Compound Turbo Setup Holset style

[BobtailedSnail]

I've been reading the threads here and in yellowbullet and I do have one question, valve and ignition timing aside, how does the amount of boost run effect cylinder pressure? Is the 53psig on a single have the "same" cylinder pressure as 53psig on a compound setup? I'm not sure if I'm saying this in best way, but I'm sure you understand what I'm trying to get at. Thanks for any responses.

 

[viperlp01]

Considering cylinder pressure is in the hundred of thousands of psi the amount of boost does not present a significant change. It does start to change density in the intake manifold which can affect the characteristics of cylinder filling but the power is coming from the mass flow. Example a 14b at 20 psi would not come anywhere near a 42r at 10psi.

Let me edit my post. Pressures would be in the thousands not hundreds of thousands.

 

[Kevin Jewer]

Considering cylinder pressure is in the hundred of thousands of psi the amount of boost does not present a significant change.

That's like saying the pressure at a compressor inlet doesn't significantly change the pressure at it's outlet. Double inlet port pressure and you roughly double pre igntion cylinder pressure. Double the air/fuel and light it off, you get a lot more pressure. Cylinder pressure increase should be roughly proprotional to inlet port pressure increase. Cylinder pressure roughly correlates with torque, if that helps illustrate the point. Add 15 psi boost to an NA motor, and you get roughly double the torque. In other words, if boost didn't significantly increase cylinder pressure, we wouldn't bother with turbos at all. I must be missing something here.

Is the 53psig on a single have the "same" cylinder pressure as 53psig on a compound setup?

In short, yes. There will be two main areas of difference. One is air temperature, the other is turbine drive pressure.

 

[BobtailedSnail]

In short, yes. There will be two main areas of difference. One is air temperature, the other is turbine drive pressure.

Ok thank you. Now my question is which is more efficient? I'm not hearing of any BAT problems with compounds so I would assume compounds are more efficient since the PR are lower at each turbo versus a single? I'm assuming the temperatures are not compounded (either by multiplication or addition), but is only as hot as the hottest outlet charge.

 

[viperlp01]

Pressure and airflow are so extremely variable based on compressor flow...Boost Pressure and horsepower are not constant.... Mass airflow and horsepower are generally pretty spot on right?? Cylinder pressure is what makes horsepower so I am very confused as to why you would think that unless I am missing something... Increasing static compression ratio made 20hp difference on a maxed out setup(Tyler's 16g record car. Went from 11.5:1 to 7.8:1) That's my theory on it if I wasn't blunt enough in the first post.

15psi on a 14b makes maybe 150ish tq. 15psi out of your precision 6466 I would hope would make more than 150 tq.... I am not doubting pressure in general increases cylinder pressure, their is no argument for that, but I have a hard time relating to the argument presented.

For Bob- IAT is higher with a compound setup. Not insanely higher but your air hits two compressors and is essentially heated twice. From my personal experience and talking with Paul V there is not doubt it increases the mass flow(compressor map) of the large turbo. Paul made 604 or something like that on an Old school 60-1. The mass flow of my 67mm is supporting 645 awhp through an auto and is only at 2:1PR(28psi falling to 25psi). If I can have tq stay put the horsepower should climb like crazy but the torque curve follows the boost curve.

http://www.epi-eng.com/piston_engine_technology/bmep_performance_yardstick.htm

BMEP (psi) = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

 

[Kevin Jewer]

Pressure and airflow are so extremely variable based on compressor flow...Boost Pressure and horsepower are not constant.... Mass airflow and horsepower are generally pretty spot on right?? Cylinder pressure is what makes horsepower so I am very confused as to why you would think that unless I am missing something... Increasing static compression ratio made 20hp difference on a maxed out setup(Tyler's 16g record car. Went from 11.5:1 to 7.8:1) That's my theory on it if I wasn't blunt enough in the first post.

15psi on a 14b makes maybe 150ish tq. 15psi out of your precision 6466 I would hope would make more than 150 tq.... I am not doubting pressure in general increases cylinder pressure, their is no argument for that, but I have a hard time relating to the argument presented.

There is no doubt that horsepower is tied to mass airflow more than it is to boost. I was under the assumption that all things otherwise were being considered equal based on post 301. With all else equal, cylinder pressure is roughly proportional to MAP. I was responding to the first line of your post, which with all things equal, would be incorrect. I thought you also implied that boost is insignificant because combustion pressure is so high, which would also be incorrect. I'm sure we're both right and just talking about two different things.

The compression ratio example changes everything again and throws out the hp to mass flow ratio. For example, the old 10 hp (potential) per lb/min mass airflow assumes ~9:1 compression, gasoline, etc.

The 6466 at 15 psi would likely make less torque than the 14b at 15 psi due to the higher rpm at which it would make that boost, but that's outside the scope of your example and I know what meant. If the bigger turbo makes more than the small turbo at the same boost, it's mostly due to the larger turbine.

For Bob- IAT is higher with a compound setup. Not insanely higher but your air hits two compressors and is essentially heated twice.

