I am working to install a 5.7 into my 3.1 RS, and I have a ported plenum, and an edelbrock manifold. I have read that MAF sensors can compesate for increased airflow due to these types of mods, among others, while a MAP will need a new PROM burned (Is this true? What if I make the mods, and *don't* burn a new PROM?).

I don't really want to burn and test and burn and test a new PROM while I'm trying to get this engine to work, so I was thinking that I would use the MAF, and downgrade my ECM ('91) to an '89 to drive the MAF. But I discovered that the Speedo and VSS signals are different for 90-92 ECM's (VSS high/low, etc). I like the 91 style guage cluster, and don't want to put in '89 guages. So, how can I get the '89 ECM correctly run the 90-92 guages? Or will I need to either swap the guages, or go with the MAP? Thanks in advance

 

The porting and the edelbrock base shouldnt require a new chip.
It helps but those dont change the vacuum like heads or a cam would so it shouldnt be a problem. I changed from a stock 305 to a 350 with aftermarket heads and a big cam and the car started and ran with the 305 chip. And that was on a MAP system. It didnt smell great but it ran and got like 16mpg and I even beat a mustang(haha). MAP really isn't bad, and if the mods get crazy you will have to burn chips with MAF anyway.