if that's legit that's incredible
if that's legit that's incredible
I am currently building an 5.3L L33 LS Chevy engine to go into my 1971 TE27 Corolla. I have not decided whether to cam it, or turbo it since I will be fabricating my own intake for this engine as well. I bought it from Cordova Truck Dismantlers with 5,000 miles on it from a burned 2005 silverado. I believe stock it makes 315HP, but I'm fairly sure I can get near 400HP with cams/springs. The engine that's in it is a tired 300HP turbo/lpg 3TC with over 180,000 miles I personally put on it after buying it used from pick-n-pull.
Interesting stuff from my own experience. Naturally, it's from Miata engines, because when faced with anything else I am helpless.
The 1999-00 Miata intake has a set of butterflies in it that open a resonance chamber. It's not a flow path for the air and I'm not sure it properly counts as intake plenum volume because it's basically stagnant - at least, that's how I imagine it. They just let the air jitter around a bit more.
Run 29 is with the butterflies locked shut, run 30 is normal operation, run 31 is with butterflies locked open. Cool, huh?
I also put a set of individual throttle bodies on my Seven engine. I played with runner lengths a bit. No airbox. Red is long runners, blue is short runners. Not a big difference, but it still shows what a difference a slightly longer pipe can make.
I'm going to play with the intake on my Targa car engine soon. First, fuel pressure and injectors. Then, a big fat intake followed (maybe) by some individual throttle bodies.
Keith, if you dont mind my asking, how long are we talking about in that ITB setup? I had done some calculations about my own proposed itb setup and came up with a length of 8 inches from butterflies to the head.
I don't recall. No more than 8", possibly less. Planning consisted of "oh look, here's that old set of TRM prototype throttle bodies that have been kicking around here forever. I wonder how they'd work?"
Here's the difference between the long and the short runners above.
wow, not much difference eh? like 1/2 or 3/4 inch difference?
I'll measure them someday. I'd put the difference at pretty close to an inch, but it's been years since I had them side by side. It was interesting to see how much of a difference that little extra length made.
A book that I own Titled: Motorbooks Workshop, How to Tune and Modify Engine Management Systems by Jeff Hartman, states that pressure waves in the intake and exhuast develop frequencies based on the valves opening and closing. Engineers using a plenum intake runner with quarter wave organ pipe combined with a Helmholtz resonator can tune the exhust pulses to actually enter the intake from the combustion chamber and bounce back and pull the intake charge with the resulting pressure wave. The resonation effects cause an acoustic pulse to travel at the speed of sound but varied by exhust temperature. As the positive(+) pulse arrives at the end of the pipe and enters the atmosphere it triggers a negative(-) pulse that travels back up the pipe. The -pulse continues through the combustion chamber and out the intake valve(valve overlap) where it speeds up the intake charge. The - wave travels out the intake port to atmosphere where it bounces back into the intake as a +pulse. This is the power wave that rams the air into the combustion chamber. At this point the length of the runner "tunes" this pulse to carry additional air just as the intake valve closes. At all other RPM's but the target "sweet" spot the effect hurts volumetric efficiency. By boxing the end of the runners, engineers can dampen the strong pressure waves and flatten the torque curve. The air in the box is like a spring, and the runner is like a weight. At the target frequencies the air vibrates back and forth without ever leaving the runner. Volume in the box and the runner determine the frequency of the system. The strong pressure waves excite the box into resonance at a matching impedance, dampening the pressure waves and flattening the torque curve. Here is a table to determine working intake runner length: begin by computing an effective cam duration (ECD), which typically involves subtracting 20 to 30 degrees from the advertised cam duration. Use 30 degrees for solid-cam drag motors, 20 degrees fo less radical powerplants. ECD=720-Adv. duration -30. For a 305 degree cam: ECD=720-305-30, the ECD would be 385. The formula for optimum intake runner length (L) is: L=[(ECD x 0.25 x V x 2) / (rpm x RV)] - (D / 2). Where ECD=Effective Cam Duration, V=pressure wave speed (400-1250 ft/s), RV=Reflective Value - the utilized pressure wave set, and D=runner Diameter in inches. So if an engine with a 305 degree cam needed tuning to 7000 rpm using the second set of pressure waves (RV=2) and has a 1.5" diameter intake runner, the optimum intake runner formula would look like this: L=[(445 x 0.25 x 1300 x 2) / (7000 x 2)] - 0.75. Or, 19.91 inches. Always terminate runners with trumpets inside the box (plenum) so that the air charge does not slow down.
thats a lot of good stuff, but why easter sunday such an old thread?
