adamlewis

If you were to run your car @ WOT on 93 octance and got an A/F reading of X, would it be the same ( if all other things were the same ) if you did it on 109octane?

600HP CLUB

i would like to know this also

West TX RX-7

well 109 doesn't burn till a higher temp but I think it burns faster and more complete.

You might not burn it all depending on your compression and spark.

poor college student

i thought higher octane burned slower?

chris_stampe

Im pretty sure it would be the same a/f ratio. Higher octane helps detonation, but not by richening out your mixture. ............I think

Barwick

higher octane burns slower as far as I know.. that's why SCCA racers use the lowest octane (within reason) they can find in their 12A rotaries (and 13b's also).

FC_Iria

A higher octane will let you run a leaner mixture of fuel to air and not detonate. So your a/f ratio will be the same but you won't detonate as easily.

J-Rat

iTrader: (2)

Okay folks,

HIgher octane gas will do nothing for you, except burn slower and foul up your plugs, unless you are set up to burn it.

There are a million documents supporting me, but I am just going to link you to the LAST thread about octane in this section.

https://www.rx7club.com/forum/showth...ghlight=Octane

Jarrett

SonicRaT

iTrader: (6)

Amen with J-rat. Your readings will be the same.

Steel

eh... i wish they made 83 @ $1 a gallon or so for us N/a dudes, so even though we go through more gas than those ... honda's and what not, we can still laugh at them. For.. paying for more gas.... aww jeez, im gonna go drive the rex now.

Evil Aviator

Yes, an AFR of X is the same regardless of the fuel because the AFR is a ratio of the weight of air vs. the weight of fuel, and nothing more. For example, 8 pounds of oranges per crate is the same ratio as 8 pounds of apples per crate, since both are 8:1 ratios regardless of the fruit involved. However, X will mean different things with different fuel. For example, 91 octane (PON) makes its best power around 12:1 AFR, while racing leaded 100 (RON) makes its best power around 13:1. Therefore, if that X AFR was running well in your car with the 91 octane, that same X AFR will be too rich with the 100 octane.

Also note that once you leave the realm of pump gas, the chemical compositions vary greatly. At this point the higher octane fuel may actually yield more power per pound because the fuel is composed of more powerful components.

Rotory

iTrader: (1)

ive always been told to run 93 in a my Turbo II it helps pinging

Rotory

iTrader: (1)

but not to mention 93 burns cleaner, sorry for being a post *****, 50th post im a rotorite

J-Rat

iTrader: (2)

Wrong...93 octane does not burn cleaner.

The ONLY reason to run 93 in your turbo, as I do, is for extra protection against detonation.

Jarrett

Rotory

iTrader: (1)

In some circumstances oxygenates such as methyltertiarybutylether (MTBE) or ethanol are added to gasoline to achieve the required octane or to reduce certain emissions.

Other additives that may be added to gasoline include octane enhancers such as methylcyclopentadienyl manganese tricarbonyl (MMT), corrosion inhibitors, stabilizers, antioxidants, metal deactivators, demulsifiers and deposit control additives.


GOT FROM: http://www.boucherandjones.com/gasolineinfo.htm

adamlewis

Ok...I read this all and nobody told me anything I didnt already know...And my question wasnt really answered..

Thats all my fault though...

Lemme change "A/F ratio" to "O2 sensor voltage".

so...

If you were to run your car @ WOT on 93 octance and got an O2 sensor reading of X, would it be the same ( if all other things were the same ) if you did it on 109octane?





I still think it would because you wouldnt get as complete a burn with 109.5octane as you would with 93octane.


The reason Im asking is because when I get the car running with the Haltech, the first place its going is to a dyno with a wideband.
I have a base map for the car, but seeing as how rotaries are so fragile, Id rather not take a chance. I was thinking about running some Turbo Blue (109.5) in the car while on the dyno to tune my A/F but then I thought that it would probably show the WBO2 a different reading than it would with 93octane...

