I found this excellent post on fourm.miata.net by Emilio @ 949Racing.com where he summarizes the effect I/H/E mods have on NA/NB engines and how power to weight ratio compares to the S2000 and Scoobie. Read the whole thread here: http://forum.miata.net/vb/showthread.php?p=5588114#post5588114
When considering power improvements for an N/A Miata engine, you need some perspective and how it affects the car in the real world.This puts things in perspective.
2445# Base model 90, 200lbs of occupant, half tank of fuel90whp Typical whp of healthy 1.627lbs/hp
2595# NB1 with usual factory options, driver, fuel112whp23lbs/hp
Now to the fun part. The S2000 leaves the factory very highly tuned. It's well known that even the most nasty race exhaust for an S adds maybe 3whp. Header maybe 5, cat delete about 4. Run all together and you're at 112db and maybe 210whp. Intake adds nothing on an S. You'll also lose about 50# in exhaust weight so 14.0lbs/hp, a gain of about 7%.
NA6 with street exhaust, high flow cat and racing Beat header, K&N intake. That's worth about 15whp typically so 105whp. Weight stays about the same so 23.2 lbs/hp for about a 14% increase. Twice that of the S2000 at a fraction of the cost I might add. Add an ECU and you're at 115whp.
NB1 with I/H/E will make about 135whp, weight about the same. 19.2 lbs/hp, about 16% increase. Add an ECU and and you're at 145whp.
3644# 2012 Subaru Impreza STi 5 door, driver, 1/2 tank260whp14.0 lbs/hp
Take a base NB1, delete A/C, P/S, bumper supports, lighter seats, plastic rear window etc. Easy to pull 200# out of the NB1. Add Mods-that-add-very-little-power and you're at 16.5 lbs/hp. This theoretical Miata with decent suspension and 225/45 R compounds on 9's will run circles around a stock S2000 or ST1 on a road course despite the power "handicap".
Since the Miata is so light, even 5whp can be felt and will affect lap times.
Our NA6 example with I/H E and ECU jumps from 90 to 115whp. About a 26% increase. Ask any owner who has done these tweaks and they'll tell you it's a different car.
While the power figures will not impress anyone these days the actual on track performance of a 140 whp Miata on R-compounds are nothing to be embarrassed about. Our Euro-spec NBFL VVT engines will give ~ 10whp more with the higher C/R pistons as well.
People, at least here in Norway, are too hung up in (claimed) power figures and feel the need to have x00 whp BEFORE going to the track. Bullshit. Last season in what would be the heaviest N/A powered Miata ever (MSM with no turbo) was one of the most fun and trouble free seasons ever.