Covered my Cat Converter ( bellypan )

[Nerds laugh at me]

I installed an aluminum bellypan that covers my exaust to the edge of the catallic converter. (This is on a '93 Honda Civic DX auto )
I'd like to ask what problems this might cause. I have already noticed a drop in my FE, as well as what seems like less power, and now I am developing holes from rust just in front of my muffler on my exaust. This is from the excess heat ..right ?
The cat itself is completely covered.

I just averaged 40.56 MPG on a trip that I used to get 45+ MPG on.

So why would I do something stupid like this ?? Well, except for long trips to my folks place ( where I am now ) of over 100 miles, I only use my car to get to work and back. The trip is 7 miles one way.
I had read that the cat. converter needs to heat up before the engine really starts to run efficiently.
With short trips of only 7 miles, there seemed to not really be huge threat of burning up my cat. , and it would certainly help warm things up to cover the cat.
I guess I was wrong.
My FE numbers actually went DOWN.

I just realized that I put this in the wrong forum. It really should be in the 'experiments' forum.
I had hoped to get some advice from some of you that are mechanics so I put it here.

I'll try to include pictures later, but I am on my parents computer ( the keyboard sticks - can you tell ? )

[Danronian]

I really don't see how this could drastically decrease MPG. My only guess is that somehow your bellypan is catching air instead of making it flow better.

I would guess your car needs some type of tune-up item. If you haven't gone over the engine lately, it would probably be a good time. My best guess is that it's a coincidence.

[bones33]

Originally Posted by Nerds laugh at me

I'd like to ask what problems this might cause. I have already noticed a drop in my FE, as well as what seems like less power, and now I am developing holes from rust just in front of my muffler on my exaust. This is from the excess heat ..right ?

Additional heat will not cause rust to your exhaust system, water will though. Could be that you're just now noticing this as winter comes.

Originally Posted by Nerds laugh at me

I had read that the cat. converter needs to heat up before the engine really starts to run efficiently.

This is a little backwards, it should read: "The engine needs to warm up before the cat starts to run efficiently."

Both the cat and the engine need to be warm to operate efficiently. I think the core of the cat needs to run something like 800F to burn all the excess fuel and complete the conversion process. It gets its initial heat from the exhaust gas then creates it's own from it's own process. Cats love heat and unless you're dumping really large amounts of fuel into a hot cat there is no worry of melting the core leading to increased back pressure and reduced fuel mileage.


Addressing reduced mileage, winter weather can really kill your mileage, especially if you do alot of short trips. How has the temperature changed since the belly pan was installed?

[Nerds laugh at me]

So not the fact that it is overheating the cat. converter?
The thing is covered over entirely.
( I go take some pictures of it now.)

[bones33]

Shouldn't be a problem. I've run track days with a wrapped exhaust to the cat with no problems. This is full throttle, full rich conditions for 20 minute sessions, 5 or 6 sessions per day. When I removed the cat to pound out it's innards it looked perfect. You're not going to melt it doing this.

How has your ambient temperature there changed recently?

[trebuchet03]

Originally Posted by Nerds laugh at me

So not the fact that it is overheating the cat. converter?
The thing is covered over entirely.
( I go take some pictures of it now.)

Is it really overheating the cat? Covering doesn't necessarily mean it's overheating


When did you add the cover? Do you have receipts to setup a gaslog? That drop seems consistent with winter fuels...

[Nerds laugh at me]

Actually guys I've been wearing shorts lately .... I live in Texas ;-)
So...the drop in FE is not due to the temperature.
I'll keep you guys updated on any tests that I do.