Red Line SI-1 contains:
30% to 50% PolyEther Amine (PEA)
1% to 10% Isooctanol
5% to 20% Aliphatic Naphtha
http://www.redlineoil.com/msds/49.pdf
Based on the MSDS for SI-1, it appears as though the range provided for each ingredient is listed in terms of its percent of the fluid's total volume.
Amsoil PI contains:
44.4% to 53.8% Hydrocarbon Solvent
27.7% to 36.9% PolyEther Amine (PEA)
4.5% to 9% Petroleum Naphtha
4.5% to 9% Substituted Aliphatic Amine
0.2% Naphthalene
http://www.amsoil.com/msds/api.pdf
Based on the MSDS for Amsoil PI, each ingredient is listed in terms of its percent of the fluid's total weight. Specific gravity is used to designate a fluid's weight in relation to the same volume of H2O.
If the above information is correct, then Red Line contains 30% to 50% PEA by volume and Amsoil PI contains 27.7% to 36.9% PEA by weight. Comparing percent of PEA by weight against percent of PEA by volume is not an accurate means for determining which product contains more PEA.
I am too tired to try to figure out which product contains more PEA, but my money is on the PI. By the way, I treat each tank in my 2007 Civic LX with 1/3 ounce of SI-1 per gallon of gasoline. SI-1 is a great product and has excellent UCL properties.
I use Amsoil PI to clean up the fuel system in my wife's 2006 Pilot before each oil change. She does not want to add fuel system treatment to each tank of gas, so I rely on PI instead.
When all is said and done Amsoil PI and Red Line SI-1 are both top notch products. I wish that Amsoil would market a version of PI that could be used in each tank of gas like the SI-1. For now, however, the PI is geared towards periodic cleaning every 4,000 miles.