How hard on an engine is hitting the rev limiter

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jet1
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How hard on an engine is hitting the rev limiter

Post by jet1 » Tue Jun 19, 2018 10:27 am

Watched a boat race this weekend and one guy was hiting the rev limiter every 5-6 seconds. well 60 miles of racing later he has a hole in his block. tried telling him about the rev limiter thing but he just said thats what its for and just walked away. Thoughts?

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Re: How hard on an engine is hitting the rev limiter

Post by mag2555 » Tue Jun 19, 2018 10:45 am

Being into the rev limiter for that amount of race time is not good as in 5 seconds of being into the limiter unburned fuel is likley close to Hydro locking the cylinder at high rev's and the believe it or not the main failure factor is how the killing of the spark massively throws the engine balance off!
That's why you can feel being into the limiter!!!
If forget what the exact number is , but at only 6K rpm each cylinder of a V8 is firing 7 times a second.

jet1
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Re: How hard on an engine is hitting the rev limiter

Post by jet1 » Tue Jun 19, 2018 10:49 am

Ya I looked at the G2X chip and he was into the rev limiter constantly. Sometimes real hard. It might not be the whole reason for the failure but it was obviously a factor in it. Thanks.

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Re: How hard on an engine is hitting the rev limiter

Post by Belgian1979 » Tue Jun 19, 2018 4:24 pm

mag2555 wrote:
Tue Jun 19, 2018 10:45 am
Being into the rev limiter for that amount of race time is not good as in 5 seconds of being into the limiter unburned fuel is likley close to Hydro locking the cylinder at high rev's and the believe it or not the main failure factor is how the killing of the spark massively throws the engine balance off!
That's why you can feel being into the limiter!!!
If forget what the exact number is , but at only 6K rpm each cylinder of a V8 is firing 7 times a second.
More like 50 times a second.

A fuel cut is better but is only possible with EFI.

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Re: How hard on an engine is hitting the rev limiter

Post by Circlotron » Tue Jun 19, 2018 5:48 pm

Seems there are two types, the OEM style that cut the fuel to all cyls for about half a second, and aftermarket that cut the ignition to random cyls. I can imagine the OEM type being very hard on the whole drive train. Would be better overall if the fuel was cut to random cylinders, but that might not give enough indication to the dumbest category of drivers.

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Re: How hard on an engine is hitting the rev limiter

Post by peejay » Tue Jun 19, 2018 8:15 pm

Rev limiters kill engines. The on/off shock plays hell on everything.

It's a safety device, not cruise control!

This is why I have a built in "soft limiter" in my car where it starts dumping all the fuel in the world into the engine near my max RPM. It simply stops making power because it runs so rich.

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Re: How hard on an engine is hitting the rev limiter

Post by Truckedup » Tue Jun 19, 2018 8:38 pm

Some bike riders like to bounce the engine off the rpm limiter lot while doing stupid burnouts or drifting....Many have a two stage limiter, a soft and hard limit. Most of the bike limiters sound like spark plugs misfiring
Motorcycle land speed racing... wearing animal hides and clinging to vibrating oily machines propelled by fire

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Re: How hard on an engine is hitting the rev limiter

Post by pamotorman » Tue Jun 19, 2018 8:53 pm

don't modern FI engines cut off the fuel as a rev limiter ???

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Re: How hard on an engine is hitting the rev limiter

Post by In-Tech » Tue Jun 19, 2018 9:18 pm

pamotorman wrote:
Tue Jun 19, 2018 8:53 pm
don't modern FI engines cut off the fuel as a rev limiter ???
The newer GM stuff can do throttle(DBW) or spark or fuel,(any choice or all of this) depending on bit settings in a flag area of the code. They all work well, sequential fuel if tuned correctly, in my mind, is the least offensive.

I'm curious if Clint has any logs he could share of different rev limiters in action.

In all the GM stuff I have logged so I could set the hysteresis, again, sequential fuel cut with a good hysteresis vs. RPM is the key to making it less violent. Without all the great equipment that Clint(TFX) has, my monitor is also visual if you watch the serpentine belt. The smoother the belt acts the better everything is.

If you don't trust your knock acquisition, watch the belt. :mrgreen:
Heat is energy, energy is horsepower...but you gotta control the heat.
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Re: How hard on an engine is hitting the rev limiter

Post by ijames » Tue Jun 19, 2018 9:33 pm

The one circumstance where fuel cut is dangerous is with an external alcohol injection system. Many years ago when alcohol injection started taking off in the the turbo Regal world there was an epidemic of blown head gaskets as people came out of the water box. They would hit the rev limiter in the water box doing their burnout, the stock ecm would cut fuel but they were making enough boost to trigger the alcohol injection and it would inject enough fuel to keep the engine running but way, way lean. Too long and pre-ignition and/or detonation would set in and destruction soon followed. It seemed to happen about as the driver would lift and roll out of the water so a lot of guys thought it was the sudden jump as the tires bit, but it was soon sorted out and the chipmakers all learned to remove the stock rpm limiter in their alcohol chips.
Carl Ijames, chemist not engine builder
carl ddott ijames aatt verizon ddott net

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Re: How hard on an engine is hitting the rev limiter

Post by Circlotron » Tue Jun 19, 2018 10:00 pm

The Australian Holden VN Commodore was initially fitted with the Buick 3.8 litre 90 degree V6. Toward the end of their life they were often strongly associated with the bogan/redneck (insert appropriate local word) crowd. The sound of the fuel cutoff rev limiter that spent so much time working when in the hands of these social trendsetter gave rise to VNs and similar being colloquially called mang-mangs. Not hard to see why. https://m.youtube.com/watch?v=l5dKcrTvJ6I

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Re: How hard on an engine is hitting the rev limiter

Post by KnightEngines » Tue Jun 19, 2018 11:58 pm

Get it right man, it's Moo Mang, not Mang Mang!

The local burnout boys found their valve trains lasted much longer if they just wound the limiter up out the way - excessive rpm was less harmfull than smacking the limiter hard & often.

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Re: How hard on an engine is hitting the rev limiter

Post by shoedoos » Wed Jun 20, 2018 12:45 am

any limiters out there that retard ignition instead of dumping cylinders? Didn't the 7531 from MSD do that?

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Re: How hard on an engine is hitting the rev limiter

Post by emsvitil » Wed Jun 20, 2018 8:14 am

shoedoos wrote:
Wed Jun 20, 2018 12:45 am
any limiters out there that retard ignition instead of dumping cylinders? Didn't the 7531 from MSD do that?

My stock Harley ignition does that. Smooth, but massive loss of power
Ed

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Re: How hard on an engine is hitting the rev limiter

Post by 77cruiser » Wed Jun 20, 2018 8:59 am

How does Pro Stock do it now with fuel injection? They used to sit on the limiter for several seconds sometimes.
Jim

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