I've been reading a lot of technical information regarding header sizing and it's effect on engine performance. I understand the relationship between primary diameter and length, as it pertains to V8 engines. Lately, I've been focusing my attention on collector specifications, particularly collector length and it's effect in a full exhaust system. What is difficult to find an answer to is at what point the collector no longer a collector. If for example, my headers have a 3" diameter pipe measuring 6" long (from the tips of the primaries to the gasket flange) and I run 3" exhaust to the rear of the vehicle and then into low restriction mufflers, have I effectively increased the collector length?  There's lots of tech talk about putting mufflers at the end of the collectors (suitably spec'd mufflers) and calculating length based on that addition, however for a daily driven street car that sees drag strip duty, a full exhaust is desirable. In my application, the mufflers are behind the rear axle.
Any insights?  

hmmm... open collector legnth is what most of the discussions are about ...if they are too short open.. there will be less scavanving of the rest of the system... the final part of the cumbustion will happen outside of the collector and make a lot of noise and be totally wasted in my opinion ... testing on a dyno may show differnt..

some more inventive header designs reduce the transition from the primarys to the collector to increase velosity and scavanging on the other primarys.. then it goes back to full size to allow the flow...  this almost works like a check valve...


other header designs have dual diameter primarys so the still expanding gasses can expand without  loosing to much velosity...

running full legnth 3 inch pipes on a car with mufflers is just a good idea...  

it will have a lot less restriction than smaller pipes..  

It's the tunability of the secondaries I'd like to investigate. I've already got the headers so there's not much I can do about primary sizes and the like but it seems there's a lot of potential horsepower and torque that needs some tuning to be realized. That's where the secondaries come in.
Short of doing what David Vizard did for his friends Corvette, (and that's a lot of work!) I'm at a loss for technical information.  

Have you been studying this article by Mr. Vizard?

[url]http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/index.html[/url]

Here he mentions that chambered mufflers (Flowmasters for example) don't change the tuned length of the exhaust system. The exhaust sees the end of the chambered muffler the same as the end of the exhaust system, whereas a glasspack style muffler acts as providing length to the secondary length of the exhaust system...  

Hey GibTG,
Vizard has some excellent articles. And you're correct on both points as I understand it. With the glasspacks the benefit comes from ending the exhaust right after the muffler without any extension into a tail pipe. Behaves like open headers. The article explains how the perception of an open atmoshpere (which is where the benefit of tuned secondaries on LT headers come from) can be incorporated into a full exhaust system with resonator boxes and properly spec'd mufflers.
What I was asking when I started this thread is if I use chambered mufflers and install them at the rear of the vehicle(after the rear axle)is all that exhaust pipe that extends from the collector to the muffler considered part of the tuned collector length? And what result would that give? (Provided I don't change the i.d. from the collector back and also be sure there's enough cfm.)
What's your take on it?