How To Know Whether The Engine Is A High Compression Or A Regular One

kasun001 · May 8, 2012

I have a Vitz 1.3 U (2010) and the compression ratio is 11.5 :1

How to know whether it has a high compression engine or a regular one?

I've only used 95-octane petrol so far. (I was told only to use super petrol by the sale I bought from)

But while reading other threads I came to know that there's no performance down in using 90-octane.

Is this true?

plz enlighten me.

Junkfriend · May 8, 2012

I know many ppl using 90 for 95 recommended cars and run without problems for Vitz Pajero Mini etc...

Komisiripala · May 8, 2012

Octane is a measurement of combustibility of the petrol. So 95 burns better than 90. Which means 95 is more efficient. But think about this a little before jumping and pumping 95 with glee.

There's no point in using a more efficiently combustible petroleum to be stuck in traffic on your daily grind. Use it for highway runs/ outstation trips, and you will get better mileage and better performance.

And all this hogwash about 95 being cleaner and better for your injectors is utter bollocks. Some cars come specified for 95 octane fuels. If not so there's no harm in 90.

America has 88 octane as regular and 91 octane as premium fuels. 95/98/100 is rare to find. Food for thought, no?

Read up on it online. The interwebs are a wonderful place for learning!

Edited May 8, 2012 by Komisiripala

kasun001 · May 8, 2012

Thanks..

but while reading on I found out that 95-octane is used in engines with high compression. So let's just assume a car is used for highway runs and then without a doubt 95-octane is better to used as you say.

But how can we determine whether it's a high compression engine or not?

What is the link between compression ratio with the above?

Pericles · May 8, 2012

On 5/8/2012 at 6:33 AM, kasun001 said:

But how can we determine whether it's a high compression engine or not?

Read the manual?

kasun001 · May 8, 2012

Yap.. All i could find was compression ratio, max power and etc. It says nothing about high compression or not-(well of course common sense leads me to believe it's a regular engine though)

But I just need do know how to separate a high compression engine with a regular one.

Can it be determined by mere cylinder capacity and compression ratio?

CARBON B4 · May 8, 2012

On 5/8/2012 at 6:33 AM, kasun001 said:

Thanks..

but while reading on I found out that 95-octane is used in engines with high compression. So let's just assume a car is used for highway runs and then without a doubt 95-octane is better to used as you say.

But how can we determine whether it's a high compression engine or not?

What is the link between compression ratio with the above?

Well.. usually high performance cars have a higher compression ratio and will need to be fed with 95 oct, by that definition I doubt the 1.3 Vitz will fall in to this category. So you should be ok with the 90 oct.

But if money is not an issue just go ahead and use 95 oct, there is nothing wrong.

Komi : If 95 gives a better/cleaner burn this means there is less impurities and residue in the fuel, so wouldnent this mean it will be better on stuff like fuel lines, injectors etc ?

kasun001 · May 8, 2012

On 5/8/2012 at 7:07 AM, CARBON B4 said:

Well.. usually high performance cars have a higher compression ratio and will need to be fed with 95 oct, by that definition I doubt the 1.3 Vitz will fall in to this category. So you should be ok with the 90 oct.

But if money is not an issue just go ahead and use 95 oct, there is nothing wrong.

Komi : If 95 gives a better/cleaner burn this means there is less impurities and residue in the fuel, so wouldnent this mean it will be better on stuff like fuel lines, injectors etc ?

thanks...

But in theory combustion of 95-octane releases more pressure than 90-octane. Therefore don't you think using 95-octane on a regular engine causes to reduce the life time of the engine?

jdnet · May 8, 2012

On 5/8/2012 at 7:07 AM, CARBON B4 said:

Komi : If 95 gives a better/cleaner burn this means there is less impurities and residue in the fuel, so wouldnent this mean it will be better on stuff like fuel lines, injectors etc ?

What does the octane level have to do with the fuel bieng clean? burning cleaner and cleaner fuel are two different things.

heavyD · May 8, 2012

On 5/8/2012 at 6:06 AM, Komisiripala said:

Octane is a measurement of combustibility of the petrol. So 95 burns better than 90. Which means 95 is more efficient. But think about this a little before jumping and pumping 95 with glee.

There's no point in using a more efficiently combustible petroleum to be stuck in traffic on your daily grind. Use it for highway runs/ outstation trips, and you will get better mileage and better performance.

But afaik there's also no point pumping a high octane petrol into an lower compression engine, no matter whether you're driving in traffic or on the highway, simply because the engine cannot get the best out of that fuel. You wont see any change in performance nor mileage.

CARBON B4 · May 8, 2012

On 5/8/2012 at 7:46 AM, kasun001 said:

But in theory combustion of 95-octane releases more pressure than 90-octane. Therefore don't you think using 95-octane on a regular engine causes to reduce the life time of the engine?

The amount of energy ( calorific value) in one ltr of 95 is more than 90, so theoretically what you say is correct but the engine is built to withstand much more than this difference, so nothing will happen to the engine internals by using 95. But lower octaine fuel could result in engine knocking which is worse.

On 5/8/2012 at 7:46 AM, jdnet said:

What does the octane level have to do with the fuel bieng clean? burning cleaner and cleaner fuel are two different things.

I know, but a fuel which burns cleaner means its more refined right ? if I am not mistaken the 95 is extracted from a greater level of refining and not only by mixing additives to the 90 ( hence the additional cost ) . So which means it should have less impurities than 95. Less impurities in the fuel means there will be less residue in the fuel system. Kind of like a triple distilled Vodka will be more smoother than normal one...

JadeyBlitzen · May 8, 2012

Dude first of all check if your engine is a 1NR-FE. only that came with 11.5 compression and it was put in JDM vitz's only after 12/2010.

here's why high octane fuel is good. you can compress it better without pre-igniton i.e. knocking. And the rule of thumb when it comes to choosing octane levels is 10*compression ratio is the limit on the amount of octane your car can appreciate. so if you got an n/a engine with 9.0:1 compression 90 octane is the best that it can appreciate. This is the principle most tuners stick to when increasing compression or boost. Anyway production engines can operate within a certain threshold of octane levels depending on its engine management. for example all corollas and other cars with the 1NZ engine run fine on 90 octane fuel even though it has a compression ratio of 10.5:1. It gives better performance when you pump 95 but doesn't complain running on 90. It only becomes a waste when you exceed the octane level the engine can appreciate. hint: indian car owners who pump 95

Then we gotta keep in mind what the manufacturer recommends with respect to what sort of fuel they have in the country its manufactured for. See in japan regular is 95 and premium is 98. So in theory you should stick to 95 here even if the catalogue says regular. But most cars run fine with the exception of GDI's. but I think that's mostly gotta do with 90 being not as refined as 95 here.

So to sum up. as with most cars the manufacturer recommends regular for your car. but considering the high compression ratio I wouldn't recommend you switching to 90 octane. Anyway this is the most economical engine toyota makes at the moment. so what's wrong with spending a little extra?