highest boost with stock turbo?
09-05-2007, 03:08 AM
#47
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OK, well I'll try to redeem myself.
If we want to build a truck like AlpineRam describes--one that has instantaneous response for squirting into that next lane or a quick pass on a mountain road-- then let's think about how we're going to go about this.
The first thing we have to do is define the outcome we want. What speed do what want to have instant response at? Which gear in the trans? What load conditions?
I can only speak for my truck. For mountain road driving, I find myself in 4th gear and 5th gear at speeds from 25-40mph. Often, I'm climbing in elevation and the air is getting thinner. Under these conditions, the stock HX35 I'm running works quite well. The limitation I encounter is the power support. The spoolup is good enough, but once I get past 30psi, the truck is huffing for air and just needs more.
So making twins out of the stock charger makes sense. We want what we already have, just more, right?
Well, we can't just get more of the same. Using the stock charger in twins will give us something that's not quite the same just a "better stock turbo". We'll give up some spool, and we're not really wanting to do that. Remember, we're sacrificing peak HP support to gain response.
So we go smaller. In Garrettland, we're typically looking at a Gt37 size turbo for a CTD. But we're gonna go all the way down to a GT3576. Truth be told, though, it's actually pretty close to the stock turbo- 54.8mm inducer, 76mm exducer, and 68mm turbine wheel. We'll choose the 1.05 A/R housing if we pick this, but honestly an HY35 is probably a better choice. We'll have to pair it with a huge external gate because this little guy won't stay in the game too long.
For a "big turbo", I'd suggest a Garrett GT4094. With a flow of up to 80lb/min this thing is a reasonable choice for up to 500hp and maybe more than that. We could go with a 4294, but this smaller hotside will spool faster than the 4294.
These are pretty small twins, as far as twins go, but they will spool in a blink and should support 450hp or so pretty cleanly.
There you go, Alpine-- let me know when you hit the lotto and have nothing better to do than experiment with my ideas and swap turbos around all day
If we want to build a truck like AlpineRam describes--one that has instantaneous response for squirting into that next lane or a quick pass on a mountain road-- then let's think about how we're going to go about this.
The first thing we have to do is define the outcome we want. What speed do what want to have instant response at? Which gear in the trans? What load conditions?
I can only speak for my truck. For mountain road driving, I find myself in 4th gear and 5th gear at speeds from 25-40mph. Often, I'm climbing in elevation and the air is getting thinner. Under these conditions, the stock HX35 I'm running works quite well. The limitation I encounter is the power support. The spoolup is good enough, but once I get past 30psi, the truck is huffing for air and just needs more.
So making twins out of the stock charger makes sense. We want what we already have, just more, right?
Well, we can't just get more of the same. Using the stock charger in twins will give us something that's not quite the same just a "better stock turbo". We'll give up some spool, and we're not really wanting to do that. Remember, we're sacrificing peak HP support to gain response.
So we go smaller. In Garrettland, we're typically looking at a Gt37 size turbo for a CTD. But we're gonna go all the way down to a GT3576. Truth be told, though, it's actually pretty close to the stock turbo- 54.8mm inducer, 76mm exducer, and 68mm turbine wheel. We'll choose the 1.05 A/R housing if we pick this, but honestly an HY35 is probably a better choice. We'll have to pair it with a huge external gate because this little guy won't stay in the game too long.
For a "big turbo", I'd suggest a Garrett GT4094. With a flow of up to 80lb/min this thing is a reasonable choice for up to 500hp and maybe more than that. We could go with a 4294, but this smaller hotside will spool faster than the 4294.
These are pretty small twins, as far as twins go, but they will spool in a blink and should support 450hp or so pretty cleanly.
There you go, Alpine-- let me know when you hit the lotto and have nothing better to do than experiment with my ideas and swap turbos around all day
09-05-2007, 11:12 AM
#48
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Alpine, I'm with you. I think we are like-minded in what we want twins to do.
