Wastegated VGT
- Thread starter x MadMAX DIESEL
- Start date
We do it and machine the turbine housing and so that the gate can be bolted right to the side of the housing or an adaptor pipe and you can remote mount the gate if needed. Mainly used in twin turbo setups. Can post a picture Monday for ya.
The only reason I see to gate a stock VGT besides in a twin application would be if you were spraying the piss out of it. Nitrous is boost in a bottle, so little turbo a lotta fuel=smoke and high drive pressure. Little turbo+a lotta fuel+external gate+nitrous=powa lol
I dunno about gating a stock one, but from my understanding keeping the drive pressure and boost as close to a 1:1 ratio as possible is a good thing. Honestly the only reason I'm looking to do it. And mine's a 4094. Didn't think about the nitrous though. Could be fun down the road. 
If I was to do it over. For a street truck. I woulda kept the stock turbo and ran a max effort tune, then a externally gated stock turbo and nitrous with a kill tune for fun.
If I was to do it over again. I would buy a zf truck and put a second cp3 on it with a big single and spray the piss out of it
About $200 to do it and you would have to be close to 2:1 drive vs. boost to really see a gain from it. We use a 38mm Turbonetics wastegate.
Gonna bump this one back up. Closest thing to the topic my question is about. Bear with me my brain is fried from reading about 20 threads before this one lol
So my initial question was drive pressure with VGT vs fixed. From what I’ve read, VGT creates excessive drive pressure because of the instant spool. So in theory, a fixed vane charger of th same mm could keep a stock engine together longer. Correct? But this can of course be negated with tuning for starters or if you really want to get deep a wastegate setup.
Basically my thoughts are this. I love the idea of a big single. But as a DD, I don’t love the idea of a laggy smoky pig up till a certain rpm while laying into it. Marks 72mm VGT is the biggest I’ve seen. I don’t want instant spool from a charger that big. So to wrap this up, could the VGT be tuned to help keep smoke down while spooling by bumping up the boost pressure a bit to burn the fuel more efficiently, while still keeping drive pressures at a reasonable ratio, and performing like a very efficiently setup fixed vane big single?
I hope this makes sense because my head hurts typing it. If not, I’ll take my slap on the wrist and read more.
So my initial question was drive pressure with VGT vs fixed. From what I’ve read, VGT creates excessive drive pressure because of the instant spool. So in theory, a fixed vane charger of th same mm could keep a stock engine together longer. Correct? But this can of course be negated with tuning for starters or if you really want to get deep a wastegate setup.
Basically my thoughts are this. I love the idea of a big single. But as a DD, I don’t love the idea of a laggy smoky pig up till a certain rpm while laying into it. Marks 72mm VGT is the biggest I’ve seen. I don’t want instant spool from a charger that big. So to wrap this up, could the VGT be tuned to help keep smoke down while spooling by bumping up the boost pressure a bit to burn the fuel more efficiently, while still keeping drive pressures at a reasonable ratio, and performing like a very efficiently setup fixed vane big single?
I hope this makes sense because my head hurts typing it. If not, I’ll take my slap on the wrist and read more.
Yes your question makes sense bud! The problem with this discussion as always is everyone focuses on drive pressure without know the big picture. Everyone wigs out about drive pressure but it isn't the big picture item but helps to create it. Cylinder pressure is the culprit at the end of the day. I'll use simple math to make it easier to understand for everyone. So say you are producing 50psi and 100psi drive pressure which is a 2:1 DRIVE TO BOOST RATIO. A lot of people will freak out about this but it actually isn't that bad a deal because turbos prefer a positive drive to boost ratio. My personal preference is to keep it in the 1.2-2:1 range for best charger life. Reason being is if you are 1:1 or better then your turbo will not last very long at all because of the sever unloading when you let off will chew the thrust bearings right out of it quickly(turbo bark is the name of this action). So say you have a 100psi drive pressure
eek: Oh my, your world is about to end!) but it is a small piece of this puzzle and you have to take the other pieces into the equation before freaking out. Stock motor is capable of up to 3000psi cylinder pressure before shit goes south quickly. A good stock motor makes 400psi cylinder pressure just rolling it over without injecting any fuel... At idle they average 600-800psi... You starting to see where I am going with this now. The main reason why the common statement that vgt's hurt motors more than big singles isn't the drive pressure but the ability to produce torque quickly. Torque and cylinder pressure go hand in hand but not horsepower. Rpm is your friend in the cylinder pressure battle as it becomes more difficult to produce the cylinder pressure as the motor spins faster and is the reason why your torque peaks at a lower rpm and falls off while the rpms increase. I have already proven a couple of years back that you can take a stock motor and throw big fuel and a single vgt(I used a junkyard LMM motor with my 250%inj and 12mmcp3 and 68stg2R in White Lightning) and make right at 800hp and ran low 11's without hurting it because I cylinder pressure tuned it to keep torque at a certain level and increased the hp as the rpms increased. If I would have had twins or triples I think I could have gotten a lot closer to the 1000hp mark without shit falling out of it because I could have made more rpm hp but would have needed valvetrain upgrades to handle the boost and rpms. So, back to the pressure stuff in your question. Drive pressure is a necessary evil when talking about drivability because it helps produce torque and helps keep them cleaner burning. Tuning plays the largest role in all of it. You can take a truck that is a smoky laggy pig and won't produce any torque and never hurt itself and change the setup around to light up faster and all the sudden shit is laying on the ground because you now are burning the fuel more efficiently and producing cylinder pressure. Hope this makes sense. Here is another example of it. You take a stock twin turbo truck that produces 500-550hp and egt's never go over 1200degrees yet the rods are bent and half the pistons are cracked. Customer doesn't understand how this happened since it never got hot on the egt gauge and the tuner said it was a safe 500hp tune. You take this same setup on the dyno and pull a run in 4th gr and it barely makes 40-45psi boost and hits 540hp 1150ftlbs which is technically safe... They you think to yourself...wait it makes closer to 60psi on the street when it grabs gears and keeps it up there... So you take this same setup and run it in 5th gr fully loaded up and get it to make 58psi boost and now you dyno numbers are 600hp 1400ftlbs and bingo you now know why it failed. With the extra load and boost your cylinder pressure jumped 1000psi from the safe pull and your shit is now broken. I sure hope this makes sense but it isn't the easiest thing to explain and there is a ton more info that goes along with this but I tried to keep it as basic as possible but get the points across.
