Cruise AFR and timing
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Joined: Jun 2013
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From: Orange, Texas
Cruise AFR and timing What are you guys running for timing and AFR at steady cruise? I think I have a good handle on the full throttle tune now but now I'm working on drive-ability. At steady cruise it's got a bit of a miss that just annoys me, not much but I can hear it.
'55 Chevy with 6.0/4L80E
S480/1.32/96mm
Holley Dominator
Holley 120 lbs. inj
93 octane pump gas
Vic Jr and elbow
9" with 3.55 gear
28 inch tall tire
75 mph is about 2400 rpm with converter locked
I've gone as high as 45 degrees on timing at steady cruise just to see what it does and it's still there.
'55 Chevy with 6.0/4L80E
S480/1.32/96mm
Holley Dominator
Holley 120 lbs. inj
93 octane pump gas
Vic Jr and elbow
9" with 3.55 gear
28 inch tall tire
75 mph is about 2400 rpm with converter locked
I've gone as high as 45 degrees on timing at steady cruise just to see what it does and it's still there.
I typically idle in the high 15 to low 16s and cruise at high 14s to mid 15s. But my timing is typically in the mid 30s. I don't see a need to sit in the mid 40s as you'll likely drive better with it a little leaner and less timing.
Thread Starter
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Joined: Jun 2013
Posts: 487
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From: Orange, Texas
I've really got to stop over analyzing this and give the motor what it wants. It just wants to be rich......and richer than I think it needs to be.
On idle it likes 13.8 AFR, I keep thinking that's too rich but it just doesn't like to idle good on anything leaner. Moving the idle timing around doesn't really change it much. IAC motor is at 10%-12% without the AC on so I'm good there.
At cruise it wants 14.0 and that just seems too rich, but that's what it wants. Plugs show rich as well. (TR6 gapped at .024)
Saturday I went to a rod run in Beaumont and I tried leaning out the cruise and it just didn't like it. I've tried from 14.5 to 15.5 and the leaner I go the worse it gets.
Bottom line is give it what it wants just like the old days tuning Holley carb before wide band O2 sensors.
On idle it likes 13.8 AFR, I keep thinking that's too rich but it just doesn't like to idle good on anything leaner. Moving the idle timing around doesn't really change it much. IAC motor is at 10%-12% without the AC on so I'm good there.
At cruise it wants 14.0 and that just seems too rich, but that's what it wants. Plugs show rich as well. (TR6 gapped at .024)
Saturday I went to a rod run in Beaumont and I tried leaning out the cruise and it just didn't like it. I've tried from 14.5 to 15.5 and the leaner I go the worse it gets.
Bottom line is give it what it wants just like the old days tuning Holley carb before wide band O2 sensors.
Depending on the camshaft these numbers can all vary. Some big cams will drive smoother at 13-14:1 at cruise and be a bucking bronco at 14-16:1. More timing at part throttle will help fuel economy. I run as high as 50* at really light load and taper down to MBT at high load. The OE ls tunes are in the 45-50 area at real light load. Larger cams will often drive smoother with much less timing though.
Thread Starter
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Joined: Jun 2013
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From: Orange, Texas
Tick stage 2 turbo cam - 231/231 | .630"/.605" | LSA115+5
I'm going to get my wife it drive so I can sit in the passenger seat and fine tune it. Now that I've decided to just let it be fat I'll experiment with some higher timing at part throttle cruise.
Doesn't seem to be much vacuum at part throttle cruise but that may just be normal for a turbo and this is my first. Around 55 kpa at cruise.
I'm going to get my wife it drive so I can sit in the passenger seat and fine tune it. Now that I've decided to just let it be fat I'll experiment with some higher timing at part throttle cruise.
Doesn't seem to be much vacuum at part throttle cruise but that may just be normal for a turbo and this is my first. Around 55 kpa at cruise.
Last edited by squarles67; Jun 12, 2017 at 09:54 AM.
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Tick stage 2 turbo cam - 231/231 | .630"/.605" | LSA115+5
I'm going to get my wife it drive so I can sit in the passenger seat and fine tune it. Now that I've decided to just let it be fat I'll experiment with some higher timing at part throttle cruise.
Doesn't seem to be much vacuum at part throttle cruise but that may just be normal for a turbo and this is my first. Around 55 kpa at cruise.
I'm going to get my wife it drive so I can sit in the passenger seat and fine tune it. Now that I've decided to just let it be fat I'll experiment with some higher timing at part throttle cruise.
Doesn't seem to be much vacuum at part throttle cruise but that may just be normal for a turbo and this is my first. Around 55 kpa at cruise.
The fact that your cam has positive overlap has a much bigger effect.
Thread Starter
TECH Regular
Joined: Jun 2013
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From: Orange, Texas
Depending on wideband most on the gas scale read 14.7 = lambda of 1.0. So it really makes 0 difference on what fuel you're running. First of all get those TR6 plugs the hell out of there, they do not belong there at all. If you have an audible miss you should investigate into mechanical issues. Cracked plug, bad plug wire, coil issue, exhaust leak, vacuum leak etc...
Thread Starter
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Joined: Jun 2013
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From: Orange, Texas
I've replaced the plugs and plug wires but it's still there, I'm checking the coils next.
I did do a compression check just to make sure and all were within 2 lbs. of each other.
I did do a compression check just to make sure and all were within 2 lbs. of each other.
Thread Starter
TECH Regular
Joined: Jun 2013
Posts: 487
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From: Orange, Texas
Thread Starter
TECH Regular
Joined: Jun 2013
Posts: 487
Likes: 6
From: Orange, Texas
Since I started this thread I made a good hard pass then pulled all the plugs and they were all clean except #8 which was just as black as it could be. The water/meth is what cleaned them up from my pass so I'm going to change the #8 coil and see if that makes a difference.
Weather is crappy right now with a Tropical Storm bearing down on us so it'll be a few days before I can test again but I'll come back and update.