Why is the A/F ratio so fat?

[fastkevin]

I was looking at the F/S ads and noticed one that boasted his A/F ratio at 11:1.
I own a Kawi dealership and we road race. I have my own dyno and tune bikes regularly. My target A/F ratio is above 13:1. There are factors that will change this a little, such as timing etc.., but if I were to set a bike in the 11:1 area, the thing would vomit raw fuel (not really, but it'd run like crap). We're talking fuel-injected inline fours, not too dissimilar than cars with inline 4's. I ran a search on it which showed me posts with A/F ratios (some as low as 9:1), but not the reason why these motors need so much fuel related to air.
TIA

[nothere]

kevin,,


mitsu added a lot of fuel as knock protection. some tuners add more still.

however it is not to uncommon to find an evo tuned to near twelve or in the low twelve area. more so when water is injected... or alky.

the practice is to add fuel so you can raise timing. conversely take some timing out and lean it out.

[fastkevin]

By "Knock", do you mean detonation?

[LoBoost]

Usually on turbo'd motors you run them a little rich compared to NA to keep temps down and for added safety.

[denolloyd]

Originally Posted by LoBoost

Usually on turbo'd motors you run them a little rich compared to NA to keep temps down and for added safety.

+1. IIRC NA motors tend to hover around 14.5ish. Turbo motors under 12.5 on the high end. Mid to low 11's on the safe end..

[nothere]

better take some memory pills.
na cars tend to run around 12.5 wot. some very highly engineered new motors can make power with less fuel~ 13.5

14.7 is the magic number for low emissions and it happens to be the correct balance of fuel to air. iow every fuel molecule has an air molecule to dance with.

[RFH]

turbo afrs are rich to protect the tubine. Turbine inlet temps are usually brought down by excess fuel. Also they are rich to add additional detonation protection.

For bikes and such why are you so lean?
12.5 is about the peak flame speed for gas and its on the safe side for deto. I tune everything NA to 12.5.
13.5 is getting a little close to the detonation limit for what? a little extra milage?

[fastkevin]

Originally Posted by RFH

turbo afrs are rich to protect the tubine. Turbine inlet temps are usually brought down by excess fuel. Also they are rich to add additional detonation protection.

For bikes and such why are you so lean?
12.5 is about the peak flame speed for gas and its on the safe side for deto. I tune everything NA to 12.5.
13.5 is getting a little close to the detonation limit for what? a little extra milage?

Mileage? No. Power. Sportbikes nowadays come stock with upwards of 13.5:1 compression, and run just fine on 91 octane. Your typical 600 sportbike produces power in the neighborhood of 230hp per liter, normally aspirated of course.
Most racebikes run on oxygenated fuel, and some of these fuels like 13.6:1 or so. Typically as I wrote, you want to set it at 13.1-3:1, and then see if the particular motor likes it leaner or fatter.
What I'm trying to figure out, is if cars are lacking in ignition timing, and/or just can't run the numbers neccessary to use higher compression (which is what forced induction does), and more optimal fuel mapping.

[denolloyd]

Originally Posted by nothere

better take some memory pills.
na cars tend to run around 12.5 wot. some very highly engineered new motors can make power with less fuel~ 13.5

14.7 is the magic number for low emissions and it happens to be the correct balance of fuel to air. iow every fuel molecule has an air molecule to dance with.

Hopefully you can find it in your heart to forgive me kind sir...

[nothere]

What I'm trying to figure out, is if cars are lacking in ignition timing, and/or just can't run the numbers neccessary to use higher compression (which is what forced induction does), and more optimal fuel mapping.[/quote]

think some new design race motors (cars, na) can run in the 13afr.

its a matter of quality of design. it takes a really good chamber to burn all the gas at those afr.

12.5 was just a way to guarantee that every fuel part would have an air part to work with it. better to have to many girls at the dance than not enough for all the boys.

if the chamber makes all the girls look hot then all the boys will want to dance with them. if the chamber hides some girls in the dark corners they will never get to dance, so you need way more girls available.

[DTM]

Originally Posted by nothere

kevin,,


mitsu added a lot of fuel as knock protection. some tuners add more still.

however it is not to uncommon to find an evo tuned to near twelve or in the low twelve area. more so when water is injected... or alky.

the practice is to add fuel so you can raise timing. conversely take some timing out and lean it out.

Mitsu added fuel for cooling the tops of the pistons and combustion chamber.
In colder climates WOT will be slightly leaner with an exhaust upgrade and minor bolt ons.
Also with slightly smaller combustion chambers than earlier 4g63's the atomization characteristics of the MPFI changed.
Additional fueling does not aid in knock prevention. The right A/F charge and ignition lead deters detonation.

[nothere]

Indeed, I misinterpreted the factory rich design. Nevertheless the net result is an attempt to preclude pre ignition. (?)

personally I like a little less fuel and time to suit.

[RFH]

obviously leaner and more timing is better,
but boost, slow engine speed and low octane fuel = BOOM. so you need less timing and more fuel to combat this.

bikes are nice because of the high engine speed which is almost impossible to detonate at and there is no boost.

What is the power drop off of tuning 12.5 instead of 13.1 for bikes?

[DTM]

Originally Posted by RFH

obviously leaner and more timing is better,
but boost, slow engine speed and low octane fuel = BOOM. so you need less timing and more fuel to combat this.

bikes are nice because of the high engine speed which is almost impossible to detonate at and there is no boost.

What is the power drop off of tuning 12.5 instead of 13.1 for bikes?

I'm not sure what your version of "engine speed" has to do with anything going boom....

[RFH]

when engine speed is slow (car engine rpms) there is alot of time for knock to happen

at engine speeds above 10000 rpm the timescale for knock to happen is very low.

i was comparing a car engine to a motorcycle engine