I've got a technical question about a speed-density LT-1 and K&N air filters....If there's no MAF sensor on a speed-density system, what effect would any changes on the intake system (ram-air, K&N, etc) have if the computer doesn't know how mauch air is coming into the engine? Isn't that a pre-programmed table based on factory air induction systems?

 

Anytime you can get more air into and out of the engine you're going to make more power. The computer will deal with the extra air just fine, don't worry about it.

 

Speed-density is a method for calculating the air mass flow. If your CAI is really effective, it improves air flow by reducing the pressure lost in the air intake system. That will net you a higher MAP. Higher MAP means a denser air charge in the cylinders. The speed-density calculation uses MAP to determine the density of the air... so it knows exactly how much air is flowing into the engine.

The only things that upset a speed-density system are changes that significantly effect the volumetric efficiency, since the VE table is based on the engines original configuration. But a simple change like an air filter or CAI isn't going to change VE. That will be affected by things like a more radical cam, tuned inlet runners or altered velocity in head ports, highly effective "tuned" exhaust systems, etc.

 

Thanks! That makes a lot of sense! I'm getting ready to buy a CAI for the 'vette and diddn't want to waste my money if the computer couldn't recognize the difference..

I wonder what problems GM encountered that made them use that technology only for a couple of years?

 

GM had very bad experiences with the Bosch MAF sensor they used in some of the 3rd Gens. It was a major obstruction to air flow, unreliable, and required an 1,000degF "burnoff" cycle every time the engine was shut down, to clear dirt off the sensing wire. It was only after GM developed their own MAF sensor - not a big obstruction, fairly reliable and not requiring the burnoff cleaning - that they felt a mass-air system was the way to go.

Direct mass-air measurement elimininates the "VE" issue, making the system much more responsive to changes.

There is nothing inherently wrong with speed-density... it just requires good up-front programming, and maintenance of the VE tables as changes are made that affect "breathing".

 

just going thru some old posts . I just had my car 944 Porsche with 92 LT1 vette engine in it on the dyno and when I pulled the K&N off the inlet tube I actually got richer a/f don't have any scanning tools so didn't know what the ecm was doing.