93 vs. 91 Octane gas w/ tune

[marshall834]

Just set an appointment up for JHM tune in January with Piggies! Problem is, they offer both a 91 and a 93 octane tune. Here in Reno, I have yet to see a 93 option, but I also don't plan on staying here much longer (maybe another year). Would there be a noticeable difference between a 91 and 93 tune? Could I get the 93 and use 91? Anyone else have experience with this?

[simplesedan99]

i dont think the differences will be noticable with just k&n drop in a piggies

[envious]

it wont be that noticeable until you start shooting more fuel and air in the engine. and if you ever raise the compression, the higher octane fuel is necessary. one of the things that the higher octanes does is resist pre-combustion that way you can compress more gas and fuel without it igniting on its own due to the high pressure (kind of like a diesel) and then light it when the spark plug shoots it. so once you run some sort of forced induction system or raise the compression, is when the higher octane becomes more critical

[Stubek]

Also depends where you think you are going in a year or so. West of the rockies is 91 octane, east is 93. Also, you could get reflashed

[beemercer]

when you get tuned call them and request a 91 and 93 chip so you can swap them if need be, its a 10 minute procedure once you do it a few times

you'll get the throttle response benefits and more power, but not as much as the 93 tune will give you

with piggies your timing retard is gonna be high anyways, on either 91 or 93, though the 93 tune should be able to be marginally more aggressive with the timing



one thing to keep in mind is Jay@JHM typically runs california piss-91 in his car at the track, so the 91 tune hasnt been neglected in its development and you can definitely make more power with the 91 tune, just not as much as the 93 tune


so long story short, get the 91 tune now and request a 93 chip with your tune

[Justincredible]

There is going to be a noticable difference between the 91 and the 93. I would start with the 91 and see how it goes. JHM likes to work with people and have them send back info so I Would use the 91 for a while and then send them logs to see if your car would be able to use the extra octane. I know there 91 file can adapt up so that might be enough.

IN the end. There is a very noticeable difference between the 91 and 93.

[Foofie_Kitten]

their 91 tune has the ability to adapt up to about 100 octane fuel. so if you were to move somewhere with better fuel (ie. 91 octane) you'd be able to see the advantages of 93 octane fuel without swapping in a new chip.

HOWEVER, if they can get you a new chip for minimal cost increases like Justincredible says, I would go with that route and just save that extra chip for when you move out of the "bad-fuel" states.

[S4Bennett]

Since we're inquiring about the different octane tunes, I've always wondered if the 91 octane tune was done using California oxygenated or 48-state 91 octane.

A couple of things I've noticed are that the last 2 sets of plugs I went through, on a stock tune, had sign of detonation. I use 93 octane 99% of the time and in the last 20k miles, there were still signs of detonation.

Also, the dyno plots I've seen with before and after of the JHM tune, the AFR's lean out. Whether that's because the ignition timing is more optimized, they've taken injector duty cycle out, or both is unknown by most end users.

Based on that information, I would recommend using only 93 octane with a 93 octane calibration, and if you have to play it safe because you can't control octane 100% of the time, then get the 91 octane tune.

Feel free to contradict anything I've said. What I've observed may not be the assumption for all cars.

[tampas4]

octane is a measure of how much the fuel can resist detonation. On an NA car you will stop making more power through timing advance way before detonation occurs. Engines also make the best torque over a range of air to fuel ratio's. You can be tuned to lean best torque, rich best torque, or somewhere in the middle. So best case scenario running 91 on 93 tune = runs the same, second case = runs safely but not in the engines optimal power zone, third = runs too lean or rich detonate's and blows your engine to smithereens :)

Choose wisely(hint ask the guy tuning your car)

[Apat]

I just asked JHM this question a week ago since in my area 93 can be tough to find but 92 is at 80% of stations. They suggested I get the 91 and then send in some logs so they could adjust it based off the fuel quality in my area. I was told its adjustable up to 94 octane

[S4Bennett]

What are you logging and what are you using to log?

[beemercer]

^probably vcds and timing retard on both banks

do you have stock downpipes (S4bennett, regarding the detonation)

[diaftia]

I just asked JHM this question a week ago since in my area 93 can be tough to find but 92 is at 80% of stations. They suggested I get the 91 and then send in some logs so they could adjust it based off the fuel quality in my area. I was told its adjustable up to 94 octane

There is a gas station on my way home that sells race gas out of the pump. Trying to remember off hand but I think they have 95,97,100 and 110 out of the pump. Does the JHM ecu take advantage of the higher octane automatically or does it require a different map from JHM to take advantage of it?

