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compound charging/twin charging


d.p.n.s

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just dont double compress shit and keep in mind that a simple turbo setup is 1000 times easier and more efficient

yeah i know mate and thanks for your input.

im just wanting to try something else and differant

that ive never done befor.

and ill be the 1st to admit its about 99% for wank value lol

dan

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Compound charge it properly please. i.e. compress it twice.

dont do this as its not a fucking plane, if you want boost just loosen valve clearances and let it the churbro fuck itself, flow is key. big churbro and minimal boost

thats what im planning mate

\big turbo low boost not comressing it twice

they will have theyer own air feed and flow

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Gah. Mike-e, read up about this shit. The reason behind compound twin-charging is more than just getting more boost. There is no point in twin charging if you don't do a proper compound setup. You will never get the change over between sc and turbo smooth. And it will be gay.

Compound charging will

a) give you more boost than the sum of the SC+Turbo.

B) let you properly scavenge the cylinders as the inlet manifold pressure will be higher than the exhaust manifold. This is impossible with a turbo setup, and why compound setups work so well.

Seriously, read this thread - http://www.alfabb.com/bb/forums/engine- ... oject.html

They discuss the engineering behind twincharging

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ok so i was talking to a mate about this

and hes into his supercharging the shit out of everything.

we looked at it all .i.e differant ways around it

and came up with this

compond4.jpg

the sc running all the time feeding from the airbox and blowing into the intercooler

the pressure from that will keep the flap doors closed.

the turbo starts to spool feeding from the air box and when the pressure gets biger then the sc it will

push the flap doors open and flow into the cooler.

now with the sc running all the time it will stop the turbo trying to force air into it.

and you will have both flowing to the cooler.

best of both worlds i think.

dan

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amen to voldo

There is no reason to bypass the supercharger apart from when you close the throttle. The supercharger compresses the air at a pressure ratio. It doesn't care if the air coming in is 14.7psi or 25psi

To save you from trolling through buzzed's thread start here:

http://www.alfabb.com/bb/forums/engine- ... ct-14.html

Quote from Greg Gordon

"It might be best to explain this with some simple math (not technically complete or perfect by any means). A Roots blower creates a pressure ratio which is defined as outlet pressure/inlet pressure. We tend to express supercharger outlet as boost and a lot of people like to talk about flow, but in this case it's easier to understand it via pressure ratios. Roots blowers create pressure ratios, and that's critical to understand when building a compound system.

Here is an example: atmospheric pressure at the supercharger's inlet is 14.7psi (sea level standard day), in this case our supercharger is set up to provide 7.35 pound of boost so the outlet pressure is 22.05psi. Outlet pressure divided by inlet pressure is 22.05/14.7=1.5. So our pressure ratio is 1.5:1

Now lets keep everything the same with this supercharger except we will add pressure to the inlet side with either another supercharger, or a turbocharger. The pressure ratio will stay the same but boost from the supercharger will increase. To keep it simple, lets add 5psi to the inlet.

Now we have 19.7 at the inlet and the supercharger will give us a pressure ratio of 1.5:1. When we multiply the inlet pressure by the pressure ratio we get 29.55psi. Subtract 14.7psi and we find we have 14.85 pound of boost. What happening here? The supercharger by itself only gave 7.35psi and we only added 5psi. Add those two numbers together and they total 12.35psi but we have 14.85 pounds of boost! This is one of the beautiful things about a compound system.

Greg "

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amen to voldo

There is no reason to bypass the supercharger apart from when you close the throttle. The supercharger compresses the air at a pressure ratio. It doesn't care if the air coming in is 14.7psi or 25psi

To save you from trolling through buzzed's thread start here:

http://www.alfabb.com/bb/forums/engine- ... ct-14.html

I've just read through that whole thread over the weekend.

I've come to the conclusion bypassing the supercharger is not only unnecessary but even a bad idea, a turbocharged engine has higher exhaust manifold pressure than inlet manifold pressure, so there is a lack of decent scavenging. With a supercharger AND a turbocharger the inlet manifold pressure is always higher than the exhaust manifold pressure, so there is much less contamination of the next cycles fuel/air mixture = more power for a given boost level.

Plus compounding lets you run lots of boost whilst keeping both compressors closer to where they are most efficient.

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Why is high boost important?

The mass of air is important to me, more air needs more fuel which makes more power.

A big turbo makes big power because it can flow more air, one of the reasons is because they run a bigger AR in the exhaust. Put simply the AR of the exhaust housing is how much of a restriction it creates to increase the velocity of the exhaust gas before it hits the exhaust turbine. Look at the big power turbo cars and they have no power until high in the RPMs when the exhaust gas gets enough energy to get the compressor compressing.

Running a blower and a big AR turbo should give the best of both worlds. The big AR exhaust housing means the exhaust is nice and free for the blower, the blower will make boost low down which will increase the exhaust gases and either get the turbo on boost earlier than it would by itself or allow Dan to run and even bigger turbo making even more power.

The crossover point shouldn't be an issue because Dan is running the blower full time and the turbo is blocked by a flapper valve until it's making enough boost to open the valve.

By having the blower and turbo running in to a Y pipe Dan can run a crazy big turbo that you wouldn't run on that engine by itself as it would only get on boost way way up the revs

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Yep, easily. Contrary to popular belief roots blowers are pretty efficient if sitting in the peak of their effieciency range. Generally within 10% of an equivalent turbo. Its only when you overdrive them (i.e. some tool with a 4agze running 20psi) they start cranking the heat out.

So just size it right in the first place and you'll be fine.

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Its not about high boost. As we have been explaining, a compound charged motor running X boost will make more power than a turbo'd motor with the same X boost. This is due to the possibility of cylinder scavenging.

You need the high boost on the inlet to get the cylinder scavenging, for it to work the inlet manifold pressure must be higher than the exhaust manifold pressure to create a pressure differential to cause inlet -> exhaust direction flow.

Speaking generally a factory turbo car will have an exhaust manifold pressure 3 times that of the inlet. This is why generally turbo engines like nanna cams with little over lap, big overlap with the turbo and you get the exhaust contaminating the inlet charge.

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You could have a low boost setup with a sc+turbo in compound and still have cylinder scavenging.

Yes as long as the the inlet manifold pressure is higher than the exhaust manifold. However what's the point of making a low boost compounding system?

You may as well just use the blower as they do low boost and instant response.

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