Completed Project My 98 super charged EX

Exhausted

CDW6212R,
like you mention, I have to agree with results on real vehicles. Sometimes things just work that are not supposed to and vice versa. When people post their dyno runs and time slips the results speak for themselves.
I don't concern myself with low end torque either(can loose some with bigger pipes), I have enough to spare.
Unfortunately I am limited by certain available parts and space.
Everyone thinks they have more power than they do even me. Online calculators say you need so much power to move a vehicle that weighs 4410 in a 1/4 mile with a time of 12.9. But what about gear ratio's and how about torque.
Some people say to go with an exhaust system with HP numbers 5% or so less than what you think you need. There are a lot of variables that effect things too, I am sure I am not including them all. Just interesting to see some equations to experiment with, and to see 10 lbs of back pressure at wot with my current set up.
I failed to mention that I have a different supercharger, 2 more lbs of boost, and the water methanol since that 13.34. And the 12.93 is a 13.19 in the warmer weather now. The 13.34 was in cold weather also. Cant wait to see the effects of the exhaust work I am having done.

2000StreetRod said:

Do you have stock exhaust manifolds? Do you plan to replace them?

Click to expand...

I have JBA shorty headers, they have a 2 1/4 outlet, the stock ones were 2 inch. The exhaust shop said they could not put 2.5 inch pipes on a stock manifold, but probably could on a 2 1/4 JBA header.

It's a shame no one makes a long tube header for the explorers with 4.0's.

I was thinking along the same lines with how the exhaust cools down and volume drops, a larger outlet probably wont be needed.

I have heard that the tailpipe can effect the flow due to atmospheric pressure trying to push in. I don't know how much that applies to tail pipes that are as long as mine. I think it was more of a short tail pipe where the muffler is almost at the end of the system.

anxious for the results

I have the stock manifolds and the exhaust shop used the first few inches of the stock downpipes. The shop expanded the pipes to 2 1/4 inches to match my high flow cats. Then after the cats the pipes were expanded to 2 1/2 inches to match the Y pipe inlets. The Y pipe outlet is 3 inches to match the Dynomax VT inlet/outlet. I added a 3 inch Dynomax Vortex turndown at the end of the tailpipe to reduce cold start, idle and light throttle driving sound levels.

One review of a Dynomax VT installation compared the results to a "muffler" that was essentially a straight thru pipe. Below 3,000 rpm the RWHP was greater with the Dynomax VT. At high rpm the RWHP was greater (only a few)with the straight thru pipe. Speculation was that the engine airflow was insufficient to fully open the valve and that if the displacement was greater or with forced induction the high rpm RWHP for the mufflers would have been comparable. My results with no changes other than exhaust were an increase in RWHP and RWTQ over the entire engine range at WOT.

One disadvantage of my exhaust system is the sound attracts attention (police) from many blocks away when I accelerate "briskly". For a street and strip vehicle (yours) electric cutouts might be a better choice - quiet on the street and more performance on the strip.

2000StreetRod said:

If you assume that the pressure is constant from exhaust manifold to tailpipe (not necessarily valid) then the volume (CFM) exiting the tailpipe is only 64% of the volume (CFM) exiting the exhaust manifolds.

Click to expand...

This would be consistent with the results I have seen with my rear mount turbo. I did need to get a smaller exhaust turbine housing for it so it would spool. A turbo at the front of the vehicle needs a larger housing than a rear mount and my experience says 2000StreetRods calculation is probably pretty close.

Loud

My exhaust is also an attention grabber, then again so is my supercharger whine. Lucky for me I live in a highly congested area so when I make noise, I just let off after that and if anyone comes around they look right passed my explorer and go after the sportier looking cars. lol.
Normally, I do most of my wot stuff at the track.

Exhaust

Dono said:

This would be consistent with the results I have seen with my rear mount turbo. I did need to get a smaller exhaust turbine housing for it so it would spool. A turbo at the front of the vehicle needs a larger housing than a rear mount and my experience says 2000StreetRods calculation is probably pretty close.

Click to expand...

