IS this exhuast too much, or not enough...(yes ANOTHER thread..)

fastsc92

Registered User
Time to do my exhaust again. I currently run consistant 12.7's @108. As it is now the exhaust is: ported manifolds, no cats, flowmaster resonator, 2.5 middle section into dual 2.25 to dyno max muffs. Basically...very very restrictive for my power levels. Here is what i have floating around in my head, but not sure if its too big or not big enough.

Long tube headers ( 1 5/8...2.5" collectors), no cats, magnaflow resonator dual 2.5" in, single 3.5" out, 3.5" middle pipe, flowmaster y-collector into dual 2.5" into dual borla xr-1 muffs.

My concern is whether to go 3" for a middle section or 3.5". I think the dual 2.5" pipes into the resonator should be fine, but I dont want to be too restrictive after that, and also not too big either. I have a great knowledge of these cars, and have gone the exhaust route before, but its time to upgrade. I know exactly how i want to route it all...just need to make a desision on a middle pipe so i can order my resonator and not hurt my low end power with too big of an exhaust, but also not be holding back power.

I've heard that the magnaflow and borla muffs make a great combo that sound good and flow great. Overall they are expensive, 90 for the res and 135 each for the muffs, but I hope they are worth it. I'm not really too concerned with the sound of the car, i love the way mine sounds now with the cam, and dont want that flowmaster v6 sound. Just want a nice tone to it, with no rice.

Anyways, please don't take this as another basic exhaust thread that we see every day. I'm just trying to judge the size of my middle pipe and the combo that I have chosen. Let me know if its too small or too big or hopfully just right for my set-up. I currently put down about 330rwhp running a 65 shot of nitrous. I hope to hit 350 rear wheel once i make a custom front mount and do this exhaust.
 
fastsc92 said:
Here is what i have floating around in my head, but not sure if its too big or not big enough.

Long tube headers ( 1 5/8...2.5" collectors), no cats, magnaflow resonator dual 2.5" in, single 3.5" out, 3.5" middle pipe, flowmaster y-collector into dual 2.5" into dual borla xr-1 muffs.

Why not just go with a the dual 2-1/2" inlet and outlet magnaflow muffler (resonator)? That would free it up just a bit more than the single 3-1/2" and less tourbulence due to dual pipes going into one? Just a thought.

I'm doing mine in Dec, and going with that set-up with Borla's out back...good to hear that it sounds good.
 
I dont know if i want to mess around with squeezing two pipes past the tank. Right now there is one 2.5 pipe in there and its tight, I dont want to struggle with two pipes. I'll be doing all the bending myself with a mandrel bender.
 
I've got cats and a single 3" pipe on mine, it's not too restrictive because I've pulled as much as 374 rwhp on motor and 459 rwhp on the bottle with it. But I do think no cats and the 3.5" center pipe would be better. It isn't going to hurt performance to have the 3.5" pipe and will give you plenty of room to grow, so you might as well go as big as you can.

David

PS: I thought the long tube headers came with a 3" collector.
 
David Neibert said:
I've got cats and a single 3" pipe on mine, it's not too restrictive because I've pulled as much as 374 rwhp on motor and 459 rwhp on the bottle with it. But I do think no cats and the 3.5" center pipe would be better. It isn't going to hurt performance to have the 3.5" pipe and will give you plenty of room to grow, so you might as well go as big as you can.

I tend to disagree just a little with this. I would not go 3.5" as I feel it will really hurt your driveability, throttle response and hp below 5000rpm.

Mandrel bent 2.25" pipes with 3" center section will keep velocities up and therefore reduce pumping losses. Stay with very unrestrictive resonator/mufflers. I don't think David's exhaust is hurting him at all.
 
"Big Dawg"

David Neibert said:
I've got cats and a single 3" pipe on mine, it's not too restrictive because I've pulled as much as 374 rwhp on motor and 459 rwhp on the bottle with it. But I do think no cats and the 3.5" center pipe would be better. It isn't going to hurt performance to have the 3.5" pipe and will give you plenty of room to grow, so you might as well go as big as you can.

