Supposedly the TSX is just a larger tweaked version of the engine in the CRV. I'm assuming the CRV takes 87 Octane.

Secondly... the Acura line is big on maintaining the semblance of luxury. Much as parts for an Acura run much more than the exact same part labelled Honda... is it possible that the 91 Octane rating is part of the same scheme to lend an air of luxury to the TSX? My GF's Accord is rated for 87... is it just a matter of tuning?

Usually I pay attention to the manufacturer's rating... but on this one I'm a bit suspicious. It's an idea of evil brilliance if I'm right... MUAHAHAHAHHAHA.

 

Yes the TSX requires 91 octane. Some of that "tweaking" you refer to...is raising of the compression. The K24 in the TSX runs very high compression 10.5:1, which is why it needs the high octane. Octane is an addative which basically makes the fuel hard to ignite...so if the octane is too low in such a high compression engine..you will get pinging and knocking..which is the fuel igniting when you dont want it to.

However, supposedly if you put lower octane in the TSX ... its equiped with knock sensors which will detect this and retard the timing to compensate. This will prevent unwanted detonation ... but it will reduce the overall power output of the engine.

 

It's not just an Acura thing. The K24 engine is used in Honda Accords too. The JDM and European Honda Accords with the K24 engine require premium too, and their engines have a trifle bit less HP at 160.

I don't know what the gas requirements for the current CRV or US-style Accords with the K24 are.

 

The K24 in the US Accord has lower compression, and does not require 91 octane.

 

And it has the same specs as on the CRV.

 

Correction. The euro-spec K20, not K24 engines, are 153hp (155 ps) and require US 91 octane (or 95 RON). The Euro K24 makes 190 PS (187.5 hp) and also requires US 91 octane (or 95 RON, they rate octane differently in Europe).

I did some digging back in the day before, and found that the euro K24 had a lower compression ratio but I'm not sure what it was. There may have been some other differences also.

 

wut the hell is a compression ratio?

 

It's the ratio of: (displacement volume + clearance volume) to clearance volume. Basically, it's how much (volumetrically) the air/fuel mixture in your cylinders is compressed by the action of the piston moving from the bottom of its stroke to the top of its stroke.

 

Seems like a thread like this comes up every other week or so.

 

Sure does. We need a FAQ.....

Heck, I'd even volunteer to write it.

 

Yes!. I posted about that a long long time ago in the comments section. It would be usefull, especially for rattle info and other common problems.

 

I'm no expert on fuel, but I'll bet it's 90% appearance of "premiumness", 10% performance gain.

And yet I still use 91. Doh!

 

Yes, we need 91. Yes, we need a FAQ.

 

Its not ..read my first post above.

To take the point even further. We can bring over the RSX (integra) type-r because its compression is far too high for our gas. We need higher octane gas.

 

lol, i think you meant "can't".

Well the Toyota 2ZZ-GE (Celica GT-S engine) runs fine on US 91 octane with an 11.5:1 compression ratio. The K20 in the JDM ITR has the same 11.5:1 CR but Honda would just have to detune the engine a little bit so that it would run okay on the US "lowest common denominator" 91 octane fuel.

 

In Germany they have 100 Octane gas.

 

All octanes were not created equally.

http://www.btinternet.com/~madmole/R...RONMONPON.html

European 100 "RON" octane would be equal to US 95.8 "PON" octane. Higher overall, yes, but not as big as many believe because they are unaware of that octane levels are measured and advertised differently in different parts of the world.

On a business trip in Finland I was filling up my little Mitsubishi Charisma (US Mirage) with "92" octane which was the lowest. But it was RON octane, not PON like in the US. In PON terms, that's 88.5 which is more or less just regular and nothing special.

 

I understand... I just wonder how much of a decrease in performance you get if you use the 'wrong' octane mix, and the engine compensates for it. How much of a decrease in overall performance would you get?? 5%?? 10%??

I don't use enough gas/month to really care, but the academic argument is interesting. Here premium is about 12% more expensive that regular... does a 5% increase in performance justify a 12% increase in price??

 

Your a dummy the tsx doesent need anything more then 87 its a 4 banger!

 

 

 

Floozy strikes again. Of course, you couldn't know, you don't drive a TSX...

It is written in the manual the TSX needs 91 octane, and it's CR justifies it. I can't why some of you have such a hard time understanding this. I mean, they wouldn't make a point of writing and saying it everywhere it needs 91 if it really didn't, don't you think?

I believe I have heard that with 87 octane, the engine detunes itself to about 185hp, but don't quote me on this, I am not sure of my source.

 

Again, it's an academic discussion. I believe the manual says 91, but 87 may be used 'with reduced performance.' I am just curious to know what that is.

 

Even though the engine can compensate for the lower octane, I dont think its healthy to do that in the long run. The engine was not made to run that way.

But if you are really curious how much difference it makes, why not try it out

 

The "manual" also says ol change every 10,000 miles witch is a crock of shit to.your a moron!

 

 

And you'll be sorry in the long run...

 

It refers to decreased sexual function. There's no point spending the whole weekend waxing your car and waiting for hot sex if you're going to put low octane fuel in the tank. You won't be be up to the task when the critical moment arrives.

 

There wouldn't be any long-term harm. The only thing that will suffer is fuel mileage and performance.

 

Floozy, obviously, it's not one of your better days on A-TSX, so I think I'll just forget about you in this thread.

jcg878: What happens (takes professor ruler and chalk...), is the K24A2 is equipped with a knock sensor. This particular sensor's role is to detect detonation inside the engine, translated in an unusually loud knock on the engine block, or anything attached to the block.

