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-   -   14' launch control, why so low rpm? (http://www.jeepgarage.org/f161/14-launch-control-why-so-low-rpm-58828.html)

speed_racer 04-21-2013 11:53 PM

14' launch control, why so low rpm?
 
hi,
I'm just curious about the launch control, why is it such a low rpm? If you look at GTR's or BMW's etc.. the launch control is at something like 4k or higher.. With the LSD and AWD system in the SRT, I would of thought you would get a heaps better take off in a higher rev range?

Of course its combined with some tyre smoke and rocket style G force into the back of your seat. ;)

JoeD 04-29-2013 09:19 PM

Re: 14' launch control, why so low rpm?
 
I would asume it was plenty of trial and error to get the best times but some caution built in to increase the lifespan of the drivetrain.

Srt8_hmi 04-29-2013 10:16 PM

Re: 14' launch control, why so low rpm?
 
The 6.4 makes plenty of torque and doesn't need to be screaming to launch. Im sure the SRT crew knows the sweet spot.

reevlak 04-30-2013 11:39 AM

Re: 14' launch control, why so low rpm?
 
because the large majority of cars using launch control are Forced induction (mostly twin turbo) therefore to overcome turbo lag in the low RPM range they need to launch for higher up the range. Also with the amount of torque and the huge mass of the Jeep launching at anything higher will significantly decrease the life of the transmission.

Jeep_addicted 05-02-2013 09:26 AM

Re: 14' launch control, why so low rpm?
 
My guess is the transmission is the reason.

Most of the other cars you used as an example have gearboxes that have actual clutches where as the SRT tranny is full auto planetary gear style and does not have a high rpm stall type torque convertor some some race cars that run a slush box.

This is just a guess but probably why it is like that.

2005JGC 05-03-2013 03:31 PM

Re: 14' launch control, why so low rpm?
 
Its 1 word, this one word has been known to be non existent in the import world since the dawn of imports, its what separates the men from the boys (or the men from the men with a lot of extra scratch to blow on a lesser product). This word I speak of is called TORQUE. 6.4l V8 has WAY more torque which is usable power below 5252 rpms, with this power down lower, naturally it needs less RPM to perform a perfect launch. Now the imports that rev to 8k rpm dont hit their max torque till after 5252 rpms which means to get the power to the wheels the rpms have to be higher.

This 5252 number is the magic number that dictates if the car has more torque than horsepower or visa-versa.

Even then with the gtr if you use this launch control your kissing your warranty good by on a 20k dollar transmission, so YES, a lot probably has to do with drivetrain longevity, taking the option and the argument for warranty repairs more out of the customers hands by being a little more gentle.

JoeD 05-09-2013 08:45 PM

Re: 14' launch control, why so low rpm?
 
Quote:

Originally Posted by 2005JGC (Post 816656)
Its 1 word, this one word has been known to be non existent in the import world since the dawn of imports, its what separates the men from the boys (or the men from the men with a lot of extra scratch to blow on a lesser product). This word I speak of is called TORQUE. 6.4l V8 has WAY more torque which is usable power below 5252 rpms, with this power down lower, naturally it needs less RPM to perform a perfect launch. Now the imports that rev to 8k rpm dont hit their max torque till after 5252 rpms which means to get the power to the wheels the rpms have to be higher.

This 5252 number is the magic number that dictates if the car has more torque than horsepower or visa-versa.

Even then with the gtr if you use this launch control your kissing your warranty good by on a 20k dollar transmission, so YES, a lot probably has to do with drivetrain longevity, taking the option and the argument for warranty repairs more out of the customers hands by being a little more gentle.

5252 is just a number used to calculate HP. HP = Displacement, bore and stroke and cam profile dictate what rpm your peak TQ will come in at.
This is a quote I found online that sums this up,
"An engine that is tuned to have peak HP below 5252 rpm will always have more TQ than HP, engines with peak HP above 5252 rpm will always have more HP than TQ

2005JGC 05-10-2013 12:14 AM

Re: 14' launch control, why so low rpm?
 
How is that different from what I said? Not sure I am following.

JoeD 05-10-2013 09:22 AM

Re: 14' launch control, why so low rpm?
 
Quote:

Originally Posted by 2005JGC (Post 820636)
How is that different from what I said? Not sure I am following.

I was lost when you said,
"This 5252 number is the magic number that dictates if the car has more torque than horsepower or visa-versa. "
Most won't know what the 5252 rpm refers to.

2005JGC 05-11-2013 11:28 AM

Got ya.

Sent from my SCH-I500

HammerTm2 05-14-2013 09:54 PM

Pretty sure the low launch RPM @11-1200 is to advance the ignition timing.

2005JGC 05-18-2013 11:23 PM

Re: 14' launch control, why so low rpm?
 
Ignition timing can be adjusted at ANY rpm, not sure I follow the logic.


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