The Mega Supercharger 4AGZE thread, using twinscrew charger

[RonRob]

Maybe start a new thread detailing your kit etc. for us newcomers?

Sure thing! Will do so with pics of the Sprintex line in a few weeks. Kits will be available to everyone by summers end with new Sprintex dyno numbers. It appears as though Sprintex is now putting out a very efficient and reliable compressor. Hopefully preorder customers will post dyno numbers for their cars.

Thanks,
Ron

[jondee86]

Kind of off topic, but this seems to be the place to come to ask the question on my mind at the moment
There is a Opcon Autorotor OA3150 (1.5l/rev) for sale locally at a reasonable price. I am looking to use this on a smallport 4AGE with standard 10.3:1 compression and 10 to 15 psi boost. While I have not been able to find a performance graph for the OA3150, looking at the Lysholm LYS 1600 AX (1.6l/rev) graph, it seems that gearing down the OA3150 could be a viable option ?

Is this a good idea ? As a total noob to superchargers, I would like some opinion from wiser heads.

Cheers... jondee86

[knightrous]

Just some googles

http://www.hi-flow.com/HP002dSuper.html

SR 3150

Output: 1.50 L/rev - 18.0 m³/min - 637 cfm
Potential power: 315 kW (422 HP)
Max. rpm (cont.): 13000 rpm
W x H x L: 126 x 196 x 288 mm
Weight: 13.0 Kg

[jondee86]

Thanks for the link. Interesting site but not quite what I was after.
Based on a 4AGE 1.6 llitres, 8500rpm, 100kPa boost, and using the Sprintex calculator to compare 0.94l/rev and 1.46l/rev chargers, I get the following...

Large charger
8663rpm, 269hp, 447cfm, 1.02 drive ratio
Small charger
13455 rpm, 269hp, 447cfm, 1.58 drive ratio

Assuming that the characteristics of twinscrew compressors are similar from one brand to another, the small graph would seem to indicate that there is no downside to operating the large charger slower @ 100 kPa boost. But the VE drops off quite sharply when the charger rpm drops down into the range of engine speeds that would typically be seen in normal everyday driving.

In my mind this equates to a loss of the "instant response" that gives the twinscrew its edge. So what I guess I am really asking is if it is possible to compensate for the loss of low rpm response ? The logical answer (to a noob) is to drive the charger faster at low engine rpms, and limit the boost at high engine rpms with a "wastegate" setup. This would put the charger in front of the throttlebody, with an ECU controlled wastegate/bypass adjusting manifold pressure according to a target boost vs rpm table.

So what I would like is some input as to the merits of the above setup compared to just spending the coin to buy a smaller charger and run it faster ? With the throttle in front of the charger and a manifold vacuum controlled bypass valve, the system is kept simple, and the only trick part is gearing the charger to top out at the maximum desired boost.

Cheers... jondee86

[trdee]

Bear in mind also that the bigger charger will have more parasitic loss. The smaller charger will be spinning pretty hard at the top end and you will probably lose some potential power through heat etc but should be in its happy zone for more of the time.

Considering said extra parasitic loss, and the fact you need to run a headfuck of a wastegate/bypass system for the overspun bigger charger option, i would go with the smaller charger. That's a preference thing though.

[jondee86]

Yeah... my gut feeling is that a smaller charger is the way to go, but I can get into the Opcon selling here for at least a grand less than a new unit, and that helps pay for fabbing entry and discharge connections. Actually, thinking on it a bit more, the whole reason for looking at twinscrew chargers is to get these kind of curves...



The beauty is in the curves. A big fat midrange that starts to rollover at high rpm's, so there is no need to spend a lot of time at redline. All the fun takes place between 2500 to 6500 rpm. And as said, it is a much easier system to control if the throttle is in front of the charger. It seems that a vacuum controlled bypass to unload the compressor at low manifold pressure is all that is needed.

Anyone run a Sprintex S5-210 on a 4AGE ? What engine compression ratio ? And how did it go ?

Cheers... jondee86

[knightrous]

Personally I would go with the smaller unit and focus spending more time and money to getting a quality W2A intercooler setup to take out any extra potential heat at high RPMs.

[jondee86]

Current wisdom seems to lean towards only needing an intercooler is you plan on extended high rpm usage. One of the reasons I am looking at twinscrew is to avoid having to use an intercooler. The temperature rise through a twinscrew is low enough that the power loss by not using an intercooler is acceptable for "normal" driving. Of course, if trying to run the thing on 10.3:1 compression makes det a threat, then I may have to reconsider.

Cheers... jondee86

[trdee]

what sort of temperature rise do you normally see through one of these twinscrews at the PR you are aiming for? if you're aiming for 269HP/190KW, I would reckon you would need 20psi or more, which sure means a fairly large temp increase...

[nick.parker]

Hi jondee86,

There are at least two types of SC efficiency to consider volumetric and adiabatic. It is easy to see how volumetric efficiency is lower with a bigger blower - there is a much larger leakage path because of the physically larger case and rotors. Adiabatic (extra heating of the air not due to compressing it) is a bit beyond me for now - however - I wonder if the extra air leaking back would impede the efficiency of the blower much?

I suspect the spreadsheet doesn't take into account adiabatic or volumetric efficiency, which likely will be worse for the bigger blower at low speeds.

