Intermediate Pipe Diameter

[2.8 Bird]

Re: Intermediate Pipe Diameter

That was my original thought. But guys have been saying that 3" is too much for the 6 cylinder, and I'll loose bottom end and mid range, and I am afraid of loosing either. I want some top end too, but I dont want to loose anything.

I don't know why 3" would too much for a V6 when there are guys here running with true dual exhaust pipes that are 2 1/4" for each one.

But it's up to you if you plan on keeping you car near stock with just a few bolt on then go for what you have planned.

[nwilson44]

Re: Intermediate Pipe Diameter

I don't know why 3" would too much for a V6 when there are guys here running with true dual exhaust pipes that are 2 1/4" for each one.

But it's up to you if you plan on keeping you car near stock with just a few bolt on then go for what you have planned.

Well duals is a different story. With an X-pipe the extra scavenging does wonders. I have the pacesetter set up.

I just want gains at every part of the RPM band. It doesnt make since to me that the pacesetter y pipe is 3 inches, but people are saying that 3 inches is too big?!?! I'm going to ask the guys that are going to do the custom tune. This is too complicated.

[Hib Halverson]

Re: Intermediate Pipe Diameter

When I put my 3" cat on I also went 3" from the cat back to my Flowmaster exhaust's inlet.

Here's the way I covered that in Pt. 5 of the THRS series.

"We returned to the Westech Performance Group for another session on its Superflow AutoDyn chassis dynamometer. Three more runs on the AutoDyn showed that, compared to our last visit to Westech for Part Four, performance increased by an average 4.5-rwhp and 5.5-lbs/ft rear-wheel torque in the mid range and 3.6-rwhp/3.4-lbs/ft at high rpm. Our best run with the new S-pipe and cat was 223.3-rwhp@5780-rpm and 218.4-lbs/ft@4630-rpm. There was another benefit of the 3-in. S-pipe and new cat: the THRS sounded even better than before–the sound was deeper and a little louder."

The idea that going from 2.25" or 2.5" to 3.0" will kill mid range is :bs:. V6es like low restriction just like V8s. In fact, I saw the biggest gains in the mid-range from the 3" cat and S-pipe.

If you want to read the entire story, click here. The stuff about the cat and the S-pipe is towards the end.

[nwilson44]

Re: Intermediate Pipe Diameter

When I put my 3" cat on I also went 3" from the cat back to my Flowmaster exhaust's inlet.

Here's the way I covered that in Pt. 5 of the THRS series.

"We returned to the Westech Performance Group for another session on its Superflow AutoDyn chassis dynamometer. Three more runs on the AutoDyn showed that, compared to our last visit to Westech for Part Four, performance increased by an average 4.5-rwhp and 5.5-lbs/ft rear-wheel torque in the mid range and 3.6-rwhp/3.4-lbs/ft at high rpm. Our best run with the new S-pipe and cat was 223.3-rwhp@5780-rpm and 218.4-lbs/ft@4630-rpm. There was another benefit of the 3-in. S-pipe and new cat: the THRS sounded even better than before–the sound was deeper and a little louder."

The idea that going from 2.25" or 2.5" to 3.0" will kill mid range is bull****. V6es like low restriction just like V8s. In fact, I saw the biggest gains in the mid-range from the 3" cat and S-pipe.

If you want to read the entire story, click here. The stuff about the cat and the S-pipe is towards the end.

Pretty good story. However, my car is not cammed nor does it rev out to 6400, so I shouldnt expect similar results, right? I may do a cam later down the road, but for now, I am working with full bolt ons and a tune later. Despite having the stock cam and a 6000 RPM limit, do you still think a 3 incher is the best choice?!

[EarlR]

Re: Intermediate Pipe Diameter

Here's my $0.02; I upgraded the exhaust on my Camaro to full 3" from the cat back a couple of years ago, including fabbing up an 's' pipe from a 3" mandrel bend to run from the cat to the intermediate pipe. I haven't had the car on a dyno since then, but I will say that subjectively the car feels like it has more power.

I read a good article once about this (wish I could remember where), and what I took from it was that where pipe diameter hurts performance is the point at which exhaust gas velocity slows enough that scavenging is affected. This would logically be more of an issue with smaller displacement engines, as there is less gas being expelled with each exhaust stroke. The larger diameter pipes allow the lower volume of gas to expand and lose velocity more quickly. With larger displacement engines this should be less of a problem.

