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fcdrifter13

Anyone running a compound setup on a L-series

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fcdrifter13    10

I am a big diesel guy an I run a set of compounds on my cummins and absolutly love it, But I havnt even seen any kind of mention of a compound set-up on a L-series. Has this ever been done on these engines?, I know a couple of L6 toyotas, and 4g63s have been done but nothing on the L.

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fcdrifter13    10

Well, you can get 50psi from one turbo, why compound? Petrol engines aren't built like diesels where you can have 100 or 200psi inlet pressure.

 

I dont think it should be done to achieve a maximum amount of boost pressure on a gasoline engine. On the L-Toyotas I see it being more advantageous in the broadened tourqe curve.

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Tony D    143

So you are not talking compound supercharging, indeed you are talking about a volume enhancement by twins...in parallel as opposed to pressure through series application (compound)...

 

Or do you mean sequential with a smaller turbo coming in early, and eventually a larger turbo n parallel with it taking over for boosting at higher RPMS?

 

Mainly because the power produced and limited rev range most use. With standard single turbos you can get full boost by 3200 rpms, and pull to over 8000 rpms. There's really no reason. For a smaller one to handle off-idle to 3000....

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kiwi303    29

If you want low down boost, a Supercharger (screw not centrifugal) would be the better bet, same boost at idle as you get at max rev, since being mechanically linked to the engine revs it delivers the same extra air every revolution as the engine turns and turns the supercharger.

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fcdrifter13    10

So you are not talking compound supercharging, indeed you are talking about a volume enhancement by twins...in parallel as opposed to pressure through series application (compound)...

 

Or do you mean sequential with a smaller turbo coming in early, and eventually a larger turbo n parallel with it taking over for boosting at higher RPMS?

 

Mainly because the power produced and limited rev range most use. With standard single turbos you can get full boost by 3200 rpms, and pull to over 8000 rpms. There's really no reason. For a smaller one to handle off-idle to 3000....

 

From ATS Website

There is a small turbo charger and a large turbo charger plumbed in series to one another. The small turbo charger is referred to as the high-pressure turbo charger and the large turbo charger is referred to as the low-pressure turbo charger or the atmosphere turbo charger. In a "Compound" turbo charger set up the small turbo is responsible for generating quick turbo response and rapid air flow right off idle. As the engine is accelerated from idle the small turbo begins to produce boost immediately wile the large turbo slowly starts to produce a positive pressure to the small turbo. The large turbo when matched properly should be supplying boost pressure to feed the small turbo shortly after the small turbo is making boost in to the engine or intercooler. If the large turbo charger is not matched properly it will cause the small turbo charger to stall and the low-end performance will suffer.

 

Like I said above I, personally, would not use this setup for the maximum amount of HP but to lower the tourqe curve and increase efficiency

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Tony D    143

There is no efficiency increase. It's a sales presentation with marketing terminology.

Asked and answered.

 

If you want performance from 1,700 to 8,000 run a 0.48A/R and this gimmickry B.S. is unrequired. Added complexity and imposition of multiple cascade failure points with the added issues of multi staging compressor map matching.

 

Conventional sequential turbocharging is proven and does not suffer the complexity of trying to multi-stage the compressors, you simply deactivate the smaller turbo at higher rpms and let the big one sing. Far greater capacity possible then when nt restricted by the stonewall point of the smaller turbo.

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fcdrifter13    10

I know that on my truck (hx35 under a hx60) before I ported the wategate, changed exhaust housings, and eventually  started to run a external dump valve into the downpipe feeling the larger turbo, I was getting surging out of the smaller turbo and that the drive pressure was increasing. I am seeing positive boost at 1600rpm and the second turbo coming online at 2800, it is a little hot but alot better than not spooling the hx60 at all. Maybe its just different on a gas engine

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Bernardd    3

I'd like to see someone install a Holset variable vane HE351VE.  As good as or better than stock spool along with high end flow.  The turbo has few downsides to it like the weight and how to control the vanes or rather how to tune them to what the L28 needs.  Best setup other than the stock electronics I've seen is using exhaust back pressure and an internal wastegate actuator connected to the arm that controls the vanes in the turbine housing.  The exhaust housing can flow enough for a 5 liter v8 and be brought down to enough to fully spool a 2.0 liter 4 cyl.  

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WizardBlack    13

By the way, that is not compound but rather asymmetric sequential operation that you described. It can be sequential to efficiently achieve high pressure levels with lower tech turbos. Assymmetry is pointless unless you use a valving system to only keep one turbo in the loop at low rpm and even then, you get two instances of spool delay if you rev high enough to hit the second turbo. Mkiv supras do that, actually. The only other use aside from marketing is if you have packaging issues (ie., fitting it in the engine bay).

