my car is running a JRSC - at close to 10psi according the the map sensor - an intercooler and DC5 cams
its been tuned on a hub dyno and produced around 330bhp at the hubs - and I'm very happy with the WOT performance

however on a run - or going A2B over any distance i notice I'm getting only 22mpg ( UK gallons = 4.54 litres) which seems excessive
the car has a small tank - approx. 35litres so its also a bit limiting in terms of range

so i started doing some datalogging via the Honda Kpro ECU to see if there was anything obvious i could do
it is running in closed loop - with a target of 14.7 at part throttle - so i notice that its trimming fuel up to -20% a lot of the time - so the basic fuel map in the cruise regions is on the rich side which will not help - as it takes a few seconds for the closed loop to compensate every time you touch the throttle - which you do a lot in a light car like this with a fairly powerful engine.

so i am thinking of reducing fuel in the cruise regions of the fuel map on the low cam only - using the amount of fuel trim after 5-10 seconds of steady state in the logs - as this is where it sits at cruise - and leave the WOT mapping well alone

my question is - up to what Manifold pressure is it safe to run leanish mixtures
obviously it is set so it will default to open loop once its driven hard
but its still in closed loop and on the low cam at 80mph and the MAP is showing around 65kPa

my question is - how much of a risk is it for heat and potentially lack of fuel for lubrication if you lean this out say 10% less fuel than stoichiometric / 14.7:1 - not that that is my intention - just trying to understand how much risk there might be tweaking the map in this way.

or more specifically - does anyone have any information on where safe mixture limits are as you transition from cruise ( where mixtures are typically 14.7: or leaner ) and WOT ( where mixtures are typically 12.1:1 to 12.6:1 on SC engines )?

much appreciated
Garz

 

14.7:1 AF is good to about 8" vacuum... then you should slowly richen up to 13.2:1 at 0 vac/0 boost. Once you reach a couple pounds of boost, you should be down to mid to low 12's as you stated above.

It is never a good idea to set the raw maps at 10% lean and expect fuel economy to improve significantly... the downside is you put the engine at risk. It is better to set the raw tables 2-5% richer than you want to target, especially this time of year, since the car will naturally lean out when the outside temperatures cool down in the fall and winter.

 

thanks for that - perfect input and just what i was looking for

yep - I'm targeting around 2% on the rich side of intended mix as the basic map.

BTW - i believe the Ecu has intake air temperature mixture correction tables that is using to adjust for air temperature induced density changes so hopefully that will prevent any undue leaning out

just in terms of understanding the risks - and how it all works - in terms of det - i understand this can occur really quickly and damage an engine in probably a few seconds if it occurs at WOT.
at part throttle / cruise conditions is this still the case - or does temperature build up much more slowly and therefore damage occur only after more prolonged time of less severe det

 

anyone?

 

Twenty two miles per gallon isn’t really that bad for a twin cam car with a supercharger and probably more mods. I wouldn’t even mess with tuning it if you are just trying to get better fuel economy.
As far as pre-detonation goes, it is really bad and you should try to stay a little on the rich side of things to avoid it. Might as well stay rich and safe rather than trim fuel just to get a few more miles per gallon.

 

Detonation will not damage the engine anywhere near as fast at part throttle operation compared to WOT. While datalogging, watch your knock count. In the places that you get any knock, simply increase fuel values AND/OR reduce ignition timing in that area of the maps... and don't forget to make sure you are making the changes on the proper VTC utilized tables.

 

MPG: i guess its not that bad - i looked up the standard EP3 type R and that will do around 31mpg at a steady 80 ( i thought they might be mid to high 30's ) - which is where i was getting 22ish

still - the charger has a bypass when not in boost - and its well away from boost at 80mph - so the charger is still turning but not really pumping or doing much work so i wasn't really expecting a big impact on economy - after all that's the purpose of a bypass - and i'm getting a 30% drop even with the charger bypass - seems alot

ref det - I know its an easy way to kill an engine - and for that reason i am leaving the WOT map points well alone - but my understanding is it is much less of a problem at part throttle - and hence my question

 

thanks for that - yes - my knock sensor is active - ( sometimes they are not able to be used with roots type chargers as too much background noise ) but i haven't had any knock at all on datalogs with the current map - i think the mapper was really focussed on peak power and relatively little time spent elsewhere in the map - it was typically 10-20% rich everywhere and running way less ignition than it needs for MBT in all the cruise areas - so it was needing more throttle at cruising speeds - and as a result MPG was poor. but it was safe and driveable - just not optimised.

will do small tweaks at a time and continue to watch the logs for knock

at least thats what i think was going on