This seems to hold true in my real world experience. I have a Nissan 240SX that I race in SCCA's IT class. When I originally built the car, I had a custom 2.5" exhaust fabbed up to run from the header connector pipe back. The connector pipe was a smaller diameter (2"-2.25") pipe, about 2' long, that was meant to connect the header to the cat on the street car. The car ran pretty well, but was never close to the top cars. A few years into racing I read somewhere that a larger exhaust was the way to go with this engine; so I pulled the exhaust and the little connecter pipe and made up a full 3" pipe to run right off the header; the very next time I went to the track I ran lap times 1.5-2 seconds faster than my best to date. Another guy I knew who also races a 240SX asked me what I had done, when I told him he went home and had a 3" exhaust made up for his car; and immediately dropped more than a second from his laps times (he was faster than me to begin with...). Keep in mind the 240SX, while only a 4-banger, is a fairly large displacement 4-banger (2.4L), which holds true to the theory of larger displacement (relatively) engines liking larger pipes. The Honda guys I race with say there is no way their 1.6L engines would run well with a 3" exhaust.

[nwilson44]

Re: Intermediate Pipe Diameter

Here's my $0.02; I upgraded the exhaust on my Camaro to full 3" from the cat back a couple of years ago, including fabbing up an 's' pipe from a 3" mandrel bend to run from the cat to the intermediate pipe. I haven't had the car on a dyno since then, but I will say that subjectively the car feels like it has more power.

I read a good article once about this (wish I could remember where), and what I took from it was that where pipe diameter hurts performance is the point at which exhaust gas velocity slows enough that scavenging is affected. This would logically be more of an issue with smaller displacement engines, as there is less gas being expelled with each exhaust stroke. The larger diameter pipes allow the lower volume of gas to expand and lose velocity more quickly. With larger displacement engines this should be less of a problem.

This seems to hold true in my real world experience. I have a Nissan 240SX that I race in SCCA's IT class. When I originally built the car, I had a custom 2.5" exhaust fabbed up to run from the header connector pipe back. The connector pipe was a smaller diameter (2"-2.25") pipe, about 2' long, that was meant to connect the header to the cat on the street car. The car ran pretty well, but was never close to the top cars. A few years into racing I read somewhere that a larger exhaust was the way to go with this engine; so I pulled the exhaust and the little connecter pipe and made up a full 3" pipe to run right off the header; the very next time I went to the track I ran lap times 1.5-2 seconds faster than my best to date. Another guy I knew who also races a 240SX asked me what I had done, when I told him he went home and had a 3" exhaust made up for his car; and immediately dropped more than a second from his laps times (he was faster than me to begin with...). Keep in mind the 240SX, while only a 4-banger, is a fairly large displacement 4-banger (2.4L), which holds true to the theory of larger displacement (relatively) engines liking larger pipes. The Honda guys I race with say there is no way their 1.6L engines would run well with a 3" exhaust.

So you think that the 3" is the best for our application?! With the borla muffler and 3" intermediate pipe, it should run substantially better than the stock cat back, at all RPM levels?!

[EarlR]

Re: Intermediate Pipe Diameter

So you think that the 3" is the best for our application?! With the borla muffler and 3" intermediate pipe, it should run substantially better than the stock cat back, at all RPM levels?!

Let me say this - for me personally, in either the race car or the Camaro, I don't care what it does at lower rpm levels, and I have no idea how the larger pipe affects that. The race car rarely runs much below 4k rpms on the track, and when I say the Camaro feels like it has more power I mean when I'm "giving it the beans". So while it seems logical that the larger pipe could cost you some power in the lower rpm range (I don't know this, just speculating), IMO the gains at the higher rpms make it worth while. Plus, if like me you plan on adding to the engine (right now my Camaro only has I/H/E + tuning), it will probably pay off later on.

[nwilson44]

Re: Intermediate Pipe Diameter

Let me say this - for me personally, in either the race car or the Camaro, I don't care what it does at lower rpm levels, and I have no idea how the larger pipe affects that. The race car rarely runs much below 4k rpms on the track, and when I say the Camaro feels like it has more power I mean when I'm "giving it the beans". So while it seems logical that the larger pipe could cost you some power in the lower rpm range (I don't know this, just speculating), IMO the gains at the higher rpms make it worth while. Plus, if like me you plan on adding to the engine (right now my Camaro only has I/H/E + tuning), it will probably pay off later on.

