2018 SLT 6.2 4x4 91 or 93? Tune/ mod options

[tray3185]

I recently bought this truck back in April and recently bought an AFM disabler (OBD port) which works amazing driving in V8 all the time. Curious to know if there even is a point of putting 93 in over 91. I’ve been doing both since not all gas stations have 93 but if it’s available I’ll always put 93. So far, can’t tell a difference in MPG. I still at least want to know if I should still stick to 94 no matter what. 
 

As far as tuning. Would it be pointless in buying one since it’s already at 93? Or should I still get a tuner to wake up the engine and add HP/TQ IF IT WILL DO THAT. 

[M1ck3y]

I can't speak for everyone but my truck always runs better on 93; on 91 I get pinging. But I've been told cdn fuel isn't as good as fuel south of the border.

 

As far as tuning goes, it should add 30ish horsepower. My butt dyno couldn't really tell a difference though.

Edited May 26, 2025 by M1ck3y

[CamGTP]

I don't know about 30hp, seems a bit high for real world gains. If a tune did that, people wouldn't swap camshafts to gain 60-70hp for 5x the cost.

 

GM did rate the 5.3 at like 30hp higher with E85 though, a much different fuel that allows for more timing and leaner air fuel mixtures than regular premium gasoline.

 

I notice zero difference in fuel mileage between 87 octane and 91+ octane, that's not what the fuel is going to do but okay. I still got 24mpg on junk 87 octane on my last trip (60+ miles) with my truck doing 65-70mph, so to me it doesn't matter if you run 91 or 93 octane. Without data logs it's hard to say if either fuel is better to see spark knock and ignition timing numbers.

[M1ck3y]

12 hours ago, CamGTP said:

I don't know about 30hp, seems a bit high for real world gains. If a tune did that, people wouldn't swap camshafts to gain 60-70hp for 5x the cost.

 

GM did rate the 5.3 at like 30hp higher with E85 though, a much different fuel that allows for more timing and leaner air fuel mixtures than regular premium gasoline.

 

I notice zero difference in fuel mileage between 87 octane and 91+ octane, that's not what the fuel is going to do but okay. I still got 24mpg on junk 87 octane on my last trip (60+ miles) with my truck doing 65-70mph, so to me it doesn't matter if you run 91 or 93 octane. Without data logs it's hard to say if either fuel is better to see spark knock and ignition timing numbers.

Just quoting black bear. That would be at the crank not whp.