Air Fuel Ratio ????????????

tasroadster · Postby **tasroadster** » Sat Jun 24, 2006 11:49 am

I have read on the forum that a AFR of 12.7 is ideal.

The technically correct AFR is 14.7

So is the 12.7 required for max power output ??

Under high loads ?

Thanks for your help.
Regards

Matty · Postby **Matty** » Sat Jun 24, 2006 6:54 pm

Steve 818 wrote:
An AFR of 14.7 is the stoichiometric mix for petrol. In other words it is the most efficient ratio of air to fuel.

To clarify, stoichiometric means that there's exactly the right amount of air to combine with all the fuel and combust completely, with neither fuel nor air in excess. It's not the most efficient A/F ratio (that's somewhere around 16-17:1 IIRC)

Alf · Postby **Alf** » Sat Jun 24, 2006 7:00 pm

I can imagine that even that 14.7 could vary by 0.5 or so depending on the exact mix of components in the petrol.

Cheers,
Alf

Alf · Postby **Alf** » Sat Jun 24, 2006 8:18 pm

THE REAL BORIS wrote:Have you seen the stock SE on a dyno re A/F ratio?

It's extremely lean, until by 3000 rpm it has enriched to 13:1 & by the time you see 4,500 rpm it is off the scale (and remains off) somewhere less than 10:1!!!

Yepp, seen mine today! Have chart in front of me. Mine's flat until 3k, then reduces in a straight line to reach 10 just below 4.5 as you say. I wonder just how far down it goes. If that line remains straight, it'd be down somewhere about 8:1 at 6500 rpm. Can't be good for economy.

Don't forget, though, that's under load and at full throttle. I'm sure the AFR increases when you reduce the right foot pressure.

Cheers,
Alf.

tasroadster · Postby **tasroadster** » Sat Jun 24, 2006 8:35 pm

SO.......what would be a nice AFR goal for an NA6 under high loads from 3500 to 7200 rpm ? (really 4500 - 7200)

(NA6 with cat back - headers - CAI)

For a performance improvement......

For that matter, is there any benefit in using 98ROM fuel as apposed to 95ROM fuel ?

Thanks for your help.

Regards.

Matty · Postby **Matty** » Sat Jun 24, 2006 9:13 pm

Honestly, 12.5 is a good starting point. It won't make a massive difference if you're one way or the other around it, but slightly richer is safer.

Without compression ratio or cam changes, you won't majorly benefit from 98RON fuel.

tasroadster · Postby **tasroadster** » Sun Jun 25, 2006 9:56 am

I am playing with a Jaycar AFR intercepter....... $80

+ RX 7 AFM

So just wanting a ave. AFR setup figure without the expense of stand alone ECU +/- dyno time etc.

Also hope not to melt the ?#@%$ out of the internals !

Thanks for your help.
Regards

The Pupat · Postby **The Pupat** » Mon Jun 26, 2006 11:28 am

12.5 then maybe even 12 I'd say.

I wouldn't trust that for a tune as far as I could kick a very fat elephant* .

*Note I am not Popeye, Hulk Hogan or the Incredible Hulk so I don't reckon I could kick an elephant very far at all.

Astroboysoup · Postby **Astroboysoup** » Mon Jun 26, 2006 11:45 am

id like to see what would happen if you tried.

trader · Postby **trader** » Mon Jun 26, 2006 12:29 pm

Hi Tasroadster

My 1.6 NA has a JAM racing (non programable ECU) which last week showed on Dyno as AFR of 14:1 around 4000 rpm, and 12.0:1 WOT.
I am guessing that the manufacturer would have tuned it for optimum performance of a stock 1.6. Comments on this thread seem to agree.