The air is heated twice, but to a lesser degree each time. My car runs the same AIT at 40 psi on the compounds at at 40 psi on single turbo. This is after the IC so any change is effectively reduced by the efficiency percentage of the IC, but the numbers are nearly identical. Anyone interested in the details of this can do the math by using an online compressor calculator. For the second turbo inlet temp, use the outlet temp of the big turbo. Total outlet temp is the sum of the minimum temp increase caused by the pressure increase and the additional temp added by inefficiency. The bigger factor is pressure, so 40 psi from one turbo or 40 psi from two turbos doesn't result in much difference. One of the turbos would have to be horribly inefficient to really make a dent in total outlet temps, and that gets cut down by the IC in proportion to its efficiency anyway. The advantage that can be gained from compounding two turbos is the possibility of keeping them both at a higher efficiency than one turbo at double the PR would run and still be able to spool it.

From my personal experience and talking with Paul V there is not doubt it increases the mass flow(compressor map) of the large turbo. Paul made 604 or something like that on an Old school 60-1. The mass flow of my 67mm is supporting 645 awhp through an auto and is only at 2:1PR(28psi falling to 25psi).

The hp at only 2:1 PR is irrelevant. To make a fair statement out of that you'd have to multiply displacement by small compressor PR. Same way V8s make more power at lower PRs. I'll bet that almost everyone running compound turbos like us is maxed out on primary compressor, whether they know it or not.

Those numbers still don't convince me that it's possible to outflow the rated capacity of the atmospheric turbo. Your motor plus small turbo is effectively just a bigger motor to the atmospheric turbo. With nothing but atmospheric pressure at the big compressors inlet, there is nothing to help it flow more like you have at the small turbo. You and Paul have been saying this for years, but with nothing within the laws of physics to account for it, the burden is on you guys to prove it.

My data shows the primary compressor maxing out at exactly what it should according to the MAP for the PR it runs, in airflow, not horsepower. Air mass flow capacity is reduced at lower PRs. This is one of two potential disadvantages of compound turbos that I've found.

BMEP (psi) = 150.8 x TORQUE (lb-ft) / DISPLACEMENT (ci)

That doesn't seem to add up to the hundreds of thousands of psi mentioned previously. You can arrive at roughly the same value by adjusting torque for stroke length to get force, then use piston area to get pressure from that.

 

[BobtailedSnail]

Wow thanks to both of you for the info. And Kevin, you did touch on something else I had been thinking about.

I've been wondering about the displacement multiplier. What I hypothesized is that the reason big V6's and V8's can have higher HP at lower boost, is because "boost" is a unit of measure to the resistance of flow. V6 and V8's have more volume to which can be filled and thusly the turbo doesn't have to work as hard to "pack" the air into each cylinder, which is why most of these engines operate at the bottom of the compressor map.

I do agree that 4 cylinder engines get the displacement modifier on the exhaust side, which is why it can spoil the atmospheric turbo sooner. But being that the actual cylinder displacement hasn't changed, the atmospheric turbo still must operate at a higher PR than it would on a V6/V8. I am going to play with this more once I get my set up running.

I'm probably just rambling on about things you guys already know, but I'd figured I give my input nonetheless.

I also wonder what benefit compounds could have on a V6/V8 application with extremely high (1500+HP) goals, being that they tend to operation on the lower portion of the map.

 

[Kevin Jewer]

I've been wondering about the displacement multiplier. What I hypothesized is that the reason big V6's and V8's can have higher HP at lower boost, is because "boost" is a unit of measure to the resistance of flow. V6 and V8's have more volume to which can be filled and thusly the turbo doesn't have to work as hard to "pack" the air into each cylinder, which is why most of these engines operate at the bottom of the compressor map.

Bigger motors move more air at atmospheric pressure, so you need less pressure multiplication (PR) to move a given mass flow. With all else equal, an increase in displacement could be met with an equal decrease in pressure (absolute) to get the same mass flow. For example, double the displacement, half the PSIa. Bigger motors are almost always too different from smaller motors for this to work out exactly, but it illustrates the point.

I do agree that 4 cylinder engines get the displacement modifier on the exhaust side, which is why it can spoil the atmospheric turbo sooner. But being that the actual cylinder displacement hasn't changed, the atmospheric turbo still must operate at a higher PR than it would on a V6/V8. I am going to play with this more once I get my set up running.

It's the other way around, but only slightly. Consider a 2 liter engine with a small turbo on it running a PR of 2. That 2 liter engine now puts out the same exhaust energy as a 4 liter engine at a PR of 1 (NA). By the way, density ratio is a better indicator, but PR is easier to work with. Now up the 2 liter to a PR of 3, and you have the exhaust flow of a 6 liter NA. This is how my car can spool a 96mm turbine in a 1.32 AR T6 housing with a 2 liter engine.

