Max Torque with open rules on engine build
 

Lets say you wanted to run in a hp/weight class.

The rules are open, so intakes and porting are free.

Take your HP and divide it by .08 to get your race weight, so 180 hp is 2250 lbs, 200hp is 2500 lbs.

I have pretty much every generation of rotary laying around. 13bREW, 13b Tii, S4 13B 6port, GSL-se, old school 13b 4 port, along with various old school 12a irons too.

what combination of plates, ports, and intakes is going to get the most torque for 180-200HP.

Forced induction will maximize torque, so that seems to say turbo.

increased displacement is next, so that's probably saying 13B unless you have a 20B hidden in the closet somewhere. :fingersx:

From there you're into porting, so you'd want to minimize port overlap.

Hope this helps!

No, on an NA build for max torque you want to maximize overlap and have an early intake closing timing to make the most torque.

A full size D shaped peripheral port with the flat on top, but down low on the side where people put semi-peripheral ports. You just have to make sure the closing timing is right around 50deg ABDC so torque drops off fast after 5,000rpm (this is to limit HP).

Keep the peripheral intake runner/port smaller than the traditional high rpm peripheral port size. Don't mess with the exhaust port.

These charts are from the Norbye rotary book from the development of the rotary engine. Note how overlap increases power at all rpm on a production (not race) sized/spec'ed peripheral port.

NSU KKM-502 test engines
https://www.rx7club.com/attachments/...-photo0202-jpg

Curtis Wright RC-60 test engines
https://www.rx7club.com/attachments/...-photo0204-jpg

and this last one is small side intake ports versus large side intake ports to give you an idea of how much port velocity matters for low rpm power (hence the double throttles and 6 ports in production NA rotaries).
https://www.rx7club.com/attachments/...-photo0203-jpg

As long as your engine power nose dives at 5,250rpm you will make more torque relative to horsepower. HP = Torque x RPM ÷ 5252.

Its an automatic disadvantage to "oversquare" engines like the rotary which make power with revs.

Realistically, you are shooting for a ~140rwhp engine in order maximize the torque to hp on a 13B, can you get your car down to 1,700lbs?

The smallest (single- not the old three holes ones) stock exhaust ports are probably what you want- whatever rotor housings those are in.

And for intake-
Here is a pic of NSU RO-80 rotor housings (from Banzai) so you can get an idea of how small you want the peripheral intake ports for max torque.

http://www.banzai-racing.com/Roof/Re..._housings1.jpg

Forced induction and a decent ECU is the real ticket here. Get something small and responsive like an EFR 7163 and a ton of wastegate. You could have boost come in early and hard and taper off fast. You'd be able to maintain 200whp everywhere. I've seen a dyno curve of a class-built Miata that made almost exactly 300whp for something like 4500rpm. The HP curve looked like a really nice NA car's torque curve.

I guess i should have clarified no turbos just yet. The rules doesn't really want built turbo motors to the max torque just yet.

The class is the Grid Life Touring Cup new wheel to wheel class. Which is 3-4 short sprint races over a weekend, aimed at full body production cars with the idea of introducing the thousands of grid life attendees to grassroots wheel to wheel racing.

2250 is the ideal weight as that is what my Miata already weighs. The motor in it now makes 130. But i have been wanting to build an STL rotary to put in the the car for that class. But we have so much rotary crap from over the years, the Grid Life thing seems pretty awesome as it is not your typical SCCA grey beard weekend... plus there would ACTUALLY be spectators.

The easy button would be to just wire 6port actuators closed and limit RPM. Which i did a dyno pull like that on a S4 6port and the power was like 130.

The NSU housings are kinda cool, I wonder if you can get someone to semi pp both the intake and exhaust on a renesis housing to get the timing you want.

I also thought this Scoot intake manifold that has been for sale in the 3rd gen classifieds is pretty interesting. It would work with the double throttle FD UIM, but they probably open too early and loose all velocity for the pports without some serious testing ability.

https://cimg7.ibsrv.net/gimg/www.rx7...2016f7e6dc.jpg
https://cimg4.ibsrv.net/gimg/www.rx7...a8639559be.jpg

Ah - I missed the "no turbos" part. My bad!

OK, so then Blue TII has you on the right path. Minimize pumping losses to maximize torque.

What kind of tracks does grid life have in mind? if it's like an autocross kind of thing, then super short gearing could be a thing. In that case gear short and the lack of rotary torque becomes an advantage in RPM. And it's sounds awesome too. :)

I didn't say " no turbos" specifically as i figured it might be understood that this is the NA performance section lol.

