Tuning for Power or Economy
 

What is the difference between tuning for power or economy?

I've got a Haltech setup with LS1 coils and two injectors per intake, wideband O2.
(PP NA) Don't have EGT yet.

Timing curve? Sequential or simultaneous injection? Fuel/Air ratio?

There isn't a difference.

You can forget about economy down low with the PP but you still tune for both. Light loads don 't need to be rich in mixture (your just wasting fuel). Light throttle you tune for as close to 14.7 as you can get or slightly higher A/F ratios while cruising without bogging. WOT you tune timing and A/F for whatever your set-up makes best power (12.5 A/F and up to around 13.5 depending on timing). This is a general range because every PP set-up varies based on runner intake length and exhaust.

For a street car, fuel economy and power are generally tuned separately.

Fuel economy will depend mainly on part-throttle conditions, and you will tune full-throttle to achieve reliability and power.

For racing, it can be different.

https://www.rx7club.com/attachment.p...1&d=1385847928

On a race car, you can tune for fuel economy at full throttle as well, but you will probably only see the difference over the course of a 24 hour race.

I have tried tuning for "economy" and every time, I find that making the engine make the most power at a given throttle setting WILL get the best fuel economy. This is by tuning for lowest duty cycle for given conditions.

On a high overlap engine you do need to run it excessively rich at low load for drivability reasons. The difference between 13:1 and 12:1 at a 30mph cruise is minimal as far as fuel consumption goes, but if the engine isn't happy there, then you find yourself pushing past the unhappy parts and THAT makes fuel consumption go up.

Most people who drive my car comment that it drives like a stocker, except for sounding really happy at idle and how there's just more power everywhere on the tach.

I cruise at 12.5:1 down the highway and get 24-27mpg depending on the ambient air temps. Hotter temps mean better fuel economy. I can lean it out but it starts bucking, which means you need to pull timing away, and the engine makes less power and you end up using more throttle and it ends up being a wash fuel consumption wise.

Under heavy load it is perfectly happy to run as lean as 16:1, though. Because of the nature of how I use my car, I run it quite a bit richer than that in an effort to keep the engine cool. :) If I had a lot more radiator, I would lean it out to about 14:1 at full throttle because there's a bit more power to be had there, but temps go up quickly. I'm not exactly power limited so I'm happy with losing a couple percent power and running excessively rich.

Very interesting observations peejay - thanks for sharing. This confirms what I've been noticing in my tuning endeavors, that is that making it leaner is only really hitting drivability down low.