Premium vs Regular

Hi!

Before you think this is another "pro using Regular" thread don't worry this isn't one. Instead I want to explain in a simple common man words why you should be using PREMIUM in the MDX or in fact in any High Compression Engine included the new Honda engines that only "Recommend" using Premium but does "Not Require it".

WARNING: If you don't like to Read then this is not for You.. But if you take your time to read through all this word fest you might learn something new and save money in the end. I had some free time and wanted to explain this in detail and in an easy to understand manner.



First the Basics:

What is Premium Gas? Premium is just a fancy way to call a high octane gasoline this means that premium is a gasoline with +91 octane.

What is Octane Rating? The Octane rating states how difficult it is to ignite the gasoline but you may think why would you need a Gasoline that is hard to ignite? Well this has to do with Compression.

What is Compression? Compression is when the Air and Fuel mixture is compressed in the combustion chamber this is calculated by the Stoichiometric ex: 11:1, 12:1, 13:1, 14:1 which means that the mixture of air and fuel is compressed a lot, This is referred as High Compression. Gasoline stoichiometric ratings for compression stop at 15:1 this is because only Gasolines with Higher Octane ratings (+100 Octane) can handle such compression. Since those gasolines aren't mainstream made engines use the most out of 91 and 93 octane which has a maximum stoichiometric of 14.5:1
These numbers refers to the amount of air vs gasoline that enters the combustion chamber, Having very little gasoline per air volume creates a Lean Mixture which in turns creates a LOT of heat.

The advanced stuff:

Honda Engines.
Honda since the very beginning is trying to make the most out of the displacement of the engines they make, by making high compression engines they can take the most out of the Combustion Stroke without using as much fuel. This is why most if not all their engine are High Compression Engines.

What about Regular?
Regular gasoline has an octane rating of 87 which means it can pre-ignite faster than Premium. Now that you know that High Compression engines run hotter this means that Regular fuel can pre-Ignite before the compression stroke ends.

What happens when the engine pre-Ignites?
Knocking, Ping or Detonation they are all results of pre-Ignite. What happens is that the engine is turning clockwise, the compression stroke builds up and when ignition occurs the piston is pushed downwards to keep the crankshaft turning clockwise. If Regular fuels pre-Ignites before the compression stroke can end it will fire up then the Piston is moving Upwards which then will be pushed Downwards causing the crankshaft to force it to turn counter-clockwise. This will cause SEVERE Damage to the Piston Rod which is pushing the piston upwards.

How come my Honda Engine can run Regular then if its High Compression Engine?
Since the dawn of Computer Controlled Ignition (PGM-FI) the ECU (Car computer) can control when to fire the spark plug, how much gasoline enters a combustion chamber and know when the engine is going to pre-Ignite. What the ECU will do in this scenario is simply put retard Ignition thus Timing.

What is Retard Timing?
Timing is referred to the exact moment the valves closes to start the compression & ignition stroke, the ECU can use the spark plug and timing (i-VTEC) to reduce the combustion chamber HEAT this is done by opening the exhaust valves sooner during the ignition stroke and by igniting the spark plug as late as possible (VTEC) so part of the combustion can exhaust sooner.

What are then the consequences of Retard Timing?
An Engine with Late Timing has more wear on the exhaust valves since its letting hotter combustion gasses pass through. This allows the combustion chamber to run cooler in order to prevent Regular gas from self-igniting but it also mean the Power Stroke is losing force thus the engine runs weaker and less efficient.

So why am I using Regular in a Honda Engine?
You might think you are "Saving Money" at the pump but in reality you have more wear and less MPGs using a Gasoline that technically is not made for High Compression Engines.

Why Honda then is Pushing "Not Required" in the 3rd Gen?
Simply put because of Demand and Supply.. People want to save money so if you are cross-shopping 2 cars and one demands premium and the other not then you have a higher chance of losing a sale.

What Honda did to make it able to run Regular on the 3rd Gen?
Honda engines can run Regular because the ECU can pull timing in order to run less efficient but safe. At this point you might be thinking Perhaps my 3rd gen MDX does not have a High Compression Engine! and you are wrong.. the J35Y5 has a compression of 11.5:1 making it a High Compression Engine.
This means it DOES require Premium because Regular is not meant to be used in such environment's. This means that every time you fill up with regular your engine is running less efficient and with less power than what Honda states.

But.. The car feels fine running Regular?
Of course it does silly we already made clear that the car can Pull Timing in order to run Regular!

But but.. People say I can run Regular if I don't WOT the car or Tow or Push the Car?
This is true again because the ECU will pull Timing so it doesn't really matter if you WOT (Wide Open Throttle = Floor It).

But but but.. People say that at lower RPMs Regular and Premium does not make a difference, it only matters at High RPM?
This is not only silly but completely untrue, The Engine was designed to run optimally with Premium in Mind this is becase again this is a High Compression engine they need to make out the most of the displacement and order to do that it needs Premium.

When the engine is running the ECU is trying to run the maximum compression it can, this is how the engine gets those lovely MPGs. So when you floor it the engine starts to hit an Air Volume Wall (Low RPMS) this is where VTEC kicks in, It makes the Intake Valves open longer and thus adding more Volume of Air which also needs more fuel to compensate and get that High Compression that makes all the power.. This means Compression ALWAYS STAYS HIGH! there is nothing like ohh yes when I am not flooring it, Regular is totally fine! again the engine runs LEAN as much as it cans because this is how you get MPGs. No one wants an engine using loads of fuel.

So if my Honda Engine is always trying to lean out to save fuel? What happens if I am Using Regular at low RPMS?
It happens the same as all the power band, the ECU will pull the timing like it or not. Lean = Hot = pre-Ignition Condition. So unless you make the engine try not to give the best MPGs there is no possible way to make the engine run efficient with Regular.

But if the ECU is preventing Knocking then its safe to use Regular Right?
But it is not normal to try to run the car in a less efficient way to save money. Just look it at this way.. If the engine needs 10oz of fuel for 1HP it means that using Regular the engine do 0.5HP for 10oz of fuel.. You are losing power which means you need more gas to move the car.. Honda states that the engine makes 290HP for the J35Y5 that is using PREMIUM! at low speed you might not feel the difference since the engine makes those 290HP at 6200RPM at normal Daily Driving RPM speeds its making way way less than that. So if the engine already has a low output using the gasoline it needs then using regular is making even LESS.

This requires to compensate by giving it more gas to do the same thing it can make with less gas. In the end you are NOT SAVING MONEY by using Regular on a High Compression Engine. Running Premium makes the engine run at its optimum performance giving you the HP you paid for, Making it last longer too.


This is the bottom line.. Its not what you THINK it is or how you THINK it works because nothing bad has happened..
This is Physics, Thermodynamics and Basic Mechanics..
High Compression NEEDS Higher Octane Fuel.
Unless Honda starts making engines with a sub 10.0:1 compression ratio then Regular is not the fuel you should be running on your +50,000 Dollar CUV.

This is why Low Compression Engines do not benefit from Higher Octane Fuel, They wont make enough heat to ignite Premium efficiently and thus might be ran less efficient running Premium than Regular a Good example is the HEMI 5.7L that states NOT TO USE PREMIUM BECAUSE IT WILL LOSE POWER.

PLEASE Do not said you are getting more MPGs out of Regular on a High Compression Engine this is Physically Impossible. You can run Regular on the car because ECUs are that smart and avoid a catastrophic failure but in no way shape or form a 11.5:1 Engine was made to be ran on Regular... Any engine that has that high of compression is pulling timing running Regular on daily basis.