Can anyone thoroughly explain how Speed Density replaces MAF, and what componants each has in relation to each other? I know what I'm building is a 1992 TPI, so should be Speed Density. I am doing a custom cold air intake, and will not want to miss any sensors or anything like a MAF before the boot kind of thing. Thanks, pics would help.

 

MAF = Mass Air Flow sensor; it uses a hot-wire anemometer to directly measure the mass of the incoming air, it "counts" the oxygen molecules that way, and knows how much fuel to add based on how much oxygen is coming in.

S/D = Speed/density; it uses intake vacuum, temperature, and so forth to "infer" how many oxygen molecules are coming in. As a result, it's much more sensitive to changes in the engine mechanicals, especially the cam and cubic inches, because its lookup tables don't match the engine's requirements any more. It only needs the MAP (Manifold absolute Pressure, in essence vacuum) and Intake Air Temp sensors in the intake tract.

Both types need throttle position, coolant temp, and O2 sensors, in addition to the ones mentioned above.

 

Okay, excellent description. That helps me a lot. This engine will be installed in a 1977 Vette that has NO CATS, and NO O2 sensors at all. Where will I need to install these and do I need just one, or both. Thanks...

 

You can get by without a cat converter(s) if you like, but may need them if you have required emissions inspections in your area. As I recall, '77 model years included cats on passenger cars. Many states have inspection requirements that stipulate that all original emissions equipment is installed and functioning for certification. Many states also exempt older vehicles. You'll have to check to see what, if anything, applies to you.

You will need a single O˛ sensor installed in either exhaust manifold as close to the engine as practical. Keeping it close to the engine insures good heating, which is necessary to get a zirconia type sensor active.

The stock TPI O˛ location on an F-body is here:



If you are using stock Y-car exhaust manifolds (the welded SS tubed type) the O˛ sensor is right above the LH collector.

 

Excellent info Vader. I will not worry about the CATs then, because I have never been hassled about my emissions at any of the local shops. Now, the trick comes in here. The Vette has Hooker headers and sidepipes. I'm assuming I will have to take the header to an exhaust shop, and have the O2 sensor bung welded in. Roughly how many inches down the tube would be practicle, and would any cylinder be better than any other for location? Thanks so much for your help guys...

 

you want the O2 sensor in the colector, as close to the primaries as possable, but where the wires won't touch the hot exauast