Perhaps we should consider the twins thing in three phases:
1) Low rpm. (say 1500). Here's we want to have enough drive pressure to where the small turbo is already making some kind of positive pressure. As long as it is making SOME boost, we will have dramatically improved response over none at all.
2) Medium rpm (say 2000). Here we want to have instantaneous response available, We also need compounding because the PR is going to be be very high. We wa
3) High RPM (2500+). Now, we don't need as much compounding because the RPMs have risen enough to move the air we need without cramming. Hence, we don't need as much "compounding" effect. For example, we can make 450hp at 2000rpm with a PR of 4.5, but it only takes a PR of 4.4 to make 550hp at 2700 rpm. The RPM helps alleviate the need for more PR.
So what we can do is think of this now in terms of turbo workload. Phase 1 is basically all small turbo. Phase 2 is both, and phase 3 is mostly large turbo.
We'll have to manipulate turbo workload via wastegating. Because on the top end we'll be bypassing a LOT of flow, we'll need a huge gate-- like a 60mm Tial or a t-netics NewGen HP or such. We need a wastegate that has two pressure references so it will "see" a pressure differential, not just compare a pressure signal to atmospheric pressure.
We do this because we don't just want the WG to pop at 25psi or so. What we REALLY want is for it to pop when the top turbo is making 25psi MORE THAN it's receiving from the big turbo. So we need two boost references- the crosstube and secondary compressor discharge.
This allows us to shift proportionally more and more workload to the big turbo as total boost pressures rise. This relieves a lot of the restriction a small turbo would pose because we can bypass more gas.
For example, just before the wg pops, the top charger is operating at a PR of ~2.7-- it's taking in 14.7psia and spitting out air at 39.7psia.
But at high boost levels, the proportional PR the small turbo is making drops. Let's say that the big charger is feeding it with a PR of 4:1-- or about 44psig boost. Now when our top charger adds its 25psig, we have 69psig boost-- but the PR of the top charger has fallen because it's "multiplying" 58.7psia to make 83.7psia-- which is a PR of only ~1.4.
The trick is finding a way to configure the WG to only see the pressure differential-- and I'm not sure how to do this. I don't know how most externals work. I'm under the impression that there's a nut on top that adjusts spring preload, and then there's also some kind of pressure signal. The wastegate we'd need to do this would have two pressure ports-- one on either side of the WG diaphragm. So we just drop in a 20psi spring or so, connect the "spring opposed" side to the secondary boost signal, and connect the "spring aided" side to the crosstube.
Finally, we'd need a wastegate on the big charger. This would be much simpler, since we could just set it up to pop at whatever PR we want from the primary (say 4:1), and dump the gases into a blowdown tube-- no need to plumb it back into the exhaust, imo. After all, the wg on the primary would only be open for very brief moments.
Anyone know of a wastegate that has the "dual boost" references that I mentioned? Do we think a dumb wastegate is fine if you use a smart boost controller to it's lone boost port?
IMO- the wastegate tuning is a pivotal element of getting twins to function right-- second only to turbo and housing selection.
JMO
Perhaps we should consider the twins thing in three phases:
1) Low rpm. (say 1500). Here's we want to have enough drive pressure to where the small turbo is already making some kind of positive pressure. As long as it is making SOME boost, we will have dramatically improved response over none at all.
2) Medium rpm (say 2000). Here we want to have instantaneous response available, We also need compounding because the PR is going to be be very high. We wa
3) High RPM (2500+). Now, we don't need as much compounding because the RPMs have risen enough to move the air we need without cramming. Hence, we don't need as much "compounding" effect. For example, we can make 450hp at 2000rpm with a PR of 4.5, but it only takes a PR of 4.4 to make 550hp at 2700 rpm. The RPM helps alleviate the need for more PR.
So what we can do is think of this now in terms of turbo workload. Phase 1 is basically all small turbo. Phase 2 is both, and phase 3 is mostly large turbo.
