This may be the retard question of the century, so please excuse me if the theories that follow are incredibly stupid...







In a boosted motor, would the motor not benefit more from shorter but fatter intake runners?



Allow to me elaborate

I realize that for N/A purposes the intake runners on the betas are made long and slender for a reason. But going FI, this would, in my mind, create flow restriction. In my readings (interwebs and books) I seem to be coming across the idea that RPM range is based more on the volume of the runner themselves and less the shape. Now I fully understand that a certain level of aerodynamic turbulence is required for proper atomization of fuel, and for this reason the runners are often tapered and reshaped to encourage air "tumble" so to speak. Also, unless I am just horribly misinformed, the intake vales have a 33mm diameter at the base, and 34mm for the standard upgrade. SO just going off that number (33mm stock) the area of intake (the actual circular opening) itself internally is roughly 8.55cm², times 2 because there's two intake valves per calendar for a total of 17.1mc². Granted we know the opening is tapered, the valves overlap a bit and I (haven't actually measured but) doubt doubt that the surface area of the intake side port on the head takes up a full 17cm². Still, this gives us a solid number and goal so one could easily argue that the port-side of the head is roughly 15 cm² +/-. By applying simply geometry (Ï€r² or √(15/3.14159265) * 2) we get a result of 4.36cm² or 43.6mm² as the theoretical flow friendly intake diameter. But that's only a small portion of the equation! Now that we know a 42-44mm runner is preferred the length needs to be calculated. Going off the closest calculations I could find (not really going to deep into that because its accuracy is questionable), and begin that I don't [yet] have a spare manifold to dissect and measure via micrometer, the going assumption is 35cm length (which should be pretty close for 5th wave tune) and 23.5mm diameter. Halving the diameter (11.75mm) and going back to our old trusty Ï€r², the surface area of the runner opening is ~433.74mm²; hence the volume should be roughly 151807.6mm³ or ~15cm³. Now back tracking for a moment, if, for argument, we went with a 42mm runner, geometry again: 42/2 = 21³ = 441 * pi ≈ 1385.44mm² , 151807.6/1385.44 ≈ 109.6mm. This means that at 11cm length and 42mm diameter the RPM range should be roughly equivalent to the stock configuration. So basically we can solve for any runner length, again, in theory. Obviously getting down and dirty, actually making the big bore manifold would require precise measurements and more accurate calculations, but for argument sake the current theory applies. BBTBs and larger intake should be more advantageous under this kind of application since, given the same equation, the head should now in theory be able to flow higher numbers at the same rpm. In fact, given this, one could theorize TB bores of up to 87.5mm which is just shy of 3.5".



Feed back? Opinions? Claims of witch craft?

 

cannot read block text. eyes going googly..



Typically manifolds MADE for turbocharged vehicles have shorter, bigger runners from what I have seen.



People usually just port the stocker though as it is a LOT easier than re-fabbing the manifold and most people aren't competition racing their cars for that little extra oomph needed in a competition.



I think I answered your question without suicide attempts from reading the epic block text of 2012.

 

I read until the maffs

 

I see what you are talking about. I think that you have the general idea covered. There are also the effects of laminar flow to consider in your calculations.





I suspect that with F/I setups that most of the 'pulse' tuning goes out the window... if you want to get tricky with it you can throw a helmholtz resonator to see what happens. Big plenum volume also kills pulse tuning and throttle response, but you get more peak power.

 

long paragraph is long



and with that note....LONG CAT GO!!

 

Well, that was fun.

 

The plenum design is something I am still researching. I keep seeing that the plenum volume should be 1.5-2x the engine displacement for FI but a 3-4L plenum just sounds frightening. I needed to know the diameter of the runner prior to plenum anyway because I plan to incorporate airhorns inside the plenum to reduce flow restriction and need to buy a few appropriately sized. Since Socks basically corroborated I'm going to fab up a test product shortly and get some real-world numbers.

 

Picked up a spare IM to hack apart because this struck my curiosity so much. My fist impression, the casting on these just sucks. Found a bunch of inconsistencies in the porting, so much that the #3 runner had almost a millimeter in variation on either side of the injector bung. I'm beginning to suspect that the stock IM wont even be sufficient as a flange source. I took 4 measurements per runner as detailed in the image below.



H = the horizontal length in mm

two V readings, for the vertical height on either side of the injector bung

and i = the horizontal length of the injector cutout.

Here are the readings I got from each runner:



#1

H = 47.94

V = 30.63 & 30.64

i = 16.41



#2

H = 47.7

V = 31.43 & 30.84

i = 16.02



#3

H = 47.23

V = 30.18 & 31.17

i = 15.64



#4

H = 47.71

V = 30.24 & 30.83

i = 15.91





These, despite the inconsistencies, should still be adequate enough to average out and get some reliable figures. Below are the averaged numbers for length, width and inlet width:

H(avg) = 47.645

V(avg) = 30.745

i(avg) = 15.995



You'll notice that I averaged the heights together to make measurements slightly easier. In the end the runner size will have to be rounded up to the next mm so this shouldn't affect flow too terribly much. As shown in the image below I virtually cut the runner port into 3 easily calculable parts. Now comes the maths. b*tches hate maths.





The next step is to take the height average (v(avg)) and divide it by 2 to find the radius (r) of the rounded edges.



V(avg)/2 = r = 15.3725



Now that we know the radius, both side can be combined into one circle to make an easily calculable surface area.

πr² = 742.402 mm²



Now solve for the area of the main rectangular space:

[H(avg) - V(avg) = 16.9] * V(avg) = 519.5905 mm²



Add the 2 values together (519.5905 + 742.402) and we get: 1261.9925mm². This becomes the presumed surface area of the port minus the injector area. Just to be thorough though, I'm adding the surface area of the injector ports, because if we're doing custom runners that's inclusive of the port on the head. Or in terms of flow, more space to force-feed air. Plus if our N/A friends want to go totally crazy and uses this formula ( *hint* *hint* ) one could easily produce ITBs from bike TBs, which could move the injectors further up the runner, clearing the flow area at the head. Calculating the remaining area:





You'll see in the illustration that this area is trapezoidal in shape and almost square once modified. There were very heavy deviations in the height between the 4 so I'm going to calcualte this as a square to make matter slightly easier. As you can see, cutting off one side and mounting it to the next, this is pretty close, so, again, the calculation will be within a fraction of a mm, not enough to worry about. So taking i(avg) and multiplying it by itself we get 255.84mm². Now added to the previous result and we're given 1517.8325mm². And I must say, is frighteningly close to the first assumption. The rest is gravy, divide by pi and take square root you get a resulting radius of 21.9805mm. Which means that our given diameter, after rounding will be 44mm.





Some time this weekend I plan to finished the calculation for the average volume of each, given that the outer runner seem to be quite a bit longer than the inner, and this should give as close to an exact number as we can get. My end goal is to have something for boosted apps that will replace the stock mani without being as illusive as an Air Ram (for those that even rmeber that.)

 

Let me start by saying, f*ck yeah for actually getting out there and doing it!







It would be interesting to build a 'stock' intake manifold to see how an aftermarket manifold of the same specs performs compared to the OEM unit and theoretical calculations. Also most of those pics didn't work for me man.

 

I can see the pics, but they made my head hurt.