Car is a 03 Z06 with typical off the shelf LT 1 7/8" headers with 3" collectors. The layout of C5's allows for some "fun" in exhaust design. Currently run LT's 3" collector > 3" pipe to 3" high flow cats > 3" to 2.5" transition/reducers > 2.5" x pipe > 2.5" Corsa catback.

I have the itch to "tinker" and think outside the box making a PWTB and in order to position it in the car, I think it would be ideal to begin the box where "tuned collector lengths" are ideal. "Tuned collectors" typically refer to drag race guys adding pipe equal to the diameter of the header collector which is roughly 18" worth and letting them dump to atmosphere.

Clearly I can't run dumps on a street car and the plan is to determine proper collector length then the PWTB will serve as "atmosphere" (box volume >1x motor displacement) while still exiting out through a catback for sound purposes.

Question is, how would you guys determine when a collector is ended on a full street system?
-When the motor/exhaust sees a significant chamber volume change?
-When the exhaust hits the cats being a "restriction"?

This is a David Vizzard "no loss" system for presumably a C4 corvette which would be a similar layout:


My system would be very similar but I would need to keep cats due to having a cam and the exhaust fumes get annoying without cats.

 

Cool idea! Curious to see how it turns out. I moved it over to external, though, since I doubt the collectors will be going inside the crankcase

 

I debated where to put it! Thank you.

I may just end up calling some header manufacturers like Burns etc to get their take on it.

 

what is the math in figuring out something like this ?

 

What is the end goal...More power? Better sound? Both?
Engine Masters has done tons of exhaust testing, They tried different lengths of pipe/ Different diameter of pipe/ Two types of Crossovers/No crossover/ Several different muffler brands and styles/ No mufflers/ They even tested mandrel bent tube versus non mandrel and several different sizes and types of headers. Surprisingly most of the time there was very little difference, Basically if you have decent headers/mufflers and no big kinks in the pipe there isn't much to gain after that.

 

Do you have a link to collector length testing?


One COULD use PipeMax to get all the calculated lengths. With that, you need to know A LOT about your motor. Cam specs/distance from back of intake valve to head port/primary tube lengths etc etc. But since I don't know some of those and that I have "off the shelf headers, I can't change them so they are what they are.

Another theory that has held up is to run headers+long extensions at WOT with a spray painted stripe on the sides. Where the paint burns is where to cut for collector length. This method takes all the calculations out and "the motor tells me what it wants". At least, again a theory.

Yesterday I sent the afternoon under my car to get all the dimensions of the chassis/tunnel. Today I modeled everything and started to "build" the system before buying anything. I would say all my measurements are within 1/6" of what is actually on the car. I modeled the formed collectors for OD and length. I know where the 4 primaries merge in relation to the collector exit etc.

Next step is to get some 3" 30* "test pipes" and some 3" straight sections. Get a base pull on the dyno, remove my current extensions+midpipe and replace it with these painted test pipes. Run it on the dyno a couple of times and see what happens on where to cut them. Cut them where paint is burned then re-dyno to see results. One of three things will happen. 1) I see power loss 2) I see no gain or loss 3) I see gains worthy of continuing this project.

If there are gains AND my extensions are around ~18" then I have room to make a ~700+ cu.in. box under the car according to my modeling.

Car is a 2003 C5Z with intake/cam and 1 7/8" headers>3" extensions to 3" hi flow cats>3" to 2.5" transitions>2.5" midpipe x pipe>Corsa Sport catback. I'm at 396/344 on a Mustang dyno and I've been itching for 400+/350+ so if that happens I'm calling this project a success. Also making something "unique" will be fun.

There has been two people that have done this and had positive results. One on a G8 (but I don't think his box was big enough nor did he plan out collector length) and another on a 3rd Gen Camaro that used PipeMax.

 

8:17 mark proving extensions are worth it. What I would like to see more of is a longer and shorter on in comparison to 18".

What this video shows is 2.5" to 3" comparison....BUT the 2.5" test was with no "collector extension" technically. It looked like a header with a 3" to 2.5" reducer right at the end of the header to 5' of 2.5" pipe then the muffler...same for 3" test. I would have liked to see both tests WITH 18" collector then neck down to 2.5". For 3" test, yes it would be one long extension.

They also don't mention how much each of those Magnaflow mufflers can flow for CFM. It could be that for that size motor...THOSE 2.5" mufflers can't support the flow. But this video leads you to believe 3" > 2.5" across the board.

But I guess to answer my own question, painting the extensions then seeing where it burns will "figure itself out" in terms of where you measure collector length from.

 

so pipemax software is a good way to design your headers....anything on the rest of the system ?

 

Pipemax can be used to design the whole exhaust from what I hear. I don't have it or know how to use it.

General consensus is tuned collectors at right diameter and right length with a box of the correct volume is what is needed. Once you do that, make sure the mufflers you use flow enough CFM for your motor and "theoretically" the exhaust system after the box is "invisible" to the motor. Meaning it is not seen as any type of restriction.