I think detonation has been explained but let me just re-iterate: As the combustion chamber heats up, with every stroke of compression, the air/fuel mixture is literally compressed 10½ times it's normal atmospheric pressure (14.3 PSI). Now, imagine how easy it is to light up fuel outside with normal air temperatures. Compress this air with the fuel 10½ times, and what you have is a bomb. But added to this, compress it in a chamber that has an ambient temperature of 800°C (if I am not mistaken). How long do you think it would take to explode? It will in a flash, in fact in an engine with that sort of compression, the mixture will have a tendency to explode before the piston has reached TDC (Top Dead Center). Remember, the explosion is what gives th piston the push back down. So if the explsion occurs before the piston has reached TDC (detonation), can you imagine the forces the lower engine must withstand? Gas engines are not designed to withstand this, and they will die a lot quicker than you can imagine when it occurs.

So, in order to prevent detonation, you have a few options: You can increase the gas octane level. Octane is an additive that will make the gas a lot less prone to explode early, or detonate. This is the most obvious solution, and why we need to use 91 octane for the TSX.

Another solution, if you are not going to be able to fill up with 91, for some remote reason, is adding a knock sensor, which I just talked about. What the knock sensor will do, is once it has sensed detonation, it will send a signal to the ECU, and make it retard the ignition. This has an effect of detuning the engine a little bit, and it will have a tendency to run a little cooler (in engine dynamics, cooler is not always good, BTW, especially for emissions). The fact that the combustion chamber is cooler will help the mixture be less prone to detonate. In fact, since it is said we can use 87 octane here and then, it means the spark retard is efficient enough to make the engine run with pretty much no risk. Only, and this is where I am guessing, a cooler burn usually means an incomplete burn, and thus much higher emissions. Since our car has a good deal of emisssions control, making the engine run on 87 octane constantly would induce premature wear of parts like the o2 sensor, the catalytic converter, as well as pretty much the whole exhaust. If the problem becomes too pronounced, basically, the ECU could switch to limp mode, and you don't want that, because then your car will really run like shit.

Well. I hope it helped make things clearer, and show that 91 octane really isn't an option, it's a must.

 

It would be interesting to see if the engine, being more efficient with 91+ octane, would have an increase in fuel econmy enough to compensate for the increase in fuel costs compared to the lower octane fuel. This would have to assume a controlled course to test fuel efficiency.

87 $xx = yMPG
91 $xx + 12% = xMPG

Anyone want to test the theory?

 

But you would also have to take into account theoretical premature wear of emissions control equipment.

 

This is completely untrue. In order for the knock sensors to do their job (retarding ignition and all that good stuff), a knock has to have already happened, and by then its damage has been done.

Even if you assume that the knock sensor and your engine controller can change conditions after just one knock, you'll get that initial knock at every high peak pressure condition (every time you open the throttle fairly wide). So if you're running your 87 octane fuel over the life of the car each one of those single knocks will add up to a good amount of engine damage. The money savings that you get from buying regular gas is not worth this.

 

this thread is still going on??

 

Of course it is. And it will continue to until we get a FAQ on this site. :P

 

Thanks professor Let me ask another question then, which is probably more to the point of my original inquiry. How much of a gain in performance does an engine optimally tuned and designed for 91 have compared to the same engine optimally tuned and designed for 87?? Is it a trivial difference, or a substantial one? All I really want to know is if these luxury car brands are giving substantial gains in performance by designing their engines to use 91. I understand that it allows higher compression -> more efficiency/power, I just want to know how much. Then I'll get back to work

 

While I don't have a TSX, I can say for certain that my TL 3.2 (C32 engine, same as the Legend) gets 26 mpg on premium and 24 on unleaded, under the same driving conditions. It says premium should be used, so thats what I use. I paid for a premium car, thus I will put premium gas (which really isnt all that much more expensive). 2 dollars per tank extra really isn't going to bankrupt someone with an Acura.

Now what I don't get is how my Dad gets 32 mpg on regular in his '03 TL base...

It would be interesting to see if octane really does affect MPG as well as peak power.

 

It should be a lot more, because part of that "tuning" includes allowing a higher compression ratio on the higher octane. The compression ratio is the most basic measure of engine efficiency. The higher the better for any given configuration. The difference could be substantial, but the anti-knock difference between 87 and 91 octane isn't that great. If I had to guess, I'd say you could make the compression ratio 10% higher (i.e. from 8:1 to 8.8:1). This is just a guess, don't take it as truth or calculation. Also, it's different if you start with different compression ratios (the difference between 8:1 and 8.8:1 is much smaller than from 10:1 to 11:1 even though both are 10% increases).

Anyway, the expression for the efficiency of the Otto Cycle (a thermodynamic cycle designed to approximate a spark-ignition engine) is:

eff = 1 - (1/r)^(k-1)

where, r is compression ratio and k is the ratio of specific heats of your gas. For air k =1.4, so the exponent becomes 0.4. Try out some different compression ratios and see what effect compression ratio has on efficiency (or just try the 8 and 8.8 I mentioned earlier). It's a good comparison because this efficiency is defined as work output per fuel input. Enjoy.

 

Ah ha! So that thought process/marketing tool works!


True, so none of this discussion really matters. But isn't that part of the fun of a car forum??

 

Here is my seat of the pants test: I have, over the last weeks, tried 87, 89, and 91. From 91 to 87, I noticed a big change. The car ran fine, and I didn't seem to suffer a great loss in fuel economy. But, the engine just wasn't very responsive. When I used 89, I again did ok in fuel economy and didn't have any trouble with the engine. At highway speeds, I noticed absolutely no difference in performance. The engine seemed slightly less responsive pulling away from lights, etc.

Now, keep in mind that I'm driving around a city that is (mostly) flat and at a low altitude. Also, nearly all of my driving is in stop and go traffic.