for V8 - dual vs single exhaust ? headers ? high flow cats ?

[68 GT]

I came from a long background of moded Mustangs so I'm thinking all the same rules apply to this 4.6 but the parts don't seem to be available. I really would like to put on some longtubes and high flows cats and dual my ST out with stock GT500 mufflers to keep it semi quiet. Is single exhaust better for torque though on these. Really what would be the highest performing exhaust set up on a 4.6 ST ????

thanks

 

[rhauf]

I came from a long background of moded Mustangs so I'm thinking all the same rules apply to this 4.6 but the parts don't seem to be available. I really would like to put on some longtubes and high flows cats and dual my ST out with stock GT500 mufflers to keep it semi quiet. Is single exhaust better for torque though on these. Really what would be the highest performing exhaust set up on a 4.6 ST ????

thanks

There is absolutely no advantage, ever, to having exhaust pressure. more exhaust staying in the cylinder means less new air/fuel that can come in. restrictive exhaust lowers volumetric efficiency.

in other words, you're exhaust cant breathe too good.. and yes, all the same rules apply as mustangs. if you're engine is stock you wont gain much by exhaust mods as the stock exhaust is adequate for a stock engine. but if you want to change the sound, go for it, IMO on a V8, dual exhaust always sounds better than single.

headers would be nice if you can get them, high flow cats are probably more marketing than results, and good mufflers are always nice. remember, larger diameter pipe = lower pitch, and the mufflers determine how loud it is.

 

[68 GT]

thought I read somewhere that these V8's loose torque with too free flowing of an exhaust set up and guys were recommending sticking with single exhaust for some reason.

wanting to change the sound first and get some performance gains of course while I'm at it knowing other mods and tuning later will benefit more from a better flowing exhaust too.

thanks

 

[rhauf]

thought I read somewhere that these V8's loose torque with too free flowing of an exhaust set up and guys were recommending sticking with single exhaust for some reason.

wanting to change the sound first and get some performance gains of course while I'm at it knowing other mods and tuning later will benefit more from a better flowing exhaust too.

thanks

the "backpressure = torque" thing is a very popular myth. probably more people believe it is true, than realize it's not.. do some research on exhaust scavenging, and exhaust tuning (i mean real reading, not hear-say by others) and you'll find that emptying the cylinder of as much exhaust gas as possible, and filling it with as much new fuel and air as possible, results in the most power. all the time, no matter what. at all rpm's.

if you really want to get confused.. here are some facts
It IS true that (with headers) too large of pipes (both on the header tubes as well as the first couple feet after the collector) will result in a loss in power..
the reason for this, is NOT because of "back pressure" in fact, it's quite the opposite. the smaller header tubes will give more exhaust velocity, and at the collector, the (correct) sized pipe will give optimum vacuum to the adjacent header tube (the tube coming from the next-to-open exhaust port) that vacuum (or just low pressure pulse) will help to draw air out of the next header tube, as well as that cylinder as the valve opens (but once again, if the header tube is too big, it will waste all its draw sucking the air volume from the tube, and the tube will have less velocity). this effect is called exhaust scavenging. it helps to actually suck the exhaust out of the cylinders, giving (possibly greater than) 100% VE to the engine.

"tuned port" intakes work in much the same way, only with vacuum on the intake side of the engine.

 

[68 GT]

thanks I think lol

 

[CDW6212R]

The headers are the most important exhaust part, select them based on rpm's and power levels. Stock headers are 99% of the time too small.

I agree select the mufflers for sound, they affect sound more than everything else.

Power is never lost, you don't lose(not loose) power with bigger exhaust. That is ignorance, because what happened is the A/F ratio changed and not enough tuning was done to correct it.

People keep changing exhaust, but nobody seems to ever retune the A/F ratio. The problem is not the exhaust, it's the altered A/F ratio. Best power occurs at certain A/F ratios, anywhere away from that makes less power. The bottom end shows up more because an engine makes so little there already. If you get the A/F ratio off some at low rpm, ding, "loss of power." The answer is to restore the A/F ratio, all power comes back, plus gains.

Opening up the exhaust leans the A/F mixture.

If you were from the old school, what did you do when you installed big headers and exhaust? Why of course you immediately swapped to bigger jets, to correct the lean condition created by the higher flowing exhaust.

A V8 should have about the equivalent exhaust of two 2.5" pipes, that is a stock V8. Any high performance V8 needs at least a dual 3" exhaust. Do the math for area and figure what that means if you run a single exhaust.

Our SUV's have a great exhaust for an efficient cross over. Normal cars lose what they try to gain with a cross over, because the bends and piping to bring them together creates as much restriction as the cross over is supposed to add.

With a truck the two pipes are typically side by side, and there is room for two mufflers. There's no reason to not have a great exhaust past the point where they come together. Regards,

 

[JohnnyO]

I'm not aware that anyone makes headers for the Gen 2 Sport Trac, either V6 or V8. JBA makes headers for the Gen 1 V6 and if anybody does make them for the Gen 2, it would be JBA. Putting true duals on a Gen 2 will be somewhere between very difficult and impossible because of the fuel tank on the passenger side and very tight clearance around the rear suspension.

