquito fogger and mom abandoned the car. What a damned shame. Of course, the idiot denied all responsibility.

I don't rev motors up in neutral.
I seen what I believed was the same situation once, a friend had just bought a car from a "little old lady" tuned it up and was revving the crap out of it in neutral. Long story short it wasn't too long after that he was rebuilding the engine.

I too do not rev them to the limits in neutral, i believe in the load-no load theory, true or not???
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Old 03-05-2010, 07:54 AM
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The pistons, rods, rings, valves, lifters, rockers, cam, oil pump, etc, etc. neither know nor care if the engine is in neutral or drive. All these parts see is loads based on RPM. 6000 in neutral is no different than 6000 in drive. The only difference is the RATE of RPM increase. This does not increase the structural loads.

The crank is the only part that sees different loads in neutral or drive, and the loads are HIGHER in drive.
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Old 03-05-2010, 09:45 AM
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I kinda agree with Joe. It's just a machine. I guess you could analyze it death and look at instantaneous acceleration of the rotating parts. A blown fuel motor with the clutch is probably looking at 200 pounds of rotating stuff. When you look at the data recording and see that under load the motor gets to 7500 in around 3/4 of sec, it makes you wonder what it can do unloaded. All I've seen is a spike and the coast down from at least 6500 just whacking the throttle. The load on the crank is probably pretty high in either case. The shock load from an unloaded rev could start to get significant as the time element is very short and the effort to accelerate the mass could get very high.

On a street motor you simply can't even get close to this so I don't see a real problem as long as you stay away from extreme rpm.

Turn this inertia around on a little different subject. Ever had trouble braking drums loose on the rear end of your dually truck?? Jack the truck up and securely 'stand' it. The simple way is to remove the wheels and put a couple lug nuts back on loosely. Put it in reverse and rev it then slam on the brakes. Then do the same in forward. It usually only takes once to knock them loose. An old guy showed me this and it sure made a usually hammer pounding, cussing project easy.

The bottom line is rev the crap out of it but make sure there is a video camera going just in case us naysayers are wrong.
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