We'll have to manipulate turbo workload via wastegating. Because on the top end we'll be bypassing a LOT of flow, we'll need a huge gate-- like a 60mm Tial or a t-netics NewGen HP or such. We need a wastegate that has two pressure references so it will "see" a pressure differential, not just compare a pressure signal to atmospheric pressure.
We do this because we don't just want the WG to pop at 25psi or so. What we REALLY want is for it to pop when the top turbo is making 25psi MORE THAN it's receiving from the big turbo. So we need two boost references- the crosstube and secondary compressor discharge.
This allows us to shift proportionally more and more workload to the big turbo as total boost pressures rise. This relieves a lot of the restriction a small turbo would pose because we can bypass more gas.
For example, just before the wg pops, the top charger is operating at a PR of ~2.7-- it's taking in 14.7psia and spitting out air at 39.7psia.
But at high boost levels, the proportional PR the small turbo is making drops. Let's say that the big charger is feeding it with a PR of 4:1-- or about 44psig boost. Now when our top charger adds its 25psig, we have 69psig boost-- but the PR of the top charger has fallen because it's "multiplying" 58.7psia to make 83.7psia-- which is a PR of only ~1.4.
The trick is finding a way to configure the WG to only see the pressure differential-- and I'm not sure how to do this. I don't know how most externals work. I'm under the impression that there's a nut on top that adjusts spring preload, and then there's also some kind of pressure signal. The wastegate we'd need to do this would have two pressure ports-- one on either side of the WG diaphragm. So we just drop in a 20psi spring or so, connect the "spring opposed" side to the secondary boost signal, and connect the "spring aided" side to the crosstube.
Finally, we'd need a wastegate on the big charger. This would be much simpler, since we could just set it up to pop at whatever PR we want from the primary (say 4:1), and dump the gases into a blowdown tube-- no need to plumb it back into the exhaust, imo. After all, the wg on the primary would only be open for very brief moments.
Anyone know of a wastegate that has the "dual boost" references that I mentioned? Do we think a dumb wastegate is fine if you use a smart boost controller to it's lone boost port?
IMO- the wastegate tuning is a pivotal element of getting twins to function right-- second only to turbo and housing selection.
JMO
Joe
09-05-2007, 07:20 PM
#51
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This is really interesting reading,I only understood about half of what I've read. I'm coming back later to read again. You all have given me an ice cream headache. Keep it up I'm learning tons....
09-05-2007, 10:23 PM
#52
Registered User
OK, well I'll try to redeem myself.
If we want to build a truck like AlpineRam describes--one that has instantaneous response for squirting into that next lane or a quick pass on a mountain road-- then let's think about how we're going to go about this.
The first thing we have to do is define the outcome we want. What speed do what want to have instant response at? Which gear in the trans? What load conditions?
I can only speak for my truck. For mountain road driving, I find myself in 4th gear and 5th gear at speeds from 25-40mph. Often, I'm climbing in elevation and the air is getting thinner. Under these conditions, the stock HX35 I'm running works quite well. The limitation I encounter is the power support. The spoolup is good enough, but once I get past 30psi, the truck is huffing for air and just needs more.
So making twins out of the stock charger makes sense. We want what we already have, just more, right?
Well, we can't just get more of the same. Using the stock charger in twins will give us something that's not quite the same just a "better stock turbo". We'll give up some spool, and we're not really wanting to do that. Remember, we're sacrificing peak HP support to gain response.
So we go smaller. In Garrettland, we're typically looking at a Gt37 size turbo for a CTD. But we're gonna go all the way down to a GT3576. Truth be told, though, it's actually pretty close to the stock turbo- 54.8mm inducer, 76mm exducer, and 68mm turbine wheel. We'll choose the 1.05 A/R housing if we pick this, but honestly an HY35 is probably a better choice. We'll have to pair it with a huge external gate because this little guy won't stay in the game too long.
For a "big turbo", I'd suggest a Garrett GT4094. With a flow of up to 80lb/min this thing is a reasonable choice for up to 500hp and maybe more than that. We could go with a 4294, but this smaller hotside will spool faster than the 4294.
