I recently picked up a set of Acell/Lingenfelter runners and a ported plenum as well as a gutted airbox for my 1990 LB9. I was wondering if these mods will work with the factory prom or will I have to get a new one? What kind of HP increase can I expect with these mods?

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1990 Iroc convertible,305 tpi,Black with black leather interior,lowered,Taylor 8mm wires,K&N's,gutted airbox

 

If it is just the "ported" TPI intake and not a Superram, you CAN use the stock Memcal as it tends to be overly rich anyway.

However, for max hp/tq, a reworked eprom will definitely help. The two areas to look at are the VE tables and the Spark Tables. Spark Tables tend to be the key for max power as (generally) the more Spark Advance (without detonation) will yield the most power.

However, stock GM heads do not seem to like a lot of spark advance and there is a very narrow "sweet spot" of only a couple of degrees where any lower and your engine doesn't seem to perform well and any more, and you encounter detonation.

This is something that separates a purchased eprom from a "diy prom". With DIY, you can find that narrow "sweet spot". With a purchased eprom (custom or otherwise), they MAY hit the "sweet spot" or they may not. This is where every engine has it's uniqueness.