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AFR's what to aim for ?

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nedski
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AFR's what to aim for ?

Postby nedski » Thu Jun 13, 2013 9:32 pm

Ok some knowledgeable guys on here. What Afr's do you aim for from 4000-6500 revs on full throttle? I'm running around 11-13 psi on band aids.

This is a a quick run videoing my dials. There's no detonation but does slowly go rich. It does pull well to be honest but fuel consumption is terrible. I fear running weaker will cause more problems, at least rich is safe.
Don't tell me i need a Pnp ecu i know that! I'm just squeezing the best out of what I have .The white dial is in Bar and nudges .9bar oh its upside down too. Didn't know wether to post here or in help post.
thanks Neil

[youtube]http://www.youtube.com/watch?v=RR-FcN594Kk[/youtube]
Mk1 1.6 Turbo. Gaz shocks. Tr Lane roll bar.
Garage Owner, Lincolshire
Helper to the Scunny track day crew and North Linc's Track Day Club.
www.stokesofkelsey.co.uk
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BenF
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Re: AFR's what to aim for ?

Postby BenF » Thu Jun 13, 2013 9:51 pm

It was drilled into me that you aim for 14:1 on a road car, 14.5:1 on an NA race car, 12.5:1 on a turbo, 13:1 on a vintage and or supercharged...
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Re: AFR's what to aim for ?

Postby BenF » Thu Jun 13, 2013 10:03 pm

(I'm assuming you've read up on stoichometric ratios Neil?)
http://en.wikipedia.org/wiki/Air–fuel_ratio
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Re: AFR's what to aim for ?

Postby nedski » Thu Jun 13, 2013 10:07 pm

Ive been trying for the 12:5 .
It jumps weak when changing gear but drifts rich as you hold the throttle down.
Maybe having a 12:1 rrfpr is too much and i maybe should have gone for a 8:1 rrfpr . Even so the full boost is there early so why it creeps rich I dunno. It's been quite an exercise in getting old technology to work.
If I wasn't still building my garage i would have a pnp by now.
Mk1 1.6 Turbo. Gaz shocks. Tr Lane roll bar.
Garage Owner, Lincolshire
Helper to the Scunny track day crew and North Linc's Track Day Club.
www.stokesofkelsey.co.uk
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Re: AFR's what to aim for ?

Postby BenF » Thu Jun 13, 2013 10:13 pm

So it's pulling 12 ish when accelerating and leaning back on overrun? That's exactly as it should be!! :handgestures-thumbup:
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Re: AFR's what to aim for ?

Postby BenF » Thu Jun 13, 2013 10:19 pm

Confession- just watched the clip :wink:
Mate, there's not much wrong there. No detonation, and no risk either with a range I clocked between 9 and 13.5, with a flash 8 for a nanosecond.
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Re: AFR's what to aim for ?

Postby nedski » Thu Jun 13, 2013 10:23 pm

BenF wrote:(I'm assuming you've read up on stoichometric ratios Neil?)
http://en.wikipedia.org/wiki/Air–fuel_ratio


You can assume mate but you would be wrong :-D
actually I thought I read somewhere that petrol to air completely burnt at 12:1 (probably wrong). I did get a chemistry "o" level but that was long ago along with my engineering diploma, All forgotten now !

The extra unburnt fuel keeps combustion temps down though I think. So better slightly rich than hot and weak. Although i'm too rich.
Mk1 1.6 Turbo. Gaz shocks. Tr Lane roll bar.
Garage Owner, Lincolshire
Helper to the Scunny track day crew and North Linc's Track Day Club.
www.stokesofkelsey.co.uk
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Re: AFR's what to aim for ?

Postby nedski » Thu Jun 13, 2013 10:27 pm

Just to add on track days I'm getting about 60 miles to a tank of fuel.
£1 a mile :eek:
Mk1 1.6 Turbo. Gaz shocks. Tr Lane roll bar.
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Helper to the Scunny track day crew and North Linc's Track Day Club.
www.stokesofkelsey.co.uk
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Re: AFR's what to aim for ?

Postby Lazza » Thu Jun 13, 2013 10:31 pm

Mine is running a bit more power than yours but at full throttle around peak torque I aim for 11. Always safer to aim rich. Nobody ever damaged an engine from being over fuelled. The more boost you run, the nearer to 11 you need to aim.
Lazza

2001 Mk2.5 MX5 1.8 Sport
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Re: AFR's what to aim for ?

Postby BenF » Thu Jun 13, 2013 10:33 pm

nedski wrote:
BenF wrote:(I'm assuming you've read up on stoichometric ratios Neil?)
http://en.wikipedia.org/wiki/Air–fuel_ratio


You can assume mate but you would be wrong :-D
actually I thought I read somewhere that petrol to air completely burnt at 12:1 (probably wrong). I did get a chemistry "o" level but that was long ago along with my engineering diploma, All forgotten now !

The extra unburnt fuel keeps combustion temps down though I think. So better slightly rich than hot and weak. Although i'm too rich.


14.7:1 :handgestures-thumbup: and yes you're rich, and yes it does, also stops you melting your turbine - this is why LM and the old group B's deliberately stuffed unburnt fuel directly into the exhaust manifold to stop the turbo melting. Cue huge flames when that lot meets oxygen at the tailpipe :auto-layrubber:
In practice all engines prefer rich to lean, although the closer to that ratio you are the more of the fuels energy you can extract, which is why NA race engines are 'lean as you dare'.
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Re: AFR's what to aim for ?

Postby BenF » Thu Jun 13, 2013 10:35 pm

Lazza wrote: Nobody ever damaged an engine from being over fuelled.

Being a pedant, ever heard of borewash? :teasing-neener:
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Re: AFR's what to aim for ?

Postby nedski » Thu Jun 13, 2013 10:55 pm

Of course
The MRS says I'm a Bore and everything washes over me !! :happy-jumpyellow:

Out of curiosity what mpg are others getting on track days ?
Mk1 1.6 Turbo. Gaz shocks. Tr Lane roll bar.
Garage Owner, Lincolshire
Helper to the Scunny track day crew and North Linc's Track Day Club.
www.stokesofkelsey.co.uk
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Re: AFR's what to aim for ?

Postby Lazza » Fri Jun 14, 2013 9:27 am

I try not to think about it but I don't get better than 12mpg on track. Fuel usually costs me more than the track day entry fee.
Lazza

2001 Mk2.5 MX5 1.8 Sport
Hard Dog Deuce
GAZ Gold Pro
Mk3 seats
17” OZ Racing Superturissmo wheels (for the toad)
15” Rota Circuit 10 wheels (for track use)

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