2008 GMC Yukon Denili

[Burkard]

Welcome to the Forum from NH.

As folks have stated, the 6.2 was not built for great gas mileage. That being said, how you actually drive the truck will certainly have an impact on your gas mileage (I'm sure that I'm not telling you anything new).

Before adding mods to my truck, driving 'carefully and efficiently', I could get 12-13 mpg driving in the city, 15-17 on the highway, and 18-19 on the highway with my wife in the truck.

However, if you are like most folks with the 6.2, you are going to find it very difficult to drive the truck 'carefully and efficiently', as it is just too much fun not to.

That is true. Love the way it gets up and goes. Im like you love the way it handles on road and doesn't have a problem getting qhere I need to go

 

[Burkard]

Was looking at the air flow system and noticed the plastic parts that come from air filter seem like it would restrict the air flow going to manifold. Wondering if I made my own out of pvc. If it would mess up computer. Because on whats on it now there seems to be alot of unnecessary parts on it. It doesn't go straight into manifold. Seems like it restricts alot of the air flow. Curious if anyone else noticed this. It seems if I use all of the computer sensers I should be fine. I'm not fimilar with all the computer stuff. Any advice on this matter. Thanks.

 

[91RS]

It isn't that restrictive. It's a resonator that keeps it quiet.

 

[Burkard]

It isn't that restrictive. It's a resonator that keeps it quiet.

Ok. Just noticed that some of it runs along the manifold on top back towards the firewall. It just seemed like alot of unnecessary space where the air could go. Ive noticed there is no throttle cable. Has a motor built into the manifold. Haven't taken it apart yet. Was afraid something might brake. Was wondering how do those motors hold up over time. I know I never had a problem with the cable. Just seems like another part that could brake.

 

[avalonandl]

Ok. Just noticed that some of it runs along the manifold on top back towards the firewall. It just seemed like alot of unnecessary space where the air could go. Ive noticed there is no throttle cable. Has a motor built into the manifold. Haven't taken it apart yet. Was afraid something might brake. Was wondering how do those motors hold up over time. I know I never had a problem with the cable. Just seems like another part that could brake.

All those extra space is not restricting any airflow, its keeping the car quiet by absorbing the engine intake noise- google helmholz resonator.

You can clean the intake throttle body that will help a little.

The new engines use a fly by wire throttle body.

If you change the plugs that's about the best you can do. You have 403 hp and a 5600 lb vehicle.....

 

[gooffeyguy]

I think in '08 the engine was rated at 380hp

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[thompsoj22]

I think in '08 the engine was rated at 380hp

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403 HP forget about gas mileage! Just keep feeding it good premium and enjoy your road limo. Your vehicle is good at just about everything but fuel efficiency.

 

[mikeyss]

All of the L92, L9H, and L94 had 403 horsepower. It was how marketing advertised the horsepower numbers.

 

[iamdub]

Ok. Just noticed that some of it runs along the manifold on top back towards the firewall. It just seemed like alot of unnecessary space where the air could go. Ive noticed there is no throttle cable. Has a motor built into the manifold. Haven't taken it apart yet. Was afraid something might brake. Was wondering how do those motors hold up over time. I know I never had a problem with the cable. Just seems like another part that could brake.

None of it is unnecessary as in "pointless". Engineers wouldn't add such chambers to induce turbulence and cause a restriction just to be dicks. Inversely, they're all about increasing the efficiency of the engine since they have to meet the standards set by the NHTSA and EPA that are always being tightened.

Them "unnecessary" chambers are for sound. The boxy chamber under the duct and the tube that runs alongside the intake manifold are calculated designs that reflect low sound frequency waves back into the duct where they collide with the other low sound frequency waves, cancelling them out so they're muted. This is why aftermarket air intakes are much louder and make a growl under throttle.


Don't take apart your throttle body. The design is just fine and there's no easy way to convert it to a cable-driven TB. Mine has over 200K miles on it and there are plenty of others here with even higher mileage on them with no issues.

There will always be "just another part to break". If you wanna minimize parts that could brake, get a skateboard or some good walking shoes.

 

[chucksrt]

I think that both Black bear performance and PCM for less say that their tunes will average you about 2mpg more and about 20 extra hp.