DogonCrook

Actually I'm still pretty curious how an rx8's ve doesn't change with mods or time, and how believing it does makes people loudmouth experts.

9krpmrx8

iTrader: (46)

There are plenty of great books on engine management and tuning.

DogonCrook

Which describe no coasts method. And hell Maf scaling is important too. I'm just trying to figure why him pointing it out warrants abuse, and why anyone would defend that. But you got your way, the discussion has been killed and none of your super secret information leaked. Bravo. You guys could learn far more from no coast than you think...

9krpmrx8

iTrader: (46)

You revived a dead thread, no one killed anything. Theories are one thing, experience actually Cobb tuning an RX-8 is another. If I had a dime for every "professional tuner" that claimed tuning an RX-8 was no different than any other platform I would be rich. None of these tuners seem to every actually successfully tune an RX-8 with any degree of actual success. Talk is cheap. Every RX7 tuner on the block claimed tuning a turbo RX-8 would be no big deal back in the day with an aftermarket ECU. Then the Cobb came out and everyone that it would be simple then and yet even today there are probably only a handful of guys in the whole country that could successfully tune a turbo RX-8 with a Cobb.

DogonCrook

A rotory is not a mystical beast, it operates in the same physical dimension as all other engines do and because of that follows the exact same laws. Your intake tract operates under the same principals as an f150's does. This is basic stuff, we aren't talking about wringing every last drop of performance, we are talking about building a base to remove trims... If you think this car is different than any other car In that regard then you don't understand either.

DogonCrook

Sorry for that last sentence, I was being a jerk and a bit of a hypocrite there.

200.mph

iTrader: (9)

bullshit noob, rotaries run on magic, unicorn tears, and fairy dust. btw 9k has no idea what hes talking about

logalinipoo

Wow Dogon, it's pretty simple MAF and RPM is used to calculate load. The VE table in Access tuner race is not a true VE for the engine. It is a pinpoint adjustment.

MAF can very greately at the same engine rpm if you're coasting, cruising or accelerating.

You need to use the MAF scale to get LTFT's below 5 with almost no STFT's. Because LTFT is used in open loop. Then you use the VE table to fine tune your afr's.

Why would changing the exhaust affect how much air the engine can hold? It wouldn't! It would just let it get rid of the air faster. The same thing about the intake It might get air in smoother and with less restriction, but those corrections should be made by the MAF. That doesn't change how much air the engine can actualy hold.

DogonCrook

But the Maf doesn't know anything about air that has already passed it. I'm not saying Maf scaling isn't necessarily, just that it isnt the sensor itself that's wrong, (well not by much). Your just tricking it. Why would you not want your af tables to be actual instead of arbitrary? The engineers that wrote that table used lambda, not arbitrary numbers. Your asking the Maf to do more than it was ever intended to do. It's your engine that's off spec not your Maf.

logalinipoo

Yes and no, Every sensor is going to have some variance from the factory calibration(probably not much). If you have to make more then a couple of percent change to your MAF scale then you should be looking for mechanical problem with the car.

Either way you are not looking for performance from your engine during light loads. You're normally looking for economy. The closed loop side of the system is providing that for you. You are tuning for performance and not destroying your engine in the upper power band. You do not need Fuel trims getting in the way so you want to tune them out. This isn't going to matter as much NA it might cost you a little power, but if you are FI then it will cost you an engine.

Lambda is great but it does you no good. The RX8 does not have a fuel sensor. It does not know what type of fuel you are using so it can not adjust the target lambda based on fuel type. There are not very many vehicles that do. So it uses an arbitrary number 14.7 as lambda.

Also lambda might be the best for the enviroment and economy it is not the best for power. That is why you chase an actual number. In the end it doesn't really matter what numbers you use or where you make the changes. If you get your desired result who cares. but If you go adjusting just VE or just Injectors to reach your targets then when the weather changes or when you fill up at a different station your tune might go to **** and you will be constantly adjusting it. If you tune it with the PCM then It will work to keep your resulta as desired.

9krpmrx8

iTrader: (46)

This is the exact type of statement we have heard a million times. Like I said, talk is cheap.

DogonCrook

I'm not saying the stock af tables are right, what I am saying is if you tune out your fuel trims with ve then your af tables won't be arbitrary numbers anymore, your af tables will match what you are measuring. Ie if you know the fuel you are using has a lambda of 14.3, putting 14.3 in that cell will actually give you 14.3. Maf scaling also does nothing to address abrupt throttle changes, so if you rely solely on maf scaling you will have to more radically alter your af tables, and even then there will be spikes that happen so fast you can't address them. Weather changes actually throw off maf scaling far more than adjusting your ve. Your maf isn't the reason an 8 doesn't hit commanded. Reread no coasts posts, he says it far better than I can. At the end of the day yes, the numbers don't have to matter to get a good tune, but if you haven't adjusted ve to match reality there is a hole in your tune. Throttle response isn't an 8's strong point, so why not improve that too, and get easier to understand numbers while your at it?

DogonCrook

Yes well you haven't backed up any of your statements with evidence. As for mine this forum is full of successful tunes, as a matter of fact no coast has his dyno numbers posted elsewhere that make your claims of super special snowflake tuning a bit dumb.

9krpmrx8

iTrader: (46)

Huh? This forum is full of successful tunes that were made from scratch by the owner of the car? Not. Very few actually, but I guess if you call loading a tune on your Cobb and flashing your ECU successful then you are right.

And I hate to burst your bubble but dyno numbers generally don't mean dick unless you have other RX-8's done on the exact same day to use as a comparison. They are cool for bragging on the internet though.

logalinipoo

Weather changes don't affect your MAF that is the main benefit of a MAF sensor. The MAF measures based on weight. If the pressure drops it has less weight and if the pressure rises it has more weight. By the same volume. The MAF sensor has a built in temp sensor that automaticly adjusts for temp. The MAF responds so fast that you might have a fraction of a second delay to an abrupt change. During that fraction of a second you are still at low load.