[marshall834]

octane is a measure of how much the fuel can resist detonation. On an NA car you will stop making more power through timing advance way before detonation occurs. Engines also make the best torque over a range of air to fuel ratio's. You can be tuned to lean best torque, rich best torque, or somewhere in the middle. So best case scenario running 91 on 93 tune = runs the same, second case = runs safely but not in the engines optimal power zone, third = runs too lean or rich detonate's and blows your engine to smithereens :)

Choose wisely(hint ask the guy tuning your car)

I did just that. Keaton at JHM said "there will be a significant difference in mid-range power and torque." He also said I can definitely use 93 with a 91 tune as the ECU will actually ADAPT UP to the best octane available. Apparently it can adapt up to 100 - answering diaftia's question. Think I'll do just that for now.

Also one more question - will the extra power have any impact on the transmission? I don't plan on getting any additional mods anytime soon.

[Apat]

There is a gas station on my way home that sells race gas out of the pump. Trying to remember off hand but I think they have 95,97,100 and 110 out of the pump. Does the JHM ecu take advantage of the higher octane automatically or does it require a different map from JHM to take advantage of it?

I really don't know now as there is a lot of conflicting information showing up in this thread. I was told the 91 Tune would adapt up to 94. Now I see Keaton told the OP it will adapt up to 100 so I'm a little confused myself. Hopefully someone who knows more than I do will chime in here.

@OP Your transmission will be just fine. There's plenty of guys running s/c and nitrous with no issues. Your clutch will be tested a little more due to the additional power.

[tampas4]

To understand a little more about the tuning google open loop and closed loop fueling. During warm up the ecu will be in open loop which means it is not using the sensors it is running off the fueling map made by the factory/tuner. Once the sensors have warmed up the ecu switches to closed loop, which means that the computer reads the maf then reads the oxygen sensors and adjusts the fueling accordingly. Google LTFT and STFT, long term fuel trim and short term fuel trim to understand what happens here. At a certain load(how hard the engine is working) the computer switches back to open loop; why? Because things are happening too fast for the computer to read the sensors and adjust. Depending on the ecu it might either follow the last adjustment that was made and apply that adjustment to the fueling until the load lowers or it will follow the base map saved by the factory/tuner.

I've worked with Denso ecu's a lot and the majority of those can compensate up to about +- 20% of the base map. So even if the ecu can handle 100 octane in closed loop what happens when you floor it and go into open loop? Buy the 91 tune and fill it with 91, when you move get the 93 and fill it with 93 !moar powa!

[B6JoeS4]

If you are going to switch gas like that, be it 91->93, 93->91, 93->100, etc. It is VERY important that you reset the ECU by either unplugging the battery for 20 min or so, or going into VCDS and hit 'Clear codes'. Another thing, our engines cannot really do much with anything higher than 98 octane, so a mix of race gas and 91/93 is optimal.

To answer the question about the 91 tune being developed in a state with 91oct. other than California: The tune was not technically written in California, so it saw lot's of beta testing on cars in both California, and other 91oct. states.

[beemercer]

I really don't know now as there is a lot of conflicting information showing up in this thread. I was told the 91 Tune would adapt up to 94. Now I see Keaton told the OP it will adapt up to 100 so I'm a little confused myself. Hopefully someone who knows more than I do will chime in here.

@OP Your transmission will be just fine. There's plenty of guys running s/c and nitrous with no issues. Your clutch will be tested a little more due to the additional power.

the amount it will adapt is dependent on other conditions, on a cold day with a car running a fully catless 2.5" fullback and a 91 tune it may be able to reach its timing goal without better fuel... whereas a car with pre-cat gutted piggies, stock catback running the 91 tune on a hot/humid day may need 94-100 octane to zero out/bottom out the timing retard

[Justincredible]

I really don't know now as there is a lot of conflicting information showing up in this thread. I was told the 91 Tune would adapt up to 94. Now I see Keaton told the OP it will adapt up to 100 so I'm a little confused myself. Hopefully someone who knows more than I do will chime in here.

@OP Your transmission will be just fine. There's plenty of guys running s/c and nitrous with no issues. Your clutch will be tested a little more due to the additional power.