I used to have a Megasquirt and iirc there were some more complex issues in getting the variable nozzle to work on some of the turbos.

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Six_Shooter    13

Compound can work very well on a gas engine, broadening the torque curve.

 

I've been doing a lot of research on this, since I'm seriously considering it on another engine I plan to build. I also want to run enough boost, or better yet flow to support 600+ HP on a small displacement engine, but want to lower the boost threshold as much as possible, when I smash the loud pedal.

 

The only way you're truly going to know how well it will work is to build it yourself and not listen to ney-sayers.If I listened to them, I wouldn't have successfully built half the stuff I have. ;)

 

Edited by Six_Shooter

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HowlerMonkey    12

Most useful compound turbo setups as used on high performance gasoline engines are there because the horsepower level they desire requires a turbo so large that the engine has trouble spooling it.

 

Some of these engines run such a low compression ratio that the engine cannot spool this large turbo when off boost.....regardless of rpm.

 

Sure, the smaller turbo can greatly decrease lag but most are using the small turbo simply to give the engine enough boost as to greatly increase exhaust flow in the interest of spooling up the main turbo.

 

The simple answer is that nobody has built a L28 that could handle the horsepower level......and it's possible that the L28 head will never flow enough to make it worthwhile vs a well researched single turbo.

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Tony D    143

1100HP single turbo L28's have existed since the early 80's. And those are the endurance-race ones, Drag Racers made even more (sub 10 second full body ZX's), Exactly how much are we looking for here to justify it?

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TimZ    21

Some of these engines run such a low compression ratio that the engine cannot spool this large turbo when off boost.....regardless of rpm.

Sorry, I'm not buying this.  Compression ratio has very little to do with ability to spool.  If anything the lower efficiency of a lower compression ratio means more energy sent unused to the exhaust, which would result in a _faster_ spool.  And I'm dubious as to whether even this effect is measurable.

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Six_Shooter    13

As usual, people are missing the point completely.

 

It's real easy to use a large single to make impressive single point (peak) HP numbers, no real science to that.

 

The idea here is not just about making huge power, though that is usually part of the equation, but the main idea is to be able to get a wide torque curve, while having the ability to support high HP output.

 

Contrary to what people believe the small turbo does not become a restriction, it does become a pressure multiplier. With the increased inlet pressure, it flows more than it would if the inlet pressure were lower.

 

I agree with TimZ, compression ratio is a very small part of an engine's ability to spool a turbocharger, if it has any effect at all. The volume of air pumped, along with the heat has a much larger effect, since compression ratio is really only key in the combustion process, not the ability of the engine to pump air. Regardless of compression ratio, a 2.8L engine will pump 2.8L of air every 2 revolutions, if it had 8:1 SCR, or 20:1 SCR. The volume of air, heat of that air, along with the pressure differential between the inlet of the turbine and the outlet of the turbine is what causes the turbine to spool.

Edited by Six_Shooter

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HowlerMonkey    12

I've compared my car with stock F54 and flattops (stock), pulled the engine, installed dished pistons, and went to the drag strip a week later with no other changes to the engine and found a substantial difference in spooling time between flattops and dished.

 

When staging on the brake to build boost with an automatic at the drag strip, you will immediately notice the difference.

 

Compression equals heat.

 

Turbo technology has advanced to the point that getting a "wide torque curve" is possible with a newer design single. I just don't see needing compounding for a street car even though our shop makes daily drivers with 1500+hp.

Edited by HowlerMonkey

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Tony D    143

Yes, there is a functional break in semantics and engineering terms  versus Salesmen Hype Marketing Babble. i don't know how much wider than 1700-6500 you want to get, as that's  what I had with my 350-375HP L28. not peak horsepower, but wide torque.

 

The new hybrids and compressor wheels make it possible that the same turbine wheel driving a newer compressor design would flow to over 475HP now, with the torque being above a set level at 1700 rpms.

 

Additionally, there was a prior device on the marked 'Turbo Group Fueler' which incorporated an inverse-rpm boost fueling scenario. At 2000rpms you ran higher boost than you did at higher rpms, and fueled accordingly. The sizing of the turbo then was difficult, but with the new wheels today, that really has promise for 20psi+ at 1700rpms (possible on a stock L28 with a 0.48A/R T3 housing) tapering back as rpms climb keeping torque constant and flat.

 

Sequential turbocharging is complex, and the 'benefits' have yet to be proven over current technology turbocharger wheels.

 

The Ford Diesels now run dual compressor wheels off a single turbine driver to keep inertia down and increase flow to TWICE what was possible with the same size single. The exhaust power is plenty to turn BIG wheels for BIG torque boost at lower rpms.

