MPI Twins Are In!!! (Pics Inside)
05-31-2008, 08:37 PM
#46
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06-01-2008, 04:07 PM
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06-01-2008, 04:12 PM
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they're the poor-man's way of controlling boost when you can't afford or fit a wastegate on the bottom turbo. not a desirable way to control boost as you aren't controlling turbine shaft speed 
06-01-2008, 04:17 PM
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Yeah, I only needed them because I still haven't installed head studs yet.
06-01-2008, 05:57 PM
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I'm pretty sure wastegating the primary is more effective at controlling boost than wastegating the secondary. When you wastegate the secondary all of that exhaust hits the primary anyway. I sure hope so, I'm waiting on an s300(no wastegate) over a GT4202(wastegate) from Nathan. I don't plan on studs in the near future and I will be happy with 50psi of driveability bliss.
06-01-2008, 07:11 PM
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Max pressure without studs seems to be in question, some say 45psi, some way 60psi is ok (3rd gens only). I dunno, I wont worry about 50psi on occasion. I've seen that on sps66 with pretty high egt 1400-1500deg f, not very often though, and everything is still intact. It seems like I have heard of more head gasket problems from improperly torqued studs than stock bolts. But that might just be because not many people run high boost on stock bolts. Now there is a good poll for the forum.
06-01-2008, 07:21 PM
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you definately want to wastegate the secondary (top) turbo!!! you want to keep the boost down to a nice efficient level for the compressor (20-30psi?) and let the bypass exhaust gas have a chance to really spool that primary (bottom) turbo.
wastegating the bottom turbo gives you the most adjustability with best spool
wastegating the bottom turbo gives you the most adjustability with best spool
06-01-2008, 07:49 PM
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I'm pretty sure wastegating the primary is more effective at controlling boost than wastegating the secondary. When you wastegate the secondary all of that exhaust hits the primary anyway. I sure hope so, I'm waiting on an s300(no wastegate) over a GT4202(wastegate) from Nathan. I don't plan on studs in the near future and I will be happy with 50psi of driveability bliss.
06-02-2008, 06:50 AM
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You really only need to WG the top turbo. That allows you to tune the setup for maximum efficiency.
Wastegating the bottom turbo gives you control over the max boost. The only time that's really needed is to for head gasket or drive pressure reasons though.
Wastegating the bottom turbo gives you control over the max boost. The only time that's really needed is to for head gasket or drive pressure reasons though.
06-02-2008, 05:59 PM
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For controlling drive pressures, no.
WG'ing the bottom charger (in the case of an S400) would require using an external WG. That's not cheap and adds a good amount to the price. I think the only time you would really need a WG on the bottom charger is if you're heavily fueled with huge HP.
