A/F ratio
10-14-2013, 02:57 PM
#1
A/F ratio It seems to me that it would be helpful to all if we have a thread with peoples builds and what they wound up with for their perfect A/F ratio. I know they are all a little different, but it may help with trends on a good starting point for those that haven't dialed theirs in yet.
I have this on my mind because my car has picked up a crank up issue with the Fast EZ on my LS3. I had slowly leaned the idle A/F to 14.6, but now am having an issue with cranking and then stalling right after the idle starts to come back down. I am thinking the A/F is too lean for the big ports on the LS3 heads. I just moved it to 13.8 and it seems to have fixed the problem.
I just think it may be helpful to see what other have come up with. Whatcha think?
I have this on my mind because my car has picked up a crank up issue with the Fast EZ on my LS3. I had slowly leaned the idle A/F to 14.6, but now am having an issue with cranking and then stalling right after the idle starts to come back down. I am thinking the A/F is too lean for the big ports on the LS3 heads. I just moved it to 13.8 and it seems to have fixed the problem.
I just think it may be helpful to see what other have come up with. Whatcha think?
10-14-2013, 07:20 PM
#3
none of my carbed setups have been able to idle with wideband readings leaner than 13.00, but then again, you cant trust an idle speed wideband reading if your cam has ANY amount of lope to it.
I just set it to idle as lean a I can get away with.
WOT seems best at about 12.8ish up to 13.00 even, on the n/a LS combo's Ive had
EDIT: I need to clarify, I re read my post and I worded it incorrectly , I did not mean that my stuff wants exactly 13.00at idle, I should have stated a/f's in the 13's for idle. I think this is a combination of a lopey cam, and my desire to have the car start and idle on its own from a cold start. Once hot it will idle at leaner wideband readings.
I should also add that my stuff has been happy with cruise and part throttle a/f's as lean as aprox 14.5, but I have needed to get fuel in quick on transitions to prevent hesitations. The stick shift is unforgiving in that area.
Last edited by 3pedals; 10-17-2013 at 07:36 AM.
10-15-2013, 07:58 AM
#4
See, that is what Im talking about. Zones setup is happy at 13.7 to 14.0 at idle, 3 Pedals cant get his leaner than 13.0 at idle. WOT is close on the 2 opinions at 12.7 and 12.8 to 13.0.
If we knew the exact setups on the engines, this would give a noobie something to go on. I think it would be a worthy data base. With enough data, trends could be found. Like maybe the rec port heads require a richer A/F than cathedral ports, or a lower static compression might work better a little rich, just as examples.
Let us know what you came up with, carb guys !
If we knew the exact setups on the engines, this would give a noobie something to go on. I think it would be a worthy data base. With enough data, trends could be found. Like maybe the rec port heads require a richer A/F than cathedral ports, or a lower static compression might work better a little rich, just as examples.
Let us know what you came up with, carb guys !
10-15-2013, 09:51 AM
#7
That has to do with the idle circuit in the carb and is WAY over my head. Things like air bleeds and small holes drilled in the metering blocks go beyond my carb tuning expertise . I have built several Holleys over the years and have tuned them for WOT power and good drivability , but getting the idle circuit to work with a radical cam and have decent idle A/F ratio is above my knowledge level. That's why I have the Fast EZ on my carb intake. Pushing a button to adjust my idle, part throttle and WOT A/F makes it possible for me to micro tune my ratios without having to learn everything that goes into making a carb work flawlessly in a hotrod. Its a cop out ,but I don't have the patience I had in my younger days, LOL.
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10-15-2013, 12:59 PM
#8
I'm close to 15:1 at idle. No issues.
One thing that helped tremendously was setting the idle screws so the transfer slots showed 20 thousands on the primary and secondary. I'm running a stock LS2 cam that has like 27 inches of vac at idle. I ended up backed off on the idle timing to get the idle speed right.
Before when I had a lot of timing at idle the idle speed screws were so far out that the primary butterflies were resting on the stops. This caused a stumble with slight throttle movements (tip in?). Getting the transfer slots right fixed that.
What is your timing doing on that Fast unit?
One thing that helped tremendously was setting the idle screws so the transfer slots showed 20 thousands on the primary and secondary. I'm running a stock LS2 cam that has like 27 inches of vac at idle. I ended up backed off on the idle timing to get the idle speed right.
Before when I had a lot of timing at idle the idle speed screws were so far out that the primary butterflies were resting on the stops. This caused a stumble with slight throttle movements (tip in?). Getting the transfer slots right fixed that.
What is your timing doing on that Fast unit?
10-15-2013, 01:29 PM
#9
The ignition timing? I cant seem to see much difference so far in the settings. I have 12* starting to 30* by 1500 all in at 34* from 2000 to 3800, a dip to 30* from 3800 to 4500, then back up to 34* to red line. Ive kept that basic curve , but gone anywhere from 28* max to the 34* it is at right now without much effect. The only 2 times Ive been to the track for testing have been spent trouble shooting other things, so tweaks on the timing haven't shown much one way or the other. I think Im done with fixing the things that held me back now and am hoping for some good numbers this next time out and enough consistency to see what timing the engine wants.
10-15-2013, 10:07 PM
#10
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My car idles at around 14:1 and seems to be fine. And a motor pass at wot was around 11.5-11.9:1. It went 9.87. but it was a lil fat.
Just for kicks, I sprayed a .082 nitrous jet and at wot I seen 12.1:1 just before the 1000' mark. It was screaming to a 9.04 pass at 150 mph lol.