That is a great example of how the exhaust gases cool and become condensed (smaller volume) at the end of the exhaust system, slowing down and not spinning up the turbo. Really shows a difference from front mount to rear mount. The turbo manufacturer probably used the equation that 2000streetrod posted to figure out what exhaust housing you needed.

If you look at some performance vehicles from the manufacturers you often see the muffler as far back on the system as possible since the effects of a restrictive muffler at the end of the system are minimized due to the exhaust gases cooling. Look at the newer Mustangs and Corvettes as an example.
With the effects of the cooled gases, you can still get a quiet muffler on there and not hurt performance very much.

I am just having the front pipes and cats done right now, later I may try to have quieter mufflers installed at the end where the spare tire used to be.

The factory SOHC 4.0 exhaust manifolds are very good for the engine size and rpm. The aftermarket versions look even better, and only for a high boost engine could they benefit from being a little larger.

The possible tuning inside an exhaust system can only happen in the manifolds and the collector "section", but not after those. A full on drag race vehicle tests the collector length by painting them as extra long pipes, and they are cut off at the hottest point where the paint burns off. That's where the exhaust ends for racing, anything added past that is a restriction and thus cannot tune/gain power.

So for practical purposes, what should be done is optimize that header/collector section, and eliminate or open up the rest as much as possible. Of course we know that sound levels make us do what we do for mufflers etc. Plus a turbo placed in the back requires careful sizing all the way back to it.

I'd find a way to work on the V6 headers, the collectors, making the transition there to the cat pipes as smooth as possible, and sized well of course. That's time and money well spent. Past that the rest is not tuning, but reducing restrictions(back pressure).

Wow, you guys covered a lot of ground. Don, we used to paint the collector and cut as you mentioned. Now, we strap it to a dyno and make changes. As for our trophy trucks (many use mufflers though they are not required), we do see tuning effects all the way through the mufflers including the distance from collector to muffler. Many of our "street cars" benefit from a crossover about 18 inches from the collector as measured from the union of the primaries but sacrifice ultimate HP.

As for formulas, don't forget the boundry layer. That may be why 2000Streetrod has noticed a benefit of larger pipes then those predicted by the formula.

4pointslow said:

My exhaust is also an attention grabber.

Click to expand...

that aint no lie. i have never heard another truck sound like that. i cant even describe it or compare it

Exhaust

joecrna said:

As for formulas, don't forget the boundry layer. That may be why 2000Streetrod has noticed a benefit of larger pipes then those predicted by the formula.

Click to expand...

Care to elaborate on that statement?

Also, which formula?

Thanks!

Actually I was referring to your formulas and the statement by Don in the following post. Sorry that I attributed both to Streetrod. See post #598 .

The pipe diameter and approximate HP supported by that diameter. You must increase the size to account for the boundry layer. That is, the air that is directly against the pipe wall. This portion of exhaust will not flow at the same velocity as the more central exhaust stream. Also, there are Eddy currents generated at every pipe joint, curve and transition from one component to another. In practice this all leads to a need for even larger pipes to minimize resistance. It was Don that made that observation in his following post.

Well said Joe, and thanks for the recognition. It's all been done a million ways. The tough part is going through it all and finding the key details or facts among the tons of less than correct information.

I concentrate on the power potential and look to match the headers and collector portion to that. That's where you should not compromise if at all possible. The 302's need a vastly better and bigger manifold than stock(or FMS or TM).

Then as I've said countless times before, after the collectors you can't really hurt anything by going bigger, it's all some amount of restriction. That's why it's wise to look at many great fast vehicles with similar power, and see what size exhaust they used.

The space under the vehicle is the biggest factor to limit what can be done. These trucks are great for any V6 exhaust in general, since they have much better header space. The front differential makes it hard to fit a decent left pipe near the collector. But behind that there is plenty of room until the rear diff, and then you have to decide what you're willing to do to add a second tail pipe(move spare or left brake line etc).

joecrna said:

Actually I was referring to your formulas and the statement by Don in the following post. Sorry that I attributed both to Streetrod. See post #598 .

