Hi guys,

Question for those that are running 5 star perf/tow tunes. I have been running the 87 perf/tow tune for about a month now and love it. I recently changed it back to stock to take it into the dealer for oil change, tire rotation etc. That is when I really realized what a difference the tune makes. The truck felt like a slug when returned to stock so I couldnt wait to get the tune back on it. I filled the tank with 91 octane and threw on the 91 perf/tow tune. I really couldnt feel a difference at all between 87 and 91 tune....I thought this is weird. The 91 tune definitly felt better than stock, just not a huge jump from 87. So my question is for those running similar tunes...what kind of differences did you notice between an 87 and 91 tune? Or are my expectations too big on this change? I should mention too that I was almost bone dry on gas, so my 91 octane isnt mixed with very much 87 at all.

 

Interesting. My 5star 91 tune is significantly more powerful than the 87 tune. Maybe your 87 tune is better than mine though? We'll never know. My latest VMP 91 tune is really good too, much better than the 87 5star, but not so sure it's as good as the 5star 91.

Have Mike take a look at the 91 tune he sent you and see if he can sharpen it up for you.

 

Thanks Cheef for the input. Reading all the reviews I was expecting my 91 to be much better than 87. I have a message into Mike at 5Star.

Anyone else go from 87 to 91 tune and notice a difference?

 

I went from 87 to the 93 from Mike and it is defintly more snappy. At around 3K it is pulling hard. Far more than the 87 tune from Mike. Stock air box and a Wix drop in filter as well.

 

Some things came to mind...what time of year did you run the 87 vs 91? I know little about california weather other than it's warm most of the year. Was it drastically more humid when trying the 91? We had some crazy humidity in SW Ontario the past couple of months (off and on) and those really humid days I'd swear someone lopped off 4 cylinders. In the morning's when it's cooler and less humid the truck runs like a champ.

I doubt you have to deal with winter gas though, which is a bonus.

What about your ethanol content? I think the custom tuners will tune for specific ethanol content, was this mentioned to Mike? Maybe your 91 has a higher/lower ethanol content than the 87...just a thought.

FWIW my truck is stock, no washooooobis here! I have a 22" maggie on stock piping which doesn't make any difference flow wise.

 

I don't know if this holds true for anyone else, but besides the power from a 93 tune, (which is what I have) to an 87 tune, I get significantly better mileage with the 93 than the 87. When I (try) to run the 87 tune I lose about 3 miles to the gallon, that's 100 miles a tankful. Though I figure that to be the difference in octane and maybe a cleaner fuel and depending on what anyone else gets, maybe the setup from one truck to the next. Anyone else seeing better fuel gains like that?

 

About the same for me. On the interstate I pick up 2 -3 MPG. In town it is about the same as the 87 tune. Still better than stock by a long shot performance wise. In town I average around 13.5 - 14. With a 5500 lb truck, I am happy with that.

 

Mitch, I'm going to comment on one thing you said here, because many people don't really understand what high octane fuel is all about.

First, it is not "cleaner", it just contains additives that make it more difficult to ignite and that cause it to burn slower. That's really all it is.

Those two properties are needed if you have an engine that has a higher compression ratio than our trucks. 87 octane would pre-ignite (detonate/ping) badly in a high compression engine. But, since the flame advance is slower with high-octane, you can set the timing ahead a bit when using it in our trucks and you get a slightly more efficient power stroke as a result. This generally gives you better gas mileage. But, it is not "better" for the engine.

High octane gas CAN cause starting problems in the winter if you live in a very cold climate.

Now, different suppliers CAN and DO distribute "cleaner" gas. And some include additives that help keep the fuel delivery system and other areas clean. I won't try to tell you who's the "best", because I simply don't know. There are plenty of people on this forum who have opinions though and you could find those opinions with a search.

- Jack

 

Not exactly, Jack. High octane fuel is refined to a higher octane, it's not the additives that make it higher octane. The additives that are used are for other purposes, and generally the higher octane fuels have a higher concentration of them. Example - Chevron puts Techron in all their fuel, but the high octane has more of it. So - indirectly, high octane can burn cleaner.

In the old days, tetraethyl lead was used to raise octane. The only "additive" used today that raises octane is ethanol - 10% raises it about 2 points.

 

Interesting info guys. Not to get too side tracked but...GLC would E85 then equal an equivalent of say 16pts of octane? What is the starting point, 87? So E85 is recognized by our motors as 87+16= 103 octane? A custom tune in that scenario would be quite entertaining!

To the other fellers - I get some real nice HWY mpg on 91, definitely worth the extra cost because the extra mpg makes the cost a wash and you get the added performance on top of that.

My latest 91 octane VMP tune is netting some pretty sweet HWY mpg. 2.5 hr trip two nights ago netted me 21+ US MPG doing about 110km/h. Fairly flat hwy, unloaded, minimal cross wind, minimal traffic.

 

Here in north Alabama it is anything but flat. In the rolling hills sort of places I have had the lie-o-meter give me a 21.2. I hand calculated it to 19.9. Again with a 5500 lb. slug w/ 3.55's I am happy with that.

 

I'm assuming my ultragauge is still lying to me since it's running off the ford computer. I have not hand calculated in a while but comparing tuned vs stock this 91 tune is getting 3mpg better.

Happy camper all things considered 5.turd and 3.55s!

I did however guzzle my buddies 2011 scab gmc 5.3 (untuned) in a 0-50 mph jaunt, and I gave him a truck length head start LOL!

 

Here's a good source for information on octane ratings and what to expect if you use high octane gas in your vehicle: http://www.ftc.gov/bcp/edu/pubs/cons...tos/aut12.shtm

I think it might be more correct to say that high octane gas is "formulated" to have the higher knock resistance. If 87 octane gas is a mixture of 87% octane and 13% heptane, then you could simply increase the ratio of octane to get the higher octane number. But, I agree, my use of the term "additive" to achieve the higher octane rating is not accurate. This source: http://mn.gov/commerce/weights-and-m...ctaneFacts.pdf states that high octane gas goes through additional refining steps (that increase the price). I stand corrected, glc, it is "refined" to the higher rating, as you said.

I stand by what I said about high octane gas not being "cleaner" though. Virtually EVERY source I find says it is not cleaner.

- Jack

 

The octane rating of E85 depends on what octane the gas is that's used to blend with it and several other factors. Tests show that E85 really has an equivalent octane of about 96 in spite of the theoretical figure of around 105.

 

As well as having a lower energy content (than non-alcoholic gasoline).

Alcohol also has an affinity for water. This has been brought up now and then as a possible problem, but so far, it seems ok. Still, I'd be nervous (possibly without good reason) about using E85 in a humid climate. I suppose it COULD act a bit like the "dri-gas" additive.

- Jack