Region: Florida
Year : '92 Posts: 17
Status: Offline
posted
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.
-------------------- '90 SM 2006 SSM North East Enduro Champion
Qik Nip
Loose Member '09 & '10 Great Lakes Regional Points Champion
Region: Cincinnati Great Lakes
Car #: 60
Year : 1990 Posts: 1487
Status: Offline
posted
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
-------------------- Fortune Cookie Racing SM 60 Directions for use: Race, Rumple, Repair ... Repeat!
Region: Florida
Year : '92 Posts: 17
Status: Offline
posted
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
-------------------- '90 SM 2006 SSM North East Enduro Champion
Region: South East
Car #: #92
Year : 91 Posts: 189
Status: Offline
posted
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?
Region: NASA FL / CFR SCCA
Car #: 25
Year : 1991 Posts: 374
Status: Offline
posted
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.
Region: Mid-South
Car #: 76
Year : "You Pick" Posts: 4422
Status: Offline
posted
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.
Region: CFR
Car #: 97
Year : 1990/99 Posts: 788
Status: Offline
posted
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.
-------------------- 2010 ARRC Champion 2010 CFR Champion 2010 instigator of the year 2010/2011 Andrew Von C Wingman
Region: SFR
Car #: 82/73
Year : 1991 Posts: 2015
Status: Offline
posted
Engine goes BOOM...too lean...
-------------------- Kim
91 BRG SMT RIP 06 MX-5 Cup
"Life's journey is not to arrive at the grave safely in a well preserved body, but rather to skid in sideways, totally worn out, shouting 'Holy sh*t...what a ride!'" - Unknown
Region: Oregon
Car #: 00
Year : 1992 Posts: 294
Status: Offline
posted
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.
Region: Florida
Year : '92 Posts: 17
Status: Offline
posted
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.
-------------------- '90 SM 2006 SSM North East Enduro Champion
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 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.
Region: 11
Car #: 09
Year : 99 Posts: 143
Status: Offline
posted
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
Region: NASA Texas
Car #: 8
Year : 92 Posts: 697
Status: Offline
posted
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
-------------------- William Keeling a.k.a. Willie the Tard
Region: NCR
Car #: NA
SMIM: NA Posts: 125
Status: Offline
posted
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?
-------------------- hoop '91 Spec Miata '90 NA Beater/Track Day car '06 RSX Type S
Region: mid south
Car #: 2
Year : 1999 Posts: 4275
Status: Offline
posted
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.
Region: Central Florida
Car #: 01 & 99
Year : '92 & '94 Posts: 137
Status: Offline
posted
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?
-------------------- Steven Elicati '92 Protege ITA#01 '94 Miata ITA#99
Region: 11
Car #: 09
Year : 99 Posts: 143
Status: Offline
posted
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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