These are pretty small twins, as far as twins go, but they will spool in a blink and should support 450hp or so pretty cleanly.
There you go, Alpine-- let me know when you hit the lotto and have nothing better to do than experiment with my ideas and swap turbos around all day
If we want to build a truck like AlpineRam describes--one that has instantaneous response for squirting into that next lane or a quick pass on a mountain road-- then let's think about how we're going to go about this.
The first thing we have to do is define the outcome we want. What speed do what want to have instant response at? Which gear in the trans? What load conditions?
I can only speak for my truck. For mountain road driving, I find myself in 4th gear and 5th gear at speeds from 25-40mph. Often, I'm climbing in elevation and the air is getting thinner. Under these conditions, the stock HX35 I'm running works quite well. The limitation I encounter is the power support. The spoolup is good enough, but once I get past 30psi, the truck is huffing for air and just needs more.
So making twins out of the stock charger makes sense. We want what we already have, just more, right?
Well, we can't just get more of the same. Using the stock charger in twins will give us something that's not quite the same just a "better stock turbo". We'll give up some spool, and we're not really wanting to do that. Remember, we're sacrificing peak HP support to gain response.
So we go smaller. In Garrettland, we're typically looking at a Gt37 size turbo for a CTD. But we're gonna go all the way down to a GT3576. Truth be told, though, it's actually pretty close to the stock turbo- 54.8mm inducer, 76mm exducer, and 68mm turbine wheel. We'll choose the 1.05 A/R housing if we pick this, but honestly an HY35 is probably a better choice. We'll have to pair it with a huge external gate because this little guy won't stay in the game too long.
For a "big turbo", I'd suggest a Garrett GT4094. With a flow of up to 80lb/min this thing is a reasonable choice for up to 500hp and maybe more than that. We could go with a 4294, but this smaller hotside will spool faster than the 4294.
These are pretty small twins, as far as twins go, but they will spool in a blink and should support 450hp or so pretty cleanly.
There you go, Alpine-- let me know when you hit the lotto and have nothing better to do than experiment with my ideas and swap turbos around all day
I was thinking about using an exhaust brake flapper as the "wastegate" for the secondary- a y connection from the manyfold, one side going to the secondary, the other side going straight to the next "y"- where the exhaust from the secondary and the "direct exhaust" meet in the turbine of the primary.
This should allow us to use some non-wastegated secondary (which I'd like because they are usually a bit more efficient, and the internal wastegates of small chargers are much too small for what we want in compounds)
This should also give quite undisturbed flow to the primary. And a much bigger effective area than an external wastegate.
Naturally I'd like to build that set.. but can't afford it at the moment.
Hohn, let's make a twin turbo lotto fund- everybody who contributes the slip with a major win on it will get a scale drawing of the turbo piping etc to build his own without much experimenting around ?
AlpineRAM
09-06-2007, 12:15 AM
#53
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Interesting idea on brake flapper. It might work, but heat loss with any twins setup is a huge consideration, and coatings can only take you so far. Still an interesting idea. In this situation, you'd basically be using parallel turbos, not so much compounds.
I think an external gate will be more effective than than the flapper, and with a largish gate (44 or 60mm) you'll have plenty of flow. From what I can tell, a 60mm gate will flow very well, plenty to feed a larger turbo with a very high bypass ratio. Keep in mind that even if the opening of the 60mm wastegate is smaller than the turbo, it's possible it might flow more if the "effective" area of the turbo is small, as it would be with your fast-spooling top charger.
A 60mm gate is almost the same as a 2.3" diameter pipe, so that's pretty good flow compared to the manifold outlet and the turbine inlet.
One thing I'm really thinking about is how to reduce heat loss in the exhaust flow. On the new Powerstroke Fords they have two turbochargers bolted directly to each other, which I think is genius. It's almost like one unit with two sub-assemblies.