If it puts out the exhaust of a 4 liter with the small turbo at 2:1, it also takes in that much air. So the big turbo will act like it is feeding a 4 liter engine. This is how my S475 moves 90+ lbs/min at 17 psi, and John's big turbo can move what it needs to for 645 whp at 28 psi with an auto. Our motors flow a little better than most V8s, so our big turbo PR will probably be a little lower than it would be on a V8 of the "same" size.

I also wonder what benefit compounds could have on a V6/V8 application with extremely high (1500+HP) goals, being that they tend to operation on the lower portion of the map.

Such setups are being built right now, up to ~2500 hp. Running high boost moves them back up on the maps. The benefit is the same that it is for me, and for John. Spooling big turbos on a torque converter without nitrous. The turbos are just bigger on the V8s. Real big.

 

[BobtailedSnail]

Ok thank you for the clarification. In the midst of all the adding and multiplying I got mixed up. I should have asked, but didn't know if you or John had measured the boost coming from the atmospheric turbo.

 

[viperlp01]

Pulled the car on the dyno tonight. The Eboost2 is installed and ready for some tuning. Pretty stoked to have all these features so easily accessible via the Eboost2.

 

[Archer Fabrications]

Vids or it didn't happen

So what did those beautys put you at?

 

[BobtailedSnail]

If its not too much trouble, post up a dyno sheet with boost logged. I'd like to see your torque and boost curves.

 

[viperlp01]

I am doing some boost tuning after work tonight and will start making so big boost changes once the boost curve is doing what I want it to. I will go until I run out of pump.

 

[thecman02]

I can't wait to see this thing with the boost cranked. It should respond real well because I would think your not even in the high efficiency islands of the big. I'm just curious what increasing the boost of the small would do. Ideally you would want both turbos in their most efficient part of their compressor maps, but Kevin was saying less energy is available for the big if the small does more work. I'm scared that I'll have to do a detailed analysis for my senior design :-/ . At some point there is the optimal amount of work done by each turbo. So much to play with and test this summer!

 

[Kevin Jewer]

At full tilt there's plenty of exhaust energy for both turbos, you'll just get less wastegating on the big turbo. During spool up there is a trade off. You might hear diesel guys talking about "early wastegating" on the small turbo, this is what they're talking about. Small compressor to big turbine spread will affect this as well, as I found on my setup. You need to get enough airflow/boost from the small turbo to create enough exhaust energy for the big turbo, without the small turbine using it all up to get there.

Good luck on the tuning tonight John, hopefully everything does what you want it to.

 

[Archer Fabrications]

Need videos!!

 

[jeffrox]

any updates?

 

[BOOZTDSM]

He broke a rod,and damaged another , he says his oil clearances were wrong for his aluminum rod combo .

 

[Archer Fabrications]

Fucckkk

 

[Rsawd95dsm]

Was at there shop Tuesday and its all in pieces with broken shit laying all around.

 

[JohnTSI]

He broke a rod,and damaged another , he says his oil clearances were wrong for his aluminum rod combo .

I run the same rod bearing clearances on the RNRs as I did on steel rods? Didn't you break a eagle rod as well?

 

[BOOZTDSM]

well he also says the rod let go since e85 is inconsistent. so who knows .

 

[loco4G63]

Simply sex on wheels bro. Baddest Talon period! Hope you get her squared away. I'm a diesel mechanic myself and a holset DSM guy : ) keep up the great work and innovations for the rest of us to learn from

 

[viperlp01]

Yep going back together this week. Waiting on the 1 piston I need to complete the set. I had too much timing in it. I was tuning it on last years batch of E85 which had to be a decent ethanol content. I went to the local station, got 10 gallons, and tossed it in there and started making rips. I noticed a drop in torque above 7k so I tossed some timing at it and pop. Right when I let off at 8.5K the rod let go. Too much timing damaged the bearing which caused the piston to hit the head and that's when it snapped. I changed some things up this time but it should only compliment the build and not be the reason why it lives. I actually tested the ethanol content after it broke and got E72 . I just tested it last week when an Evo came in for a tune and we got E80. Its getting better but makes me really want to invest into my own barrel and mix it myself.

50 psi of pressure is a completely different animal when it comes to tuning. BUT!! I also had this built for it!

These are one of those things that not many get to without learning the hard way. Should have her in the car running sometime next week and back on the dyno for some tuning in the 50psi range and see what she makes with a safer tune.

I run the same rod bearing clearances on the RNRs as I did on steel rods? Didn't you break a eagle rod as well?

I did snap an eagle rod on the stall converter. I ran .002 on that combo but it showed no clearance issues. The AL rod engine I ran to start the season off with was at .003. The new one is .0035 with added oil squirters/reliefs at the 12 o'clock position of the rod to allow some oil passing through the bearing and well as using it to help heat up the rod.

 

[jeffrox]

It's great that you'll have your car running again shortly! Onto some questions.

1. How much weight are you saving by running that tubular k member?

2. Your holsets, Do they both have divided turbine housings (I read the beginning of this thread and must have missed it)? Did you knife edge their dividers at all?

3. Are you still on the stock converter?