Trans would be a stock miata trans modified to fit a rotary, which has way closer ratios. Might be too short if you start to limit RPM to keep HP down.

Here is the link to the grid life stuff:
Introducing The #GRIDLIFE TOURING CUP (GLTC) ? #GRIDLIFE

Mid-ohio, black hawk farms, gingerman, and road america. A little bit of contingency is offered, but the big focus is on close wheel to wheel racing.

I suspect they might do an invite only one at their Road Atlanta event this year, but the schedule is tight at that event with time attack and some serious pro drifting. I would be doing the Road Atlanta event as its the closest grid life gets to me.

One of the creaters or Grid Life was an SCCA wheel to wheel guy before Grid life blew up.

Rules-
https://drive.google.com/file/d/1NYm...iqnncs9bf/view

Ok, so for this year "low torque" engines like 4cyl and rotary run at the standard weight of hp/0.08.
6cyl NA add 1% more weight, 8cyl NA add 2% more weight and any forced induction adds 3% more weight.

Note: they will make adjustments to the formula as the class/results progress.

Do you really want engineer/build an engine system to maximize the rules when you will likely just get it dialed in the first year only to have them take away the handicap if you are successful the next year?

Only advantage I can see with the rotary is you could run artificially low horsepower and maximize horsepower over many rpm to save you a bit of time shifting.

I mentioned 140rwhp because about 140ft/lbs torque is all you are going to be able to get in the low rpm with a 13B NA.
This would let you make 140rwhp from 5,000rpm to 10,000rpm pretty cheaply if you can do simple machining yourself. So that would be 140ft/lbs torque at 5,250rpm dropping to 73ftlbs by 10,000rpm and actually a decent powerband 3,000rpm-5,000rpm as well.


If you don't want to build and engine-
A 6 port with aux ports wired shut won't do it- those usually only make 90rwhp dynojet. Its going to be a balancing act.

A 4 port 13B-MSP from a renesis will get you 140rwhp and with the flat torque you want.
The engine is already good to 9,000rpm, but limited to 7,500rpm factory to preserve the automatic transmission.
Or a 6 port 13B-MSP with aux ports capped- but the engine costs more.
If your Miata is NC you can swap the 13B-MSP easily with factory parts.

If your Miata is another gen, its going to be a whole project to put the rotary in.

An NA FC might actually be a better chassis for the track.
Suspension isn't as good, but brakes and aero are MUCH better and can easily be stripped as light as a Miata and it has longer wheelbase and more front/rear overhangs to bump for track advantage.
Plus it already has a rotary in it.

Ditch your rotary idea and build FWD with an EF civic- its awesome in the bump and grind of touring car as when you get pit maneuvered you gas and don't even have to counter steer away from the apex to avoid spinning. And they get to weight 3% less?

Unless the heats are really long and front tires won't last on FWD.

Yeah, there is a LOT of contact in touring car racing.

You know, my kneejerk reaction is just "6 port Renesis or whatever with electronic throttle, have ECU run to a lower maximum opening angle if vehicle speed is below 5mph measured by GPS, done" but I tend to think the popular idea of club racing sanctioning bodies being able to police HP levels that way is pretty naive.

edit: Or hell, don't do electronic throttle just do electronic control of the 6-port actuators, cheaper ECU that way.

Highest torque tends to happen if you can rev the engine high enough to REALLY get some intake velocity happening, so you can get 180-200ft-lb.

This, of course, is counter to the goals of minimizing horsepower, since that torque is going to be happening at 6000-7000 rpm.

I am thinking that the best bet would be a small-runner peripheral port engine. I tried to do something like this years back with this goal in mind, but there were issues with the build. (My throttle body was way too small, and it also kept fouling plugs) I suggest peripheral port and not bridge port because a peripheral port will have less runner surface area for the same cross sectional area, so less energy is wasted (pumping losses).

Or you could just run any engine you want and gear the car accordingly. Horsepower is horsepower no matter what RPM it's made. 200hp at 9000rpm is the same as 200hp at 5000rpm once you gear the car accordingly.

lots of stuff here!

1. the luke warm ticket (its not hot...) in the miata, is the 2001-2005 VVT engine, once you put an ECU on it the VVT lets you dial in a pretty flat hp curve. the one we had would do about 147rwhp peak, and with the intake restrictor to bring it down to 136rwhp. we had 136rwhp from like 5000rpm to 6500rpm, i should say with a flat hp curve, torque is falling off a cliff. does well in racing, but its really slow, and on the street you're wondering how they drive it on the track. the plus is that the engine can be stock, and you only need to put headers and an ecu on it. hp/dollar is really bad with the miata engines.

