Questions about octane and canned tunes

[Jackpine]

Originally Posted by Longshot270

I'm pretty sure that the truck's MAF sensor is able to adjust for the altitude since its primary job is to measure the volume of air that enters the engine. I know that old vehicles and the diesels sometimes have a problem with it since they dont have MAF sensors or any way to correct automatically. I do know that Bill makes adjustments to the WOT fuel based on altitude because during WOT the truck fuels based on that number instead of the sensors.

Usually 5000 ft is the limit of low to high altitude tuning. Since you hover there all the time your truck (most of the time) experiences changes of about 3000 ft. The altitude section on the order form just helps give a ball park of where to set it.

I'll see if I can get Cody to comment, he actually knows what he's talking about.

Maybe I do too!

Since your vehicle is fuel injected and computer controlled, the PCM is able to adjust the fuel input during closed loop operation based on what it's getting from the O2 sensors. In the past, with a carburetor, you had to use high altitude jets (less fuel) to prevent running rich. In Open loop (such as at WOT), Bill would adjust the extra fuel added according to the altitude you normally drive at. But, as Longshot says, the difference between Sea Level and 5,000 feet is relatively minor.

You of course lose power at altitude, because you are bringing in less oxygen and fuel AND, because your actual compression is reduced. (This is kind of misleading - if your engine compression is say, 9.8:1, that ratio doesn't change. But the effective pressure inside the cylinders is less due to the less dense air that was taken in. This makes it possible to burn fuel with a lower octane rating, since the lower pressure makes it less likely you'll get pre-ignition. It's common to see "regular grade" fuel at 85 octane above 5,000 feet.

Hope this all makes sense.

- Jack

[Skip_1074]

I was trying to come up with a creative way to tell everyone that my CTS is here, well at least I have a UPS slip (this is where the creative story was coming from as it was dated yesterday and my wife failed to tell me) to pick something up from the apartment managers office and the only thing I am expecting is my CTS. Off to get it, then update with Fusion just to be sure and installation. Wish me luck...I'm thinking getting at least my 87 Performance ordered by the weekend, but we will see.

[Skip_1074]

So I installed my CTS Thursday without issue. I have somewhere around 200 miles on it now running the canned 87 Tow tune. I just placed my order for my 87 Performance tune. I do realize that it is not even 0300 where I live, but I'm working nights. I provided all the information about elevations and what not in the order and I'll let the brighter minds that write the stuff sort it out for me. Thank you all for the input.

I've said it elsewhere on this forum, but of the forums I have been a member of, this place has more brains that understand the dynamics of making power the any other site I have been on. Please keep the information coming so I may become portionally knowledgeable about this as well...at least beyond the simple air in, plus fuel in, plus fire equals exhaust and a smile.

[88Racing]

Originally Posted by Skip_1074

So I installed my CTS Thursday without issue. I have somewhere around 200 miles on it now running the canned 87 Tow tune. I just placed my order for my 87 Performance tune. I do realize that it is not even 0300 where I live, but I'm working nights. I provided all the information about elevations and what not in the order and I'll let the brighter minds that write the stuff sort it out for me. Thank you all for the input.

I've said it elsewhere on this forum, but of the forums I have been a member of, this place has more brains that understand the dynamics of making power the any other site I have been on. Please keep the information coming so I may become portionally knowledgeable about this as well...at least beyond the simple air in, plus fuel in, plus fire equals exhaust and a smile.

That's great!