Pre-Detonation, Knocking and RON Rating

First of all, I am not thermodynamics engineer and I am not in the oil and gas industry but I read a lot online and I have seen many people posting on our Facebook Group about the usage of RON95 and RON97 and its effect on Volkswagen cars – some even compared it to Naturally Aspirated (N.A) cars they previously own.

Trying to put everything as layman as possible  so that we don’t need a degree to understand the relationship between Pre-Detonation and Ron Rating.

If you are up for it, the internet is really an awesome place to find answer, you can literally find everything online and that makes illustration and explanation so much easier.

Let’s have a look this particular illustration of how engine works;

Source : https://animagraffs.com/how-a-car-engine-works/

Take note of the process of 2/3 – This is where octane rating matters and the debate of “knocking”comes into play.

Octane rating is a measure of fuel performance; the higher number, the more compression (and heat) the fuel can take before it auto-ignite / pre-detonation, a detonation other than ignition spark. When fuel auto-ignites, it creates ping/knocking to pistons and on a long term basis will damage piston rings and in some severe cases melt pistons.

Power is produced during power stroke, the further a piston can travel in its compression stroke, the more power it produces. All these processes are controlled within ECU’s parameter; fuel-air mixture (air fuel ratio), boost and ignition timing. The higher timing means the pistons will travel further in its compression stroke but this is irrelevant because we are talking about a stock car and not a tuned car. Any turbo car with chiptuning on it will benefit from higher RON (community service reminder that chiptuning will void your warranty blah blah blah…. ).

Ok before I get carried away, so what does all these means?

  1. Higher Ron rating lowers chances of pre-detonation means less chances of knocking but if you car engine is designed for lower RON, then you should not have issue;
  2. Does using higher RON means more power? Theoretically no, unless you have advanced ignition timing but we have seen dyno results of GTI running on higher RON 97 better off than a RON95;
  3. Does using higher RON means better fuel consumption? Theoretically, higher octane fuel running on engine designed for lower octane can result in incomplete combustion and worse off fuel consumption.

The million dollar question, is your Volkswagen car safe with RON 95? A stock car tuned for RON 95 usage obviously means acceptable ignition timing, proper AFR which allows spark ignition before any pre-detonation. If so, why do we hear stock cars having blown pistons?

  • Could it be a pistons design flaw or;
  • Wrong Fuel Air mixture (too lean) for our fuel and climate or;
  • Climate too hot causing too much pre-detonation for a turbo car or;
  • Maybe owners are not educated about misfiring (causing knocking) and they continue to drive causing damage to pistons.

I leave you to connect the dot but I can tell you from experience, a number of 1.4tsi on RON 95 with extensive timing retard (knocking) but runs perfectly fine after changing spark plugs and coilpacks.

I can tell you there are owners continue to push their car despite misfiring and blew their piston (stock cars).

I can tell you too that a stock 1.4tsi AFR is quite lean – possibly to get the desired fuel consumption from the numerous dyno session we used to have.

I can tell you that CAVE/CAVD engines have piston revisions but what I can’t tell you is how to spend your money. The difference in savings between 95 and 97 is quite substantial over time but more importantly, if you have misfiring symptom, please do not take it lightly.

Throttle off, pull over and take out your phone and dial 1-800-88-2389. Stay safe and happy motoring.

One thought on “Pre-Detonation, Knocking and RON Rating

  1. Greg

    For us in this country, our situation is rather unique because the different RON ratings are also tied to different blending methods, where 95 complies with Euro 2M while 97 complies with Euro 4M. If it only boiled down to differences in knock resistance then 95 is still ok, but with much less soot and other unwanted byproducts, going with 97 yields not only immediate benefits but also long term benefits where your engine will remain cleaner over a longer period of time. I highly recommend going with Euro 4M 97 for better performance and longevity.

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