The Mule rides again (sort of) - pics.

[The Dark Side of Will]

Installed the door detent springs:
http://realfierotech.com/phpBB/viewtopi ... =3&t=17515

Plastic fender repair:
http://realfierotech.com/phpBB/viewtopi ... =3&t=17516

[The Dark Side of Will]

The Jones Exhaust V414R side inlet muffler looks promising: http://www.jonesexhaust.com/products.cfm?ProductTOC=7

Jones also has 4" overall 2.5" flex sections... I emailed them to see if they have any in stock.

The Spin Tech 333SCT muffler looks like a possibility if they can relocate the inlet for me...

[The Dark Side of Will]

Got a start on the X-pipe:











My initial guess was to make the "entrance" and "exit" centerlines align as in the layout above, but seeing that in steel it's obvious that's not enough overlap... Going to have to figure out what a good X-pipe design criteria should be and cut some more before the halves are ready to tack together.

Interesting to see that the donut halves are machine welded and ground down.

[The Dark Side of Will]

Ran it out to the speed limiter in 4th today (115) and the left headlight door popped up... First time that's ever happened for me!

Also hammered through a bunch of math to figure out how far to cut the donuts to get an X-pipe with the window area equal to the remaining cross section of a single tube. I'll get that cut this weekend and see how it looks.

That comes out to the total cross-section at the merge being 1.82 * the CSA of a single tube. Advice from www.corner-carvers.com says the number to shoot for is 1.5-1.75x... Hmm...

[The Dark Side of Will]

In addition to getting started on the 2.5" stainless X-pipe exhaust that I realized I could fit, I swapped out a couple of coil packs.

The "ignition drops" I've mentioned before were getting pretty bad. The car was difficult to drive in higher gears below 2000 RPM under load and pretty much wouldn't pull cleanly from 1000 RPM in 4th or 5th.

I swapped out one of the two coil packs I had out in the shed. It was worse. In addition to ignition drops being at least as bad as the original coil pack, it also had a bad coil and dead miss. Bleh.

The second swapped pack was much better than either original or the first swapped pack in terms of ignition drops and did NOT have a miss. I left it installed. It seems to have ignition drops based more on time than anything. When I was out for the test drive, sometimes it would pull cleanly from 1000 RPM in 5th uphill and not have any problems until it had a cluster of 3 or 4 drops at 1800, then keep pulling. Sometimes it would have 2 or 3 drops at 1200, then keep going. Sometimes it would be clean all the way from 1000 to more than 2000.
The original coil pack wouldn't allow the engine to idle for more than a few seconds before an ignition drop stalled it. The current coil pack allowed the engine to idle for more than a minute when I got back from my test drive. During that period, it experienced a couple of ignition drops, but none of them stalled the engine.

I've never seen the ignition drops happen above 2000 RPM. An ignition drop, if you remember from earlier in this thread, is a momentary loss of ignition. I can be seen by a flicking of the tach, heard in the exhaust note and felt via a split-second power interruption. Since the power delivery is actually interrupted and the tach flickers, the problem must be either in the trigger signal path or power. The trigger signal starts at the crank sensors then goes to the coil pack (ICM) to be translated into something the ECM can understand as well as driving the ICM's tach output, which goes to the tach. Somewhere in that path is the problem.

I guess it *could* be something esoteric with the ECM, causing it to drop the coil trigger signal while keeping the bypass line active. Not sure how the ICM would react to that. I suspect that's a long shot because the tach is showing signs and it is driven by the ICM using crank sensor signals, not by the ECM.

Ideas?

[Atilla the Fun]

Posts like that make it easier to hang on to the obsolete HEI dizzy and the SBC 350 it goes in. Torque at 1000 RPM? ALWAYS!! UNCONDITIONAL!!

[The Dark Side of Will]

Absolutely... being able to completely replace my ignition system in 5 minutes without having to reset base timing is way too practical.

