straight causing burnt valves?
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Elder User
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From: Alpharetta
straight causing burnt valves?
this morning i hacked off my muffler and tail pipe. i like the sound so i went by a muffler shop to see how much it'd be to just add pipe behind it. the guy told me that without a muffler i'd burn up my valves over time. this didn't sound right to me, but i figured i'd ask anyway. will this happen?
5th Wheeling
Joined: Mar 2002
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From: Lufkin, TX
I bought a 3/4 ton extended cab longbed that the fellow that owned it before me had had a guy gut the cat, put in a y-pipe and then dual straight 2.25's out at 45 degree angles behind the rear tires with big tips. I asked my muffler guy that question and he told me not to worry about it "with that much pipe back there." I figured he wouldn't lie to me cause, I was wanting to spend the money.
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From: Alpharetta
what do you think he meant with "that much pipe back there". as of now i have the exhaust manifolds, into one pipe into a cat into another cat and now straight back. i talked to another muffler shop my mechanic recommened they had not hear of having messed up valves. he just said there maybe some perfromance decrease because of no back pressure. he's going to mock up a system for me sometime next week. he said he'd put different mufflers into place so i could see which one i like. sounds like a good deal to me. all this for half the price of what mineki is offering. mineki wants about 1000 bucks for two new cats and everything behind them. this guy ways about 500.
Posting Guru
Joined: Jun 2002
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From: Rio Rancho USA
IMO, the muffler shop doesnt know what they are talking about. Dont get me started about needing backpressure. You dont. Searching a little will give you way more info than you could ever want on that subject.
I will say this- MOST problems that occur after opening up the exhaust will fall into 2 causes.
1. The engine was not tuned to work with the extra exhaust flow, and as a result, torque or power increases may not be much, or power may actually drop.
2. Burning valves caused by the exhaust, or some other engine problem. Sometimes people will modify things after the engine already has so many miles that something is about to break anyway. Do an exhaust mod and a couple of months after the fact something breaks. The mod is blamed since "it ran so good before" and thats how myths and wives tales are started since there is no proof, just speculation.
However, in an extreme case, I can see an engine running so lean after opening up the exhaust that cylinder temps rise high enough to knock or burn a valve.
Reset your PCM to work with your new exhaust. Regardless of where you go, if they cant give you mandrel bent pipe, look elsewhere.
I will say this- MOST problems that occur after opening up the exhaust will fall into 2 causes.
1. The engine was not tuned to work with the extra exhaust flow, and as a result, torque or power increases may not be much, or power may actually drop.
2. Burning valves caused by the exhaust, or some other engine problem. Sometimes people will modify things after the engine already has so many miles that something is about to break anyway. Do an exhaust mod and a couple of months after the fact something breaks. The mod is blamed since "it ran so good before" and thats how myths and wives tales are started since there is no proof, just speculation.
However, in an extreme case, I can see an engine running so lean after opening up the exhaust that cylinder temps rise high enough to knock or burn a valve.
Reset your PCM to work with your new exhaust. Regardless of where you go, if they cant give you mandrel bent pipe, look elsewhere.
5th Wheeling
Joined: Mar 2002
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From: Lufkin, TX
Originally Posted by kjg26
what do you think he meant with "that much pipe back there"..
The problem that I have heard old timers talking about with straights is that when you let rev up the engine and let off of it is supposed to suck cool air back up toward the engine and if it hits the valve which is hot then it can burn it. I don't know if this is true or not but thats what I hear old guys saying. If it were true then I could see 10' or so of pipe causing less problem than say open headers cause the longer pipe would theoretically heat the air some. Like I said thats what I hear old guys at car shows saying.
Senior User
Joined: Sep 2004
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From: Fort Payne, Alabama
I'm always surprised at how much muffler shops DON'T know. They told me my straights would mess my truck up and it wouldn't go anywhere, I told them to go ahead like I said, and, ofcourse, it worked perfectly, they got their money, and I was on my way. The only way you are going to burn up your valves is if you run no manifolds or anything; or your engine is running that lean; or you're engine overheats in general.
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Elder User
Joined: Apr 2004
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I think the greatest problem with exhaust valves is caused by running an engine
hard and shutting it down without a cool down period. If the exhaust valves can't loose their heat to the valve seats and one stands open it can warp, it sure will
burn thru on the side thats not tight. By the way all you turbo guys the same holds
true for those turbo bearing and seal problems they need the oil to carry away the
and bring those temps down.
hard and shutting it down without a cool down period. If the exhaust valves can't loose their heat to the valve seats and one stands open it can warp, it sure will
burn thru on the side thats not tight. By the way all you turbo guys the same holds
true for those turbo bearing and seal problems they need the oil to carry away the
and bring those temps down.
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From: Kuna ID
The only problems I am aware of result from running no manifolds if it's really cold outside. I have no mufflers/cats on my 67 mustang(13k miles) or my truck(121k miles). Both of them run just fine. If you are still leaving cats on the truck, I think you will still have plenty of backpressure as they are a lot more restrictive than a muffler.
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