Where I Live The Gas Is Shit, So I Have A Question On Rb25 Turbo On Rb20

[Kanaric]

Where I am we only have what you guys would call 95 octane but here is called 91. I have the opportunity to buy a RB25 turbo on the cheap but being that this car would be running untuned stock ECU, which many people do here successfully, would have only access to this octane cause problems with such a setup?

[R_34]

Which octane scale ?

RON or R+M/2 ?

On stock ECU/stock tune I've never encountered knock even at 15psi/1b with maxxed injectors and 14+ AFR right before the rev limiter.

And on the initial tuning the tuner added so much advance that the turbo was making 0.3b less boost without touching the actuator or the EBC, so the stock tune is extremely conservative.

[Kanaric]

Which octane scale ?

RON or R+M/2 ?

On stock ECU/stock tune I've never encountered knock even at 15psi/1b with maxxed injectors and 14+ AFR right before the rev limiter.

And on the initial tuning the tuner added so much advance that the turbo was making 0.3b less boost without touching the actuator or the EBC, so the stock tune is extremely conservative.

It is 91 AKI which I believe is 95 RON.

United States so we have to have weird measurements for everything.

[R_34]

Ok, i'm running 98 RON and 95RON is sufficient, you won't have problems IMHO.

So true for the imperial system, I wonder how science is teached in the US with such a unit system.

[Kanaric]

Ok, i'm running 98 RON and 95RON is sufficient, you won't have problems IMHO.

So true for the imperial system, I wonder how science is teached in the US with such a unit system.

It's been a while since i've been to college or high school, lol. I remember using metric for weight and distance measurement but temperature we usually ran Fahrenheit

[MJTru]

+1 here i still dont understand it. Kml:D:D

[Matvei27]

If you plan to tune the car and want to make power don't use 91 AKI.

You need to mix your own fuel to get a higher octane rating such as 93 AKI or above (98 RON or higher).

The simple solution is to mix Sunoco 100 AKI race gas (street legal) with 91 AKI at a 50/50 ratio to produce ~95 AKI (100+ RON).

This will get you the best results.

Let me put it this way: no point in upgrading intercooler, injectors, MAF, turbo, etc. and then cheaping out on gas.

edit: another option is E85 but depending upon where on the west coast you live this may be harder to find than Sunoco race gas (which by the way is sold all over the place, go on their website and look at the store locator).

Edited May 18, 2015 by Matvei27

[Kanaric]

If you plan to tune the car and want to make power don't use 91 AKI.

You need to mix your own fuel to get a higher octane rating such as 93 AKI or above (98 RON or higher).

The simple solution is to mix Sunoco 100 AKI race gas (street legal) with 91 AKI at a 50/50 ratio to produce ~95 AKI (100+ RON).

This will get you the best results.

Let me put it this way: no point in upgrading intercooler, injectors, MAF, turbo, etc. and then cheaping out on gas.

edit: another option is E85 but depending upon where on the west coast you live this may be harder to find than Sunoco race gas (which by the way is sold all over the place, go on their website and look at the store locator).

I used 91 aki with a Subaru WRX and made around 300whp. I don't need 93 to make power if I tune it. I will make less power, yes, than 93 octane people. However that's what I have to live with because it's just not available here.

I have to use 91 AKI this isn't "cheaping out", lol. There isn't anything higher that isn't $6 per gallon for multiple states away. There are a few stations here that sell 100 and leaded 110 octane. I'm not paying double premium for that and having to drive across town to get gas for a street car. E85 is only in 4 gas stations here as well. My goal isn't to make as much horsepower as possible. It's to make what I can with the mods I install on regularly available gas. As an example, not real numbers, if I don't make 350whp on 91 octane with like a 18g turbo or whatever people are doing on 93 and I make 320whp instead that is fine.

It's not my daily driver but I drive this car around to Arizona and California on occasion for example. I don't need to hunt for gas when doing that, i'm going to be going to get whatever premium is regularly available which out in the south west is only 91.

My goals with the car are not to make a drag racer to beat everyone else. It's to build an autocross street car that I can also bring to meets that runs on freely available fuel. The top end gains would be hugely beneficial and I know someone who rebuilds turbos for when I eventually want to go further in my mods and I would have the platform (rb25 turbo) to rebuild ready to bolt back in. My end goals are only like 250-300whp. My other car has 420hp so I don't need this car to be more powerful. I was perfectly satisfied with the power in my WRX when I had it after modding. It's intended as mostly a road car. If it was a track dedicated vehicle I would use the 100 octane at the Rebel stations. That being said my question wasn't if 91 is viable, I know that it is from experience, my question was if I could run this small turbo upgrade without a tune and without it getting too lean on 91 octane.

[Matvei27]

You'd be surprised. You can buy Sunoco 100 AKI gas almost everywhere, hell even the Shell station around the corner from me sells it. Just not at the pump.

You aren't so lazy that you can't deal with gas that comes in a can, are you?