Really interesting idea about driving the charger faster and dumping some air. I plan on a stepper motor bypass valve (the ne that comes with Estima/Previa SC14) though not to run a bigger SC, just for boost control and a valet mode for my car. The Toyota Estima supercharged van achieves a flatter torque this way (reduces boost near engine peak VE :-/ ). If you can control the stepper motor 'bypass' valve that come with the Previa/Estima (I can ) then it's job done after some software / mapping time.

Final thought, a bigger blower will need more torque to push boost though it for the same speed - could this cause crap performance off idle? Here is a scenario - you open the throttle at 1000 - 1200rpm and all of a sudden you need a lot of torque to turn the blower (particularly a big blower)? There will be a few instants before the manifold is pressurised...I'm not sure? The bypass wont help here either, since the compression is within the supercharger between the rotors, and you cant bleed the pressure from here!!!

Nick.

[jondee86]

Here is a typical twinscrew diagram...



The adiabatic efficiency is the ratio of the temperature rise due solely to compression, to the actual total temperature rise across the charger. It can be seen that there is an island at the centre of the chart where adiabatic efficiency reaches its highest value. And looking at the other parameters on the diagram, I would think that operating at the centre of the island would be a happy place for the charger

But from a practical point of view, the engine will only see that point briefly, as the power being produced would probably be about right for cruising at 200 kph !!! In real world driving, the engine will spend most of its time making lower boost at lower rpms. And this is the part of the selection process I would like to get a handle on.

Cheers... jondee86

[jondee86]

Final thought, a bigger blower will need more torque to push boost though it for the same speed - could this cause crap performance off idle? Here is a scenario - you open the throttle at 1000 - 1200rpm and all of a sudden you need a lot of torque to turn the blower (particularly a big blower)? There will be a few instants before the manifold is pressurised...I'm not sure? The bypass wont help here either, since the compression is within the supercharger between the rotors, and you cant bleed the pressure from here!!!

Hiya Nick... as far as I can see from what I have read, the latest generation of factory installed twinscrew chargers all use a bypass arrangement to unload the charger when manifold vacuum is high. Air is returned from the discharge side to the inlet side of the charger to reduce parasitic losses when boost is not required. When the throttle is opened, manifold pressure rises and the bypass valve shuts immediately, allowing a very rapid buildup of boost. Obviously there will be some small difference depending on whether the engine is idling or simply off-throttle at 3000 rpm.

Cheers... jondee86

[jondee86]

Really interesting idea about driving the charger faster and dumping some air. I plan on a stepper motor bypass valve (the ne that comes with Estima/Previa SC14) though not to run a bigger SC, just for boost control and a valet mode for my car. The Toyota Estima supercharged van achieves a flatter torque this way (reduces boost near engine peak VE :-/ ). If you can control the stepper motor 'bypass' valve that come with the Previa/Estima (I can ) then it's job done after some software / mapping time.

I started off looking at centrifugal superchargers, and discovered that they don't make much boost at low engine rpm's. To overcome this deficiency, it is not unusual to drive the charger a bit faster to get it making pressure earlier. The downside is that at high rpm's there is danger of over-boosting the engine, so the wastegate/blowoff valve is used to limit boost. These are installations where the throttle is between the charger and the engine. Various techniques are used to control the valve including electronic modulation to produce a specific boost vs rpm curve.

Cheers... jondee86

[trdee]

1 - bear in mind that the twinscrew should be providing constant boost at lower revs. The manifold pressure may differ due to the throttle position, but the PR inside the supercharger ought not change.

2 - 190kw or thereabouts (approx 12m3/min if using your 447cfm) would require at least 20psi imo, which is a PR of 2.3-ish, that compressor curve doesnt even go that far (and the blurb says "max PR 2.2"). Even if the lysholm doesn't just go kablammo, you will be well out of the efficiency range of the charger. Which means lots of hot air. Looking at the chart, it would seem that if the chart extended upwards you would be seeing discharge temps of about 160C at a PR of 2.3

[jondee86]

The question I am struggling with at the moment, is relating the theoretical (maybe actual) conditions that apply when you you run the engine at constant load on a dyno, to the real world conditions that exist in normal driving. If your engine is 150kW capable @ 7000rpm, how is it possible to hold the engine at that load on the road ?? Towing a heavy trailer up a grade is about the only situation I can think of.

In reality, on the road 150kW will cause rapid acceleration, and you will quickly run through the gears and be in licence loss territory. So the amount of time your engine will actually be making 150kW @ 7000rpm is measured in seconds. And the circumstances that would prevent the engine or charger running continuously at that load point, simply do not apply.

This leads me to believe that having a small charger topping out around 7000-7500rpm is preferable to a larger charger that doesn't top out until it is making more boost and more power than your engine and transmission can handle. Reality says that high load conditions are transient in road driving, and that an average car only needs 25-30kW to cruise at the legal limit on a level road.

My aim is simply to have a 1600cc engine that behaves more like a 3000cc engine. That is, having a decent amount of torque in the 3000-6000rpm range, which is where I do most of my driving. In my mind that is far more useful that a dyno slip that says I have 150kW @ 7000rpm. And having a charger that does not need intercooling, water cooling or an engine oil supply, appeals to me. Besides, these things a fkn interesting

Cheers... jondee86