2. the NC miata shares the same platform as the Rx8, so the renesis will bolt right in. working on a spread sheet to do this (getting the engine in is easy, its more the other systems. i would be looking to have a street legal swap). with an ecu, you could vary the throttle opening to get whatever rwhp you need.

3. how are they going to measure hp? we run NASA and they put us on a dynojet that reads +/-20rwhp, so the miata VVT setup was great, because we could adjust the hp it made (the dyno we tuned it on was +/- 1hp). for the BMW crowd, who have an ECU that sees the front wheels stopped, and then cheats, like VW, they put a box in it, and it can derive hp from accelerations (or something).

4. a rotary in an NA/NB miata is not easy, everything is close, but just a little off, so its a pretty big fab project.

5. a 13B with a small runnered and mild P port would work well. i've done a couple, and the P ports have really instant response, and good low end (with the throttle open). a full spec PP through a T2 trans will do about 320 at the flywheel, but only put down about 240 (t2 trans sucks, btw), so making it one step milder should just help everywhere. they are simple like rock, and basically bulletproof. they actually are pretty mild mannered on the street.

6. the 90's hondas do make good race cars, we ran hondas for almost 10 years. power is easy, there are tons of go fast parts (no shortage of go slow stuff too). they are good in sprint races, but in enduro races, it is an economy car, and they basically fall apart. so they also get expensive, as you need to buy a lot of stuff. our prep list for a 25 hour race was an engine, trans, clutch, all the axles, bearings (which you need to repack), steering rack, alternator, radiator, fuel pump, distributor, calipers, etc etc (its about 12K), and then you have a car which will only last about 10-14 hours, so for the rest of the time you need that roll of duct tape! needless to say if we took the money we spent on the honda, and bought an Rx7, we could race a museum piece...

7. since NASA has new rules this year, FWD is appealing, you get to run more power. we want to run a Mazda, because they have a contingency, but which one? i have voted for a 95-98 Protege, it has a miata engine, but its an undeveloped chassis, so it would be a challenge. anyone can run a Mazdaspeed 3 and be fast...

The funny thing is that there is a stage rallyist in Michigan who worked for Ford/Mazda in some fashion and had access to all sorts of stuff. (Hearing about the fun he had trying to make a touring car transmission not fail was hilarious) He had been running the Protege type chassis, and when he shifted to the Mazdaspeed3, they stripped out the rear suspension, fabricated strut towers, and ran the Protege setup.


I vaguely remember that the CX-9 axles were used because they had EIGHT balls in the outer CVs, not six like everything else, so they were marginally less likely to explode.

To be honest, pie in the sky theoreticals aside, I'd seriously look into starting with a 4 port RX-8 engine as-is. It should have the intake velocity to get you there, the higher compression should help you get some more midrange oopmh, and if you accidentally make over 200hp then you can either set a rev limiter or pull ignition timing/add fuel at the peak, so it makes 200hp for a long time. Anything Megasquirt MS2/Extra and above will be able to natively read the 36-2-2-2 wheel.

I'm still a fan of the Turbo II block/S4 NA intake and internals combo, as I made way more than 120ft-lb at the wheels on a Dynojet (like to say it was around 145). But those parts are bit hard to come by in 2019, while 4-port RX-8 engines abound.

All the same, any time you are placing low end and mid range at a premium, compression sealing needs to be yoru highest priority. Superflat side housings, new or extremely good used rotor housings, new seals and springs toleranced to the extreme tight end of spec. I'm also thinking of biting the bullet and switching to Evans NPG (your rules may not allow this) to combat rotor housing warpage near the spark plugs.

might as well just start with a new FD engine, for the price of a pair of rotor housings and seals, Mazda will throw in the rest of the engine.

not sure about the Rx8 engines, that is a valid option too, although if the Rx8 engine is a reman, you would want to pull it apart. for some reason they can replace all the seals, gaskets and most of the housings and still have a failure rate of what seems like 50%

Oh, hell, I was thinking of the $1000 eBay import engines all over the place.

VERY minimal, he can't even touch the short turn radius. The repeatability is all in the clearances for those things.

I have done various combination of FC irons/housings/manifolds/exhausts/engine management systems/carb/various ignitions and I still can only get 120-132wheel torque.

this is easily 5 different combinations.

HP wise has been from 120-192whp

so I dunno