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Old 06-25-2012, 11:07 PM   #1
bkone
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Default 93 octane and JDM engines?

I've done a FULL JDM STI Ver 3 (BONE STOCK)swap and plan on using vehicle for daily driver(no racing, no beating, just a fun ride to use for commute).....Now, I've read in Japan that higher octane fuel is used. Obviously all I can obtain here in central FL is 93 Octane. Car runs great.....no obvious detonation under a load, so I'm assuming 93 is ok on it's own. I've also read some bad things about octane booster and don't want to go that route. Am I going to be ok running 93 for the life of the engine?
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Old 06-25-2012, 11:15 PM   #2
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I dont think the older engines were tuned to be as high strung as the newer motors. I think you will be OK, just keep an eye out for knock and go easy on the boost.
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Old 06-26-2012, 12:16 AM   #3
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after living in florida from 1985 - 2011

i would use shell 93 or exxon 93 only.....and Hess 93 as a back up and I dont think you will have any issues

BP was very hit or miss and the rest just werent as good as the shell or exxon
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Old 06-26-2012, 07:17 AM   #4
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I did some research about octane in Japan, posted results and evidence in the EJ207 owner's thread.
Search that tread with my username and you'll find your answer. 93 AKI (US) should be as good as JDM premium.
Like the Uncle posted, the quality varies from one supplier to another, but JDM premium being 100 AKI is an urban legend.
And a very profitable one....
Mind you, they sell 100 AKI in Japan, so do we in US in a CAM 2 100 unleaded, available where racing fuel is sold.
But they call that "Superplus" in Japan and Subaru does not indicate that in the Owner's Manual for Japan. They only indicate to fuel premium, that's it.
The disclaimer is that the Owner's manual is for V7-V9, I have not read the one for V3.
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Old 06-26-2012, 10:08 AM   #5
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^^Vlad, Im thinking that Japan works on RON numbers AFAIK (as opposed to quoting AKI figures). So I've been told by used car dealers who frequent there to import cars to our region.

So JDM 98 RON is equivalent to a USDM 93-94 AKI generally speaking (loose approximation of course).

Similarly, USDM 91 "octane" (i.e. R+M/2), is around a 95-96 RON (ask me how I know - seriously. One of my old jobs involved gasoline testing/blending - for export etc)

So it's quite possible the USDM 93 AKI should work fine.

Last edited by Omega_2nr; 06-26-2012 at 10:27 AM.
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Old 06-26-2012, 10:48 AM   #6
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Yes, you are right.

The first obstacle was that if you look at photos of a Japanese gas station, no number is displayed, octane-wise. They sell by names.
We sell by name and octane rating.
So, I found a white paper from Shell I think, that rated the premium (hi-octane) name against a JIS.
Then I found a copy of the JIS in english and looked like the JIS was actually RON.
Here's what Shell says:


"High-octane gasoline is gasoline is highly effective compared to regular gasoline has a higher octane rating, that reduce the abnormal combustion inside the engine knocking. JIS standard, the octane number of high-octane gasoline is 96.0 or more, the octane number of regular gasoline is defined as more than 89.0. In addition, the high-octane petrol is characterized by a variety of companies, to performance. (Shell Pura) can drop the additive (carbon) in the dirt inside the engine, to prevent adhesion, to keep clean the engine is being used is characterized by Shell Pura."



Then I looked up RON against AKI, without knowing the MON number and indeed the best case scenario would be 93 or 94.

A "not so stellar" case would be 93 AKI is quite equal to 96 JDM RON, because other countries 96RON, as listed in Wikipedia, equate to 92 US AKI.

CN:

93AKI < JDM premium hi-octane = 94 AKI possible but not likely

93AKI = JDM premium possible and likely with a quality US supplier
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Old 06-26-2012, 11:12 AM   #7
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IF you look at the JDM stock maps I would be inclined to believe its higher than 93, the stock maps never dip below 30 degrees of timing. Basically don't try and run a stock v7-v9 ECU on 93, it will be right on the edge. A friend mixed up some 94 oct using 100 and 91 and he was getting knock on the high end with a stock v8 ecu.