[Atilla the Fun]

And don't forget the fun of re-setting the base timing as the timing chain stretches. But I cheat myself out of that by using Cloyes roller timing sets. $57 per engine. What an idiot I must be, paying $57 to have less fun...

[The Dark Side of Will]

The car habit is all about masochism. Can't blame you for wanting to have less fun.

[The Dark Side of Will]

I got some more metal cut on the tubes...







This time I made the cut such that the area of the ellipsoidal window was approximately the same as the remaining area of a single tube. This gives a total cross section at the merge of about 1.83x the area of a single tube. I've read elsewhere that 1.5x to 1.75x is good.

This looks a lot better than the first cut, but doesn't look quite like all the pictures I've seen of X-pipes.

Yes, I did cut the hole in the 90 a *little* bigger than the hole in the 180. That was accidental. If I pic this configuration, I'll enlarge the hole in the 180 to match. If I cut more, I'll compensate for the difference in these cuts to get them to come out the same.

Thoughts?

[Atilla the Fun]

If you want maximum exchange with minimum loss of cross-section, then spot-weld what you have, make a flat steel strap, wrap that around, fully perimeter weld it, then cut away everything inside it.

[The Dark Side of Will]

Based on pics of other X-pipes that I've looked at on www.corner-carvers.com and seeing how this looks in the steel, I'm pretty sure I'm going to make another set of cuts to make the window larger before having the final product tacked together. This is the basis for what will end up being a fairly intricate welded assembly. Dual exhaust with X-pipe, dual cats and dual mufflers is going to end up being made from four donuts and less than 36 inches of straight tubing.

[Atilla the Fun]

The larger you make the window this way, the more cross-section you lose. Flow is much more important than sound and balance combined. Best to have a smaller window and more cross-section. And while I understand why this looks like the best way to have a crossover, it also disrupts flow the most. The wall you're cutting is where the flow gets re-directed. You're removing it's ability to do it's job.
If you don't want a conventional crossover like real musclecars get, then consider the solutions from MAC Performance and Bassani, and even SLP. IIRC. Maybe I better go look then post links.

[The Dark Side of Will]

An X-pipe isn't just for sound...

Here's what I think an X-pipe does (had already written up for SpeedTalk and Corner-Carvers)

1) Creates an abrupt change of impedance for the pressure pulses from cylinder blow-down. This is the same function as performed by an exhaust "expander box" at the end of the collector, although with a lot less volume required. The change of impedance assures that the tuned length of the collector is correct. I would *not* expect an X-pipe to decouple the headers from the rest of the exhaust system the way that an expander box does, however.

2) Allows both banks to use both pipes. With a true dual exhaust, each bank has use of a single pipe. With an X-pipe, each bank has use of *BOTH* pipes. Double the cross-sectional area downstream of the collectors.

3) Provides "jet pump" effect for opposite bank. The blow-down phase of each cylinder's exhaust strokes occurs during the pump-down (post-blow-down) phase of the previous cylinder in the firing order. When the previous cylinder is in the opposite bank, the venturi effect of the blow down exhaust flow should help create a draw on the exhaust of the cylinder in the pump-down phase. This is the same principle in action as when exhaust flow is used to pull down crank case pressure. This allows one bank's blow-down to enhance scavenging on the opposite bank's pump-down.

4) Reduces exhaust noise. With a true dual exhaust, the entire acoustic energy generated by one bank of the engine comes out one pipe. By splitting the energy of each bank across two pipes, the peak intensity of each acoustic source (which is what we perceive as loudness) is reduced by at least 3 dB. The total acoustic power delivered is the same, but by "spreading it out", the perception of peak intensity is reduced.

