TeamRX8

iTrader: (25)

teaspoon or not as Rotaman pointed out it's a stagnant area that corrosion can propagate and spread into the rest of the cooling system

consider that cavitation is a function of the liquid vapor pressure, the temperature is not higher if you have adequate cooling capacity and control of the fan temps, that the system boils over easily on shutdown with the typical ethylene glycol/water liquids but not with the Evans waterless propylene glycol, that the NPG-R was developed to work with smaller passage radiators, that if the cooling system isn't keeping localized areas well under 500 degF that you have problems that no coolant can ever solve not to mention extremely short engine life, and the list goes on

you can post theories all day long, but it matters not a wit if you don't really understand what you're posting about

shadycrew31

iTrader: (6)

Would love to see if this helps with the cracking around plug holes...

j9fd3s

back in the day the "fix" for that is colder plugs and this RX7 1975-1985: Engine - Services: Rotor Housing Water Jacket Modification -

actually the competition prep book has you measure the crack, at some point the rotor housings are a wear part...

shadycrew31

iTrader: (6)

Yea, we tired that on an engine down here, we wont be able to see if it worked for a few more years.

olddragger

iTrader: (3)

The temperature of the metal that is being cooled can be several hundred degrees above the temperature of the coolant. yea 500F on the outside of the housing and such is ridiculous. That was off the top of my little pointed head during a low caffeine state.

Here are some more accurate temps on an older model rotary putting out less brake whp than us.

______________________________________
Rear Rotor Housing
Conc.,
Housing Temp., °F.
Coolant Vol. % 70 MPH 80 MPH Acceleration
______________________________________
Water -- 264 293 349
Ethylene Glycol
34 283 310 367
" 50 301 333 393
" 70 316 353 419
Methoxypropanol
34 280 306 364
" 50 288 315 376
" 70 298 326 390
______________________________________
TABLE II
______________________________________
Front Rotor Housing
Conc.,
Housing Temp., °F.
Coolant Vol. % 70 MPH 80 MPH Acceleration
______________________________________
Water 261 282 328
Ethylene Glycol
34 287 310 353
" 50 309 334 383
" 70 329 359 409
Methoxypropanol
34 281 300 344
" 50 287 306 351
" 70 297 318 363

so well over 400f could reasonably be expected during certain times. More than enough to boil waterless coolant under no pressure.

Jim B say: "I recommend that you never exceed 195-200 degrees Fahrenheit water outlet temp and 205 degrees oil inlet temp at high power. At light power, the engine can tolerate somewhat higher temps, but don't push it. We aren't saying that the engine will fail if you exceed these temps, we are saying that higher temps will shorten the engine's life at an increasing rate."

I really dont want to get into a debate about waterless versus regular coolant. Waterless coolant has some advantages, normal coolant has others. But, regardless, not only does the heat need strict control, but also the pre ignition/detonation that goes along with it.

I never turn my engine off while it is running hot. Localized boiling? Sure--I wish we all had electric water pumps to keep the coolant circulating for a little while after shut down---but we dont. Hey--maybe that could be another "project"....!
Now back to Bretts thread.
I think I will bypass that coolant flow and not cap it.

j9fd3s

if you ask Jim M (everyone at racing beat is Jim) about oil/water temps he says something about delta T, and he is talking about WOT high rpm, and he expects to be able to run WOT high rpm for a long time too. so with a street/drag car you'd have some leeway.

shadycrew31

iTrader: (6)

Yea every builder, race team, rotary shop, etc has differnt theories and proven facts about how a rotary should be built and driven.

If you were to listen to everyone you'd have a 5 port long tube header to a rear turbo. with tons of cooling mods running 50 different radiators a battery pack meant for a hybrid to power all the fans and gauges. You'd only drive it at 9,00 RPM and cover the entire engine with heat shielding.

Engines in general are flawed by design, the rotary in particular has hundreds of people coming out with new theories daily as to how it shoudl be fixed. Eventually someone will get it but it wont come from any random shop, it will come from Mazda in about 20 years after extensive R&D and $$$ has been dropped on it.

That's my theory at least, who knows that could be wrong as well.

j9fd3s

yes, but Racing Beat has experience. they ran GTU and GTO for years, among many other things. they were running 320hp and 5 figure rpm numbers on a 13B in the 70's, and sure the renesis has a few important differences, but things like the oil system are the same, or better

Delta T, is engineer for the difference in two temperatures. basically he is saying the bigger the difference in oil temp vs rotor temp, the more heat the oil can remove from the rotor. if there is not enough difference in temp, the oil cannot cool the rotor enough.

an engine is just applied physics, its not some magical mystery device delivered from the gods, although an english translation would be nice

olddragger

iTrader: (3)

I have spoken personally with Rick, Cam and on the phone with Jim when he was speaking with someone else. They all have said the same basic thing. Don't let the oil stay over 200f (on the cool side) and the coolant not over 200 while it is under a heay load.
That is if you want the engine to last.
That is kinda of a hard thing to do.
Sorry Bret didn't mean to derail your thread.
Back on subject?

skc

Those targets will be impossible at a track day where ambient temps are high. I have let my oil get to 230F and then back off for a cool down lap and go hard again. I am usually at 200f by the second or third lap. Certainly far from ideal as generally my last lap is usually the best.

Even the stock car sees higher temps at the track. So the solution may be V mount, secondary radiator and larger oil coolers amongst other things. The only concern I have with a V mont is that the intake pipe sits in the middle so it will get blasted with hot air from the intercooler.

olddragger

iTrader: (3)

oh it can be done--but like you say it will require some fairly significate changes.

