The ‘what octane? - what gas?’ questions will of course go on for as long as we burn gasoline. This thread is not an attempt to start another one of those threads. I am also not going to attempt to deep dive into engineering terminology and more. I simply want to share a little about my experience and share fairly accurate data I have accumulated.

Car: 2018 EX CVT, using Sport Mode and Paddle Shift. Mileage is around 75,000 miles.

Modifications: No performance Mods

Future Mods: Changing to K&N Filter from a Wix that has maybe 10,000 miles.

Controlling what octane is used: I am attempting to fill up when I need about 9 gallons of gas. So…. It’s not perfect, but now you know.

Data gathering: iPhone on video, pointed at a ScanGauge2, then review video later.

Acceleration method: Pedal to the floor

Location: A safe place. Also, flooring a Fit in 2nd gear isn’t going to wake the neighborhood.

The primary reason using an octane rating is talked about is because it is the method used to explain at what point gasoline detonates when heat and pressure are applied. Years ago, like 30+ years ago, and further back, it was common to “advance the timing” of the engine and then commit to running premium fuel. I believe 2-3 degrees was common, and just like today, increases in horsepower was debated. Usually people saying, “I think I can tell.” So, my curious side wants to know if the Fit will advance the timing 2-3 degrees when the sensors can tell there is higher octane fuel being used. I believe the “knock - detonation” sensor is critical for supporting this judgement. I’m sure MAF and Intake Temp come into play with this too.

I will edit this original post as I gather more information. Each group of numbers is data from a single acceleration. I only get a tank of fuel every 2+ weeks, so octane changes will not come in too quickly.

 

Fascinating.
Please continue gathering data.

 

Indeed fascinating. I don't know what we're talking about yet, but I will try to follow along.

Are we supposed to see the Ignition Timing column produce higher numbers with the higher octane fuel?

 

Yes, sort of, probably…. Haha.

Generally speaking, the ECM is going to take a look at the mass airflow, knock sensor, and intake air temp and try to make good decisions. There could be more to it, but generally speaking octane is going to influence it along with those other readings.

And in most cases, I believe you’re right in your question. Higher octane, more advanced, higher number.

 

Are you unhappy with the factory recommendation for fuel? In your view, is there a problem with 87 octane in the Fit?

 

No problem at all with the 87 recommendation. Just a reminder to understand Top Tier Gasoline, because that is key for cleanliness.

My interest at this time is to use the tools available to me to see if there is a difference in how the car tunes itself.

I’ll admit…. I cannot stand when people say “it was tuned for 87.” The reality is that it was tuned to run on 87, but it knows how to run on higher octane.

Thanks for asking!

 

Worth noting BMW added atomized water injection through essentially a fuel rail w/ injectors at top end to achieve similar results. Added around 50 hp; lower charge temps, EGTs, higher "octane", liquid to gas works as a spring essentially, list goes on. Would be great to add to the GDI system with a spray in manifold system. Could switch over to fuel temporarily also to clean valves over time...

 

This is amazing to hear about. I need to google into this. Maybe 15-ish years ago when I heard about water injection in modified diesels, it made me wonder if a gas engine could dose water at a certain frequency, but I never thought about dosing both in the same stroke.

 

Current short-term goals, so everyone knows where I hope to go with this:

• Gather 5-10 more pulls with this 87 octane that is in the car now.
• Drive through gas station from last tank of “premium” and see if it was 91 or 92, update table if needed.
• Next tank go to 93 octane
• The VERY tiny amount of data gathered has me curious why the timing pulls back so much around 5300rpm. I am sure I need to understand variable valve timing and where it starts to step into the equation.
• The microscopic amount of time I have with higher octane, the car did not pull timing at higher RPM.
• I want to see what differences occur with 3rd and 4th high rpm, probably merging onto the highway.

 

I think you will see some slight gains for sure. Especially since its a high compression ratio motor (11.5:1) that can utilize the higher octane. I don't think there is an octane sensor, so AF ratios would have to be read on the exhaust as well as via monitoring knock.

What will be helping you the most is its VTC or cam phase timing. It will be able to adjust valve timing on the fly. Here's an excerpt from their 2015 newsletter:

"The VTC system assists in this process by adjusting intake cam phasing to retard valve timing at lower engine speeds for better fuel efficiency and advancing timing at higher speeds to increase valve overlap for reduced pumping losses and more power."
https://hondanews.com/en-US/releases...rtrains?query=

 

Thank you for this share. I had never really thought about VTEC in terms of timing/phasing the cam lift. I have simplified in my mind that it’s more simply just switching to “big cam” instead of regular cam. The article explains, as you know, "At higher engine speeds, i-VTEC triggers more aggressive cam profiles that produce longer valve operation and greater valve lift for more horsepower. The VTC system assists in this process by adjusting intake cam phasing to retard valve timing at lower engine speeds for better fuel efficiency and advancing timing at higher speeds to increase valve overlap for reduced pumping losses and more power. “ Again, thanks!

I wish I knew more about the customization with the ScanGauge2. I am guessing it would be able to pickup on the VTEC engagement and VTC. To see VTEC as on/off, and VTC, and Ignition timing all at once would be super cool.

Edit: Adding more…. I looked at ScanGague2 xGauges and it appears I can add short term and long term fuel trims. This should allow me to see four data points at once. (RPM, Ign. Timing, Short Trim, and Long Trim) Seeing that short term trim adjustment may be super cool if I see the car pull back timing. Again, thanks for supporting my fun.
https://www.thedrive.com/cars-101/38...m-fuel-trim-be

 

Do our L15s have a "big cam?" I was under the impression that it was all computer mapping with a regular cam and no actuators?

 

Due to EPA regulations no. Cam profiles are small to minimize pollution and make your car run efficient at low rpms. V-Tech is nice as it adds a second profile that really opens up the flow of air at higher rpms. See illustration:



V-TECH

 

Yea, its actually great how much technology was implemented in these budget cars (VTECH, VTC, Direct Injection, High compression ratio, Oil squirters, etc.) . More than most vehicles at the time. Goes to show how much dedication Honda has towards its products.

Will be interesting to see what you log. Ideally you will want to mimic the same scenarios. Several dyno runs would probably be the most telling.

 

I like that image. Thanks.

I love VTEC.

 

Posting in the thread seems easier than editing the first post each time. I accidentally deleted the entire first post for a moment…. Luckily it was open on my laptop.

A lot of 87 octane data…. 93 octane coming soon, hopefully less than a week.

 

interesting study . in the 92 octane chart does that air intake temp have to do with the ambient temp at the time ? i remember reading about a test with
a Honda CRV using different octanes . it did show a slight increase in performance and mileage with the higher octane fuel , which is counter to the
general narrative that it makes no difference . at any rate the Honda's computer is doing some very clever stuff with it's ignition and fuel mapping .

 

Air intake temp is really the air intake temp. If I idle it will go well above ambient and even if balanced, it will fall quickly just by jumping on the throttle.

It does increase performance, I think most just don’t see the value in the small gain, or maybe cannot feel the gain.

More to come….

 

91 octane in the tank for this post…. I did the math based on adding 93, multiplied by the gallons added, and then added the gallons that should have been left, with those multiplied by 87. Then divided by the tank size. It worked out to 91.2. It is not scientific, but as honest as I can get.

 

I don't have them side by side, but it appears your timing hangs out closer to 20 deg. for longer than the 89 octane.