The 91 will adapt up to say 94 or what you would normally see as a swing in good gas.
The 93 will adapt up to say 98 I think thats what was said in the past.

Using race gas or higher Octane just assures you that you will be getting 100% out of your tune 91 or 93. While 93 would obviously give you more the higher octain works to help repel heatloss so it has lots of uses and can add power out side of it just being a higher oct.

[S4Bennett]

^probably vcds and timing retard on both banks

do you have stock downpipes (S4bennett, regarding the detonation)

I switched to single cat FI Downpipes 8k miles prior, so 12k out of the 20k were stock Downpipes.

[beemercer]

^it'll be interesting to see if you still observe the same signs next time you do plugs... I'd lean towards the stock cats heating everything up a ton

[Justincredible]

^it'll be interesting to see if you still observe the same signs next time you do plugs... I'd lean towards the stock cats heating everything up a ton

I agree. they really cause too much heat. SO it would be great to see how this plays out

[Apat]

The 91 will adapt up to say 94 or what you would normally see as a swing in good gas.
The 93 will adapt up to say 98 I think thats what was said in the past.

Using race gas or higher Octane just assures you that you will be getting 100% out of your tune 91 or 93. While 93 would obviously give you more the higher octain works to help repel heatloss so it has lots of uses and can add power out side of it just being a higher oct.

Now that makes sense. Thanks man

[V8S4Ryan]

Ok so throwing this out there if I mixed 93 with 1/4 tank of e85 so a 25/75 split more 93. Will this mixture cause any damage to the motor? And if not im under the impresion you will gain some octane out of this but would it be benifical? Sorry for the crapy punctuaion

[beemercer]

Ok so throwing this out there if I mixed 93 with 1/4 tank of e85 so a 25/75 split more 93. Will this mixture cause any damage to the motor? And if not im under the impresion you will gain some octane out of this but would it be benifical? Sorry for the crapy punctuaion

be very careful mixing oxygenated fuel in without compensating for it

[V8S4Ryan]

Im just doing a little poking to see what everone thinks before I jump head first. thank you for that input though

[beemercer]

more food or thought






make your own conclusions lol

[Justincredible]

Ok so throwing this out there if I mixed 93 with 1/4 tank of e85 so a 25/75 split more 93. Will this mixture cause any damage to the motor? And if not im under the impresion you will gain some octane out of this but would it be benifical? Sorry for the crapy punctuaion

Short answer. Yes this will be an issue. don't mix E85 in to that extent. The long answer will take a long time to explain.

[V8S4Ryan]

Nice graph and justin got it thank you maybe one day we can dig into that conversation.

[beemercer]

but really, ethanol has a much richer stoich AFR (hence why you need massive injectors when running E85)... so in adding more ethanol into a E10/standard gas tune you are going to lean things out terribly. So cool idea, but don't melt your pistons trying it. If you want to bump octane on the cheap try using xylene.

[B6JoeS4]

Xylene? I have always heard of people using Toluene. 2 gallons mixed with a full tank of gas gets you ~98oct.

Just found this cool calculator. Toluene has an octane rating of 114
http://www.serioussolutions.com/evo/octcalc.htm

[beemercer]

both xylene and toluene work, I can't seem to find toluene around here

[SquiddyB6S4]

Just please be careful using such things. Both are very potent known carcinogens. Working in the remediation industry has put me a little on the worry wart side of the fence when it comes to such things, but I figured it bears mentioning. If you want more info, check out the NIOSH (the OSHA is more lenient for various monetary-related reasons while NIOSH cares a lot more about your health).

Just wondering, why would you want 98 (R+M)/2 for your S? I assume you would only add it up to 93 or 95 or so. I have zero issues at 93. Also other VOA's should also be effective in increasing resistance to knock, such as benzenes, MTBE, etc, though toluene and xylene are probably the most available at hardware stores. VOA's are already used as sparingly as possible by refiners due to their potent toxicity, as I said, so use at your own risk.

When looking at that chart, please bear in mind that gasoline isn't the layman's term for the chemical known as octane. Gasoline contains octane, but it also contains many, many other compounds, with no single compound being the main constituent. So looking at a chart that says "octane" and lists chemical properties can be misleading if you think that those properties equal the properties of gasoline.