5) Changes exhaust sound. With a true dual exhaust, each bank has a pulse output of "bang-wait-bang-wait-bang-bang-wait-wait" (X _ X _ X X _ _ ). The overlap of the two banks and the sequentially firing cylinders in each bank creates the beloved "throb" of a V8 exhaust. With an X-pipe, each pipe transmits each pulse from both banks ( x x x x x x x x )... Smoother and more Ferrari-esque, but not as much so as 180 degree headers (or a flat crank).

6) (Pure speculation... no test results) Changes *WHERE* behind the car the peak sound intensity is heard. In a true dual system, the alternating pulses from each bank create a two-element phased array that's out of phase. This *should* put peak sound intensity at 45 degrees off from directly behind the car. With an X-pipe and both outlets radiating in-phase, peak sound intensity should be directly behind the car

[The Dark Side of Will]

The larger you make the window this way, the more cross-section you lose. Flow is much more important than sound and balance combined. Best to have a smaller window and more cross-section. And while I understand why this looks like the best way to have a crossover, it also disrupts flow the most. The wall you're cutting is where the flow gets re-directed. You're removing it's ability to do it's job.
If you don't want a conventional crossover like real musclecars get, then consider the solutions from MAC Performance and Bassani, and even SLP. IIRC. Maybe I better go look then post links.

I think in the interests of #2 above, I want a large window area to try to split the volume of gas from each bank down both pipes.

[Atilla the Fun]

That might have merit if both pipes were too small. But the goal is to keep the exhaust gas velocity high. Giving it twice the area will result in half the velocity.
For example: with a 440 HP V8, dual 2.25" would be best for velocity, but most guys would say it needs larger pipes. The fact is that NO 2.25" cats and most 2.25" mufflers can't flow as well as a 2.25" 45-degree mandrel bent pipe.
Putting an H-crossover on this example, with no cats or muffs, would help very little, but should alter the sound. However, fit dual 3" instead, and you have way too much area, even without any balancing.
You're gonna do it your way, but I'd do it both ways, use some flex joints to accommodate, and dyno it both ways. Weld up what you pictured above, then do another just like it, but minus the window.

[The Dark Side of Will]

I agree that the goal in header primaries and collectors is to keep the velocity high to help scavenge the port and cylinder.

Downstream, I don't think the velocity will be high enough to be concerned about, ESPECIALLY if the rest of the exhaust is decoupled from the collectors via an X-pipe or expansion chambers.
I think per #3 above, the X-pipe helps the exhaust energy from one back scavenge the opposite bank.

Remember that the exhaust gas loses heat as it travels down the pipe. As it loses heat, its density increases, volume goes down and velocity slows.

With the downstream system, I'm more concerned about noise. I don't want to be getting a noise ticket every block when I get the car DD-able.

According to measurements posted in the thread I started on Corner-Carvers: http://www.corner-carvers.com/forums/sh ... hp?t=45627
The Dr. Gas X-pipe--which is supposed to be the best available, at least for Mustangs--is very close to what I have now... I still think I'm going to cut the pipes a little bit further, though.

[The Dark Side of Will]

If you want maximum exchange with minimum loss of cross-section, then spot-weld what you have, make a flat steel strap, wrap that around, fully perimeter weld it, then cut away everything inside it.

No reason I can't also do this later, after trying it out with the "conventional" setup pictured above.

[Atilla the Fun]

I'm the first to agree that quiet is most important, no sense in being way over-powered if you can't use it. And when a car is way over-powered, then giving up 20 horses is less of a problem.

[The Dark Side of Will]

I don't think the difference between d=0.75 and d=0.625 is going to cost me 20 HP when I also have stock manifolds, 22 degrees less duration on the exhaust and currently have 2" dual straight pipes...

The 2nd cut pictured above is d=0.830. As d gets smaller, the window gets bigger. d is the distance from the centerline of the pipe to the plane of the cut, where the two tubes get welded together.

Speaking of which, I did cut the pipes down to d=0.625 today... pics to follow. They should be tacked together next Friday, BUT with drill in Atlanta next weekend, I won't be able to do much with them until the 29th.