[kscoyote]

Originally posted by Justang
dude, that is absolutely not true. It's the exact opposite.

LT's are the way to go, wether it's a track car, or street car, LT's will improve HP and TQ. LT's will increase TQ way more than a shorty would ever dream of. I have shorty's but that's only because I have to worry about emissions.

And LT's only delete 2 of our cats (we have 4). So technically you will still pass the sniffer, but you won't pass visual. I have been toying with the idea of LT's so I can get my TQ numbers up.

But a set of headers won't give you any power gains on a stockish car. Wait till you're pushing more power. The consensus is that the stock tubular manifolds can handle up to 300bhp before you need more.

And for a good cam you need to go to Redlined Performance Mustangs. They have a cam that is making awesome power! A couple guys are making upward of 220rwhp with just the cam and no porting! It's the 207/215 cam that I have. Unfortunately I was gonna do that, but then I decided to stroke the engine... now I've got a cam that's too small for what I have. ahh well, still has great driveability. This cam will require new springs though. Here's the website: http://www.rpm-mustangs.com/
The owner is an awesome guy, great customer service. I reccomend him to everybody! A really great guy with an awesome product!

Nope, the long tubes have longer individual tubes which scavenge the exhaust manifold more effectively, making for low backpressure. this is important for high RPM engines.

Look at all the drag racers, they use long tubes, not short - unless they are street/strip machines.

[revmaynard02]

Go with JBA headers if you do. They are built far better than MAC and also much much easier to install. I have heard of several V6's gaining power on the dyno with headers. They were not huge, but still 9RWHP is a nice gain any day.

[Justang]

first, the Boss V10 was never made. so it doesn't matter what they put on it. But I don't see the point of your post. 'splain.

second. you're still wrong about the LT's. LT's produce more TQ for the same reason long runners produce more TQ. Resonating Frequency. It has been said that 30" primaries are the best for the 3.8 Mustang. 22-24" primaries are best for the people who want to rev really high. And it's a general consensus that shortys are never ideal for any setup.

read this and enjoy... this will explain why LT's are better for TQ:

"Inertial scavenging and wave scavenging are different phenomena but both impact exhaust system efficiency and affect one another. Scavenging is simply gas extraction. These two scavenging effects are directly influenced by tube diameter, length, shape and the thermal properties of the tube material (stainless, mild steel, cast iron, etc.). When the exhaust valve opens, two things immediately happen. An energy wave, or pulse, is created from the rapidly expanding combustion gases. The wave enters the header tube (or manifold) traveling outward at a nominal speed of 1,300 - 1,700 feet per second (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity). This wave is pure energy, similar to a shock wave from an explosion. Simultaneous with the energy wave, the spent combustion gases also enter the head tube and travel outward more slowly at 150 - 300 feet per second nominal (maximum power is usually made with gas velocities between 240 and 300 feet per second). Since the energy wave is moving about 5 times faster than the exhaust gases, it will get where it is going faster than the gases. When the outbound energy wave encounters a lower pressure area such as a larger collector pipe, muffler or the ambient atmosphere, a reversion wave (a reversed or mirrored wave) is reflected back toward the exhaust valve without significant loss of velocity.

The reversion wave moves back toward the exhaust valve on a collision course with the exiting gases whereupon they pass through one another, with some energy loss and turbulence, and continue in their respective directions. What happens when that reversion wave arrives at the exhaust valve depends on whether the valve is still open or closed. This is a critical moment in the exhaust cycle because the reversion wave can be beneficial or detrimental to exhaust flow, depending upon its arrival time at the exhaust valve. If the exhaust valve is closed when the reversion wave arrives, the wave is again reflected toward the exhaust outlet and eventually dissipates its energy in this back and forth motion. If the exhaust valve is open when the wave arrives, its effect upon exhaust gas flow depends on which part of the wave is hitting the open exhaust valve.

