Nemesis8

iTrader: (3)

Have you read this article? It's 40% more powerful than the old 13B :D

http://www.rx7.com/techarticles_rx8power.html

Psylence

Yes of course it is, when both are stock.

I'm interested in what ported 13B's put out. More than a Renesis?

Ajax

Theoretically speaking, if you tuned 2 NA engines to their limits and could properly control every aspect necessary in either car (fuel, ignition, throttle body, everything), the renesis would produce more power unless the 13b was fully peripheral ported and even that may not help.

How much air can you possibly flow into an NA engine? Is it enough to even take advantage of a P-Port or would that hurt you more than it helped? I don't know the answers to these questions.

Anyway, tuning is the biggest problem with the renesis. If you want to achieve maximum NA power, expect to spend a ton on tuning.

zoom44

what good are giant ports if the stock intake manifold with the tuned variable length runners(s-dais) doesnt flow anymore air? what good does raising the rpm do if the air runs out? what good does making huge exahuast ports do if you cant make a header that actually flows any more/better?

this engine with the stock injection and manifold is already tuned to nearly all it can be. porting isnt ever going to big gains to 280crank hp unles the air systems are changed. period.

port the engien in and out put on a bigger throttle body and intake system tuned to use it plus get rid of your cat so you can have a decent exhaust manifold(ask rg about where it would need to collect) change the injectors new computer etc etc etc

really when you think about it- it wouldnt be that difficult or consume much money

Ajax

So many bottlenecks.. I'm gonna replace my cat with a coffee can! I think that'll flow the bestish!

MadDog

My personal belief is that the lack of overlap between the opening of the exhaust and closing of the intake ports is the biggest factor affecting the achievable NA power with the Renesis. The overlap was eliminated when the exhaust ports were moved to the side instead on the periphery. Perhaps you could port it in such a way was to gain overlap, but without it, you can't scavenge.

Psylence

Hm.. hadn't thought about the intake system and how well that flows. Of course one "mod" always precipitates another, thats the name of the game. You just have to know where to stop to maintain maximum reliability and driveability. And power

I just assumed that porting would be part of the complete NA package...

zoom44

well mad dog is right. i actually was going to write something "and make a port job that will give us some overlap for scavenging" but decide against it. pobably should have tho given that this is a poting thread

Mazmart

iTrader: (12)

This is what I've been saying all the while. The lack of overlap is going to limit the potential. Right now this thing is a marvel to create what it does with low emissions. It has wonderful intake manifold design and huge ports. If you give it back overlap you will kill some low end performance and the idle will lope like a good street-port. Without bridged intakes I doubt we'll see much more than maybe 260 flywheel hp.
Paul.

rotarygod

There are good and bad benefits of zero overlap. The old way of thinking says that you want less overlap for lower rpms and loads and more as the rpms rise. While the highest powered rotaries all have huge overlap, there is no denying that the Renesis with zero overlap makes tons more power across the board than the nonturbo 13B's did. It takes some pretty nice porting to get the older nonturbo rotaries up to this power level and they still did it at the expense of other areas.

I feel there is still more to be had from this engine without getting into the world of overlap. How much more remains to be seen. The exhaust ports do not flow very well. The stock exhaust manifold isn't the greatest either but it isn't as bad as the ports which makes it good from a functionality point of view. I am leaning towards a process called negative supercharging. This can only be accomplished with a zero overlap engine. In order to take advantage of negative supercharging we also need to have very high velocity intake and exhaust ports. This is where some heavy exhaust port work (not making them larger but rather flow more air) and a properly designed exhaust will come into play.

There is room to make the stock exhaust smaller on the Renesis and still make more power! This can't be done by just bolting on a small exhaust pipe though. It will take a complete redesign of the exhaust sleeves in the engine. Fortunately they are removable so new ones could be made and inserted. These new sleeves would keep total runner area as small as possible yet with good shaping and port profiling, they would still flow what they do now. I'm not too concerned with making them flow better than they do now as this would be a larger port with less velocity. Now that we would have a smaller exhaust port (and searate for the center iron), we need to make a perfectly done header that also matches this size. The runners would collect at a merge collector that would expand in size over a short distance to promote scavenging then we'd have a nice exhaust all the way out.

