So I have heard that true dual like rb's is ok, but collected makes more power. And I have heard that the collected rb header collects to soon and the collector is too short?

So, using the power range of 3500 to redline, keeping dual exhaust, and running some kind of presilencer so its semi quiet, whats the best step-up?

 

Actually the RB header collects too late for an optimum "short primary". Under 24" is good and they and everyone else with a commercially available header are way past this length. It's much better than stock though.

 

So collecting early is better then later?

 

Not necessarily. There's a "but" for everything. due to tuning harmonics there are actually several different lengths that work. It all depends on what your tuning goals are and what order of harmonics you want to tune to. Think of tuning as a sine wave with troughs and peaks. You have spots you aim for. If you go too long or too short you may fall off of the peak and into a valley. Go even longer or shorter and you'll eventually get back to a peak. There's no way to tell where you engine will be absolutely happiest as each engine is a bit different. There are just general ranges to shoot for in length. A long primary system works by tuning based on a different order of harmonic so they are much longer. Typically 3 to 4 times the length of a good short primary depending on the goal. Racing Beat has a good guideline for exhaust lengths listed. They give ranges and they work well within those ranges. As with any other system, the last few percent gain comes from trial and error.

 

So for boughten headers, is corksport or rb header better?

 

What about no collector (true duals)?

 

From what I understand collected yields a higher power up in the rpm range and true dual loses its efficienticy(sp) up top.

 

The more port overlap you have, the less you want true duals. By the time you get to a bridgeport or a peripheral port it's an absolutely horrid choice. It works good for stock or most streetports though. The less overlap you have, the better they work. For street use the powerband is actually quite nice. I personally think they sound like crap but that's just an opinion. Many people love it. There is no one right exhaust (or any other system) design for every engine setup even though many people treat it as there is.

 

The RB "street port" system is not quiet. It's not loud, but it's not all hush-hush like their regular exhausts.

It seems like for a stockport you can pretty much bolt anything on to the engine and it will work well enough, the main restriction is the exhaust port itself.

 

My RB streetport exhaust is VERY quiet. In fact if the fan is going I can barely hear the exhaust. Unless of course I open her up. RB did a good job with it. It's good and quiet when you need it to be, but it'll scream when you want it to.

 

I love my RB SP system...except the fact that the pipes get smaller after the mid-section before collecting to the 2.5 into the muffler. They go from 2" to just under 2" after the flange....wierd. For a streetported rotary, this exhaust IS quiet compared to hack-jobs.

Most full race cars, Streetport on up seem to live on 2" primaries, presilencers spliced into each if needed, merging to a 2.5 to 3" just at the rear diff, up and over. 3" is used for BP's and PP's to get max power when corked at the end.

 

Actually I don't think of it quite the same way. I don't look at the exhaust port as the biggest restriction. I think of the exhaust pipes as being too large for the job. When I made my own exhaust sleeves that kept the total port area constant all the way to the header flange, the end result was an exhaust pipe that could be as small as 1-5/8" yet the airflow out of the engine would increase by as much as 30% due to far less turbulence. I actually settled on 1-3/4" pipes on that engine and collected them to 2-1/4". Worked great. Sadly that car is in rotary heaven now.

 

Good point on the diameters. Not too many people play around with that sort of thing.

 

I used the formula that Rotary God posted for calculating exhaust length for collection -
((1080-EPD)x650/(RPMxRV) -1/2 pipe diam.
EPD=Effective Port Duration
RPM=Peak Horse Power RPM
RV= Reflective Value
My question is about the relective value & which wave fundamental to use. You stated that a value of one for a short collected system & a value of 4 for a long collective system.

What about a reflective value of .5? Or effectively tuning for half the RPM's peak? Wouldn't that still use the resonant frequency of the wave form? I mean the pulses are lining up so what difference does it make as to where I jump on the train so to speak?

Using this formula I get about 72 inches for collector location which is workable for me with my current setup. Strangely enough all of my port openings seem to be timed at intervals of 12 - 3600rpm for aux's and 4800 for the VDI... The exhaust collected at 72 inches would put the calculated peak HP at 3600 - would I get an effective resonant doubling at 7200? I'm going to have an small Peri-Port open at 6000 rpm's for peak power at 7200 and a 8400 redline with my original ports all stock.

