True Dual Exhaust.. Questions!

[Ryan91]

Greetings... I wanna bounce my Idea for a true dual exhaust system off anyone who's reading this message..

First, I have a stock '91, and the only mods so far are a drop in K&N Filter and a single Flowmaster (direct replace from stock muffler & resonator).

Here is what I'm thinking about: Completly axe the current exhaust system. Everything from the manifolds back, gone.

Replace with new pipe out the manifolds to flowmasters, and then end right underneath the truck, angled out and downward, so the exhaust doesnt go straight down. The system does NOT go all the way out the rear. It's real similar to the setup you would see on some muscle cars.

Now then, my plan does NOT include cats. Lets not worry about smog. Also, I consider the sound a secondary issue. Perfomance and simplicity of design is my number one deal here.

HERE is where I need some advice: how will the performance be? What about backpressure? This is a real short exhaust run, with no cats, so there will be hardly any restrictions.

Should I go with cats? there would be two, one for each 'side' of the engine.

This type of setup wouldn't be too costly, just totally custom...

Anyways, lets get a good discussion going here. Your advice will help me decide what to do.

Thanks alot,
Ryan91

 

[Ryan91]

Addendum....

I forgot to mention that the O2 sensor would obviously be re-used, and will remain in the same physical location. Therefore it will only monitor the exhaust from the right (passenger) side of the engine.

I'm also open to suggestions/advice concerning headers...

Ryan91

 

[Scott B.]

I doubt the truck would run very good with the existing computer. They are designed to run with a certain amount of back pressure. Actually, back pressure is also needed to maintain airflow at low rpms.

At the very least, you will need to reprogram the computer (as in, install a specially programmed SuperChip). You would have to talk to them to see if they have such a modification.

The 4.0L motor was not designed to be a high rpm engine, either. It's anybody's guess how it would run.

Why not run a single pipe into a Flowmaster, and just run duals out of the muffler (as some others and I have done)? I have a good Flowmaster sound - but it is only a V6, so it doesn't sound like a V8

 

[<<MONOCHROMOUS>>]

i love the idea for true duals, fortunately on my 98, i already have two stock cats and "muffler-in" pipes, so it would be much easier for me.

my exit idea was to run both pipes side by side to one of the sides in front of the rear tire, like you see on the Lightning F-150s. That would be original have to save me up some money

 

[jimbo74]

i noticed you live in california ARE YOU FREAKIN CRAZY OR DO YOU WANT TO INSTALL A SEAT ON THE BACK OF YOUR TRUCK SO THE COP CAN RIDE WITH YOU RATHER THAN BEHIND YOU AND HELL SAVE GAS TOO???!!!! I know this is way illegal and your performance will suck!!!!!

 

[mrboyle]

Something to think about!
Crawl under your Explorer and take a good look at the scene. Assuming you were to run duals, what do you see that might block the path of the left (driver) side that would prevent you from installing a pipe on that side? If you haven't guessed its the gas tank! Now, Since you can't run a pipe down the left side of the truck that means you will have to run both pipes down the right (just like stock)then back over to the left at the rear. This makes the left pipe at least half again as long as the right. Add up the extra restriction from all the bends, and you have an unballanced exhaust system (something duals are famous for).

Put aside what I just said.
In the October '00 issue of Petersen's 4wheel&Off-Road they did a comparison to "see how closley matched a 2.5-inch dual exhaust system, a dual system with a crossover tube, and a good 3-inch single exhaust system would be."
The results: Single 3" - Max Tq.-251, Max Hp.-184
Dual 2.5" - Max Tq.-264, Max Hp.-185
w/crossover - Max Tq.-261, Max Hp.-184

Tests were measured from 1600 to 4000 RPM. As you can see the difference in horsepower between single and dual setups was only 10ft/lbs of torque and there was very little (1hp.) gain in Hp.

Hope this hepls!

 

[Ryan91]

Hmm... interesting discussion....

Hey, I appreciate the response this message has received. I wanna respond to what "mrboyle" was saying about unbalanced exhaust. I know this is true, but I did mention in my original post that this would not run all the way back, it would exit as close to the manifolds as possible (basically, right after the mufflers)

Otherwise, the whole issue with performance and lost backpressure is more-or-less what I expected to hear. Remember, this is just an IDEA...

Now then, back to the exhaust. If there were cats added to each side of the exhaust, it would increase the length and add some backpressure. Would one cat/side of engine be too much backpressure that it would cost performance?

We're dealing with a catch 22 situation here. If i'm understanding things correctly here then: Too little backpressure = performance cut @ low end; too much backpressure = other performance costs (engine cant breathe properly).

Ryan

 

[jimbo74]

ending the exhaust before the rear axle is also illegall. trucks can do it because the bed isnt part of the passenger compartment. in our explorers it is illegal to end the system anywhere before the rear wheels

 

[Brian Ward]

Safe, legal, cool duals!

