2.5 to 3.0 Exhaust

[CluelessMopar]

I have a 69 Dart with a fairly stock 360 and 2.5 inch exhaust currently. If I go to 3 inch exhaust with an H-pipe will that cause any loss of scavenging since I'm operating around 8:1 compression? I'm trying to see if going to 3 inch will ultimately do more harm than good.

 

[roccodart440]

What size are your collectors? That is what size your exhaust should be.

An H pipe will always be advantageous, partly in balancing each side, but also in quieting it down a bit. An X-pipe is better in function, but not always possible.

 

[33IMP]

I have large exhausts on my cars, (3 and 3 1/2), but for your low compression 360, 2 1/2 is just about perfect. Going to a three in your case will gain nothing but loud, and maybe hurt.
Engine masters have done 2.5 vs 3 on both a stout big block, and a mild 350/383 .
Big benefit on a 600 hp big block, nothing but louder on the small block.

 

[CluelessMopar]

What size are your collectors? That is what size your exhaust should be.

An H pipe will always be advantageous, partly in balancing each side, but also in quieting it down a bit. An X-pipe is better in function, but not always possible.

Yeah I probably should have specified that, my apologies!

I have TTI headers with a 3 inch collector. I was also thinking about going the X-pipe route but from what I've heard in videos it's not as "muscle car" sounding, a bit more modern. I'm hopefully trying to achieve a loader, deeper exhaust sound without sacrificing whatever performance I currently have.

 

[CluelessMopar]

I have large exhausts on my cars, (3 and 3 1/2), but for your low compression 360, 2 1/2 is just about perfect. Going to a three in your case will gain nothing but loud, and maybe hurt.
Engine masters have done 2.5 vs 3 on both a stout big block, and a mild 350/383 .
Big benefit on a 600 hp big block, nothing but louder on the small block.

I did see that episode of Engine Masters but I knew their 600 hp setup is going to have drastically different results than my setup. I primarily have a stock 360 with Sniper EFI & Hyperspark setup. So I have a tad bit of performance added, but no changes have been made to the cam, heads, etc...

 

[TT5.9mag]

3” will definitely get you louder but there will be no performance gain, or loss for that matter, between the two with a mild/stockish 360. I’ll say this, if you introduce drone in to the system with 3” exhaust youll hate it.

 

[toolmanmike]

3" exhaust on a stock 360? Nope.

 

[abodyjoe]

i don't think it will hurt any but is a waste of money if ya have a good 2.5" system on it already..

 

[Scody21]

I’m right at 400 HP out of my current setup in my 340 in my 72 duster. Have TTI headers ( that don’t hit the ground) to 2.5 in with H pipe, to Moroso spiral flows and then over axle to rear exit under bumper. Car sounds great. Has a nice deep rumble, and once the motor starts spinning high, it’s like open headers. The nice thing about this setup, is you can talk inside the car with the windows down cruzing at 2800 and not be over ran by loud exhaust. I’m leaving it alone this winter when I pull the motor for YellowRose stage “crazy” ported Eddy RPM heads and airgap along with a cam swap. So long story short, best thing you could do is dump your mufflers for something with less packing and keep the money in your pocket from not buying 3in pipes and build yourself a “hot rod” motor.

 

[33IMP]

Agree with above. Keep your system, change the mufflers. Lots of people like dynomax ultraflow. I've used magnaflow, hooker aero, and Flowmaster. I love my fm's, lots don't because of the drone, but mine don't drone. I certainly wouldn't endorse a two chamber flowmaster.

 

[CluelessMopar]

Agree with above. Keep your system, change the mufflers. Lots of people like dynomax ultraflow. I've used magnaflow, hooker aero, and Flowmaster. I love my fm's, lots don't because of the drone, but mine don't drone. I certainly wouldn't endorse a two chamber flowmaster.

That's probably a solid idea. Add the H-pipe and swap out the mufflers. I'll have to check those brands out. Appreciate the suggestions!

 

[rumblefish360]

The “X” pipe sound doesn’t pulsate between pipes like a true dual or an “H” pipe will. When your at WOT, the exhaust will shriek as if it is turning another 1,000 - 1500 rpm’s higher. It is an awesome sounds, not a crappy one.

The X pipe is ever so slightly better than an H pipe. This is according to the “Engine Masters” show. How much it changes at other HP levels IDK but would bet a weeks check it ain’t much via the price of a change over for us street guys.

You would do much better figuring out how much of a header collector extension the engine wants for added low speed torque more than anything and then add on your cross over before a pressure wave termination box. Make sure you add in the cross over length as a part of the whole of the collector extension length before the pressure wave termination box.

The finish up your exhaust system. Go to a car meet and check out exhausts. Ask the owner what he did and has for “That Sound!”

 

[CluelessMopar]

The “X” pipe sound doesn’t pulsate between pipes like a true dual or an “H” pipe will. When your at WOT, the exhaust will shriek as if it is turning another 1,000 - 1500 rpm’s higher. It is an awesome sounds, not a crappy one.

The X pipe is ever so slightly better than an H pipe. This is according to the “Engine Masters” show. How much it changes at other HP levels IDK but would bet a weeks check it ain’t much via the price of a change over for us street guys.

You would do much better figuring out how much of a header collector extension the engine wants for added low speed torque more than anything and then add on your cross over before a pressure wave termination box. Make sure you add in the cross over length as a part of the whole of the collector extension length before the pressure wave termination box.

