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Old 07-22-2007, 10:26 AM   #1
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Question Ram Air <> pressure Question

I cannot find my prior thread so will start anew. I am making a 'ram air' for my Steeda SRI (I enjoy metal working so its a hobby thing). Let me cut to my question. If known or reasonably sure. How much boost (in PSI plz) could a stock 2.0 Duratec take before I run into trouble?
(Stock meaning factory tune, stock injectors and fuel pump).
Thanks.


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Old 07-22-2007, 11:05 AM   #2
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You'll never get THAT much PSI from running just a ram air intake...
If your car could do 200 MPH, you might get 1.5 or 2 PSI. But every little bit helps, right? And the added benefit of running cooler, denser air from the front of the car instead of from the engine bay will help noticeably...

Things to remember though, is when you restrict the intake tract (increase air velocity) your DECREASING pressure. Think of a carb venturi (it's actually called the Venturi effect)...the carb passageway narrows, speeding up the air flow, cause negative pressure over the metering jet, drawing fuel up the bowl...
So, keep your ram air intake tract constant diameter straight into the engine...
You get pressure from trying to stop the air flow, not speeding it up. The ideal setup would be a large diamter duct, mounted at the very front/center of the car, away from aero effects of the bodywork, travelling straight to a large air box, which then leads to the filter/MAF/engine...
Dumping the air into the air box will pressurize it. The larger the air box, the more pressurized volume is available for the engine. Think of it like this...
You can have a tiny little turbo on your car that produces 30 PSI, but it won't flow enough to feed the engine...cubic feet/minute...the engine might draw more air than the turbo can put out, eliminating all the boost!
PSI is only part of it...like a water tap hooked up to a 3/8" pipe, and a similar sized tap hooked up to a 5" pipe...both give you 80PSI, but which one flows more?
A large airbox will be able to maintain pressure even if the engine is drawing a lot of volume (full throttle, 6000RPM), at least, that's what you want...
G'luck, and post pic's!!
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Old 07-22-2007, 12:04 PM   #3
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Thanks WuNgUnSVT. I agree with what you said. some detail. I have calculated a 10 sq inch (area) scoop and a "pipe" of 3x4 (12 sq inch (to reduce the 'carry velocity)). This 'dumps' into a box which holds the air filter (I have not calculated the volume of the box yet as I am still building it) . I was having a bugger of a time trying to calculate how much static pressure would be 'apparent' in the box doing 60mph. The reason for my post is this. My brother gave my numbers to a friend (funny car tuner) and he gave me back (for the day in question so he had current air density figures) a calculated 1.77inch of mercury. This equals a (stunning) .86 PSI. WAY more than I thought possible. As temps drop, air density will rise resulting in a potential rise in PSI. What I need to know is where to "draw the line" so to speak so I do not overstep the fuel delivery capabilites (I.E. leaning out during worst case scenarios like a stiff headwind or a big truck passing at speed).
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Old 07-22-2007, 01:48 PM   #4
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youll b good til about 6 or 7 pis thats what a turbo kit would run so 6 or 7 but like he siad without a power adder good luck getting that much
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Old 07-22-2007, 04:07 PM   #5
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Wow! 6-7 PSI on the stock tune and fuel delivery? I had know idea it was that capable. Cool! No worries then. After it's installed I will try to take some manometer readings. With those I can finish my spreadsheet.
Thanks again!
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Old 07-22-2007, 04:45 PM   #6
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^^^ No Way Without Tune !!!
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Old 07-22-2007, 05:14 PM   #7
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Quote:
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Wow! 6-7 PSI on the stock tune and fuel delivery? I had know idea it was that capable. Cool! No worries then. After it's installed I will try to take some manometer readings. With those I can finish my spreadsheet.
Thanks again!

The engine can handle no boost with stock tune and stock injectors. But a SRI isnt adding any boost at all. It is reducing intake restriction ...but no boost is being made at all. Even with ram air...you are funneling cooler air into the filter...and it may be less restrictive than pulling it in on its own...but still no positive pressure past the filter.
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Old 07-22-2007, 05:22 PM   #8
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^^^ No Way Without Tune !!!
Thats why you get an SVT. They handle alot.
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Old 07-22-2007, 05:59 PM   #9
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Thats why you get an SVT. They handle alot.
The SVT can also handle no boost without a tune...
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Old 07-22-2007, 09:35 PM   #10
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With no tune your engine will run like crap and blow with any boost no matter what kind of focus.
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