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Why I'm glad to have gone down the difficult path with tuning my RX8... because I knew that the knowledge will come in handy later in life. That time has come.
Tuning my F22 is as beautiful as it is uselessly complicated. That ECU has 5000 tables, the RX8 ECU has ~650. Out of those, you need 120 for the F22 and 15 for the RX8. But the end result is that boost is controlled to 1 psi, fueling is on point and as easy as plugging in your required targets. Damn, it beats having to scale MAFs and fuel injectors and VEs and hoping it won't blow up.
Funny how mazda didn't put any safety in its ECU, while bmw did but they are too forgiving to do anything. For example I can have the bmw ECU cut down the torque as much as I want if coolant or oil temps get to a certain temp. Nifty!
On the other hand, I would be hopeless in tuning this modern ECU if I hadn't had a go with the 20yo old ECU in the RX8. As the saying goes in my native language, all difficult things lead to better times.
They've even mapped out a pressure loss in the exhaust vs. mass air flow. Multiply that MAF [kg/h] by 0.278 and you get the more familiar g/s.
Note how lean a 11:1 CR direct injection engine runs under boost. Pretty much stoich ALL the time - the richer areas aren't reached by the stock tune at all.
Logging is a dream!
Business as usual here.
How much power will that turbo require to give this much flow? The turbo is computed in all aspects, which is nice, I guess.
The difficult part in tuning an RX8 is getting boost and fueling on point. The difficult part in tuning the modern stuff is finding out the 40 ish limiters that cut your boost, timing, load, torque etc. And handling the autotragic slushbox so that it doesn't slip or cause torque caps. Wished I had a manual but couldn't find one to buy.
And here is how they compare: B58 running 17-18 psi @ redline, renesis running only 10 psi and a bone stock renesis.
Last edited by ciprianrx8; 08-18-2023 at 04:08 PM.
It's called metric. Not my shoe size over whatever was measured to end up being called a pound. Too many units boggle my mind so I switched the 8 to metric too:
I did actually see HP listed there then forgot in my second reply trying to joke about it, but didn’t notice torque listed in NM. So it definitely won’t line up that way and makes sense then. Appreciate the clarification.
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You may recall me bitching complaining about a hunting idle/stalling during coasting that lasted 30-50km after reflashing the ecu. Theories varied from terrible maf setup, bad maf, lack of reat o2 sensor, poor compression, 20 brake pedal stomps etc.
While any or all of those hold some truth, I wasn't keen on tackling any. I got fed up with this issue when randomly during a cold start, my idle started jumping around terribly.
I just changed the accelerator pedal vs throttle position tables so that the first 3 rows read 2 instead of 0 or nearly 0.
I have never seen an RX8 idle better. Stock or not. I've had 4 of my own, tuned locally 5 others and some others remotely. It helps buckets when driving very slowly in 1st gear with no accelerator input. Has to be the absolute best idea I've had in a long while.
The only downside noted is that during coasting, idle is 100-200 rpms higher than set in idle tables(1050). I can accept that. Before this change, it would idle at 600-700 or stall entirely before it learned how to do it right.
In other news: I've upped the boost in the midrange up to 14psi, tapering back down to 10psi past 6500. Turbine seems to run out of steam.
Clocked a 100-200kmh run at 12 seconds. ME says 330whp. That's decent for a street car with all oem features.
Clutch started slipping as soon as turbo spools beyond 70kpa boost. Had to dial back down to 50kpa to avoid turning everything into mush. Guess this is how much a new, stock one can handle; fitted it about 10k km ago and has been through a lot of boosted pulls; anywhere from 350 to 400whnm.
Open to suggestions on what I should run this time. I'd loathe a on-off clutch as I street drive this quite regularly.
In other news: I've dialed my wonder table of APP vs RPM = TPS in that area where I've set 2 back down to 1.4. This perfectly aids idle quality with no idle overshoot during coasting.
Last edited by ciprianrx8; 09-18-2023 at 11:57 AM.
I would switch to sintered pressure plates. They are not as on/off as people set them to.. Or one side sinter one organic (towards flywheel to save it a little from wear).
The more pucks the clutch has the softer the engagement.
(metals in general have a higher load higher friction coeficient curve, ie raising friction as opposed to rubber where the higher the load the lower the friction).
I didn't comment because I'm really not doing anything special and am not one to punish clutches like some do.
FWIW though I just run a heavy duty Exedy organic ..... couldn't even tell you which one because I just went into the Exedy supplier and said this is how much power etc so ....'wadayareckon' and took what he gave me. That was 3-4 years ago.
I have an Exedy twin disc in my REW swap, it engages very similar to stock, my car is only a street car so I get the want for the no on/off engagement. I recommend it highly, but the cost of it may be unappetizing.
Had the first trackday with this car and have to say it fared much better than anticipated. .
Great car! do you have any onboards from the track? I'm impressed with your temps as I'm ruining stock engined RX8 in local time attack and I have higher temps!
I thought about moving to another class next year and car should be with forced induction... it is pretty fast as is so i though i migt try to turbocarge it rather than swapping REW for 300 whp...
