Could you just put a pipe plug in the turbo instead of a boost elbow? Doesn't the amount of fuel you put to the engine limit the boost?

 

Boost elbow still keeps the wastegate functional via a controlled boost leak. If you don't have enough fuel to get it to open the wastegate, then a pip plug in the compressor housing would be just the same. I ran my 12v like that until I put an S300 turbo on it. Worked well enough for me.

 

I really don't like the idea of disabling the waste gate. You WANT it to open once it hits choke point. There is nothing to gain from disabling it. Once you hit choke point at the exhaust fan, the excess exhaust is let through. Without this happening, the exhaust backs up, egt's climb, and boost climbs as the exhaust backs up pressure into the intake.

Fuel limits the boost POTENTIAL. If you deliver enough fuel to need more than the boost elbow mod allows, you NEED a bigger turbo anyhow.

It is a safety device that some turbos do not have, but there is NO benefit to fully disabling it. If it's a hx35, you can simply unbolt the actuator and rotate it to adjust the boost. (cut the hose and put a new one on)

 

i had mine plugged and wasn't watching my gauges after a fuelling box upgrade . . . this resulted in wrecking my stock turbo . . . prior to adding the fuel box i was golden though . . .

 

A few different opinions here.
As long as your fueling doesn't allow you to exceed the stock turbos efficiency limit of about 35 psi very often it makes no difference if you plug the wastegate or use a boost elbow.
Don't just plug it if you don't have a boost gauge though.

 

Boost doesn't increase because back pressure 'backs up' into the intake. Its because the turbine is driven harder, creating more boost. Unless you have a cam with more overlap, there won't be that much exhaust gas getting into the intake.

Your thrust bearing was hooped in your's. That indicates surge or bark, which is what autos like to do, as you well know. Only affect the fueling box would have on that was you were at a higher boost pressure when it barks.

 

Sorry tate, but you are half wrong. When choke point is reached, the drive pressure gets backed up, the boost cannot pass freely through the engine, and the boost climbs, without benefit. Better to let the excess exhaust sneak past the wastegate. The boost pressure will go down, but in reality you are flowing more air. It's just not getting backed up because of an exhaust obstruction.

Don't get me wrong, below about 400hp it's probably pretty hard to overspool anyhow. But there really aren't any benefits to disabling the wastegate other than it being an easy way to get the turbo to deliver more boost. Which can usually be done by modifying the wastegate instead. Which since the exhaust won't choke it up actually makes it safer for the engine AND turbo.

Not sure on this detail, but I *think* the gate also helps prevent high spool bark by smoothing out and limiting compressor surge.

 

This is only partially true. The 35 psi rating on the hx35 is based on a functioning waste gate. With the waste gate disabled, you must derate that down from 35, since at 35 psi boost with a functioning WG it is already well past cracking pressure, and at 35psi the turbo is letting *excess* drive pressure past the gate.

The limiting factor for the hx35 is choke point. Disabling the WG negatively effects choke point.

Please take no offense, folks. Just trying to present good information, and this is how I understand the system to work.

 

This is incorrect^^

Boost never passes 'freely' through the engine. These engines have very little overlap in their cams. So most of the time, the boost pressure and drive pressure never see each other.

Tate's understanding is correct. When the power stroke completes and the exhaust valve opens, you have gas pressure in a conduit from the top of the piston to the turbine. This causes a huge spike in pumping loss because the piston has to work so hard to pump out exhaust into a saturated conduit. Saturated conduit means the flow is trying to go supersonic in the turbine housing.

Only for that fleeting moment when the valves are both open (overlap) does the high drive pressure want to cause reversion. But the exhaust valve quickly closes, and the boost pressure is pulled into the cylinder by the piston going down the bore. So boost is not "backing up" by any means. If anything, you'll get a little cylinder jumping where a tiny bit of exhaust reversion from one cylinder ends up getting sucked into a neighboring cylinder (or more likely, the one just in front of it in firing order because that cylinder is sucking on the intake manifold at the instant when the other one is reverting).

When the flow in the turbine housing tries to go supersonic, you will hear it. The turbine will growl loudly and the engine will act *very* unhappy. This is pretty bad on turbines as the shaft stress goes ballistic and radically accelerates fatigue.

