I thought I might jump in here and try to answer his
original question-skipping all of the politics. From
what I understand Ford had at least two types of EGR
systems. Both systems let the computer modulate the
amount the EGR opens for different conditions. The
computer verifys how much the valve is open by:
1-an EGR position sensor mounted on the valve itself
2-a pressure sensor that senses pressure in the exhaust
line feeding the EGR valve.
The latter type is where you can sometimes run into problems
taking the cats off. It will cause a check engine light
because there is not enough exhaust back pressure for the
pressure sensor to pick up and verify the valve actually
opened. I'm not sure but I think alot of trucks used the
kind mounted on the valve itself and probably it will be ok.

 

Well, I was always brought up to believe that an engine was designed to run on a certain amount of back pressure, and also created with a certain purpose in mind. Now, removing the cats would create better flow for the exhaust, however, sometimes that much free flow is not desirable, right? Like I said, I've been told that a well tuned exhaust system is better than running straight pipes. It helps retain low end torque and obtain a flater power curve versus a spike in power at 6000rpm (which we don't drive at...normally). From the "running right" perspective, now, Ford designed the Speed Density Injection system to run off of pre-detirmined rates of flow...including exhaust flow (exhaust flow changes intake flow; free volume left in the cylinder after what exhaust is capable of being expelled leaves.). Removing all restriction from the exhaust side will throw off the computers calculations and result in less than satisfactory performance in around town driving...or just in plain potential. Lets also try to remember that louder does not equal more power.I've seen some pretty mellow sounding vehicles spank some window rattling, straight pipe cars. Think about it smart. Think about tuning rather than creating some pathetic monster. Think about Nissan (get over the foreign-hatred for a second) and the 270 hp 3.0 LITER v-6 in the pathfinder. Think they're running multiple cats and a factory muffler? Yeah. Try smarter not harder.

Hope my rambling helped...and didn't crunch any toes like so many posts here have...

 

[font size="1" color="#FF0000"]LAST EDITED ON 28-Dec-00 AT 10:49 PM (EST)[/font][p]I'm not reversing my position but I remember an article I read in four-wheeler magizine at a B&N bookstore or maybe online said that engines do not need back pressure whatsoever. It said an engine could do its best work with no backpressure at all. However I have read in an article by Midas (http://home.earthlink.net/~tfiller/exhaust.htm) that it helps regulate engine temperature.

Daywalker
92' F-250 351 4x4 xlt 4.10 5spd sprcab lngbed

 

[font size="1" color="#FF0000"]LAST EDITED ON 28-Dec-00 AT 10:45 PM (EST)[/font][p]I have opened up the exhaust on my 88 F-150, and noticed a performance increase, not decrease. I simply changed out the stock (plugged soplid) convertors, and put in 1 high flow convertor. This one convertor does the job of both the factory pre-convertor, and the convertor. Also, I added aftermarket shorty headers, and a custom Flowmaster system built by the only muffler shop I trust.

I got a price quote the other day to dual outa 1966 F-100, from the engine back, and put in a crossover tube (that I would supply no fab work on their part required), can you believe he wanted to charge me $600! I got a price from the same shop to do my system on my 88 model. Think about this, $375.00 for a two chamber single inlet dual outlet flowmaster, and dual 3.5" chrome tips 24" inches long.

I had my system done in a town 20 miles away, for $237. Same system. That is the only reason I'll trust the one exhaust shop to do my systems.

[link:www.geocities.com/hotrodford_88/|Hotrodford_88's Webpage]

 

[font size="1" color="#FF0000"]LAST EDITED ON 28-Dec-00 AT 11:43 PM (EST)[/font][p]
engines need no back pressure whatsoever...all it does is help to push exhasut gases back into the cylinder while the exhaust valve is still open, which in turn causes the engine to try to burn the exhaust gases over, the key is to get the right sized pipes with the least possible amnt of backpressure, an exhaust system that has the correct pipe size helps the pulses from the combustion chamber to scavenge themselves out ( i tried to put that simply). If your pipe diameter is too large, then the scavenging effect is diminished and the engine is forsed to "push" more of its it's exhaust out , (the key is velocity, think about how an engine makes torque, when you have very large intake ports you will have very crappy low -end torque, when they are smal and designed for high velcity, the result will be a low rpm torque producing engine that is very flat, this also results in a very efficient and smooth engine) so when you hear someone say that they lost low rpm torque when they cut off their muffler, its probably because they went with too big of a diameter pipe(s), newer computer controlled engines are designed to run the the very restrictive factory exhausts...if the computer was reprogrammed for something like correctly sized straight pipes vs. 4 cats and a muffler into a single pipe, there should be an increse in performance all the way around, this is why headers and crossover pipes work so well,. all they do is increase the scavenging effect, therefore more power at differnt rpm ranges (depending on the sizes of the primaries), more gas mileage and a cooler running engine

jus my two cents, correct me if im wrong all yall engineers and physics guys =)


1985 F-150/351Ho/4wd/6inch with 33's
1979 f-250 429/4spd/6inch lift w/33's, soon to be 36's

on a quiet night your can hear the chevys rusting away

 

I don't know if some of you guys know this or not, but...

Some of the new cars are coming from the factory with multiple cats on them. I'm not talking 2 or 4. But some are coming with 6.

Take the chevy caprice for example, 4 cats. The mustangs 87-93 came with 4, and the new crown vics, 4 or six (I can't remember which.) To me that would say that they pollute more, unless my mind isn't thinking right.

On the 66 Mustang I used to have, it was dualed out completely. I could kneel down behind the car with it running, and it would not have half of the smell that my 88 F-150 has. That tells me something, either the vehicles know aren't as efficient as they should be, or something else is wrong.

[link:www.geocities.com/hotrodford_88/|Hotrodford_88's Webpage]

[link:www.geocities.com/westlake_vfd/Westlake.html|Westlake VFD Website]