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#MAF with Air Horn Velocity Stack

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 Post subject: MAF with Air Horn Velocity Stack
PostPosted: Fri Feb 20, 2015 5:20 pm 
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Joined: Sat Jan 17, 2015 3:04 pm
Posts: 51
I been wanting to incorparte velocity stack on my intkae and was having difficutlies figuring it out. I was looking at REVI8 for the mazda and gave me this idea. Air filter just came in today and its a little big but good enough to give it a try.
I machined the alum adapter ring to fit the MAF and hold the air horn and be alble to hold the air filter. I would like to remove the screen but not on this brand new MAF.
I will post pics installed and how it works.
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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Sat Feb 21, 2015 3:38 pm 
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Couple pics installed, no chance to test before the salt came. Has the ITB sounds when reving up. Axious get it out but snow and salt.

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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Sun Feb 22, 2015 8:26 pm 
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The roads clear up here and got to take it out and it feel so smooth, no hesitation what so ever and pulls up to 5500 rpms efforttsly. Still have hit the rev. limiter.
Next up I want to remove the according flex part of the intake tube.


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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Sun Feb 22, 2015 9:58 pm 
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Nice work!

I'd recommend keeping the MAF screen on.

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1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm


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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Wed Feb 25, 2015 12:42 am 
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Location: SF Bay Area, CA
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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Wed Feb 25, 2015 2:11 pm 
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Joined: Sat Jan 17, 2015 3:04 pm
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I cant leave well enough alone and did some research and been testing 3 differnt versions. I will post pic later. Here is what I was reading and help me understand what is going on with all the air and MAF sensor. I reduced the ID of the velocity stack and I like how I have the power band.
http://www.cnlperformance.com/MAF_info.php?section=15


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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Wed Feb 25, 2015 3:38 pm 
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Joined: Sat Jan 17, 2015 3:04 pm
Posts: 51
Here is a couple pics. I went with the smallest one just about 2" and It pulls pretty hard from 2100rpms up to 4-5000rpms, excellent mid range on the higway. The air filter was the second best, but not as much low end. The biggest air horn same size as MAF would be good for light car.

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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Wed Feb 25, 2015 6:33 pm 
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I will caution you that without a wide band O2 sensor monitoring the engine's air-fuel ratios you may be altering the engine's fueling to a potentially dangerous limit.

There are varying AFR's and what may be considered "safe" vs. what produces the most power may not be the same thing. For example, on turbo cars, 12:1 AFR's will produce the most power and feel the best, but is not really a safe AFR because any slight change in the combustion process in the cylinder could cause detonation or pre-ignition. Because of this, tuner will typically tune for around 11:1 or 11.5:1 depending on the boost level. While your engine is non-turbo and the exact AFR's may be different, the concept still holds true.

Since the smaller diameter velocity stacks are essentially tricking the MAF sensor's reading to the ECU, this results in different fueling. At the end of the day, you just want to make sure you have all the information so you can make an appropriate decision on engine/performance modifications, and a wide band O2 sensor is an invaluable tool.

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surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm


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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Sun Apr 10, 2016 2:47 pm 
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Location: Beautiful Downtown Goode, VA
Josh, quick question about the MAF sensor readings and AFR...on a NA engine, wouldn't detonation/pre-ignition show up and be handled by the ECU and the knock sensor? And wouldnt it be possible to circumvent that issue by going up one grade in the fuel used? Now if the engine is running too lean then cylinder temperatures would be higher especially under load, and that would lead to burned valves or cracked pistons. Won't the O2 sensor detect the lean condition and adjust the computer to account for it? Additionally, I read on one of the many forums that the 2.2 NA engines run quite a bit 'fat' on the fueling curve, that is rich...so isnt the velocity stack likely just taking out some of the built in headroom subaru designed in?


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 Post subject: Re: MAF with Air Horn Velocity Stack
PostPosted: Wed May 04, 2016 6:06 pm 
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Sorry about the delay in replying....I've been a bit MIA recently due to work.

My comments above were mainly around turbocharged engines. For a normally aspirated engine you'd really have to be running at the ragged edge to I think cause an issue, and yes running higher octane fuel could help mitigate problems.

Regarding the O2 sensor, they don't do anything under open loop fueling which would be the case for full throttle or heavy acceleration. The knock sensor should always be monitoring and reduce timing if knock is detected, but I don't know if I'd 100% rely on the stock ECU and stock knock sensor to keep everything safe.

Yes, the fueling is probably a little on the richer side and so a little leaner shouldn't be a big issue, but without a wide band O2 sensor and monitoring things to ensure any changes are consistent and safe I'd hate to make a blanket statement that everything is ok.

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surrealmirage.com/subaru
1990 Legacy (AWD, 6MT, & EJ22T Swap)
1997 Impreza OBS

If you need to get a hold of me please email me rather then pm


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