IMHO Ian whilst there are many people in other countries "claiming" to have 100 BHP/litre (normally aspirated)... few of these are
verifyable....many are pub figures and lack any scientific foundation, thats not to say it can't be done just that we have to "weed" out the wheat from the chaff so to speak
100 BHP/litre is BLOODY difficult to get out of ANY normally aspirated engine never mind the single cam non cross flow L series, without major investment in both time and money... I know I have tried
Another fly in the ointment is the BHP fixation that never gets really discussed.....BHP is only a factor of torque multiplied by RPM and yet torque is hardly ever mentioned even though it is a better indicator of "grunt"
In order to get close to 100 BHP/litre, major major surgery is needed such as welding the head up to get compression ratios up to and exceeding 12:1 (have seen figures 13+:1)....10:1 and below just wont cut it.
Serious investment is needed in porting/polishing
Race fuels
Biggest valves possible sometimes exotics such as titanium etc
Big lift cams (try 600 thou plus
)
Custom inlet and exhaust systems (experimentation in runner length)
Custom fuel systems such as throttle bodies
Intruded crown forged pistons (also raising compression and maybe improving the flame front/burn)
Exotic rods (rod/stroke ratio)
Race prepped cranks/blocks (to withstand the increase)
The real kings of L series tuning are the Japanese
who achieve credible and verifyable figures but even then we are talking 320 - 330 bhp out of the most out and out modified 3.1/3.2 litre screamers. Across the pond the likes of Rebello etc dont profess to get any more.
All of these mods leave the car less and less streetable every time even the great Sato san
intimates somewher on his brillaint web site that his car is not the sort of thing that you would want to drive to the shops in as power is made much higher up the rev range than a normal car would be (if you can find the dyno traces check out power under 4000 rpm)
When the new 3.0 litre gets built I must admit I am
hoping to get close to these figures but its going to take A LOT of work and £ and take probably wont happen before next season.
One factor is parts and engineering availability in the UK....your good self for instance had a head prepared in the US
The Japanese have considerable access to wonderfull cams, headers etc from the likes of Kameari etc plus their workmanship and passion is absolutely without equal.
Just my 2 farthings worth