matts85vet

my exhaust needs some work from the end of the headers back.
its 2 1/2" true dual, h-pipe, w/cats no mufflers right now, but its getting rusty and i want to replace it with 3", x-pipe, and some high flow mufflers
anyone regret going to 3" dual?
mods are in sig.

thanks in advance

matt

cv67

its going to resonate a bunch
Id try dual 2.5

mechguy79

My Dad did dual 3" pipes and his car is almost unbearable, noise wise. I did dual 2 1/4 on my stock L98 with no cats and it is MUCH better. If I put on some high-flow cats I think it would be perfect.

Just how much flow do you thing a 350 needs? Dual 3" seems like serious overkill to me.

mnstrlt1

Wow- it's not often i come across a thread that goes against larger volume exhaust piping. Of course, it's going to come down to the use of the vehicle and your end goals.

It looks as though exhaust systems on the c4 platform don't really yield a trumendous amount of power (except for the L98 platform and excluding headers).

I think it comes down to exhaust note rather than power gain in this department.

I think it's also important to note that experienced exhaust guys will tell you that 2.5" or 2.75" pipe is more than enough to support nearly 90% of street application NA small blocks

coupeguy2001

Gentlemen.
It's not the pipes that make the noise, it's the mufflers.
He can have 4 inch pipes with good mufflers, they will be quiet as a cadillac.
as for the 3 inch pipes, they will rob him of the low speed torque, but will be aiding his quest for a high revving engine.

mnstrlt1

There you have it!

BTW- i'm running the magnafow cat-back kit. I eliminated the center resonator. I am currently running the older version of TPIS' long tube headers (wrapped) and NO cats, and this thing is actually pretty quiet!

McGirk94LT1

I figure the factory has to know what they're doing right? Even the ls2 vettes run 2.5" piping. Only the z06 and zr1 run 3" piping. Pretty sure any 350 making little over 400hp (as im assuming yours is) is better off with 2.5".

matts85vet

thanks for all your replies!

i am thinking of this system:

http://www.summitracing.com/parts/PYE-SCC40R/

anyone have it?

why will i lose torque with a 3" system?

87stocker

Back pressure and volumetric effieciency. Its like cylinder heads, if they are too large for what you have to put into it, you will not have good throttle response and there is poor efficiency. Much like your exhaust, if your motor does not have enough flow to fill it you end up loosing your volumetric effiency for the size of pipes you have and you will loose your low end torque. Then as your motor starts flowing enough to fill the pipes your torque range starts coming in again. 3" exhaust is too large for sure.

69427

[QUOTE=matts85vet;1572940099]thanks for all your replies!

i am thinking of this system:

http://www.summitracing.com/parts/PYE-SCC40R/

anyone have it?

why will i lose torque with a 3" system?[/QUOTE]

You won't. That's an old wive's tale that refuses to die.
A larger exhaust system will have less restriction, allowing the engine to get rid of the exhaust easier, and with less residual exhaust gas remaining in the cylinder. Less residual exhaust means a higher VE, and more power.
An engine makes power by being able to pump a lot of fresh air in, and a lot of combusted air out. Any restriction in the exhaust system reduces this (mass) air flow through the engine.
It's just simple physics.

Beach Bum

I put on a true dual 3" exhaust with an H-pipe out through 3" Flowtech Warlock mufflers with a removable plug on my 85 with an 11 second 383 motor.

I regretted it back then.... not because of sound, it was basically the same when I had the Warlocks plugged (A little louder, but not a lot)...... it was because I did not experience an et improvement. True 3" Duals add weight to your car, thus any small gain my motor might have seen with the 3" exhaust, it did not translate to an improved timeslip.... which of course is the goal.

In my opinion, a 350 11-1cr street motor such as yours does not need 3" true duals....there are other places you could improve your set-up with and see an actual et benefit vs Big exhaust.

good luck !

M.J.L.

I have true duals 2.25, no cats, and flowmaster 40 series. It's so loud it sets off car alarms.

mnstrlt1

40 series is definitely loud! that's for sure. prior to my magnaflow, the last owner had installed a set of 40 series mufflers under the car with the stock tips. still retaining the stock exhaust system, the damn thing was LOUD! inside and out!

I think Beach Bum is right, the increased size simply doesn't yield a significant improvement on power.

GlennS87

I never regretted mine

Strick

This is from an old school guy, me. I, too, thought the larger exhaust would yield more power. Then came scavenging. With headers, scavenging actually helps "pull" the exhaust out of the cylinder. If your exhaust is too large the speed of the gases slows down hampering the scavenging effect. I realize that this is splitting hairs for most engines out there. So, my advice is to go for the sound you want and let the horsepower thing fall where it may. You won't lose anything noticable. Now let's talk about C4 verts, with the X-frame, the clearances become very tight and if you don't hang the exhaust just right, it may bang when you hit a bump. If the exhaust touches the frame, resonance will travel right to the cockpit. Not pleasant. Ask me how I know. I think the velocity of the gases through the pipes is a player in removing condensation and improving the sound while reducing the resonance. I've been through several catback exhausts. I have the B&B 3" catback that looks awesome and is very deep in sound. But the one I like the most is just a LT1 stock cat back with muffler elims. I added an extended "H" pipe just before the split to the mufflers. With my Hooker Shorties it sounds the way I like it, aggressive. I'm sure you've seen this set up before.

coupeguy2001

I have true duals with an H pipe, twin cats and 91 factory mufflers that are LT-1 clones with twin pipes.
it's too quiet

Disarray_kid

Would it hurt my 90 C4 vette if I make it where everyone can hardly hear it? If not then what set up should I go for.