David

PS: I thought the long tube headers came with a 3" collector.
I'm not making as much pwr as Uncle Dave or XR7Dave, & I went with the Big Dawg SCCoA exhaust. No Cats, No resonator. Yeah it's Ricey, but that only a problem for people behind me!

68COUGAR
 
XR7 Dave said:
I tend to disagree just a little with this. I would not go 3.5" as I feel it will really hurt your driveability, throttle response and hp below 5000rpm.

Mandrel bent 2.25" pipes with 3" center section will keep velocities up and therefore reduce pumping losses. Stay with very unrestrictive resonator/mufflers. I don't think David's exhaust is hurting him at all.


Dave,

I based that reccomendation on the fact that Kurt K. has the 3.5" center section and his car doesn't suffer with poor throttle response or other driveability issues. I believe that John Shelton also has the 3.5" center section.

It just seems like a waste to go to long tube headers and then limit the center pipe to only 3". A 3" pipe may be plenty for any of our cars, but the ones with 3.5" don't seem to be suffering either.

David
 
David Neibert said:
I've got cats and a single 3" pipe on mine, it's not too restrictive because I've pulled as much as 374 rwhp on motor and 459 rwhp on the bottle with it. But I do think no cats and the 3.5" center pipe would be better. It isn't going to hurt performance to have the 3.5" pipe and will give you plenty of room to grow, so you might as well go as big as you can.

David

PS: I thought the long tube headers came with a 3" collector.
I'm using mustang long tube headers in my application, and they have 2.5" collectors. I just wasn't sure if dual 2.5" into a 3.5" then back into 2.5" would be too much. I really dont want to hurt any low end power.

XR7 Dave said:
I tend to disagree just a little with this. I would not go 3.5" as I feel it will really hurt your driveability, throttle response and hp below 5000rpm.
Mandrel bent 2.25" pipes with 3" center section will keep velocities up and therefore reduce pumping losses. Stay with very unrestrictive resonator/mufflers. I don't think David's exhaust is hurting him at all.

So you think I should go 2 1/4"??? and not 2.5"?. Like I said, not sure what is too much, seeing that I wont be running cats, and having 2.5" long tubes, dont want to loose lots of low end. The car pulls great now, but I'm def loosing mid range as the exhaust just cant keep with the MP blower and cam.

Basically I'm very un-sure what resonator to order. I think the dual 2.5" pipes into the resonator should be good, and back into duals for the back half. Now for the middle section...I'm still undecided. I'll prob. be making roughly 350rwhp on nitrous, and 300 without.
 
Do you know that you have to modify the mustang long tubes to work. I hear that they are a real bitch too.
 
Yes i was aware of that. I have a mandrel bending machine available to me, as well as a tig, stick, mig, and torches in the gararge. Its great when your dad is a welding instructor. LOL. I plan to make new lengths of primaries on the drivers side to clear the steering.
 
So do you guys think the dual 2.5" before the res is going to be too much?

Also, its still up in the air about what to do for a middle pipe. Is 3" good for my application, or should I step to a 3.5". Oh... decisions decisions.... :rolleyes:
 
I don't think 2.5" down tubes are too big, and as I've already said I don't think a 3.5" center pipe is too big either....especially if your running nitrous or plan to go with a more agressive cam or better flowing heads in the future.

I totally agree with what Dave is saying if it were a Normally Aspriated motor, but I don't think high exhaust velocities and scavenging is a concern on a Forced Induction motor.

Dave knows alot more about these cars and motors in general, but this is one of those rare times that we don't agree. It's for that same reason that I don't think long tube headers are needed either.

David
 
I thank you for your knowledge on this subject and others that I've had in the past that you were able to help clear up. I'm really just more worried about loosing a lot of low end and throttle responce. I think i should be ok, seeing as I will still be running a resonator and dual muffs to keep some back-pressure there.

As for running the long tubes, I just dont think the stock manifolds are cutting it, and its time to up-grade. Basically the only reason I am running long tubes, is because it is going to cost me about $150 total(including the price of the headers) to moddify the new headers that I have. So it was a matter of using the stockers...or going for something that flows good like these.

