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258 Exhaust

Then run a straight pipe out the back with no muffler.
 
Straight pipes will pop and back fire more if thats what you want, glass packs might do the same, flowmaster 40s sound nice and loud on the AMC 258 i6 / 4.2l i would keep a muffler for back pressure i dont know if we need it LOL!! i run a magna flow no constant rumble at crusing speeds but when you stomp on it heads turn :D
 
2 problems...possibly 3 with your plans.

#1. Exhaust dispersion. Your exhaust needs to exit at the corner of the vehicle or off to the side to prevent fumes from filing up the cab and killing you...or the commuter in the next lane when you pass out and hit him head on.

#2. Back-pressure. Most engines require some amount of exhaust backpressure to perform correctly. The AMC 258 i6 / 4.2l is no exception. There are ways around this, but they require rebuilding the engine to take advantage of increased intake and exhaust flow.

Andddd...#3. Valve damage. You probably wouldn't run into this problem cutting the exhaust behind the CAT, but keep in mind that a hot exhaust system is a benefit to the engine. You're exhaust system "breathes" much like you do. Although the primary operation of the exhaust is to, well, exhaust.....it also pulls a slight amount of exhausted gas back into the combustion chamber (by action of the valves and pistons working together) If the engine pulls even a slight amount of cool air into the exhaust valves, it's all over. This is unusual....but it does happen. I ran my engine once with just headers and a short pipe, and it resulted in a broken exhaust valve from the cold air being pulled back in. So it does happen.

If you want a good sound, try a glasspack. I ran one on my AMC 258 i6 / 4.2l and it sounded really good. I run dual glasspacks behind my 401 now and it sounds beyond intimidating.
 
CJim7 said:
2 problems...possibly 3 with your plans.

#1. Exhaust dispersion. Your exhaust needs to exit at the corner of the vehicle or off to the side to prevent fumes from filing up the cab and killing you...or the commuter in the next lane when you pass out and hit him head on.

#2. Back-pressure. Most engines require some amount of exhaust backpressure to perform correctly. The AMC 258 i6 / 4.2l is no exception. There are ways around this, but they require rebuilding the engine to take advantage of increased intake and exhaust flow.

Andddd...#3. Valve damage. You probably wouldn't run into this problem cutting the exhaust behind the CAT, but keep in mind that a hot exhaust system is a benefit to the engine. You're exhaust system "breathes" much like you do. Although the primary operation of the exhaust is to, well, exhaust.....it also pulls a slight amount of exhausted gas back into the combustion chamber (by action of the valves and pistons working together) If the engine pulls even a slight amount of cool air into the exhaust valves, it's all over. This is unusual....but it does happen. I ran my engine once with just headers and a short pipe, and it resulted in a broken exhaust valve from the cold air being pulled back in. So it does happen.

If you want a good sound, try a glasspack. I ran one on my AMC 258 i6 / 4.2l and it sounded really good. I run dual glasspacks behind my 401 now and it sounds beyond intimidating.
Click to expand...

thanks for the info. i am planning on getting an exhaust system soon i just wanted to see what it would sound with out the muffler. I just cut it off and I can certainly tell a difference with regards to the fumes.. I have the top off right now so i should be ok haha but If i decide not to get a new exhaust system i plan on fitting a pipe to the cat and attaching it to the tail pipe. i have never heard of the glasspacks but i just did a little research on them and they seem pretty cool/ reasonably priced haha. Ill definitely look into those. Thanks!
 
Glasspacks are cheap.....what drew me to them initially however, was their small diameter, and they are extremely tough. Both of these attributes are desirable when building a Jeep for the rocks. Thus my attraction to them.

Sooo...for me minimal price, small-diameter, tough profile, and good sound won out to high-dollar bulky mufflers.
 
Napas version of a flowmaster is 29.00 at this napa and 3" pipe makes it sound even better. After I did mine rumors started that I had well over 78 hp at the tires! People were even confusing it with the 440 jeep!
 
I just put a couple baseball cards in the flywheel makes for a wicked rumble. Huh thats kinda my spot on for my budget..........sad.
 
pkarren123 said:
I have been trying to find a new exhaust for my CJ7 but im not having to much luck.. I want it to similar to how it sounds with no muffler. Again I have a AMC 258 i6 / 4.2l straight 6
Click to expand...

Why:confused:
Gets old on a long trip.........
BTDT as a 1960's 'motor-head'.
Get a Flowmaster 44 and you'll be happy.
LG
 
I picked up a Thrush Glasspack from Advance Auto Parts last summer for mine and it sounds great and gets compliments all the time. It is not, however, annoying at high speeds and obnoxious enough for your neighbors to hate you.

If your cheap cut the cat off, run a pipe to a Glasspack, and then a pipe out the side somewhere.

I'm currently looking for a way to run the exhaust out of the side on mine since I'm getting some smell back into the cab from the air pocket behind the jeep when driving down the road and I smell like a 2 cycle weedeater on a hot summer day.
 
If it still has the stock Cat on it it will give the back pressure you need. I had a old Buick wagon that the muffler rusted out and whe I removed it it wasn't that loud so instead of putting a new muffler on I just the shop run a pipe from the Cat out the back. I was surprised how much the Cat quieted it down. By the way it had a 413 in it and sounded good afterwards.
 
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