would it be safe to just bore out 1 cat, and have a turbo muffler on there??, I have 2 1/4 inch pipes behind the muffler.To me it isn't loud enough, but I also don't want to mess up my valves ect....
also, loosing that .343239483274th horsepower doesn't bother me , I had to run just the cats for a while ( a day) and noticed no decrease at all, and noticed no increase when I put the t-muffler on there either, don't you just love the 2.9!!.

Charlie D.

 

 

Hi, my suggestion is go to the local 4 wheel, or one of the local speed shops. Sounds like you already have the larger pipe after the muffler, thats good, but it won't give you anymore horsepower at all. What I did was to install a high flow, high performance exhaust system from the outlet of the exhaust manifold to the tail pipe. Forget headers,difficult to install (if you can find them) and in my opinion not much horsepower gain. Stick with the stock exhaust manifold. The high flow system consists of a high flow catalytic converter that attaches to the existing exhaust manifold, then a high flow muffler, and a complete set of 2 1/2" pipes thru-out. Also, if you install the high flow exhaust you have to install a high flow air inlet. Which was simple, just replace the existing paper air filter, (I have the 2.9L fuel injected Bronco 2)with a new K&N air filter. My GOD, I picked up alot of horsepower! Made that Bronco2 darn scary when passing gear kicked in on the freeway. Seemed like it was going to leap in the air! First time, my auto transmission went into passing gear I almost had a heart attack. That Bronco2 was a screaming banshee changing gears at redline on the tach. Wow! I didn't like it so loud so I installed a pipe resonator between the muffler and the tailpipe. That lowered the volume a bit, and but also cut the horsepower down some. Still overall, the pick-up in horsepower was impressive, I'd say at least 20%. Takes a mild mannered Bronco and makes it a screamer. My gas mileage dropped by 1 to 2 miles per gallon,in city and highway when I drive it hard.
I did also put in a new set of spark plugs,and set of plug wires, to make sure I had a good spark. Pretty amazing, the fuel injection and the computer adjusts for best ignition, emissions,etc. If you have a carb Bronco, you might need to increase the jet size, or at least the needle size on the carb, but with fuel injection, just install and forget.

The problem with the Bronco 2 is most of the horsepower of the engine is not available since they restricted the exhaust system so much. After the mod, most of the horsepower is available, I could go to redline easily on the tach like I said. I have the 89 fuel injected Bronco2, and did not make ANY changes to emissions systems, black box, etc,. All I did was install a new high flow exhaust system. The K&N air filter improves the air flow to the engine, but without a high flow exhaust there is only a slight gain in horsepower. Also, unless you install a high flow catalytic converter, the exhaust system is still radically strangled. SO, you have to make the whole modification to make a difference.

I put the K&N air filter set in myself,(easy), but had a shop remove the old exhaust system and install the high flow cat, high flow muffler, and larger pipes. The high flow muffler gives a low throaty rumble, just too loud for my taste. Like I said, the whole mod increased my top end on the highway, and took me to redline on the tach! After I put the resonater in, it decreased me about 600RPM. Interesting side note is really improved horsepower at higher altitudes,scrambles really nice at 8,000 ft, but I live at 1,000 ft elevation. I recommend the change. If you have access to welding torch or have a shop, the work is easily done in a garage, but forget wrenches, you'll never remove all that old pipes cause they are welded and rusted. Cost was about $650 installed I think and worth every penny! Plus, my emissions look better than a new car with that new high flow catalytic converter! I found out that this type of mod is pretty standard for anyone wanting more horsepower. The shop I went to did all kinds of 4 wheel vehicles that needed to meet emissions and wanted better sound and more punch! Call around and good luck.

 

Now put a larger throttlebody from an '86 or '87 and you will see that much gain again !!

 

If you really want to open up the exhaust, have a muffler shop make you a new Y-pipe with 2" - 2 1/2" pipe, then add a high-flow cat (or even better yet, leave the pipes 'split' and get 2 2 1/2" inlet/outlet universal hi-flow cats...) and a 2 1/2" inlet / 3" outlet muffler (or 2 2 1/2" inlet/outlet mufflers with H- or X-pipe) and run it/them to the stock exit location. I suggest the 3" from the cat back if you're going to leave the system more stock-install looking, but 2 1/2" is plenty big -- too little backpressure can also be a bad thing. I can't wait until I have the time and $$$ to start my buildup(s) and project on my '87

 

You'll want 2-1/2" piping on there, the 2.9's don't put out enough exhaust to get good flow with a larger pipe.

If you really want to open the exhaust up, get a set of headers, split the exhaust and run 2 Flowmasters on there. That along with a K&N filter with the 86-87 TB will give you all the air you can use.