Mark can you start a diary thread on everything you know about the duramax?
You have definitely forgotten more then a lot of us will properly ever know lol
Back on topic
How would a waste gate affect the turbo braking?
And how much does cylinder pressure increase when using that feature?
You have definitely forgotten more then a lot of us will properly ever know lol
Back on topic
How would a waste gate affect the turbo braking?
And how much does cylinder pressure increase when using that feature?
Mark you are the freaking man. I was praying you’d be the one to respond. Everything you said makes perfect sense. I know drive pressure is necessary and I’ve read your threads about the 1:2-2:1 ratio is golden. So that’s obviously where the VGT comes in. VGT can produce gobs of torque with a large turbine at lower rpms. This means boom. Switch to big single. Can’t spool as good which means less torque at lower rpms which means stays together. So. I think what I was trying to get out last night was this. Let’s say I have 2 tunes for a VGT. Your 72mm in particular. One tune, can it be tuned to drive closer to stock with less power let’s say around the 450-500 range and keep the engine together because you’re not making ridiculious power and torque at lower rpms. Then tune 2 be tuned to behave like a big single but use the vanes to aid in spooling to keep smoke down. Not instant power, but just not a smoky pig till the charger lights. So basically. Best of both worlds.
I definitely have days where I feel like this is the case lol. A wastegate would make the turbo brake not very good at all because the spring seat pressure is most likely not enough for the drive you can create depending on the vane size(LML, LMM, LBZ, LLy, 4094 in order of effectiveness of the braking feature). Cylinder pressure isn't really affected as much as you think it would be. I can tell you that if you have a big twin/triple setup making 60psi boost at 3500rpms and you can see upwards of 2000psi cylinder pressure from the amount of air being pumped in and the temp of it mixed with the static compression ratio. If I was to put a number on it I would think it wouldn't be more than a couple hundred psi increase at max. Rarely do you see over 10psi on the boost gauge so the increase isn't going to be a bunch because the egt's also drop super fast in turbo brake mode so cylinder temp is also dropping and in turn the pressure is dropping even though you are seeing pressure on the boost gauge. This also brings back the whole reason for diving into the cylinder pressure based tuning because I have seen it a bunch that what you think is right isn't always the case. Being able to see what is actually happening in the cylinder is beyond useful info but also not cheap unfortunately. At the end of the day the goal is to produce as much power as possible with the least amount of cylinder pressure.
Lol, I don't know about all that but I've been at it a very long time. To answer your question, it all comes down to how much fuel you throw at it and when you do it. The Rpm range that you work in also has a huge affect on this too. Most S400 trucks don't make peak torque until 2500+rpm range where a strong single vgt can do this at the 1500-1900rpm range. That's where knowing what the pressure is matters. You really don't have to worry about this til you get up past the 500hp range unless the tuning is just stupid aggressive. Hope this helps.
So as far as a daily driver goes that’s also a weekend warrior, what would better suit me to keep a stock motor in tact with let’s say... 10mm pump and 100 overs? S472-76 or your 72mm VGT?
Both will have no problem destroying a stock motor it ran hard enough! Honestly comes down to tuning and setup. The S472 has the ability to make more peak hp since it has a much larger turbine and flow capacity and will produce more boost pressure when pushed hard. The VGT will drive circles around it on the street for daily driving but the S472 will shine in the 5% of the time that you run it wide open. I honestly don't like to run the 72mm VGT as a single since I designed it for compound applications where guys want a 1200++Hp daily drivable truck. I have guys that do run them as singles but it isn't my preference. I would run an S468 on a stock motor long before I would run the 472. In the end it comes down to what you like personally. I've run S400's on my truck and I always end up back with the vgt cause I hate the lag of big singles but that is just me.
Definitely some good info to think about mark. Decisions decisions. It’d be nice to be able to drive a truck with both setups to see what a man would prefer lol
I wonder if there is a way to adjust a waste gate to follow RPMs , where if you were running the 72mm vgt at lower RPMs where drive pressure is more of a concern , it would release pressure and gradually as RPMs rise the gate would follow to be fully closed at say 2500 RPMs to make use of the larger vgt top end , Or just stick with a 68 stg2r and be happy ?