90firstgen wrote:
Well you need to have an idea of how much boost you'll be running with that turbo. There's obviously some exponential equation when it comes to figuring out how much the boost is multiplied by the second turbo. One thing I'm not sure on is whether you'd say you're running 50 psi out of that turbo, or whether you'd say that you're compressing 15 more psi to make "x" amount of boost.
The turbo isn't really "adding" pressure, it's multiplying the atmospheric pressure that is already there. With most turbo maps, you'll see a PR on the left side instead of psi. The pressure ratio (PR) is just the ratio of the pressure after the compressor to the pressure before it. For example, let's say a compressor is efficient to a pressure ratio of 3:1. Atmospheric pressure is 14.7psi; that compressor is efficient to 44.1psia, or 29.4 psig.
With twins, you're basically just multiplying the pressure... twice. If the primary is operating at a pressure ratio of 2 and the secondary operates at a pressure ratio of 2 as well, then you'll end up with a pressure ratio of 4, or 58.8psia (44.1 psig). This way you can achieve higher pressure ratios while still not exceeding the compressor map of either turbo.
So if you want to end up with an efficient 60psi boost (a pressure ratio of 5.1) and you have a primary that will efficiently provide a pressure ratio of 2.2, you'll need a secondary that's in it's map at a pressure ratio of 2.3 (which isn't hard to find).
The advantage of the HTT upgrades is found more in flow than in pressure. The wheels are taken from H1E's, which are on 8.3 L Cummins engines. They're more efficient at higher flow rates, which is why they're good at higher RPM's on 5.9's. As for picking a wheel for twins flow-wise, I'm pretty much lost...
This is the "basic-est" of basics on twins, based on what I've learned from reading. I ignored efficiencies as well. Feel free to correct any inaccuracies you find
1992.5 W250 pump tweaked, straight pipe, gauges, 3200 Gov. spring, AFC lever partially ground, timed at 1/8", Fuel pin ground, BHAF, HTT Stage IV H1C/E 60/12wg (ported), Transgo shift kit, KDP clothes-hangered, 202,000 miles - 36psi, 1250°