My 08 Panel is approaching 150,000 miles, and although I'm not getting any CEL codes, I am preparing to do the timing chain/water pump as preventative maintenance.

My question is, did anyone who has done this notice either a decrease in performance or gas mileage before the chain replacement, or an increase in performance/gas mileage after?
I'm currently averaging 23mpg, with the 2.4. When I had my black 08 panel with the 2.2 (bought new) it was getting 27mpg average. I'm sure the 2.4 might be thirstier, but a 4mpg difference seems a bit much.

TL;DR:
Should I expect an increase in performance/mileage after a timing chain replacement?

 

Your fuel mileage may have decreased as the timing chain stretched over the years, you should notice an increase in fuel mileage, but then again you might be pushing the throttle pedal a little more with the new chains!

You may consider the new ZZP front guide and their front guide upper bolt!

 

Seems you all treat chains as a maintenance item. That's a bit much I think.

 

Has anyone tried advancing the exhaust cam one tooth? I did this on my motorcycle and the torque difference is impressive it pulls from down low all the way to as fast as the bike has ever gone.

 

That is because it’s better to replace a stretched chain than the whole engine! You haven’t seen the damage done when the timing chain breaks or the front guide breaks apart, the valves hit the pistons, weakening the connecting rods and suddenly there’s a hole in the block, usually #1 let’s go.
You can get 150,000 miles but I’ve replaced chains at 20,000 miles broken guides at 15,000. If you’re good at listening to these Ecotec engines they will tell you , even before they throw a code like P0016.

 

You could try that, the computer might not like it, and throw a code from the camshaft position sensor or the pistons will get fresh with the valves, they are close but not kissing cousins.

 

I've seen at least 50 engines that jumped time enough to bend valves, bust pistons and even hit so hard to bend a rod. When that happens you will have a busted piston as well. These engines give you plenty of time to fix. It will let you know you have a problem long in advance.

 

My gut tells me that cam may have been off and you fixed it.

 

Avoiding getting stuck on the side of the road is bad enough to make me consider thinking about it.
I don't see changing the chain as maintenance, but if it is bad change it before it breaks.
It is bad if the top guide doesn't have any plastic left on it, it is bad if you can see slack between the sprockets. There is a tensioner that can only take up so much slack, a loose chain means it is stretched past the point the tensioner can fix, that is pretty far it has a good inch of travel.

I do consider inspecting the chain after 100,000 miles on a regular basis as a maintenance item. Simple enough to pop the valve cover and use eyes. One of the wonders for a rubber O-ring valve cover gasket is it is reusable.

Avoiding getting stuck on the side of the road is bad enough to make me consider thinking about it. Disregarding any internal damage.

I don't think intentionally messing with the valve timing will do much on a VVT engine. Maybe, in firmware not physically.

 

No. On the KLR it's called the MC mod. When I was adjusting my valve shims I decided to give it a try. The results were great to my butt Dyno. I can feel every power stroke the engine makes. It's not as smooth but the torque is way better. It's like an entirely different motorcycle. It would be like the difference between a nicely setup 4 cylinder car engine and a 4 cylinder tractor engine.