87 vs 91 vs 93 Tune on LM7 5.3 w/ Mild Cam?
 

I have an early ('00) LM7 5.3 with a newly installed BTR Truck Torque cam, TBSS intake manifold, shorty headers (factory exhaust) and electric fans. I did these mild mods to gain additional power/torque when towing since this is an early, lower power 5.3. No more mods are planned. Tuners in my area are pushing me hard for a 93 tune but it's $0.85 more per gallon. 91 is $0.50 more per gallon.

Would an 87 or 91 tune net me enough gains to make my mods worthwhile? Would a 93 tune gain me better fuel economy along with more power/torque that would even out the added cost?

You spend all that money on mods to neuter it with regular gas? C'mon man.

It's going to cost you how much more per fill up? $15-$18?

We don't mod vehicles to save money.

cheap insurance running higher octane

You also blew some money on shorty headers and a TBSS intake on a 5.3, wouldn't say those are the greatest mods.

Personally I would consider 91 over 93 though. ONLY BECAUSE there are places in the US that don't have 93 gas and I am sure they have people modding cars and running 91 lol

I got a great deal on the parts but because you asked, $0.85 x 32.5 gal tank = an additional $27.63 per tank which is very significant.

You didn't even answer my original question :offtopic:

The headers and intake were very inexpensive and a fun project for me so it is what it is. Dumping on my mods when they're already done isn't helpful. :shrug:

In Virginia, where I am currently located, 91 is actually harder to find than 93. It's mostly 87, 89, and 93 here but Sunoco carries 91 so I can get it.

Nevertheless, I would still like someone with tuning experience considering these variables to chime in.

The 99-02 PCMs you can run a switch and be able to run 87 or 93 octane.
You could always get it tuned for 87 octane and get a feel for how it runs. Then later get it tuned for 93 octane.

My 2500HD i can get more timing with 93 octane but you cant tell a difference towing.

Oh wow, this is super interesting. Do you know of a write-up on installing a switch? Is this basically two separate tunes installed on the same PCM? Something else?

Only EFI Live does this.
Its a 2 wire setup and simple to do. It only works on the 512kb PCMs tho with COS5.


(J2,pin56)

Maybe if you ask your question a 3rd time someone will give you the answer you want.

https://www.performancetrucks.net/fo...-559977/page2/

yep. I was getting that vibe. I knew I been there before. 🤦🏻‍♂️

Run 89 octane, better than 87 and gives you some wiggle room.

All those tooners that say it's a 91 or 93 octane tune just lean it out more and slap more timing in it. It's pretty stupid if you ask me. Run it at 12.3-12.5 AFR and 20-24 degrees of timing. Who gives a flying F about the 10-15hp you miss out on when it's run at 12.8 AFR and 28 degrees of timing when you're doing regular driving for 99% of your day.

This is helpful advice, thank you. I've been trying to get a dyno tune in VA and the tuners have been sorta a-holes via email honestly. One even told me it was 93 or he's not gonna do the tune. Another told me, weeks after I was very specific on what I wanted, that he only does sport truck tunes, nothing for towing. 🤷

Mail Order Tuner is the way to go!! You’ll have to have the HP Tuner program and they can dial it in!! They did mine and I will never use anyone else! Tons of choices out there GOOD LUCK, hope it all works out for you.

For the most part with many places that do lots of vehicles they basically just have a cookie cutter file that they can start with. That file is likely not to change much unless the vehicle really requires it and if the tuner actually cares enough to spend time with it. Obviously not all places are like this but I hear about it often enough.

To me when someone says it's gotta be a 93 octane tune or nothing means they don't care enough. They just want to slap in a tune with lots of timing with a leaner air fuel ratio and if the engine doesn't show knock, they send it on it's way. High octane fuel lets them get away with it at that point in time in a very specific situation on a dyno. Time is money to most shops and if they can get you in and out in less than 2 hours, they will just keep earning money faster.

Running a lower octane fuel like 89 octane with a cammed engine is totally possible without sacrificing a lot, it can just take a little bit of time of real world tuning to dial it in.