So I bought this header with plans to fab up a custom long primary exhaust. Long story short the header isn't close to being equal length. Flange to flange R1 is 29 inches and R2 is 26 inches... And we wonder why the SDJ header made more power than both the RB short and long primary exhausts.

 

Not sure I understand your point. Why would they need to be equal length when they are still separated at the flange?
Another q, it's my understanding that the "primary", as in the RB long primary or street port system, is indicative of the length before the 2 pipes of the header collect into one "primary" pipe. Is that not what it means?
If they were separated all the way to the end without being collected then wouldn't there be separate pulses for each rotor? I imagine that would create an undesirable exhaust note.

 

because I am making a long primary collected exhaust.

 

Yeah but if you were **** about them collecting at equal length, you could compensate for that with bends & a longer pipe on one side before collecting, since they are still separated at the flange. However I'd be willing to bet that since both rotors don't make power at the exact same time, RB has engineered their exhaust systems to compensate for that if it is indeed an important factor. Inversely, that could also be the exact reason that there is a 3" difference in the pipe length on the headers.

Can you tell me exactly what "long primary" means, if my assumption in the post above was not correct?

Regarding the SDJ's, do they extend straight out further from the motor before bending back to the rear? That might be an explanation for the power difference.

 

No, the uncollected headers are not equal length. Nor do they need to be. A 3" difference over the total length of the primaries on the full system is tiny.

Besides that, perfectly equal length primaries are overrated. Too many people try to build their headers' primaries to be as close to equal length as possible while completely ignoring the poor flow qualities of all the bends they have to add to get it that way.

 

^^That's what I was thinking, and also since both rotors don't send exhaust out at the same time, having equal length on the 2 pipes would be quite unnecessary.

And it's too late to correct my earlier post, but regarding the "long primary" I meant to ask if that was indicative of the length of the 2 pipes before they collected into one.

 

They should be equal length because the rotors exhaust stroke are exactly 90* apart. Therefore you want the exhaust to collect exaclty evenly for the negitive pulse to help scavange the next exhaust pulse. Extra bends to make them equal length is just retarded. If I'm being **** about 3 inches, then what makes one think that I'd want to add an extra horsepower robbing bend? Every single HP counts here. That's why I'm going through the trouble to make a system that collects the runners at exactly 92 inches... small carbed cars should collect at 22-25'' or 120-125''. bridges at 10-18'' or 113-118'' and perry ports at 10-18'' or 89-94''... remember you can collect the header at 25'' and make peak torque at 5000 rpm or collect at 18'' and make peak torque at 6250 rpm... Exhaust tuning has a much bigger role then people let off especially on a rotary with huge the amounts of overlap even with stock ports. Racing beat is the most over hyped company in the industry so i'm just letting the facts out.

 

not 3 inches at the colector but at the flange on just the road race header... you have to have the collect equally on a rotary for negitive exhaust pulse tuneing... search and learn people.

 

If you think that then why the hell did you buy it, Einstein? Maybe you should start your own company, and dream that it was at least 10% as successful as theirs.

It's that kind of ******* bs that is chasing people away from here. A forum is supposed to be an environment for people to learn. I posed questions and wanted explanations. I wasn't looking for you to just sit up on your high horse and look down upon us like we're a bunch of retards. Where the hell do you get off? That being a moderator stuff has put you on an unrealistic power trip man. Get a grip.

 

Not to threadjack, but I agree 100% with the anti-"search and learn" comment.

I am a senior moderator at TeamFocus (http://teamfocus.mywowbb.com) and although I have been a part of the site since the very beginning over 6 years ago, I still have yet to tell someone to search. If you have a question, I'll do my best to answer it or direct you to who can.

Forums should be about helping one another, not acting like you're better than another member because you have mastered use of the search button.

How hard is it to either; A) give someone a real answer, or B) do a search and direct someone to the proper thread? As a moderator this should be your responsibility. A moderator should be someone to be LOOKED UP TO, not just another way to direct someone to the search button.

If you're a moderator that obviously means you know your stuff, and therefore should be willing to share this wealth of knowledge at moment's notice, without whining that NewMember693 didn't search first.

