Removing Catalytic Converters Reduces Gas Mileage?

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I was talking to a mechanic/technician today regarding removing both my rear cats off of my 2000 F150 4.6 V8. He told me if I did that ,that I would get worse gas mileage. Is this an actual fact?
 
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I vote false; although your OBDII system is not gonna like your non-functioning cats. It should throw codes and illuminate the MIL for loss of efficiency from the cats
 
you wanna max out the cats. Pull the Vacuum line off the fuel pressure regulator and drive around moderately to load up the cats with a little richness. Reconnect and take the car for a 1/2-3/4 hr drive in a lower gear that will allow you to run the engine at high RPM and not get arrested. Its a hold over from carb days. AKA the Italian tuneup. The engine management wants to see those cats.New O2 sensors up front may help. Taking off the cats may probably throw the timing and fuel maps off is a wild guess.
 
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Originally Posted By: lawnguy
I was talking to a mechanic/technician today regarding removing both my rear cats off of my 2000 F150 4.6 V8. He told me if I did that ,that I would get worse gas mileage. Is this an actual fact?
I would say 'possibly'. Your exhaust system is designed to provide an optimum amount of back pressure. Too little, and the engine will lose low-end torque (and thus use more fuel at low RPM). The cats provide some of the back pressure, so removing them may hurt idle quality and low-end torque. (The advantage would come at the top end, where the reduced back pressure would result in better flow and thus more HP at higher RPM.) It's a truck, not a race car - I'd leave them in place.
 
Removing the secondary catalysts is going to provide nothing but a stronger exhaust note and will require a tuning device to disable the rear monitors or anti-foulers to trick the ECM.

What are you trying to accomplish?
 
Exhaust systems do not need any backpressure at all to run right. Look at the video made by Engineering Explained. Exhaust VELOCITY is needed for low-end torque, not backpressure. However, to get higher exhaust velocity, the diameter of the pipe must be decreased, and a negative consequence is increased backpressure. When tuning an exhaust, you have to find a balance between sufficient exhaust velocity for low rpms, and the least backpressure possible for high rpms. If removing the cats doesn't decrease the velocity, then it wouldn't lose any low-end torque or mpgs.
 
Better airflow equating to more HP.


Originally Posted By: OVERKILL
Removing the secondary catalysts is going to provide nothing but a stronger exhaust note and will require a tuning device to disable the rear monitors or anti-foulers to trick the ECM.

What are you trying to accomplish?
 
Originally Posted By: ZraHamilton
Also, where I live, there are no emissions requirements, so a lot of people drive around without cats lol. There are a lot of diesels blowing black smoke everywhere too.
does not matter. It's still against federal law to tamper with emissions.
 
Originally Posted By: lawnguy
Better airflow equating to more HP.


Originally Posted By: OVERKILL
Removing the secondary catalysts is going to provide nothing but a stronger exhaust note and will require a tuning device to disable the rear monitors or anti-foulers to trick the ECM.

What are you trying to accomplish?


Yeah, that's gonna be another monumental waste of money.

We have talked about this how many times now? Buy a Lightning, you can gear this thing to the moon with 4.56's, spend 2K on a full custom tune with programmer, another 2K on a full exhaust system with shorty headers and you still won't make as much power as a stock PI 5.4L and a Lightning bone stock, would decimate you in every possible metric and have cost you less money than what'd you'll have into this rig.

This isn't a 302 where you can toss heads/cam/intake on it and make >300HP for a couple K. I've been there and done that. The 4.6L Modular is expensive to build and your best improvement is going to come from forced induction.
 
Originally Posted By: tomcat27
I vote false; although your OBDII system is not gonna like your non-functioning cats. It should throw codes and illuminate the MIL for loss of efficiency from the cats


If the ECU throws trouble-codes it may also go into a semi-limp mode which certainly could hurt engine efficiency and gas mileage.
 
Originally Posted By: ZraHamilton
Exhaust systems do not need any backpressure at all to run right. Look at the video made by Engineering Explained. Exhaust VELOCITY is needed for low-end torque, not backpressure. However, to get higher exhaust velocity, the diameter of the pipe must be decreased, and a negative consequence is increased backpressure. When tuning an exhaust, you have to find a balance between sufficient exhaust velocity for low rpms, and the least backpressure possible for high rpms. If removing the cats doesn't decrease the velocity, then it wouldn't lose any low-end torque or mpgs.
Agreed, it's not the back pressure itself, but the velocity of the exhaust gas (which is, of course, dependent on the back pressure). Think of trying to blow through a straw that's too bid - the air velocity will be quite low. I believe that the exhaust system is designed around the cats such that exhaust gas velocity is maximized for idle and low RPM. Without the restriction of the cats, the exhaust gas velocity may be compromised. Make sense?
 
There are more than a few donkey holes out there these days illegally jacking with their exhaust systems to make their vehicle louder, supposedly faster (but mostly not really) and most impressively to make thick black smoke. The extra noise, pollution, smoke, and the clearly evident obnoxious stupidity and insecure selfishness that goes with it is very impressive.
 
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Originally Posted By: lawnguy
Got it. Thanks OverKill!


I've been where you are, that's why my DD is 475HP
wink.gif


Before my wife and I upgraded, our previous vehicle was a 2002 Expedition Eddie Bauer with the 2V PI 5.4L backed by the 4R100 and with 3.55's in the pots. I looked into whether there were any cheap mods for it. There weren't. I deleted the silencers from the factory intake plumbing, ended up putting a Magnaflow muffler on it when the stock one rotted off and we just drove it. Modifying it wasn't like with my 5.0L cars, which benefited significantly from inexpensive upgrades. I had a mildly done-up 302HO build in my '89 Town Car and a full H/C/I 302 in my '87 Mustang GT. Also swapped out the 4.9L I6 from my '88 F-250 for a 302HO. The 302 and 351W were great motors to play around with as gains were cheap and they were a breeze to wrench on.

I know I might be coming off as Debbie Downer in your threads, but you really would probably be out less money if you bought a Harley or Lightning than what you'll have into this truck by the time you are happy with the performance.
 
Lawnguy..........

I wish you would just give up .... and JUST DRIVE your darn F150.

It will NEVER be a "Lightning" equivalent, no matter hoe much money you throw at it.

If fact - It will never even give a V6 Mustang a run for it's money.

If you want a go fast toy... you should just buy a cheap Mustang and throw your performance parts at it, instead.
 
Originally Posted By: Chris142
Originally Posted By: OVERKILL


What are you trying to accomplish?
looks like he wants to pay a huge fine for tampering with emissions equipment.


Precisely. Appears illegal so lock time.
 
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