does no muffler affect the performance?
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Joined: Sep 2008
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does no muffler affect the performance?
1990 f250 351 E4OD 4x4 ,
i bought the truck with no muffler, just about 1 foot of pipe after the cat , the rest rusted off, just wondering if this if affecting the way the motor runs , seems to not run very smoothly???? does this have something ot do with not having back pressure?/
i bought the truck with no muffler, just about 1 foot of pipe after the cat , the rest rusted off, just wondering if this if affecting the way the motor runs , seems to not run very smoothly???? does this have something ot do with not having back pressure?/
Junior User
Joined: Apr 2008
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i have a 1990 f150 with a 302 i had the same issue when i bought it, rough idle not very responsive, it turns out the cat was clogged. I simply took a sawzall to the cat and cut it off then welded the pipe back together with no muffler or cat. seems like i had way better performance. and you dont want back pressure it causes over heating and unnecessary engine wear. its probably illegal in your state to run with out a cat(just like in my state) but it can sure help you in the long run by taking it off, or even replacing it with a new highflow cat. hope that helps sorry for the length...
Street Queen to the extr3m3
Joined: Jan 2005
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From: Lubbock, Texas
stock cat, should supply proper back pressure... But the one foot of pipe after it isnt exactly safe, the end of the exhaust needs to be pass the cab, for it to be safe AND legal...
Street Queen to the extr3m3
Joined: Jan 2005
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From: Lubbock, Texas
i have a 1990 f150 with a 302 i had the same issue when i bought it, rough idle not very responsive, it turns out the cat was clogged. I simply took a sawzall to the cat and cut it off then welded the pipe back together with no muffler or cat. seems like i had way better performance. and you dont want back pressure it causes over heating and unnecessary engine wear. its probably illegal in your state to run with out a cat(just like in my state) but it can sure help you in the long run by taking it off, or even replacing it with a new highflow cat. hope that helps sorry for the length...
Proper amounts of back pressure help the engine run properly...
Please dont run around passing out bad information... Do some research first.
But you are right on the plugged cat... that could be a factor in the engine running bad...
Junior User
Joined: Apr 2008
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not the amount of backpressure a clogged cat would supply, that could severly limit your vehicle when i removed my cat and cut it down the middle i was amazed at how any air was making it throughg at all the thing basically had a brick in it...sorry i sounded a little harsh if i did i didnt mean to make anyone screw up their truck
Street Queen to the extr3m3
Joined: Jan 2005
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From: Lubbock, Texas
Yes i agree clogged cats are bad news... Been there done that, but for an engine to run at its peak efficency, it will need some (read: SOME) back pressure,
I say pull the cat any way, as it does choke the engine down some... If the truck runs better, get an aftermarket high flow cat, if not... The weld the old cat back on...
I say pull the cat any way, as it does choke the engine down some... If the truck runs better, get an aftermarket high flow cat, if not... The weld the old cat back on...
Post Fiend
Joined: May 2004
Posts: 11,289
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From: Lakewood, Ohio
1990 f250 351 E4OD 4x4 ,
i bought the truck with no muffler, just about 1 foot of pipe after the cat , the rest rusted off, just wondering if this if affecting the way the motor runs , seems to not run very smoothly???? does this have something ot do with not having back pressure?/
i bought the truck with no muffler, just about 1 foot of pipe after the cat , the rest rusted off, just wondering if this if affecting the way the motor runs , seems to not run very smoothly???? does this have something ot do with not having back pressure?/
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Street Queen to the extr3m3
Joined: Jan 2005
Posts: 4,554
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From: Lubbock, Texas
did you read the op?
Says doenst seem to be running to smoothly...
Says doenst seem to be running to smoothly...
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Senior User
Joined: Sep 2007
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From: Iowa
Factory cats even when new are restrictive to flow as are the pipes. Old, half plugged ones are obviously bad. Engines need a small amount of backpressure to run at peak efficiency. It creates a back vacuum or 'scavenging' effect and actually helps pull the exhaust through the system. If emissions are an issue, I would have an exhaust shop put in a new, higher efficiency cat and a good low restriction muffler. Many guys around here actually just don't run a muffler but do run a converter but I think that actually hurts daily drivers. At a minimum though, your exhaust should extend past the cab area, even if just pipe to the rear axle with a dump or out the side.
Elder User
Joined: Jun 2005
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From: northeast, KY
Wouldn't the restrictive factory exhaust manifolds create enough backpressure to run straight pipes? I gutted my cat on my bronco and given it did give it more growl...it wasn't enough gain to notice. If you were running something like headers I would say you would need some type of exhaust to give it the backpressure it needs, but with factory exhaust manifolds I'd say I wouldn't worry too much about it.
Matt
Matt
Posting Guru
Joined: Apr 2008
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From: Wendover, NV.
I still have the cat on my truck but do not run a muffler. After taking my muffler off I also gained a boost in mileage from 14 MPG average to 15 MPG average. And yes, it is my daily driver.
Post Fiend
Joined: May 2004
Posts: 11,289
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From: Lakewood, Ohio
watching football and nascar and surfing the web at the same time made me miss that.
oh., well.
who here is perfect?
Senior User
Joined: Sep 2007
Posts: 336
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From: Iowa
Yes, the factory manifolds are restrictive vs LT headers but not enough to provide adequate backpressure. Oh, BTW...the manifolds aren't cracked are they? It is a common problem on the 351's especially but...if that is the case, not only does it noisy up the exhaust (sounds like crap) but introduces cold air close to hot valves (definitely not good).
Street Queen to the extr3m3
Joined: Jan 2005
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From: Lubbock, Texas
lol
NOT!
Its all good, just keeping the uninformed informed... No hard feelings...
Lead Driver
Joined: Nov 2002
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From: Concord, NC
Backpressure in any amount is undesirable, but is often confused with flow velocity. For an engine to run at its peak, flow velocity must be tuned for the desired powerband of the engine to maximize scavenging effects. As backpressure rises, the amount of residual exhaust gases in the combustion chamber increase, which decreases the cylinder volume available for fresh air and fuel, decreasing volumetric efficiency and power.