Target Air Fuel ration N/A engines.?
08-03-2016, 09:44 PM
#32
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Many things have an effect on afrs . Weather plays a big part.
On my setup, 2 jet sizes all around, meaning 2 numbers, resulted in .5 afr. Meaning if it was 12.7, it went to 12.2. Single carb setups seem to be even more sensitive to jet changes.
Something i think we all need to realize , is these portable widebands we all use, are not nearly as accurate as the analyzers companies like general motors or ford use.
I personally think flirting with lean afrs on a carbed engine with chitty fuel distribution, is a risky operation. I saw mid 12s on my wideband at wot when tuning my old combo. Cracked porcelin on the plug. Last dyno session, the dynos supply pump was forgot to get turned on. Afrs went lean at 6000rpm, into the high 13s, cracked a plug. Tim, i remember you cracking some porcelin as well last summer. We dont want that
I take afr "suggestions" with a grain of salt. What some guys think is nasty, pig rich, ring washing number, is the same number, some oem forced inductions are setup to run at.
On the dyno, tims engine showed mid to upper 12s if i recall the way they were jetted. Adding some jet, brought the afrs to 11.8ish. The engine picked up torque, and lost what, 5 or 6 peak HP? Barely 1% loss .
I was seeing idle afrs in the 11s last weekend, floats in new carbs were set high. I lowered floats to the proper level. Restarted engines , and left the dock. One engine stalled when i put it in gear. Why? Becaus my afrs at idle now pegged the meter at 16.0. I had to re adjust idle mixture screws, to get the idle afrs back to where they were.
SB knows why this happens. Float level has a significant effect on fuel delivery of a carb.
08-03-2016, 09:52 PM
#33
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yea, I can look at the messages to see what we went with last week in carbs we agreed on what I should do, I am going to verify air volume into bilge before I mess with it more I think and make sure that's no my "richer" issue, just shows so rich in boat over what we had on dyno... you know exactly whats up because I norm ally talk to you first lol
we figured 2 jet sizes was a safe "take out" of fuel started there..
we figured 2 jet sizes was a safe "take out" of fuel started there..
From our convo, you said you were low 11s at wot. I recall talking about pulling 3 numbers from primary, ans 1 number from secondary.
Many things have an effect on afrs . Weather plays a big part.
On my setup, 2 jet sizes all around, meaning 2 numbers, resulted in .5 afr. Meaning if it was 12.7, it went to 12.2. Single carb setups seem to be even more sensitive to jet changes.
Something i think we all need to realize , is these portable widebands we all use, are not nearly as accurate as the analyzers companies like general motors or ford use.
I personally think flirting with lean afrs on a carbed engine with chitty fuel distribution, is a risky operation. I saw mid 12s on my wideband at wot when tuning my old combo. Cracked porcelin on the plug. Last dyno session, the dynos supply pump was forgot to get turned on. Afrs went lean at 6000rpm, into the high 13s, cracked a plug. Tim, i remember you cracking some porcelin as well last summer. We dont want that
I take afr "suggestions" with a grain of salt. What some guys think is nasty, pig rich, ring washing number, is the same number, some oem forced inductions are setup to run at.
On the dyno, tims engine showed mid to upper 12s if i recall the way they were jetted. Adding some jet, brought the afrs to 11.8ish. The engine picked up torque, and lost what, 5 or 6 peak HP? Barely 1% loss .
I was seeing idle afrs in the 11s last weekend, floats in new carbs were set high. I lowered floats to the proper level. Restarted engines , and left the dock. One engine stalled when i put it in gear. Why? Becaus my afrs at idle now pegged the meter at 16.0. I had to re adjust idle mixture screws, to get the idle afrs back to where they were.
SB knows why this happens. Float level has a significant effect on fuel delivery of a carb.
Many things have an effect on afrs . Weather plays a big part.
On my setup, 2 jet sizes all around, meaning 2 numbers, resulted in .5 afr. Meaning if it was 12.7, it went to 12.2. Single carb setups seem to be even more sensitive to jet changes.
Something i think we all need to realize , is these portable widebands we all use, are not nearly as accurate as the analyzers companies like general motors or ford use.
I personally think flirting with lean afrs on a carbed engine with chitty fuel distribution, is a risky operation. I saw mid 12s on my wideband at wot when tuning my old combo. Cracked porcelin on the plug. Last dyno session, the dynos supply pump was forgot to get turned on. Afrs went lean at 6000rpm, into the high 13s, cracked a plug. Tim, i remember you cracking some porcelin as well last summer. We dont want that
I take afr "suggestions" with a grain of salt. What some guys think is nasty, pig rich, ring washing number, is the same number, some oem forced inductions are setup to run at.
