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13280, Results of math long very long Posted by bigbrent88, Jan-29-02 07:32 PM
I would first like to thank those that helped me with the diameter question, it helped a lot since I'm at college and the cars at home! Anyway I was trying to find a common factor, or something like that, between the flow of air from the intake, TB, and valve area to see how much porting is needed. I derived these two formulas at 1000rpm, sounded like a good starting point: (Volume of air needed per sec(ft cubed)/ft squared crossection of area in use)(i.e. CAI, or TB), and <2(pi)radius(height)>. The first one is used to find the velocity of the air moving through the set sized tube, this would be used to find a velocity constant. The second was used to find the area of inlet at full valve opening, needed to find velocity of air in next formula.These formulas will work at any RPM just correst for your rpm. OK, the amount of air needed for the engine at 1000rpm is .586ft(cubed)per sec, at 8000rpm its 8 times this. The other info needed is the squared area of the crossection in use, for the OEM intake I found it to be about .4109 square feet(guessed on this one), a 3in. aftermarket intake is .589ftsquared at its largest point, OEM TB is .25squared feet, bored TB is .306squared feet, regular intake is .103667 squared feet, and the #0012 race cams are .126742 square feet. I may use inches later to be more exact but this will do.
With this I found at 1000rpm at the intake its 1.3 fps(feet per second) for OEM, OEM TB its 2.5 fps, and at the OEM valve its moving 1.45fps. The afermarket is as follows: intake is .99fps, TB is 1.77 fps, and valve is 1.15 fps. This shows that the velocity will go down at low rpm, which is why people get less "engine" at low rpms with porting, remember I can't factor in drag and such so this is a rough estimate. The high RPM's are what is most helpful so here I go. I used 8000rpm since thats what I plan to achieve as a shift point later on, just correct to were you need it. For OEM: intake is 10.5fps, TB is 18fps, and valve is 11.5 fps. The aftermarket is as follows: intake is 8fps, TB is 14fps, and valve is at 9.4fps. Again a slow down, but like the early post "I hate backpressure" this allows an easier airflow at high rpm, using my graph, which I will post sometime soon, I can see that the engine at 8000rpm with aftermarket parts is doing the work of around 5000-6000rpm. I also noticed that all the aftermarket parts dropped the velocity to about 79% of the OEM part, allowing all the parts to have close to the same ratio as before, just slower. In conclusion, I have found that some race cams and some very small porting, will add a good combination to a CAI and bored TB. I can't make power claims. Again I'm no mathmetician, so don't go by this until I'm sure, getting it checked by a few teachers. If anyone is good at math check this out, if you need more just wait, ill have more on the math later, along with a graph. Hope this helps all you out there. Respond if you find a problem.Its late some of for some sleep Brent
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13281, RE: Results of math long very long Posted by evan2, Jan-29-02 10:59 PM
3+2= 5..
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13282, RE: Results of math long very long Posted by trwebb26, Jan-30-02 05:15 AM
OK...
Granted I have not taken a REALLY good look at this, but there are a few things I can see that trouble me.
1) Your calculation for the volumetric flow rate of our engine is a little off. For our engine it will be closer to 0.483 cubic feet/sec. Check out: http://home.att.net/~t.vago/waste-money-howto.html
2) Our engine won't go up to 8000 RPM - only 7200 RPM.
3) You really need to take a university level fluids class... You can see HUGE velocity losses around bends in intake, surface roughness of intake tube (including those fold lookin' things in the stock intake, and rough surfaces...hence the purpose of the port and polish), over butterfly valve in Throttle body, and in the intake manifold. Anywhere there is a bend there will be added turbulence which will SLOW DOWN THE FLUID (the fluid being air in this case). These losses can not be ignored when talking about such small differences in velocity and intake size.
4) It is tough to say (without running the calcs myslef) that the air speed will change from 10 fps to 18 fps and back to 11 fps in the small lengths between the intake, throttle body, and valve. A good way to model this is to find airflow at the valve and treat the rest of the intake manifold, throttle body, and intake tube as a restriction in flow to the air entering the engine.
Look... I'm not trying to bring you down about this, I just think it is a little more complicated than you have let on. Bottom line is that the more air you cram into your engine with the right (14.7:1) air-fuel mixture, the more horses you get. You get more air into the engine by getting rid of restrictions in the air intake and/or changing the timing of the valves relative to TDC. You are thinking correctly about the basic equations of airflow, but it is a little more complicated.
Hope this helps - post up if you have questions.
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13283, RE: Results of math long very long Posted by bigbrent88, Jan-30-02 09:47 AM
1: I just figured it by taking how often the engine intakes 2L at 1000rpm, considering it takes 2 rotations to do this I just divided the rpm by 2, divided by 60 and multiplied by 2. Then used my pda to convert to cubic feet.
2: I know about the redline od 7200, but I plan on getting the internals balanced and strengthened.
3: I'm not going into engineering, yet, but I understand there are parasitic drag losses throughout the engine, expecially that damn accordian hose intake. I just used this so I could find a relationshp and I did, in a very simple calculations. If I take a fluid dynamics course I will update this.
4: Yeah, I was expecting the valve flow to speed up, and it probably is faster than that considering its right near the piston, but I figured that the valve opening and closing sorta negated this. Also remeber there are four valves pulling in the air from the TB, so one cylinder can't eat more pressure, maybe.
Again, if anyone has done a calculation like this before or is goo at math try to figure it out. Brent
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13284, RE: Results of math long very long Posted by Fast420A, Jan-30-02 11:50 AM
> >2: I know about the redline od 7200, but I plan on getting >the internals balanced and strengthened.
AGAIN I AM GOING TO POINT OUT. . . just because the engine has been balanced and can rev to 10,000 rpm or what ever doesn't mean your able to do it. The ECU on our car stops the engine at 7200 rpm. The Neons can replace their ECU and rev the stock bottom end to 8200 rpm but we have no ECU replacement so we can't rev past 7200 rpm. Now if you go the route of Stand alone engine management system then thats a different story but you haven't mentioned that in your posts.
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13285, RE: Results of math long very long Posted by bigbrent88, Jan-30-02 12:49 PM
Yeah, I was looking at getting a Haltech E6k , I think thats it, that would do it, bit on the pricey side, but I think its worth it.
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