The VE table is based on load which is calculated from MAF. so if your MAF has a delay then the you will have the delay in it and an aditional delay as that data is processed by the VE table. so that is twice the delays

DogonCrook

Have you ever tuned a car? It's really not that hard, even if you don't know what you are doing, but know where you want to end up you'll get there. 8's aren't special get over it.

Still waiting for you to actually mention a reason you believe any of the things you do..

9krpmrx8

iTrader: (46)

Again, talk is cheap noob. Here is my reason for believing.



http://www.flickr.com/photos/9krpmrx8/11794009674/

DogonCrook

But it's processed by the VE table one way or the other so I doubt it adds a delay.

If your maf is 1% off and your VE is 2% off then adjusting the maf by 3% to account for it would make more radical changes to calc load than correcting each respective table wouldn't it?

The maf is upstream of a throttle plate and your ssv, and sits on top of an engine that has a pretty variable temperature range during normal operation, your maf can't measure any of that. On a daily driver that probably hardly matters, but it's fixable by changing both, so why not?

DogonCrook

@RX8 lol you post that after telling me that dyno's numbers don't mean anything. All that proves is you can rev your engine. Do you have no self awareness? What point are you even trying to make?

You do have just the most super special 8 ever... It looks really hard to tune thats for sure!

just lol...

logalinipoo

I would think that Mazda knows the VE of this engine. They've done a whole lot more testing then you could ever hop to do. The engines are made to very close tolerances. If they were not then the thing would not seal up.

The throttle is also upstream of the APV valve and the VDI, what does that have to do with anything? They help the engine breathe easier but they don't allow it to hold more air.

Why would your MAf sensor need to measure that tempeture? if the air slows down behind it due to thermal expansion then it slows down as it passes through the MAF also and it still measures the total weight of the air that moves through it. The weight of air moving through it gets an equal amount of fuel by weight to make the ratio requested. It doesn't matter what the VE of the engine is. If it's a 4 rotor then it will pull in twice as much air and need twice as much fuel, but the VE of the engine does not matter.

Again the map marked VE in Cobb is not an actual VE of the engine. It is a adjustment table. The Actual VE of the engine is built into the load calculation.

logalinipoo

Dyno numbers don't matter. They can change daily or be tweked to make it look better. The only way the actual number matters is if you are doing 2 different cars on the same day with no changes to the setup of the dyno. Then they can actually prove something. He wasen't doing it to get a number for bragging rights. I don't think I've ever seen 9K make a post about his Dyno numbers.

He posts that because whatever the numbers are. If you start at x and get x+ then you've tuned your car and gained power.

DogonCrook

Your Maf does not see all of those changes.

"Adjusting MAF scaling is effective if the MAF housing has changed (such as with an aftermarket intake). If no changes in the MAF housing have been made, why bother with something Mazda got perfect? If your MAF is reading differently than what that table says, it means your MAF is failing and should be changed.

Yes, there are production variations, but you're talking like 1-2%.

The trouble with MAF scaling is this:

It is only effective for the VE curve you tuned it to (such as the load cells the engine sees on a dyno at WOT).

Let's say you have a MAF voltage at a given RPM and load where the engine has 50% VE. At that same MAF voltage at a different RPM/load you could have a VE of 100%. The actual amount of air entering the combustion chamber is much different between these two situations. This will throw your AFR's over the place in a situation like road racing, where the engine will see all sorts of weird load cells. (this is a huge exageration, on a stock car, you have variations of less than 15% between the lowest and highest VE). This leads to some weird behavior in transient or part throttle situations.

For drag racing it doesn't matter as much.... unless your air density changes. Then you're back to square 1.

The VE table on a stock car is quite good on an engine that fits the engineers statistical model for engine wear and other tolerances. If you had an engine that wore (and hence breathes) the exact same way as their average statistical engine does, there would be no reason to touch the VE table. We don't live in that perfect statistical universe.

Start throwing mods on a car, and the volumetric efficiency will change. You actually predict about how much more power your engine will make based on changes in the VE table. 10% more VE due to your mods, and you will see about 10% more power.

This is why COBB recommends that you don't use their stage 1 map on a car with mods. The VE changes are too big and you will go lean near peak torque."

Unless there is something unique about a rotory this still applies.

DogonCrook

He posts that because he has nothing to back up his bizarre claims. He is clearly not interested in discussing anything he's just trolling so he starts arguing points nobody is arguing with. I guess one could chose to believe a proffessional tuner couldn't effectively tune his 8, but I happen to believe someone making that claim is just throwing a tantrum.

logalinipoo

You don't tune The MAF across the board you just adjust it in the ranges that it develops fuel trims so the fuel trims do not throw off the rest of your tune.

MAF curve is not perfect. Go get another MAF sensor. I've seen 3% differance between my MAF sensors. It could easily be more.

Again the VE table being referenced in this thread is based on the MAF so if it is off then your multiplying the problem.

And no matter what external mods you do you will not change the engine's VE. Unless you start modifying your rotor or rotor housing your VE is going to no ever change in any noticeable amount.

You predict power based on Air flow. If you flow 10% more air then you will get 10% more power. If you were doing a MAP(pressure) based tuning then I would agree but this system uses air MASS not pressure.

9krpmrx8

iTrader: (46)

Dyno HP numbers don't mean **** fruity. Dynos are a valuable tuning tool though. Bizzare claims? Post up when you have some actual practical tuning experience with an RX-8. Until then your opinions mean nothing.