I've asked this question in another thread and it wasn't really answered so I'll start a dedicated thread. From the factory, the fuel and/or spark cutoff is programmed for 6850 rpm on the Coyote. I've read where several people who got a custom tune reprogrammed the cutoff for 7100 or 7200 rpm. How did you choose where to set it? If the engine can safely have a redline of 7200 rpm, why did Ford program it for 6850? Are they just being overprotective? Or do some people race their cars, and figure that the engine will need an overhaul eventually anyway? I'd really appreciate some education on this topic.

 

i too, would like to know, wonder why no responses.

 

It's a little bit of both.
Redlines are set based on the power the engine makes too.
No really reason to raise redline on a car if it's dropping in power several hundred rpms before that.
But as you stated, it's also engine longevity. The higher the revs the more stress on the pistons, rods, valves, fuel injectors/pumps, etc. in the way of heat and other factors.
It also requires more air and more fuel.

Higher revving engines high end power also affects it's lower end torque.
Engines that make a lot of power in really high revs make less power down low.
The 5.0 and the Mustang GT is known for low end power too. Putting an engine like the M3's into it would change the character of the car.

So I'm sure the Ford engineers wanted an engine that revved sufficiently to make very good higher (above 6000 rpms) power, but still have the low rpm torque (390 lbs ft of torque from a NA V8 of only 5 liters is VERY impressive.

As you surely know, they changed to forged rods and pistons in the Boss 302 which safely allowed the engine to rev 500 rpms higher and make 440 hp instead of 412 (or really 416) but it was at the cost of 10 lbs feet of torque down low.

So in summary, I'd say they set the 6850 redline and 7000 rpm fuel cut off MOSTLY due to warranty and longevity of the engine, but also because after that the stock engine is just losing power anyway, so no real reason to go higher.
I'm no engine engineer, but like most anything made these days that has a "limit" put on it, it's often set below what they can really safely take for warranty and legal reasons as well.

I personally think raising the rev limiter by 200 rpms on a tuned car with an intake is perfectly fine.
The intake is giving the car the extra air it needs and the tune is giving it the proper Air/Fuel ratio it needs. As long as you put in the proper octane gas that extra 200 rpms should be no sweat what-so-ever on the 5.0

 

Thanks, Driver72. Here's another idea, just a theory out of thin air. Might it be that Ford set the redline at 6850, knowing that the engine can safely run at that speed for an extended time? Maybe the engine can safely rev to 7200 rpm, as long as you are simply revving it up and shifting and not keeping it there for minutes at a time, but Ford wanted to be cautious in case some idiots do run their engines just short of redline for extended periods? I'd love to hear from an engineer or engine builder. Several people on this forum have installed custom tunes so I would think there would be more contributions to this thread.

 

Actually you are not far off on this assumption. Except where you mention "minutes" duration at that RPM... It's more like hours. If you want an idea of what engine durability cycling looks like, check out the video on the Ford website talking about the "torture test" of the new Ecoboost F150. That is not a specific test for that engine, its the same program that is used for all new engines.