On the dyno, tims engine showed mid to upper 12s if i recall the way they were jetted. Adding some jet, brought the afrs to 11.8ish. The engine picked up torque, and lost what, 5 or 6 peak HP? Barely 1% loss .
I was seeing idle afrs in the 11s last weekend, floats in new carbs were set high. I lowered floats to the proper level. Restarted engines , and left the dock. One engine stalled when i put it in gear. Why? Becaus my afrs at idle now pegged the meter at 16.0. I had to re adjust idle mixture screws, to get the idle afrs back to where they were.
SB knows why this happens. Float level has a significant effect on fuel delivery of a carb.
08-03-2016, 11:02 PM
#35
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9.5:1 comp
roller is used in the 502/502 crate engines.
The duration at .050" tappet lift (intake/exhaust) is 224/234
Lift with 1.7:1 rocker ratio (intake/exhaust) is 527/544.
Valve lash is zero/zero
Lobe centerline is 110 degrees.
08-07-2016, 09:56 AM
#37
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Need some recommendations. And also, does this make sense?
I'm starting with #78 primary jets, #86 secondary jets, and 6.5 power valves (850 QF) front and rear and getting pretty much 11.2 on the wideband across the board with the 502 struggling to get up to 5200. I changed the secondary jets to #82 and it made a HUGE difference with wot afr at about 12.5, but the shocker was it screamed all the way to 5600rpm - for a 400rpm gain even after adding 50g of fuel! Even while cruising at 5200 I could bump the sticks and it would still accelerate hard! It acted like a completely different boat.
So I messed with the idle circuit and it really seems fat, dumb, and happy in the mid 11s. I leaned it out into the 12s but it didn't start as well and needed some bumps on the sticks to get going so I fattened it back up for now. That circuit only seems to effect it up to about 1000rpm.
From about 1000 to 3500 it was still pig rich in the low to mid 11s, and then from 3500 on it gradually leaned out with 4000 close to 12 and 5000+ dancing around 12.5-12.8.
Now the weird stuff.
Just for kicks I pulled the cheap 3"x8" round flame arrestor off and it fattened up! I'm on a small bumpy lake so it's hard to maintain and repeat experiments, but I was seeing afrs down into the 10s. I have my own figuring of the flame arrestor providing a velocity channel, taming swirling air, etc, but was surprised to see that much difference.
Now the kicker. as discovered in the other thread that air volume available can be an issue, so when I was tapped at 5600 I popped the hatch a bit and it spiked past 5800 - but the afr never changed! It's only a single engine 502 at about 500hp in a 272 Baja so I didn't think that it would be struggling for air.
What would the brain trust recommend for jetting from here?
I'm starting with #78 primary jets, #86 secondary jets, and 6.5 power valves (850 QF) front and rear and getting pretty much 11.2 on the wideband across the board with the 502 struggling to get up to 5200. I changed the secondary jets to #82 and it made a HUGE difference with wot afr at about 12.5, but the shocker was it screamed all the way to 5600rpm - for a 400rpm gain even after adding 50g of fuel! Even while cruising at 5200 I could bump the sticks and it would still accelerate hard! It acted like a completely different boat.
So I messed with the idle circuit and it really seems fat, dumb, and happy in the mid 11s. I leaned it out into the 12s but it didn't start as well and needed some bumps on the sticks to get going so I fattened it back up for now. That circuit only seems to effect it up to about 1000rpm.
From about 1000 to 3500 it was still pig rich in the low to mid 11s, and then from 3500 on it gradually leaned out with 4000 close to 12 and 5000+ dancing around 12.5-12.8.
Now the weird stuff.
Just for kicks I pulled the cheap 3"x8" round flame arrestor off and it fattened up! I'm on a small bumpy lake so it's hard to maintain and repeat experiments, but I was seeing afrs down into the 10s. I have my own figuring of the flame arrestor providing a velocity channel, taming swirling air, etc, but was surprised to see that much difference.
Now the kicker. as discovered in the other thread that air volume available can be an issue, so when I was tapped at 5600 I popped the hatch a bit and it spiked past 5800 - but the afr never changed! It's only a single engine 502 at about 500hp in a 272 Baja so I didn't think that it would be struggling for air.
What would the brain trust recommend for jetting from here?
08-07-2016, 10:38 AM
#38
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what afr meter are you using?
08-07-2016, 03:51 PM
#40
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Now the kicker. as discovered in the other thread that air volume available can be an issue, so when I was tapped at 5600 I popped the hatch a bit and it spiked past 5800 - but the afr never changed! It's only a single engine 502 at about 500hp in a 272 Baja so I didn't think that it would be struggling for air.
