IROCBOY

I'm looking for an exhaust system for my otherwise stock IROC-Z. What system will give me a deep muscle car sound? (I have a 305 with single cat)

No4NJunk

Flowmaster! Beat ya mark Haha! If you want a very deep sound then have turn downs put on.

Mark A Shields

Hooker cat-back, I can't believe you beat me, damn Monday Night Raw.

Sound clip is in the signature.

IROCZTWENTYGR8

iTrader: (1)

LOL

Flowmaster!!

spartyon

CHERRY BOMBS, hey i like mine

No4NJunk

LOL!! I'm on a mission.

One of the only things we agree on.

jesse83cfi

ok first get full 3 inch exhaust (some exhaust shops tell u that they can't do it but they really can so make them)
remove cat before u get the 3 inch tho
flowmaster 3 inch in 2 1/2 out 80 series
3 1/2 inch boom tubes (basically big chrome tips)
hooker shorty headers 1 5/8
custom y pipe 2 1/2 inch
this exhaust supposedly flows better then
dual 2 1/2 inch so go with this and u wont be dissapointed

i got the exact same exhaust on my car and man does it
sound like a damn big block marine boat
ive scared a bunch of 5.0 and 4.6 mustang gt's with the sound
of her, i usually dont have to rev it up to scare them when i ask them to race, they just say no man ull beat me and i tell
them it's just a little exhaust work and they still refuse to race!

No4NJunk

beats duals????

You don't know what you're talking about.

Go with duals. I would put money on my system flowing better than yours jesse, especially with the H-pipe.

jesse83cfi

no really single 3 inch is better then 2 1/2 duals on our cars i sh*t u not! ask an exhaust shop which is better for our sbc and they'll tell u single 3 inch!

No4NJunk

Kid me not huh? lets do the math..

Area=PI (3.14) *Radius (squared)

Meaning area=(3.14)*radius*radius

now

Area of dual 2 1/4 -7.95 sq inches
Area of the single 3"-7.07
now if we subtract out the thickness of the walls (because we want to know the inside area).
14 guage pipe- (.064")
for single 3
1.5-.064=1.436
3.14*1.436*1.436=6.478
for dual 2 1/4
1.125-.064=1.061
3.14*1.061*1.061=(3.523)*2=7.0735 sq inches

More....now say it with me now....A R E A!!!

not to mention that the single exhaust uses a Y pipe which is a bottle neck. Think about it. A lot of turbulence and gases meeting at one smaller pipe.

now lets add in the possibilities of and X pipe or H pipe which BTW is NOT availiable on the single system. HUh....wonder why stangs run duals from the factory. Probably not because they don't flow as well. I also wonder about the 1st and 2nd gens running duals. The only reason singles where put on our cars was for ground clearance. But there are ways to get around this.

I have results with my system. Do you??

BTw- I used dual 2 1/4 instead of 2 1/2 for your advantage and also because this is what I have. Do I need to do the math for you on dual 2 1/2??

88Bravo

the best sounding system, first your motor can't handle the 3" pipes. The size of the pipe goes right with the hp your motor puts out. I am not sure what you have for funds, but your best bet is to start with a "Y" pipe and headers. Second, gut the cat if you can. And as far as the muffler goes, flows are nice but if you have the money, I would go for the Ravon. It runs about twice as much, but has a sound all its own. I have a stock 305 and when I rev my motor to 4 1/2 to 5 and let off it crackles. Almost sounds like a 350. The other muffler to look at is the loud mouths. I am sure you can find a web site that has a sound of them. Once again they have a sound all there own.

Mark A Shields

Like No4N said, 2.5 duals flow more than 3", 2.25 duals is what is comparable to 3", but 2.25 duals still have slightly more flow than 3" plus they don't have the y-pipe, which is an advantage.

jesse83cfi

single 3 inch is good up to what 300 or so hp at least before u need bigger diameter pipe?
then dual 2 1/2 is for about 400 hp-450hp before
u need bigger pipe
how many third gens do u know that have over 300 hp that arent heavily modified?
this guy has a STOCK iroc z and if u go with duals u loose back pressure. but with single 3 inch u dont loose near as much back pressure so in his case bigger isnt always better!
do i need to get diagrams for u guys to show u that exhaust experts prefer single 3 inch over 2 1/2 duals for better performance gains with 305's and 350's under 300hp?

Mark A Shields

But you said 3" outflows 2.5" , which it doesn't. Now yes, 3" would be better for him than dual 2.5"s.

