Yowzer Posted April 9, 2015 Share Posted April 9, 2015 Well actually Rookie, you can get better results with a sequential twin charge system than a compound setup on a petrol engine, as compound is far less efficient and generally unnecessary as there's only so much boost you can run before things start popping. Diesel is a different story as you can force feed them as much air as you like, however the efficiency still comes into play. Sequential won't require as much intercooling and has less parasitic loss up top as once the turbo takes over the supercharger is just freespinning, or you could have it on a clutch like the SC12/14s and shut it off entirely when not in use. Or you could do away with both an run a shittonne of NOS instead. 1 Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 9, 2015 Share Posted April 9, 2015 Actually with 2 stage compression ie compounding setups and correct intercooling you get a more efficient compression. Yes there is a problem with cooling the charge but the physics of multiple stage compression says your statement above is wrong. Quote Link to comment Share on other sites More sharing options...
Rookie Posted April 9, 2015 Share Posted April 9, 2015 I agree that you can make a sequential system work better than just a turbo, but you can't make it better than a compound setup. There are a host of things that make a compound setup work better on a petrol motor than either a sequential or turbo setup, and vs a sequential setup you lose out big time. You could make an argument that with today's turbo tech, the gains probably aren't worth it compared to the extra work, but a compound setup will always shit on a sequential setup. Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 Actually with 2 stage compression ie compounding setups and correct intercooling you get a more efficient compression. Yes there is a problem with cooling the charge but the physics of multiple stage compression says your statement above is wrong. Perhaps with a twin turbo compound, but a supercharger + turbo being more efficient than just a single turbo pumping the same boost? Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 9, 2015 Share Posted April 9, 2015 If you are talking about efficiency in terms of overall loss it is going to be greater with turbo into sc setup vs a big turbo then yeah your right. But that isnt the point of the compound twincharge setup. Its about power EVERYWHERE, the best way to achieve that IMO is a well sized turbo blowing into a positive displacement blower. If you are after max power then go to Davejacksonville and buy a big assed turbo. edit: That doesnt really say what Im trying to get across. If the point of having a turbo and a blower is to do doorts then the most efficient way to compress the air is to compound charge it with intercooling between stages. You still have the same parasitic loss from the supercharger whether you compound charge it or sequential charge it so you may as well compress the air more efficiently to better make up for it. The first top bit doesnt make sense. The rest is solid Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 9, 2015 Share Posted April 9, 2015 note: I am just another internet warrior. 1 Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 Most of my knowledge of the matter is from internet warriors so I'm open to any info. Anyway there's a particular setup I found interesting which when I get home I'll post Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 9, 2015 Share Posted April 9, 2015 Im applying my knowledge of physics to all of the youtube videos ive watched. Quote Link to comment Share on other sites More sharing options...
Rookie Posted April 9, 2015 Share Posted April 9, 2015 This thing is a weapon. http://www.lancerregister.com/showthread.php?t=315815 Well worth the read. Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 This diagram has probably been posted, but I found a similar setup on an '80s rally car (can't find the article now) Which begins as a compound while the turbo spools, then the supercharger is bypassed and the turbo takes over the boost duties. This is the setup I'm keen to replicate one day. The theory behind this kind of system is to use a small positive displacement (roots style) supercharger. Supercharger performance efficiency is typically its highest at lower engine and supercharger rpms (for example from idle to 4000 rpms). Above 4000 rpms the supercharger’s performance and efficiency starts to drop, the horsepower required to drive it starts to rise exponentially, and the air temperature coming out of the supercharger starts to rise dramatically limiting performance.On the other hand, using a generously sized turbocharger will allow us to feed the engine efficiently with cooler air (than that from an overworked supercharger) and maintain high rpm performance. The problem with using a larger turbocharger is that a generously sized turbocharger typically doesn’t spool before 3000 to 4000 rpms giving us a limited power band and thus providing no performance boost at lower rpms. The idea of twin charging is to use both a supercharger and a turbocharger to have each one do what it does best, have the supercharger boost the motor for low end torque, and as it runs out of steam, the turbocharger comes online to carry us through to redline. Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 Compound-sequential using turbos Quote Link to comment Share on other sites More sharing options...
Rookie Posted April 9, 2015 Share Posted April 9, 2015 That first one you posted is from the lancia delta s4, and the supercharger never got switched off. Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 9, 2015 Share Posted April 9, 2015 To have a turbo small enough (compressor side) for a well boosted compound setup is going to be blowing some pretty hot air if you make it work alone for max top end power. Your already making heaps of boost why not just leave them in a designed efficiency and just crank the boost through the blower more. If its a poisitve displacement setup so if you up the boost 1psi on the inlet it just means its 1psi higher at the outlet. You already have the intercooling in place to deal with it. Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 That first one you posted is from the lancia delta s4, and the supercharger never got switched off. In the Lancia system it didn't, the article is actually referring to the HKS twin charge kit for the 4AGZE where the charger does get switched off once bypassed. The pic is just an example. In any case, in the Lancia system the charger is still bypassed and just freespins once the turbo kicks in. Quote Link to comment Share on other sites More sharing options...
Rookie Posted April 9, 2015 Share Posted April 9, 2015 Also you realise that as soon as you turn the blower off you immediately make the turbo think that the engine has reduced in size by the amount of pressure ratio that the super charger was operating at, this usually results in a torque hole. Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 If its a poisitve displacement setup so if you up the boost 1psi on the inlet it just means its 1psi higher at the outlet. Nahmate it multiplies it by the boost ratio. A blower geared at a 2x PR will double whatever you put into it (absolute pressure) Quote Link to comment Share on other sites More sharing options...
thegreatestben Posted April 9, 2015 Share Posted April 9, 2015 I read the blurb on Scanias turbo compound unit and it has a geardriven unit that works off've the crank additional to the turbo. Would you guys like to read it? I have access to the service info on my laptop. Quote Link to comment Share on other sites More sharing options...
Brock-Lee Posted April 9, 2015 Share Posted April 9, 2015 Wel then thats even more of a bonus. More boost! Quote Link to comment Share on other sites More sharing options...
Yowzer Posted April 9, 2015 Share Posted April 9, 2015 Also you realise that as soon as you turn the blower off you immediately make the turbo think that the engine has reduced in size by the amount of pressure ratio that the super charger was operating at, this usually results in a torque hole. Yeap, that it does. The idea is to gradually open the bypass to smooth the transition, but it'll still have that changeover issue regardless Quote Link to comment Share on other sites More sharing options...
Rookie Posted April 9, 2015 Share Posted April 9, 2015 I promise you that lancia did not by pass the supercharger. Watch any video of an s4 and you can hear the blower whine all the way through the revs. Quote Link to comment Share on other sites More sharing options...
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