The book goes on about runner area stating that: in contrast to tuning runner length that only affects narrow rpm ranges, runner area affects power at any engine speed. As a rule of thumb the larger a port the less strength pressure waves will have. By gradually tapering the runner to the intake valve the resulting charge is speeded up due to the bernouli effect. Air that moves faster exerts less pressure. A taper over 2.5 percent will not help airflow though. Think of the plenum as a capacitor in an electrical circuit. It smoothes out air flow through the throttle. The trade-offs in plenum volume are too small and no resonant tuning effects and too big and sluggish throttle response. Different plenum volumes are used for tuned runner or restrictor based intakes. Restrictor type intakes often found on V8's need plenum volumes 1 to 2 times the displacement of the engine. Tuned runner V8 plenum volume would be 50 to 60 percent of diplacement. Tuned fours, 50-60 percent. Tuned threes or sixes with twin plenums, 65-80 percent of three cylinders. Tuning an engine at 7000rpm you should reduce volume 10 to 15 percent.. Tuning at 3000rpm go 30 percent larger. The next step in tuning would be the ram pipe diameter. The book states that the velocity here should never go over 180 ft/s at max rpm and horsepower. The formula here is: D=sqr(CID x VE x rpm) / (V x 130). Where D=pipe Diameter, sqr=square root of, CID=Cubic Inch Displacement, VE=Volumetric Efficiency, and V=Velocity in ft/s. Last in tuning is the pipe length. Doing this last so that you can leave it long and shorten it while on the dyno. Starting with a 13" pipe that gives enhancement at 6000rpm, adding or removing 1.7" will change power 1000rpm, shorter=higher rpm. The inlet should be radius for smooth flow of air into the chamber. As all the books I have collected this book is very useful. I strongly recommend owning this one.
Funny i was thinking who dug up this old thread too.
But in Keith's photo above hes got longer on the other cylinder and you know many of the motorcycle air boxes with EFI do too. when you pop the lid the other two are close to an inch taller on then the inner. Why? i don't know, i could be cause those two header pipes are slightly longer.
44
Good stuff. I may tackle a custom intake manifold this winter. Factors in play are runner length, plenum volume, possibility of dual plenum, and alternate styles of throttlebody (a slide throttle between 2 chambers of a dual plenum for instance). I'm boosted, so I need some kind of plenum - no ITB to atmosphere for me.
actually, me too - 3 cyl metro with short runners and a universal type plenum thick enough to drill and tap for whatever you want to plug in. Like I said, theres good stuff going on up there, and the book is probably a big help in such an endeavor, just questioning what prompted the revival of said thread...
44Dwarf wrote: Funny i was thinking who dug up this old thread too. But in Keith's photo above hes got longer on the other cylinder and you know many of the motorcycle air boxes with EFI do too. when you pop the lid the other two are close to an inch taller on then the inner. Why? i don't know, i could be cause those two header pipes are slightly longer. 44
From what I remember from my sportbike days (and I could be wrong) the two different lengths were more an attempt to equalize the powerband between upper and mid range power.
I had an '04 R6, and a common mod was to use Graves short velocity stacks to really focus the power up top at the expense of some midrange. I think on my bike the velocity stacks picked up (with proper tuning of course) around 5hp between 12k-15k RPMs at the expense of some 8k-10k power (not that it mattered, on that bike 10k is where the power really took off anyway).
I miss that bike. 420ish lbs, 111whp. Of course it was more like 600lbs with me on it.
I know one big issue with designing and the use of the many equations they have out there, is that the intake needs to be symmetrical to work. Otherwise, and like most cars have, the non-symmetrical versions are more trial and error in terms of plenum design. You can always design the runners regardless of plenum to try and tune to a specific power band, but it is impossible to calculate flow rate on a non symmetrical plenum and the use of a flow bench is necessary to properly make the plenum.
If I am wrong, please let me know...
I know this is an old thread, but does anyone have any thoughts on a dual-plenum solution?
http://www.jasperintegration.com/intake-kit.html
I know that Audi used them on the Group B cars and on their LeMans efforts.
In reply to fabron:
Has anyone been able to get a reasonable answer from this equation? When I run the numbers for my engine, a 2.3 (140 cu in), VE of 85%, 6500 rpm, divide by 23,400, I get 33, sqr= 5.75". The first thing I notice is there is no provision for number of pipes. Divide 33 by 4, (number of cylinders) = 8.26 sqr=2.87". I don't think so.
Bill
In reply to OrangeAlpine:
The above post is in response to this portion of fabron's post: "The next step in tuning would be the ram pipe diameter. The book states that the velocity here should never go over 180 ft/s at max rpm and horsepower. The formula here is: D=sqr(CID x VE x rpm) / (V x 130). Where D=pipe Diameter, sqr=square root of, CID=Cubic Inch Displacement, VE=Volumetric Efficiency, and V=Velocity in ft/s."
By the way, this forum has a very obtuse format in use to make a post! Almost too much for this newb.
Bill
Aloha,
first post and it's a re-resurect. 
Just for illustration purposes... here's my 87 325iC with m20b25 engine, dbilas itb and Miller W.A.R. CHip/AFM delete.
This particular carbon airbox requires brake booster relocation or delete due to lack of clearance on rear most runner., dbilas plenum does not., so last runner could have been made to resemble it.
Well, what I'm really after is variable lenght runners inside airbox.
Also, short video with PVC pipe intake. don't laugh too hard, made it for fun. it works, it clears brake booster and it sounds grrrreat! , lol.
http://youtu.be/8D1basq0RTk?hd=1
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