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  #1  
Old 08-27-2010, 01:30 PM
httrdd httrdd is offline
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Is modifing the stock air box bad?

I was on rs25 with my swap thread and found that one of the guys had something to say about the eg33 AFR at WOT. He also says I need to run 93 octane. Not saying he is wrong just need more clairification. Thanks. TJ


Him: Don't dick with the filter or airbox, run 93 and you should be fine.
My stock ecu ran 15.4 AFR at WOT at 6000.. that's STUPID lean

Me: I am actually running a k&n cone since the air/filter box did not fit where the ABS pump was. Run 93 for the track you mean?

Him: no, run 93 all the time.
You are playing with fire having a non-stock filtering system on the stock maf on the stock tune.
You will for sure be more than 15.5 AFR at WOT. That means bad bad things for a 10:1 compression motor that likes to eat up 40+ degrees of timing

Me: Alright I will run 93 to be safe, but how does modifing the air box change the air/fuel mix?

Him: the maf is metering MORE air moving at a faster rate. The stock maf is maxed out at stock power levels.
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  #2  
Old 08-27-2010, 01:48 PM
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Re: Is modifing the stock air box bad?

Subaru advises 93 octane, as well.

As far as the MAF is concerned, a lot of intake modification information involving MAFs and custom work, although conducted on more modern MAF NA Subarus, can be found <here>. You really want to duck removing any Helmholtz hardware if you can, all told.

Odd, because he agrees with the results of removing the anti-resonance hardware, but that should make it run rich, yeh?
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Old 08-27-2010, 02:09 PM
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Re: Is modifing the stock air box bad?

The snorkus is still there, but the stock airbox is not. I think by reading that should I be ok with using the stock piping and mating a cone after the MAF?

Also what ocatane fuel are you guys running stock?
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Old 08-27-2010, 02:51 PM
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Re: Is modifing the stock air box bad?

The owners manual and gas cap all say to run 93 octane.
I do what they say. I'm used to turbo cars anyway, so I can't recall owning anything in the last 10 years that didn't require premium.
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Old 08-27-2010, 03:21 PM
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Re: Is modifing the stock air box bad?

I will run 93 then. How about using the cone? Do I need to run a certain length piece in between the MAF and cone?
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Old 08-27-2010, 04:15 PM
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Re: Is modifing the stock air box bad?

Tons of people use cones. You won't have a problem other than what effeciency loss would be expected by sticking your air intake in the hotter engine compartment vs. the fender.

Ideally you would want something that would allow you to put that cone in the same spot that the stock airbox inside the fender resides.
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Old 08-27-2010, 05:32 PM
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Re: Is modifing the stock air box bad?

Quote:
Originally Posted by immortal_suby View Post
Tons of people use cones. You won't have a problem other than what effeciency loss would be expected by sticking your air intake in the hotter engine compartment vs. the fender.

Ideally you would want something that would allow you to put that cone in the same spot that the stock airbox inside the fender resides.
+1 Hot intake air means reduced power and torque. Exactly the opposite effect people buy them for interestingly.
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Old 08-27-2010, 07:18 PM
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Re: Is modifing the stock air box bad?

Quote:
Originally Posted by immortal_suby View Post
Tons of people use cones. You won't have a problem other than what effeciency loss would be expected by sticking your air intake in the hotter engine compartment vs. the fender.

Ideally you would want something that would allow you to put that cone in the same spot that the stock airbox inside the fender resides.
Plus, sticking a cone right near the MAF, I would think would cause a bit of turbulence in the tube compared the more restrictive snorkus and box system.
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Old 08-27-2010, 07:40 PM
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Re: Is modifing the stock air box bad?

I am thinking of adding piping then to get the cone closest to the snorkus box. Like I said the stock box will not fit with the ABS pump in there.
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Old 08-27-2010, 09:13 PM
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Re: Is modifing the stock air box bad?

i just yanked my snorkus deluxus assy, but left stock box, no issues.
you only need 93 if you want max power, cuz w/ knock sensors the ecu will automatically take timing out. when i'm near sea level i run 93 but here 4200' i use mid/reg.
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Old 08-27-2010, 09:18 PM
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I run 90 (with cheap bottled help) because that's all we have up here and my knock sensors go nuts if I put the throttle down.
That started happening after the stage 2 was installed though and I never really had a problem with factory management and fuel delivery. Just use whatever you feel comfortable using. The car will let you know if it wants something better.
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Old 08-28-2010, 09:51 AM
httrdd httrdd is offline
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Re: Is modifing the stock air box bad?

I put 89 (plus) in when the swap was finished and the knock sensors are going nuts (lots of knocking). Is there a octane booster I can use so I do not have to drain a full tank of 89?

Thanks for all of the info guys you helped clear things up more.

What brand cones are you guys running. I am told oiled cones are hell for our MAFs.
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Old 08-28-2010, 12:33 PM
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I not in the camp that cones are more efficient than the stock airbox. I think K&N type cones are the worst. Just get something with a good filter that won't allow mosquito bits into your engine.

You could dump some toluene in the tank (1:5 toluene:fuel) to bring the RON rating up to the minimum recommended octane of 91.

Far as a bottled octane booster.. find something that claims to raise levels by 20 points.

I have heard claims that boosters can destroy your plugs over time but after 40k miles mine seem to be fine.
Just make sure to get the appropriate fuel to begin with, though.
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Last edited by NikFu S.; 08-28-2010 at 12:46 PM.
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  #14  
Old 08-28-2010, 01:00 PM
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Re: Is modifing the stock air box bad?

Ok thanks!
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Old 09-03-2010, 08:43 AM
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Re: Is modifing the stock air box bad?

I have always used the lower octane fuel (86/87) in my SVXi and have never had a problem with any of them at sea level or high altitude or at any speed. My 94 that I bought new has over 200K miles on it and is still being driven by my granddau.

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