A wave is comprised of two alternating and opposing pressures. In one part of the wave cycle, the gas molecules are compressed. In the other part of the wave, the gas molecules are rarefied. Therefore, each wave contains a compression area (node) of higher pressure and a rarefaction area (anti-node) of lower pressure. An exhaust tube of the proper length (for a specific RPM range) will place the wave’s anti-node at the exhaust valve at the proper time for it’s lower pressure to help fill the combustion chamber with fresh incoming charge and to extract spent gases from the chamber. This is wave scavenging or "wave tuning".
From these cyclical engine events, one can deduce that the beneficial part of a rapidly traveling reversion wave can only be present at an exhaust port during portions of the powerband since it's relative arrival time changes with RPM. This makes it difficult to tune an exhaust system to take advantage of reversion waves which is why there are various anti-reversion schemes designed into some header systems and exhaust ports. These anti-reversion devices are designed to weaken and disrupt the detrimental reversion waves (when the wave's higher-pressure node impedes scavenging and intake draw-through). Anti-reversion schemes include merge collectors, truncated cones/rings built into the primary tube entrance and exhaust port ledges.

Unlike reversion waves that have no mass, exhaust gases do have mass. And since they are in motion, they also have inertia (or "momentum") as they travel outward at their comparatively slow velocity of 150 - 300 fps. When the gases move outward as a gas column through the header tube, a decreasing pressure area is created in the pipe behind them. It may help to think of this lower pressure area as a partial vacuum and one can visualize the vacuous lower pressure "pulling" residual exhaust gases from the combustion chamber and exhaust port. It can also help pull fresh air/fuel charge into the combustion chamber. This is inertial scavenging and it has a major effect upon engine power at low-to-mid range RPM.

If properly timed with RPM and firing order, the low pressure that results from gas inertia can spill-over into other primary tubes, via the collector, and aid the scavenging of other cylinders in that bank.
There are other factors that further complicate the behavior of exhaust gases. Wave harmonics, wave amplification and wave cancellation effects also play into the scheme of exhaust events. The interaction of all these variables is so abstractly complex that it is difficult to fully grasp. The author is not aware of any absolute formulas/algorithms that will produce a perfect exhaust design. Even factory super-computer exhaust designs must undergo dynamometer and track testing to determine the necessary adjustments for the desired results. Although there are some exhaust design software packages available, the author has found none that embrace all aspects of exhaust physics."

this too... but to a lesser extent:

When a pulse of sound ( exhaust gas acoustic pressure front ) hits an open
volume it generates a negative pressure wave that travels back up the header
to the exhaust valve. We want the negative peak of this wave to arrive at the
time both valves are open "overlap" to gain maximum effect. That is the
theory behind ram tuning exhaust. With the ability to swamp that effect with
the Helmholz resonance, think ringing a bell - with a variable sized bell - we
can retune the resonance downward as much as practical.

Since the only thing that matters ( assuming a reasonably well designed
otherwise exhaust system ) is the arrival of this negative pulse, we need only
measure the instantaneous port pressure in this crankshaft angle region and
then tune the system to a maximum negative pressure.

Adding blind volume to the resonating volume simply lowers the resonant
frequency - a good thing since the additional volume does not have to flow
gas. Adding area/shortening the length of the tuned pipe raises the resonant
frequency.

so... we know what length our primaries should be for TQ and for high revvers. And we know understand resonating frequency and why it's important to exhaust. Thus we can conclude that LT's are better for TQ. Shorter exhaust primaries are better for high end HP. And shortys are never wanted... (unless your me, and don't want to deal with LT's at this point. )

Race cars have longer tubes because they are tuned to the exact specs of the engine.

[kscoyote]

Originally posted by Justang
first, the Boss V10 was never made. so it doesn't matter what they put on it. But I don't see the point of your post. 'splain.

second. you're still wrong about the LT's. LT's produce more TQ for the same reason long runners produce more TQ. Resonating Frequency. It has been said that 30" primaries are the best for the 3.8 Mustang. 22-24" primaries are best for the people who want to rev really high. And it's a general consensus that shortys are never ideal for any setup.

r.[/i]"

this too... but to a lesser extent:

When a pulse of sound ( exhaust gas acoustic pressure front ) hits an open
volume it generates a negative pressure wave that travels back up the header
to the exhaust valve. We want the negative peak of this wave to arrive at the
time both valves are open "overlap" to gain maximum effect. That is the
theory behind ram tuning exhaust. With the ability to swamp that effect with
the Helmholz resonance, think ringing a bell - with a variable sized bell - we
can retune the resonance downward as much as practical.

