austinramsay

I'm definitely not building anything 600+hp but im curious. My FD probably has around 400whp on 13psi with a greddy t78. How do people build 600+hp rotaries? I mean all you can really do is stronger seals right? Like if your building a 13b on 40psi of boost, what apex seals are you going to use? What about side seals, corner seals? How do you deliver that much fuel (I mean what injectors and fuel pump would you use for that??), how do you build a rotary that will hold up under that much power? And another question I had, do you just have to keep the tuning rich to keep a rotary from blowing? (from detonation/knock) Is that what mostly matters when building a motor like that? How else do you strengthen a rotary? Sorry for so many questions im just curious about how all this is done haha

First gen man

iTrader: (24)

The first failure, assuming you don't detonate, is that the rotary engine plates blow apart at around 30-35 psi, I believe? That is when people starting cracking the iron plates due to the boost forcing the engine plates apart, and some twisting motion shortly after which cracks the plates where the engine alignment dowel pins land.

When people plan to go to that PSI, during the engine build phase, they add dowels, or enlarge the torsion bolts to get increased strength. This is just all hear say, meaning I haven't tested any of this information.

I've seen one crack after hitting 37 psi on the dyno. Drops 5 quarts of oil on the dyno fairly quickly. I believe a handful of people even re-route the oil around that spot that cracks, so if it does crack, you can still use the engine.

Some of the other stuff they use is pretty basic, I think they use most of the common apex seals companies, I see a lot of ALS brand apex seals on at the dragstrips. For the fuel, they have crazy 16 injector setups, usually running alcohol.

Hopefully someone will come chime in with alot more info. I've always wondered how much boost/power some of those really fast 6-7 second rotary cars run.

t-von

iTrader: (8)

Whoa there buddy! The plate failures have nothing to do with boost forcing the plates apart. 35psi isn't gonna warp a 2 1/4" thick steel plate. If that were happening, you would be snapping the tension bolts. The plate issue is due to the casting differences between the generations in the upper dowel areas. I can't remember what years but most if not all 2nd gen rotary have less casting material around the upper dowel area. As the rotor spins around the stationary gears, the rotational forces carry through those plates making them want to rotate as well. The dowel pins are the main thing that keep the engine from twisting apart. When you start combusting more boost pressure, you also increase the load on the engine and those weak dowel pin areas. So when those weak castings give out, so will your engine. Some early model 20b engines have this same problem. Adding a thick base plate to the bottom of the engine can help relieve the stress on those dowel castings.

First gen man

iTrader: (24)

Ah yes! Thank you very much sir! I stand happily corrected.

First gen man

iTrader: (24)

So does that state that the cracking of the plates is from the sheer power associated? Compounded by RPM? Could some of problem be blamed on unbalanced rotating assembly?

peejay

if the cracking issue was from rotational forces, they would crack in the other direction.

The cracking is from the rotor housings trying to force themselves outward, away from rotor, at the spark plug area, pulling the dowel down. Detonation causes this, and one thing that can cause detonation is misfiring... and misfiring is easier at high chamber pressures.

You can still break stuff even with the most badass parts and doweled everything, but you can also make a lot of power without all that if you pay close attention to the details.

Monsterbox

iTrader: (6)

Big power is made from race gas or auxillary injection on these motors. If knock is suppressed and intake temps are low, a stock mazda block will do 600+ with the right supporting mods.

IIRC, member by the name of enzo tested stock blocks with huge turbo and supporting mods to over 600+hp without issues.

RotaryEvolution

iTrader: (30)

+1

detonation causes the rotor to fire before the ideal time in the combustion event which stalls the rotor and tries to force the rotor housing in the opposite direction of movement towards the 12 o'clock position on the engine. the lower dowel is far enough away from the event that it rarely is affected by and acts more like a pivot point.

most people tend to avoid this by using experience and alternative fuels. water injection also helps to buffer the failures caused by detonation but at the same time it is easier to foul ignition when spraying tons of water into an engine producing lots of boost, this reduces the target AFR range making tuning even less for the novice.

reinforcing the engine by studding/dowelling is a preventative of failure caused by the above. the changeover point where the blocks got casting revisions is on the late s5 USDM turbo and slightly earlier JDM engines close to the end of 1991.

reinforcing the block may cure one major failure point but if an engine is detonating it will continue on to the next weakest point which will be the seals, rotors, or deflecting the e-shaft and bouncing the rotor tips off the irons and scuffing them which has a high chance of sticking the corner/side seals. race clearancing the rotors alleviates the deflection issue so the next likely cause of failures are apex seal warpage/breakage and rotor face collapsing. most of the major names in aftermarket seals like ALS/Goopy/RA can handle some moderate detonation cycles which can even allow the last components to fail, which is rotor face collapse.

if enough twisting is present the rotor tips can hit the rotor housings, usually by this time the end iron plates are well beyond cracked.

diabolical1

iTrader: (3)

you know something? i've been around for a while and i've learned quite a lot. however, moments like this show me that what i know has some serious holes in it. my understanding of detonation and how those forces led to cracked housings were lacking something.

i swear to you, this is the CLEAREST and most comprehensive explanation i think i've read for the actual physical mechanism of cracking a plate. i felt that i understood all those Barry Bordes and Afgmoto threads, but a light bulb just went off illuminated them in a different way, now Peejay.

thank you so much!!!

this is the God's honest truth. even if you are capable of building and tuning an engine to perfection, there is still a luck-of-the-draw element to things that increases proportionate to the power level you're trying to achieve. you need that ace in the hole whether it be alcohol, water, radical mods (housings, water flow, etc.) or any combination therein.

