OK, so I know that they really aren't that great a motor. Gas pigs, no torque, et cetera. But let's say that you were installing one in a 1400 lb car, and you liked the high-reving nature and kinda liked the distinctive exhaust note. Also figure that smog is not an issue. So what would you do? Take a 13b from a 2nd gen, bridgeport it, throw on headers and a Weber or Mikuni? Or would you try and make a later engine from a RX-8 work? 238 HP sounds a lot better than 146. Forget Turbos - not on the table.
I think the RX8 13B variant out of the box struggled to squeeze out the alleged 238 hp. It is also pretty limited due to the side exhaust ports unless you want to build something nutso that combines the RX8 irons with the older housings. Of course that needs a special header because nobody has a five exhaust port header on the shelf. Apparently that can be made to breathe rather well, though.
I think the easy button that makes getting power a tad simpler is the older 13B.
Kreb (Forum Supporter) said:
Take a 13b from a 2nd gen, bridgeport it, throw on headers and a Weber or Mikuni?
In the exact same 1400 lb scenario that was my plan. What I actually did was buy the 2nd gen donor cheap as hell then wuss out on the spinning Doritos because I'm apparently not man enough for them.
In reply to Stampie (FS) :
Wuss
I've never done it, but my impression is that it's a lot easier to get 238 hp out of a bridgeported 13b than it is from a stock renesis...
In reply to EvanB (Forum Supporter) :
Well yeah.
Personally, I think it's silly to spend time and money on trying to make a N/A make big power when they respond so well to turbocharging. But that's just me.
And for the record, the rotary is the best race engine ever made. The fact that it has slain giants despite having but a small fraction of the development man-hours and cubic dollars of boinger engines pretty much says it all.
Well at 1400 lbs, for starters at least, I'm happy with 200-250 HP. Turbos would produce too much heat.
Kreb (Forum Supporter) said:
Turbos would produce too much heat.
Eh. Extra heat, yes, but the power is worth it. And that extra heat is negligible except under boost, and that rarely happens for more than 10-15 seconds at a time. I have no experience with rotary stuff, but plenty with air cooled VWs. The extra heat was a non issue even daily driving that thing through the summer here (110-115f all the way through July and august)
A well built 13B street port will make 220-230 HP, rev to 9K and still be reliable.
Cough cough Turbohyabusapower
j_tso
Reader
6/12/20 9:45 p.m.
I'd be tempted with the RX-8 engine because I see much more of them than RX-7s at the pick'n pull, and from the factory the hardware can do 9000 rpm. I have not seen a Renesis with aftermarket injection or carbed, so I don't how well the block performs without the fancy OEM intake. From what I've read there's not a lot of gains to be had with the exhaust.
I have a couple of racing friends who put 6 port renesis motors in first gen rx7s.
Stock intake and exhaust manifold and megasquirt. They dyno about 195 to the wheels. (hp, Def not torques1).
Interesting question.
A stock RENESIS will be more civilized than a bridge or peripheral port on a 13b. A peripheral port 13b will scream near redline all day long.
We've not even considered using milled RENESIS rotors in 13b housings, and since we're talking hypothetical, we should.
Or 20b. We should always consider a ported 20b as an option.
Kreb (Forum Supporter) said:
OK, so I know that they really aren't that great a motor. Gas pigs, no torque, et cetera. But let's say that you were installing one in a 1400 lb car, and you liked the high-reving nature and kinda liked the distinctive exhaust note. Also figure that smog is not an issue. So what would you do? Take a 13b from a 2nd gen, bridgeport it, throw on headers and a Weber or Mikuni? Or would you try and make a later engine from a RX-8 work? 238 HP sounds a lot better than 146. Forget Turbos - not on the table.
Bridge ports make all the torque. It is a night and day difference from a stock port or a 'street" port. The powerband starts at 2000 instead of 5500.
I'd make a '74-78 style 13B and bridge port it, with fuel injection.
I say I'd do this, because it is what I did. The '74-85 engines have a lot more room for a bridge port than the '86-02 engines because of where the water O-rings are.
The most potential for HP is the 13b 4 port or 74-78. Back in the day a well done bridge was able to make 310hp when a 12a bridgeport could get to 270. These are rare now though
Genesis are very fragile.
2nd gen 13bs came with a turbo, if you want reliability, this would be my choice
In reply to Pete. (l33t FS) :
Sorry to thread-jack, but I was out at my buddy's shop, and he has a row of 12a rotors he won't be using if you're interested in taking some off his hands. There's probably 11 of them there.
Waaaaay back when I had my FC, I did a bunch of reading on what would make the ultimate street NA rotary. The 13B-RE from the Cosmos has some of the biggest and shortest intake manifold runners, can take a pretty big street port and will make good power when NA. I seem to recall that some of the throttle bodies (FD maybe?) had a larger lower opening compared to many earlier ones and would therefore be a bit less restrictive.
For higher rpm durability, use S5 NA rotors (or RX8 milled to take earlier 13B apex seals), RX8 stationary gears and bearings and run an external oil supply line to the front bearing. Run higher oil pressure, bypass the oil pump outlet in the front cover and tap the front iron for that instead (front cover can flex and bleed oil pressure). Rotor gears can come loose, but some of the spring pins can be pulled and replaced with set screws to keep the gear from walking out at higher rpm. If going above 8000 rpms, consider adding a little clearance to the rotor tips so that they don't touch the irons, or if wanting to go really extreme.
You're not going to find it in a local scrap yard, but if starting from scratch, maybe not the worst idea.
All that said, a Renesis is the easy button, other than making the ECU happy in something other than an RX8.
Do we get to use those individual LeMans variable-length trumpets? Cause man oh man, I wouldn't care what rotary I had if I got to use those.
wspohn
Dork
6/13/20 11:06 a.m.
Knew a guy with a Bugeye Sprite that had fitted a Mazda rotary (think it was an RX-3 engine). Had all sorts of vibration based issues including having every fastener in the car vibrate loose, and back in those days the exhaust was a real problem - any normal tubing would often rip apart and they often ended up using water pipe to get something that would withstand it (I assume that this sort of thing has long been sorted out).
It didn't half go, though - and you could certainly hear it coming (and going).
In reply to wspohn :
That's a tad unusual, though. A decently screwed together rotary shouldn't really produce that much in the way of vibrations.
Having blown up many 12a and 13b. If I was thinking this I would hit my thub with a hammer to snap me out of it and start looking at a S2000 motors.
BoxheadTim said:
In reply to wspohn :
That's a tad unusual, though. A decently screwed together rotary shouldn't really produce that much in the way of vibrations.
Yeah my 13B in the Midget is solid mounted. Other then the exhaust you can't feel the engine at any RPM. Like literally no engine vibration.
I'm not sure what all was done to the 13B in the MG I bought it from the forum. It was the engine that GRM did articles on and put MS on at the Mity. I believe it is a a street port with Renisis rotors, and a lightened flywheel. I'm running a stainless steel flowmaster baffleless tube type muffler near the header and another flowmaster chambered muffler at the rear. For track and autox use that keeps sound under 94DB. It is still loud so for around town I built a tip with a smaller diameter tube that has holes drilled to quiet it down. It works great I call it my neighborhood pipe.
GRM dynod the engine at 165 WHP, the MG weighs 1500Lbs. It's fast enough but runs out of steam at 120 MPH.