98 JDM gas would be close to 94-95 here.

93 US is close but when they add in all the ethanol to reduce CO it looses knock resistance, specifically in the summer.
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Old 06-26-2012, 11:51 AM   #8
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1. If you're going to state that the factory ran too much timing, you have to base it something other than "a friend mixed up".
FYI, I am running a V9 ECU and have used the timing map unchanged, while my mods were close to stock, it does not knock.
2. Have you seen the JDM map (for the JDM high grade fuel) for the EJ257 A line? You cannot compare timing maps between EJ207 and EJ257.
The timing map is engine-specific.
3. If you're going to make a statement about octane, base it on something (as in a link to a document, that you can post) don't repeat what you've read someplace.
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Old 06-26-2012, 01:15 PM   #9
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1: we used the volumetric mixing rule to achieve 94 oct by adding 100 oct and filling the balance of 91.

I live in AZ, home of the ****tiest gas on earth and it was 100F. NY/east coast is known to have much better fuel so it does not surprise me you can get away with it.

2: no I have not seen the A-Line map, I was talking about the stock JDM 2.0L maps that run close to 42 deg of timing at redline. And the timing is more dictated by the turbo than the engine specific STI motor since they all have very similar cams.

3: Japanese gas must contain less than 3% ethanol(http://petrofed.winwinhosting.net/up...ota_sII%20.pdf), US gas must contain at least 6%(EPA) but as much as 10%. Ethanol drops the knock resistance unless you run a slightly richer mixture. Places that are hot add more ETOH for better summer emissions so in the summer AZ gas gets way worse while NY gas may stay basically the same.

I am not repeating things I have heard, these are my observations while tuning JDM motors to run on crappy 91 in summer heat. We use mainly E85 for power down here because the gas is so inconsistent and bad, even worse than cali 91! I have the same motor as you running speed density e85 and 22psi, If I was you I would watch my fine learning knock to make sure the car is always happy if you frequently spin out past 6500 rpm. Since all the knock we were seeing was around 7k on the way to 8K

Last edited by lukeskywrx; 06-26-2012 at 01:26 PM.
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Old 06-26-2012, 11:19 PM   #10
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Your friend's mix is not representative of 93 Fuel sold at the pump (in NY at least). I think we agree here.

It's a good advice for anyone to keep an eye on IAM and knock correction, with stock timing. I do this all the time and this is how I know it did not knock.
Of course everbody should check for themselvs and watch the parameters closely.
Eventually, if all the people that run 93 in an EJ207 put together the info, conclusions will emerge.

The article you found is a good find and I found interesting to read in it, just like I read in the JIS, that the premium is only mandated to be 96 RON, not 98.
This means that misc petrol companies have the option to sell 96RON under the premium/high octane designation and Subaru owners will fuel that, per the owner's manual.
The pump will not be marked "96RON", the pump will be marked "premium".
You can bet Subaru engineers know that as well...
You always engineer for the worst case scenario, in this case...96RON.

As far as timing:
It is influenced by a lot of things, among which cams and compression ratio, different for the EJ207. It is engine-specific.

The other thing is that when you look at the factory's timing map and you think that the timing is too advanced, you have to compare with something else that the factory gave you, which is "correctly advanced".

The EJ257, for example, does not run as much timing as the EJ207, stock. People see the 257 timing table for US and start to think that the 207 has "too much" timing, stock.

But timing is engine specific and Subaru determined that for Japan, with Japanese fuel, the EJ257 (found in the Sti A-line in Japan) gets the same base timing as it gets for USDM.

So Subaru does not think that the EJ257 can run as much base timing in Japan as the EJ207, with Japanese premium fuel.
At the same time, the 257 runs the same base timing for US....

