The technology is 17 years old, I would call that taking a step back. Not in turms of power but in terms of progress.

A 350 hp rew has been done and done again, nothing new there. We have several 330 whp rennies running around (I'm sure 400hp will be obtainable when the ignition problem is solved). Are they reliable? I don't know, only time will tell. But sticking in a 17 year old engine just does not peak my interest especially when products for the rennie are just finnaly rolling out.

 

Most people would choose the easy way.

Most people would say Why bother with the trouble when the old stuff works ?

but these people forgot that, without people who pushed the limits back then. There would be no *easy power* today.



Samething is happening to Renesis now, its a painful process I know.

I prefer new technology over older technology, even if I have to go thru a painful process.

 

Your not taking into affect other aspects. The 13b maybe 17 years old however, it is proven, possible and reletively easy to make the power people want. Now here is the kicker, price. What will it be? There are variables such as the going rate for an engine and what not but you get the idea. all other info aside, if you could pick between 2 engine options, both about 10k, one making 500hp and is proven and reletively reliable and one that is 350hp and no one knows if it will last even a year yet, which would you choose? Sometime old relaible tech is better anyway. I do believe the renesis is good and i will most likely turbo mine however, im playing devils advocate because i can see either option as being good ones. Find the hot version video of the JIC D1 8 and you will quickly say hmmmmm....what if? Great car. Thats one option path and it is a good one. It already is putting down 530hp. Mazsport is close to the 400 goal and will most likely break it soon enough and im not knocking scott, he is great at what he does, however his stuff is still in uncharted territory. It end up being very reliable,maybe not, we dont know. 13bs on the other hand have been doing this for a while and tuners already know how to make that big power. Granted no one has tried much porting (except guitarjunkie to some extent) and even less with a port job and a turbo. But again, thats still uncharted territory. People want power and they want it now. A lot of people say just wait but think about it. You will have to wait 10 or more years to have similar experience with the 13b as the renesis. Yes i do know that some of the experience will carry over from one to the other butyou get the idea. Lets be honest, how many people want to wait 10 or 15 years for the turbo set up to finally be right? Not any i know. This is an option for those who want the power, want it to be known, understood, and predictable and want it now.

 

The 13B-rew first came out in 1990 (Hint the REW did not first show up in an rx7) and yes it is an old motor. The design is almost two decades old. Just because they were putting the same engine in a car up until 1999 does not make it a newer engine.

With your thought process we would still be putting around in steam powered cars.

If you want to be a follower you can stay in the past and do the samething that has been done before, if you want to be an innovator try to push the envelope with something new.

 

just recognize that they're different not necessariy superior or inferior to one another.

in my mind, you're the follower for doing what everyone else is doing and installing a turbo on a renesis.

just as another example, i'd take an RB26DETT over VQ35DE. just because something's new doesn't mean it's better or will be better. if it's the ideology that compells you, i fully respect it; i just happen to respect dyno numbers slightly more.

 

^ my point exactly




BTW i'm not putting a 13B-REW, just so you guys know i am a first time Rotary owner and frankly the design hasn't exactly won me over

i have been tuning toyota and nissan inline piston motors for years and its like totaly different worlds.

thats not to say i didn't try, i had blast every time i drove the car from before the turbo all the way till after i blew (I think) one rotor
but i just don't know if this is the motor for me, there is NO way i would put a LS1 in, that would be crossing a big line IMO but thats not to say i convert back to pistons

but we shall see in the future months and i will keep everyone that interested informed with what ever direction i go in

thanks to everyone for their support and input

 

I feel another 'First ever 2-JZ swap' comming on...

 

+1

-Cody

 

What are the static compression ratios of the rotors available for the 13B-REW?

 

Rew = 9.0:1

 

One thing I have considered as a mod is blocking the Renesis exhaust ports and using a set of '85 GSL-SE rotor housings for exhaust purposes. This way we could either turbo or go extreme N/A. Imagine all the nice intake porting with the classic overlap. It just might work.

 

The 13B-REW came out with the 1993 RX-7 but that car also had a very limited run in England in 1992. It was NOT in the 2nd gen at all.

 

i thought the REW debuted on the cosmo

 

Yes I coulda sworn the REW was originally a Cosmos engine... but Id definitly take RGs word over mine.

 

the RE was in the JC Cosmo, not the REW.

 

The engines in the Cosmo and the 3rd gen are different although similar. The intake runners in the Cosmo 13B's were larger and the intake manifolds different. It is true that some aspects of the REW did appear in that engine such as the rotors. The twin turbos in the Cosmo are also different. They are very similar engines in many ways but not the same.

 

Well, what I wanted to know whether there are aftermarket rotors offering much lower compression ratios? Or what is the lowest anybody tried?

 

The earlier FC Turbo rotors were 8.5:1 compression, off the top of my head.

 

There are none that will work in a Renesis right now. The 87-88 Turbo II RX-7's had 8.5:1 compression. The 89-up turbo RX-7's had 9.0:1. Many people have made tons of power with 9.0:1 compression.

I know a few people have tried 13B rotors in a Renesis. I have no confidence in the long term reliability of this setup. The side seals on the 13B rotors are not the same. This is the biggest issue to contend with. The cutoff seal is there for emissions reasons. The flat profile side seals of the 13B will not allow carbon to get out easily and will ultimately break as a result. It may not be right away but it's been proven by Mazda to be a longterm issue. That's why the new wedge shape is used. That was actually why Mazda didn't use the all side port engines back in the 70's when they first tried them. The side seals were breaking and they didn't know how to get around it at the time.