Just for kicks, I sprayed a .082 nitrous jet and at wot I seen 12.1:1 just before the 1000' mark. It was screaming to a 9.04 pass at 150 mph lol.
10-15-2013, 11:03 PM
#12
The part throttle cruise is affected by the idle air bleeds, the idle fuel restrictors and the primary main jets. In general, the idle air bleeds and idle fuel restrictions affect the low RPM more ie: below around 1800 RPM. Whereas the main jets have progressively more influence as the RPMs increase.
Pretty much the standard process for setting your cruise a/f ratio is to find your best WOT jetting and make note of your A/F ratio. Then start reducing your primary main jets until the cruise A/F ratio is around 14.5:1. Once you achieve that, you drill your power valve control restrictor orifices until your desired WOT A/F ratio is restored. Once that is done, you change powervalves until your part throttle transitions maintain roughly 14 to 15:1 A/F ratios.
Ignore the stuff you read about choosing your powervalve based on your idle vacuum. Choose the powervalve that keeps your a/f ratio where you want it at part throttle and in transitional driving. Light part throttle should be kept lean ie: 14 to nearly 16:1
Pretty much the standard process for setting your cruise a/f ratio is to find your best WOT jetting and make note of your A/F ratio. Then start reducing your primary main jets until the cruise A/F ratio is around 14.5:1. Once you achieve that, you drill your power valve control restrictor orifices until your desired WOT A/F ratio is restored. Once that is done, you change powervalves until your part throttle transitions maintain roughly 14 to 15:1 A/F ratios.
Ignore the stuff you read about choosing your powervalve based on your idle vacuum. Choose the powervalve that keeps your a/f ratio where you want it at part throttle and in transitional driving. Light part throttle should be kept lean ie: 14 to nearly 16:1
Last edited by speedtigger; 10-15-2013 at 11:10 PM.
10-16-2013, 06:57 AM
#13
A wideband is a beautiful thing for this. I keep wanting to log a throttle position sensor and MAP reading into the LM2. Now that would allow dialing things into a gnats ***
10-16-2013, 06:34 PM
#14
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The part throttle cruise is affected by the idle air bleeds, the idle fuel restrictors and the primary main jets. In general, the idle air bleeds and idle fuel restrictions affect the low RPM more ie: below around 1800 RPM. Whereas the main jets have progressively more influence as the RPMs increase.
Pretty much the standard process for setting your cruise a/f ratio is to find your best WOT jetting and make note of your A/F ratio. Then start reducing your primary main jets until the cruise A/F ratio is around 14.5:1. Once you achieve that, you drill your power valve control restrictor orifices until your desired WOT A/F ratio is restored. Once that is done, you change powervalves until your part throttle transitions maintain roughly 14 to 15:1 A/F ratios.
Ignore the stuff you read about choosing your powervalve based on your idle vacuum. Choose the powervalve that keeps your a/f ratio where you want it at part throttle and in transitional driving. Light part throttle should be kept lean ie: 14 to nearly 16:1
Pretty much the standard process for setting your cruise a/f ratio is to find your best WOT jetting and make note of your A/F ratio. Then start reducing your primary main jets until the cruise A/F ratio is around 14.5:1. Once you achieve that, you drill your power valve control restrictor orifices until your desired WOT A/F ratio is restored. Once that is done, you change powervalves until your part throttle transitions maintain roughly 14 to 15:1 A/F ratios.
Ignore the stuff you read about choosing your powervalve based on your idle vacuum. Choose the powervalve that keeps your a/f ratio where you want it at part throttle and in transitional driving. Light part throttle should be kept lean ie: 14 to nearly 16:1
10-17-2013, 05:12 AM
#15
ebay is full of numbered hobby drill bits. Or hit a hobby shop. Make sure you get a pin vice with them.
10-17-2013, 06:55 AM
#16
If you get a #73 - #40, you should every size you would ever need to work on a 4150 Holley carb. Or roughly .024" - .096"
http://www.gearhob.com/eng/design/drill_eng.htm
http://www.gearhob.com/eng/design/drill_eng.htm
10-17-2013, 08:59 AM
#17
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I run my car squared up for drag racing but it is super fat at part throttle. It should have a power valve setup for street driving.
The guy who built it for me off Ebay(Mr.manifold) sent a street setup with power valves and diff jets. It worked great on the road. But the car is 90% drag race.
The guy who built it for me off Ebay(Mr.manifold) sent a street setup with power valves and diff jets. It worked great on the road. But the car is 90% drag race.
10-17-2013, 10:46 AM
#18
I run my car squared up for drag racing but it is super fat at part throttle. It should have a power valve setup for street driving.
The guy who built it for me off Ebay(Mr.manifold) sent a street setup with power valves and diff jets. It worked great on the road. But the car is 90% drag race.
The guy who built it for me off Ebay(Mr.manifold) sent a street setup with power valves and diff jets. It worked great on the road. But the car is 90% drag race.
10-19-2013, 07:51 AM
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Is your ezefi a multi port or TB version
I tried leaning mine out that much on my multi port ezefi with that much timing and yeah you will have issues. The idle afr I wasn't so worried about as I'm not idling for hours trying to save fuel. My idle and cruise were within a small amount of each other
I cruised at 13:1-13.7 range on mine
I tried leaning mine out that much on my multi port ezefi with that much timing and yeah you will have issues. The idle afr I wasn't so worried about as I'm not idling for hours trying to save fuel. My idle and cruise were within a small amount of each other
I cruised at 13:1-13.7 range on mine