94 xlt exhaust questions

[ryf]

I am replacing the entire exhaust from the manifolds/headers back, including the Y, I just bought this explorer with the knowledge it would need exhaust, I was not aware it needed two Cats, and so forth.

so, where I live, there are no inspections, no sniffers, I'm thinking upping the pipe size and dropping the cats all-together, I don't see a senser hooked onto my exhaust (check engine lights not on either) so I don't think its much of an issue even if the one did fall off from the rusted out sections, these are after the 2nd cat though. anyone know what I should expect if I drop these two cats and up it from 2 to 2.5, my muffler guy (friend of wifes family) suggests I use V-force mufflers (he'll give me them for the same price as a turbo muffler) any ideas if these are any good/better? I'm aware they aren't magnaflow/flowmaster, but hes not steered me wrong before, he advised against a 3inch exhaust or it would sound tinny and ricey with out the cats. the truck is fairly stock, I'm welding up a custom intake for it but its not completed.

thanks for any help. I found you guys about a week ago while looking for hood-latches, been lurking eversince.

 

[Redrig]

I believe the 4.0 relies on back pressure to produce torque. Removing the cats probably isnt a good idea.

 

[huskyfan23]

I removed the cats and replaced them with a test pipe. I did this strictly for sound and noticed a significan decrease in torque. I'd replace your dead cats with high-flow cats. I'm thinking about doing that too. I wouldn't buy a no-name muffler brand. Go with Flowmaster, Borla, Magnaflow, Dynomax, etc.

 

[ryf]

so what your saying is, any changes at all could decrease my "performance", this goes against the generalities that I understand about combustion engines. is there an amount of backpressure I should try to maintain as a ratio or something tangible, as the intake changes will increase inbound air so is this a ratio I can maintain, or are you suggesting I just leave it all alone?

Im not trying to be smart about it, I guess I just don't comprehend it yet.

 

[sonik]

You won't have much back pressure without cats and 2.5" piping from the header. Most people recommend 2.25" for the 4.0 OHV. That's what I'm running from the cat. You may want to consider getting a high flow cat to replace the two stock ones. Huskyfan23 has a '94 without cats, maybe he'll chime in.

Edit: Guess he already did chime in

 

[huskyfan23]

Back pressure is required for torque. Removing the cats will get you a slight HP gain, but our X's need torque to get going. Since these aren't light, high-performance vehicles we want torque over HP. Believe me, you lose more torque than gain in HP. There's no ratio you should maintain, but for optimum performance you should use cats, and run 2.25" pipe. An open-air intake would compliment the exhaust in performance and sound.

 

[huskyfan23]

AND.. just ordered a high-flow cat fit for my X. I'll have an offroad pipe for sale soon. All it's good for is a sweet sound, but if you're interested hit me up.

 

[ryf]

well, hmm, alot to consider. I guess my mind doesn't comprehend 2 cats, I will at least put one cat on, because the general populace here agrees itshould be so, will this leave enough back pressure? I priced the cats at the local Parts store, it was just under $190 pre tax, what would be an option to not almost double my exhaust price?

sorry husky, he's cutting me a deal on the stuff new since he's my step dads buddy, but thank you for the offer. not to mention it'll need to be done by the end of the week!!

 

[huskyfan23]

You can buy high-flow on eBay for that price shipped. I just ordered this: http://cgi.ebay.com/ebaymotors/ws/e...&item=7950999475&rd=1&sspagename=STRK:MEWN:IT Ignore where they say it's for front only, that must just be part of their template. Magnaflow's site lists 23388 as front and rear.

 

[ryf]

ok, so if I increased the pipe diameter and use a high flow cat, how is this not going to still negatively affect my torque, as a free flowcat would obviously still lower back pressure.. I guess I'm just not keeping up. I'm sorry. thanks for all your great responses.


Lucky for me this was purchased as a secondary vehicle, so this wouldn't be horrible, but it is intended for light towing now and then, so torque is definitely needed. thats why I'm sorta trying to break this down.

 

[huskyfan23]

Well.. the stock exhaust is restrictive. Unrestricting the exhaust does lose some back pressure, but you gain torque in a different RPM range. Removing the cats takes away most of the back pressure. Adding an open-air intake forces more air to help make up for the back pressure loss.

 

[ryf]

well crudolio, I'm feeling spunky, single high flow aftermarket cat, 2 1/4 pipe and totally custom bent pipe, and we'll pick out a muffler..

right now I'm glad I didn't do my first choice, true dual with no cats on 2 1/4 that he talked me out of.

ok, I'll let you know what I end up with once me and the exhaust guy have a talk about it in the next few days when I drop it off.

I learned about engines with my '77 camaro, and it always like the straight pipes... guess I need to get re-educated, thanks guys!!