Since the only thing that matters ( assuming a reasonably well designed
otherwise exhaust system ) is the arrival of this negative pulse, we need only
measure the instantaneous port pressure in this crankshaft angle region and
then tune the system to a maximum negative pressure.

Adding blind volume to the resonating volume simply lowers the resonant
frequency - a good thing since the additional volume does not have to flow
gas. Adding area/shortening the length of the tuned pipe raises the resonant
frequency.

so... we know what length our primaries should be for TQ and for high revvers. And we know understand resonating frequency and why it's important to exhaust. Thus we can conclude that LT's are better for TQ. Shorter exhaust primaries are better for high end HP. And shortys are never wanted... (unless your me, and don't want to deal with LT's at this point. )

Race cars have longer tubes because they are tuned to the exact specs of the engine.

That's from Hot Rod a couple of years ago, I've read the article more than once. . . .

"It may help to think of this lower pressure area as a partial vacuum and one can visualize the vacuous lower pressure "pulling" residual exhaust gases from the combustion chamber and exhaust port. It can also help pull fresh air/fuel charge into the combustion chamber. This is inertial scavenging and it has a major effect upon engine power at low-to-mid range RPM.

If properly timed with RPM and firing order, the low pressure that results from gas inertia can spill-over into other primary tubes, via the collector, and aid the scavenging of other cylinders in that bank.
"

Most are NOT timed correctly, and the LT headers from MAC seem to me to be copies of V8 headers more than computer optimized headers.

Only a dyno will tell, but unless it's part of a system (such as Holley's). LT headers will generally lose torque.

Mainly because you lose backpressure which affects computer performance.

[Dom]

first, the Boss V10 was never made. so it doesn't matter what they put on it. But I don't see the point of your post. 'splain.

Have you not seen any of the new 5.0 or MM&FF Magazines?

http://www.mustang50magazine.com/50m...8_0402_cvr.jpg

They have had it build for awhile. It's been on Rides on TLC.

[Justang]

Seriously, this place is just full of misinformation. It's pathetic.

LT's will give you more TQ than shortys.

LT's > equal length > shortys > stock

backpressure won't be affected that much. Hell, I have Mac shorty's right now... I'd stand to gain some good tq if I got some LT's.

[kscoyote]

Perhaps, but you can't just put on a set of headers, based upon other applications and think it will work.

Why did you put the MAC shorties on when most testing shows you lose both hp and TQ?

[kscoyote]

The Hot Rod article you quoted was about building your own custom headers. If you have the manufacturing capability, by all means go for the LTs and build 'em to spec.

But, there's a reason Ford put the shorties on most of it's applications, and that is for American drivers and the torque needed for stop and go traffic and for expense.

For custom high revving vehicles (read SVT) they use long tube headers. (Focus and Mustang). I suppose SVT doesn't know as much as we think they do.

The MAC headers were originally built for 94-97 3.8L vehicles. I've NEVER seen a dyno that shows they're anything more than eye-candy.

Given the difference between the heads, the flow of the engines, and the engine management software, do you REALLY think these are the best headers for a 99+ application? Much less a modified application?

Show me the dyno, my friend! And I'll believe you, but there's nothing gained from comparing a hypothetical custom tuned LT application to mass production spec headers.

[Justang]

I had the headers on my 3.8 when I was just doing bolt ons. Honestly, before I knew what I was doing. I want LT's so I can get more tq.

You are still wrong. They don't put shortys on cars because they produce more tq. I'm starting to wonder if you just sit there and think things up and figure thats what the engineers were thinking too. They put shortys on because that's whats cheap, that's what will fit. It really comes down to money.

And have you ever looked on a new SVT... like say... the Cobra? They don't come with LT headers. gimme a break.

Mac primaries are about 26" long. As stated before, with the resonance frequency, we want our primaries to be about 30" long. And high revvers want about 22-24" long. You can see the Macs LT's are still a compermise. Really the best thing to do is build your own.