Tial now has available turbine housings for certain Garrett models that use a round V-and inlet instead of the square inlet we're used to seeing. I posted the pic of them in another thread ("Think I found the perfect primary").
So I'm trying to think if there's another way we can package the twins instead of the "normal" way of hanging the big charger underneath with a large 90º elbow. That big elbow loses a lot of heat.
I wonder if we could fit the larger turbo PERPENDICULAR to the small one-- like the exhaust would come out of the secondary and go straight into the round V-band opening of the big charger. You'd have to fab an adapter, but the heat loss would be cut drastically. I don't know if it's possible to package the turbos this way, but I'd like to see if it's possible. You'd have to fab a short spacer to allow the bypassed gases to enter the primary.
Another packaging option would be similar, but involve a short 90 elbow and put the primary side-by-side with the secondary. This would make the wg plumbing much easier.
It might be that the "traditional" arrangement is best, but I'd feel the need to revalidate that assumption. I don't want to just reinvent the wheel for it's own sake, but I'm not inclined to follow the status quo just because "it's always been done that way before."
I'm thiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii s close to getting a TIG and trying my hand and pulling off some twins.
Which is to say, not close at all
I think an external gate will be more effective than than the flapper, and with a largish gate (44 or 60mm) you'll have plenty of flow. From what I can tell, a 60mm gate will flow very well, plenty to feed a larger turbo with a very high bypass ratio. Keep in mind that even if the opening of the 60mm wastegate is smaller than the turbo, it's possible it might flow more if the "effective" area of the turbo is small, as it would be with your fast-spooling top charger.
A 60mm gate is almost the same as a 2.3" diameter pipe, so that's pretty good flow compared to the manifold outlet and the turbine inlet.
One thing I'm really thinking about is how to reduce heat loss in the exhaust flow. On the new Powerstroke Fords they have two turbochargers bolted directly to each other, which I think is genius. It's almost like one unit with two sub-assemblies.
Tial now has available turbine housings for certain Garrett models that use a round V-and inlet instead of the square inlet we're used to seeing. I posted the pic of them in another thread ("Think I found the perfect primary").
So I'm trying to think if there's another way we can package the twins instead of the "normal" way of hanging the big charger underneath with a large 90º elbow. That big elbow loses a lot of heat.
I wonder if we could fit the larger turbo PERPENDICULAR to the small one-- like the exhaust would come out of the secondary and go straight into the round V-band opening of the big charger. You'd have to fab an adapter, but the heat loss would be cut drastically. I don't know if it's possible to package the turbos this way, but I'd like to see if it's possible. You'd have to fab a short spacer to allow the bypassed gases to enter the primary.
Another packaging option would be similar, but involve a short 90 elbow and put the primary side-by-side with the secondary. This would make the wg plumbing much easier.
It might be that the "traditional" arrangement is best, but I'd feel the need to revalidate that assumption. I don't want to just reinvent the wheel for it's own sake, but I'm not inclined to follow the status quo just because "it's always been done that way before."
I'm thiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiii s close to getting a TIG and trying my hand and pulling off some twins.
Which is to say, not close at all
09-10-2007, 07:04 PM
#55
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I have a question for everyone, whats the most boost anybody run on stock inectors in a 24valver regardless of turbo set-up. I put in my stockers just to try out. I got around 40psi and around 1100 deg's egt's at wot. To my suprise there is still smoke even at these boost numbers. No box, no smarty, no smoke and no egt's. Very slow and sluggish. With speed stuff turned on, its ok power, so I kinda wonder if there not stock injectors.
09-10-2007, 07:09 PM
#56
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I never saw more than 26 psi with stock injectors and a blocked WG-- but that's just empty.
I've heard of guys getting 30-32psi with stock injectors and a timing box with a blocked wg, but they were towing heavy uphill.
JMO
I've heard of guys getting 30-32psi with stock injectors and a timing box with a blocked wg, but they were towing heavy uphill.
JMO
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