What will all of this do? Notice I mentioned scavenging. Scavenging however is useful during overlap and not zero overlap so what do I really mean? We need to get the combustion chamber as clean as we can before the intake air hits it. With traditional scavenging, during port overlap the exhaust velocity creates a low pressure zone which interacts with the incoming air to help speed up the air in the intake and help pull it into the engine. A little intake air may pass through the overlap zone though and go out but overall it will benefit. By doing it my way, we are relying on a high velocity exhaust stream that scavenges with the other side of the engine really well. These exhaust gasses will be moving very fast and they will suck the chamber clean behind them. The faster we can get these gasses moving, the lower the pressure behind them in the chamber will be. The goal is not only to remove everything out of the engine, but to remove more than that. In other words, we want to let these gasses actually pull the pressrue in the engine down below atmospheric pressure to give us negative pressure. This will leave the chamber open to only good gasses when the intake opens but it will also do another thing. It will scavenge the intake. When the intake ports open, the negative pressure will want to equalize with the incoming air. This will get the intake velocity up very quickly and suck in more air and you'll make more power. This technique is mroe beneficial at lower rpms than at higher rpms and what you would find by doing it this way is that low end power and economy would go up noticably. We are still boosting the engine. -2 psi is no different than 2 psi. Does it matter if we left 2 psi worth of space in the engine waiting to get filled up or that we are forcing 2 psi into a smaller space with boost? It's the same thing. Either way we are getting more air into the engine. I'm not specifically saying that we will get 2 psi from this technique. You might get 1 or you might get 7. It all depends on how it is done but the point is that there are gains to be had by thinking differently. Look up "negative supercharging" on the internet to see more info about how it works. You can not do negative supercharging with overlap or forced induction. I feel this would be more beneficial to the Renesis powerband.

Speaking of different ways of thinking, I am currently running my RX-7 with negative timing split. That means that under most loads and rpm's, I am firing the trailing plugs first! The car runs great!

zoom44

you want to do what the intake does only going out as well

rotarygod

Basically what I am saying is there is no need to go bigger when going smaller or staying where we are but thinking unconventionally can get us power gains. The first thing everyone always wants to do is to make things bigger. More, more, more... More runner area, more rpm's, more port overlap. Bigger is not always better. Find ways to optimize what we have first but think differently. Get the terms more and bigger out of here. Bigger is only better after you have maxed out smaller. We haven't. Thinking differently is what will make us all better. Remember, I am firing my trailing plugs first and not only at idle!

patrick_andraste

has anyone tried expansion chambers on a rotary?

Psylence

That almost sounds like what rg is implying with the negative supercharging idea. I'd love to have something like that on my car.. I can only imagine what that would sound like! *drool*

patrick_andraste

I used to build two stroke race bikes. we would use the hot gas flow to do the initial scavenge, when the ports overlap we use the scavenge to pull from the intake, but the major difference is the exhaust port actually stays open after the intake closes, so the idea is we pull fresh charge into the pipes, then use sonic wave resonance and a converging chamber to push the fresh charge back into the combustion chamber. Somewhat like passive supercharging.

Norton Played with the first part off the expansion chamber on their race bike rotaries, using the opening cone to do a chamber scavenge making sure all the spent charge was out and creating more of a vacuum to pull more charge into the chamber.

BaronVonBigmeat

From http://www.impulsengine.com/newproducts/index.shtml

Hmm...small exhaust ports...no overlap...super long headers...where have I heard of that before? Actually if the factory exhaust ports are so small, maybe Mazda had something like this in mind from the beginning, but had to change it for some reason? Like, long headers = slow warmup time for the catalysts?

BTW, that website, are they for real? How come you don't hear about anything like this in Hot Rod or whatever magazines? Or did I just miss an issue.

rotarygod

Those guys are for real but understand that they are actually choking their engines down to get more low end but at the expense of top end. I do not fully want to do what they did by choking our engines off but rather utilize the same principles to give us more power everywhere. Maybe not to the extent that they are getting it, but a gain never the less. Since I want an exhaust port that flows what it does not but has a much higher velocity, I know that we can get a gain at lower rpm's but still flow enough for good top end. We don't want to flow less than stock so we can keep the same redline as stock.

