5.3 Compression and fuel

[Bowhunt24]

Hey all, I can't seem to reliably find the compression on my '14 5.3L. I'm trying to nail this down because I'm quite curious about the fuel debate. I know there are a lot of opinions out there regarding which octane you should use, if it's better for the engine, better for mileage, etc, etc. Well, opinions shouldn't matter here, right? Based on the compression of the motor we should be able to do some basic math and figure out if a higher octane is even being fully burned or not. 

 

Maybe I'm off here...but maybe I'm not! Weigh in!

 

-Evan

[m3n00b]

What do you mean by fully burned?

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[Bowhunt24]

34 minutes ago, m3n00b said:

What do you mean by fully burned?

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Maybe not the best word usage, but essentially, if you're engine compression is low enough, the extra cost of high octane fuel is absolutely worthless. IF the compression is high enough, the engines could actually take advantage of the higher octane. I can't seem to find what the compression is on my 5.3. 

[Bowhunt24]

Ah, I think I found it. 11:1. 

 

GM 5.3 Liter V8 EcoTec3 L83 Engine

The L83 V8 engine is produced by General Motors for use in pickup trucks and SUVs. It is part of GM’s Gen V Small Bock engine design that’s known in trucks as EcoTec3, replacing the Vortec line.

• Overview
• Specifications
• Vehicle Applications
• Pictures

Type:	5.3L V8
Displacement (cu in / cc):	325 / 5328
Bore & stroke (in / mm):	3.78 x 3.62 / 96 x 92
Block material:	cast aluminum
Cylinder head material:	cast aluminum
Valvetrain:	overhead valve, two valves per cylinder, variable valve timing
Ignition system:	coil near plug, platinum-tipped spark plugs, low-resistance spark plug wires
Fuel delivery:	direct fuel injection with Active Fuel Management
Compression ratio:	11.0:1
Horsepower (hp / kW @ rpm):	355 / 250 @ 5600 (gas – SAE certified)
	380 / 283 @ 5600 (E85 – SAE certified)
Torque (lb-ft / Nm @ rpm):	383 / 519 @ 4100 (gas – SAE certified)
	416 / 564 @ 4100 (E85 – SAE certified)
Recommended fuel:	regular unleaded or E85
Maximum engine speed (rpm):	5800
Emissions controls:	close-coupled catalytic converter, Quick Sync 58X ignition, returnless fuel rail, fast-response O_ sensor
Estimated fuel economy (city / hwy):	16 / 23 (2WD)
	16 / 22 (4WD)

Read more: http://gmauthority.com/blog/gm/gm-engines/l83/#ixzz4xCguSAxt

[brendon444]

It's not that simple many factors to consider. Cam profile, combustion chamber design, tuning, and also these engines are direct injection.

Run the same engine on a dyno with 87 and 91/93. Determine whether you are getting knock with 87 and if it is pulling timing resulting in a power loss. 

[O_J_Simpson]

To find the compression, pull a spark plug and attach the compression gauge to the spark plug hole. Turn the engine over...

[brendon444]

6 minutes ago, O_J_Simpson said:

To find the compression, pull a spark plug and attach the compression gauge to the spark plug hole. Turn the engine over...

He's referring to the compression ratio. Totally different measurements. 

[swathdiver]

6 hours ago, Bowhunt24 said:

Hey all, I can't seem to reliably find the compression on my '14 5.3L.

Do you have the Gen V L83 engine?  If so it is 11:1.

 

The Gen IV LC9 is 9.95:1 while the LMG is 9.6:1.

[Bowhunt24]

16 hours ago, swathdiver said:

Do you have the Gen V L83 engine?  If so it is 11:1.

 

The Gen IV LC9 is 9.95:1 while the LMG is 9.6:1.

I posted above, it's the L83 with 11:1. 

 

Doesn't seem like there is a right answer out there, mostly just preference on what octane people think is best to run for economy/perf. 

[swathdiver]

The higher the octane rating, the better your fuel economy will be.  There are plenty of people who disagree with that statement but I have proven it true in over thirty years of driving and testing with all manner of cars and trucks.  There's even a difference in performance between brands, even among top tier fuels which you'll have to work out on your own.  

 

Sunoco once offered the best performance for my vehicles but something changed and we get better mileage with our different vehicles using Mobil's 93 now.  Chevron is about equal to Mobil in our area as well.