I have heard that on a N/A car, you want to use the exhaust scavaging as much as possible. And header selection is important. This is why they make equal length headers, so that the gasses in each cylinder have to travel the same distance. But on a forced induction car like you said, it seems the major concern is being about to get the exhaust out the easiest and quickest route.

However, I could be wrong on this subject, but I hope it all made sense.
 
I think 2.5" is perfect going into a dual in dual out resonator. Long tubes arent going to do anything but help you and i agree with doing them because they are cheap and you are willing to do the work necessary to make them fit.
Correct me if i'm wrong but LT's give you about 10-15hp over stock manifolds. It might be even more since you are currently running 12's. The advantage of having the LT's is going to be good enough to where 3" mid-section and a 3.5" mid-section just wont make much of a difference if any at all.

I would do a 2.5" out into the mufflers also. You could get cut outs for track only use. That helped me alot. I only use them at the track though.

My exhaust consist of 2.25" downtubes into 2.5" pipe, then that goes into cutouts. after the cutouts i have two individual summit glasspacks y-ed into 3" midsection and y-ed back out to 2.5" into two hooker aerochamber mufflers. It's quiet, smooth and it sounds good. Its obviously a good exhaust set-up since i ran my time listed in my signature with only exhaust and an intake with a stock late model blower.
 
hey fastsc92 could i aks you a HUGE favor , if you get the magnaflow/borla combo could youe please get a soundclip i ve heard good reviews all around but no one seems to be able to get a sound clip of the borlas.
 
I will, but wont be able to do it for a while. Here is my current sound clip of my car....ported manifolds....no cats. flowmaster resonstor into a dynomaxx cat back. The quality isn't that great, but I'd like to mimick this sound that I have now.

http://home.comcast.net/~fastsc92/my_idle.wav

I think 2.5" is perfect going into a dual in dual out resonator. Long tubes arent going to do anything but help you and i agree with doing them because they are cheap and you are willing to do the work necessary to make them fit. Correct me if i'm wrong but LT's give you about 10-15hp over stock manifolds. It might be even more since you are currently running 12's. The advantage of having the LT's is going to be good enough to where 3" mid-section and a 3.5" mid-section just wont make much of a difference if any at all.

I would do a 2.5" out into the mufflers also. You could get cut outs for track only use. That helped me alot. I only use them at the track though.

My exhaust consist of 2.25" downtubes into 2.5" pipe, then that goes into cutouts. after the cutouts i have two individual summit glasspacks y-ed into 3" midsection and y-ed back out to 2.5" into two hooker aerochamber mufflers. It's quiet, smooth and it sounds good. Its obviously a good exhaust set-up since i ran my time listed in my signature with only exhaust and an intake with a stock late model blower.

I'm going to go into a single middle section rather than dual pipes after a single resonstor ( single in, dual out), only because of the tight fit. Like i said...its still up in the air with my decision of that pipe. I think 3" will be enough seeing i'm using long tubes and no cats, but should I risk loosing low end....hmmm....still doing more research online on this subject.
 
A 3" mid-section will be good. What ever you lose low end you will gain on top end performance with exhaust so it will help you more than it will hurt you. I dont think that you will lose any low end off of the size of the mid section. If anything you will lose low end from having LT's without cats, but like i said, it will help you with top end performance.
If you have an early model SC, i would see a 3" mid-section as a minimum size because of all of the numerous bends you have to form in it where as the late model SC's have a little bend into the mid-section and then it goes straight on back.
Like you and i have just stated, the advantage of the LT's makes it so that 3" and 3.5" wont make a difference, so go for the 3" because it will be easier to work with.
 
i'm not a guru on this subject, but to me it would make sense to do what D. Neibert said, because with forced induction, it's all about how well the supercharger can keep the boost up inside the engine in combination with an extremely low backpressure exhaust system. I would think that the limiting factor would be backpressure from the heads (reaching the flow limits). The supercharger would have a large influence on exhaust velocity and scavenging i would think. In an N/A car, there's nothing to push it out hard, so exhaust velocity and pipe diameter would be a concern, imo.

Does this make sense- anyone??
 
