IM a Huge Fan of TRUE DUALS!! tru tru is just ( dont kill me santiago ) that reading a couple threads on the forum i found that true duals might not give me as much horsepower and torque as it is advertised to give, since my engine is lightly ported. everything else is stock on the engine 1988 GXL N/A. I just emailed mazdatrix i will post their answer. thanx guys

 

Id go for a collected if I were you. The scavenging effect you get from the collected exhaust will help move the gases out at a higher velocity, which will help out the top end of a ported rotary alot. This of course is just my opinion, Im sure others will have their own. Whether you choose a collected singe, or a collected dual is up to you. Id go dual, for the looks and sound. If ALL that you are concerned with is power, then go single.

 

Between Kevin and I we have played with all the major “pre-made” exhausts on the market. In my honest opinion the true duals with the Racing Beat mufflers have shown the most gain up top. So much in fact that when you wire the 6th ports open you can really feel the lack or torque down low. I would suggest making arrangements to have your 6th ports operational if you use this exhaust.

A while back there were several threads floating around about using the true dual header and fabricating a collector pipe that would feed a 2.5”-3” pipe all the way back to single or dual muffler. I believe banzitoyota did one of those as well that he is in the process of testing right now. That I believe this would be the best way to go because you could tune to your specific wants/needs. But not everyone has the time, cash, or experience to R&D a custom exhaust system.

So out of the “pre-made” verity I vote true duals

- Dana

 

what about the low end torque?

 

Most people decide to wire there 5th and 6th ports open because 89% of the time they don't work. You don't feel the loss in low end torque when you do this if you are running the stock exhaust manifold with a down pipe/pre-silencer combo, and you start to feel it (though not that much) when you use a header with a single collected outlet. But once you go to the true dual's it is obvious that you are missing some power down there. I was just saying that if you use the true dual exhaust I would make sure they work or fix your 5th and 6th ports to work so you don’t loose that power down low especially with a ported motor.

- Dana

 

You said that your engine is "lightly ported". True duals works best with stock or near stock porting. The key is that the intake doesn't open any earlier and the exhaust doesn't close any later. In other words not increasing the port overlap. If your engine is lightly ported my guess is that the overlap isn't increased or at least not an appreciable amount. A large streetport (or an extend port if you are an Aussie!) wouldn't like the dual as much but yours may do very well with it. I would be willing to bet that Mazdatrix tells you that the dual will be your best gain.

The "best" system would be the one that you design and dyno test and build yourself.

 

here im attaching a picture. Everything on the engine ( long block) including the 5th and 6th port are working perfectly and even though i cant rev my engine more than 3000 rpms due to the recent rebuild i can feel the torque wanting to increase right when im in 2900 to 3000rpms. thanx everyone so is the porting job small enough to go tru duals and gain about 90% of those numbers ( 30 hp gains). or is it too big and i should go collective one muffler exhaust system. Im running premix by the way FLAMES!! wowow0

 

I am in the process of revising my current "system". Details to follow. I need to get the fuel/ignition/power issues resolved. John

 

 

That looks closer to nicely ported than slightly ported Do you have a pic of the exhaust ports too? It doesn't appear too extreme but the exhaust port will tell it all.

 

no unfortunatly i dont.
they were ported nicely all of them in my opinion.
the rotor housings were also ported well a lil. the diffusers where the exhaust holes are on the rotro hosuings were taken out and a lil porting was done. barely any though. so now i ahve no exhaust diffsers on my engine tru tru!!

 

If it is mostly no exhaust diffusers but no much enlargening then you should be OK for a true dual. I personally am partial to a long primary collected system though but that is just me. The duals work great on stock to mildy ported engines and your may respond well with either.

 

go read mazdatrix's webite
they explains everything abt true dual

 

Straight headers dumped on the side behind the right left wheel would be the best. It would be loud as **** but it would be the best.

 

Alex I am gonna kick your ****. lol!

j/p

Anyways if it is a small port the true duals will still offer the better overall power. I hope you cleaned your 5th and 6th while the engine was apart trust me it sucks when they are not working or wired. Your not going for all out HP I know this because you didn't do a major port job so you want something that will give you overall HP not just a peak like a collected(tuned) exhaust. MS and the rest forget to mention that they tuned exhaust usually makes less power out of its range than an uncollected does which limits your power to a specific situation instead of just boosting the entire range.

Anyways I still vote for the duals because MS looks like he has other reasons for bashing on the Duals and MT so I don't buy much of his talk.

Santiago

 

So then, what is a good exhaust setup for a large street port/small bridgeport?

 

Generally the collected exhaust but not just a bolt on. You need to make your own specifically tunning it for the engine it is to go on. But this is just talking about peak HP and not overall power. Still no dyno sheet of a tuned exhaust. well I think Banzai had one but that thing is making crappy numbers. lol

 

tru

 

Hey guys, um my 5th and 6th ports are not working as whoever had the car before me put on a free flowing exhaust (some kind of headers and straight pipe to a single exhaust) they also took the air pump off. The little hook thing of the actuators moves fine when I move it. How do I wire my 5th and 6th ports open.

Thanks

Jon

 

Do not wire them open. You will only loose low end. Get them to work. You can use an air pump and some other stuff to make them operate at 3800 or 4k like they should. Wiring htem open should not even cross your mind! It sucks ***** with them wired open.I suggest you get a pre-silencer combo if you don't wanto get into the air pump deal. Not to mention single outlet looks

 

That is a clean port job. Who did it? Got a pic of the center plate?

 

No it isn't.
The length of the exhaust is way to short... Plus, if they are uncollected, the dynamic scavenging effect between the two is lost, huge power loss.
I've run my car with just headers too, just to make sure that my own theories and prevailing logic holds true, and it does- it's much slower. (When it was N/A BTW)