i just bought a 90 lx w/347 that has mac long tubes w 3inch collectors,no cats and 3inch pipes ending into flowmaster 3inch dumps,2 chamber.its way too loud for me so i'm wondering would a mac catback be quieter,and if i went to 2.5 inch system would the 2.5 h-pipe bolt up to the 3inch collectors.the mac web site says they bolt up to all their long tube headers but how?would i be giving up much in the way of performance with the 2.5 system?
mac longtubes
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Just adding the cats will quiet the car a bunch. If they are a good hi-flow cats they may only cost you about 5-10 h.p. By going with the 2.5" exhaust, you will pick up some bottom end and mid range h.p. and torque but may suffer some top end h.p. loss. This of course is dependent on the h.p. and torque curve of your engine now. The 3" exhaust system may be killing the power that the engine makes now. If this is a street engine, my guess is that the 3" exhaust is overkill unless your "street" engine is turning some serious rpm's.
Vipersix
Founding Member
A 2.5" exhaust would actually be better suited for a 347 n/a motor and you may even gain some power. It would obvioulsy be best to have a complete 2.5" system since every bend and diameter change affects the airflow and resonance (e.g. back pressure) of the exhaust, but it won't be detrimental. You will need an adapter to fit the 2.5" to the 3" pipe. Summit sells them for cheap and you can likely find them at any decent local exhaust shop.
95Vert
New Member
I'm betting the 2.5 flange will still bolt up to the 3'' header collector, but that's a guess.
Also the title of this thread made me think you were blaming the headers for the car being loud? In my experience full lengths tend to quiet down an exhaust system, especially inside the car. With a rowdy 347, most mufflers are going to be loud, and i wouldn't go with Mac because they're one of the loudest out there. I'd look into Flowmaster 3 chambers or their Hushpower series if you want it quiet.
Also the title of this thread made me think you were blaming the headers for the car being loud? In my experience full lengths tend to quiet down an exhaust system, especially inside the car. With a rowdy 347, most mufflers are going to be loud, and i wouldn't go with Mac because they're one of the loudest out there. I'd look into Flowmaster 3 chambers or their Hushpower series if you want it quiet.
Because unless you're making 500hp, or running a turbo, you don't need mor than a good mandrel bent 2.5 system. Stepping up to 3'' when you don't need it will just kill off a crap load of low end torque.
95Vert
New Member
How, where, when, who, and why do you say this? Who told you all of that good stuff?
Well, it's a simple fact? Haven't you guys ever read any books on this crap? I'm not talking magazines either. There's a reason cars are manufactured with the size exhaust that they have. In most cases it's not the optimal size when it comes to racing and modifying, which is why people step up from 2.25 to 2.5. The only thing you're going to gain with a 3'' exhaust is maybe a little more top end, and that depends on a whole slew of other things like what RPM you can run and how well your h/c/i can breath.
This is like the people who think running without mufflers makes more power or people who want giant cams in a stock long block, or guys who wanna put an 850 double pumper on a stock 302. There's more to it than just throwing bigger pipes on and expecting to get gains. If your engine doesn't need it, it's not going to do jack crap for gains and might even hurt you in the long run.
I bet next someone is going to tell me that aftermarket mufflers "make power"?
1. The OP here is not 'stepping up' to anything... he already has the 3" stuff. You are proposing to spend money in order to DOWNGRADE.
2. Please present something that might convince me that smaller exhaust will make more torque. There have been a lot of bogus 'tests' done to come to this conclusion... so a good discussion might be worth the time.
I have several books, so maybe we could actually have a discussion here
You don't sound very confident following that BOLD statement with a question mark
I have NO problem with you citing a book or 2 in order to make your argument... but be warned... there are a lot of books out there that are actually WORSE than MM&FF or 5.0Mustang.
I'm not sure you understand how profound that comment is
The factory setup has a CUSTOM intake, CUSTOM exhaust, CUSTOM cam, and even a CUSTOM tune.
As mentioned above... is the COMBINATION of parts being properly selected, or are we running a chassis dyno test in which 2.5" exhaust is being swapped for 3.0" exhaust, without re-evaluating any other components in the setup?
This is like people who think........ backpressure is a good thing for an engine
The OP in this case is not 'throwing bigger pipes on'... The pipes are already there.
Your argument in this case needs to be that the OP will GAIN performance by running 2.5" exhaust.
And that this performance gain will be worth the $$$ to make the downgrade
This is the argument you are making in this thread, correct
I bet next you're going to tell me that backpressure makes torqueI bet next someone is going to tell me that aftermarket mufflers "make power"?
jason
joel5.0
Member
Why have I always run better with a "free flowing" exhaust setup?....... no magazines or books articles here. Does the intake need to be changed/tuned?..... of course! ... one complements the other, that's what "combining" is all about.
Open headers do make more power, if YOU know how to set it correctly, intake included + tune the exhaust........ yep, tune the exhaust. Restricting the exhaust of an IC engine is detrimental towards performance upgrades...... talk about crutches. If you increase exhaust flow and performance drops, it's the intake side you have to work on in order to maximize its potential, not restrict the exhaust.This is like the people who think running without mufflers makes more power or people who want giant cams in a stock long block, or guys who wanna put an 850 double pumper on a stock 302. There's more to it than just throwing bigger pipes on and expecting to get gains. If your engine doesn't need it, it's not going to do jack crap for gains and might even hurt you in the long run.
I bet next someone is going to tell me that aftermarket mufflers "make power"?
