???

 

isnt optimal like 14.7:1

 

correct, this is known as stochiometric a/f ratio, depending on what is best for your engine as far as POWER is concerned it can fluxuate between 12.5-15afr depending where and when you need fuel. typically guys like to fuel more where the VTEC changeover event is happening and lean it out up top between 6-8K. this is just what I have seen that seems to make more power. if I was an engineer and understood things more I may have another answer.

 

Whatever A/F ratio makes more power is what is best.

 

No.

Stoich is too lean under load.

Best power is between 12.6:1 to 13.2:1, motor dependant of course.

 

you need to tune it on a dyno with a wideband 02 sensor or an a/f lambda meter so you can see your a/f ratio. Then change it and see if it makes more power or not.

s

 

I used to think optimal was 14.7:1 (stoic), but its not.
Good for idle, but not good for under load especially with I/H/E + different cam & ignition timing than stock. Some motors like it 13.2:1, others 13.6:1.

 

14.7 means nothing.
All it is, is the number parts of air it takes to use up 1 part fuel.
Thats all.

 

My car worked best around 13.3:1 A/F, my friends car with the same motor but slightly bigger cams like it closer to 13:1 A/F. I would say that all motor cars make the best power within the 12.8-13.5 range.

 

that is consistent with what I have seen make power, like I have said
I am no engineer but have hung out at the shop long enough to see it
happen

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">My car worked best around 13.3:1 A/F, my friends car with the same motor but slightly bigger cams like it closer to 13:1 A/F. I would say that all motor cars make the best power within the 12.8-13.5 range.</TD></TR></TABLE>


Adam, was this on the dyno or were you using an on board wide band on the street?

Also,does anyone know if there is a typical amount of difference from on the dyno to on the street?

 

On the dyno, at Streetflight actually. My car likes being richer than leaner. I have yet to see what A/F I am running on the street. I would like to find out though. From what I hear, you tend to run leaner on the street if you tune on the dyno. But on NA cars, you can run whatever A/F makes power, to a certain extent.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TodaSi &raquo;</TD></TR><TR><TD CLASS="quote">&lt;BLOCKQUOTE&gt;quote:&lt;HR&gt;is nt optimal like 14.7:1&lt;HR&gt;&lt;/BLOCKQUOTE&gt;

No.

Stoich is too lean under load.

Best power is between 12.6:1 to 13.2:1, motor dependant of course.</TD></TR></TABLE>

I dont understand what A/F ratio has to do with load? Someone explain this please.

 

"Perfect" air to fuel mix is 14.7 pounds of air to completely burn 1 pound of gasoline. That is called stoichiometric. That only works in the laboratory. Most engines in the real world will be 13 to 13.5 to 1 at idle, 15.0 to 1 at cruise, 18 to 20 to 1 upon decel, and 12.5 to 13.0 to 1 under acceleration. This is because very very few engines are 100% volumetrically efficient, and those that are are only 100% efficient at a certain rpm and temperature.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jappower &raquo;</TD></TR><TR><TD CLASS="quote">"Perfect" air to fuel mix is 14.7 pounds of air to completely burn 1 pound of gasoline. That is called stoichiometric. That only works in the laboratory. </TD></TR></TABLE>

 

anyone know?

 

More load = more fuel.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by IN VTEC &raquo;</TD></TR><TR><TD CLASS="quote">More load = more fuel.</TD></TR></TABLE>

Ok but why? Nobody knows.

 

Different A/F's affect different motor/power adder combinations differently.

I always keep the RX-7 on the rich side.

The Supra is happy at 11.7:1

 

SGT, here is a question for you.

my 11.2:1 ITR motor is using 310cc injectors...and they are at 88% duty cycle. on a different dyno (i know numbers vary..etc...as i've witnessed myself) a friend of mine made 202, 140 in 70 degree weather...and was using the stock 240cc injectors. i made 180-135 on south florida performances dyno in 110 degree heat, which equates to something closer to 190, 140 in 70 degree weather...

now where is the compromise here...as the 310's i'm running are nearly at 90%, and neal (kid who went 11.94's in his all motor setup with 202 whp) said his injectors were not even at max duty cycle....as he could have richened the air/fuel up.

just wondering...because frank smith tuned my car and he currently has the fastest front wheel drive setup in the world...in the full interior class. (www.sfp.net)

basically, he knows what he's doing...but it seems like something isn't adding up...as neal and i have nearly identical setups (same comptech 4-2-1 ITR Tig header) although he has an ITR intake manifold, ITR TB, b16a head w/ ITR cams)

 

i'm not sgt but here is a helpful tool on rce's site:

http://www.rceng.com/technical.htm#WORKSHEET

assuming bsfc of .5, 20% drivetrain loss, and fuel pressure at 50psi.. the calculations are right in line with what you are seeing..

310cc injectors would be at 90% duty cycle to make 228 crank hp.

i don't feel like doing the math but maybe your friend is running super high fuel pressures to satisfy his motor.. there are drawbacks to that though.

90% duty is a little on the high side. i experienced some sticking with my 310's at 90%.. not good

 

can anyone answer my question?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TraKtioN &raquo;</TD></TR><TR><TD CLASS="quote">can anyone answer my question?</TD></TR></TABLE>

Read the above posts. When underload it requires more lbs of air per lb of fuel.

That was a given.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by poison &raquo;</TD></TR><TR><TD CLASS="quote">

Read the above posts. When underload it requires more lbs of air per lb of fuel.

That was a given.</TD></TR></TABLE>

ya but WHY does it need more fuel under load, doesnt make any sense, the rpms either climb, stay, or drop according to load. What does that have to do with fuel?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TraKtioN &raquo;</TD></TR><TR><TD CLASS="quote">

ya but WHY does it need more fuel under load, doesnt make any sense, the rpms either climb, stay, or drop according to load. What does that have to do with fuel? </TD></TR></TABLE>

Because in order for the RPM's to increase, combustion temps go up and more of a combustion is present, in a recriprocrating mass, will increase the revolutions per minute (rpm).

That is why when you decelerate, it is leaner, there for the RPM's going down.