Turbo-Geist

The picture above of the exhaust that I created was similar to a Borla Stinger except the mufflers and tubing were 3". It did neck back down to the tips sourced from a 2.5" borla system. It did pick up about 25hp on the dyno and was a little louder than the C5Z Ti catback. Interior resonance wasn't too bad.

As most people have mentioned, when you increase exhaust pipe diameter and flow, you also increase resonance and the sound frequency becomes lower and more noticeable (drone) on a V8. This is where a tuned exhaust can really be beneficial. The Corsa Ti is so free flowing that I can hear the turbos spooling at idle and cruise, but when cruising on the highway, the interior resonance is almost zero. It pretty much sounds like stock inside the car

ajrothm

Good post! Thanks Ben. I'll read through your old threads tonight... Should be interesting to see your results..

Pekka_Perkeles

Do you measure pressure in the exhaust pipes in various points?

If not, how do you know what is restrictive and what's not?

It may be too scientific, but knowing the difference of pressure values between stock mufflers and some aftermarket vendors products would be nice. And how it correlates with dyno runs. And if it's in the limits of dyno testing tolerances. If there are any. Are there?

Headers are of course different animals. But pipes and mufflers? Well, is there anything else than backpressure?

vrybad

Yea, I had the LG Big 3 and I did the same thing, took a look inside.

As was mentioned there is an area at the far end that allows full flow.

Up close, it actually looks like a pretty low-restriction muffler.

I actually have the old setup on hand, so I might take a few measurements to see just how much of a space there at the far side.

Maybe a few pics, too.

I think it is a very nice system.

Turbo-Geist

Thanks, AJ. Here is a link to the thread that discusses the C5Z mufflers and durability. http://forums.corvetteforum.com/c5-z...exhaust-3.html

Then, within that thread, another thread is started where someone cuts open the C5Z muffler to see the internal design. http://forums.corvetteforum.com/c5-g...6-muffler.html

While these are interesting and provide some supporting background information, it doesn't get us to the original question of the thread and that is

"Does flow improvement transfer to anything we can see on the timeslip or in Mexico?"


My answer would be yes and I would word the Q & A like this based on questions that have been asked already in this thread.

In comparison to straight flowing full 3" exhaust from the manifold to the rear of the car:

1. Does making the exhaust turn 180 degrees before exiting cause some HP loss? Yes

2. If I have a 3" exhaust, and it is chambered internally or has to make a 180 degree direction change, will it cause some HP loss? Yes

3. Does a 3" exhaust that has an internal reduction inside the muffler cause some HP loss? Yes

I'm sure there are similar questions that can be asked, but you get the idea. The amount that it will cost you powerwise depends on each system's design.


A C5Z stock Ti catback is 2.5" piping but necks down internally to 1.875" tube inside the muffler. This is a restriction and will limit power. Does it matter on a 400 rw car? Probably not and it doesn't matter if you aren't looking for every last hp. Also, I'm not saying that aftermarket mufflers don't make more power than stock, because I think almost 100% of the time they will if they flow more.

However, if you are looking for more power and quicker ET's, I don't think you will beat a straight through 3" or larger exhaust system that is non-chambered, non-baffled and doesn't have a 180 degree flow direction change. The trick will be living with the internal resonance in the cabin and that is where helmholtz resonators, tuned noise cancellation, etc., becomes needed.

Turbo-Geist

Also, someone could argue, "keep it simple" and install cut-outs. I would agree. Make sure your mid-pipe is atleast 3" diameter, install cut-outs that have a 3" diameter or equivalent exit and you could have the best of both worlds.

I'm not looking to go that direction because I'm building a system from scratch. I currently don't want to fool with electric cut-outs or the need to manually remove a flange although the thought of cut-outs sounds appealing. You could have a quiet catback and then go all out when needed.

I'm more interested in a high flowing low restriction 3" exhaust that is tuned to eliminate drone at highway speeds. It will more than likely be very loud at WOT and attract attention, but that is to be expected.

Turbo-Geist

You are correct, it's basically about measuring backpressure and trying to reduce it. Grab one of those twisty straws with multiple loops and blow through it and then grab a straight straw. Which one provides less resistance?

To state it another way, you are inside the exhaust pipe and just travelled over the axle and are ready to exit. Will you get out quicker by taking a route that involves a 90, a 180, and another 90 or just going straight out?

Minor bends and overall pipe length cause some restriction to flow, but reduction in pipe size and 90 and 180 bends are going to cause much higher losses.

I think the current C5 muffler designs hinge on noise control and ease of installation to maintain the factory mounting points and packaging.

ajrothm

I agree 100% with EVERYTHING you said..... And I concur. The cutouts would be an immediate fix for the problem... However, I don't want to fool with opening cut outs every time I'm gonna make a hit on the street.....And if there IS a significant loss in power through the catback, I would want that power gain all the time...

I don't mind a loud-ish exhaust, I just don't want the drone/vibration inside the car...

In all honesty, the XSP 3" system I have sounds great, its perfect inside you can carry a conversation and has a nice deep throaty idle, great sound when accelerating with no raspy, crackly sh*t..... I just question the muffler flow...

I am pretty sure that this muffler is similar to the Big 3, a straight perforated tube in, stopping 4-5" from the side of the muffler, a big chamber, and a 2.5" outlet from that chamber, wrapped in ceramic packing to 2.5" outlet pipe/tips...

