I just need some clarification here because I'm not quite grasping the concept.
Compounds are a combination of a large turbo and a small turbo. The larger of the 2 is feeding the smaller. There is less smoke and lag with this combination.
Larger feeds the smaller on the intake side. On the exhaust side, the smaller is first.
If we're feeding a smaller turbo with a larger turbo aren't we exceeding the maximum boost for the smaller turbo once the larger one is spooled?
Yes, and no.
Turbos aren't rated in 'boost'. They're rated in pressure ratio. Pressure ratio = outlet pressure/inlet pressure.
A single (small) charger making 30psi boost at sea level: PR
=14.7+30/14.7 = 3.04
A single (large) charger making 60psi boost at sea level: PR
=14.7+60/14.7 = 5.34
Example - GT42 feeding a stock H2E. Hypothetically speaking, the H2E is about to grenade @ 60psi, but the GT42 is certainly capable of pushing that sort of pressure through the H2E. Manifold pressure is above what you would normally see with just an H2E, so how is it surviving?
Let's take the two chargers in the examples above, but work it out differently.
We want 60psi 'boost' at sea level going into the engine, which is 74.1psi absolute. In general, most good compound systems will roughly evenly divide the pressure ratio between the two turbos.
So, Total PR
= 14.7+60/14.7 = 5.34, now divide that between both chargers and you have a PR
of 2.67 for each.
The first (large) charger will be: 2.67*14.7-14.7 = 24.5psi outlet pressure.
The second (small) charger will have the same pressure ratio. But, it will have a different inlet pressure. So: 2.67*(14.7+24.5)-(14.7+24.5) = 65.464psi boost pressure. The extra 5 psi
came from rounding during the calculations.
Are the drive pressures multipled or diminished when you run compounds?
Either, but overall they should be diminished for the same boost pressure since both turbos should be running closer to 100% efficiency than they would individually.
What is the difference between a compound setup and sequential?
Literally, compound means
composed of two or more parts, elements, or ingredients: Soap is a compound substance.
Machinery. noting an engine or turbine expanding the same steam or the like in two successive chambers to do work at two ranges of pressure.
The sequential is a more specific term.
1. the following of one thing after another; succession.
2. order of succession: a list of books in alphabetical sequence.
-In other words, the definition of a 'compound' can be intrepreted as having two seperate turbos of the same size, one on each bank (in the case of a V motor), and having the compressor outlets tied together to the inlet of the engine.
-The sequential is very specific that there is no branching, and that the supply is from the same source. This is probably the most correct term.