85rotarypower

Ok, I've done a search on this and read for about 4 hours about various setups. I've found that true dual exhaust is actually quite good on a rotary, but some people say only for stock port engines while others say it works good on any porting job. I'm quite confused on the subject actually. I really don't see how porting could affect how well a true dual setup would work compared to a stock port engine. Both have the same exhaust pulses, the only difference is how long that pulse lasts. Mabey it has something to do with port overlap or something like that, but I don't fully understand porting yet.

I've started leaning toward true duals because of how good everyone says they work, but the fact my engine is ported puts this into question since half the people say it sucks for ported engines, while the other half say it works fine. Could someone clear this up a little for me?

cewrx7r1

iTrader: (2)

For a NA ported engines on first gens, RB had a dual exhaust.

On my 1983 12A street ported engine with a Weber 45DCOE, Rotary Engineering headers and complete exhaust ( 1987), it was not that much faster than with stock ports. When I extended the headers with their extension kit, the engine came alive. The kit kept the two exhaust tubes seperate for about another 2 feet.

Thus for maximum power, run either dual exhaust or very longer headers before converging into one pipe.

Jobro

iTrader: (2)

Pretty sure its good to keep the size of the dual system nice and small, something about keeping the exhaust velocity nice and high to make the scavenging effect work for your advantage.

Think twin 1 and 7/8" INTERNAL DIAMETER pipes is a good choice, with nothing in the exhaust path until just before the diff. Join them into a 2.5" straight through muffler just before the diff, and then a normal muffler after the diff.

Been told that that would be very very loud but very low restriction and fast.

85rotarypower

I'm talking about "true" dual exhaust which means no collecting. Having an exhaust as mentioned above would be totally out of the question because it is going to be to loud a stated and this is going to be a road car. Please stick to the original question guys and gals. I don't want to be told what might work better, I just want to know how good a true dual exhaust is on a streetported 13B N/A.

Hamza734

Don't get it: it sounds like absolute ****. Reason enough for me to avoid them.

85rotarypower

I've listened to the sound clips that I found and I really liked the way it sounds. I think that I'm just gonna do it. Turns out that the engine I got has a pacesetter header on it, so I'm going to hack it off just before it collects and go out with two pipes from there. The true duals have got to perform better than that POS collected header thats on the car.

Hamza734

Well, sound quality is totally subjective so if you like it, Godspeed. However, I would contend that a PROPER collected exhaust will handily outperform a non-collected exhaust. Just take my word on it: I have a background in mechanical engineering and fluid mechanics. If you want more info: check this out: http://www.burnsstainless.com/TechAr...ry/theory.html

smnc

From what I undestand, you want to collect the exhaust at some point, due to "exhasut pulse scavenging" effect? But you want to keep the runners as long as possible...

So no a "true" dual exhaust isn't recommended.

However, I do have a workable dual exhasut plan.
My plan is dual exhaust, all the way back to right before the mufflers, where there will be a crossover, and split back to dual mufflers.

Gives me the longest possible runners, still get scavening, and dual exhaust... without being too loud.

85rotarypower

I know I could get better results with a collected exhaust, but theres the factor that this is on an FB and length is quite limited. I really don't think I could make it long enough before it collects while still having a muffler on the car. I also know that collected exhausts are very loud unless you have a RB system, which is totally out of the question. I ran a 3" single on my 12A with stock exhaust manifold with an 18" long magnaflow and 2 other mufflers and it was still loud, not too loud, but loud.

smnc

I don't quite follow...

Here's what I have planned...

(sorry for the primitive sketch)

85rotarypower

Ok, I understand what your saying now. Basically you mean to use an X pipe. I've read that these don't work very well on a rotary, but hey, I'm all confused to hell right now so I guess anything could work. I think I'm just going to try the true dual exhaust and make it so I can "modify" it fairly easily with either a y pipe or x pipe at about the rear axle.

My car is going to be "unique" with its exhaust anyway. I want dual exits for the look, and there is going to be 1 exit on each side of the car, like the FC.

smnc

Yours sounds cool.

Someone was talking about doing that a few years ago. I think he got shot down pretty hard.