Evil Aviator

I guess I don't understand the question. Please choose one (12:1 AFR is used as an example):

A) If I am getting a reading of 12:1 AFR on my meter when running the engine on Turbo Blue, is that really 12:1, or is the meter now out of calibration because I'm not using pump gas?

B) My engine is currently running at 12:1 AFR with 93 octane. If I switch to Turbo Blue, will I still get 12:1 AFR if I don't make any tuning changes?

C) None of the above.

BTW, you do realize that the leaded Turbo Blue 110 will ruin your O2 sensor very quickly, right?

eViLRotor

iTrader: (2)

Translation: Your AFR will be identical no matter what grade of fuel you use. Your Haltech voltage will also be the same.

Dyno tune your car with the octane you want to run, since your tuner will want to adjust your timing curve as well, and for that fuel octane does matter...

dr0x

Myth #123980712 put out by the gas companies to get people with low compression NA vehicles that were built to use 87 to buy 91/93.

adamlewis

Itd be more like B. And yes, I know leaded gas will mess up your O2 sensor.

I want to tune the car at first on a dyno with a WBO2 tailpipe sniffer. Just to be safe, I wanted to run higher octane fuel while doing so.

The question Im asking is that if I were to tune with high octane fuel, and the WB02 says Im at 12:1, would it still say 12:1 when I ran regular 93 back through it?
My fear is that I wont burn all the fuel while tuning on high octane, and the WB02 will say Im running rich even though Im really not...Its just not all being burnt.
So I dont want to tune to 12:1 with high octane and end up getting a 13:1 or something with 93.


I realize the same amount of fuel is being injected...But I dont think the same amount of fuel would be burned. And if a different amount of fuel was burned, wouldnt the WBO2 show something different?

Evil Aviator

OK, I see. You are worried about blowing up your expensive engine so you want to tune it with a more anti-detonant fuel to be safe. This isn't going to work. Like eViLRotor posted, you need to tune your engine with the actual fuel that you plan to use. If you can use the same brand, then this will be even better.

A wideband O2 sensor and display unit is about the same price as professional tuning. Your money is better invested in a good tuner with insurance that will cover your engine if it blows. Let him buy the expensive wideband equipment himself, lol.

Also, a fresh rebuild will greatly reduce the chances of detonation. Most of the blown engines that you hear about on the internet are due to people slapping a turbo on an old nasty engine, and/or trying to tune it to some magical AFR number that somebody's cousin's brother's roommate read was good on the Honda forum.

If you would like to learn more about how an O2 sensor works, these sites are good. Look closely at how the reference voltage is based on a stoich condition that is dependant on the fuel's composition. This is one of the many reasons why switching fuels will not yield the same results.
http://auto.howstuffworks.com/question257.htm
http://www.sts.sae.org/membersonly/t...xygen13-17.pdf

jeyjey

Interesting thread guys I run my TII on 98 octane and the lowest available in the u.k. is 95 octane.........
I also thought that you set your timing for the fuel you plan to use.
Thats my nose stuck in anyway and I have just done in about fifty dollars worth in a couple of hours but I guess thats what its all about (racing a boxter did not help much I guess)

Wankel7

Tune your car on the fuel you wil be using.

Just a note on the dyno guy with a "Tailpipe sniffer". If you have a cat and he still wants to use the tail pipe for the reading. Leave. And do not go back.

Also, that sensor should be 90 degrees to the exaust flow. Not parallel to it. On your dyno day you would be better to have the sensor in your stock sensor hole.

If you are super concerned about detonation make sure you have a good intercooler setup. And if you are still fretting then run water injection.

James

adamlewis

Ok...Look guys. Theres only one thing I want to know and nobody has yet to answer it.

I wasnt asking if you think I should tune this way or that, all I was asking is if different octane fuel will give the WB02 sensor a different reading.

I do appreciate the input, but you all are giving suggestions on things that you dont know the full story about and I dont feel like typing it all out.

So for the last time, will different octane fuel give the WB02 sensor a different reading?

HAILERS

Something I always suspected: ****Most of the blown engines that you hear about on the internet are due to people slapping a turbo on an old nasty engine****