87stocker

[QUOTE=69427;1572941078]False.....

I am also a dirtbiker (4stroke) and a street biker (600 ninja) When you change the exhaust you change the power range aswell as sound. I know at best we are talking 4 less cylinders, and in the case of the dirt bike 7 less but the same principle applies. If you take a regular v8 say a 80 malibu and hack the exhaust right off and run it wide open(and thats the ultimate flow), it will have considerably less low end power. Its not until you start revving that you start having some grunt. I actualy had that experience on a highish performance level aswell. My Malibu Wagon had a 9.5:1 400ci small block in it. Nice aluminum heads, cammed, performer intake, 675cfm carb, headers. When that car had open headers it had little to no low end. 2.5" true dual, I could roll those tires all day long. So no its not a wives tale.

87stocker

Wikipedia sourced info.

[edit] Exhaust Scavenging
When an engine starts its exhaust stroke, the piston moves up the cylinder bore, decreasing the total chamber volume. With the exhaust valve opens, the high pressure exhaust gas escapes into the exhaust manifold or header, creating an exhaust pulse comprising three main parts: The high-pressure head is created by the large pressure difference between the exhaust in the combustion chamber and the atmospheric pressure outside of the exhaust system. As the exhaust gases equalize between the combustion chamber and the atmosphere, the difference in pressure decreases and the exhaust velocity decreases. This forms the medium-pressure body component of the exhaust pulse. The remaining exhaust gas forms the low-pressure tail component. This tail component may initially match ambient atmospheric pressure, but the momentum of the high- and medium- pressure components reduces the pressure in the combustion chamber to a lower-than-atmospheric level. This relatively low pressure helps to extract all the combustion products from the cylinder and induct the intake charge during the overlap period when both intake and exhaust valves are partially open. The effect is known as scavenging. Length, cross-sectional area, and shaping of the exhaust ports and pipeworks influences the degree of scavenging effect, and the engine speed range over which scavenging occurs.

The magnitude of the exhaust scavenging effect is a direct function of the velocity of the high and medium pressure components of the exhaust pulse. Performance headers work to increase the exhaust velocity as much as possible. One technique is tuned-length primary tubes. This technique attempts to time the occurrence of each exhaust pulse, to occur one after the other in succession while still in the exhaust system. The lower pressure tail of an exhaust pulse then serves to create a greater pressure difference between the high pressure head of the next exhaust pulse, thus increasing the velocity of that exhaust pulse. In V6 and V8 engines where there is more than one exhaust bank, Y-pipes and X-pipes work on the same principle of using the low pressure component of an exhaust pulse to increase the velocity of the next exhaust pulse.

Great care must be used when selecting the length and diameter of the primary tubes. Tubes that are too large will cause the exhaust gas to expand and slow down, decreasing the scavenging effect. Tubes that are too small will create backpressure against which the engine must work to expel the exhaust gas from the chamber, reducing power and leaving exhaust in the chamber to dilute the incoming intake charge. Since engines produce more exhaust gas at higher speeds, the header(s) are tuned to a particular engine speed range according to the intended application. Typically, wide primary tubes offer the best gains in power and torque at higher engine speeds, while narrow tubes offer the best gains at lower speeds.
Many headers are also resonance tuned, to utilize the low-pressure reflected wave rarefaction pulse which can help scavenging the combustion chamber during valve overlap. This pulse is created in all exhaust systems each time a change in density occurs, such as when exhaust merges into the collector. For clarification, the rarefaction pulse is the technical term for the same process that was described above in the "head, body, tail" description. By tuning the length of the primary tubes, usually by means of resonance tuning, the rarefaction pulse can be timed to coincide with the exact moment valve overlap occurs. Typically, long primary tubes resonate at a lower engine speed than short primary tubes.

Some modern exhaust headers are available with a ceramic coating. This coating serves to prohibit rust and to reduce the amount of heat radiated into the engine bay. The heat reduction will help prevent intake manifold heat soak, which will decrease the temperature of the air entering the engine.

69427

The OP asked about his exhaust system size, not his header pipe size. No one is suggesting three inch primary pipe size.

Your Malibu example is just anecdotal evidence. (In science, you have what we call a "sample size of one". Doesn't mean much.) My Corvette does just the opposite of your car. Mine has more power (due to the reduction in exhaust backpressure) when it's uncorked. When it's uncorked, the engine's pumping efficiency increases (at all RPMs), making it more responsive, and increasing power.
It sounds like your Malibu needs the carburetor looked at. A restrictive exhaust increases the magnitude of the intake reversion pulses, causing the intake air to pass by the venturi multiple times, richening the mixture. A low restriction exhaust decreases the amount of intake air enrichment due to the reduction of the reversion pulse magnitude, leaning out the mixture, often resulting in a power loss. This is a carb tuning issue, not a magical phenomenon where choking the exhaust makes (low end) power.
As I said before, an engine makes power by pumping fresh air into the cylinders, and pumping out the combusted air, with minimal restrictions in the intake and exhaust systems. This is why small throttle sizes and small (restrictive) exhausts are not the hot setup to make power.
As I said earlier, some old wive's tales just refuse to die.