For me I'm estimating 3" x ~18" long collectors (paint test will determine length) dumping into a 4x8x24 box totaling ~770 cu. in. (more than double the motor cu. in.) then to 3" high flow cats (to keep the gas smell from my cam to a minimum...yes I know that makes cats WAY down stream) then to Corsa catback.

 

I don't have the link, I watch them all on my TV using the app.
IMO I think you are chasing something that isn't worth chasing.

Just put a good exhaust on it and be done with it, There is so little to be gained it's not worth the trouble.

 

I go off of proof and testing lol. Plus if everyone thought that way nothing would get improved upon . There is enough evidence out there done by grassroots type guys and magazines proving this theory.


This can be done with under $100 in materials and a weekend. It's worth the experimenting, tinkering keeps me sane. I have a friend with a speed shop and a dyno who is also intrigued and willing to play in the sandbox.

 

The biggest issue is with exhaust is space, You don't have a lot of options when it comes to where to place mufflers/Crossovers and so on. The chassis dictates that. As far as gains are concerned, If you run headers and decent free flowing exhaust that has no restrictions then that will be your biggest gain over stock, If you want to see any of the tests done, Do a search for the engine masters series on youtube or subscribe to Motortrend.

 

You better watch the video again, The gain from the extension was on open headers, Not a full exhaust. Tuning the collector length has been done is drag racing and circle track racing for decades and they didn't run exhaust after the collector, As soon as you add pipe past where you just tuned the collector you just changed the point of doing it in the first place because the pipe you added is basically a collector extension.

 

Never seen this before and it got me interested.

High level concept: It seems the pressure wave termination box essentially isolates the back section of exhaust from the forward section of exhaust so that the "secondary pipe length" can be tuned via location of the pressure wave termination box. The rear part of the exhaust system (with muffler) is then simply sized to meet flow rate requirements and no longer has any effect on the cylinder scavenging. In other words, no more worrying about how muffler selection and pipe lengths effect the cylinder scavenging.

Is that pretty much the gist of it? Reminds me of the C4 Corvette exhaust system.

Question: How does a Y-pipe factor into all this? The David Vizard article didn't talk to that matter.

 

Nope, read QwkTrip's explanation below on the concept.

It is. I have a C5 so the system pictured would be very similar to what I would make. I would ASSUME you could make a PWTB then make a single outlet since once the exhaust hits the box, it is simply about getting it routed to the back of the car with pipes/mufflers that flow enough. I could run a single pipe to the back but then that means I'm getting rid of the Corsa system which works so well at no drone and putting a single muffler back there capable of flowing almost 880 CFM (2.2 CFM per HP). Not impossible, but not exactly in the scope of this experiment.

 

I understand the concept and have read about it in the past, It's still going to change the expansion point over open headers because it changes where the hot exhaust gas is exposed to atmospheric pressure and temperature change, I'm not saying the expansion box doesn't work...I'm saying that tuning the collector then adding anything after it will change the sweet spot.
You also need to keep in mind that most of the tests where done on a dyno at wide open throttle. Little power differences can mean the difference between winning and losing if you are racing in a class where everything is governed by rules such as Weight/Engine size/Carb size/ Tires and so on to keep the races fair, You are racing similar cars under similar weather conditions on the same track at the same time so everything else is equal. They will literally spend thousand upon thousands of dollars to gain a small advantage. On the other hand a street car isn't bound by rules so you can make larger improvements by lightening the car, bigger engine/ Power adder/ Ported heads stickier/bigger tires and so on. All I'm saying is a street car isn't a class race car and isn't driven like a race car....even if it were is it really worth spending the time and money for a gain so small you won't feel the difference in the seat of your pants? Hell even trying to get real A-B test results on a dyno would be difficult unless you were able to reproduce all conditions between sessions. I've seen the same race engine run on a dyno with no changes have 10-20 HP swings due to different conditions in the dyno room and different oil/coolant temperatures so measuring a 3-4hp gain is going to be difficult.
If it's what you want to do then I say go for it, Just don't expect to rock the world with the changes.

 

Very well put, LLLosingit!

 

We are on the same page. When doing this I will be getting a baseline as the car sits, make the changes to long extensions with paint on them then re-dyno. Cut extensions if the paint theory works and re-dyno again. All same day, all same conditions. If I see a substantial loss then project is over with and no point on continuing. Also depends on where the changes happen. It's a street car that i autocross so low/mid range is very helpful to improve.

Under 5 hp/tq up or down I don't get excited about as I see that as "noise" during a pull. I have back to back graphs showing improvements from things like porting a Dorman LS2 intake, running a 20b lighter SPEC clutch and going from a Halltech CAI to a stock LS7 air bridge. All showed gains in different ways.

If I didn't have access to a dyno for free for a day I wouldn't do this. It's something I've been curious about doing for a while.

 

I have PipeMax Pro 4.70. PM me if you're interested in sending me data to model.

 

Mickey Thompson was into this "box" theory decades ago....
His Super Scavenger headers had a square collector, and equal length pipes in it.
MICKEY THOMPSON SUPER SCAVENGER HEADERS | Team Chevelle (chevelles.com)