"LB9 and L98 platforms updated with new speed density fuel injection"

What exactly is it? is it just a reprogramming of the PROM or something

 

Different method of fuel control. older TPI systems were mass air flow sensor controlled. It measured incoming air mass and used that to caculate fuel required. Speed density uses a Manifold absolute pressure sensor and based on that along with other parameters like temperature, it will calculate the fuel required.

 

Is it possible to convert to the newer style? Does it make a difference?

 

If you had a TPI MAF setup car and wanted to go speed density, yes you can easily convert the systems. Just need to add a MAP sensor and get a speed density based computer and PROM.

Its just a few wire changes to the harness where it plugs into the ECM. Speed density has 3 plugs while MAF has only 2. So you need to add a plug and wires for a few things.

I did the swap, its not all that difficult to do. Tech articles here are a huge help.

As far as a difference, depends.... there could be a point where stock MAF and inlet ducting could become a restriction in flow and thus make less hp than capable. But this wont happen until your up over 500 hp.