Rotary Inspired

iTrader: (1)

Also someone touched on the subject of the 20B in the miata. While this would be awesome but it would throw the balance off as the 20B is considerably heavier. Attached is a 20B build I am in the process of completing so I can vouch for knowing the difference.

RIWWP

iTrader: (2)

sideways-dan,

I got linked your thread. I'm gonna send you an email if I can, or PM if I can't....

Silver6

Nice. I haven't seen your build before. What are you plans in terms of hp? I would love a 20b but unfortunately that takes money to do. Which unfortunately I have none. Well at least not enough for that kind of project.

sblethen

iTrader: (3)

I apologize for offending anyone. I wanted to subscribe and figured I would share what small amount of knowledge I have learned. I didn't go into any details because I personally don't have any dyno numbers to back myself up. This is why I only gave some broad things to consider. Good luck in your build, as I said in my original post I am subscibed to see what more experienced members may share. I can only run NA in the class I am racing in as well.

Stephen

PS: If it wasn't for us a-holes we wouldn't have any ********* -- couldn't resist and don't take that personally!

reddozen

iTrader: (1)

Not sure if Brian wanted me saying or not, but the last time I talked to him, they had the street port engine up to 230HP.

shadycrew31

iTrader: (6)

This should be answered/considered before any more posts come up

sideways-dan

thanks for the replys. we currently race in the NSSCC here in the uk and basically mods are free but dictate the class you are in.. with a rotary we would be in the under 2.0l class where as with our current turbocharged 1.6 we are in the over 2.0l class as there is a 40% displacement increase for rotaries and a 70% increase for turbos. we can have any engine we like as long as it is mazda and we can do anything to it. the current setup is around 250whp so something around the same would be great but ideally with room for improvement later on. reliability is pretty important as with all race builds. do you guys think a 13b would be a better more cost effective motor? as many will know low to mid range power is not so important in a race car as it spends most of its time screaming...

reddozen

iTrader: (1)

I would compare weight too. If the renesis is only 20lb lighter than your current engine + turbo setup, then it may not be a huge savings. I have had BDC bridge port my renensis. I wish I had definitive numbers to give you from the dyno, but we haven't gotten that far yet. Brian is pulling 230HP from his street port, and I have the same porting plus the bridge, so I should be able to make more than that, but only tuning will tell.

sideways-dan

the current engine + turbo set-up weight approx 110kg (242lb) and from what i can find a full renesis weighs roughly the same if not a little more but the weight would be a lot further back than it is now and a lot lower down. always good!!

shadycrew31

iTrader: (6)

well for starters the renesis is essentially a 13b. so long as you keep it NA and don't mind rebuilding it from time to time as it slowly loses compression you are good.

That said I don't professionally race these things, neither does most of the guys who have posted in here. Theres a few members on here that do and one of them has already posted.

Personally I would wait and see if they can shed some light on your questions. I can tell you this running a rotary powered car on the track is going to be costly.

Also the reliability of running a bridge-ported engine has yet to be determined, I know for a fact that running a mild street port is reliable. Bridge-porting is still uncharted territory, I know of 2 bridge-ported renesis engines and one of them is not running.

RIWWP

iTrader: (2)

sideways, not sure if you got my email.

Some points to keep in mind in favor of the swap using the renesis that you haven't already covered:

- The Renesis can sit lower, and farther back, than the RX-7's 13B given the same engine bay placement, the former due to the shorter height from the e-shaft to the bottom of the splash pan, the latter due to the 'stepping' of the accessories and top side of the block that Mazda did to make it fit farther back in the 8. If you are thinking you will eventually turbo, the older 13b is probably the way to go, if not, the Renesis is superior N/A

- I can't find a reference to what series Miata you have, only the 1.8L reference, so I am guessing NA or NB. The NA would be the hardest swap, most limited room, most firewall modification. The NB is slightly easier. The NC is nearly a direct swap, as the NC and RX-8 share ALOT of components. There is SOME modifications that need to be done, such as motor mounts, but it fits in the space you have, bolts up to the NC transmission (same transmission), and shares alot of the wiring harness in common with the 8. There are 3 Renesis NCs that I know about (Mazmart, Denny in Austrailia, and 1 other private project), only 1 Renesis NB (in the UK), and no Renesis NAs.

- The whp numbers being quoted and used above are all for the Renesis in the RX-8. You should see slightly higher numbers in a Miata than the exact same engine and mods in an RX-8, simply because of the physically smaller drivetrain, less drivetrain loss.

- I personally would take 230whp with the Renesis's flat powerband over what is probably a peaky 250whp turbo'ed 1.8L More area under the curve, more usable powerband.

- Don't forget the stock ECU from an RX-8 as an option for the ECU side. Your budget will pretty much determine which route you go, but with a stock ECU and an AccessPORT is entirely viable. You have to deal with/address issues like the immobilizer, ABS/DSC/TCS (depending on trim level you get the ECU from, etc..., but far far cheaper than the level of stand-alone you need to get full oil injector control.