Their headers actually collect at a shorter distance overall. It's their expansion that makes it long. I would rather just use an expansion cone rather than multiple steps. Overall I'm not trying to copy everythig about their system and then apply it to the Renesis. I just feel that there are certain aspects of it that would work very well with the Renesis.

guitarjunkie28

as far as the porting goes,

our initial 4th gear run was 150whp....dismal
after the porting (same gear), we got like 186, but that was at like 50% throttle!!!

now 50% throttle doesn't necessarly mean 50% power, but if we hooked up a cable to the throttle plate or found some other way to defeat the factory safeguard, we'd see an easy....EASY 200-210+ to the tires.

i've been talking with snoochie about doing the haltech or some other method of controlling this thing and it pretty much boils down to lack of money and time.


if anyone else wants to give it a go with porting+ ems, let me know.

rotarygod

Richard responded on this topic but in the wrong thread so I thought I would address it back here.

Yes I am running negative split on my RX-7. The trailing plugs fire first. The most positive split I have is...well I never have positive/conventional split! It goes to no split at full load/higher rpms. As load decreses and rpms decrease, the split widens, just negatively. I can only run -12.5 degrees of split this way since I am doing it mechanically through a distributer but others have gone as high (low?) as -35! The RX-8 runs a 5 degree negative split at idle and low loads but quickly gets it up to the conventional positive split up to 15 degrees. Negative split should NEVER be used when under boost! Only under vacuum. It won't do anything useful for your needs. Negative split is still a fairly new concept to me but it does work. That I can attest to.

guitarjunkie28

i've heard of a few guys talking about that lately, but i've never been able to do it since i'm mainly into haltech and microtechs. i'll definately try it once i use an ems capable of doing so.

i've heard good things about the fuel economy with a negative split.

David_M

Looking at the impluse headers I have to say that stepped headers are nothing new. Aftermarket complanies have been making them for years. The basic principle is the same as with impulse but only the primary tubes are stepped not the collector. I can say from personal experience that stepped header do have a real effect on low and midrange torque but lose effectiveness at high rpms where they're roughly equal to a standard header of similiar length. The reason that the steps lose effectiveness is because the overlap happens to quickly at high RPMs for effective scavenging ( I know I'm stating the obvious but I don't want to assume that everyone knows. ). I do have to wonder what effect a simple stepped header would have on an engine with no overlap. Will it work until redline or will it perform like with conventional valve openings and drop off to no gains as RPMs increase.

rotarygod

You need to go read their entire engine design to understand their use of it. I want to apply certain aspects of it to the Renesis. The most important part for me is the merge collector but this is one of the most important and overlooked areas of headers anyways. I really have no desire to make the primary tubes stepped. I am more concerned with velocity.

PoLaK

iTrader: (1)

Didn't Racing Beat make serveral FB exhaust headers/systems that took advatange of the scavenging effect, I remember browsing their website said it was good for some 20-40hp on the FB

How big are expansion chambers? Is there room to fit one on the underside of the Rx-8? If so how much does an expansion chamber really help in producing a negative atmoshereic pressure inside the chamer?

rotarygod

Headers on the old rotaries and headers on a Renesis are 2 totally different phenomenon. Racing Beat did try a couple of header designs on the Renesis with very small gains (4-5 peak horsepower). I feel that by taking a different approach to headers and the Renesis exhaust ports we can find some bigger gains. Will they be what the old headers got on older rotaries? Probably not but I want a gain over the usable rpm range. This is what the car really needs. On the old RX-7's, it wasn't uncommon to see a 30% gain in power from a set of headers and a good exhaust! Too bad those days are gone.

I don't want an expansion chamber but rather just a megaphone type of expansion. An expansion chamber as used on a 2 stroke does 2 things. The expanding side helps scavenge the exhaust gasses behind it. The contracting side on the far end sends a reverse pulse back towards the engine and actually pushes some exhaust back into the engine. We don't want this. That may be fine on an engine with overlap which has very good scavenging and some intake comes into the exhaust, but on a no overlap engine such as the Renesis, why would anyone want to put some of the exhaust back into the engine? 2 stroke engines have alot of intake charge get pushed out of the engine which is why this chamber needs to be designed well to push some fresh charge back in. We don't need that. We just want the good scavenging of the divergent megaphone side of an expansion chamber. Our goal should be to over scavenge and leave a vacuum inside the engine that will help pull more air in as the intake ports open.

Nemesis8

iTrader: (3)

The sound is going to be thunderous with a megaphone header. Are you thinking to increase up to 3"?