hey. im just wondering which engine gets better gas mileage, the L98 or the LT1? and they both probably require premium gas right?

 

An LT1 requires 89 octane (R+M/2) fuel. An LT1 with 3.08 gears in a 4,400 pound Impala has an EPA estimated 27MPG highway mileage. I actually get around 24MPG with a non-stock cam and other modifications. Pretty good for a land-yacht. I doubt that an L98 in the same vehicle would squeeze out the same mileage without some significant EPROM changes. The biggest advantages for the LT1 are the sequential injection and much more sophisticated PCM, with both MAF and MAP, plus individual cylinder spark and injector control.

I'll bet Glenn could get an L98 very close to the OBD-II mileage and performance on the older S/D ECM, but I'm thinking there would be a couple of PROM burns along the way.