98jeepsrt6

Hey guys, Well not much to update other than i got the headers heated coated and heat wrapped... And installed.. If you want to see how it came out check my profile..

Now im suprised i didnt ask this before but what size piping should i be looking for?? I was going to go with 2.5 but the more i thought about a true dual with 2.5 and very lil or no backpressure would hurt the purpose of this setup..

I started thinking that 2.25 would be my best bet.. It will give me some back pressure at each bank, and i think the tone of the exhuast would sound better..

Now i am debating the Cat Conv. situation, i know by law we cant discuss it or anything or say we are not goin to use one, but for this one we can just overlook.. If i do the 2.5 piping i want to add the cat for back pressure purposes.. would this be a better route than the 2.25 with no cat?

Thank guys... sorry im taking some time getting this done but i have a bad habbit of pushing **** off, and spending my money on other jeep related things.. lol

dukie564

you're probably right about the 2.25 so you have enough backpressure - i would use that CAT or no CAT. They sell aftermarket universal cats that are small and space saving - i'd look into 2 of those since they each don't need to filter as much.

another thought - how are you dealing with the o2 sensors? You will not be able to run no CAT at all because of the downstream one. Are you planning to put the o2 sensor on only one side? seems like this might screw up the A/F mixture?

98jeepsrt6

1.. Yea im looking at some space saving cats that are on the vendors list.. good price too...

2.. As for the o2 sensor, i have had several discussions with others on this forum as well as other resources... and came to the conclusion that this will be a test setup.. if it performs well itll stay if not have to figure out a new desing, which the fix would be an Xpipe..

3.. The o2 sensor(s) will be placed one on each bank one connected to factory harness to determine A/f for the vehicle, and the other will be connected to a A/F gauge that will help determine the differnce in each bank.. Two A/F Gauges one for each bank reading the air fuel...

Now technically speaking, but not in genius terms, the o2 detects the difference in a/f and sends a signal .01-.05v to the ecm and u know the rest..

(1) o2 reading 6 cylinders would equate to the same as (1) o2 reading 3 cylinders... im guessing that it would read the amount of a/f as the 6 but half..

Now i can explain this bettr or someone else can but i tried to keep easy...

If this works then great if not the xpipe is going in.. sorry for the poor *** explanation..

opake

I haven't done much research on this, but I know on my old Ford 4.9 I6 either dual 2" (no cats) or dual 2.25 (with cats) was recommended. Different engine, bigger size I know, but if I was doing a dual exhaust on the 4.0 I think I'd look at 2" piping to preserve backpressure the best.

That said, I ran dual 3" pipes on that 4.9 with a dual port intake, 4 barrel carb and long tube headers and it was a beast. Definitely gave it more top end.

dukie564

sounds like it would work. You're the Guinea pig

I would think the only problem that might arise is if you have a problem, like one of the injectors/plugs not firing right on the cylinders that exhaust out the other pipe, and not have the computer realize it because it thinks the a/f mixture is ok. Maybe that's a stretch....i dunno

98jeepsrt6

lol, Well if that does happen its a noticable failure, and since the whole rail would be coming off i just test which one would be bad or just check it meter.. But i just replaced all injicter with ford 19 yellow stick ones, and next time i get to the JY ima c if there are any 703s. Last time i went they were all gone..

Yea 2.25 sounds like the way to go, even with the cats...

any other thoughts on this??

prerunner1982

You may also do a "cross over" pipe between the duals to equalize pressure between them.

rich

I think you will be disappointed at the lack of room under the xj this is going to limit your options down quite a bit.No room for a cross over pipe,I dont think you will have much room for a true dual system either I think you will have to modify if quite a bit,but keep us posted.

Metmknice

For most applications, especially stock to mild modified. Larger single exhaust is the way to go. Its not like you have a big block V8 under hood or anything. Cost/space/performance, single is the way to go.

djb383

Git 'er done and post pics......I also think dual 2" would be plenty big and a few less clearance issues. Don't let the naysayers discourage u.

98jeepsrt6

Yea im not worried about people sayin anything to change my mind its already set with all the parts ready... Just need to get to the shop to getter done. Ima do the 2.25 with cats to preserve back pressure but the least the better... There will be a crossover (h-pipe) And would be set right after the tranny mount. Beneath the driveshaft..

The only clearance problem i see is the ebrake cable.. Which can be moved and mounted in the driveshaft bezel.. That will give even pressure for the ebrake as it will be centered...

Also long tube headers will help with torgue at lower rpms..

prerunner1982

For an Inline 6 to have duals... the pipes start out right next to each other so a "crossover" shouldn't be a problem..

98jeepsrt6

Thats correct.. if the hpipe doesnt work well and the o2 sensors don function properly that what im goin to do just making a small xpipe after the headers and placed o2 in the center.. Should be done by next week if i get a chance to go to the shop..

freegdr

top os sensor i would not move it ot far from it orig location may thro off its reading

rich

What type of header are you running is it a single or dual outlet for the 1998 I'm asking cause I dont know,I have a dual outlet on my 2000, and banks also offers a single outlet,which is better ,well your opinion on it.