 

Romer, it may not put out that much flow (stock), but a single exhaust from the cat back might benefit with the 3" pipe... or not *shrug* The idea of a dual exhaust (esp. on a 4x4) is good, however, a true dual exhaust is almost impossible on a BII unless you do a lot of extra fabrication (crossmembers, trans. mount crossmember, etc.) if you wanted a true 'tuned' dual exhaust -- equal length pipes from both exhaust manifolds / headers back. Also, putting $800 alone into headers isn't a fair trade, however, if you were to fabricate some shorty headers that somewhat matched the stock manifold layout, that would work. If you were to do that, you'd want at least 1 7/8" pipe off the exhaust ports dumping into a 2 1/2" to 3" collector -- if not larger. Then, you could reduce it to 2 1/2" and pipe it through hi-flow cats and flowmasters or v-force's or even glasspacks. The only issue to address, though, is the O2 sensor -- which a smartly placed H-pipe / X-pipe configuration would work, IF it were ahead of the cat(s). This is why most computer/emissions-controlled V engines are somewhat limited as far as what you can / can't do with the exhaust. A hi-flow OEM replacement cat and larger piping from the cat back is a plus, though. Especially if you put the $$$ into a set of modified / hi-performance heads, larger cam, MSD ignition or similar and add-on performance chip for the ECU. Of course, you'd probably also want to port out the intake and put a larger throttle body on there, along with a better flowing air intake with a K&N or some such. Just my $0.02

 

Are you saying run dual 2-1/2" exhaust on a 2.9?

 

I said split the exhaust as in a Y pipe, you would need a bit of fab work to get true duals. And with the 2.9L it really wouldn't be worth it. You would be able to put in a new engine and run true duals on it with headers for probably about the same price as doing all the mods onto the 2.9.

But a simple dual exhaust would help it out.

 

Romer - ah, so basically, a single inlet/dual outlet muffler or in-line Y-pipe after the cat. That works too.

Osin - yeah, dual 2 1/2" on a 2.9. Ludicruous to some -- however, if you're going to do what I plan on doing, it'd be easier to squeeze out that 200+ hp if you had a large enough exhaust to let 'er breathe

As it stands, www.tsperformance.com is the only place I've found that can sell you a custom performance chip and there aren't many 'generic' or otherwise plug-in tuners for these ECUs. Although, my research is far from over

 

Diablo chips (I think they're an FTE sponsor) also offers custom performance chips. So does JET. There are quite a few out there that offer the custom chips for the 2.9's.

I've done tons and tons of research on these things. The dual 2-1/2" exhaust on the 2.9's do add a bit of power, and sound good too. It's all about the personal preference.

 

TS Performance can actually customize your chip to all of your modifications (bigger injectors, headers, exhaust, throttle body, etc etc etc.). I would just prefer to be able to recalibrate the computer myself, without having to install a chip *shrug*

 

If you want that power band lower in the RPMs like you would on most 4x4s then you'd be far better off with a single 3" and even that is overkill unless you are pumping 200hp. In that case then you’re right where you want to be. One 3" pipe flows more then 2 2.25" pipes. More flow does not always equal more power. A well laid out dual system on a 2.9 would be more like 2". A dual 2" system would have a 55% flow increase over the stock system. A 2.5" dual system would get you a 150% increase in flow that you just won't use it and you'll be cheating yourself out of usable low end torque. The better you match a system the more you'll get out of it. This is similar to carb sizing, you can make more work but it’s not going to be tuned to its optimum.

 

The recommendation by a few shops around here was to modify the existing Y-pipe or fabricate a new one that dumped into a 3" collector and use a single 2 1/2" - 3" inlet/outlet hi-flow cat and equal-diameter piping from the cat back. However, going by research and my own experiences, OSin hit the nail on the head. Match your exhaust to the rest of the engine/modifications. You could probably get by and put out some decent numbers with a OEM replacement hi-flow cat and single 2 1/2" exhaust, regardless of cam/valvetrain/fuel system/computer mods. The thing to keep in mind is, you need -some- backpressure, but too much and/or too little is bad and does NOT benefit you. I think I made some mistakes in my earlier posts -- WHOOPS. 2" - 2 1/4" -- at most 2 1/2" full, tuned dual exhaust is probably optimum, even overkill -- IF you build everything else up along with. I was heading in the more extreme direction (i.e., 24+ lb/hr injectors and 70+ mm throttle body/ported intake plenum/mainfold, larger cam/higher ratio rocker arms, etc.). My goal is to try and squeeze out around 225-230 hp, and hopefully not end up rendering a completely siezed engine in the process

 

I put a TB from '87 and a K&n filter up front, with a 2 1\4 " from Y pipe to hiflow cat to Dynamax to rear on my '89. Reads 0 vacuum at WOT.