 

Things that make you go hmmm!

 

Gee Paul I wonder where we've heard of that before?

 

now im not a rotary genius.......but i have a general understanding of how cars work, heres my thing if a company is really into rotary performance such as racing beat or mazsport.......ok one main problem with the renesis is the 10:1 we all know that good for N/A not soo good for FI..... now to lower compression on a piston motor......most companies that makes stronger pistons, usually offer them with a bigger dish on the top of the piston to lower the compression some...........y couldnt we take that idea, basically make a bigger dish with the same design rotors of the renesis...... that way u can have stronger rotors that the renesis has, with a lower compression such as what the FD has.........now no flaming is needed. just one idea bein thrown around any company tried of that???

 

just geometry i guess.

pistons are perfect cylinder in a perfect tube. rotors are semi-rounded triangle in a semi-oval housing.

 

It's much easier to cast and machine a piston than it is a rotor. A piston is a basic cylinder shape. It can easily be cut on a lathe or CNC. Burt Munro who the movie "The Worlds Fastest Indian" was about used to dig a hole in the sand at the beach ( I'm simplifying it a little bit but that's basically it) and melt aluminum and pour it into the "mold". He'd then take the new "piston" back to his place and turn it on a manual lathe. He mad many pistons this way that worked. After you get the shape you want milled out, then you only need to mill out the ring grooves on the outside. Again very easy to do on a lathe. There a bit more to this but that's mostly it. It's something that a backyard mechanic who is very creative could do with the proper equipment. Burn Munro did it! It doesnt' mean it was easy though. He also hand filed his own camshafts!

A rotor is a very different prospect. It's shape adds complication which in turn adds costs. Remember that a piston is not hollow. If you flip one over it almost an ashtray but you can see all of it. You can not see the inside of a rotor. This means that it must be cast. You can't machine that from a solid piece of metal. A piston could be originally cast or it need be machined from a cylinder of aluminum. They are usually cast and finished though.

A rotor will need to be made from cast iron and has an internal shape that is hard to copy. It has bracing internally that you just can't see unless you cut one apart. Oil flows through our rotors whereas on a piston it merely sprays onto the back of it. We would need to make a mold of the internal shape of the rotor with the appropriate casting thickness adjusted. This mold would most likely be made out of sand. An outer mold would also have to be made in which the inner mold fits inside. Now you need to think of a way to attach these together in a way in which when the sand comes out, there is nothing in the way. This isn't that hard to deal with though and is actually the area that oil ends up draining out of the rotors from.

If you've gotten this far, you need to machine the outside of the rotors to the proper shape. Remember you've got 5 total sides to do and get right. You need to get it perfectly centered to do this as you can't get this wrong. Then you need to machine the bearing surface in the center of the rotor. You also need to have a jig set up that allows you to machine out the rotor dish for the appropriate compession ratio. The success of this will also be determined by the shape of the dish itself as this has an effect on internal engine airflow. Once you get a dish machined out, you need to be able to copy it again on all sides.

Now you've got to go machine all of the seal grooves. You've got some very small tolerances which aren't hard to do on the outside of a cylinder shape but are hard on a rotor. We can't just turn the rotor and use a lathe bit to cut out this groove. The side seal grooves follow the shape of the rotor. Now we need to program this shape into a machine that will follow it. This would be extremely difficult on a manual machine but not impossible. You need to be able to get this same cut 6 times per rotor. You need to machine 6 corner seal holes. You need to machine 4 oil control ring grooves and 2 cutoff seal grooves per rotor. You need to cut 3 apex seal grooves. These grooves are also not the same depth across the entire length. The outsides are deeper.

Now after you've gotten this far, you need to balance it all. Mazda has gotten their technique down pretty good with the Renesis engines so they don't need to take the same steps that they did with RX-7 rotors when it comes to balancing them. The RX-7 rotors were blanaced by drilling holes near the corner areas to equalize their weight and on top of this they were all equalized to the same predetermioned weight as other rotors.

Making a piston is child's play by comparison. While not impossible, the amount of effort to do it is quite considerable and labor intensive. This means it would not be cheap. A company doing this would have to sell a very high amount of them to get any money back off of the initial investment. Especially if they didn't previously have the equipment. Contracting it out to someone who does have the equipment faces it's own issues but still wouldn't be cheap. That's why no one else has done it.

 

Thanks for the explanation (I wasn't necessarily interested in the Renesis option), I guess nobody has tried to cut out these rotors to lower the compression ratio even more?

Let's say one were to add a supercharger with a pressure ration of 1.5, the air flow through the 13b would roughly be the same as through a 20b NA. If one would add a turbo to this set up in series (turbo -> supercharger -> 13b -> turbo) it could theoretically produce the same power (including powercurve) as a turbocharged 20b. (Because the airflow through the supercharger engine combination is the same as far as the turbo is concerned.) Obviously, this would only be viable if the compression ratio on the 13b rotors would be reduced sufficiently to reduce max pressure and temperature at ,TDC'. (Or in other words, brake mean effective pressure would need to be increased by probably around 40% on each rotor of the 13b to essentially develop the same power as a 20b, which requires a significant reduction of the compression ratio.)
Lowering the compression ratio on a rotary engine by increasing the indent on the rotors would have secondary benefits since it would improve the shape of the combustion chamber (better surface to volume ratio). Also the supercharger would improve scavenging which otherwise might not even possible if a turbocharger was used.

A twincharged 13b would be lighter and smaller than a 20b. It probably would also be more efficient at partial throttle settings.