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258 exhaust options?

15K views 12 replies 8 participants last post by  dres 
#1 ·
Hey everyone...

I have an 86 CJ-7 with a fresh 258 I-6 running with a howell kit. It runs awesome, but the exhaust is trashed. It's the original exhaust that had the ports for the pulse air system (which is now missing and therefore leaks), and using a stock manifold. I've been told that it's pointless to use a header unless you port and polish the head, because that's where the biggest hangup is. So what's the best exhaust setup for a pretty basic 258? What size tubing would be best? What type of muffler? The engine is slightly built with a mild cam and HEI ignition besides the howell. Any suggestions?
 
#3 ·
The power gained from a good system would be minimal, like 1-2 hp. 2-3 foot/lbs torque. I would just go to buy like any kind of header, and a flowmaster 50 series exhaust, and have a muffler shop just run you a 3in pipe exhaust. excluding the price of the header, muffler, and maybe cat, if you need one, it should run you about 100-150 bucks to get the pipe run.
 
#4 ·
I hit the same problem, I live in CA, and the smog regs are strict, so I think I am gonna find a 4.0 head and get all the work done to it, and do the swap. then go and find a smog legal 4.0 header which are dime a dozen. this is the best option I have found. and the new head is a better option anyway.
 
#5 ·
Having just done this (www.bustedjeep.com/projects/rebuild.asp) I have some advice...

A 4.0L head and 4.0L header will require some slight modification (denting) of some of the down pipes in the header so that it lays flush against the head with a 4.2L stock intake. It does work well once that is taken care of.

The 4.0L header pipe is 2 1/4 ID and the stock exhaust is 2" ID so I basically ran header, cat, muffler all the way back with new exhaust.

The header is a Borla and it sounds great...it's not loud or throaty...it's almost like stock.
 
#6 ·
So, the stock manifold requires using 2" tubing? My engine has only about 600 miles on it, so obviously it's got fresh gaskets, and I'm not really into the idea of swapping it for a header since I'd have to mess with the seal on my intake manifold to get it all apart. I guess new 2" tubing with a high flow cat and a flowmaster would be the best bang for the buck? I know an exhaust isn't going to add to performance much even if that's what you're aiming for. I'm just looking to stop my Jeep from sounding like an angry swarm of bees.
 
#7 ·
Yeah I would get a "decent" stock width exhaust at Midas or whatever and call it a day. You could also use a 4.0L head with a Cherokee exhaust manifold and that uses stock exhaust tubing I think. Save you the headache of the header.
 
#8 ·
who ever told you a header wont do any difference unless you port and polish is wrong. the header will help and if your doing the exhaust you should definately do the header. It's not that big of a task to take the intake and exhaust manifolds off. the gaskest is only 20 bucks also. What I run on my 258 is a hedman header(i found the cheapest but lifetime warrenty). This opens up to 2 1/2 inches where i then just have a piece of regular straight exhaust pipe to a 2 1/2 inlet on my 50 series flowmaster muffler. My jeeps old enough where i dont have to pass emissions so that straight piece is where you would have your cat. Then the muffler comes a 2 1/2 inch outlet where i just used exhaust pieces from autozone to size the 2 1/2 down to stock where i have the end sock tail pipe hooked up to keep a good back pressure. This was before i completely redid everything on the engine and people would ask me when i started it if it was a v8. Now that i have completely redone the whole engine i am still running the same exhaust system.
 
#9 ·
I also went with headman headers but upgraded and got the dual output headers so to let it flow out better. It sounds great with the 2 glasspacks I put on it. I was going to go with the 50 series flowmasters but couldn't get it to fit. I have also had to change my gasket and it is real simple. The hardest part is getting the spacers the right size. The spacers take the place of the old exhaust manifold so you can tighten down the bolts correctly!
 
#10 ·
I just ordered the Headman headers for my 86 CJ7. So if I bypass the cat and buy only a Flo 50 with Midas bending the pipe so the whole thing will fit I will be ok??? I plan to have a new carb installed at the same time as the exhaust is installed. Will I have enough back-pressure? Good gains from the carb and exhaust?
 
#11 ·
if your engine is a I-6 they yeah you will be fine. Heck I had enough back pressure with open headers. I don't have a cat and just got the pipe bent and muffler put on a little while ago. as far as gains from the carb I have a single bbl carter and no problems yet.
 
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