I love how it sounds and it looks decent, especially for a $700 system.... But if there is 50hp lost in the muffs/bends etc etc....I'm gonna change something...LOL

ajrothm

More pics of a C5Z TI muffler cut open I shamelessly stole from MadMatt9471..












Well....I can see why they are so quiet.... There is no way that flows for sh*t....

a/c man

Allen your car does sound nice with that 3'' catback!! Now I thinking just how much my stock Z TI ex. is holding me back!! I love the ti sound I have gone 9:30 with them but what am I loosing or leaving on the table....

Some member on here did straight ex. catback like a c6 he cut the bump out in the trunk and made it flat. He posted results I wish I could remember who?? I found it here it is.http://forums.corvetteforum.com/c5-z...-a-c5-z06.html

a/c man

Here's a cool setup!

ajrothm

Yeah I remember when Larry did the c6 exhaust setup. I thought about that as well.... A lot more options that way....although not many in 3". It would also make it way easier to pull out broken drivetrains without the big tub under there...

Not sure I want to cut my car up that much yet.....hell that's the reason I haven't done a high ram intake yet..

vrybad

Just doing some quick math, there is a 44% increase in flow going to a 3" pipe over 2.5", all other things being equal.

I remember someone in FI posting a gain of about 60-70 rwhp with the change to 3", but can't remember who.
A while back.

Rookieracer

Don't confuse area with flow.

vrybad

If the volume of, say, a 15 ft piece of pipe is 44% greater, I would expect the flow to be greater as well.

Using a simple flow rate calculator, it gives an approx. 44% increase in flow rate, all other parameters being equal.

NemesisC5

At one time I was considering installing some 3" chambered mufflers from "Classic Chambered Exhaust" into my Kooks 3" X-Pipe. After that there was no 3" over the axle straight setup similar to the one that Borla makes in 2.5" without going custom bent mandrel. A couple of shops in the Houston area could have done it for me but I didn't pursue because I would not know the sound characteristics until the project was complete. I didn't want a loud drone so I sat back and waited for a manufacturer to make one. Look at the link below, I think it may answer a few questions and have some solutions.

http://classicchambered.com/index.html


I spoke with Corsa when the Extreme C5 system first came out and asked if they would do in 3" and mentioned the interest from the forced induction crowd and they said the 2.5" would handle our needs. Obviously it will flow well for a 2.5" but I was looking for an optimized 3" system. The LG system was an option at the time also but I heard that it had drone and also didn't like the factory style mufflers with all the bends. With a 3" bypass like the Ti-Mod it may work well but I wasn't willing to purchase it, modify it and hope I liked the sound.

Recently a CF member that road races his C6z had a custom muffler system manufactured by Burns Exhaust in 3". Currently in the Autocross/Roadrace section they are trying to put together a group buy. It's possible that Burns could do something similar for the C5 at least for the over the axle part in mandrel 3" but not sure of the mufflers. I still think the 3" straight mufflers from "Classic Chambered Exhaust" installed in a 3" X-Pipe would be the best muffler solution. They come in many lengths which determines how loud it will sound and IMHO are the best "muffled" option I've seen for C5 fitment.

The link to the Burns Exhaust thread on CF:

http://forums.corvetteforum.com/auto...group-buy.html

There seems to be several threads from this one link so it may be a lot of reading.

Link below with pictures seems to be original thread:

http://forums.corvetteforum.com/c6-z...t-exhaust.html

Rookieracer

Sorry, I should have elaborated.

All other parameters will not be equal. There will be a corresponding drop in exhaust pressure with the larger pipe. While there certainly will be an increase in overall flow with a 44% increase in area, it will not equal a 44% increase in flow.

vrybad

Likewise, I should also have elaborated!
I had a feeling you would response as such, and I concur, there will likely be a drop in exhaust pressure.
In terms of this discussion, my point is that when increasing an engine's output by over 100% from stock (for example, from 500 fwhp to 1000 fwhp), a 3" exhaust would definitely offer beneficial increases in flow, though perhaps not quite 44%.
On these high hp engines, I can't see any negatives, other than maybe increased noise production.

Rookieracer

Agreed. In fact given the airflow required to make 600+ a benefit could be realized from even larger diameters.

_zebra

see Helmholtz resonance. basically, the exhaust blowing past the J bend creates a frequency that bounces down to the endcap & back. when it bounces back, it's out of phase with the sound bouncing in & therefore cancels the sound out. the length of the J tube determines the frequency (pitch) of the tone canceled out. manufacturers tune these pipes to the highway drone frequency so it's quiet when cruising.

same as above

that's kinda the road i chose. i've got 1 7/8 LTs, 3" X down the middle, and 2.5" B&B TriFlow axle-back with 2.5" cutouts on the down pipes behind the diff. that setup still dumps the exhaust out the back when open, so the drone is much less than the ones under the trans and also has better flow out the cutouts. it's still quiet as a mouse closed for cruising, and when i want to play around, it's literally only 3 seconds to go full open (not that much of a hassle).

i chose to keep the rear section necked down to 2.5" because i won't never require the extra flow of 800-1000hp in this car. my goal is 700 with a cathedral TVS, and right now @ 540 on an LS1, i believe my current setup's a little big on the front side.