My effective port duration for the intake is 80* - 80* and final stage intake length is 15.75 inches. So you can see how the factor of 12 is working here - aux's at 3600, VDI at 4800 and the PP's at 6000 and the tuned exhaust at 7200 with a RV 0f .5.

Of course I will have an aftermarket ECU to control this monster and the PP's will have their own throttlebodies & injectors while using the stock throttlebody and intakes for the stock S5 ports. I'm adding another level of switchable ports instead of making the existing ones larger thereby preserving my intake velocity and the effective intake tuning of the stock S5 components.

I'm also curious as to the volume and length of the collector... any ideas on how to calculate?

Ramses666

 

What about useing stainless? I havent seen many people talking about useing it here. But My engine builder stressed how stainless flows better the reg steel headers/exhaust pipe. Said that a car dynoed with a stainless exhaust will make more HP then if it had steel pipes.

Heres a good article to read.
http://www.burnsstainless.com/TechAr...s_article.html

Also talks about the angle of the collector being very critical to giving better flow.

 

I would say stainless may flow better due to the wall thickness meaning you may be able to make tighter mandrel bends....thick wall steel holds down the noise IN the pipes....stainless piping itself will not flow more than any other type due to construction....stainless = lighter weight and the aforementioned positive of malleability.

 

Guess you didnt read the article. Its got nothing to do with weight or wall thickness.

"quite a bit more heat stays inside the stainless header tubes and does not get passed into the surrounding air. By not allowing the contraction of the cooling gases as they flow down the tubes, more exhaust velocity is retained which promotes better scavenging at the collector. This retention of velocity increases the overall header efficiency."

 

There is also one little tidbit of it that also affects flow but it's over time. Stainless doesn't rust. The inside of the pipes will stay smooth. A mild steel pipe may rust and as rust build up inside, it gets rougher causing more surface tension and resistance to flow. If we were just testing 2 pipes in perfect condidtion of the same size on a flowbench with their only difference being material, we would see the same numbers. However heat retention plays a significant role in exhaust tuning and flow.

 

Just wanted to comment... running an experiment doing my own sleeves as well on a PPort motor. May have found a rather less involved way of doing them than milling the things out of unobtanium; will have to see how it works.

 

Good point
They also talked about what if a piece of internal rust broke loose and ended up in your turbo or inside the motor.

I agree that on a flow bench the 2 pipes would flow the same the difference comes in to play is when the fire is put threw it and the better scavageing effect that stainless pipe gives. Prob not a ton of HP but when racing or when trying to get every last Hp out of a motor every new found hp counts

 

I have done them another way that works as long as you don't have n/a sleeves with the diffusers still intact. You just use a smaller exhaust tubing and cut it so the top of it extends through the exhaust flange and goes right up to the upper edge of the port. It's pretty easy to do and much cheaper than machining new sleeves.

 

Sure, but why machine 'em anyway? Started with a piece of 1/8th wall 304 stainless tube, hammered it to the shape of the port, cut the angle thing on so it matches up with the inner contour of the housing, and welded it to a disc. $40 worth of steel, day or two of smithing and welding, voila.

 

I just have a thing for looks.

 

I suppose so... but on a manual mill, seems like it would take a lot of time to cut an insert. Actually, based on port area, I'm thinking of trying to go as small as 1.5" ID primaries... worth a shot anyway, and I've a friend with a jig for the SDJ layout...

 

Does anyone know when the SDJ header was produced? I was looking thru some old Japanese mags (AP - Auto Parts Magazine) from April 2001....they have an FC running a 13B P-Port and it displays the header....looks EXACTLY like the SDJ. Stainless with smaller primaries than the RB...1.5 or so, and merge to a 3" collector.

It's a white Anniversary Racing Factory FC that claims 300PS at 9500RPM....since the PS rating is a little higher than our bhp ratings, that would make numbers in the high 200's. Looks like a 48 or 51 Weber IDA providing fuel. Ignition was dual Ultra M.D.I. boxes and electronic dizzy!