Well the reason why I say what I did about the low end torque, is because my car is auto with the stock stall. So if I loose low end torque the car will feel noticeably laggy taking off from a dig. The upper RPM gains I was unsure about because I did not know if my engine would get enough exhaust flowing by the 6000 RPM shift point. I definitely understand where you are coming from though!

[ssms5411]

Re: Intermediate Pipe Diameter

You can always make up for low end TQ by adding some 3.73 or 4.10 gears. I think a aftermarket stall will just increase top end but I don't really know but will find out in about a couple of weeks when I get mine.

[2.8 Bird]

Re: Intermediate Pipe Diameter

I don't know any low end torque lost or if I did lose it it certainly is not noticeable to me.

Both my birds have 3" catback. My 3.8 has a Borla catback and my 2.8 Flowmaster 80 series catback.

[nwilson44]

Re: Intermediate Pipe Diameter

You can always make up for low end TQ by adding some 3.73 or 4.10 gears. I think a aftermarket stall will just increase top end but I don't really know but will find out in about a couple of weeks when I get mine.

You know thats not a bad idea. The only issue I have with my situation is that the car already turns alot of RPMs on the freeway (75-85 MPH for me) with the stock 4L60E. I would need to do a 5 speed swap if I was going to go any higher than a 3.42:1 thats in it now.

So no one with a 3" system has seen a loss of low end torque?!

[htmabe]

Re: Intermediate Pipe Diameter

If your trying to fast ONLY then bigger is better. A restriction is a restriction. That's why race cars run open headers for less restriction. Less restriction equals more hp, more torque, more noise,less gas mileage, less overall "driveabilty" and overall "streetabilty".
Everything is a compromise. When you change anything from stock form you give up some of the built in compromises gm engineers into the car.
Typically if a car is a "grocery getter" it is perfect stock. Used in a performance nature requires mods. Just how far one goes with the mods will determine "streetabilty"/"grocery getting" ability.

[nwilson44]

Re: Intermediate Pipe Diameter

If your trying to fast ONLY then bigger is better. A restriction is a restriction. That's why race cars run open headers for less restriction. Less restriction equals more hp, more torque, more noise,less gas mileage, less overall "driveabilty" and overall "streetabilty".
Everything is a compromise. When you change anything from stock form you give up some of the built in compromises gm engineers into the car.
Typically if a car is a "grocery getter" it is perfect stock. Used in a performance nature requires mods. Just how far one goes with the mods will determine "streetabilty"/"grocery getting" ability.

So if I want something that sounds good, gives me an overall increase, and doesnt hurt the MPG's too much, then I go with 2.75?

[Hib Halverson]

Re: Intermediate Pipe Diameter

Pretty good story. However, my car is not cammed nor does it rev out to 6400, so I shouldnt expect similar results, right? I may do a cam later down the road, but for now, I am working with full bolt ons and a tune later. Despite having the stock cam and a 6000 RPM limit, do you still think a 3 incher is the best choice?!

No, you won't see similar results, but you likely will not loose on the top end and you may gain a little in the mid-range, but...once you do add an aftermarket cam and some head work, your engine will love you for it.

That said, if you're still running a stock cat, if you're going to spring for the 3" S-pipe and so forth, make sure your exhaust shop does it right. The stock cat on a 3.8 V6 has a 3" outlet but it reduces almost immediately to 2.5 and then, a little more down stream, to 2.25. Your exhaust shop will have to cut the old system off right at the first weld downstream of the cat. A good exhaust guy can do that.

An alternative is to use that aftermarket 3" cat I used in the article.

This old wive's tail about 3" exhaust killing power on V6s with full exhaust systems has been around for years. Now, I'll admit, if the car has tuned 3-into-1 headers and the proper collector length and open exhaust, then the collector diameter and the primary pipe diameter starts to be important.

On a street car, however, with a 2-into-1 Y-pipe, a cat and an over-axle exhaust and, if necessary, the a calibration change to go with the lower restriction, the idea that 3" is going to kill power compared to 2.5 is, IMO, nuts.

But, hey...I'm still "Lookin' for 13's"...right?:eek:

[WarShrike]

Re: Intermediate Pipe Diameter

The issue with our cars is the stock y-pipe internal diameter is crap. It's really tiny.

My dyno with open headers, unlocked 3800 stall on my current engine mods, estimate probably 220-230whp with the T-56.


I'm currently running 3" all the way out the back through a dual outlet turbo muffler. The car still has good grunt, will hopefully get it back on the dyno this spring. I have plans on going turbo anyway, so 3" is what I went with to give me headroom performance-wise.