 

[kkreit01]

I can honestly say, it feels like I lost low end torque when I swapped to Magnaflow, and cut the resonator out. I'm tempted to try to weld a Magnaflow resonator where the stock one used to be.

 

[68 GT]

thinking I may go side exit on both sides just before the rear tires with a oval shaped tip with rolled edges. I'd like to get the adrenalin side skirts and cuts holes or notch them for the tips if that would hide any exhaust pipeing. I'lll probably find some take off 05-10 Mustang exhaust, or GT500 exhaust to use. I'd love to run some longtubes and high flows cats with a stock Mustang muffler of some sort.

 

[CDW6212R]

I can honestly say, it feels like I lost low end torque when I swapped to Magnaflow, and cut the resonator out. I'm tempted to try to weld a Magnaflow resonator where the stock one used to be.

That may be a perfect example there. If your truck was running anywhere on the lean side before the exhaust work, it became more lean afterwords. Your issue would not be the mufflers, but the resulting A/F ratio due to the higher airflow out of the engine.

From the ideal lean A/F ratio at any given time, altering the airflow will produce less power at that time. Pushing the A/F either way then needs more or less fuel to restore the A/F ratio. PCM Tuners can see that in real time when they monitor a wide band O2 sensor.

I hope that as time passes it becomes very common to reprogram the PCM for common modifications.

 

[eppd00]

eppd00

Did you disconnect the battery for a short time and then reconnect in order for the computer to reprgram?

 

[CDW6212R]

The computers do not reprogram themselves, or learn new airflow conditions. Do not disconnect the battery.

 

[BigV]

I can honestly say, it feels like I lost low end torque when I swapped to Magnaflow, and cut the resonator out. I'm tempted to try to weld a Magnaflow resonator where the stock one used to be.

I do agree with CDW about A/F ratio but restriction is a direct result in high tq numbers. Open up the exhaust and you will lose tq but you gain hp. The more air in and exhaust out=HP. Back pressure will give you TQ but not be an efficient running motor. I have an 03 cobra I ported the blower went to a smaller pulley and increased my boost by 0 lbs. However I gained 60hp but not any significant TQ. Boost is just a calculation of back pressure I could stick a stock exhaust on and gain 3 lbs of boost. It would not result in more HP though. It would give me higher TQ numbers but lower my HP. What is important is the amount of air you are moving. When in doubt check your plugs they should be brown not black indicating rich and not white indicating lean. You are better of rich then lean if you are to lean you can melt a piston.

 

[CDW6212R]

Be careful about comparing a boosted engine to NA, the affects of exhaust work don't always compare between them well.

Also most people know that HP and torque are tied together absolutely. If HP goes up, so does torque linearly, because torque is a product of HP. The equation defines them together, you cannot lose torque without losing HP, or gain one without the other also going up. Remember to see HP and torque at a given rpm, not to talk about one at a different rpm than the other.

Still, the end goal of all of the discussions and work is the same, acceleration, not horsepower. HP does not directly define acceleration, which is why a dyno is a bad measuring device.

Here's the best example I have read about a dyno and HP, versus acceleration. Below is a quote of my favorite cam guru from SBFtech.com, he has a lot of real racing experience to say knowingly.
"Exhaust flow will never slow you down as I have EXPERIENCED.

May it affect the "dyno" yes. But HP derived from exhaust is engine acceleration.

I have said this many times.

Back in the day when a "swap" from a stock H-pipe to an off road pipe was a "big deal", the gain to the tires was 7hp. Read that again, 7HP. If you ran the 2.5" off road pipe, it was 7HP. So here come the corral type mentality that there was no difference in the two.

Really?

The FMS piece (2 1/4) would pick up 2.5 - 3.0 MPH. At 3300# that is an average of 24HP.
The MAC piece (2 1/2) would pick up 3.0 - 4.0 MPH. At 3300# that is an average of 32HP.

But the "dyno" only showed 7HP and it was the same......."

The point is this, don't rely on dyno tests or figures, that is only useful to tune the engine, the A/F ratio and timing. On the road driving, the least restrictive exhaust will be faster than any back pressure or smaller exhaust.

Have the engine retuned to the best A/F ratio and timing, then you're done.

 

[BigV]

I hear you dyno numbers are just that numbers the true test is acceleration like at the track. The most important thing for a fast and efficient running engine is A/F and timing.

 

[CDW6212R]

Agreed, and I wish it didn't have to be said repeatedly. Too many people learn what they know from their one or two vehicles, or magazines. Then they get friendly on places like the Corral and spread those myths.

68 GT, I'm sorry to go so far in detail with this, just a few words only brings out the "I lost torque" crowd. They need to hear this until they get it.

Your 4.6 V8 running close to 6000rpm can easily use the dual 2.5" exhaust just like the old Fox Mustang 302's. Just be sure to reprogram the PCM at the same time.

