This is turning out to be a better discussion tnan I thought! Now when you guys are talking about losing low end torque, how much of an estimate do you think is being lost? I mean if I am losing a few ft/lbs of torque, thats not much to lose sleep over. If I am losing upwards of 10, then thats something I may blink at. I personally don't think a little low end torque loss with 4.10's would be all that noticeable. Then again I have been known to be wrong on a lot of my guesses. I am just trying to find out how big of a loss can be expected and if they outweigh having to tie up the pipes everytime I go to the track.

Chris

Well if you've got a 4.10 posi rear, you should have plenty of low end....that extra low-end torque might actually be a hinderance to you, in terms of traction issues. But I would expect the loss to be upwards of 10 ft lbs down low...but that depends on how much power you're pushing. It cuts bottom end torque down and changes the power curve around a bit, but MIGHT add a little on the top end...but don't quote me on that. What kind of diameter are we talking about here on your pipes...do you have 2.5 in. or 3 in.? 2.5 should be right about perfect for power.

Just so I could never be accused of being closed minded, I decided to call a friend who has spent the last 20 years working on Fords and the last 7 working on performance upgrades on 5.0's with the focus on EFI 5.0's. Here is what he said. If you look at the cams in a carburated vs. EFI 5.0, there is a difference in overlap. When you talk about a carb'd 5.0 you want zero backpressure, because you can tune the car easily for the system and its components via carb, jetting and timing, etc. On the EFI 5.0 you have to be careful. Because the cam was selected to work with back pressure, if the ONLY change you make is in the exhaust system, you may loose some bottom end torque, but you will pick up some top end HP.
You will most likely see no change in your track times for that reason. I then asked what he would recommend, and here is the tricky part. In order to compensate for the design of the motor, it having been designed with a full exhaust, and NO other changes are being made, he said that try to keep the backpressure around 1.5 psi, but if it creeps up to 3 to 4 psi you will begin to loose power. He also said that in a case where you run N2O or a whipple charges and the computer has been updated, the question goes away, because they will more than make up for any loss of bottom end grunt.

In short, I think that everybody was correct. The question still remains, how do you tune for that, and again, this is where its gets tough.

Just one other opinion.

Ron

Nixon, I am running 2.5" all the way back from the headers, whic are shorty 1 5/8". The turndowns would also be 2.5" inch right out of the back of the muffler. I would be keeping the off road h-pipe, and the mufflers, just adding dumps right in front of the differential. I just didn't think taking 2.5 feet of pipe off would make a difference like that. And I definately have traction issues right now on the street due to crappy tires and 4.10's.
Chris

I have the same setup as him, but with tails. now i can tell you this. I went from my stock headers to my Mac unequal shorties. I lost alot of low end torque. didnt even feel like the same car. But what happened was i started to get more top end power from 4500 and up. Basically it moved my powerband. It used to pull hard from 3500 and up, now its at 4500 and up(roughly). so unless your car has a race motor, stick with a full exhaust. I have ran my car with an open exhaust before(no mufflers). it felt like a dog and had no power until 5500 which was a very small difference.

Smaller for the street/strip. high compression or forced induction i would stick with 2.5 to 3". Turbos are different.

Open exhaust IMOP, is only good for high RPM motors. If you engine isnt designed for it then i doubt you would gain from it. I didnt......

Ron1, you are correct, i was talking about resonant tuning. What i was basically saying was i've heard of people using backpressure as well as all the other things i talked about (diameters, lengths, etc.) to tune the torque band of a particular engine to it's intended use, and some engines don't benefit from zero backpressure....basically what you just said :D
This was a good discussion, i'm always up for learning something new.

True.... My Mustang's got no power below, say, 4000 rpms or so. Don't know whether it has factory headers or not, all I know is the guy says they're equal-length. The exhaust system is 3 in. with twin flowmasters and an X pipe.... Even with 3.73 gears in the back it's seriously lacking low end power.... But I revved it up today, and once it hit 4000 it rocketed off....I couldn't believe how high and sharp the power curve was. Damn that 3 in. system.

Well I guess there is only one way to find out for sure with my car, and that is to ditch the pipes, and throw on some dumps. I just don't want to deal with the pipes everytime I go to the track, or if I get some bigger tires on it for daily use. I think this will just cut back on the hassles. Who knows, it may also cause some. I will let you guys know when I finally do it. Thanks for the help.

Chris

My car had the stock exhaust on it when I bought it.

I installed a 2.5 O/R X-pipe with 2 chamber flows dumped in front of the rear axle.

I went from a 15.20 @88mph to a 14.79 @93.3mph.

So my experience was very positive;)