Hg

jesse83cfi: I'm pretty sure(but don't quote me) that 3 inch pipe can handle something like 400hp or so before you need a bigger system. And you don't want backpressure either...

No4NJunk

Mr. Guy who knows it all but can't provide proof,
You obviously haven't been around cars very long. You said they flow better. I provided sufficient data for my point. Duals create more horsepower and torque. Duals will out perform single 3 on any system. Yeah, go ahead and bust out your diagrams. This should be interesting.

BTW-Backpressure is bad. So a lose of backpressure would allow more horsepower.

Also BTW- I've seen lots of bolt on Z's over the 300 Hp level.

Like I stated before, the later 80's stangs came with the same Hp level as the later Z28s.....and guess what........THEY HAD DUALS.

I wonder why??!!

Mark A Shields

No4N, wouldn't 3" be better for a near stock motor, it decreases the backpressure, but doesn't allow too much velocity like 2.5" duals would for that motor. Just askin. Either way I guess what it loses in one area, it would make up for in another.

No4NJunk

Mark,
Think about it. The later fox bodied mustangs had 302s. That is a much smaller displacement than our engines. They came with duals. Now if it was too much velocity, which IMO would be a good thing because of its effectivness with exhaust scavenging, then why would they incorporate this system on their cars. Less backpressure and less resistance=better breathing engine. ANYTHING that goes towards helping an engine breath will better performance.

I've never heard of an engine losing perfomance by having a better breathing exhuast on it. NEVER. Duals will provide less backpressure, more air velocity to help with scavenging, and less resistance (y-pipe equals bad, causes turbulance).

Now whether IROCBOY wants to spend the money is his choice. I say go for it but if you don't have the money to burn, which i completly understand, then go for whatever you can afford. The duals for my car did not cost that much and have not sacrificed any ground clearance.

IROCZTWENTYGR8

iTrader: (1)

HP-------Single----Dual
200-300----3"------2.25"
300-400---3.5"-----2.5"
375-450----4"-------3"
450-550---4.5"-----3.5"
550-650----5"------3.5"
650-800-------------4"
800-1000-----------4.5"
1000+---------------5"

Mark A Shields

Yeah, but the Mustangs came with 2.25" and 4 cats.

No4NJunk

I know. I'm just usingg them for arguements sake. The 4 cats usually don't stay on very long .

Man I'm ****ing drunkk.

StngKlr

True duals would cost more money I think. And if you opt for true duals, get an X-Pipe.

Either way get Flowblocker.

Mark A Shields

Don't you know you shouldn't drink and type, someone could get hurt.

No4NJunk

AAAHHH. Well that was fun. And 12 buds later.......

Mark I couldn't really write too much last night. I was kinda inebriated:sillylol: .

As for the duals. The mustangs did come with 2 1/4 but I was just using them as a reference. They still flow better than 3" (refer to my post up near top with equations) so this is what I was using for my "real life" example. As stated before the better an engine breathes and the easier the engine can get rid of its waste the more power it will output. Duals no matter what size (2 1/4 and bigger) will always outperform the single 3". Now whether it costs more I don't know. I know the guy who owns the muffler shop so I got a great system at a nice price. Most people don't have this luxury and that's why I told IROCBOY to get what he can afford.

Jesse,
How about those big diagrams you've got.

Synapsis

Having less backpressure reduces low end torque, but increases high end horsepower. So, for around-town driving it could be considered a loss of performance. But who drives 35 mph all the time, eh?

Our engines have such an abundance of torque that I don't believe you'd notice. I'm talking from experience on smaller engines. A 2110cc VW engine with a 1-3/8" tuned header system and a straight pipe exhaust has a lot less torque than with dual mufflers, and you can actually feel it.

My 4400 pesos worth.

Mark A Shields

OH, boy five7kid, just said in another post he would slap someone the next time they said that.
BACKPRESSURE IS BAD, AND DOESN'T GIVE YOU TORQUE

Synapsis

Come to Arizona and take a ride in the car I'm talking about. It didn't make sense to me either, but with a 16" straight pipe in place of dual mufflers low end power off the line is less, and my top end is 3-5 mph faster.

I'll agree that increasing flow will increase power, or else I wouldn't have spent all the cash for my headers and exhaust. There is a low end increase over the stock components I had on the car before, and I'm sure there's a high end increase as well, limited by the TPI manifold. *But*, there is a point of diminishing returns. Putting an exhaust too big for the engine will drop low end torque and increase high end horsepower in my opinion. Why do drag cars have straight pipes for less flow? You spend more time in the higher RPMs where a higher horsepower figure would benefit, as opposed to low end torque which is only good for you off the line.

