Why do rev limiters "bounce"? - LS1TECH



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Why do rev limiters "bounce"?

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Old 03-04-2011, 05:05 AM   #1
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Default Why do rev limiters "bounce"?

I was just thinkin about this today. Why exactly do rev limiters bounce off? With technology now, I figured there'd be a way to hold the RPM at its max at a steady RPM versus bouncing back and forth fast as hell? Is there any science to requiring it to bounce?
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Old 03-04-2011, 06:40 AM   #2
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I may be wrong but owning hptuners, I have noticed two parameters that might cause this. One is the fuel cut-off, (Extreme cut-off) and another is resume (Extreme resume). Lets say the rev limiter is set at 7k rpms. The resume may be set at lets say 6800 or 6900 rpms. Ones it hits that, it sends fuel again, causing it to bounce back up to 7k. My guess is it helps keeping the engine from over-reving
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Old 03-04-2011, 08:56 AM   #3
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why would you want your motor sitting there at the rev limiter anyways?
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Old 03-04-2011, 09:20 AM   #4
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Because it was tuned by Zapp & Roger
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Old 03-04-2011, 09:24 AM   #5
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Yeah what black devil said...a rev limiter has a hard limit for engaging and disengaging. So if you keep your foot down on the go pedal then the engine will rev to it's limiter and(depending on the tune) it will get fuel and spark cut at which point it will lose power and start losing revolutions. As soon as the revolutions go down far enough (and you still have your foot planted) the fuel and spark come back on and once again the engine will rev.

If the enable and disable are within a few hundred RPM of eachother then the engine will bounce between them quickly.
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Old 03-04-2011, 11:42 AM   #6
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Quote:
Originally Posted by 96RamAirTA View Post
why would you want your motor sitting there at the rev limiter anyways?

.... Theoretically, cmon work with me here..
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Old 03-04-2011, 12:22 PM   #7
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Why cut the fuel, why not just hit a rpm and have it hold there instead of boucing?
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Old 03-04-2011, 01:06 PM   #8
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There has to be a rev limiter out there that is a constant... The NASCAR guy don't "bounce"
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Old 03-04-2011, 01:27 PM   #9
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Originally Posted by LoudmouthWS6 View Post
Why cut the fuel, why not just hit a rpm and have it hold there instead of boucing?
That's my point, why can't it be constant? IMO, it would be safer than bouncing it off a certain RPM and back repeatedly..
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Old 03-04-2011, 01:39 PM   #10
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Originally Posted by king.speed View Post
There has to be a rev limiter out there that is a constant... The NASCAR guy don't "bounce"
I think they have one, dont dont hit it much.

I found this

NASCAR limits engine speed by specifying the allowable transmission and final drive ratios for each track. The approach is not as hard and fast as, say, an electronic rev limiter, but it does keep engine speeds in the 9,300- to 9,600-rpm range.

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Old 03-04-2011, 01:42 PM   #11
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That's my point, why can't it be constant? IMO, it would be safer than bouncing it off a certain RPM and back repeatedly..
Would it? Or do you not really know and you are just guessing? Its amazing you think no automotive engineer has ever thought of this and furthermore, any company that produces and WARRANTIES said cars with "bouncing" rev limiters does not seem too concerned. Notice a pattern here?
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Old 03-04-2011, 01:57 PM   #12
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^^^ If he knew, he would not be asking. Im am sure people have thought about this way more in depth then I care to go, Think he is just wondering why it bouces, instead of being constant. We know how they work, just not sure the reasoning of the boucing.
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Old 03-04-2011, 01:59 PM   #13
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Quote:
Originally Posted by king.speed View Post
There has to be a rev limiter out there that is a constant... The NASCAR guy don't "bounce"
You don't see them bounce it because when they do they are done. Bouncing a limiter on a 9600 RPM solid flat tappet will not end well.
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Old 03-04-2011, 02:39 PM   #14
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Originally Posted by 01ssreda4 View Post
Would it? Or do you not really know and you are just guessing? Its amazing you think no automotive engineer has ever thought of this and furthermore, any company that produces and WARRANTIES said cars with "bouncing" rev limiters does not seem too concerned. Notice a pattern here?
That's why I said IMO.. Not everyone here is a freakin automotive engineer. Sure it's been done safely for years, but I don't get why... If you know so much, then explain why isn't there a steady rpm limit?
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Old 03-04-2011, 03:24 PM   #15
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There two things that pop into my head.

1st: People are stupid. So you have to make something somewhat idiot proof. If you where to have a constant rpm at red line how many people would sit there and wonder why there engine wont rev over 6500rpm and just sit there? So you have to make it somewhat noticeable that this is the MAX rpm and bad **** will happen if you keep it here for long. Bouncing off the rev limiter scares most normal people.

2nd: How much more time and money would they have to spend on making the RPM constant when at the rev limiter? It is easier cheaper to just cut the fuel and or spark. IE: On-Off-On vs at said RPM dial injectors to said amount at said load, check o2 etc. . . Remember cheaper is better, they are in it for the money.

That is all I can think of for now.
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Old 03-04-2011, 04:08 PM   #16
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The question is mute...

Why would you sit on the limiter even if you could? You are no longer able to increase speed when the rpms are maxed, so sitting on the limiter is pointless. Next time your driving put the car in any gear and leave it. Try going faster while leaving the rpms constant... you cant. (and im not talking about a stall either... im talking beyond that). So basically in first you would go 0 - lets say 40mph @ 6k rpms... There is no benefit to stay at 6k rpms as your just going to stay at 40mph... so whats the point? Youd rather be stuck at 40mph @ 6k rpms versus 2k rpms in a higher gear?


I honestly believe it bounces to tell the driver, "hey stupid, time to shift!" lol (like max said) .... They have the technology to make it constant. Look at the launch controls (M5 for example, or the GTR)... they are able to leave it at a constant rpm. So they do have the technology... they just need a way to wake up the driver if they arent paying attention.

Last edited by xxrillixx; 03-04-2011 at 04:13 PM.
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Old 03-04-2011, 04:25 PM   #17
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I had a wake up call with the limiter once lol I was passing a semi and I thought I was in 3rd or 2nd. I'm coming around the semi, felt very torquey then I noticed I wasnt passing so fast, so I gave it more throttle and bam-bam-bam-the limiter woke me RIGHT UP pretty quick! Had to hurry and shift to actually pass this thing.

/back to thread topic
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Old 03-04-2011, 05:24 PM   #18
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Most normal people would not sit at 6krpm while driving. That is not what I meant, but it reads that way. I’m talking more about the people who do hotrod their cars. They are accelerating and then all of a sudden it just stops at said rpm. People might think hey there is something wrong.

Also true story: My brother in laws sister was driving on the highway in the rain. It does not rain here much (AZ). Well she was worried about losing control so she put her SUV in 4-LO. Got back onto the highway and drive it 50 miles home at just under the revlimiter. Trust me when I say there are some stupid people out there. Yes her vehicle was messed up when she got home, badly.
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Old 03-04-2011, 05:36 PM   #19
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The reason I really asked this question. I watched a RX7 LS1 swap drift video, and just around the corners all you heard was NA NA NA NA NA NA NA NA of the damn limiter.. I wonder if it would just be better to be steady for this instance
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Old 03-04-2011, 05:45 PM   #20
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Think of it as an audible tach...
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