"unobtanium" apex seals, diamond-encrusted rotors and platinum studs only take you so far.

RotaryEvolution

iTrader: (30)

that is true, but it never hurts to build an engine and preparing for it to fail than to build an engine on basics and hoping that everything works and works well for the long term.

i've honestly been getting grief lately for giving my opinion on "overbuilding" engines, but nothing is worse than having expensive parts fail due to any of a million total random issues out of your control. of course those who have that opinion don't necessarily do it for a living, and probably don't have to sleep at night wondering if the tune the following day is going to cost you weeks of effort. those same people also tend to ignore their "luck" and tend to think that they know what you don't, and you are obviously doing something wrong.

many of the same people also do not mainly work on the older 'weak' cast engines pre-'93. the REW is more than capable even without any of the hype i tend to push, which is actually focused on the earlier engines which also had a much higher probability of those parts failing.

there's nothing like having a fuel pump fail on the dyno to make you realize just how not in control you really are. of course there's failsafes you can implement but everything costs money, what you do with it determines success or failure.

diabolical1

iTrader: (3)

oh no. i totally get that, and i agree completely. i have built on both sides of the coin. however, i have the luxury of not dealing with customers and since it's been years since i built an engine (of any kind) for someone else, the only person i have to please is me. i understand you do have to please others and do so by doing all you can during the actual build/assembly phase of the process. you and i both know that that's what it all is, a process. the prep, the parts, the assembly, the support, the tune - all MUST be right, with none really being much more important than the other.

i oftentimes kick around the idea of doing something for myself - small scale, because i don't want to grow to hate it - but this is the part that always frightens me or rather reinforces my decision so far not to. factor in the fact that i have the tendency to doubt and blame myself when things go wrong, even before someone accuses me. i've grown to love and admire your knowledge/skill, and i respect the things you do, but i sure don't envy you for this part of it.

peejay

Stages 3 and 2 of the car guy life cycle, respectively

Or getting to a certain point where the ECU reads the manifold pressure at a low spot in a harmonic inside the manifold... Or my favorite, a ignition timing problem that was traced to the oil pump. That one was fun to find.

t-von

iTrader: (8)

That sounds crazy. Care to share?

fidelity101

iTrader: (11)

People build 600HP rotaries with a lot more money than us.

peejay

Not a rotary. An engine where the oil pump was driven by the same shaft that drove the distributor. A weird harmonic was setting up that would make the cam position sensor do funky things.

j9fd3s

iTrader: (3)

must have been an interesting phone call

interior, day. shop, cars everywhere

you: we found your timing problem sir, you need an oil pump!

customer, uncomprehending silence, slowly draws checkbook from back pocket

RotaryEvolution

iTrader: (30)

i was having a difficult time comprehending how in the rotary engine that could be possible.

ATC529R

they change their engine often LOL

peejay

We deal with weird stuff all the time.

The one I'm playing with right now needed a new computer, throttle body, intake manifold, injectors, fuel rail, and we're going to have to splice a different kind of fuel filter in the lines, and I did a bunch of stuff with tweaking the motor mounts as well as having to completely relocate one of them on the chassis, and had to cut and section the frame... because of the A/C compressor.

No rest for the wicked.

RotaryEvolution

iTrader: (30)

try telling an RX8 owner that the chirp from the engine is a "normal" form of knock. i swear once they hear it the paranoia begins.

Romeallo

Should I turbo my 13B-DEI Engine or sequential fuel inject it? what would the sequential do for the fuel injection? I know that it reduces turbo lag in sequential twin-turbo

RotaryEvolution

iTrader: (30)

there is no engine with that designation: 13B 4+6 port/13BT/13B-EGI/13B-RE/13B-REW/13B-MSP 4+6 port

j9fd3s

iTrader: (3)

lol, i should send you a PDF of the bulletin, you can frame it and hang it on the wall

you can get non MSP engines to do it too, my PP chirps. its running about the same AFR and timing as an MSP....

peejay

I was able to get a 12A to do it with significantly advanced trailing ignition (think firing on the wrong rotor). Awful sound, it was.

Although at that level, the chirp was accompanied by puffs of black smoke/soot from the exhaust, and it felt like the engine was locking up with every chirp, so it definitely didn't feel "normal" by any stretch of the term!

RotaryEvolution

iTrader: (30)

if they would implement a knock system that actually works though... problem with the MSP is there is no way you can offset it short of spending $500 for a cobb AP plus tuning expenses. it's quite bad on most cars just after resetting the adaptive memories, before the car learns proper timing pull and fuel trims.