smellycat

So I took the Rx7 to the shop the cut out stuff and put in a muffler. $125 . Car sounds great. So I dirove out the gas tank and calculated 17 mpg. Heck with 27 year old stock exhaust I was getting 19 Mpg. Do I need to tune the Carb?. Will better exhaust flow make it ride rich? No back fires so I thought it was not too rich

SC

Sgt.Stinkfist

iTrader: (6)

A more restrictive exhaust will hinder gas mileage to an extent. Before thinking something is wrong, go another tank and see how it is. Maybe this tank had excessive/prolonged idling while at the shop? But a leaking exhaust could have been giving u better mileage due to its freer flowing nature

estrada42

Your results may vary, but I went from 220-230 a tank to 260-270 a tank with new changes other than replacing the factory manifold and a newer cat with a RB Race header and glasspack.

And, I think I drive it harder than before.

DivinDriver

iTrader: (15)

The problem might be in the gas pedal.

Having a new exhaust might be leading you to 'test' it a bit, which in turn results in excess depression of the go pedal, resulting in higher fuel consumption.

OneRotor

iTrader: (3)

This.

In theory, with the exact same driving conditions, you shouldn't see any difference in fuel economy with just a different pipe and muffler. Two reasons:

1. you have a carb. Your jets are fixed. There is no way for the car to compensate for any increase in flow caused by a different pipe/muffler.

2. You didn't change the flow rate of the system as a whole. You still have restrictions in the carb, intake mani, ports, cats, and exhaust mani/thermal reactor. Your cat back won't increase flow, so you won't see a change in fuel economy.

The reason why you saw a decrease in fuel economy is because you can hear the motor more, so you are in the throttle more often.

smellycat

I am driving it bit, I can bark the tires way better than before, not alot just a few show offs. I feel more power accelerating. since the precat and cat and that 50 pound muffler is out. Its probaly 100 lbs lighter.

So everyone agrees that fiddling with the mixture is not a have to thing to do.

I'll check the plugs to see if they are gummed up . SC

RX-7 Chris

iTrader: (19)

messing with the mixture may change things stightly but not much. It is most likely the way you are driving.

DreamInRotary

iTrader: (49)

I had a Chev 350 with straight 3" that exited just behind the cab. Roared like no other vehicle in my county. My mileage went down due to excessive rumbling when I pressed the accelerator a little too firmly on take offs, tire chirps, and when I saw pretty girls on the sidewalk.

Moral of story, it's probably the driving

Twilightoptics

iTrader: (1)

Seen a few guys on here say that their milage did change rather dramatically (1-3) with the mixture screw.

I find the motor doesn't run as good coming to idle or off idle if the screw isn't within 1/4 turn of the sweet spot, so if it's out of whack it might cause other problems.