As for them not being made for our cars. I don't see it. I've stated they are a compermise, the best thing to do is to make your own so you get the primary length you want. But either way, I'd choose the 1.65" ID for the tubing. And I'd probably make the length about 30". Basically that's the macs, with the length extended 4". So are you trying to tell me that the 3.8L single port, and 3.8L split port are some how different displacement wise?

Here's the end result that can't be argued. LT's are the best way to go no matter what your setup. The longer the primary, to a certain extent, will produce more tq. The shorter a primary, to a certain extent, will produce more top end power. We know that 22-24" is great for a 3.8 that wants to produce lots of top end hp. And we know that 28-30" is optimal for power throughout our powerband. Therefore, LT's are the best for everything... you just have to adjust your primary length accordingly.

Shortys are NEVER the answer. Unless you only want a small upgrade. 'Cause they are better than stock.

[kscoyote]

"The wave enters the header tube (or manifold) traveling outward at a nominal speed of 1,300 - 1,700 feet per second (this speed varies depending on engine design, modifications, etc., and is therefore stated as a "nominal" velocity)."

The wave is dependent upon head design not necessarily displacement.

"The author is not aware of any absolute formulas/algorithms that will produce a perfect exhaust design. Even factory super-computer exhaust designs must undergo dynamometer and track testing to determine the necessary adjustments for the desired results. Although there are some exhaust design software packages available, the author has found none that embrace all aspects of exhaust physics."

Very true.

[kscoyote]

http://www.steedafocus.com/charts/charts10_3.htm

[kscoyote]

The Big Tube Test

This is a great example of how larger headers affect the power curve. The larger 1 7/8-inch headers lost a tremendous 47 lb-ft of torque at the bottom of the curve. By 3,400 rpm, the big headers were actually making a little more than the smaller 1 5/8-inch headers. This may be a hiccup with the smaller header power curve that could be addressed with jetting or timing had we spent more time on tuning. By 4,400 rpm, the smaller headers were making as much as 33 lb-ft more torque than the larger headers. Then by 5,600 up through 6,600, the larger headers took over and made as much as 26 more horsepower at 6,600 rpm.

If you look at the average power curve numbers, you can see that the larger headers actually made slightly less average power. That's because the horsepower gain at the top did not completely make up for the torque loss at the bottom of the curve. So what's the bottom line here? If this engine is going into a light car with a manual trans and a deep rear gear, or at least an automatic with a stall speed of no less than 3,600 rpm, the larger headers might be a slight advantage. The important point here is that a 13/4-inch header is probably the answer, since it would improve the low-speed power while not sacrificing nearly as much horsepower at the top end.

Another point worth mentioning is that what we're seeing here with these two primary-pipe-diameter power curves is not really as much about power loss or gains as it is about moving the curve around where the engine makes its best power. Had we tested a set of 1 ¾-inch headers, we're confident we would have witnessed an average power increase over the other two primary pipe diameters. This merely reinforces the idea that engines operate best when outfitted with the right set of parts that complement the rest of the engine package.

Test 7: A 406ci small-block Chevy outfitted with a set of Dart Pro 1 heads, a healthy mechanical-roller camshaft, a set of Hedman 1 5/8-inch-diameter primary-pipe four-into-one headers, and a 2 ½-inch exhaust using a pair of Borla XR-1 mufflers.
Test 8: The same engine outfitted with a set of Hedman 1 7/8-inch-diameter primary-pipe four-into-one headers with the same Borla exhaust system.

[kscoyote]

Y'know what now that I'm looking at this stuff, I think I may be confusing Big Tubes with long tubes . . .

[Ron]

Good info, and good research. Thanks for posting this.

[Justang]

well, yeah, if you go to big the exhaust gasses lose velocity. Yeah, that's no good. bigger tubes are goona hurt you... well you want bigger, but not too big. Longer is a different story.

That Focus chart kinda proved my point. The LT's produced more hp/tq than the shortys. The race headers did more... but we don't know the specs of the race headers... I'd assume they were an LT as well. Just a better designed LT. for the focus anyway.

so anyway, the stuff I posted about length and all that should be some really good info the spread around here.

And although I highly reccomend not getting headers on a stock car because you won't see a difference... if you do have to do it, get LT's 'cause you'll get good gains, even on a car with bolt ons. But I'd highly reccomend putting your money elsewhere.