NoSeeUm

This thread is not dead, at least to me.....

Thanks of the great discussion. Hohn, I will have to re-read your "corrected gas flow" explaination a few times to really get it, but I think maybe the light bulb burns a little brighter for me. I also thinking that a 1:1 TDP/CDP is a bit optomistic. But still, to make sure I understand. You are assuming in your explanation that compressor PR = turbine PR. Is that correct?

This stuck in my head Hohn. A good analogy, but typically a garden hose passes H2O. There is no temperature change in a non-compressable fluid across a nozzle. So given that, I am thinking that I can fairly closely approximate the temperature change for the exhaust gases across the turbines by using the Ideal Gas Laws for air. Do you think this would be accurate enough to be in the ballpark?

I already have a corrected gas flow calculation in my spread sheet for a single turbine as well as all the calculations for single and compound compressors. I would like to work out the exhaust calculation for twins. The waste gate / bypass flow calculations might come after that. But not so useful I would think, as there is very little available published specific data on turbo's in general. The GT series is an exception.

PaulB told me some time ago I needed to start focusing on the exhaust side of things.

Jim

NoSeeUm

Jim
X8
Hohn
At least I typed it in first. Of course no points off for spelling....

Jim

XLR8R

Great discussion - helps everyone to understand better when the conventions are critically viewed... like looking away from an object at night to see it better!

My next blasphemy is to compare compounded turbochargers to 4-BBL carbs when explaining twins' operating characterstics to normal people (which anyone posting in this thread pro'bly isn't! )

Towing twins are analogous to square-bore carbs like Carter or Holley, and big-HP twins (at least the kind I like) are similiar to spread-bores like the QuadraJet... small primaries for efficiency & throttle response, large secondaries for high HP at RPM. My version of twins: smallish secondary for driveability & response, to quickly get the engine up into the range where the large primary works best for max power.

For my next act, I will attempt to compare Hurricane Gustav to the DNC Steering Committee...

HOHN

Jim, I know my hose analogy is a weak one, but the idea that a downstream restriction has upstream effects is all I meant to illustrate.

The compressibility of exhaust in this case means that after a restriction, you will have a loss of pressure and cooler temps.

This loss of pressure is what caused the corrected gas flow to go up after a restriction like the secondary turbine.

Yes, I assume that compressor PR=Turbine PR. Again, while some think this is hopelessly optimistic, I'm of the the mind that it's not only achievable, but anything less indicates something is wrong or improperly matched.

JH

meangreen96

Hey guys, great post. I was wondering if I could get some of basic assumptions you are making like the Volumetric Efficiency, Standard Manifold Temperature, Fuel Consumption, etc...? Thanks, I'm trying to follow along via Garrett's site. I realize I could probably back calculate some things, but you have a lot of good information here. I'm just trying to keep it straight.

- Craig

Mike Holmen

So How close are you too build your set of twins XLR8? Have you landed on a set-up? I'm building a garrett GT-3582R and a K-31 (GT4296), I have them sitting on my bench. Nothing too big but it should one sweet street set-up. I'm thinking mach 6's might even still be ok as lots of guys run them on S300's (ok its a dreamy dream). I'm going the external route as their no internal gate. It might be a waste gate of time but I have most of pieces to build so in a few months. The trick is finding a weekend to burn some metal together. Keep the good discussion going, I'm learning on what I've done wrong by doing and from you guys.

NoSeeUm

This is what I am currently using.

Assumed Parameters
Displacement 5.9 L
HP Engine 735
HP Wheels 650
Drive Line Loss 13 %
BSFC 0.38
AFR 18
IE 65 %
VE 85 %
Air Filter D/P 0.25 psid
IC D/P 2.00 psid
Ambient Temp 85 F
Ambient Press 25.6 Inch Hg
Relative Humidity 25 %

The Manifold Temperature I use is calculated, based upon boost and compressor efficientcy.

Jim

XLR8R

Mike, I am rebuilding a brand new set of MPI twins on a customer's truck - he decided to run with the big dogs after dropping $35K with another diesel shop to go fast (truck got spanked by a gasser Ram during baselining - can't even say it was a dang Hemi )... now we're tearing the truck apart to redo everything properly.

Looks like we'll retain the HTB2 (62/65/13SS) on top, but the S400 may have to go - it's a 74/74 variant, and I'm just not sure it'll give us the lbs/min we need (~ 130-140) even with air/water intercooling. I'll decide after discussing options with Nathan next week.

Everything from the exhaust ports to the downpipe will be massaged & ceramic coated, with an eye towards maximizing available drive HP. The air/water IC will happen if we relocate the battery. We will have plenty of "dyno time" on the G-Tech Pro RR to lean on the motor pretty hard... of course it has to be ready for HRP next month!

HOHN

Oh, and Jim-- I think Ideal gas would be a reasonable approximation of temp change after the turbine. The problem you will enounter is trying run ideal gas calculations on a variable volume element.

That's why I used corrected gas flow, and then I made some temp postulates based on experience of my current turbo. For example, I know that the delta t across my turbine is normally about 200F in daily driving, but I have seen up to almost 400F delta T across the little HX35 at high boost (off the map).

Pushing a little turbo too far will results in much higher delta T across the turbine because the compressor takes a lot more power to drive when it's inefficient, and the increased airflow means the turbine housing poses proportionally a greater restriction, and it will dump more temp as a result.

For daily driving temp, I'd assume TI temp at the primary of 500 on the hwy, and 800 WOT.

NOw back to regularly scheduled programming.


Justin

NoSeeUm

Maybe a little turbine 101 theory?

