Straight pipes bad?

[Jacob Ochs]

EDIT: I was wanting to put straight pipes o my 86 MJ no cat no exhaust all the way out the back, can this harm my engine? I not worried about noise I just want to know if it will harm my engine in any way. Thanks guys!

[onlyinajeep726]

Depends... is it running a 2.5L or the craptastic GM 2.8L?

On fuel injected engines, it's not likely to cause issues.  On carb'd engines, it's been said that it can cause burnt valves due to the lack of back pressure.
 

[Jacob Ochs]

The craptastic 2.8l it's been great so far

[onlyinajeep726]

Probably won't be for long if you straight pipe it... lol

[Jacob Ochs]

What's the reasoning for that?

[nitroxsteve]

If you do it just keep an eye on your spark plugs. If they show the engine is running lean then you will need to adjust for that condition.

[onlyinajeep726]

Supposedly, it can cause burnt or warped valve due to lack of back pressure, as I stated in my first reply.  Not sure if that claim holds any water, though.  It's been a highly debated topic on a lot of different forums.

[Jacob Ochs]

That's what I thought, the valves wouldn't warp because of pressure but if its cold out they could but that's if you cut it of at the headers I'm running it all the way out the back! So the air won't be cold by the time it reaches the valves

[nitroxsteve]

In my experience opening up the intake or exhaust and not correcting the mixture will cause a lean condition and can hurt things. You can run open headers if you want but you need to do it the right way or you will lose performance or potentially hurt things. And I believe this goes for any gas engine.

[Jacob Ochs]

In my experience opening up the intake or exhaust and not correcting the mixture will cause a lean condition and can hurt things. You can run open headers if you want but you need to do it the right way or you will lose performance or potentially hurt things. And I believe this goes for any gas engine.

Would you suggest a tune up after I do this?

[nitroxsteve]

Only if a tune up is due. I can't give you any more advice on the subject as I don't know enough about the 2.8 fuel system to tell you how to correct a lean condition. If you are going to read your plugs you need to at least pull them out so you know their condition before making any changes. I personally would not run open pipes you don't get anything but noise, bad hearing, and tickets. I guess I'm getting old lol.

[Jacob Ochs]

Only if a tune up is due. I can't give you any more advice on the subject as I don't know enough about the 2.8 fuel system to tell you how to correct a lean condition. If you are going to read your plugs you need to at least pull them out so you know their condition before making any changes. I personally would not run open pipes you don't get anything but noise, bad hearing, and tickets. I guess I'm getting old lol.

hahahaha or I'm just the typical 18 year old!!

[Eagle]

 

In my experience opening up the intake or exhaust and not correcting the mixture will cause a lean condition and can hurt things. You can run open headers if you want but you need to do it the right way or you will lose performance or potentially hurt things. And I believe this goes for any gas engine.

Would you suggest a tune up after I do this?

 

A tune up?

 

No, you will need to run it on a dyno, monitoring the fuel-air mix, and very likely you'll need to rejet the carburetor, and possibly rework the advance springs in the distributor.

[Jacob Ochs]

 

 

In my experience opening up the intake or exhaust and not correcting the mixture will cause a lean condition and can hurt things. You can run open headers if you want but you need to do it the right way or you will lose performance or potentially hurt things. And I believe this goes for any gas engine.

Would you suggest a tune up after I do this?

A tune up?

 

No, you will need to run it on a dyno, monitoring the fuel-air mix, and very likely you'll need to rejet the carburetor, and possibly rework the advance springs in the distributor.

so all this just to go to straight pipes???

[dankicksass]

Didn't read this whole thread but it is well documented that running with no mufflers makes less power than with a factory muffler, nice muffler or even a cheap muffler. Chevy High Performance had a shoot out a few years back, Pretty sure Borla won but straight pipes definitely came in dead last.

[91Pioneer]

Don't bother straight piping it. Spend your time and energy on other more worthwhile things.

