Fuel for Civic VX
 

The question is mostly for VX owner, but in same time to everyone.

I do run Supreme fuel in my VX since I own it (91-92 octane). Where I live, there are lost of hill to climb and since I don't want to downshift, I put supreme fuel so the car run better (especially at low rpm because VX does run often below 2000rpm). Also, since I'm crussing 60mph (100km/h) on highway, I'm telling myself that I have a better FE with supreme fuel.

I would like to have your thoughts on this.

This might not be a great idea for two reasons:

1) Premium costs more - sometimes much more than regular 87 octane. Kind of defeats the purpose of buying a car that gets good fuel economy.

2) Higher octane fuel is more difficult to ignite than regular gas and it is formulated to be more uniform - it contains fewer volatile components that burn at lower temperatures. High performance engines run hotter than econoboxes so it is more critical for the high output engines burn gasoline that won't pre-ignite or detonate. So, if you decide to drive your VX like someone delivering pizzas in 10 minutes or less, you might need premium. If you drive like your grandma (that's my driving style) you don't get any benefit from premium at all. That's the short answer.

My VX's have not run on anything but 87 octane except when my current VX's engine was overheating due to a clogged radiator. I put in mid grade 89 octane just in case the engine was reaching the point of irregular combustion with the 87. I did not need to use 89 octane for more than one tank full and only as a precaution - I replaced that radiator quickly! No blown head gaskets for me thanks.

Sold, no more SUPREME in the VX, I wonder if my MPG will suffer, don't really think, will tell, but since I don't plan to use my car for the next week, will wait.

whats the compression of the vx motor again? you understand what higher octane does right?

EDIT: nevermind I am glad you understand now. :)

Not 100%, its give a better detonation, and ?

D15Z1 (VX) 9.3 to 1.

D16Z6 (EX) 9.2 to 1.

Both are VTEC. Not high compression as you can see.

the compression is my point. it does not make the higher octane fuels volatile enough to make the best use of higher octane fuel. jadziasman gave the perfect explanation before i responded

only motors with higher compression (or forced induction) can really make the best use of a higheroctane.

My arguments (that I gave to myself...) was that when I was accelering at 1700-1800 rpm to climb a hill, it was better for the motor with high otcane fuel, and I thought I had a greater MPG to, but I never REALLY do any test. By swithing to 87 octane, I will see if the last arguments stand or not, I doubt it tho. Thanks for the fast reply.

I plan on running a tankful of Shell Premium thru my VX. I've read that it contains 10% more of chemicals to clean the engine. After that, it's back to the cheap stuff.

For what it's worth, I'm in the middle of a very informal "experiment" on that at this very moment. If you glean any useful data please consider sharing it! :)

Rick

Nah, I'm getting 47-52 mpg on the cheapest gas available for my vx.
Gary

Just put a bottle of techroline every few months. It's about 2.50 bottle at costco. It'll be like getting chevron gas (and I use the mom/pop brand gas).
Gary

I remember by old 240k miles VX motor hated to have 87 octane in it. To make it not ping I would always have to shift sooner when trying to keep the RPMs low, or I would just run mid-grade.

After I installed the 120k mile motor, it loves the cheap gas. It runs better on the cheap stuff than the old one ever did on the more expensive gas. (Both motors had a full tune-up done on them...I'm guessing the old one had a lot of carbon buildup?)

very likely it probably also had a bunch of goop in the intake manifold from all those miles. i bet the pcv valve started letting a little too much through into the intake manifold...

A mechanic whose opinion I respect said that high octane fuel will make your car burn cleaner (less polluting) but have worse FE. This is what we see with Hybrids. They get okay FE, but could do better if they weren't sooo much cleaner burning than conventional cars. Soo... not sure that it will yield you better FE, but it is better for the environment. Mean how that works, eh? heh

that is not always true. actually its definitely not true for my civic.

I should test it sometime with mine. Does yours get the same or better FE with high octane?

Wait, your Civic Si? I wonder if the sporty nature of your car has anything to do with it. Most sports cars can only use high octane gas. And the Si is a pretty sporty car. Well, that could be the reason, I dunno. My point is, your car prolly isn't going to be representative of non-sporty cars using high octane gas.

Our cars weren't built for higher octane, stock combustion would be off...if anything I would say it would hurt mileage and possible emissions (slower burning fuel doesn't combust completely without timing changes and such).

the si has a 10.2:1 compression ratio. its a tad higher than the 90s d series comrades. being sporty doesnt have much to do with it, unless a higher compression ratio is sporty :)