You read a lot about Ford heads being "intake biased", yet when a better exhaust flow situation shows up, we continue restricting the exhaust instead of matching the intake.......... ironic or what?
You are the only one making it negative.... or are discussions on a topic that "negative"?
You guys know the Viper comes with 2.5 inch exhaust? If you think you NEED 3 inch exhaust, show me dyno proof before and after and i'll believe you, otherwise you're talking out your ass. You can pick my posts apart, you're arguing your OPINION vs. mine. If 3'' was so manditory, why don't more people run it? I know guys in single diget cars running 2.5 so i would think if they needed 3'' they would have it wouldn't they?
And you're retarded if you think mufflers make power. An engine makes X amount of power and then the mufflers take away X amount of power. Getting aftermarket mufflers only reduces the loss.
And i think by "tune the exhaust" you're trying to tell me about scavenging but you don't know how to word it. Open headers won't make as much power as a properly sized (in length) set of pipes bolted to the end of the headers to enhance scavenging.
I'm done with this thread...too much stupidity for me.
And you're retarded if you think mufflers make power. An engine makes X amount of power and then the mufflers take away X amount of power. Getting aftermarket mufflers only reduces the loss.
And i think by "tune the exhaust" you're trying to tell me about scavenging but you don't know how to word it. Open headers won't make as much power as a properly sized (in length) set of pipes bolted to the end of the headers to enhance scavenging.
I'm done with this thread...too much stupidity for me.
keep all the pipes 3". just put a quieter muffler in its place or just put convertors on. keep the 3" for improvement down the road. trust me u will get the bug for more power when the 347 isnt enough, everyone does it.
jaay allen is building a cam for my buddies 347, hes got mac 1 3/4 primarys ans 3" collectors, jays not telling him to to go to 2.5"
jaay allen is building a cam for my buddies 347, hes got mac 1 3/4 primarys ans 3" collectors, jays not telling him to to go to 2.5"
joel5.0
Member
I didn't care, nor they existed, when I proved that with my little 289 against 350's and a few 396's....... I did it.
Mufflers DO NOT make power... as far as I know, they are "static" components in a setup....... they either "allow or hinder"..... so I agree with you..... but why use a setup that could "hinder".
BINGO!..... you can set for either (closed or open)...... it all depends on the combo..... quite simple, as you have stated yourself. Do you know what an extension "megaphone" does to the exhaust scavenging?....... diameter, length, opening pitch, etc? When you're trying to "tune" a 4 cylinder setup, and a 1" difference is the "win or loose" factor.......
Or is it the information to digest? Why would you limit furthermore, an intake flowing biased setup by choking its exhaust? I know of heads selection suggestions based on their exhaust flow when compared to other cylinder head alternatives....... why would this be different?
Bolded comment #1
Where is YOUR dyno proof of a car LOSING power when going from 2.5" to 3.0" exhaust...
Apply a little logic here...
An engine moves air.
The engines efficiency is determined by how effectively it can move that air.
What happens to efficiency when you add a restriction?
Could you breathe better if you were forced to breath through a straw?
I guess that an asthma attack is actually an indication that one is breathing more efficiently?
Maybe there is wavelength tuning in the lungs/windpipe, and that is why asthma attacks make breathing more efficient
Bolded comment #2....
When was the word mandatory used?
You are suggesting a guy removes 3.0" exhaust in favor of 2.5" exhaust because it will improve his engines performance.
Do you have any proof of what you are claiming? On what basis are you claiming the guy will go faster?
Bolded comment #3...
Then you started with the name calling....
Very nice...
Guys,
If the concept that 'The exhaust being TOO LARGE will hurt low end torque' is so well proven, then where is the proof?
Everyone is saying that it is true, but I don't see any proof, and I never have.
I am asking you guys to bring forward proof of a phenomena that has been readily accepted as fact.
If everyone believes it, then there should be proof all over.
But for some reason we should select an exhaust system based on 'backpressure'
Doesn't that negate all the effort just put into getting an exhaust port that can MOVE air?
Ok,
Here is some dyno proof...
A quote from John Hennesy... 2008 Viper Chassis Dyno Report - Viper Alley - Dodge Viper Forum
There's a ton of video clips out there...
Seems that 3" exhaust can provide more power after all...
EDIT:
the car was otherwise stock from what I can gather...
95Vert
New Member
Why do people that know everything get offended when they're called out? They're asking for proof, yet they can't even explain what they mean.
89_LX
Member
The air intake system and exhaust system work together, the exhaust system can only put out what the air intake system can pull in. they need to be sized in relation to each other.
Too big (diameter) exhaust systems can hurt power/torque if the intake system cant match the volume of air to keep the exhaust system flowing. Air, like gas is a fliud, it has fluid properties and will cool down(and contract) in an excessively large exhaust sytem. As the air cools, it will become dense and heavier, than hot air in a smaller diameter system. this dense heavy air will KILL the VELOCITY of the supposed high flow 3" exhaust system.
Backpressure is not the problem, you dont want excessive backpressure. but you do need enough pressure to keep the exhaust gasses flowing. too large exhaust will allow air to cool and become stagnant inside the system.
If you dont have an intake system that can keep your large diameter exhaust flowing at good velocity then its a waste and can hurt your numbers.
on top of all that putting a huge intake and exhaust system on a stock engine with poor flowing heads is an even bigger waste.
yes you proved a viper made an improvement with a 3" exhaust but put on a 4" or 5" and i bet it will be a dissapointment without other mods. so im pretty sure a 2.5" system will be enough for a 250-350hp v8.
sorry there are no proof in numbers here, but the physical explanation is enough for me to believe
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