1998 Dodge Magnum engine questions

[Kelly B.A.]

I am installing a 5.9 magnum(with the FI set up) In a 1973 Challenger.
What is the best place for the O2 sensor(pre cat) I was thinnking that the x in the x-pipe,might be a good spot,that way it would "read" exhaust from both banks(driver and pass) side of engine.
I am not sure if the sensor needs to get info from both sides of engine,or if welding a bung off one of the collectors is enough? Also for post cat O2,can anyone suggest where I could buy the correct resistor to read proper value.
After I have it running for a while to work out the bugs,I might do a mild cam swap(thinking the mopar r/t one,+46hpand 53ftlbs) Any suggestions?
Last thing on my mind is the rear gear(using the 46re/518 OD from the 5.9)
For the street 3.91,4.10,or higher(mosty stock 5.9)? What would work best?
Thanks.

[gs69350]

I don't think the X pipe would be a good place for it... The X pipe is suppose to balance the pressure on each side of the exhaust so I don't imagine it will have a lot actually flowing through it.

Probably on or just past the collector would be a good spot for pre-cat.

Someone probably makes a dummy o2 sensor for the post cat (assuming you're not running a cat).

HTH...

[Kelly B.A.]

So it will not require a "reading" from both sides of the engine to run correctly?
The x-pipe was the only place I figured it could get such a reading if needed to.

 

[gs69350]

Most factory EFI v6/v8 setups have an o2 sensor for each bank... in which case I would put the o2 sensor bung near the collectors on each header.

If the system only has 1 o2 sensor pre cat then maybe go down to a large single, like 2 x 2.5" into single 3"
just a thought..

What EFI system are you using??

[Changin Gears]

The x-pipe has all the exhaust running though it, it would probably be fine.  Just make sure you put it on the upper half so any water condensation stays out of it.

[Kelly B.A.]

I removed the 5.9 and 518/46re from a 1998 van,it had a y pipe off manifold, pre cat o2 sensor, cat, post cat sensor. So only one o2 sensor(pre cat) for all gases.
I am using the stock 98 magnum fuel injection set up. If everything works,I will swap the intake for sure and mabe cam.
So then X-pipe it is for the pre cat sensor and I will be sure to place it so h2o will not be an issue.
I know I am not ready for gears yet but with a mostly stock 5.9 magnum and the overdrive,15 inch rallye wheels,what rear end gear?
The Challenger has 2.94 in it now,and I will use them for testing,but with OD, I was thinking 3.91's or 4.10's.Any thoughts?

[shadango]

I have a 03 Durango with the same engine and (I think) tranny).

I have 3.91s in the rear and crusining rpms is great. Of course that is with the truck-sized tires on it.

I think you would be good with the 3.91s though.

[Kelly B.A.]

Well I know 3.91 w/od it will be like a 2.7,so with 4.10,should be like 3.0
I mean I want to cruise and drive it a lot and if my(2000) 3500 ram van with 5.9 and 3.91 can get 14-15 mpg on highway,with the aero-dynamics of a brick.Then once in the Challenger,if I do 3.91's mpg should only get better,or will the smaller car tire = out?
I want to cruise but at the same time I don't want mini-vans smoking me at stop lights,so I feel at least 3.91's. But I coulod be talked into 4.10's.
Just want to pick the gear that will work best,and be the most fun with this combo.