The pipe diameter and approximate HP supported by that diameter. You must increase the size to account for the boundry layer. That is, the air that is directly against the pipe wall. This portion of exhaust will not flow at the same velocity as the more central exhaust stream. Also, there are Eddy currents generated at every pipe joint, curve and transition from one component to another. In practice this all leads to a need for even larger pipes to minimize resistance. It was Don that made that observation in his following post.

Click to expand...

Thanks for replying, I wasn't quite sure what a "boundry layer" was, that's why I asked you to elaborate. I am not an expert in airflow or physics and I will never claim to be. I watched some youtube videos to see what you were talking about and kind of figured it was the airflow moving slower against the inside edges. They way you just stated it is very much understandable. Thanks!
I don't know if the 2.2 cfm needed per horsepower took into consideration the Eddy currents or Boundry layers but I would assume so. Again these are not my statements(2.2 and 115cfm), I did not invent them, I am just using them.
The 115 cfm flow was for a straight pipe, which of course is not possible on my vehicle at the moment. Taking in consideration the crazy bends and also the pipe joints a larger pipe would be desirable. Check out the factory bends in this pipe.

Left side

Unfortunately there is no room on the left side with the gas tank in the way.
If I went to a fuel cell mounted under the back in the middle then I could probably have true duals with less bends etc, if it could fit passed the transfercase(got no pics of that area right now).

I wouldn't worry too much about the number of bends or overall length of your exhaust with your application. If you can find someone capable of doing your exhaust using all true mandrel bends, you will minimize restrictions as well as Eddy currents etc. In this HP range this can be good for 10-15 HP. Definatly worth while.

Consider how you will join each "section" of the system together to avoid turbulant (and thus restrictive) flow. Butt joints (if carefully assembled) provide the smoothest flow as opposed to the much more common ball joints or typicle exhaust clamps. One way to hold them together is V band clamps but this can be expensive. This may be good for 2-4 HP.

Remember we are talking about precious few HP. Well within the tolerance of any specific engine on any specific track on any specific day. Generally this is only worth while on all out competition vehicles. Those HP estimates are based only on my experience with many vehicles. As they say, your experience will vary.

Exhaust

I dropped the truck off today at 8:00am for my appointment at the exhaust shop. They called me at 6:30 pm and told me it was done.
I asked for 2.5 inch pipes with high flow cats to the muffler. 6 O2 bungs, and a flange so I can remove the drivers side pipe when I break the transmission again.
I was quoted $900.00 - 1,000.00 just for that.
I believe the bends will look like the ones in my tail pipe, I don't think they are mandrel. It wont be perfect. I cant afford perfect. lol.
I pick it up tomorrow morning, I will probably not be able to do anything to it until Saturday. At that time I will take pictures, and do another back pressure test. Then I have to reinstall the wideband sensor. Next week I am off work, if Tuesday brings nice weather I plan to be at AtcoRaceway testing it out.

One thing that I found interesting is that everyone is kind of on the same page, we all say bigger pipes. No one was on the exhaust scavenging side of the conversation. Great minds think alike right?

Can't wait to see it tomorrow, hope I can sleep.

if you have next weekend off as well, take a drive up to carlisle (hint hint).

Exhaust

OK, it is done.
When I first looked at it, I wasn't sure about the pipe size. It was an optical illusion. I measured when I got home and the pipes are definitely bigger.
The truck is a little louder at cruising speeds. I have not had a chance to go WOT. Back pressure testing should be Saturday if the weather permits.
Here are the pictures.

which cats?

Looks good! I didn't have to worry about the left downpipe clearing the front driveshaft.

Which brand and model of cats were installed?
Are the wideband sensors upstream or downstream of the PCM O2 sensors?

Cats

I don't know what brand they are but they have a O/D larger than 2.5, the 2.5 inch pipes fit inside them.
They look stock too which is what I asked for.

The Widebands are downstream of the pre cat narrowband sensors, but still before the cats. Right now there are just old broken sensors in the bungs, I will be doing back pressure tests then reinstalling my good wideband on bank 2 (D/S) like it was before. In the future I may get the new innovate dual wideband set up with the one gauge.