But I wish you luck. I've always loved the dual twin look.

What kind of mufflers are you planning?



Mine isn't quite an x-pipe. It'll be more like a collector, leading back into a split. A simple x-pipe doesn't have the flow characteristics I want.

From my research the LONG primaries will give peak power, I'll still get exhasut scavenging, and the dual mufflers I'll be using will keep it unrestricted...

Hamza734

Why not this:
http://www.iscracing.net/exhaust.htm

cewrx7r1

iTrader: (2)

The headers come together too soon for a ported engine!

smnc

Yup... This is a MUCH better set-up
http://www.racingbeat.com/resultset....rtNumber=16424

85rotarypower

Ya, I would LOVE to get a RB setup, but its just too much money. $800US plus exchange and shipping of a big and heavy part would probably put it over $1400 canadian which is twice what I paid for my low mileage streeported 13B. If I do my exhaust the way I want to, it will probably be less than $400.

For those who are wondering, I'll be using Apexi N1 knockoffs. I've got 1 already from the single exhaust on the 12A, and I'm going to buy another at probably around $4.00US plus shipping from E-Bay. The one I got has got to be one of the better knock offs on e-bay. Stailess steel body with high temp fiberglass packing I think. Either that or its stainless steel wool packed. Either way, with the silencer in the tip, it was more than quiet enough to satisfy the piggies, and it had a VERY low tone with the silencer out, moreso than a RB system I think. I got it for the fact I could put the silencer in the tip to quiet the car down and it actually works great.

Oh ya, for those with 1st gens and wondering how I'll have FC style duals out the back, I'm trying to think of a simple way to do this without too much modification so mabey more people with limited mechanical ability can do it. Thinking about using a gas tank from a Fox body Mustang. Need to get some dimensions though.

smnc

RB does have dealers up here. It's a bit cheaper than mail-ordering from the US, but not as cheap as what you're going for.

You'd probably have a better time intalling an aftermarket fuel cell to get the clearance you need, rather than a tank designed for a carb'd car. Safer too. Try contacting Jimmy54, he recently installed a fuel cell.

85rotarypower

The car is carbureted so a tank from a carb'd car is exactly what I am looking for. I thought about the fuel cell, and I'm going to look into them a little too, but I'd like it if I could keep my stock filler neck. I'm starting to think this isn't possible though.

Who sells RB parts up here?

smnc

My bad, I thought you had EFI... your sig says 6 port, so I assumed...


There's 3 dealers in Canada. The local one is Mazdee's in T.O. There's also one Calgary and one in Langley BC...

Mazdee's Performance (Rotary)
1031 Toy Ave., Toronto, Ontario
(905) 619-8813

85rotarypower

Thanks smnc.

Ya, it is a 13B 6 port, an 88' engine to be exact, and the engine was suposedly steetported, and I don't doubt it. The last owner said it dyno'd at 150 RWHP on stock S4 electonics and nothing more than a streetport and badly designed exhaust. Besides the cone air filter, the intake was all stock, including all the emissions wiring and even the ACV. I believe the 6 port actuators were stuck in the closed position too and there was no sign of anything to actuate them. With any luck, I bet I could get 180-190 RWHP out of this engine.

The reason I am converting to carb is that the engine wouldn't run right on the EFI. It ran and was drivable, but kept flooding out VERY easily and the rear rotor wasn't running at "idle" (which wouldn't go below 2000 rpm). Another thing I noticed is that there was fuel dripping from between the flange where the header connects to the rest of the exhaust, which IMO means the engine was running pig rich to the point it was probably just dumping fuel into the rear rotor. I said screw the electronics and I'm just going to go with a carb now. Nicer power to be had with a carb anyway.

smnc

Well, the power issue is debateable, but carbs can be much simpler.

I like my EFI tho...

85rotarypower

The way I understand it, the power on an S4 engine is restricted a lot by the design of the intake manifold. I don't have any proof of this, and going by RB claims of 180 FWHP with just the swap to a holley carb setup from them, I would say this is somewhat correct. I think my guess of about 180 RWHP from this engine is within reason.