02-06-2013, 06:49 PM
No, the big turbo feeds the little turbo. Little turbo boosts up first, once that's going it effectively creates more exhaust gas - enough to spool the bigger turbo.
The best bit is when the bigger turbo comes on blow, it's not exactly what you'd expect. Two turbos boosting at 15psi makes 30psi right? Wrong. The little turbo is now compressing air that's already compressed, this creates super-awesome boost (technical term). With one blowing into the other they "compound" their pressure ratios and produce more boost than their individual capabilities added together. Say both turbos individually boost at ~2bar absolute pressure (absolute pressure = boost pressure + atmospheric pressure; ie what we know as 15psi of boost), expressed as a ratio to atmospheric pressure this is 2:1. So we have two turbos compounding their pressure ratios of 2:1 each, multiply the ratios together and we get a final pressure ratio of 4:1. Knock off a bar to account for atmospheric pressure and you're left with 3bar or 45psi of boost...
The best bit is when the bigger turbo comes on blow, it's not exactly what you'd expect. Two turbos boosting at 15psi makes 30psi right? Wrong. The little turbo is now compressing air that's already compressed, this creates super-awesome boost (technical term). With one blowing into the other they "compound" their pressure ratios and produce more boost than their individual capabilities added together. Say both turbos individually boost at ~2bar absolute pressure (absolute pressure = boost pressure + atmospheric pressure; ie what we know as 15psi of boost), expressed as a ratio to atmospheric pressure this is 2:1. So we have two turbos compounding their pressure ratios of 2:1 each, multiply the ratios together and we get a final pressure ratio of 4:1. Knock off a bar to account for atmospheric pressure and you're left with 3bar or 45psi of boost...