 

[rhauf]

I do agree with CDW about A/F ratio but restriction is a direct result in high tq numbers. Open up the exhaust and you will lose tq but you gain hp. The more air in and exhaust out=HP. Back pressure will give you TQ but not be an efficient running motor. I have an 03 cobra I ported the blower went to a smaller pulley and increased my boost by 0 lbs. However I gained 60hp but not any significant TQ. Boost is just a calculation of back pressure I could stick a stock exhaust on and gain 3 lbs of boost. It would not result in more HP though. It would give me higher TQ numbers but lower my HP. What is important is the amount of air you are moving. When in doubt check your plugs they should be brown not black indicating rich and not white indicating lean. You are better of rich then lean if you are to lean you can melt a piston.

Are you trying to say it would move the power band downward? if so, i agree with you, to a point - it WOULD move the top of the bell curve (of power output) downward, but only because it would be squelching the top end more, which may (by comparison) make it feel like it has more bottom end.

as far as "less torque but more horsepower" that's sort of a conflicted statement, because torque and horsepower are the exact same thing, "horsepower" is just a way of expressing torque numbers at a given RPM, while figuring the working power based on that RPM.

for instance, 10 ft/lb of torque at 5250 rpm's is 10 horsepower. if you double the RPM (and maintain 10 ft/lb of torque) the horsepower will double in result. if you cut the RPM in half, the horsepower number will become half.

as for the "more exhaust flow = lean" statement, i have not heard (or looked into) this before, but it seems to me that it would only apply in a speed density style injected car. MAF i believe would maintain proper a/f ratio with the added flow, the same way it does when the internal VE of the engine is raised (to an extent) by ported heads etc. of course, you could always raise the fuel pressure in the rail slightly if you wanted. i'm definitely going to look into this theory further though.

on a carb'd car thought, i don't see added flow changing the tune of the carb any, since the carb jets fuel based (crudely) on the air volume passing through the carb. the carb doesn't really care how big the engine is either (with the exception of the obvious, which is that it has enough cfm volume to feed that engine, or isn't so huge the velocity is horrible)

ohh, and fwiw, i believe the "header/manifolds" or whatever they are on a '98 5.0 are pretty good.. they dont look restrictive to me at all.

 

[CDW6212R]

That's the problem we have in explaining this. People are misinformed to think that the PCM does adjust the A/F mixture perfectly no matter what modifications are done. That is wrong. A Speed Density system is completely different and obviously every change alters the A/F ratio.

But it does the same thing in the Ford MAF systems, to a lesser amount, but it happens 100% of the time. If the PCM was magic as people think, then there would be no need for new tunes, chips or flashers. Those things would not gain anything... but they do. They do it by richening or leaning the mixture at given rpm's and conditions. It's minor, but it doesn't take much to make a big difference, a big gain. Some people "feel" it, and some hardly do. But timed at a track is where it shows up.

Look at the example I posted in bold above. I bet that those 2-4mph gains were not just after bolting on the high flowing "H" pipes. Those 24hp or 32hp gains came after richening the engine, some small amount.

Carbs are the same way, yes they allow fuel based on airflow, but it's based on more than that. Find an old race engine builder and ask what happens to the jetting needs as different headers are used.

It really is as simple as calling it fine tuning. The PCM, or the carb, they do very well given what they were tuned for. But for each modification you make, there is a small amount of power being lost or wasted unless or until you fine tune the PCM or carb.

That's how the best racers win at the track, they keep adjusting things(everything), and retest until they find the fastest combination. That includes the PCM and carburetor.

 

[68 GT]

68 GT, I'm sorry to go so far in detail with this, just a few words only brings out the "I lost torque" crowd. They need to hear this until they get it.

no problem good info share away. I guess others need to realize changing exhaust may only shows the intended gains after changing the tune also. It ouwl be interestng to see someone do a custom tune with stock exhaust then change the exhaust only and tweak the tune a little with the exhaust change only to see the real gains possible with exhaust changes.

on a side note I know how people may feel bad about loosing torque regardless if they gained HP or not. A loss in torque on a truck wouldn't be worth a gain in HP for me. Most of the driving in a truck is in the low rpm's where torque is much more important to normal driving, plus IMO a lot more fun. I had a Mustang with 708 RWHP with a centrifigual blower and it was not anywhere close to as fun as driving the exact same car with a twin screw blower that made 70 less HP to the wheels. And that wass on a much lighter Mustang. Trucks need the torque even more. But as said before a tune should fix up a loss in torque from exhaust mods (I hope)

 

[CDW6212R]

I miss my 4500lbs truck since I took it apart a year ago. The 302 feels so much better in normal driving than my V6 99. The V6 sounds quick and does do well at WOT, but the V8 is effortless all of the time. My 302 trans shifted above 4000rpm as I drove it normally, it's a well thought out truck, other than the headers. I want the 347 now though, that will be much better still.