The finish up your exhaust system. Go to a car meet and check out exhausts. Ask the owner what he did and has for “That Sound!”

I saw someone once suggest that you make lines on your exhaust with crayons and where the crayon marks burn off is typically where you want to make your connection for either a H-pipe or X-Pipe. Would you say that's a fair analysis?

 

[rumblefish360]

No. This is an excellent old racers trick that has merit but has to much wiggle room for error. Secondly, that is not where the H or X pipe goes, that’s where you cut off the pipe to run open headers or add the pressure wave termination box. The H or X should be before that….
Technically speaking

 

[roccodart440]

Yeah I probably should have specified that, my apologies!

I have TTI headers with a 3 inch collector. I was also thinking about going the X-pipe route but from what I've heard in videos it's not as "muscle car" sounding, a bit more modern. I'm hopefully trying to achieve a loader, deeper exhaust sound without sacrificing whatever performance I currently have.

So with that, the 2.5 is fine, the 3" is optimal. There is no reason to choke an exhaust down in size after the collector.

The X-pipe will not hurt the sound of your engine.

 

[rumblefish360]

So with that, the 2.5 is fine, the 3" is optimal. There is no reason to choke an exhaust down in size after the collector.

The X-pipe will not hurt the sound of your engine.

Agreed! 100%
The X will sound different once your around 4,000 - 4500 rpm. By then, you have no concern. Everyone will hear the difference and be blown away.

 

[CluelessMopar]

So with that, the 2.5 is fine, the 3" is optimal. There is no reason to choke an exhaust down in size after the collector.

The X-pipe will not hurt the sound of your engine.

Good to know! I didn't know that about the collector.

 

[d1970]

if he goes to the bigger 3 inch exhaust, he going lose some low torque, that what's get the car moving. Especially with a low compression motor, less back pressure with the 3 inch then 2 1/2.

 

[rumblefish360]

if he goes to the bigger 3 inch exhaust, he going lose some low torque, that what's get the car moving. Especially with a low compression motor, less back pressure with the 3 inch then 2 1/2.

Back pressure, or the lack off, has absolutely nothing to do with a lack of torque. None would be the goal. This has been proven time and time again.

A properly designed exhaust system can make more power than open headers for street, street/strip cars. Here again, zero back pressure is the goal.

 

[AJ/FormS]

Here again, zero back pressure is the goal.

^^ what he said^^
back pressure isn't even good for lawnmowers.

 

[d1970]

I guess back pressure is not the right word to use. With the larger 3 inch pipe compared to the 2.5 pipe you are going to lose some savaging, you will have more exhaust turbulence happening at low rpms which slows down the exhaust flow, which will effect the low end torque. At higher rpms there is no problem with the exhaust flow and the 3 inch exhaust will work better if your motor is tuned properly. Smaller diameter pipes will usually produce better low- to mid-rpm torque. Larger diameter pipes usually produce more mid- to high-rpm torque."

 

[AJ/FormS]

I have a Hi-Compression (11/1) ~400hp 367, running a 4-speed, TTIs,and dual 3s. I ran it with the H-pipe for 4 years or more, but had to ditch it when I installed a GVod.
I immediately noticed a pretty good loss of bottom-end torque. I worked on my tune all that summer, but never got it all back. It took some 10 to 16% more low gear to get the low-rpm (sub-2400rpm or so) performance back, which as a streeter with a 4-speed and 3.55s, was very important to me.
Point being, don't underestimate the value of the H.

 

[rumblefish360]

^^ what he said^^
back pressure isn't even good for lawnmowers.

I guess back pressure is not the right word to use. With the larger 3 inch pipe compared to the 2.5 pipe you are going to lose some savaging, you will have more exhaust turbulence happening at low rpms which slows down the exhaust flow, which will effect the low end torque. At higher rpms there is no problem with the exhaust flow and the 3 inch exhaust will work better if your motor is tuned properly. Smaller diameter pipes will usually produce better low- to mid-rpm torque. Larger diameter pipes usually produce more mid- to high-rpm torque."

Most of the scavenger effects are in the header.
Then comes the collector. If it is he wrong size and shape, there is a power loss. Then it is the length of pipe of the collector. It should be the same size for as long as it produces torque. To much or not enough will hurt power. If you incorporate a pressure termination box, the pipe size should remain the same afterwards. In some cases, going down a size doesn’t hurt but in some cases, it may add or loss no power in where the pipe size after the termination box outlets. (Pipe into the muffler.)

I can’t say for certain in this case since it would have to be dyno tested to know exactly what the engine likes and his particular build is void of any specs given.

This makes your as written statement a blanket one. Following your advice, as written could be more of a mistake than an era on the side of caution for what may be or not. I have used 1-3/4 tube headers on a low compression 318 and gained power very noticeably.

The one draw back for certain is the exhaust will be louder!
Until I have engine and vehicle build specs, as well as what exactly he is doing, I’ll agree that a 2-1/2 exhaust is probably dead on the money for what he is probably doing.

 

[d1970]

Most of the scavenger effects are in the header.
Then comes the collector.

I understand headers change the game.

I was going by a fairly stock low comp 360 with exhaust manifolds with 2.5 exhaust . He never mentioned headers.

 

[1971 CY Dodge Dart]

I’ll be installing a 3” exhaust on my car this Winter. It’s a basically stock 340 but I want to go big when I do my longtubes and it will allow me to grow into the exhaust as I add more power. Right now my exhaust is a mish mash of sizes from less than 2” up to 2 1/2”.