 

Adding a second turbo generally adds nothing but failure points and complexity.

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Tony D    143

To This:

 

"Contrary to what people believe the small turbo does not become a restriction, it does become a pressure multiplier. With the increased inlet pressure, it flows more than it would if the inlet pressure were lower."

 

Please look up the definition of "Stonewall"---there IS a limit physically as to what diameter and blade spacing into what torridal diffuser (and flow path dimension) will ultimately flow. You will not put the flow of a T67 through a stock turbo housing without restricting the T67's flow.

 

This gets to the differences between 'flow' and 'pressure'.... You raise the inlet pressure and flow increases. But ULTIMATELY the presence of PRESSURE at the smaller turbo's inlet SIGNIFIES RESTRICTION TO FLOW!

 

Multistaging for flow is best done in pure parallel for simplicity. COMPOUNDING is not the way you want to do it in low pressure applications, it's just NOT efficient. There may be an argument for two stages between 45-75 psi, it's a strange range to be in, and they may derate two stage machines to operate there....but nobody is pumping 45psi into an L-Motor, that would be well into the 1500HP range.

 

Show me one high-flow industrial compressor below 50PSI design pressure that is two-stage.  They don't do it.  For 100psi there is an argument between 2 or three stages, and above 100psig to around 200-250 the argument is made over 3 or four stages, between 275-400 4 stages is standard, with 4 stages being a standard offering in most 350 psi applications. At 5 stages, 700psi is easily attainable. If there is an EFFICIENT way to do it, it will show up in Industrial Compressors well before automotive applications as the marketing and costs for driver power drive the market. 1 or 2% will make or break a sale.

 

In some cases, Japanese have a culture of making things technologically complex to it's own end. That's not really engineering, it's masturbation. if you can get it done with fewer parts....DO IT!

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TimZ    21

I've compared my car with stock F54 and flattops (stock), pulled the engine, installed dished pistons, and went to the drag strip a week later with no other changes to the engine and found a substantial difference in spooling time between flattops and dished.

 

When staging on the brake to build boost with an automatic at the drag strip, you will immediately notice the difference.

 

Compression equals heat.

 

Yes, compressing a gas will increase it's temperature, but that's not what we are talking about here.  

 

Increasing the compression ratio will increase combustion efficiency, which by definition means that more of the energy from combustion goes into work at the crank and less goes out the exhaust.  All else equal, you will see lower EGTs with increased compression.

 

In your example there are several unstated and uncontrolled variables that could have caused the results you stated - was the ambient air pressure and temperature exactly the same on that run a week later?  Did you have to change ignition timing to stay below the knock limit with the increased CR?  Did you use different fuel to accommodate the increased CR?

 

You don't have to take my word for it - it's pretty well established thermodynamic rules. Here's a link to a paper from Stanford University that covers the subject nicely:  http://rescomp.stanford.edu/~efroeh/papers/RDH_Engine_Performance.pdf

Edited by TimZ

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Tony D    143

Hahaha

 

"Education comes after Anecdote in every dictionary, damn the physical laws, regardless of how well documented! It just doesn't apply in my example!"

 

I have just summarised every response from here on.

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HowlerMonkey    12

 

 

Yes, compressing a gas will increase it's temperature, but that's not what we are talking about here.  

 

Increasing the compression ratio will increase combustion efficiency, which by definition means that more of the energy from combustion goes into work at the crank and less goes out the exhaust.  All else equal, you will see lower EGTs with increased compression.

 

In your example there are several unstated and uncontrolled variables that could have caused the results you stated - was the ambient air pressure and temperature exactly the same on that run a week later?  Did you have to change ignition timing to stay below the knock limit with the increased CR?  Did you use different fuel to accommodate the increased CR?

 

You don't have to take my word for it - it's pretty well established thermodynamic rules. Here's a link to a paper from Stanford University that covers the subject nicely:  http://rescomp.stanford.edu/~efroeh/papers/RDH_Engine_Performance.pdf

 

 

Going by the point you made above, 10 pounds of boost to the same engine will increase combustion efficiency decrease the amount of gases exhausted as in your example?

 

If not, what makes it different?

 

Some variables are not being considered.

 

I'm just relaying real life observations through experience gained in the field and tony's stirring the pot.

Edited by HowlerMonkey

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TimZ    21

Going by the point you made above, 10 pounds of boost to the same engine will increase combustion efficiency decrease the amount of gases exhausted as in your example?

 

If not, what makes it different?

 

Some variables are not being considered.

 

What does adding 10-psi boost have to do with this at all?  

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