Was thinking of welding straight pipes in place of the pre cats and cats. Will this effects the emc at all? Besides the check engine light

 

Not sure what an emc is but your car should run fine. Why would you get a ses light?

 

I'm assuming you have an 85? If so, deleting the cats will not throw a code/check engine light.

 

There is no advantage to removing cats for the street.
Unless they're clogged.

Leave em on

 

If you drive very, very slow you won't notice much difference deleting the cats.

 

I never get out of first gear....

 

Replace them with 49-state Magnaflows. Still legal, still clean, more power, nearly the same as straight thru.

Only reason to delete cats is for a race car. That's because it gets you that extra tenth in the 1/4.

 

I deleted the main catalytic on my '91 and did testing before and after with video to time it and I picked up about 0.25 seconds in the 1/4 mile. See my post here:
http://forums.corvetteforum.com/c4-t...h-numbers.html

 

If you do have a 85 it shouldn't even have precats. The main car should have bolted on at both ends so no welding necessary if it is stock.

 

That's what I was thinking but didn't want to say anything.

 

You will only notice a difference at WOT (wide open throttle), that is the only time cats cause a restriction.

 

Did you do your changes at the same time as you were at the track?

If not, then your test is meaningless. Temp, humidity, time of day will make a difference, plus the biggest factor is the driver, as no one can drive the exact same everytime.

 

The tests also didn't include replacing the OEM cat with a new or aftermarket model. How plugged was the cat removed? We don't know. But, I figured that was for the OP to decide.

 

You could get the proper length test pipe and replace the cat with that.

 

Well, not being into meaningless testing I actually did do these within 1/2 a day of each other. They were not 1/4 mile runs factoring in driver error, these were simple second gear pulls from 1500 rpm to 5000 rpm at the identical place on the same road, the temperature was actually 5 degrees warmer when I ran without the cat as it was later in the day. I also only started timing when I reached 2000 rpm so that I had a good consistent time without accounting for throttle response. All captured very accurately. I am an engineer, so by nature I am meticulous about test conditions. I don't make UBAs - "unsubstantiated bold assertions"

As far as how plugged up the cat was, it was in very good shape. It's very simple physics - the catalytic provides restriction to exhaust flow, even at the low rate of a TPI engine. It is not a huge deal, but it does make a measureable difference; and the more power you make the more it makes a difference. That was also with the pre-cats in place and the stock exhaust from the cat-back. The very first TPI engine I had was an '87 Trans Am, and it picked up 0.8 seconds from a catalytic removal and exhaust change out while still using the stock log manifolds.

 

This was the test pipe I put in place of the stock main catalytic.

http://cgi.ebay.com/ebaymotors/CHEVR...item1c1a9ef4a7

 

How did you prove the shape of the cat? "Simple physics" is a side-step IMO. My comment/viewpoint raises the question of replacing cats (with aftermarket (new and clean) cats) vs completely eliminating them.

It's simple physics that you did not prove the advantage of the replacement vs delete option. Most information that I've seen states little advantage of open pipes vs performance converters. At this point, our environment needs to be included in this discussion.

 

Let it be Greg,

Its no race car.

Cats do a good job of eliminating unburned hydrocarbon smells from today's pump gasoline.
That I will agree upon.
Clean our air to breathe long term likewise.

BR

 

 

It is a proven fact that the rotten egg smell from cats causes asthma. Thet do more harm than good.