Legality issues aside (you have to have cat on any vehicle that came equipped with them from the factory), lets touch on a few other issues.

1. Back pressure can be maintained even with uneven length exhaust pipes, provided you install a crossover pipe within the first foot or so of the manifolds. This will balance any uneven pressures between each side of the engine.

2. Why bother running "TRUE" duals, anyways? You could have your stock muffler, and everything behind, it removed and then add a single inlet/dual outlet muffler of you choosing and have dual pipes custom bent from there. This would provide the best balance between back pressure, power,sound, and looks. Not to mention cost, as it allows you to keep your stock exhaust from the engine up to the muffler. Cats are not cheap!

3. MOST IMPORTANTLY, FOR YOU OWN SAFETY AND THE SAFETY OF THOSE WHOM RIDE WITH YOU, DO NOT ALLOW THE EXHAUST TIPS TO END ANYWHERE UNDER THE PASSENGER COMPARTMENT AS PER YOUR QUOTE,"IT WOULD EXIT AS CLOSE TO THE MANIFOLDS AS POSSIBLE(BASICALLY RIGHT AFTER THE MUFFLERS). THIS WILL, WITHOUT QUESTION, INTRODUCE EXHAUST FUMES INTO THE PASSENGER COMPARTMENT! EVEN IF YOU AIM THE TIPS AWAY, IT WILL! TRUST ME ON THIS. AS A STATE CERTIFIED MECHANIC, I HAVE SEEN THIS HAPPEN. ALTHOUGH IT LOOKS COOL, IT IS NOT WORTH THE RISK TO YOURSELF OR OTHERS.

Please don't take this as critisism of you or your ideas. You can accomplish your goals without shortcutting legal or safety issues. I have duals on my 98 Eddie Bauer and I think they look great. You can view my picks onder the Before and After forum. The thread is titled Pics of my 98 Eddie Bauer, now with 2(inch body lift). If you have any questions, I will be more than happy to answer them. Thanks for listening.

Brian

 

[DOGMAN]

Ryan,

Nothing wrong with being a motorhead at heart. But.....

In my opinion, with your proposed exhaust system, you won't gain that much performance, you have a better chance of hindering performance.

Many know the analogy of an automobile engine as being essentially a big air pump. In your example, you have increased the ability of the engine to let more air out, but you really havn't increased the incoming air at the same rate. Granted, you have a drop in K&N, but everything else is still stock, so in reality not much more air is needed in your motor.

Now if you were to modify or replace the heads for better flow, or change the cam for more free breathing, or install a blower or turbocharger, then your proposed exhaust system might be worthwhile. A properly matched set of headers is almost always beneficial also.

So unless you're going to modify your engine for added performance, I'd stick with the system you have now. Take the money you would have spent on your exhaust idea and install a new, high performance cam. Your money will be better spent.

 

[Rhett]

To run true duals on a 91-94, you would have to relocate the gas tank (probably to where the spare tire fits) and then relocate the spare tire to a carrier as per Bronco II.
If you could do that it might just work, but you would have to carry your exhaust straight out the back somewhere.

Someone here had the idea of putting dual straight pipes THROUGH the bumper of their Mountaineer. I have seen that on a few lowriders but never an Exp. But like I said any dual straight out would require extensive mod's to fuel tank and other things to work on a 91-94.

 

[Bill Kemp]

Most of us are on this site because we like to have our rides be different/better than the stock X.
We are limited by $, laws, safety and common sense. The last of which my wife thinks I have little of when it comes to "her Explorer".
If you got the pipes comming out the back no one but your muffler man will know the difference. Plus all the money you save in polution fines will finance many more mods.

 

[Ryan91]

Cool, cool, cool....

Hey everyone, I appreciate all the advice given to me about these exhaust ideas that I had...

I seriously doubt now that I'll modify my exhaust to what I originally spec'd out, mainly due to the performance issue and the safety issue.

Anyways, I've learned some stuff and I think it'd be cool to keep on talking about this, because I seriously doubt that I'm the first person to have questions about "true" dual exhaust. Other people can learn from this good advice as well..

thanks guys,

Ryan

 

[Rhett]

Speaking of exhaust,

Anyone know if a person can still get a Borla cat-back for a 2-door 94 with EGR? I know, I know, I missed out last summer on the $165 deal. But at that time I was ironing out little things like spark plugs and shocks. It seems I can only concentrate on 1 thing at a time on modifying my Explorer...

 

[Brian Ward]

Show me the MONEY!!

Originally posted by Rhett Browning
Speaking of exhaust,

It seems I can only concentrate on 1 thing at a time on modifying my Explorer...

That's all I can do at one time also!! Especially when four tires cost $600!! LOL!