AJ's Shinka

I'm going to install my Mazsport DR midpipe soon and I already have the Cobb AP installed.

Will the AP destroy my engine as the AP Map notes state?
From Cobb RX8 AP mapnotes:"THE INSTALLATION OF ANY OTHER
HARDWARE SUCH AS HEADERS OR CATLESS EXHAUST MAY ALLOW THE VEHICLE TO RUN LEANER THAN
DESIRED, WHICH CAN CAUSE ENGINE DAMAGE."

Will this damage happen if I go back to my stock map?

Flashwing

The installation of your mid-pipe will not cause any damage to your motor outside of your current tune. The presence of a mid-pipe allows you to run leaner fuel mixtures without having to worry about the cat.

If you are worried about the situation you can flash your PCM back to the stock configuration however I don't see any problems with simply installing your Midpipe.

Monitor your air/fuel rations and ensure that you're not running too lean for the conditions of the motor.

AJ's Shinka

Thanks Flashwing, you are alright. I haven't read anything on the forums that a midpipe would cause damage, I just needed that extra confirmation due to Cobb's warning. As long as I am in 11's and 12's during WOT I should be alright, right? Does the gear matter and/or do I have to go WOT in every gear?

04RX8man

yeah the 11 to 12 range is good it's richer than "stoich" but you will net power from it going very very rich( i know others disagree with this but i really could care less) will not net power

AJ's Shinka

Haha I always wonder what "stoich" meant. Anyhow, how do I know if I am running too lean. What AFR numbers would indicate that I am running to lean that is safe for this engine?

Lower = Richer, Higher = Leaner

Air / Fuel = AFR. if the top number gets bigger (more air than fuel...LEAN), your AFR gets bigger. If the bottom number gets bigger (more fuel than air...RICH), your AFR goes down.

So what number is an indication that I am too lean? Is 14 too lean?

MazdaManiac

iTrader: (3)

Why don't you just send your logs?

Optimum power is at 13.2:1 N/A.

The Cobb warning is only valid with a Cobb map.

paulmasoner

iTrader: (1)

i wanted to say something when you mentioned 11 or 12 in another thread but knew you wouldnt listen as you were already denouncing other's proven statements. hope you have more faith in this guy \/

MazdaManiac

iTrader: (3)

Yeah. This is wrong.
But you couldn't care less, so neither do I.

05rex8

iTrader: (7)

haha...04rx8man is on a roll today.......

the straight pipes thread he posted in was an epic fail

blackenedwings

Jeff, I'm curious... how do you detirmine the optimal AFR for a given application? Also is that optimal power at WOT or across the board regardless of load or throttle? What is the optimal AFR for a FI RX-8? It's frustrating because most of the books and websites that explain information like this are entirely devoted to piston engines and its hard to know which pieces of knowledge transfer to rotaries and which do not.

Flashwing

The same principles apply with the rotary. It's been shown that air/fuel rations of 13.2:1 generate the optimal amount of power at a particular RPM.

Your "optimal" air/fuel ratio is determined on numerous factors but it comes down to what you're trying to accomplish. If you're looking for power, then typically with 91 octane gas, 13.2 is going to be the leanest you can go while still generating power and not risking detonation.

Otherwise, in the case of the RX8 it's best to shoot for 14.7 anywhere in closed loop and perhaps a little leaner than that during cruise for fuel savings.

Forced induction finds it's optimal power around 11.5:1 and as high as 12.2:1 before risks of detonation occur.

Jeff please correct me if any of this is in error.

If you're talking about in a N/A application...no you are incorrect. You'll still see power gains till the low 13's after which you don't see much gained and simply risk detonation.

AJ's Shinka

Thanks everyone for all your input,

MazdaManiac should I send my logs now or should I wait until I buy and install the BHR ignition upgrade because then I will have to re-tune again and I would hate to waste your time. After the ignition upgrade I will be done with my engine mods for a while, unless I can find a racingbeat exhaust for sale.

Thanks,
AJ

Edit: I just reread this:
I did not know this either, after installing the midpipe I am running 11's but mostly 12's in WOT which was what I was running before the midpipe install. I am at 14's at cruising and 15 at idle. Phil told me running to lean would cause detonation, but if I run too rich I could detonate as well? Thanks again for the info Flashwing.

Flashwing

Yay! Excellent question.

That's why it's hard to say what's optimal. Technically, 14.7:1 is optimal because theat's the point where there's exactly one molecule of fuel for every molecule of air. Now, because the motor isn't perfect we know in reality those fuel and air molecule's don't always find each other.

We want to make sure ALL the air finds fuel...period. Still, there are compromises in either direction that will yield less than optimal results.

However, your operating conditions dermine what kind of fuel mixtures you can run. Cruise, for instance, allows you to run leaner than 14.7:1 fuel mixtures because the engine load is lower. We can get away with leaner mixtures without risking detonation.

It is possible to have a rich misfire as well.

In all, you've got nothing to worry about with changing your exhaust out. I'd do the exhaust swap and then take a whole new set of data logs and have MazdaManiac make you a new tune. With a new tune you can take advantage of that mid-pipe and squeak out a few horses in the process.

MazdaManiac

iTrader: (3)

Once again:
https://www.rx8club.com/series-i-aftermarket-performance-modifications-23/so-you-wanna-tuner-100333/

blackenedwings

Oops, I've actually read that... I also realized when Flash wrote his response that I actually knew the answer to my own question.

AJ's Shinka

Must read this thanks! BRB

I'm back...Quoting MM:
"The air-fuel mixture can be ignited over a fairly wide range and the optimum values will occur between the lean best torque (LBT) and rich best torque (RBT) ratios, that fall anywhere from 11:1 to 13.5:1, depending on the engine's volumetric efficiency and resistance to detonation and pre-ignition."

So it seems that every rx8 engine's "optimum power" can vary depending on it's setup and tolerance to detonation and pre-ignition. Am I interpreting this correctly? Also, are those ratio's backwards? Shouldn't it read...

lean best torque (LBT) and rich best torque (RBT) ratios, that fall anywhere from 13.5:1 to 11:1 respectively

I just want to make sure I am reading this correctly and LBT is the higher number and RBT is the lower one.

Please correct me if I am wrong. I see the importance of the logging now. I am learning a lot, Thanks!

MazdaManiac

iTrader: (3)

You are right - leaner is the bigger number.

However, it is my experience thus far that, detonation aside, the Renesis makes its maximum torque at 13.3:1 in it N/A form.

DOMINION

13? is that number stock?

04RX8man

yeah 13.3:1 is the "most powerful" ratio as NA(from what I've heard/learned)

greg985

damn i am at 11.2 at WOT so I am pretty rich