Looking for exhaust advice

I have to replace my whole exhaust. I am going to go with 2.5in. Would there be any disadvantages if I go 2.5 all the way through? I just ordered Dynomax 2.5in. catback, 2.5in. high flow cat, oem head tube(I am aware of slight restriction) My most important concern is my exhaust manifold is cracked and I am afraid my o2 sensor will misread, run engine rich, and meltdown my cat again. Should I be concerned? I do plan on buying a header. Pacesetter. Any feedback on these headers? should I wait to install new cat(use hollow) until I fix leak?
Thanks,
Harlee

What year? And 4.0??

1987 4.0 custom(according to VIN)
sorry

what about upgrading exhaust manifold (Yes, I searched for 3 hours) could not find definate answers

From a personal perspective, I'd wait and change everything from the manifold back. 2 1/2" is the proper size and Pacesetter is a good product.

If you really have to wait for the manifold, I don't think you're going to have a lot of problems with the O2. Lot's of guys run around with a cracked manifold and generally you just get poor performance.

Everyone has different experiences. That's my 2 cents.

Also, there are a lot of manifolds. Gibson, Borla, and Pacesetter just to name a few.

Not that you care, but...
I have had all stock exhaust, then cat only, then open downpipe, then 2.5" test-pipe to turbo to turndown, then test-pipe, then open downpipe, then test-pipe to flowmaster 40 to turndown, then test-pipe to flowmaster 40, then open downpipe, then 2.25" test-pipe to flowmaster 40 DF to 2.25" tailpipe. The last one is what I'm currently running, and like best.
It seems to give me better torque, but I may be dreaming. The open downpipe seemed to give me most HP. Flowmaster to turndown gave me a lot of droning. All of the others besides stock and current gave me a lot of exhaust fumes. Current set-up has low rumble until rev'd, then it gets a muscle-car like tinny sound to it. No exhaust fumes, and only drones at 1700 rpm.

Aftermarket manifolds are very expensive. I would never consider one myself, unless it's on a Stroker. I have seen a few replacement headers that look like they are high-quality for under $200 (vs $400+)

Of course I care it is your opinion that I am after and real experience.

What about the match-up between HO header to RENIX exhaust ports, how far off, where, what would it take to make it fit?
Would it be worth the extra effort?
Or would I gain more from upgrading intake man., or both?

2.5" is a good size. I say definitely get a header. Not only are they stronger than a stock exhaust manifold, but you'll get better performance out of it.

Also, you should wait on replacing the cat until you fix all the leaks, including the exhaust manifold. If you replace your cat without replacing the manifold, you'll clog it prematurely because it's running rich..

Elias

that was my feeling. I will probably continue to use hollow cat. (shhh)

I don't like to, but gotta do what I gotta do

i've read about a few people putting a flex pipe inbetween the exhaust manifold and the downpipe, of course you have to have a custom downpipe made at an exhaust shop or something

i haven't heard any bad things about it

I was thinking, when I finally choose the header I want to have a new head tube mandrel bent, that would be my chance to install the flex pipe.
Thanks Fred.

Anybody running pacesetter header? Pro's & Con's?