3" exhaust system

[Belgium R/T -68]

My GTX has a 3" exhaust system with standard 440 and stock exhaust manifolds, shouldn't it be better with 2,5"? I get a lot of irritating resonance sounds
from it and I have the feeling that the enginesound isn't as nice as it would be with a 2,5". The mufflers are TTi's standard. When do you need 3"? 

[Just 6T9 CHGR]

I would say 3" exhaust would be warrented on an engine producing over 500hp, with headers.

Stock 440 with stock HP manifolds with 3" exhaust?  Nah....I bet your killing HP with that exhaust on there....not enough backpressure.  2½" would be a better bet

[hutch]

I would say 3" exhaust would be warrented on an engine producing over 500hp, with headers.

Stock 440 with stock HP manifolds with 3" exhaust?  Nah....I bet your killing HP with that exhaust on there....not enough backpressure.  2½" would be a better bet

I never understood why a bigger exhaust system could hurt your horse power?  If you run open headers are you hurting your horse power?  More exhaust flow should be better performace I always thought.

[Goodz]

I thought I had ordered 2 1/2 inch pipes, but now that I am looking at them on the car, they look like 3".  I have a crappy little 318, so dont know if that is hurting my car too much or not.  As long as it runs, I am happy... for now.

[Just 6T9 CHGR]

I never understood why a bigger exhaust system could hurt your horse power?  If you run open headers are you hurting your horse power?  More exhaust flow should be better performace I always thought.

In a way yes....like I said unless you have a high HP engine 3" exhaust will hurt performance.  You need backpressure for exhaust scavenging.  Running open headers on a low HP engine will just be a loud engine, nothing more.

Here is a Q & A from Pypes Exhaust.....

Q:  It seems as though 3" exhaust is the popular choice these days. Is there any disadvantages?
A: Yes! A stock horsepower car with 3" exhaust can lose noticeable low end torque and affect performance. Also, 3" pipe usually requires increased installation precision because of limited clearance issues. As a general rule, cars with less then 450hp should use 2.5" exhaust. Cars in the 450hp range could potentially benefit by a 3" crossover and still keeping 2.5" tails. Cars with 500hp + should utilize 3" or even larger tube size.

A quote from the Dynomax site...

A common misconception is that the larger the diameter, the better the system. Bigger, however, is not always better.Systems that are too large in diameter can actually hurt performance.
As a general rule, switching to a performance system that is 1/4" to 1/2" larger than stock will provide the best horsepower increases. To determine which pipe diameters will perform best with your vehicle's exhaust system, decide what RPM range at which your engine will operate, most of the time. Smaller-diameter pipes will produce low- to mid-RPM torque.Larger diameters produce mid- to high-RPM torque.

[firefighter3931]

My GTX has a 3" exhaust system with standard 440 and stock exhaust manifolds, shouldn't it be better with 2,5"? I get a lot of irritating resonance sounds
from it and I have the feeling that the enginesound isn't as nice as it would be with a 2,5". The mufflers are TTi's standard. When do you need 3"? 

The 3in is a little on the large side for a stock motor but if it's on there i would just leave it and install an x-pipe crossover. This will tone down the volume, increase scavenging and improve torque. 


Ron

[Belgium R/T -68]

Good enough answers for me. 

[hutch]

good points.  I guess it works with the compression of the engine if the pipes are in the correct range based on the engine hourse power?  is it because you rob the engine of compression if you run too big of a pipe when running at below 400hp? 
Is that how the backpressure works into it?

I am just trying to understand how it works.

[firefighter3931]

good points.  I guess it works with the compression of the engine if the pipes are in the correct range based on the engine hourse power?  is it because you rob the engine of compression if you run too big of a pipe when running at below 400hp? 
Is that how the backpressure works into it?

I am just trying to understand how it works.

In a nutshell the idea is to create a scavenging effect in your exhaust system so that the spent gases make it past the mufflers. It's all about velocity and generally the smaller pipes will have increased velocity. If the pipes are too large the spent gases end up being pulled back into the motor (reversion) and dilute the next incoming intake charge....this reduces power and efficiency.