None of those would turn my gearbox housing into a pipe bomb or break apart my clutch pedal bracket, would they ?
well it’s not like you have any choice, but generally speaking a twin disc can provide the same torque rating as a single disc with 1/2 the pedal pressure, or 2x or higher torque rating at the same pressure depending on the disc friction material.
There are other factors and it not exactly or as simple as stated, but generally the more discs it has the higher the torque rating with same or less plate pressure as the single disc.
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Took this trainwreck of a car to the mountains this weekend. Was nervous because of how it would fuel itself as ambient pressure drops from the usual 100kpa I've tuned at vs the 80kpa somewhere up in the mountains. I've built a 4% fuel trim and starting was kinda weird, deff. was overfueling during cranking (or it was fueling the same as it was at sea level) but it never flooded on me, neither did I have to yank the laptop out. Once I got back in the plains, the trim went away. To not bust up the clutch any further I've dialed boost back to ~ 170kpa. Lost tons of torque though but I don't want to do a clutch job within the next year or so.
On the last oil change I've had a look at the oil filter guts. Looked at every fold in the paper element and it was clean of any metal. Least of my worries is oiling system not keeping up to the abuse, like the clutch did(n't).
The dream lives on.
And finally a cool find while digging through those 100's of maps that aren't brough forward by mazdaedit...
Minimum OMP position vs ECT!
Stock vs mine...
stock
mine
Very pleased with this finding as I'm gonna daily this car during the winter season. A bit of extra oil can't hurt! After comparing my factory tune with any other factory tune(UK/AUS/US), my stock settings injected the least oil under cold starts and overheating events.
Now, to find the map that sets AFR pig-rich during cat-heating...
Last edited by ciprianrx8; 10-21-2023 at 03:13 PM.
so just revisiting my suggestion earlier in this thread to use a 50mm wastegate size, which was larger than anyone else suggested and then disputed with many words …
which I hadn’t seen this from Turbosmart below, but rather simply understood the fact of the matter:
As Marty from Turbosmart explained, “When choosing the proper size of wastegate, here are some general rules of thumb to go by: A big turbo run at low boost requires a big wastegate, while a big turbo run at high boost actually needs a smaller wastegate. A small turbo run at high boost also needs a small wastegate, while a small turbo run at low boost needs a bigger wastegate. That said, the engine configuration will play a significant role in deciding what size wastegate to use, and there are a few applications that require larger gates simply due to their design and exhaust flow.
… (deleted piston engine examples, not relevant)
Rotary engines generate a tremendous amount of exhaust energy and heat, so for those applications, the Progate 50mm and Powergate 60mm are what we would recommenduntil you go past the 30-plus-psi boost range, at which point you can scale back down to a 45mm (or pair of 40-45mm gates) and still maintain control.”
simply stated, it has to be larger to bypass more flow. That’s why emap is high in the first place; not enough flow is able to pass through. The idea that high emap allows for a smaller WG opening only represents a lack of basic understanding. Lower emap means just that; lower pressure.
Lowering exhaust manifold pressure; which is what occurs as flow begins to bypass from the turbine into the WG, i.e. a dynamic process, the larger the opening required to continue diverting flow into it. Which is exactly as was posted about for an even larger 60mm EWG rotary engine example in a counter reply in that same linked discussion.
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simply stated, it has to be larger to bypass more flow. That’s why emap is high in the first place; not enough flow is able to pass through. The idea that high emap allows for a smaller WG opening only represents a lack of basic understanding. Lower emap means just that; lower pressure.
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The Turbosmart explanation makes perfect sense .... your comments however, don't.
Please clarify.
Are you actually suggesting that, in a system where boost is perfectly controlled at a desired level, a system with a smaller wastegate will have higher EMAP than one with a larger one?
IMO the comment you put into bold: "while a small turbo run at low boost needs a bigger wastegate"
Should really say:
while a small turbo run at low boost needs a bigger wastegate............. than when it runs at high boost!
Assuming same amount of air needs to be deverted (as turbine needs "constant" amount of energy to make certain mass flow/P.R) , the size if the WG wont impact EMAP assuming it is sufficient to controll the boost, othervise the amount diverted would change as well and than....
Assuming same amount of air needs to be deverted (as turbine needs "constant" amount of energy to make certain mass flow/P.R) , the size if the WG wont impact EMAP assuming it is sufficient to controll the boost, othervise the amount diverted would change as well and than....
If I'd learned something... no such thing as "too large" of a wastegate. Mine allows me to run anything from 40 kpa to 95kpa on the same spring and a 3 port solenoid, taken from the UIM. Have a bag of those. They work well under PWM.
If I'd learned something... no such thing as "too large" of a wastegate. Mine allows me to run anything from 40 kpa to 95kpa on the same spring and a 3 port solenoid, taken from the UIM. Have a bag of those. They work well under PWM.
Too small is definitely not good .... but too big isn't always a problem, so that's why most tend to err on the large side. That's not to say there is no such thing as 'too big' though ....it can cause issues with fine tuning.
IMO the ideal size is the smallest WG that does the job you intended it to do.
08-18-2023, 04:41 AM
but I don't want to do a clutch job within the next year or so.
