Big Cam needed for twin turbo C-5
09-14-2003, 05:20 PM
#21
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Re: Big Cam needed for twin turbo C-5 I run a 230/218 113LSA cam in my TT stang. 3600lb raceweight with heads that flow 185/155cfm (stock heads) respectively on a 331 with 10lbs of boost & trap speeds of 125mph. That may not sound impressive, but add another 75cfm to those heads....& another 5-10lbs of boost (basically a head swap & a turn of a dial) & this thing would easily do 9's of DR's.
The reason for the reverse is to keep exhaust velocity/pressure high. Open the exhaust valve too early & you lose heat....which is what drives the impeller. Keep the exhaust valve open too long & you lose velocity/pressure in the turbine housing & spool-up suffers.
Pressure in the exhaust housing (before the turbo) is typically 1.5-2 times the pressure in the intake manifold. This dictates very little overlap as the exhaust pressure would actually prevent the filling of the intake air-charge. This mainly happens below peak torque....as RPM's increase more overlap can be used as the inertia of the intake air-charge will push the higher pressure exhaust gasses out. So generally, for turbo motors that peak above 6000RPM a little bit more overlap is used.
The reason for the reverse is to keep exhaust velocity/pressure high. Open the exhaust valve too early & you lose heat....which is what drives the impeller. Keep the exhaust valve open too long & you lose velocity/pressure in the turbine housing & spool-up suffers.
Pressure in the exhaust housing (before the turbo) is typically 1.5-2 times the pressure in the intake manifold. This dictates very little overlap as the exhaust pressure would actually prevent the filling of the intake air-charge. This mainly happens below peak torque....as RPM's increase more overlap can be used as the inertia of the intake air-charge will push the higher pressure exhaust gasses out. So generally, for turbo motors that peak above 6000RPM a little bit more overlap is used.
