87oct 89oct or 91oct??

[Nothinbutv8power]

For a 4.8 in an 07 clssic sierra anyone notice a difference in power by switching fuel oct.?

[ervguy]

I do, seems to run smoother on 91 than 87 or 89.

[SilveradoLAX7]

I tried a tank of premium out of curiosity (and on the company's dime), I didn't notice a big difference. Certainly nothing I'd spend my own $ on.

 

-Jay

[dewfpo]

I've always heard that you need to run several (~5) tanks of a certain octane fuel before you really notice any difference. Yiu;ll never see a difference in just one tank.

 

DEWFPO

[C & A s Dad]

93 Octane only for me. Defpo is correct, it takes a few tanks for the ECM to take advantage of the increased octane. I have read many posts concerning this and there are opinions all over the board. I truly feel the 93 has helped me when towing and I know it has slightly increased my MPG. (Increased it by .5 MPG). I had an avg on 6 tanks with 87 oct and now have several fill ups on the 93.

 

Get a good average on your MPG and then run 3 to 4 tanks of premium.

 

BTW I tried the same thing in my work van, a 05 Dodge Caravan and I had no mileage increase at all. The little 3.3 is a low compression engine and does not need any more octaned.

 

Search this and you will find several posts.

[RyanZ71]

85 octane up here in Colorado (Denver is 5280 feet) anything higher is just pointless

[Steves95Sierra]

My '95 305 (when running right ) knocks on 85-87 octane -- or on anything that comes out of an Exxon/Mobile pump (yeah - companies do seem to make a difference -- in my truck's case anyway)...

[cmoore74]

Got about 1/2 to 1 MPG increase when I switched from 87 to 93 octane on my 5.3L. This is averaged over many tankfulls of fuel. It does take a few tank fulls for the computer to re-learn for the increased octane. The MPG benefit is almost a wash on the increased cost of premium so I stick with the premium.

 

For me I look purely at the compression ratio of the engine and if it indicates a higher octane fuel required to prevent pre-ignition. On the 5.3L the compression ratio is 9.5:1 and based just on that would indicate 91 or better octane.

 

The engine will run on 87, but the timing is being retarded to prevent pre-ignition based on input from the knock sensor. The adjustment of the timing will cause the engine to not operate as efficiently. Some also say there is added wear-and-tear for retarding the timing as well, but I don't know if it is significant.

 

I think the 4.8L has a lower compression ratio than the 5.3L so you might not see as much of a benefit.

 

Try it and let us know if you observe a difference.

[Giant]

My caddy needed Premium because of a high preformance Aluminum V8 I had in it. Now, with the knock sensors, technically you can run 87 as it will just retard the spark timing. This, however, gives less HP and hurts preformance, that can hurt MPG etc....

 

Now with engines that are made to run regular. Some companies will put more degertent in a higher octane and charge more for it, so I'm not against an occasional tank to keep things clean (once a month maybe).

 

Yet the point of a higher octane is that the fuel contains longer carbon chains (octanes) and requires more presure and heat before spontaniously combusting (what happens on the compression stroke of a high compression engine that causes pinging with normal fuel). So when a vehicle that nomally uses 87 starts to ping on 87 it is usually a symptom of bad carbon build up causing a rise in the compression ratio of the cylinder pinging.

 

So, under normal driving conditions you do NOT need a higher octane fuel for a lower octane engine. If, however, you find yourself getting better preformance our of 93 then 87 on a regular engine, you are probably in need of a tune-up.

 

just my $0.02

thanks

-Robert-

[C & A s Dad]

Robert, would you not agree that the same Knock Sensors that retard the timing in your Caddy do the same in the truck engine. The 5.3L with 9.5 to 1 compression would obviously ping on 87 if not for the Knock Sensors.

 

My contention is the 93 octane will allow the timing to be increased and in turn will allow the engine to provide more power.

[Giant]

Abolutely.. if the only thing that is keeping an engine from pinging on 87 is aretarded spark timing caused by the knock sensor then the engine is NOT run as effiently as it can be.