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Author Topic: How lean is too lean?
Wes Saunders
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My engine is at 14.3 @ 5,500 RPM gradually decreases to 13.0 by 6,200 and crosses the line at 7,300. I am obviously a little concerned at the lower RPM, how critical is it there? Plugs look good and brown with no signs of detonation. Engine sounds good etc.

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Qik Nip Verified Driver Made Donation to Website Series Champ
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Wes:
I'll defer to the engine tuning gurus hereabouts, but normally 12.5:1 is the lower end of the fuel / air ratio. The question is where yours at 6,300-7,000? Since that's where your engine spends a fair bit of its time.
Rick

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Fortune Cookie Racing SM 60
Directions for use: Race, Rumple, Repair ... Repeat!

Wes Saunders
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Qik, it is pretty flat but at about 6,700 it falls under 12.5 Since we do spend some corner exit time at 5,500 and 6,000 full throttle I am wondering if there is any room for concern. Of course legal suggestions on how to flatten the curve is also appreciated [Smile]

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'90 SM
2006 SSM North East Enduro Champion

oem steve
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Hey Wes I beleive the factory settings for the AFM are set to run the car leaner at low RPM otherwise you'd foul plugs pretty easy. Try looking up the company that advertises on here with the spin brackets, they may help and I beleive are legal they simply rotate the AFM to use the weight of the flap to open it sooner. I think its SP Inductions?

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John A - 5X Racing Verified Driver
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My research had always lead me to find that 13-13.5 to 1 on your air/fuel gauge towards the top end of the rpm scale is ideal. I use an ART tuned afm with the SP Induction Systems Spin Bracket to fine tune the air/fuel ratio, I monitor it real time in the car with an Innovate Motorsports afr gauge. This setup works well for me and I rarely have to tune it, but the capability is nice. Then again 90% of our races are hot weather affairs, so its pretty consistent.

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John Adamczyk

Owner: 5X Racing Online Race Shop
Driver: Team 5X Racing #25 Spec Miata
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Race Engineering Powered 1.6

oem steve
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Wes, also need to know if you are checking it at the exhaust manifold or at the tailpipe?

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Anyone using a programmer for the AFM? Fat middle and just right top?

1.6L cars may open and adjust, but not modify, the
OEM airflow meter. For 1.6L cars, the position of
the air flow meter may be moved provided it remains
attached to the unmodified factory intake tube.

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Jim Daniels

MAZDARACERS.COM

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quote:
Originally posted by oem steve:
Wes, also need to know if you are checking it at the exhaust manifold or at the tailpipe?

Steve's point is well taken. The best location to measure the F/A ratio is at the O2 sensor port.

That aside JD must be on vacation (he logged in as a visitor?).
Rick

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Fortune Cookie Racing SM 60
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Wes Saunders
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Measuring at the tailpipe, typical dyno set up.

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quote:
Originally posted by JIM DANIELS:
Anyone using a programmer for the AFM? Fat middle and just right top?

1.6L cars may open and adjust, but not modify, the
OEM airflow meter. For 1.6L cars, the position of
the air flow meter may be moved provided it remains
attached to the unmodified factory intake tube.

[Smile]

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Tom's Double O Verified Driver
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Which reads leaner.....measuring by the tail pipe or by the engine?

Tom

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Engine goes BOOM...too lean... [Wink]

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Kim

91 BRG SMT RIP
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Dave Lewis
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So who sells the spin brackets?

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Here's a hint - on the home page click 'view all advertisers' and look for the banner that starts with SP.

Tom's Double O Verified Driver
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quote:
Originally posted by Tom's Double O:
Which reads leaner.....measuring by the tail pipe or by the engine?

Tom

Anyone know the answer? Does it reads richer or leaner at the tailpipe as compared to reading near the engine? I don't have a wideband on my car and only had the a/f ratio measured at the tail pipe on a dyno.

Tom

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I believe it's leaner at the tailpipe. However, most dyno owners adjust the readout to compensate.

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Muda Motorsports
"We're all here 'cause we're not all there."

Wes Saunders
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Does any one really worry about their engine if it is at 14.3 air/fuel ratio @ 5,500 RPM? Enquiring minds need to know.... I don't think it is a worry but looking for more informed advice.