There are basically two types. The two types are Impulse and Reaction. Each type has a / a set of nozzle(s) and a set of moving blades.

For the reaction type the nozzles are not really nozzles. Their primary purpose is to direct the fluid (actually a gas in our case) stream so that hits the blades at the optimum angle. The blades themselves are nozzles. Think of a jet boat here, where the high velocity fluid going in one direction exerts force in the other direction causing the blade to rotate.

For the impulse type the nozzles purpose is to raise the velocity of the fluid (actually a gas in our case). To do this it converts the gas pressure into gas velocity. The high speed gas then smashes into the turbine blade causing it to rotate. The turbo's that I have seen all use impulse type turbines.

WikiPedia also explains it here.



Lets look only at the impulse type and the little chart at the bottom. This is a classic impulse turbine graph. The nozzle converts pressure into velocity with little energy loss. So notice that there is a pressure drop across the nozzles and no pressure drop across the blades. Also notice the velocity increase across the nozzles and the velocity decrease across the blades. The downward change in the gas velocity through the blades is proportional to how much energy in the form of mechanical work that the turbine is extracting from the gas. And because the velocity increase is proportional to the pressure drop, the pressure drop across the nozzles indirectly corresponds to the mechanical work extracted by the turbine. The pressure drop can be easily measured, the velocity has to be generally computed.

Keep in mind the greater the pressure drop across the nozzle(s) the greater the velocity of the gas coming out of them. The greater the velocity of the gas the more work is extracted by the turbine. This is a good reason so many of us install 4 inch exhaust pipes and get rid of the Dodge OEM turbo outlet elbow. The high pressure stays the same, but because of the less restriction (greater volume of the pipe) the low pressure drops. So the net pressure drop across the nozzle(s) ends up being more. More pressure drop means more work from the turbine.

So now ask yourself, "Where does the temperature drop occur in a turbo?".

The temperature drop essentially mimics the pressure drop line in the chart above. This is because the gas is expanding into a larger volume. As you know any time you expand a gas, the temperature drops. So the gas volume line, would also be increasing at the same time as the decreasing temperature line.

In a single turbo case or the 2nd turbine in twins, the larger volume is the turbine casing and the turbine exhaust piping. Which hopefully is atmospheric pressure. If twins are used then that would include everything downstream from the first turbines nozzle(s) to the second turbines nozzles(s). In that case that would be the 1st turbine casing, the hot pipe and up to the 2nd turbine nozzle(s).

The sizing of the 2nd turbine nozzles, of course, would also have an effect on that pressure in the hot pipe as well. So think of that pressure as a funciton of "the goes in's", "the volume" and the "goes out's".

Jim

NoSeeUm

Thanks, I was going to use pressures spinning off of compressor pressures to calculate the temperatures. From there I think I can get to corrected gas flow. Think that will work?

Jim

Mike Holmen

Which S400 you using? The maps that I have only show that it flow to 98 lbs/min for a 75mm inducer. A 130 lbs/min is one dang big turbo, bigger than a GT47, and would have to loaded hard to push those #'s. Another thought on the liquid to air cooler, just dump NOS into the air tube prior to the secondary. It will cool off the air mixture prior to the secondary. Then use another NOS nozzle at the air horn. In case of doubt just add more NOS. Is the guy have enough fuel? What kinda of gaser engine was it? Let us know what Nathan think's cause he's da twin turbo guy. A twin turbo with a S400 would/should get you into the 800rwhp, on fuel. Just about everyone uses spray anyways at drag/dyno events, unless you do, you aren't gonna win or even come close to winning. Another thought on the dang big turbo a garrett T-88. There cheap and big. They support 1200 HP.

HOHN

Jim, great post. As for pressures "spinning off of compressor pressures", I don't get your meaning.

Mike, if I may..

I'd recommend the NOS nozzle not be put right in the intake. The liquid needs a little time to fully evaporate and absorb maximum heat. You don't want any liquid nitrous to hit the intake horn. I'd shoot in in just after the CAC near the driver's side boot in that pipe.

One thing I think I've learned from this is that "big" isn't nearly as big as I thought. For a regular street driver setup when the primary running at a low pressure, even a GT45 should be doable in a towing twins setup. If you need more power, just go to a larger secondary.

I'm becoming convinced that operating the primary at a low PR is the track to take, and thus even an S480 isn't that big. When running the primary at low PRs, you have to go a step or two bigger on the charger, with the added bonus that drive pressure issues should disappear.

JMO

HOHN

1) 35K!!
2) I'd be looking at an S488 if you need the 130lb/min range. The 491 Bullseye has might be even better.
3) It appears to me that it's far better to have a primary that's too big than one that's too small. The trick in some cases is lighting it off if you don't have a big enough secondary. You'd be surprised how far apart the chargers can be though and still work pretty well if you're running low PRs on the primary. You can use something in the S480 range with the stock charger and have it work well. On my truck, a GT4508 will be almost fully spooled (2:1 PR) at only 2100 rpm WOT with a STOCK HX35 on top. So he's running that HTB2 on top, I'd certainly not go any smaller than a 480, with a 485 or 488 being more what I would expect to see.

The HTB2 is capable of lighting a substantially bigger primary, and the stocker can light a S480 just fine, so draw from that what you will.

jmo (see sig)

Mike Holmen

I don't know how well a BIG primary would respond on the street. At the track or under wot, you would have to stand on it hard, kinda like what you see at sled pulls. Dyno events, it might light, or fall on its face like my last two dyno events. Even my little 3B takes time for it to come to life. Of course thats old school, and they build better stuff today, and one day I have to get a new set-up. A big turbo might not even give you any boost until you have enough exhaust mass flow to get the entire mix working.