Boost Control Series: Single 3 Port Solenoid

all right so we've covered wastegate we've covered reference leak bypass now let's knock out the single 3 port this is probably my favorite and the reason it's my favorite is it's the simplest way that we can let the ecu actually control how much boost that the engine is going to make um the thing about a single 3 port is it's easily used in either a closed loop or an open loop situation and i'm going to do a video on open versus closed loop um shortly the thing to remember about that is it doesn't always have to be when we're talking about our air fuel ratio open versus closed loop means a lot of different applications so let's get rolling with this and we'll wrap around that later uh single 3-port uses your existing boost pressure or co2 depending on what kind of application you're using typically co2 is reserved for the drag strip in a car that's going to make you know single passes and not have a lot of street use that's going to require you to keep filling up the co2 bottle that said that doesn't mean you you can't use co2 in a street car it just means that it's one added thing you got to take care of and this is one of the reasons why i don't like meth injection systems is you can run out of meth when you're talking about co2 it's something that's very rarely going to run out the the the volume you go through is so low that the problem is when you forget to check it um now you don't have a way to make boost so if you're using a street car setup you can use the compressor pressure and that's going to be a setting in your terminator x or your holley applications where you either choose fixed or compressor if you use compressor that means that you have a variable boost source right down here for the 3 port if you used fixed and that means that you're using a regulated set pressure from your co2 bottle if your car if your car has air ride you can you can use the onboard compressor and use onboard air tank you know for that you can use a nitrous bottle there's lots of different ways that you can actually set this up but the first thing we're going to run down is doing it without co2 we're going to use the compressor pressure and hopefully this will make a lot of sense so i've redrawn my wastegate here making things a little clearer so i had a little more room for the 3 port and then we also added ourselves a cute little turbo down here and this is going to make hopefully a little more sense i think i referenced before that the line coming off the turbo is where you need to input for your reference pressure you can do it post intercooler off the manifold in some cases if there's not a lot of pressure drop but the one thing you can't do and i learned this the hard way pretty recently is you can't feed the reference with the turbo then go through the intercooler and up to the engine and then feed the mac valve with the the engine boost but the reason is you're always going to have a higher pressure coming straight out of the turbo than you're going to see in the manifold and the and the reference is always going to outrun the dome you'll never make any more boost and if you do it's going to be erratic and hard to control and not a good situation so let's add a reference line it's going to come down through here and go right into the outlet of the turbo this is a metaphorical place it doesn't have to be right on the outlet of the turbo a lot of turbos actually have a boss for you to do it there and it's a great place to put it i highly recommend it if you have the option that said if you don't you can put it in your pipe right here just past it you can put it in the pipe right before it goes into the into the intercooler if your wastegate uh is kind of near that due to the way that the the piping puts it if it makes it convenient you can put it off of that just don't put it after the intercooler and don't put it directly off the manifold if you can help it um obviously this is a fringe setup but if you are running something that you got a turbo and is going directly into the manifold then yeah okay you can use the manifold boost because the turbo is literally aimed right into the manifold you're not gonna have a big pressure drop okay so what's the three port do the three port very simply is at this time if we're at zero percent duty cycle that means that the holley has an output that is commanding a set duty cycle based on whatever parameter you want to set up and we can talk about that stuff in probably a later video that's more on the the ecu side at a zero percent duty cycle the source is blocked and the output convent the way that this gets plumbed is you t into the reference line to feed the source and then you come from the output to the dome now what this does is then at zero percent that means that the dome is effectively been into atmosphere and you're effectively making wastegate pressure at zero percent duty cycle let's change this to fifty percent all right so now at 50 that means that half the time and this is we're talking in terms of frequency half the time the source pressure is going to the output and half the time it's going to the vent so what does that mean for us if the source is half the time going to the output that means that half of whatever is in the reference line roughly is going to the dome and this is kind of a moving target and you'll you'll find that it'll settle but if we've got 10 psi in the reference line and let's say let's put our wastegate spring in here let's say we've got a 10 pound spring then that means that we're cracking the wastegate right now right we're opening up if i'm making 10 psi and i go ahead and half of that 10 now becomes 15 psi on top excuse me that's a 10 pound spring and we're gonna add five psi on top psi okay now we effectively have roughly 15 pounds of force working on the diaphragm it holds the wastegate shut we make a little more boost because of that this turns the 10 psi reference into let's say it's going to become 15. now we get half of 15 this becomes 17 you would think that it would run away it doesn't it's going to find a spot that it's going to settle and this is still gonna open so effectively what you're trying to do is command the duty cycle on the solenoid that you want to make that amount of boost that it makes for any given duty cycle and that duty cycle can be a random number really because what what we're doing is creating a sum total of what the spring is doing and what your boost pressure is doing to the dome minus the reference minus the back pressure so where we're really going with this is whether it's open loop whether it's closed loop you got to actually work on your setup and figure out what a given duty cycle is going to make the the biggest thing to remember here too is your only the minimum amount of boost that you can make is whatever you would make on wastegate so if you want to know what the minimum is what i always do is say what what spring have you got in it or how much does it make on gate only and then i'll know right out of the gate when i start commanding a set boost i've got to start my table for the the solenoid at least above that there's no way that i can make any less than in this case 10 pounds of boost uh the other thing you need to know about the the wastegate solenoid or the the mac valve whatever you want to call it the way that this system works this is kind of getting into our ecu but you need to understand this the way pwm works is it pulses it pulses the ground so at 50 percent that means that we have an equal amount of on time to off time this would be a 50 square wave and the frequency that you set often for these mac valves that's somewhere between 50 and 40 hertz that means that it's going to cycle that many times per second if you turn it up too high the valve won't ever move and if you turn it down too low it'll be very coarse and a lot of times the valve still won't move the next thing is let's say we've got let's say we got 75 we got 75 all right so now we gotta adjust our square wave right so we're on for three quarters of the time and we're off for a quarter so we're on for three quarters off for a quarter on for three quarters off for a quarter what that amounts to is not always 75 or three quarters of whatever your your reference pressure is going to be and the reason that is is mainly because there's actually a mechanical device in here there's a there's a pintle that has to actually move based on the electrical current that you send through a coil that acts like a magnet it is a magnet and will move the pencil if you get over about 80 percent and you get under uh about 20 that's basically the same thing as all the way on and all the way off so most of your resolution is going to occur between 20 and 80 and it's probably going to be the best around 50. you just got to know that going in it might be a deal where at 80 percent you command um you know you're trying to get 20 pounds of boost and if you command 100 you still get 20 and a half pounds of boost that just means it doesn't mean that 80 is not doing its job it means that all the way on is going to be 20 and a half pounds of boost there's nothing more you can do about that at that point the only thing that you can do is switch to a larger spring where your your minimum boost is now going to be higher you're going to shift the whole curve up or you can go to a four port which leads to the next video

Channel: Green Shorts Performance

Views: 560

Rating: 5 out of 5

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Id: IinhKVNUcQU

Length: 11min 15sec (675 seconds)

Published: Mon Oct 26 2020