Depending on fueling, there's no harm at all in plugging the wastegate port. The main risk to plugging the wg is overspeeding at high altitude. One could easily look at the boost guage and see 32 or 34psi and think they're OK, but at high altitude, that might be shaft speed that would make 45psi or more at sea level. Again, turbine fatigue is the main issue.

If I haven't explained this well, let me know and I'll try a better post.

JH

 

Now this is getting irritating. If you don't understand the concept, that a bummer.

As the drive pressure ahead of the turbo exhaust fan climbs, it limits the amount of exhaust the piston can push out during the exhaust stroke. These gasses remain in the cylinder after the exhaust valve closes, and this pressure acts as a restriction when the intake valve opens to be exposed to the boost air. This effectively backs the pressure from the exhaust all the way back to the turbo compressor wheel.

It doesn't make gasses travel backwards, it backs up pressure.

I am not wrong on this. Choke point limits potential flow of a turbo, and disabling the wastegate instead of adjusting it to it's maximum practical flow is an inferior mod.

As to boost passing freely, I'm assuming that anyone in this discussing this understands the BASIC concepts of a four cycle engine, and casts this flow in proper context. Only a clown who doesn't understand a 4 stroke would think that was what I meant. IE, Hohn, I think you know that's not what I meant.

If you can't understand that an obstruction in a pipe builds up pressure behind it without actually having gasses flow backwards, I can't help you.

edit: I take that back maybe I can. Let me explain WHY the turbo is set up so that choke point is an issue.

A smaller exhaust fan makes the turbo perform better at lower volumetric displacement. A larger, less restrictive exhaust fan has trouble winding up the compressor wheel at lower flow levels. Unfortunately, the smaller fan/port doesn't flow exhaust well at higher volumes.

The waste gate is a "fix" for this issue. It allows you to have your cake and eat it too. Have your cake by having adequate boost delivery at lower exhaust volumes (small fan port), but eat it too by still have adequate exhaust flow at higher volumes by letting the excess drive pressure (between exhaust valves and exhaust fan) escape.

IF your engine is not displacing enough to reach the initial pre choke flow, wastegate disabling is not an issue. But reaching this level is pretty easy.

 

The volume remaining in the cylinder after the exhaust valve closes and intake cracks open is equal to the compression volume, which is roughly 3.5 CID. So you have this very small volume, that could be at 80 psi if you're driving that poor HX hard. Now boost pressure would likely be in the 45 psi range, as would the intercooler, the tubes, airhorn, intake manifold, as well as any cylinder that happens to be open. So take the the volume that is at 45PSIG, and figure out what 3.5 CID of 80PSIG gasses would do to the pressure. If you think it raises it significantly, you need to go back and recalculate your numbers.

The real reason why you usually limit the HX35 to 35 psi is because it is going off the right side of its map into extreme inefficiency. There is generally a line on the compressor map on the right, its known as the choke line. No matter how fast you spin it, once beyond that line, any boost rise you get is because of thermal expansion, as opposed to increased mass flow.

BTW, its a TURBINE, not a fan. There is a very big difference between the two. You'd be slightly more correct calling the compressor wheel a fan.

 

I believe you are wrong that the limit is due to thermal expansion.

It's called adiabatic expansion, and doesn't play in much due to the intercooler. The intercooler is THE reason you can go past 15psi without adiabatic expansion causing "issues".

Choosing semantics about parts we all know we are referring to is a sign of lack of good arguments.

The short answer to this WHOLE THING is that if you block the waste gate, choke issues at higher fueling will back up pressure, and thus flow, which means more exhaust gasses are left in the cylinder. This means more heat left over, but additionally to get to this point obviously you are delivering enough fuel. This means that as you pass this sweet spot, egt's climb DRAMATICALLY as do cylinder pressures and temps.

It's not an issue for the most part of overspooling the turbo, it's an issue of heat.

Sooo... if you run 400hp worth of fueling with a blocked WG on a hx35, your egt's will be iffy at best, where with a functioning waste gate they will be substantially lower due to dumping excess exhaust pressure allowing more air to flow through the engine.