- Cooling for oil and water are going to have to be custom designed since it won't fit as-is in a Miata, but this isn't really a bad thing. The OEM cooling for the RX-8 isn't really sufficient anyway, and you can improve it considerably through a custom design

olddragger

iTrader: (3)

Kudos for this thought .
The rx8 subframe is a bolt on for the mx5 but in using it it sets the engine further forward than a custom set up ( about 8 inches!).
Our club has thousands of track miles on this engine. Eric Myer has all the data you will ever want.
At 220rwhp + there is really only one issue. Its already been mentioned. The engine will only last about 20-30 hrs at this level as it slowly looses compression and will fall to the 200-210 rwhp level. The engine really needs a good balancing and blueprinting for substained 8+K rpm operation --most do not go to the 9K anymore, but follow your dyno. This is without any porting. Porting may change all of this--I dont know.
It should have a larger than usual power band--about 3K rpm?
In NA form it is pretty reliable.
If you can set it back as far as the firewall will let you you will probably have the best handling car out there. And it sure will sound good
Paul at Mazmart is building one---give him a call.

Rotary Inspired

iTrader: (1)

While I love the Renesis an older 13B 6 port would be the way to go if you wanted to use the side ports. You can siamese the 5th and 6th ports in to the secondaries, balance and clearance the rotors, and with a proper intake and exhaust set up you can see 250 at the wheels. This motor will be reliable and last much longer than the renny on the track. There are several other setups that can net you the power you want and still last for years of track abuse. You will not have this option with the renny.

reddozen

iTrader: (1)

2000 miles so far and no issues other than a neutral switch being dead. Still needs more tuning. There are rough spots in the closed loop tables, but WOT it pulls pretty hard, but rich. I try to stay out of the upper RPM band until it's tuned more. could be months before I'm ready to dyno it though...

PhillipM

Well, without risking a bridgeport, or boosting the Renesis engine, you're going backwards in terms of outright power. You're not going to match the pull of the turbo 1.6 if you're putting 250 down to the road already.

What you will gain is a lovely torque spread right from 3krpm almost right until the redline. Which could be more usable provided you can get the gearing low enough. I must stress that as I currently race a Renesis engined car and the gearing is really pissing me off (but then I've got big 'ol rally tyres to gear down for).
You can slug it out of a corner from 3krpm on the torque if need be but obviously it's loosing you time.

One thing that did swing us toward the Renny though was the exact same as you - that lovely smooth power delivery reaps rewards for traction in a lightweight RWD car. And it works.

sideways-dan

see that's the decision... is it really worth it?? i love the idea of going rotary but will i gain that much? i know it will be loads more drivable, cant be any worse than it is now running almost 25psi of boost! its a bit all or nothing. it would also be a very unique race car which is always good. turbo miata race cars are also rare in the uk. i am pretty sure ours is the only 1 at the moment. suppose the only way of thinking about is will it translate to a drop in lap times?? that is the ultimate goal after all.

RIWWP

iTrader: (2)

More area under the power curve, better weight placement in the car.... I'd bet that you would see lap time improvements.

sideways-dan

i think so 2. so that leaves 1 question. which engine for the na miata race car???

RIWWP

iTrader: (2)

Reading back again, I noticed that I had it wrong, you have a turbo 1.6, so an NA.

Fitment for an older 13b is going to be harder than a Renesis, and I'd think that would be your primary decision factor.

For the NA series Miata, the 2 biggest issues that have come into play are:
- Driveshaft tunnel having to be physically higher than it exists for the 1.6/1.8L. This means re-fabbing the tunnel to be higher (the e-shaft exists from the center of the rotary 'block', contrast to the 1.6L exiting from the bottom. The engine is lower, but the output shaft is higher)
- Stick shift placement. Between the above issue, and having to modify the firewall to get it to sit in the right spot, there has been notable difficulty in getting the stick shift in a reasonable spot. Some say it's nearly impossible to get it in the exact same location.

Anything is possible, just depends on how much work you will have to go through. Being able to set the Renesis lower down will help the drive shaft tunnel issue (though it's only 1.5 inches I think), and having the flexibility of being able to place it further back with less firewall modification should give you more range to place the stick shift where you want, or at least get it closer to where you want.

sideways-dan

fabrication should not be a problem and i will have the whole off season to do it. i have found a thread though there ppl are fitting 13b's to na's using the miata gearbox with rx7 bell housing without much fabrication or modification. they pretty much fit straight in. keeping the miata box means i can keep the original ppf which saves a load of work.

RIWWP

iTrader: (2)

Yup, entirely. The NA does have that advantage of sharing more parts with the RX-7, similar to how the NC shares parts with the RX-8.

I would DEFINITELY be interested in following your progress once you get started, regardless of which route you take

bse50

Are you also free to use any pcm and rev limit you want?

sideways-dan

yea modifications are totally free subject to MSA rules. you have something in mind?

TeamRX8

iTrader: (25)

a dry sump setup will buy you HP and let you drop the engine for several inches of trans tunnel clearance, not cheap tho'

shadycrew31

iTrader: (6)

could you use the racing beat 13b dry sump front cover, or would you have to fab your own up?