I dont' propose to be guru either, but basic facts remain and the use of those facts rather than anyone's personal recommendation is going to result in the ability to make an intellegent choice rather than blindly following someone's suggestion.

First of all backpressure is not in any case good or desired. Backpressure can be compared directly to boost. Boost PSI is not good either. I would much rather achieve 200% cylinder filling without any boost than achieve 15psi. Unfortunately that is not possible except with the use of nitrous. Boost and back pressure are necessarily evils in the system. Effective boost and back pressure are key to good performance.

The fact is that 15psi can be achieved at 200rwhp whereas a 200% cylinder charge will result in closer to 400rwhp. 15psi (2x atmosphere) does not mean that you are achieving 200% cylinder charge. A similar effect occurs in the exhaust. Back pressure in and of itself does not help anything. However there is a trade off where increasing exhaust velocity improves scavenging of the gasses. The trade off is an increase in back pressure. When back pressure is induced because of exhaust velocity, it is good (up to a point). Increasing backpressure by any other means than reducing the size of the pipes (and hence increasing and maintaining gas velocity) is detrimental to performance.

Simply installing cats or mufflers to achieve back pressure is akin to reducing intake valve lift to increase boost. Doesn't work that way.

Back pressure is simply a condition that is measureable like boost and that can, all things being equal, be used to "guestimate" flow capacity of a system. If you size your exhaust pipes correctly so as to achieve a certain amount of backpressure as a result of the velocity of the exhaust gas, then the results are positive. This is simply a matter of keeping internal volume constant as you move down the system and minimizing any blockages.

It takes time to get the exhaust out of the pipes. It also takes energy to move the gas down the pipes. If the energy inherent in the gas itself can be used to move the gasses along, it's like free HP. If however, the exhaust is allowed to cool and lose its velocity before it exits the pipes, then HP is required to move it out. An exhaust that is too large will actually create back pressure all on it's own. Keep in mind that you cannot simply use dry flow data from a flow bench type device to measure flow capacity in an exhaust system. Gas temperature and speed are inseperable from the equation.

That being said, I do not believe that back pressure created by an excessively large exhaust system is an appreciable factor when under boost. In fact it largely won't even occur unless you get ridiculous with size. When the motor is operating under boost it acts like a 450cu engine and can actually effectively use a pretty large exhaust system. However, when naturally aspirated (232ci) our motors are pretty anemic and can't really spare the additional HP to empty out a huge exhaust system. Consider that a stock 3.8 makes 145hp, then add to that our heavy crankshaft and non-tuned intake manifold, and our motors are lucky to put out 110hp naturally aspirated.

Therein lies the challenge with creating an effective exhaust system on an SC. Making it small enough for the V6 yet freeflowing enough for big HP numbers. Contrary to popular conceptions around this community, exhaust back pressure is not the evil empire that destroys headgaskets. A reasonable amount of back pressure will not seriously hamper your performance under boost. Supercharged engines simply are not that sensitive to exhaust back pressure.

I have to ask, how much time do you spend driving in boost? Are you willing to trade your low rpm performance and economy for power under boost? Most would say "to a point, yes". Well, just how much will you sacrifice? What if we were to say that a big exhaust system releases 5 hp at 5500rpm vrs a moderately sized one, and robs the same 5 hp at 1500rpm, what is the trade off? Well the 5 hp at 5500rpm is worth about the same 5 in torque at that rpm. However, at 1500rpm the 5hp translates to almost 20 ftlbs of torque which is nearly a 10% loss. How attractive does that look now?

Would you notice that loss in a car that has an AOD with a loose converter? Well, since a loose converter will not fully load the motor at less than 2500rpm, the answer would be not as much as the 5spd car that sees 100% loading at all rpms.

Taking these things into account can help you decide for yourself what is best for you without relying on the experience of others. I'm not going to talk about what exhaust I have because I don't have any previous performance comparisons to draw from and therefore really don't know if or how much it helped or hurt my performance and therfore do not feel that I have any information would be helpful in your decision other than to say that mine is on the smaller side and it seems to perform well enough. Use the facts and decide for yourself.

:)
 
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