999miki

Or simply, fair amount of water injection. https://www.rbracing-rsr.com/downloads/naca_H2O.pdf

Water, apart from knock suppressing ability, is also total loss coolant. Ignition energy, or maybe the way it is delivered, limits utilization of water injection on full scale...

Many people may disagree on benefits of WI over more conventional approach of bigger and more efficiently used heat exchangers, but then again, I haven't seen high powered FI rotary on gasoline fuel which would use its full power for any longer period of time...

Brettus

iTrader: (2)

Getting back on the thread track ................

I did some backtracking and re-reading of old threads and have come to the conclusion that the MOP injection rate I employed was insufficient and that it contributed to the side iron failure.
Obviously premix did not help and from what PhillipM and Eric Meyer have said (exact same wear i had but running NA with premix only)- no amount of premix will adequately lubricate the side irons under severe conditions.
This raises the question again in my mind : What oil should we use and is two storke via the sohn adaptor really the best oil for that situation?
Maybe sticking with what Mazda gave us upping the rate and running a synthetic will give the better lubrication of that area.

Await flambe

9krpmrx8

iTrader: (46)

Well, I say clean good quality 2 stroke injected VIA the SOHN is better than dirty engine oil any day. I run Mobil1 0W-40 in the sump and it performs great (see OUA thread). I also have the OMP rates increased but I do not premix my gas. But of course no real scientific testing has been done so who knows what really helps or not.

All I know is my last engine ran the SOHN and Mobil1 it's entire life and carbon build up was very minimal (even nonexistent where the oil injectors hit the rotors) compared to a buddies engine which died at around the same mileage and ran 5W-20 Castrol and no SOHN.

FazdaRX_8

iTrader: (1)

But they both died.....

9krpmrx8

iTrader: (46)

Mine didn't. A used oil report showed traces of coolant in my oil. I pulled the engine before it died. When broken down, Pineapple found a small coolant seal failure, the seal looked "pinched" and the housing was out of spec.

TeamRX8

iTrader: (25)

In addition to Amsoil Saber Pro I would also recommend Legend ZX-2SR

Carbon Fibr

+1 on Amsoil Saber Pro. & the idea of sticking to Mazda Spec OMP & viscosity.


i figured this might help out this thread a bit.
But theres some good information as to different types of ware & causes of failure.
im not sure how reliable this source is.
i know its for an rx7 but similar cases arise.

TurboRX7.com > Criteria For Replacement of Rotary Engine Parts

FazdaRX_8

iTrader: (1)

I like it brettus. One thing I can think that would help is redesigning the coolant system so both sides of the rotor housings get the coolest water too them, looking at the flow of coolant in a 13b seems something could be done better, like separating the coolant flow from the exhaust side, from the combustion side, or forcing cool coolant into the engine from the heater hose, or throttle body line. so the exhaust coolant is cooler so it can pull more heat away

I really think heat is the enemy here, its the common denominator for most of the failures

j9fd3s

using synthetic and upping the rate can't hurt...

since you brought it up, what do the side seals springs look like, and how come Meyer broke his and you didn't?

what kind of RPM were you running? the good kind? :P

9krpmrx8

iTrader: (46)

agree 100%,

Brettus

iTrader: (2)

My engine never saw sustained periods of high rpm and was limited to just over 8000 rpm. The side seals and springs looked fine to me but I haven't measured them or anything.

j9fd3s

that is probably enough difference, sustained high rpm vs not, really road racing is like doing 7-8 dyno pulls a minute for at least 15 minutes at a time...

so synthetic oil, should work better in a high temp environment, even better if you up the quantity.

step two might be to lower EGT's/backpressure? i think the basic tune, fuel and ignition was ok, otherwise the engine would have come apart on its own.

not my car, but that's where i'd head if it was

olddragger

iTrader: (3)

I believe that most FI engine failures are due to tuning/heat issues. It gets complex though.
Most FI rx8's are producing more than or at least 150 hp per rotor. Thats a lot of hp per physical size of the engine. Lots of heat.
I think that most of us--especially those running FI--realize the value of a good cooling system and have taken steps to make sure the coolant system is up to par.
BUT, have we done the same for the oil?
Now I dont think we can compare the track ran engine with a street one---different worlds entirely. They are the only ones-except one or two that I know of--that have tried to upgrade their oil cooling systems. I think more of us need to do that.
I have a hunch that oil cooling is more important in this engine than the PP type because of the placement of the side seal in relation to the combustion chamber AND its relationship with the exhaust port. I am thinking its more important to keep this high compression rotor cooler in this side port engine. No proof--just intuition. My estrogen levels must be increasing..........

There is also one component that has not had much dicussion. The internal EGR and how FI affects it.

kustus

iTrader: (1)

Sorry for the random post here, kinda been lurking. Scouring and gathering information before I eventually wander into the realm of forced induction. You all seem to be the well knit group on here. All the threads I have found interesting have some elightening from most of you as well as a few others. Patronising aside. I do think what olddragger is saying makes sense. And also with the renesis engine (from my understanding) has limited exhaust port area do to the location on the side irons vs peripheral ports on the REW. Also they are "open" for a shorter amount of time vs. The peripheral port due to its lower location. I was interested in any information/thoughts on the MSP/REW engine set up mazdatrix was working on may have with with reliability as it has more exhaust port area (than the REW or MSP)and as such should be able to let more heat out and lower many heat associated problems. I dont want thread jack, but if heat is killing the renesis (with boost especially) because it cant remove it fast enough. Could the hybrid setup/custom housings be the next logical step in reliability?