I invite anyone to take a ride my VW and see the difference. In an all-steel car with already low torque, any difference is clearly noticable. And with a practically vertical windshield, any top end difference is also noticable in a car you can run flat out and still not be going much over 100. I'd be glad to take the car to the track to test the theory, but it has no seatbelts, battery tie down, etc.. etc..

Mark A Shields

It doesn't have to make sense, you're confusing backpressure with velocity. Backpressure will never help you.

Synapsis

Isn't backpressure directly related to velocity? I.e., backpressure reduces velocity?

No4NJunk

thank you synapsis.
That is exactly right. There is a little loss in torque but part of that is due to the fact that the peak torque is moved higher into the rpm range. Peak torque IS increased though.

Mark,
Send five7 BOY in here and we'll take care of this real quickly! I know exactly where to get some more info on this.

Glad you brought that point up Synapsis. The fact is you will not lose any PERFORMANCE.

And like mark said earlier, what you lose in one area you more than make up in another. (ok...so its not an exact quote)

No4NJunk

During the exhaust stroke, a good way for an engine to lose power is through back pressure. The exhaust valve(s) open at the beginning of the exhaust stroke, and then the piston pushes the exhaust gases out of the cylinder. If there is any amount of resistance that the piston has to push against to force the exhaust gases out, power is wasted. Using two exhaust valves rather than one improves the flow by making the hole that the exhaust gases travel through larger.

Backpressure is exactly what it sounds like. It is a high pressure area or system in the exhaust that blocks other gases from getting by. This is in a way related to velocity because the velocity is slowed because of the Backpressure. Velocity is where the power comes from.

No4NJunk

edit double post

No4NJunk

HAHA! Gotta love multiple posts

What you have to understand is that exhaust leaves the cylinders with a high pressure "front" and and almost vacuum for a "tale". This is what "pulls" the exhaust through the pipes. The vacuum created pulls the pulses through. When one high pressure pulse meets backpressure, another high pressure area, you get a collision that is detrimental to performance. If you think about it, you'll realize that since stock exhausts are so good at restricting that they'll actually ram the exhaust pulses together and actually make pretty darn good low-end torque! But this sacrifices horsepower which is not good nor is it efficient.

What does all this mean?? Well basically backpressure is BAD!

also, exhaust gas is hot. And we'd like to keep it hot throughout the exhaust system. Why? The answer is simple. Cold air is dense air, and dense air is heavy air. You don't want an engine to be pushing a heavy mass of exhaust gas out of the tailpipe. An extremely large exhaust pipe will cause a slow exhaust flow, which will in turn give the gas plenty of time to cool off en route.

This brings me to my next point. I was wrong in one of my statments.

EEEET! Wrong. What I meant to say was that the 2 1/4 and 2 1/2 will outperform. Any bigger than this and the above statment would apply therefore resulting in loss of flow and loss of power. I personally don't feel 2 1/2 is too big at all and obviously 2 1/4 isn't either. dual 3" might be a little much but not dual 2 1/2 or smaller. I wasn't completely wrong but wanted to clear that up.

Jesse......Still waiting!

Mark A Shields

I just want to clarify something, NO4N, in your reply saying synapsis was right, it sounded like you were saying you need some backpressure, then you clarified it saying it was bad. Just wanted to make sure I was reading it right, I think I confused myself at the beginning.

Don't mind me , I just woke up.

Synapsis

I didn't say you needed backpressure. I said that with less backpressure you lose low end torque, in my personal experience.

No4NJunk

no mark I wasn't saying he was right about that part. I was saying he was right about losing low end torque and that velocity and backpressure are related. But there are more variables in this equation to just go around saying that "this is this" and "that is that". Backpressure is BAD. But the way a restrictive exhaust works as I stated above brings low end torque. When going with a higher flowing exhaust this low end torque is not lost so much but merely "lifted" higher into the band. The peak WILL be greater. Mark you were right though, about the backpressure being bad.

bobbysbird

Hey there you guys
I am thinking about putting 2 1/2 duals on my 305 92 Firebird. I am thinkilng I will have to pretty much make it myself, but what I was really wondering is the low end torque going to be effected greatly or minimally??? Thanks guys Rob

Mark A Shields

Depends, but I would say for 99% of 305s you won't need that much dual 2.25s would be your best bet.