Looking for info on ITB plenum design
09-30-2013, 03:58 PM
#17
Race Car
But low lift flow isn't that big of a deal on the intake side, it is peak flow - that's how you tune the intake, and that is when the pressure wave hits the valve.
09-30-2013, 04:19 PM
#18
So, for the same given runner shape, increasing inlet port size should be done only when increasing high lift flow?
Does the diameter of the air column affect the intensity (or period) of the pulse wave?
Does the diameter of the air column affect the intensity (or period) of the pulse wave?
09-30-2013, 04:57 PM
#19
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I don't think ITBs off an E39 M5 will work on the 944 intake port despite being the correct size. From my limited experience, I think I would be more tempted to go with motorcycle ITBs. Much wider availability and their shape seems to suit the shape of the intake port better. Of course I stand to be corrected by someone who has been there, done it and gotten the medal.
09-30-2013, 05:57 PM
#20
Race Car
Tuning is a function of compression ratio, length, diameter, and the speed of sound (which is a function of temperature).
But again, this is not the kind of place one should go to educate oneself on these specifics.
09-30-2013, 06:04 PM
#22
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Is that a stock fuel rail?
09-30-2013, 07:17 PM
#23
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Before I even begin, *puts on flame suit*.
There, thats better. I've been throwing this idea around in my head for years, but recently a conversation with a friend prompted me to consider it again, and to my knowledge nobody has ever done it. I'd like to fab an ITB intake using 44mm butterflies from a Honda CBR1000, and integrate velocity stacks. They are extremely cheap, a set with the linkage can be had for 40 bucks all day long. Thats 608 cm^2 of valve area, and nearly 3 times the area of the stock 951 TB. A stock 951 intake hacked off before the plenum would let the stock fuel rail be used, and I would drill each runner and tap it for a boost/vac reference signal and delete the ISV. It wouldn't take much massaging to make the factory throttle cam and TPS work, so the main hurdle for me is figuring out exactly how long I want the runners so I know where to cut and designing the plenum. Can any of the great minds here give me their opinion on calculating ideal runner length and plenum volume? This will be going on a big turbo 2.5 liter engine with lots of breathing mods. Trying to achieve max VE at a relatively high engine speed.
Much thanks
There, thats better. I've been throwing this idea around in my head for years, but recently a conversation with a friend prompted me to consider it again, and to my knowledge nobody has ever done it. I'd like to fab an ITB intake using 44mm butterflies from a Honda CBR1000, and integrate velocity stacks. They are extremely cheap, a set with the linkage can be had for 40 bucks all day long. Thats 608 cm^2 of valve area, and nearly 3 times the area of the stock 951 TB. A stock 951 intake hacked off before the plenum would let the stock fuel rail be used, and I would drill each runner and tap it for a boost/vac reference signal and delete the ISV. It wouldn't take much massaging to make the factory throttle cam and TPS work, so the main hurdle for me is figuring out exactly how long I want the runners so I know where to cut and designing the plenum. Can any of the great minds here give me their opinion on calculating ideal runner length and plenum volume? This will be going on a big turbo 2.5 liter engine with lots of breathing mods. Trying to achieve max VE at a relatively high engine speed.
Much thanks
Regards..
10-01-2013, 02:27 AM
#24
Race Car
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I'm looking for peak power somewhere between 6500-7000. This will be on a race engine with an HX35 turbo and all the typical support mods, 3" turbo back, a worked head with oversize intake valves, modded intercooler, 2.75" OD hard pipes, and a mild cam. Looking for as much as I can safely get out of the stock rods, so 400-425 whp, with good throttle response up top and as little boost as possible. I think to start with, I'd like to figure out my ideal plenum volume ( which can always be remade later ) and then go from there to the runner length. I fully accept that it may be a case of trial and error to get the power band where I want it and to get a good balance between top end power and throttle response.
Last edited by Dougs951S; 10-01-2013 at 02:49 AM.
10-01-2013, 07:21 AM
#25
Race Car
10-01-2013, 07:57 AM
#26
RPM = 25/(3*n) * (720 - INd) / Rl * Ss
where
RPM : engine speed when the pulse wave hits the open inlet valve
n : the number of times the pressure wave will have bounced on the back of the intake valve before it opens
INd : inlet cam duration, in °
Rl : Length between the back of the open intake valve and the intake plenum, in cm
Ss : speed of sound (depending on inlet air temp), in m/s
With this calculation it's easy to plot curves showing RPM = f(n)
What this formula shows is that increasing inlet cam duration has a greater effect on ram effect the shorter the runner length.
Now if some knowledgeable people could add some proper input on how runner diameter actually affects peak torque RPM (with a formula please, not a meaningless online calculator), we may get a bit further...?
where
RPM : engine speed when the pulse wave hits the open inlet valve
n : the number of times the pressure wave will have bounced on the back of the intake valve before it opens
INd : inlet cam duration, in °
Rl : Length between the back of the open intake valve and the intake plenum, in cm
Ss : speed of sound (depending on inlet air temp), in m/s
With this calculation it's easy to plot curves showing RPM = f(n)
What this formula shows is that increasing inlet cam duration has a greater effect on ram effect the shorter the runner length.
Now if some knowledgeable people could add some proper input on how runner diameter actually affects peak torque RPM (with a formula please, not a meaningless online calculator), we may get a bit further...?
10-01-2013, 08:50 AM
#29
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RPM = 25/(3*n) * (720 - INd) / Rl * Ss
where
RPM : engine speed when the pulse wave hits the open inlet valve
n : the number of times the pressure wave will have bounced on the back of the intake valve before it opens
INd : inlet cam duration, in °
Rl : Length between the back of the open intake valve and the intake plenum, in cm
Ss : speed of sound (depending on inlet air temp), in m/s
With this calculation it's easy to plot curves showing RPM = f(n)
What this formula shows is that increasing inlet cam duration has a greater effect on ram effect the shorter the runner length.
Now if some knowledgeable people could add some proper input on how runner diameter actually affects peak torque RPM (with a formula please, not a meaningless online calculator), we may get a bit further...?
where
RPM : engine speed when the pulse wave hits the open inlet valve
n : the number of times the pressure wave will have bounced on the back of the intake valve before it opens
INd : inlet cam duration, in °
Rl : Length between the back of the open intake valve and the intake plenum, in cm
Ss : speed of sound (depending on inlet air temp), in m/s
With this calculation it's easy to plot curves showing RPM = f(n)
What this formula shows is that increasing inlet cam duration has a greater effect on ram effect the shorter the runner length.
Now if some knowledgeable people could add some proper input on how runner diameter actually affects peak torque RPM (with a formula please, not a meaningless online calculator), we may get a bit further...?
Rd : Number of type R decals
IFph : Internet Forum posts per hour of author
all joking aside - if you want to get down into the details you need to consider the effect of humidity and pressure on the speed of sound. Its pretty small but it is quantifiable.
I don't think you are going to get a relatively simple formula for this type of design unless you are just looking of a theoretical 'perfect world' answer. Port shape and curve will become an issue in the real world. I am sure Harry might have some better insight on the issued of how we figure air flow separation into the port volume tuning. Once you get to that level I am out of my league - I don't have the CFD software to deal with that!!!
BTW - Harry's comment about mach is a big deal, things just go to crap when you get to that speed! Most people would be amazed how fast the air is traveling inside an engine. example - 500cfm through a 2" pipe (like an intercooler pipe!) is approx. 400fps - about 1/3 mach.
10-01-2013, 08:52 AM
#30
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