[Eagle]

 

 

 

In my experience opening up the intake or exhaust and not correcting the mixture will cause a lean condition and can hurt things. You can run open headers if you want but you need to do it the right way or you will lose performance or potentially hurt things. And I believe this goes for any gas engine.

Would you suggest a tune up after I do this?

 

A tune up?

 

No, you will need to run it on a dyno, monitoring the fuel-air mix, and very likely you'll need to rejet the carburetor, and possibly rework the advance springs in the distributor.

 

so all this just to go to straight pipes???

 

Yes, if he wants to have it run right and not burn the valves due to a constant lean-burn condition.

[Incommando]

For one thing open exhaust does not scavenge correctly meaning the spent gases remain in the chamber. This not only hurts efficiency but can cause the cylinder pressures to increase which can damage valves and/or springs.

 

Drag and other race cars get away with it by being tunable to compensate. Even so many drag cars are now running performance mufflers. My personal bracket car ran better with about 12" of collectors and turn downs versus just open headers even though I could easily tune the timing and carbs

[86FUBAR]

I ran open for probably 2 months 3 different times in high school on my 1986 with the 2.8 with no problems and constantly redlined the poor truck nearly every shift (had to just get moving :) . All I did was unbolt the exhaust and remove everything including the cat at the 4 bolt flange and left the y in place . Those were the days !!

[Jacob Ochs]

I ran open for probably 2 months 3 different times in high school on my 1986 with the 2.8 with no problems and constantly redlined the poor truck nearly every shift (had to just get moving :) . All I did was unbolt the exhaust and remove everything including the cat at the 4 bolt flange and left the y in place . Those were the days !!

Hahah poor old Comanche! Did it sound any good? I've heard some of them straight piped and they sound really bad!

[Jeep Driver]

Straight pipe all the way out to the rear will give more back-pressure than you think.

 

Those who run no cat and a cherry bomb that dumps before the axle run with LESS back-pressure.

[86FUBAR]

 

I ran open for probably 2 months 3 different times in high school on my 1986 with the 2.8 with no problems and constantly redlined the poor truck nearly every shift (had to just get moving :) . All I did was unbolt the exhaust and remove everything including the cat at the 4 bolt flange and left the y in place . Those were the days !!

Hahah poor old Comanche! Did it sound any good? I've heard some of them straight piped and they sound really bad!

It was loud as hell ! But actually sounded good , when I got the truck it was 100% stock and one of the first things I did was slap a cherry bomb on it , then after a bit I ditched the entire tail pipe assembly and put a turn down on it . Wasn't happy with that so I fiddled with different turn downs then I went to a 2chamber flow with a turndown and cut the turn down off right at the tapper on the muffler and was finally happy with that for a couple years . So about ten years ago I torched a 4" hole in the back of the flow master and welded a short 90deg turn down to it and have been really happy with that bit now iv been wanting to hollow out the cat to make it a little louder just because . Iv got some youtube vids of the exhaust and a couple wheeling ones where you can hear it .

[Jacob Ochs]

 

 

I ran open for probably 2 months 3 different times in high school on my 1986 with the 2.8 with no problems and constantly redlined the poor truck nearly every shift (had to just get moving :) . All I did was unbolt the exhaust and remove everything including the cat at the 4 bolt flange and left the y in place . Those were the days !!

Hahah poor old Comanche! Did it sound any good? I've heard some of them straight piped and they sound really bad!

It was loud as hell ! But actually sounded good , when I got the truck it was 100% stock and one of the first things I did was slap a cherry bomb on it , then after a bit I ditched the entire tail pipe assembly and put a turn down on it . Wasn't happy with that so I fiddled with different turn downs then I went to a 2chamber flow with a turndown and cut the turn down off right at the tapper on the muffler and was finally happy with that for a couple years . So about ten years ago I torched a 4" hole in the back of the flow master and welded a short 90deg turn down to it and have been really happy with that bit now iv been wanting to hollow out the cat to make it a little louder just because . Iv got some youtube vids of the exhaust and a couple wheeling ones where you can hear it .

Can you link me to your channel? And do you have any videos of when you were just running straight pipes?