Backgound: Let's just say I lucked out and what was going to be a single turbo w/blower compound is now going to be twins w/compound.

The general setup is a ford 4.6, 9.1:1 CR, cams, ported Eaton M112 blower, 6-spd manual. Fuel and drivetrain should be able to accomodate 1200hp.

Turbo selection is the question. I've got it narrowed between two Turbonetics models, a hurricane series 66/65 0.82 ar, or a T-series 66/68 0.96 ar. General priciple would point to the 68mm turbine as being a better choice for compound use, but anecdotal evidence with the Hellion Hellraiser kit seems like the 65 would be fine, and since this is more of a street car the 65mm / 0.82 ar might be better. Of course both are fairly large and may not be much of a factor unless I'm really pushing it.

 

It's a cool idea but at a certain point that eaton will become a restriction for the turbos

 

I'm fully aware that it's a matter of trade-offs, but that's outside the scope of this discussion. I'm just trying to size the turbos accordingly for a compound setup.

 

Could be very interesting, I would think I would want the larger turbines. It appears that the Hurricanes are based on a T3 turbine housing, while the T series is probably going to be based on a T4 turbine. Although the wheels can help with that differentiation if you wanted to size up later you'd be modifying parts to go to a T4 probably, and the clearances downsizing housings are going to be way easier in general than upsizing housings. Not only that but if you're running a blower setup with a lot of overlap it's quite possible you'd want more turbine to help that out too.

 

Cool to be different. I would expect the blower just makes the engine 'look' bigger than it actually is. So if you are running 7 psi boost from the blower alone, you could approximate the engine to be 6.9L then select a turbo for that with a conventional matching program. Should get you in the ballpark. Good luck with your build.

 

There's two different 66/65 Hurricane turbos; I would be opting for the T4 housing 66/65.

Currently the cams don't have much overlap to speak of (114/114 +3).

I also think that my concerns over turbine size may be overblown. I'm going to run out of fuel long before the turbine becomes too restrictive (~1200hp capable fuel system), and if anything the larger 68mm turbine may be a detriment with the manual transmission. Maybe in the future if the blower falls off and an auto goes in, but I think for now I'll opt for the 66/65.

That was kind of where I was coming from, but there's still a lot of variables when you're talking compound. While mathematically it's a 7L engine, it may not quite behave like a normal 7L with a turbo, since the blower will probably change your exhaust velocity and volumetric efficiency, especially at lower RPMs.

I also see that you're local to me. Small town.