How to Up the rev limiter?

[Jarvis_Pants]

Im looking at a performance cam and was wondering what the easyist way to up the redline or remove it intirely.

Thanks in advance.

Jarvis

 

[JohnX]

Be careful with that. There are harmonics in the cam and crank that can cause seriuos damage at certain rpm's.

 

[Flash]

I would try and tune the cam into the RPM range that you have.
the 4.0 has inheritance Harmonics that prevent you form revving it much hire then stock.

With that said there are programmer that will allow you to raise the rpm limit.............Uni Chip come to mind, but i real don't know much about any of them.

Flash.

 

[Dr. Dyno]

I looked into the idea of raising the rev limiter last year but decided not to bother for three reasons:

1. The only way to do it is to either burn a new chip into the stock PCM or add a programmeable piggyback computer such as the Unichip. I didn't want to spend the $$$$ to do it.

2. Anything above 5500rpm would be suicide and even if you raise the limiter to 5500rpm, the performance advantage over the stock 5200rpm limiter is minimal.

3. The torque curve starts to drop off more quickly above 4500rpm and by 5200rpm the engine's already well past the peak HP point as well.

 

[BBeach]

I looked into the idea of raising the rev limiter last year but decided not to bother for three reasons:

2. Anything above 5500rpm would be suicide and even if you raise the limiter to 5500rpm, the performance advantage over the stock 5200rpm limiter is minimal.

3. The torque curve starts to drop off more quickly above 4500rpm and by 5200rpm the engine's already well past the peak HP point as well.

x2, Its no DOHC engine.

Look at any real dyno graph, I was disappointed to see mine crapping out before 5000rpm. Its a Jeep not a vette, although most of us wish otherwise. In most cases you'll be doing better by letting it shift around the stock upshift, I tried this before at a dragstrip with holding it in 2nd till 5200 or so rpm and the other time leaving it in drive. Leaving it in the 1-2 position (putting it in at 4500rpm or so so that the TC doesnt lock up as much for max accel) came out to be the same and slower than leaving it in good ole drive.

 

[gradon]

The Hypertech 50012 programmer will let you increase the revs in 100rpm increments, up to an additional 500rpm, and bump up the speed governor to 128mph in addition to the mild performance reprogram for 87 or 93 oct. It's also a code reader.

 

[streetpirate]

convert to megasquirt and find a gear drive, usually forged from pure unobtanium and commonly found on orbiting space rocks

 

[MudDawg]

convert to megasquirt and find a gear drive, usually forged from pure unobtanium and commonly found on orbiting space rocks

It would need to be unrealmium to stay together...the torsional harmonic will break the crank at the number five rod journal....and that doesnt include the cam harmonic that breaks chains...

Build your motor where it makes power below 5250 unless you like blowing stuff up...or trade in the 4.0 for a 2.5....no rpm limits beyond how good the parts are...:wow: Nahhh I love my lil ole 2.5....but it's no 4.0 untill i bottle feed itarty:

 

[streetpirate]

hmm, i thought the crank harmonic was up around like 6800?

 

[OCMI_Teddy]

the cam is around 5800 rpm

 

[JJacobs]

I keep hearing about all these harmonic issues. Who's got pics of busted parts caused by overrevving?

 

[gradon]

I just want to hear from someone that has raised their rev limiter.

 

[CommandoXJ96]

I just want to hear from someone that has raised their rev limiter.

and im here for pictures of the carnage that ensued.

 

[Flash]

and im here for pictures of the carnage that ensued.

I beleve that it is true............but i would love to see some CARNAGE as well!!!!!arty:

Flash.

 

[XJLafonda]

I beleve that it is true............but i would love to see some CARNAGE as well!!!!!arty:

Flash.

You guys are SICK!

 

[Flash]

You guys are SICK!

:eyes: assgas: :explosion


Wahoooooo luck post # 777....time to hit Veges



Flash

 

[Dr. Dyno]

I keep hearing about all these harmonic issues. Who's got pics of busted parts caused by overrevving?

I'm sure Hesco have a few so you could ask them about the harmonic issues. Unless you've built your engine to breathe well at 5000+rpm, the only thing you'll achieve by raising the rev limiter and using the revs is a shorter engine life.

 

[JJacobs]

Maybe they do, I never called to ask. I doubt anyone else on here has either. Just seems like somebody mentioned harmonics at one point and now everybody's saying the same thing, because someone else said so too.

When I took an old 4.0 to 6400 the alternator bearings failed instantly. Dang harmonics!

 

[MudDawg]

Maybe they do, I never called to ask. I doubt anyone else on here has either. Just seems like somebody mentioned harmonics at one point and now everybody's saying the same thing, because someone else said so too.

When I took an old 4.0 to 6400 the alternator bearings failed instantly. Dang harmonics!

Short transients (blip the throttle hard) will not instantly grenade the motor...and the harmonics issue is not something that "somebody mentioned". The information comes form various correlating sources including the engine builder that built engines for Jeep's race program as well as being a major R&D developer for Chryco. The torsional harmonic will eventually break the #5 rod journal...appearantly it takes a bit of accumulated stress to kill it....the camchain harmonic is a bit less forgiving..

Why not build a motor and do a Mythbusters ....if the curiosity overcomes conventional wisdom....

 

[JJacobs]

I've got a motor slated to come out of my daily driver for replacement, Renix so no rev limiter. Maybe I'll just hammer down on it and see what happens- while driving, not just sitting. I'm not sure it's even capable of hitting 5K though, she's tired.