Psh, stock rod bolts.

 

I said I wouldnt, not that you can't

I have worse luck than most people

 

Just did a MPG check with a tank of 89. Truck averages 15.6 MPG in mixed city/highway driving. The stock engine got 18 MPG for years during the same commute, so gas mileage is off a couple of MPG. The truck runs pretty good but needless to say I'm disappointed with the MPG.

I'm running a tank of 93 and driving it easy to see if the octane helps. All I did was swap the engine and a computer with a BB 89 octane tune. No CEL light or codes.

What else could be affecting the gas mileage?

 

Tune and cam. Being a mail order tune it's going to ball park the calibration, and it will be on the conservative side. Justin can't afford to tune things on the ragged edge from a thousand miles away, and understandably so. The cam has larger duration than stock, so the attaining same torque output as the stock engine at X RPM is now going to require a higher RPM...so you now need more throttle and more fuel. Had it been me I would have left the stock cam in and run the higher compression and better octane.

 

Any chance the cat converters are bad but it hasn't thrown a code?

I figured the bump in compression from 9.5 to 10.25 would offset the extra duration, so the truck should have about the same or better low-end torque. I also figured that the efficiency would be the same or better but I didn't actually compare the stock DCR to this new DCR. Truck idles pretty smooth so the cam doesn't appear that "big" to the engine.

Kinda hard to compare DCR when I don't know the intake closing event for the stock LM7 cam or the CM cam I've got now.

Light-throttle performance is better than stock but I'm not amazed. It does really come alive if I get on it, truck is MUCH faster than stock above 2000 RPM. It really hauls *** on a downshift. I guess that's the trade-off with stock gears and converter in a heavy truck. Part of my learning curve I suppose....

 

Latest update: I ran a few tanks of 93 through the truck, and I'm getting 17 MPG like clockwork. This is mixed city/highway driving 35-65 MPH. Runs pretty good when I get on it. 2000 miles on engine so far.

I'm thinking of stepping it up with a set of the speed engineering headers and a BB scan cable tune. If properly tuned, will headers help MPG and torque below 2500 RPM? I definitely don't want to lose any torque below 2500 with the stock verter and 3.42 gears.

 

I know this post is old but I'm from SC and do my own tuning on my Vette, Silverado, and a few of my friend's cars. If you're interested in a custom tune shoot me a message. And no, I won't break your bank at all.