It is true however, that the knock compensation timing is higher in the table values for the JDM EJ257.
So the total timing does have the potential to be more for the JDM.
I attribute this to the requirement that the 257 run and be warrantied in US, in both places like NY and in places like AZ where the fuel is the way you describe it.
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Old 06-26-2012, 11:31 PM   #11
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Do you know if the Suby A-line in japan has the same heads as in the US? The larger pistons have less detonation resistance than the 2.0L pistons and AVCS makes a big differences as to the timing differences between the USDM/JDM 2.5L and 205 vs 207. that would say the the 2.5L is more prone to knock regardless of octane than the 2.0L.

Then again its hard to convince someone to let me use their motor to find the knock threshold on 91 oct so it might be higher than I am willing to risk on a friends car. :-)

The v9 we were working on only showed feedback knock under power at high RPM, fine learning was always 0 and IAM was always 16.

Last edited by lukeskywrx; 06-26-2012 at 11:36 PM.
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Old 06-27-2012, 07:33 AM   #12
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It is because the larger pistons have less knock resistance and other things, that timing is engine-dependent.
The 257 can run less timing, because of this and other things, conversely the 207 can run more timing and should not be judged by 257 standards.

Seeing high timing values in the 207 table only means that this is what Subaru determined for this engine, it should not be read as high or low timing, it's what they think works.
The factory can afford to blow up engines and rebuild them during testing as much as they need. They probably have teams of people that are paid 8 hours a day, to run simulations, dyno time, field conditions, etc.
I'm trying to learn from what the factory is doing, not to dismiss their work.

The A line has the same EJ257 internal dimensions, BTW AVCS is unchanged in table between USDM and JDM, for the 257, at least on the intake side. But I think exhaust too.

It could very well be that an engine has good knock resistance on 93 and bad on 91.
Which does not mean that your research to determine what you should run on 91 fuel, is not important.
I just don't think you can extrapolate back and forth between what an engine does on 91 and what it does on 93.

The feedback at high RPM should be looked up against the MAF maxing out in the high cells.
Once I went to a large MAF I had to change a bunch of things, but I'm running a medium size turbo and other things.

Last edited by Vlad; 06-27-2012 at 07:45 AM.
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Old 06-27-2012, 11:24 AM   #13
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I understand why the 207 has the timing values it does, how else do you make a low compression motor efficient, I am an engineer in the real world. To build the base timing maps the factory engineers monitor the actual cylinder pressure created inside the engine as they increase timing.

I was more interested in the JDM vs USDM 2.5L engine having the same base timing map with having good japan gas and having to accomodate bad US 91 as well. There is either an amazing amount of timing being pulled through the learning process on the US car when running 91 (true in AZ), or the 2.5l is so knock prone even the JDM motor cannot push more timing with better gas.

Very interesting, and we are in total agreement. You cannot compare a 205 to a 207 timing map. The 207 has such high timing on the top end because the stock turbo falls off to ~12-14 psi by then, so you have to make up the loss in boost with timing to keep the cylinder pressures up.

What turbo are you running on your spec-C? If you get tired of the MAF the OS speed density rom runs the 207 amazingly well, much smoother than maf.


Quote:
Originally Posted by Vlad View Post
It is because the larger pistons have less knock resistance and other things, that timing is engine-dependent.
The 257 can run less timing, because of this and other things, conversely the 207 can run more timing and should not be judged by 257 standards.

Seeing high timing values in the 207 table only means that this is what Subaru determined for this engine, it should not be read as high or low timing, it's what they think works.
The factory can afford to blow up engines and rebuild them during testing as much as they need. They probably have teams of people that are paid 8 hours a day, to run simulations, dyno time, field conditions, etc.
I'm trying to learn from what the factory is doing, not to dismiss their work.

The A line has the same EJ257 internal dimensions, BTW AVCS is unchanged in table between USDM and JDM, for the 257, at least on the intake side. But I think exhaust too.

It could very well be that an engine has good knock resistance on 93 and bad on 91.
Which does not mean that your research to determine what you should run on 91 fuel, is not important.
I just don't think you can extrapolate back and forth between what an engine does on 91 and what it does on 93.

