subscribed,

in regards to blow by or draw through, most if not all car with turbo's and maf systems do use the draw through method.

 

What i posted was just a little clip of data from my log.. I have 503 Lines of data on that log... The STFT is averaging to 2.192405567 over the whole data log.. at an average of 4092 rpm with a calculated load average of 30.98852883. so would this mean that my STFT is in the 3% rage? and my Fuel VE adjustment should be at the 4000 rpm at the 0.31 Calulated Load Cell? change that from .99 + 2.2%??

OR each line from the data log on my STFT need to be within 3%??

Thanks.. just trying to make sure im chewing on this right.

 

Yeah if it averages 2.19 you are good. Unless you are OCD like me and freak out if it averages above 1%,

 

haha.. I am.. but im just starting so I havent started cracking the whip on myself yet.. haha.. but it will come.. when i get a better understanding of all of this..haha..

 

I have tuned/driven both and can't really say I noticed any difference either way . For a street car - draw through seems to work just fine on these engines .

 

Ok guys... This is what I got.. Im currently in the process of giving this a try..

So I did some Data Logging. And I took to it like this..

I took the average of my logs at an average of 4000 rpm. (4246 RPM) and 4500 rpm. (4491 RPM)

My Calculated Load at the 4k average came to 40.05
My STFT's at that average came to 5.275625%

And my average 45k RPM came out as 42.45 Calculated load with my STFT's at 11.90563%

I took a screen shot of the excel file i made that shows the Fuel VF table and what I did



I went to the average RPM range of 4000 and the average Load rage of 40~.38 and changed the Cell from 0.99 and added the average percent from the STFT of 5.275625% Then I took Half of that percent (2.637813%) and added that to the surrounding cells.
I then went to the next range of 45k rpm average and Calc. Load of 42 ~ .44 range and took my average STFT for that of 11.90% and added that to the cell changing 1.03 to 1.152628 and then took half of that percent 5.952815 and added that to the surrounding sells.
OVERLAPED CELLS.. so the surrounding sells that overlapped each other. I just took the average of the two 2.637813 and 5.952815 and averaged them together and came up with 4.295314 for the ones that overlapped and added that percent to those sells..

Does it sound like Im doing this right... I plan on doing more data logs for other load and rpm ranges and maybe look for some type of trend then I can interpolate more of the sells and get a lager pattern of what may be going on..

 

That's pretty much exactly what you should be doing.

 

Ok sweet. As I chew on this ****. I'm think I'm getting it more and more!

 

Eventually you will get the VE map whittled down to the point that you are only making very small changes to single cells.

There really isn't great resolution in that map, and eventually you get to the point where individual cells may actually need to be fairly far off one another and blending them begins to be counterproductive.

 

I am already seeing things like that.... From one rpm range to another and depending on the load range I see some big jumps at this point.. I don't think blending is going to work it out in the cases ive seen when the cells are right next to each other with big changes between the two.. I haven't changed them yet but I can already see what you may be saying about that.

 

Yeah, knowing where to blend is part of what makes this all more art than science at the end of the day.

The big peaks/valleys on the RPM scale are where the different ports open up. Obviously there will be some huge airflow changes there.

 

so on a boosted car if I wanted to change the VE would 1.2 ve be out of question?

what would be the best way to compensate the injector scaling for intake track pressure?
as boost goes up the injector will inject less fuel then what the calculation thinks.

 

VE will be entirely dependent on your setup. Numbers are completely arbitrary and made up until they are logged and compared with reality on your specific setup.

I merely know how to look at the hard data in front of me and tell what adjustments need to be made. There are engines where I can pull a number out of my head and it will be close. This is only because I've tuned hundreds of them. I haven't done enough rotaries to be able to know what numbers look good and what don't.

I know the COBB software very well. I know Otto cycle internal combustion very well (rotaries are still an Otto cycle engine). I bought my RX-8 because I knew absolutely nothing about rotaries up until early May when I decided to impulse buy one so I could learn new things.

The VE table can kind of fudge things on a boosted car.

Boost is basically your calc load. As boost increases, calc load increases. In those higher calc. load tables, you will end up having higher VE values (forcing the ECU to run a higher IDC to compensate for the relative drop in fuel pressure). It's a bit of a hack, but it works OK.

Honestly, for boosted cars the best option is to switch to a rising rate fuel pressure regulator that increases fuel pressure by 1psi for each 1 psi of boost (as this keeps the relative head pressure in the injector the same at all times). This isn't a small undertaking, as you basically have to switch over to a return style fuel system. This is a purely mechanical and elegant solution. It eliminates a whole bunch of variables that are otherwise impossible to pin down. Bonus points for the fuel pressure changes being instant.

It's a mod that will give you absolutely zero extra power. For reliability purposes it's huge. There are situations at part throttle where you can still have very high manifold pressure, but very low airflow rates. This will bring your calc. load way down, as it's strictly monitoring airflow. This will result in less than ideal IDC and force the engine lean. If you have a built in mechanical method to tie fuel pressure to boost pressure, it eliminates those situations.

My personal theory thus far, is that a lot of these boosted RX-8s that are popping motors despite a solid dyno tune, are due to part throttle lean conditions that were never seen on a dyno.

Difficulty depends on where you place your regulator/return.

If you totally ditch your OEM fuel rails it becomes a huge project. If you do return at some point in the engine bay before the OEM rail, it's not too bad.

I've never done this on a Mazda. I don't know the exact specifics of what's involved. I've done it on a ton of other cars though.

 

Thankfully, you were wrong

This thread is encouraging me to take another look at boost. Damn...

 

That doesn't happen on our engines . You don't see high manifold pressures unless you have corresponding high air flow . What we do see is very high pressure pre throttle which can lead to some interesting moments mid corner if boost controller/BOV is not set up to minimise this. This will not cause a lean condition however.

The fact that our stock apex seals are very brittle combined with some dubious tuning software and some really dodgy installs caused the demise of many of our earlier turboed engines. These days it's rare to blow a well tuned FI engine unless you up the boost.

 

Ok guys, Flashed to the Cobb Stock Map. Here be the logs.

Stock Idle
LTFT is less than half of what it was, but the STFT is up.



Here is the 4th Gear Cruise
LTFT is way down, but STFT is through the roof. Have basically Flip Flopped the LT&ST



Stock 2nd Gear Pull
Same trend, less LTFT more STFT



What do you think?
I want to go do the Mazda injector service and get to cleaning it up.
New plugs/coils/wires are due as soon as I can afford them.
Don't know if this will help at all, But It needs to be done anyhow.

 

What you are seeing is what happens after every flash . LTFTs zero out and take some time to re- adjust , apart from idle which doesn't take nearly as long .

 

I hate doing the reflash. It feels like murder on the car starting it up afterwards.

 

not if everything is hunky dory . Yours ................................... isn't .

 

That car just seems really bogged down after the flash. Takes a minute to get back to a normal feel. I have not let the car die, but it feels like it would.

I almost wish I didn't have an accessport. ignorance is bliss.

 

At this stage you need to spend less time learning about the Cobb and more time looking for your problem .


Still say you have a vacuum leak .

 

Alright, will do.

 

This is a bit left field but .................. do you notice a ticking noise coming from the top of the engine ?

 

Not that I can remember. My engine just has normal whirring noise. I will listen closely tomorrow, but I'm pretty sure it does not make any ticking noises. whats the ticking mean?

 

Just was talking to a guy who had his evap solenoid give out on him and that's what it was doing . similar symptoms to yours .