A freind of mine was telling me that I could Punch out my Cats and that would help remedy my gas mileage problems. I get about 11 miles per gallon. I have a 91 f-150 with a 4.9 litre ext cab with 31x10.50x15's is it maybe not my cats and just my tires and the fact the i have 243,000 miles on this old truck? If Punching out my cats will help how do you go about doing it?
Is there any thing else that I can do?

 

Idk whether or not its gonna help id assume it would because it would have less back pressure but all u have to do is cut/ unbolt yo cat depending on if its bolted or welded on take a chisel n just hammer it out. the inside of a cat it jsut like a whole bunch of little metal straws and yo can just bang em out. once uve done that get as much out as u can then reinstall it and rev the motor up n some more should come out. personally i think its the high mileage and tire size but ultimatly its your decision.

 

I have a 93 F-150 and I had twin pipes put on mine. The only thing between the exaust manifold and the back bumper is two glass packs. My gas mileage is about 16 mpg.
holla

 

When you reinstall the cut off cat, do you weld it back on? Or is there some sorta clampes that can connect the cat and pipe? The ends will be the same size where it was cut.

 

If you cut it out, you'll have to weld the empty carcass back in.

 

You can also put a coupler on each end. But this looks like hell and holds up a big sign that says "I was holowed out". I Just took mine out, so thats not any better!! Gas milege did not get any better.

clipper

 

your gas mileage should be a little better if you have taller tires.

 

I have a 4.9 and I had my front cat gutted and the rear one took off.
A new free flow muffler.
I seem to have more power but my mileage dropped .
I am confused on this one

 

Not really. Heavier tires and more contact (friction) with the road surface take away from gas mileage.


As for the 11 mpg that crossf is getting, how about letting us kow what your rear axle gears are? With 31s and knowing that a lot of 4.9s are geared at 3.08 or worse, I bet that's what is killing your mileage.

Having to stomp the pedal to get off the line isn't a good thing....

 

i have the same issue as popslide, i did the same thing and got worse miliage, but more power. as for your 4.9 giving you 11 with those tires, id say lay offf the skinny pedal a lil. i can get up to 17 of the freeway, and as low as 10 in town, it all depends on how much i lay into it. i have found that the 300s do this, wide rage of miliage depending on how you drive it. as for larger tires, it doesnt matter if they are taller or wider, or whatnot, the added mass will lower your miliage, and you will feel as though you have lost a lot of power, trust me, i know. 29s ot 35s...wow...that was a shock

Idiomaticman

 

do any of you have any problems w/emmissions? w/hollowed out cats i couldn't imagine you all doing too well.

 

I hollowed out the stock cats... horrendous loss of low rpm torque. Now, I'm not one of those enviro-****'s but I'd leave them on there if i were you. Personally I went to long tube headers with true dual 2-1/4" pipes and 12" long aftermarket high flow cats. The 2-1/4 pipe is a good combination of flow and low end torque, and the short little cats sound like a 12-18" glasspack. It's legal (for the most part) and it sounds good and performs great. Higher flow isn't always better, you need backpressure for low end torque... something I think all trucks could always use a little more of.

 

Alfred- I have 3.08 gears with the 31x10.50x15 tires along with m50d tranny and 4.9 litre motor. So my gearing might be the culprit?