But if anyone reading this silliness has any doubts, it's VERY easy to check for yourself on a hx35. Boost elbow not needed. Simply plug your port, and take a drive and load it up. Watch your egt's, then pull the plug, cut the hose, pull the bolts behind the w/g actuator, rotate the housing to adjust the gate, and put a new hose on. Now take a run and watch your egt's.

My god that description of thermal expansion is ridiculous. If it were true, all turbos would be limited to low numbers, since they would all create the same adiabatic heating at higher boost numbers.

That's so silly I just have to adress the basic science behind it. If you take a gas and compress it, the thermal energy stored in it is the same, but now it occupies less space. Thus it's hotter. Temperature measurements generally are converted to Kelvin to do the math because Kelvin is based on absolute zero, where molecules are not moving at all.

Once you reach about 15 psi, adiabatic heating starts to overcome compression pressure. More pressure still pushes more air, but the heat also is bad for engines. Basically a point of diminishing returns.

Add an intercooler, (technically an "aftercooler") and this heat is dumped to the air ahead of the radiator. This allows you to push MUCH MUCH higher pressures regardless of the turbo-as long as the turbo can flow the volume.

Blocking the WG cuts back the volume the turbo can flow by limiting the exhaust flow.

I have to admit I find this somewhat amusing. You can continue to argue weak and incorrect points, though! And I'll admit that I could use more accurate terminology.

PS The reason I'm willing to spend effort arguing this point, is that my advice may save someone's engine. Other advice here will only save someone's ego. High egt's destroy engines. Well, actually it's cylinder pressures/temps, but those are prohibitively more difficult to monitor.

 

You seem to ignore the whole efficiency islands on a compressor map. If all you have to worry about is adiabatic temp rise, why would running a compressor well off its map be a bad thing? Maybe because it has hit the choke point, and the energy that is being wasted is heating the air further. Good example is single turbo vs. twin turbos. Both are are capable of hitting 60 psi, which one will do it with lower air temps? The turbo thats way off its compressor map, or the two that are running well within their efficiency range?

You still never explained how 3.5 CID of relatively high pressure somehow raises the pressure of the entire intake tract from turbo to adjacent cylinder any appreciable amount.

 

Totalloser's explanation is valid as far as I can tell. I think I wasn't understanding what he was initially saying.

I personally have a ball-and-spring WG actuator regulator on my truck and can dial in anything from "blocked" to stock actuation.

If noted that I get higher EGTs with the wg set to regulate to 32psi or so then if I set it to be basically blocked.

Perhaps I'm not running enough fuel to see the condition that TL is describing? I think I am.

I think it's more likely that I'm not observing under the right conditions, as I'm generally not towing. This means I run out of time to observe the guages because I'm hitting 90-100mph just when things are getting interesting.

I might need to go make some trial runs.

 

The problem with Total Loser's "fix" for the wastegate is that when you adjust the rod shorter to put more pre-load on the internal spring, you shorten the available movement of the actuator.

For example, the actuator has about 1" of stroke. This translates to moving the internal wastegate puck 90* open.

If you shorten the rod 1/2" and then reconnect, you've used up 1/2" of the actuator's throw or stroke so no the wastegate puck can only open 45*.

I've tested shortening the rod quite a bit and fully tightened with just 1/8" left of wastegate movement, the wastegate starts to crack open at just 30 psi.

In short, it is possible to raise the wastegate opening pressure a few psi (24-25 cracking pressure) without severely shortening the rod and limiting wastegate opening angle.

It is not possible set the wastegate in the 35-40 psi without a boost elbow or some sort of air regulator.


As far as air mass flow of a turbo, in general, mass flow will increase as the turbo is spun faster and faster up until mechanical failure of the shaft or compressor wheel itself. The upper choke line on the compressor map is roughly equal to the point where air molecules are moving at super sonic speeds and therefore efficiency drops extremely fast due to turbulence.

A 56mm turbo spinning at 120,000 rpm has a leading edge speed of roughly 787 MPH, which means most of the compressor inducer is moving slower than the speed of sound. Also take note that, most compressor maps for turbos of this size stop very close to 120,000 rpm.