The feedback at high RPM should be looked up against the MAF maxing out in the high cells.
Once I went to a large MAF I had to change a bunch of things, but I'm running a medium size turbo and other things.
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Old 06-27-2012, 02:35 PM   #14
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I run an EVOIII 16g twinscroll, The CHRA is FP.

The A-line is currently sold in Japan, it's automatic, you can find the ROM on the net, to run it you need to install updates to Romraider.

I checked the bore, stroke, displacement, etc, to determine if it's a 255 or a 257. It's a 257. They advertise it as an EJ25.

About the SD, I have my ECU completely wired into the engine, including the Manifold Temp sensor.
I think that the Spec C ECU is hardware-wired to switch temp sensors internally, when the Group N conditions are met.

Anyway, we are deviating from the initial setting of this thread. Hopefully this added value anyway.

Last edited by Vlad; 06-27-2012 at 05:58 PM.
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Old 07-01-2012, 12:55 AM   #15
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If I swapped in a Version 6 STI into my 99 RS would I need to run 93? Where Im at I can only get 91 for now and 100LL Avgas for like $8.00 a gallon. After reading this whole thread I still dont know. BTW Im in northern Canada.
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Old 07-01-2012, 08:07 PM   #16
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Quote:
Originally Posted by flyboynextdoor View Post
If I swapped in a Version 6 STI into my 99 RS would I need to run 93? Where Im at I can only get 91 for now and 100LL Avgas for like $8.00 a gallon. After reading this whole thread I still dont know. BTW Im in northern Canada.
i would look at getting it tuned and/or using a later tuneable ecu with it

av gas has a LOT of lead in it....even the 100LL....it wouldnt be good for the plugs or the o2 sensors
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Old 07-10-2012, 01:35 AM   #17
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Like Uncle Scotty said, a tune would be ideal to make sure you are not knocking or anything like that. Now here is my story, so take it with a grain of salt.

Living in Utah we get 91 octane and on my first EJ20G swap I would mix 100 octane DOT fuel with my 91 to create something around 94-95 octane. After the honeymoon phase of my swap wore off, I just started to fill it with 91 pump, and never had an issue. On all my swaps after that it was 91 only, and never once had a problem, even had a torn inlet tube once and was running really lean(car was insanely quick though) and while im sure I was knocking a bit, my turboXS knock light was not picking up anything too bad. Use your best judgement though and always get the best fuel you can afford.

Now my professional opinion is to run 93 or above, or get the car tuned for 91 of course

Thanks,
Rick
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Old 07-10-2012, 07:29 AM   #18
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Thanks for the story, Rick.
In time, if enough people log their JDM swaps, maybe we will be able to turn the tide and bring the truth about JDM fuel to light.
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Old 07-10-2012, 11:12 AM   #19
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Here is a log from a stock V9 engine running on 91 with a bit of 100oct in Arizona so about the worst gas in the country. The car is happy and running full IAM of 16 but it is getting some feedback knock at 6K and above. The car never showed any fine learning, (fine learning stops before 6K) but it would knock again and again at this RPM range. It does not need much timing pulled to make it safe but I would not want my car running like this. For how rich the stock map is 93 oct should be OK but if you want to push harder or you get really bad summer gas like we do just watch out.

After researching it and discussing it with Vlad and others I would agree JDM gas is likely equivalent to USDM 93-94, however they do not add as much ethanol as we do and their gas formula is not as seasonal as it is in the hotter parts of the US. If you are running less than 93oct I would suggest pulling a degree or 2 of timing up top for peace of mind.


Last edited by lukeskywrx; 07-10-2012 at 11:18 AM.
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Old 07-12-2012, 06:49 AM   #20
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thats nice post bor.
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Old 05-15-2014, 10:49 AM   #21
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Interesting posts here guys! - So I just swapped in a JDM V7 ej205 into my wrx... using avcs and JDM ECU.... was concerned about potential knocking.... are you saying that if I run shell or exxon 93 i should def be free of knock at least until 6k rpm?.... the swap completely emptied my funds and no money for piggy backing and havent even found a shop that fu%ks around tuning JDM Ecus... whattaya say boys?
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