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Dino
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I've noticed that Subaru turbo engines are tuned to run lean. This is noticed particularly on cold start when its taking in even more air with electronic "choke" sensors apparently. Running lean means fuel conservation of course, but under heavy load can also lead to melting pistons I've read today. So, do these flat-4 engines run lean as designed or should they be run richer to conserve wear?

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Yeah i Think the ideal afr is around 11 which is fairly lean in comparison to most other cars .

I'd imagine that the cold start part of the map is set leaner (hotter) to warm up the engine to ideal running temp quicker . it would probably help lessen coking up the bores with over fuelling off boost. As ideally you should be off boost till it's warm and cool it down before switching it off

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yeah, I reckon you're right. I tightened up all the air hoses and air intakes and there are no air leaks at all. I also plugged the small hole The standard air filter was replaced too for a clean new one. The improvement in acceleration after this was phenomenal! Checking with the car diagnostics device I could see it was still running lean as expected... What would I be looking for to see the "afr" on the car diagnostics please? Any idea? I'd like to see if it is around 11 which would make sense when lean if theoretical values are 14:7:1 on a normal standard petrol engine.

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Has yours been mapped dino ?

Mine still needs a tweek due to a new induction set up but here's my afr at 3 different boost settings

post-1399-142748830557_thumb.jpg

Needs a trim but they're all in the ballpark at full throttle under load on the dyno but I'm unsure what adjustments the tps has made to the afr is at different throttle positions as I didn't get a printout for those

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I'm just using a standard ELM 327 OBDII scanner that I got working recently. It reads all live data and is working fine now. :) Interestingly, it works on my wife's Volvo and reads lean on start up before it settles down. Perhaps I need to run it for a while and then re-check the WRX when warmed up to see if it's still showing lean.

I'm not really sure my WRX has been mapped, I don't believe it has. How would I know or tell please?

All I did recently was tighten up all the air hoses connecting anywhere on the air induction connections, and put In a new standard air filter. The standard air box snorkel is fitted and I closed off the odd pressed holes which seemed to serve no purpose other than take air in at the back of the snorkel so perhaps this is allowing more air induction. 

 

My WRX seems like it's getting a whopping boost on acceleration. All codes are good. It just indicates its lean which concerned me a bit...

 

I'll check your AFT output against my connected up scanner and see if it's comparable. Thanks all.

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Thanks for the standard AFR info - very useful. I'll check and see what I'm getting...

Yeah its definitely got a turbo... it's a 2007 WRX 2.5 and has the turbo and intercooler. Now it's interesting steveuk260 that you say not to run it on 95 Ron. The manual says it can run on 95 Ron or higher, however it suggests the WRX STi uses 98 Ron. Mine is not the STi :)

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However I think that uk spec cars are mapped for our lesser octane fuel as standard

Does this mean that standard (non STi) UK cars tend not to be tuned for 98 Ron Super unleaded then? Just curious because I wondered whether this is why import cars are considered more powerful.
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Imports are mapped for jap fuel which is 100ron, The maps are quite aggressive. Along with the Japanese keeping all the best stuff for the domestic market that we don't so they tend to get better equipped & more powerful models as standard

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Thanks Steveuk260 - that's a good call - never thought of that. I just checked the filler cap and on a small silver factory sticker on the pop out filler cover it says "Use unleaded 95RON only"  :)

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  • 2 weeks later...

The main difference between 95 and 98 ron is the burn rate of the fuel. 98 ron is harder to initially ignite , this property reduces the risk of knocking, auto ignition and allows more aggressive ignition timing and higher compression ratios.

You don't gain "extra" power from using 98 over 95 it purely allows the engine to perform to its maximum potential without the knock sensor having to pull timing due to lower octane fuel. So if it says 98 use 98!! As for running lean I haven't checked my STI but would be very interested to find out. 

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highest ron possible is always best, even unmapped 99 ron is best for them. AFR wise 11:1 on boost is ideal, no need for that amount of fuel when not on boost hence it gets wound back a bit.

 

Mine on a 2.5 below

 

IMAG0166_zpsd8d33d75.jpg

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