I wouldn't waste my time trying to tune it if you aren't going to use something better than 91. The car is designed to run on 95 AKI (100 RON in Japan). The AUS people get away with 98 RON (93 AKI) but 91 AKI is low enough that you'll want to retune the ECU even if the entire car is stock.

Here, go buy yourself some gas:

http://www.racegas.com/fuelfinder

Edited May 18, 2015 by Matvei27

[niZmO_Man]

To answer your question, it'll be fine.

[Kanaric]

To answer your question, it'll be fine.

Ok, i'll try it.

I have a Nismo fuel pump as well might as well put that in too.

[niZmO_Man]

Just don't thrash it everywhere until you get a tune for your fuel.

[Kinks]

I thought the octane rating requirement was dominated by compression ratio.. ie if you want to use lower quality fuel you should lower the CR eg fit a thicker head gasket or use a spacer. Otherwise you will have to pull a large amount of timing out to compensate (and you will end up with a worse result than lower CR / more timing).

In saying that, the stock ECU usually has some headroom for bad fuel batches and the anti-knock algorithm is usually quite good. I always fill up on 98RON but once I could only get 95RON. Only tried flooring it once, didn't hear any ping but the engine was really gutless. The ECU would have detected low levels of knock starting and pulled a bunch of timing out. By contrast, if I can find 100RON it goes even better than 98.

[GTRPSI]

If your worried about knock, go water/meth, its been used for decades when poor fuel is being used.

I wouldnt convert to E85 just for because i had poor octane at hand if the boost pressures used were lowish.

In the next month or so we are supercharging our S2000, not dropping comp but forcing 12psi in with 50/50 water meth into a stock NA engine, been done by heaps of others in the same boat, drops intake temps and increased knock protection, good torque increases with it too.

[Matvei27]

It won't damage it on 91 AKI (95 RON) as the ECU is capable of working it out but it will be in the protection algorithm the whole time. By law in Japan for gas to be called "high octane" it has to be greater than 96 RON. The majority of stations sell 100+ RON as high octane.

Water/Meth is popular on the West Coast where 91 AKI (95 RON) is the maximum octane rating you can get at the pump.

However the downside to this is 1. you have to buy/install a somewhat expensive kit 2. if something goes wrong and you do not have a failsafe you can blow your engine depending upon how aggressive your tune is.

For E85, you would need a flex sensor and a ECU which is capable of handling various ratios of E85 and regular gas. So you couldn't use a PowerFC, for example, which is a downside in my book.

That's why I suggested mixing your own 98 or 100RON as being the best option. It isn't that difficult to find, you can still use your PowerFC and tune for maximum power.

The RB20/25/26 were never designed for the US market and were never EPA/CARB certified. They simply aren't meant to run on 87/89/91 AKI like you find on the West Coast. If you lived on the East Coast 93 AKI (98 RON) would be perfectly fine.

Some importers, like japaneseclassics, are re-tuning their cars tune before putting them on sale because of this issue.

Edited May 20, 2015 by Matvei27

[Dose Pipe Sutututu]

Connect up a timing gun and pull 2~3 degrees out of the base timing so at idle you're reading 12~13 degrees of timing.

That should be more than enough to keep your motor happy on 95RON equivalent with a slightly bigger turbo.

[scotty nm35]

Stock injectors and fuel system running 91 and a secondary system running Ethanol/methanol/C16 under boost.

[GTRPSI]

However the downside to this is 1. you have to buy/install a somewhat expensive kit 2. if something goes wrong and you do not have a failsafe you can blow your engine depending upon how aggressive your tune is.

For E85, you would need a flex sensor and a ECU which is capable of handling various ratios of E85 and regular gas. So you couldn't use a PowerFC, for example, which is a downside in my book.

That's why I suggested mixing your own 98 or 100RON as being the best option. It isn't that difficult to find, you can still use your PowerFC and tune for maximum power.

The RB20/25/26 were never designed for the US market and were never EPA/CARB certified. They simply aren't meant to run on 87/89/91 AKI like you find on the West Coast. If you lived on the East Coast 93 AKI (98 RON) would be perfectly fine.

Some importers, like japaneseclassics, are re-tuning their cars tune before putting them on sale because of this issue.

A water meth kit is not expensive (compared to a E85 conversion), there are meth kits available with fail safes to protect you, water meth injection concentation is usually around the 1/11 mark compared to petrol when working out the correct jetting and its been used in high powered applications for a lot longer than most people realize, it was the bees knees before E85 became a pump fuel.

There is of course the option of mixing your own jungle juice to increase octane, really comes down to your access to toluene and such, however its not exactly cheap, healthy and a lot of mucking around every time you want to fill.

[Kanaric]

Some importers, like japaneseclassics, are re-tuning their cars tune before putting them on sale because of this issue.

That is weird because this car runs fine on 91 (95 ron) with stock equipment and doesn't get lean at all.

[scotty nm35]

That is weird because this car runs fine on 91 (95 ron) with stock equipment and doesn't get lean at all.

It's not the fuel map I would be worried about, it's the timing map.