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shortie headers

2K views 19 replies 7 participants last post by  Mister_T 
#1 ·
can anyone tell me what brand and the part number of a shortie header that will fit a 93 cougar 5.0,the long tubes look like a ton of work so im going with the shorties to get this car back on the road again.thanks.
 
#4 ·
He ports the 4.6 manifolds, not the 5.0 ones. The 5.0s had tubular manifolds, so there isn't any material to port away. Plus while the ported 4.6 manifolds flow well enough to make decent power, the stock 5.0 MN12 manifolds are absolute garbage. The only good solution for the 5.0s is longtubes, and you won't believe the power difference from just that one mod.
 
#5 ·
The jba's are a little restrictive and a bit of a pain for serviceability and maintenance but are built like brick poop houses. The mac’s are not well designed (individual flanges) and will probably not fit back on if ever removed due to warping but they are bigger than the jba’s if you need the volume.

I cant bring myself to utilize sledge hammer re-engineering on my car to accommodate longtubes. (mostly because the underside of my car looks like it just came off the showroom floor), I ported and ceramic coated a set of macs for mine and they work fine but I also know that I will be using a hydraulic wedge head ram if I ever take them off and want to put them back on again.
 
#7 ·
Actually it is quite the opposite. Longtubes help with low end torque and mid-range. The longer the primary tubes, the lower down in the rpm range they help. But even most longtubes you buy will help you up to around 6K+. To get any kind of scavenging benefits out of a set of equal length shorties, you would need to rev the engine up ridiculous rpms that no street motor will ever see. This is why I always say shorties are completely un-suited for use on any street car. The only advantage they have is that they are easier to install. So if you only want the looks, go ahead and get a set of shorties. If you want any kind of power benefit, do it right and get longtubes, and don't waste your money on a set of shorties.
 
#9 ·
Scavenging is basically a vacuum in the exhaust right as the exhaust valve opens. This helps to suck the exhaust out of the engine, which creates a noticable improvement in power. The vacuum is created by the speed of the exhaust gases from the other cylinders leaving the header. The higher you rev the engine, the faster the exhaust is leaving, and therefore the more vacuum it pulls, and the combination of this speed and the length of the tube affects where in the rpm range this scavenging occurs. I don't know all of the fluid dynamics about it, but the simple version is that longer primaries create scavenging at lower rpms, and shorter primaries create it at higher rpms. I think part of that is because the firing order of the engine is such that you don't always have paired cylinders on the same bank. That's why some high end mid-engined cars you see the headers crossing over from one bank to the other so that each tube can join with the one that is exactly 180 out from it, so as to get the maximum benefit from the scavenging. That would be impossible to do on our cars though due to limited space in the engine bay.
 
#11 ·
ARGGH! The whole "backpressure in the exhaust" thing is another one of my pet peeves!

You never want backpressure in the exhaust, plain and simple. If you had any pressure in the exhaust at all, your power would drop like a rock. Ever drive a car with a plugged-up cat? It probably wouldn't go more than about 30mph, right? THAT is backpressure in the exhaust, and as you can tell, it didn't help the power of the engine at any point along the way. You want that vacuum I was talking about for the scavenging effect, and vacuum is the opposite of pressure. The thing is that vacuum is only created by the velocity of the exhaust gases leaving the pipes. If you open up the pipe without increasing the quantity of exhaust gas that is going through it, you have just decreased the exhaust gas velocity. Decreased velocity causes decreased vacuum for scavenging, which is technically the same as increasing the pressure in the exhaust. So going to too large a pipe is technically increasing the pressure in the exhaust system. I bet nobody on the internet has ever told it to you that way before! Increased pressure (or decreased vacuum, since they are really the same thing) means that the exhaust has to be pushed harder to get out of the engine. This means more of the power the motor made is wasted pushing the exhaust out the tailpipe instead of pushing the car forward. So ANY pressure above ambient atmospheric pressure is going to drastically hurt your power and torque curve all the way across the line. While it is true that putting too large an exhaust on a car can hurt low end, the reason is not because the stock system has backpressure, but quite the opposite it is because the stock system has enough velocity at the lower rpms to create a scavenging effect. On a high perfrormance car, it might be beneficial to you to sacrifice a few lb-ft of torque down low to gain a few hp up top, and that is what the larger diameter pipe does for you because it moves both the rpm at which the scavenging occurs and the rpm at which the exhaust becomes a restriction up higher in the powerband. If you have a completely stock engine, and you don't rev it higher than the factory set rev limiter, and you go put dual 3" exhaust on it, you have just lost some low end torque, but you haven't gained anything up top because the operating range of your engine and the operating range of your exhaust system are now nowhere even close to each other.
 
#13 ·
If this is true, why does catless systems kill torque? I figure the catless setup would allow exhaust to continue moving without interruption, yet every time someone mentions going catless you get people saying not to because they'll lost back pressure, torque, etc etc etc
 
#14 ·
If you lose exhaust velocity, it will decrease torque, and since horsepower is just a function of torque and rpm, it will also decrease horsepower at that rpm. By going too big on the exhaust system, when the engine is turning lower rpms there is not enough exhaust gas going through the system to keep the velocity up. That is why you would feel a loss in low-end power if you have too big an exhaust system. Once the revs start building, there is more gas going through the system, so the velocity picks back up.
 
#16 ·
Well removing the cats and putting straight pipe, you usually won't feel any difference. The big drop in low-end torque comes from when people just punch out the cats. The reason for this is that the cats have a honeycomb structure, and when that is in there in terms of resistance to flow, it behaves pretty close to a straight pipe of the same diameter as the pipe going into and out of it, probably just a little bit more restrictive. If you punch out that honeycomb structure though, the exhaust is going along through a 2.25" pipe, then all of a sudden it hits what is effectively like maybe a 4" diameter pipe, and then it goes back down to 2.25". Doing that means the exhaust velocity drops like a rock as soon as it hits the opened area inside the cat. Also just doing that doesn't get you any gain up top because you are still going through the stock pipe diameter.
 
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