This is where the x-pipe comes in ; the right and left banks work in tandem to pull the spent gases away from the manifolds creating a cleaner intake charge. The siamesed X joint creates a venturi effect....so the motor can inhale cleaner and doesn't have to work at pushing the gases away. The added side benefit is a quieter exhaust with reduced resonating.

That's the abreviated "Cliff Note" version....the long explanation would take several pages to type out 



Ron

[hutch]

good points.  I guess it works with the compression of the engine if the pipes are in the correct range based on the engine hourse power?  is it because you rob the engine of compression if you run too big of a pipe when running at below 400hp? 
Is that how the backpressure works into it?

I am just trying to understand how it works.

In a nutshell the idea is to create a scavenging effect in your exhaust system so that the spent gases make it past the mufflers. It's all about velocity and generally the smaller pipes will have increased velocity. If the pipes are too large the spent gases end up being pulled back into the motor (reversion) and dilute the next incoming intake charge....this reduces power and efficiency.

This is where the x-pipe comes in ; the right and left banks work in tandem to pull the spent gases away from the manifolds creating a cleaner intake charge. The siamesed X joint creates a venturi effect....so the motor can inhale cleaner and doesn't have to work at pushing the gases away. The added side benefit is a quieter exhaust with reduced resonating.

That's the abreviated "Cliff Note" version....the long explanation would take several pages to type out 



Ron

I got it,  will an H pipe produce the same effect than an X pipe if you are running 3" pipes?  I am sorry I am making you type so much. but this is some good stuff that I have been scratching my head on for a while now.

[Just 6T9 CHGR]

IIRC the H-pipe helps with resonance more than the scavenging effect.....

[SeattleCharger]

 

[Belgium R/T -68]

I was wrong about my diameter, it was 2,5". Will I get down the resonancesound by changing to a X-pipe?

[firefighter3931]

IIRC the H-pipe helps with resonance more than the scavenging effect.....

Yep, the h-pipe is more of a balance tube for the right and left banks.

I was wrong about my diameter, it was 2,5". Will I get down the resonancesound by changing to a X-pipe?

Yes, the x-pipe will tone it down and improve performance. 



Ron

[Belgium R/T -68]

 

[Belgium R/T -68]

Mounted today a new TTI 2,5" X-pipe system, have the same irritating resonance even on idle  Could it be that it hangs to stiff? 

[firefighter3931]

Mounted today a new TTI 2,5" X-pipe system, have the same irritating resonance even on idle  Could it be that it hangs to stiff? 

Do your exhaust hangers have rubber isolators on them ? What mufflers are on your car ? Pipes contacting the frame/chassis anywhere ?



Ron

[Mick70RR]

I hace a 3 inch exhaust system on the Road Runner. I fitted an h-pipe last night but I made it so I could split the two sides of the exhaust. It's got rid of an annoying resonance just off idle and toned it down a little so I can almost hear the radio. 

[Belgium R/T -68]

Mounted today a new TTI 2,5" X-pipe system, have the same irritating resonance even on idle  Could it be that it hangs to stiff? 

Do your exhaust hangers have rubber isolators on them ? What mufflers are on your car ? Pipes contacting the frame/chassis anywhere ?



Ron

Have TTI hangers and their dynomax turbo mufflers but it's really hanging very stuck, you can't moove the mufflers a millimeter (0,0394 inch). don't touch the body or frame,
no sound/heatdedeaner inside or coating under.

[Belgium R/T -68]

I am starting to think in the direction that it's my engine concept who gives this resonance sound, could this be? Maybe pocketported -906 heads with larger valves together
with standard inlet and outlet manifolds has a role to play? 

[firefighter3931]

no sound/heatdedeaner inside or coating under.

I think you've found your problem 

Install some insulation under the carpeting and insulate the trunk divider/package tray area and it will quiet down...a LOT.

The SuperTurbo's are pretty quiet mufflers compared to most. 


Ron

[Belgium R/T -68]

Will certainly do so Ron, I also think beeing a convertible, the trunk is really a space for creating resonance and forward the noice. Like a big speakerbox.

[firefighter3931]

the trunk is really a space for creating resonance and forward the noice. Like a big speakerbox.

Exactly !     Insulate the back of the seat/trunk floor and floorpans and it will cut down a lot of noise/resonance 



Ron