Contour Enthusiasts Group Archives Forums General Troubleshooting Fuel Economy vs. HP

I just came back from the second of two trips to Chicago. I checked the fuel economy and I was running close to 23 mpg. The changes to my exhaust between the two trips are as follows.

I added 2 x 2.25" 12" long CATCO cats, MSDS headers, and different style mufflers. The HP definately felt lower when I changed the exhaust, but the new mufflers should have flowed better. I had something close to 165 on the dyno with true duals, MAFS, headers, & KKM. I got it optimized to 177 with a few more tweaks.

Before the change, I dynoed at about 170 with only the catless SHOShop y-pipe (no true duals), MAFS, & KKM. I also got 30 mpg to Chicago...easily.

I am not sure if there is a correlation here, but if I lose 7 mpg, can that all be attributed to the cats or am just more inefficient now somehow? Also, is there any correlation between lower fuel econ and hp?

Thanks!

Assuming no technology changes (bad assumption), engine calibration is largely an exercise in balancing performance, fuel economy, and emissions. The rule of thumb is that in order to improve one of these characteristics, you will take a hit on at least one of the others. There are many exceptions to this rule, but for the casual tweaker, it is probably true more often than not.