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'90 SM
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If you have a graph of the AFR to post it would be helpful. It sounds lean to me but hard to tell without seeing the graph.

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Gale Corley
99 SM GRE Super Deluxe
93 SM GRE Jr. Deluxe

Kendall Jones
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The tail pipe sniffer will read equal or leaner at the end of the pipe. The leaner reading depends on how sealed your exhaust pipe is, the high velocity gas will suck in air as it shoots down the pipe (venturi effect & all). even a pin hole will make it read leaner.

I usually take the AFR readings "under advisement" on my dyno. I measure at the tailpipe (unless I get further up the pipe) & usually dont know what cobbled together exhaust may be under there [Wink] I look at the power / torque outputs (and the area under the curve) when tweaking the AFM.

I wouldnt worry about 14.X at the tail pipe; depending on intake / exhaust setup is mounted, you usually need to have a lean spot @ one rpm bandwidth to counteract a rich hump somewhere else.

Kendall

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cpdenis
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Bit of a hijack here but along the same lines.
Since both the SCCA and NASA have adopted the adjusted timing and fuel pressure regulators on the 99's, I'm looking to go that route and perform that modification. Given that there is now the potential to lean and blow the engine, what is the recommended complete gauge setup (complete hardware) and a/f ratios to be adjusting for or worry about. Or am I over thinking this,
Thanks
CP

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Email me CP, I will get you set up

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John Adamczyk

Owner: 5X Racing Online Race Shop
Driver: Team 5X Racing #25 Spec Miata
NASA FL Race Director
Race Engineering Powered 1.6

Willie the Tard Verified Driver
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quote:
Originally posted by cpdenis:
Bit of a hijack here but along the same lines.
Since both the SCCA and NASA have adopted the adjusted timing and fuel pressure regulators on the 99's, I'm looking to go that route and perform that modification. Given that there is now the potential to lean and blow the engine, what is the recommended complete gauge setup (complete hardware) and a/f ratios to be adjusting for or worry about. Or am I over thinking this,
Thanks
CP

99's run beat at about 15:1 [Smile]

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William Keeling a.k.a. Willie the Tard

iambhooper
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quote:
Originally posted by cpdenis:
Bit of a hijack here but along the same lines.
Since both the SCCA and NASA have adopted the adjusted timing and fuel pressure regulators on the 99's, I'm looking to go that route and perform that modification. Given that there is now the potential to lean and blow the engine, what is the recommended complete gauge setup (complete hardware) and a/f ratios to be adjusting for or worry about. Or am I over thinking this,
Thanks
CP

Is it just the NB's, or does it include the NA's?

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hoop
'91 Spec Miata
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CP
providing all is right on right car, good fuel pump and injectors. You want your car running 53/55 psi at idle. The air:fuel curve is not flat, but that will end up with a curve starting at 5000 is 13.3-13.5 range and end with a 12.7/12.8 at 6800 or so. IMO, taht is about as good as you can get.

Jim

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Jim Drago
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quote:
Originally posted by Drago:
CP
providing all is right on right car, good fuel pump and injectors. You want your car running 53/55 psi at idle. The air:fuel curve is not flat, but that will end up with a curve starting at 5000 is 13.3-13.5 range and end with a 12.7/12.8 at 6800 or so. IMO, taht is about as good as you can get.

Jim

jim is that specifically for the '99 or all miata?

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Steven Elicati
'92 Protege ITA#01
'94 Miata ITA#99

cpdenis
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Jim, that's great info. What about the monitoring hardware? Or do I just install parts as above, dial psi to 54, adjust timing to 15 and know that its good. Is there a way to optimize this setup at the track without a dyno? Magic numbers to look for?
Again great info and thanks to all posting.
CP

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CP, FYI.
http://classifieds.specmiata.com/detail.php?id=3318
J~

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quote:
Originally posted by Johnny D:
CP, FYI.
http://classifieds.specmiata.com/detail.php?id=3318
J~

Since when is a hammer a blueprinting tool? [duck]

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When you know how to use it correctly [Big Grin]

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