/rant

 

Perfectly equal is overrated, yes. But in order to make max power it has to be done. Try pedaling a bike up a hill. Then try pedaling up a bike with the pedals 90* apart instead of 180*. Harder, eh?

Edit: PS, he isn't a moderator.

 

The problem with searches is the info you get has been posted YEARS ago. New members might have some new ideas, and the old how-to's may have followed what was trendy at the time. Why not clean out the fridge one in a while?

Besides, a forum should be more social. If I wanted to sit quietly and read old articles to myself, I could go to a library.

 

It's not like I started a thread with some noob question without searching first, I was asking him to explain his post since he was basically just spitting out pipe lengths with no explanation of what in the hell that actually means, why it's important, or even why it's relevant enough to start a new thread on. Then he smugly attacks RB products with no supporting information. Awesome!

Now back on topic, here's part of an article I found that says the need for equal length primaries is pretty much a myth and explains why:

"Headers -- Primary Pipe Lengths
Misconceptions concerning exhaust pipe lengths are widespread. Take for instance the much-overworked phrase "equal-length headers." More than the odd engine builder/racer, or two, have made a big deal about headers with the primary pipes uniform within 0.5 inch. The first point this raises is whether or not what was needed was known within 0.5 inch! If not, the system could have all the pipes equally wrong within 0.5 inch! Trying to build a race header for a two-planed crank V-8 with lengths to such precision is close to a waste of valuable time. Under ideal conditions it is entirely practical for an exhaust system to scavenge at or near maximum intensity over a 4,000 rpm bandwidth. Most race engines use an rpm bandwidth of 3,000 or less rpm. If the primary pipe scavenging effect overlaps by 3,000 rpm then it matters little that one pipe tunes as much as 1,000 rpm different to another. Since this is the case, then all other things being equal, pipe lengths varying by as much as 9 inches have little effect on performance. A positive power-increasing attribute of differing primary lengths is that it allows larger-radius, higher-flowing bends and more convenient pipe routing to the collector in often confined engine bays."

 

Ok guys. lets settle down here.

If Hyper wants to explain his reasoning in a non-combatant approach and you guys want to put your questions in a non-combatant manner then the thread stays open.

If it gets out of hand again it's closed. :-)

Thank you,

 

I once worried about needing equal length headers. I don't anymore. I'd rather have large bends in a tight engine bay than loose sleep over non equal length headers. The 13B powered GLC is an example.

 

Yes, I know that. My point was that the center section and rear section before the collector are going to be pretty close to equal length as well, so that 3" of difference at the flange is not going to amount to much over the entire system.

 

Dumb question. But isn't the center section of the RB RR system made in a manner that causes one pipe to be longer than the other, thanks to the fact they both have to make a bend? Perhaps this has been taken into account by RB, and is the reason for the unequal length pipes on the header.
I don't hace access to an RB RR system, but I'd be willing to bet that by the time you measured from the engine flange, to the rear of the center section, they would be much more closely matched in length.

 

I still have yet to see any real dyno numbers comparing the SDJ and the "way more power" they supposedly made....and since they're not available anymore, its a mute point really...

Looking at the full long primary SP exhaust, the pipes are pretty close to the same lengh for each housing.

 

I do have access to the header and dual pipe center section so I'll take a look at some point today and get back to this thread with my observations.

 

Hyper I noticed on the numbers that you quoted for long primary lengths before collection, they all give a 5" spread. To me that would imply that you could have one pipe up to 5" longer than the other at the collector and still be in the ideal range.

 

Thanks Jeff.

 

That's a possibility. Which of the header primaries is longer before the first flange?

 

In the original post, he states R1 is 29, R2 is 26. That seems to agree with what I remember from seeing the RB RR header. Also, if memory serves me right, the shorter header tube, feeds into the longer center section tube. It's longer due to going around the outside of the bend in the other pipe.

 

Ah, I missed that.

 

Ok I just took a look. R1 connects to the pipe that is closest to the driveshaft in the center section. From my observation, it appears this pipe closest to the driveshaft is a little longer than the other pipe due to the curve.