And finally, as a personal pet peeve, why do some insist on calling 2,2,4-trimethylpentane "octane"? It's not octane; it's an isomer. Grrrrrrrr.

[beemercer]

yeah toulene and xylene are the common pick becuase you can get them very easily...

I'd personally never do it, once you get headers you'll have a 0* timing retard (with a JHM tune, not sure if other tunes are more aggressive with timing) on all cylinders all the way through the powerband on 93 so its kinda pointless for me having headers

I just wish I could get the sunoco 94, the 4.2s seem to love sunoco 94 based on logs I've seen (full piggie cars with a 0*-3* retard sweep in moderate temps)

[B6JoeS4]

What do you guys think of just a gallon of Toluene/Xylene in the gas? Either mixed with 14 gallons of 93 would give you an octane of roughly 94. I might play around with different combos next spring and get some logs of 91, 93, 94, 95.....etc.

[beemercer]

just be careful mixing it, mix it outside of the car in a well ventilated area with proper PPE... and don't use too much of it I don't think it lubricates at all. I'm not sure it'll be as good as the ethanol free shell 94 (or is it sunoco thats ethanol free? have to ask sakimano) at a 94 octane toulene/gas mixture.

[beemercer]

here's a cool list for ethanold free gas:
http://pure-gas.org/index.jsp?stateprov=IL

[marshall834]

yeah toulene and xylene are the common pick becuase you can get them very easily...

I'd personally never do it, once you get headers you'll have a 0* timing retard (with a JHM tune, not sure if other tunes are more aggressive with timing) on all cylinders all the way through the powerband on 93 so its kinda pointless for me having headers

I just wish I could get the sunoco 94, the 4.2s seem to love sunoco 94 based on logs I've seen (full piggie cars with a 0*-3* retard sweep in moderate temps)

Not well versed in this, looking to learn more - What do you mean there's a 0 timing retard? What is that in comparison to a stock S4? What are the beneifts? Thanks...

Also, I'll stick with the 91 tune for now - this thread has exploded into a wealth of knowledge Probably won't ever mix anything in, just not that interested I guess!

[B6JoeS4]

quoted from the most reliable source of info - wikipedia:

"Timing advance" refers to the number of degrees before top dead center (BTDC) that the spark will ignite the air-fuel mixture in the combustion chamber during the compression stroke. Retarded timing can be defined as; changing the timing so that fuel ignition happens later than the manufacturer's specified time. For example, if the timing specified by the manufacturer was set at 12 degrees BTDC initially and adjusted to 11 degrees BTDC, it would be referred to as retarded. In a classic ignition system with breaker points, the basic timing can be set statically using a test light or dynamically using the timing marks and a timing light.

Timing advance is required because it takes time to burn the air-fuel mixture. Igniting the mixture before the piston reaches TDC will allow the mixture to fully burn soon after the piston reaches TDC. If the air-fuel mixture is ignited at the correct time, maximum pressure in the cylinder will occur sometime after the piston reaches TDC allowing the ignited mixture to push the piston down the cylinder with the greatest force. Ideally, the time at which the mixture should be fully burnt is about 20 degrees ATDC. This will utilize the engine's power producing potential. If the ignition spark occurs at a position that is too advanced relative to piston position, the rapidly expanding air-fuel mixture can actually push against the piston still moving up, causing knocking (pinging) and possible engine damage. If the spark occurs too retarded relative to the piston position, maximum cylinder pressure will occur after the piston is already traveling too far down the cylinder. This results in lost power, high emissions, and unburned fuel.

The ignition timing will need to become increasingly advanced (relative to TDC) as the engine speed increases so that the air-fuel mixture has the correct amount of time to fully burn. As the engine speed increases, the time available to burn the mixture decreases but the burning itself proceeds at the same speed, it needs to be started increasingly earlier to complete in time. Poor volumetric efficiency at lower engine speeds also requires increased advancement of ignition timing. The correct timing advance for a given engine speed will allow for maximum cylinder pressure to be achieved at the correct crankshaft angular position. When setting the timing for an automobile engine, the factory timing setting can usually be found on a sticker in the engine bay.

The ignition timing is also dependent on the load of the engine with more load (larger throttle opening) requiring less advance (the mixture burns faster). Also it is dependent on the temperature of the engine with lower temperature allowing for more advance. The speed with which the mixture burns depends also on the octane rating of the fuel and on the air-fuel ratio.