Piston Slap: Mixing Masala Edition

Saad writes:

Mr. Mehta, how do you measure the octane rating of fuel? I have a 2008 base-model Honda Civic, with the i-VTEC 1.8L 4-cyl. It is the India-Pakistan-spec Honda Civic and is similar to the one in the US. Although it does not require premium fuel, it is recommended and I’m worried we might not find good quality petrol in the rural countryside.

Where we are going, the only signs of civilization are bombed ruins from a war in ’71. And I am weary of regular already. In the Pakistan summers, it gets really hot over here (being a Desi yourself, surely you must know, and you’re in Texas!). If regular is used while the air conditioning is on the engine timing retards terribly and it sounds as if the pistons are colliding with the valves at nearly every sudden throttle tip-in.

We have used Octane Boosters before when premium was not available. We did notice a slight difference when we used octane booster (God, I’ll have to purchase another STP product), but that could be a placebo effect. If Octane Booster raises the octane of non-premium fuel (x) by (x+1), and if premium in the city has an octane rating of (y), how will I know when (x+1=y)? And are they harmful to the engine?

I’d also like to take a small sample of fuel from the pump and somehow measure its propensity to resist knock. If it is a high rating that’s roughly equal to the rating of premium fuel in the city, we’ll use it. Is there a way to do so quickly and easily? Or will I have to build an Inflat-a-Lab to bring along with us?

Sajeev responds:

Namaste!

A US-spec Civic needs regular 87-octane fuel, which means nothing in Pakistan. The USA uses PON octane ratings, other countries use RON or MON. As far as I am concerned, these might as well be called Amar, Akbar, Anthony. And if 1970s Bollywood references don’t work for you, this website will do the trick.

The first thing to do: find out what octane rating is used in Pakistan. (In this, Google is not my friend.) Then ask the questions (presented here) to the people in charge of distributing gasoline to the country, to get a rough gauge of the octane differential between urban and rural filling stations.

From there, look at the “premium” octane rating you normally use in the city and ask what octane is sold elsewhere in the country. You can quickly find the octane deficit (y-x=?) and compensate with bottles of octane booster. Sadly, I suspect you will need a crate of octane booster to keep your Civic’s knock sensor from working overtime.

If you hear anything more than a light tapping, get your foot off the throttle and only use the bare minimum. Also, as you almost suggest, limit the use of the air conditioning (e-mail me for Piston Slap liability release forms).

I mention these more elementary “solutions” simply because I don’t know of a quick, simple way to test gasoline’s octane ratings on the fly. The best you can do is

And if possible, please tell us when you will be making this trip, so we can purchase stock in the Octane Boosting manufacturer you’ll be favoring with your custom. Best of luck!

[Please send your technical queries to sajeev.mehta@thetruthaboutcars.com]