I've spent the past couple weeks tuning my '84 Olds's 231, after converting to an older M4M carb and vacuum advance distributor. I thought I'd post my findings and final configuration to help anyone else doing this. I'm not saying this is the best settings, just what I finally ended up with. I also did have the advantage of an O2 sensor and a scan tool, so these settings shouldn't be totally on crack.
First off, the carb I'm running came off a buick or olds 350. So it's not necessary at all to get a V6 specific carb. Any smog 350 should work fine. Watch out for big carbs though, I had a 400 Pontiac carb on there and couldn't get it to meter idle fuel properly. Then I used a factory 231, pre computer distributor from an earlier model car. The only modification to that distributor was an adjustable vacuum advance can from Crane.
Now on to the important stuff!!!
Fuel Settings:
69 Primary Jets
43 Primary Rods
7"/3" Power Piston spring (begins raising at 7" Hg, fully out by 3" Hg)
H Secondary Hanger
CP Secondary Rods
87 Octane fuel
Timing Settings:
12* BTDC Initial
20* Mechanical with two heavy springs from the Crane recurve kit
20* Vacuum advance, begins dropping out at 11" of vacuum and is completely gone by 5"
Vacuum advance running off manifold vacuum
1100RPM in park
700RPM in drive
Important vacuum readings:
High idle (cold engine): 20"
Idle, park: 17-18"
Idle, drive, vacuum advance on manifold: 15.5"
Idle, drive, vacuum advance on ported: 14.5"
Standing start, 1/2 throttle (approx), flat ground: 5-6"
Cruise, light throttle: 15-17"
Cruise, medium throttle: 11"
Decel, no throttle: 23-24"
WOT: 0"
WOT, secondaries disabled: 2" above approx 4000 RPM
Only other modifications are a factory 4.1L Qjet intake and a GN rear (3.42 posi 8.5").
A few notes:
First, the carb was calibrated originally for a smog V8 that made a good bit more torque than this motor--maybe even in a lighter car. The power system, as originally configured, kicked in at about 11" Hg. As a result, the power system was on any time except for idle and very light cruise, and gas mileage suffered badly. The cure was a much, much softer power piston spring. I chased this problem for a while, and might never have found it without the scan tool and a vacuum gauge so I could SEE exactly when it was kicking in.
Once that was done, it was a simple matter of driving, reading the laptop, making changes, and doing it again. Once I had the fuel curve mostly nailed, though, I did run into a part throttle detonation problem that drove me up the wall for a few days. It would detonate under load, even with the vacuum advance disconnected. I went to the heaviest springs I had and it still did it. I finally ran some top engine cleaner through, which helped, but didn't eliminate it. I finally had to back the base timing off from the factory specification of 15* to stop the pinging. I figure I'm still getting 32* of total advance so that ain't bad.
Anyhow, it took a bunch more time getting the vacuum advance set right. I spent time monkeying with it the way Crane told you, then I said screw it and set it with a vacuum pump and a motor off. Since I had been watching the motor VERY carefully on a vacuum gauge for the past two weeks, I knew what vacuum the advance had to be all gone by, so I just set it that way.
Now that everything is set I'm pretty happy with it. Only real issue is the cruise mixture is pretty lean. There's no surging or anything, but it might be too lean for maximum economy. I may end up slimming down the rods to 41s. But other than that I'm pretty happy with it as is. Too bad there's only so much performance you can get out of the factory cam!
Incidently, as the original carb was an E4ME, I can't tell you how much of a change in the primary jetting. However, I can tell you the secondaries were originally CN rods on an N hanger. After the non-ECM swap, the secondaries were so lean it was scary. I'm not quite sure why it wants so much more fuel but I'm not complaining
Oh and one other thing: For anyone who thinks the 3.8L doesn't need a Qjet... look at the last spec posted in the vacuum section. Yep, that's right, on primaries alone my 3.8L is pulling a vacuum at WOT at the top of each gear.
First off, the carb I'm running came off a buick or olds 350. So it's not necessary at all to get a V6 specific carb. Any smog 350 should work fine. Watch out for big carbs though, I had a 400 Pontiac carb on there and couldn't get it to meter idle fuel properly. Then I used a factory 231, pre computer distributor from an earlier model car. The only modification to that distributor was an adjustable vacuum advance can from Crane.
Now on to the important stuff!!!
Fuel Settings:
69 Primary Jets
43 Primary Rods
7"/3" Power Piston spring (begins raising at 7" Hg, fully out by 3" Hg)
H Secondary Hanger
CP Secondary Rods
87 Octane fuel
Timing Settings:
12* BTDC Initial
20* Mechanical with two heavy springs from the Crane recurve kit
20* Vacuum advance, begins dropping out at 11" of vacuum and is completely gone by 5"
Vacuum advance running off manifold vacuum
1100RPM in park
700RPM in drive
Important vacuum readings:
High idle (cold engine): 20"
Idle, park: 17-18"
Idle, drive, vacuum advance on manifold: 15.5"
Idle, drive, vacuum advance on ported: 14.5"
Standing start, 1/2 throttle (approx), flat ground: 5-6"
Cruise, light throttle: 15-17"
Cruise, medium throttle: 11"
Decel, no throttle: 23-24"
WOT: 0"
WOT, secondaries disabled: 2" above approx 4000 RPM
Only other modifications are a factory 4.1L Qjet intake and a GN rear (3.42 posi 8.5").
A few notes:
First, the carb was calibrated originally for a smog V8 that made a good bit more torque than this motor--maybe even in a lighter car. The power system, as originally configured, kicked in at about 11" Hg. As a result, the power system was on any time except for idle and very light cruise, and gas mileage suffered badly. The cure was a much, much softer power piston spring. I chased this problem for a while, and might never have found it without the scan tool and a vacuum gauge so I could SEE exactly when it was kicking in.
Once that was done, it was a simple matter of driving, reading the laptop, making changes, and doing it again. Once I had the fuel curve mostly nailed, though, I did run into a part throttle detonation problem that drove me up the wall for a few days. It would detonate under load, even with the vacuum advance disconnected. I went to the heaviest springs I had and it still did it. I finally ran some top engine cleaner through, which helped, but didn't eliminate it. I finally had to back the base timing off from the factory specification of 15* to stop the pinging. I figure I'm still getting 32* of total advance so that ain't bad.
Anyhow, it took a bunch more time getting the vacuum advance set right. I spent time monkeying with it the way Crane told you, then I said screw it and set it with a vacuum pump and a motor off. Since I had been watching the motor VERY carefully on a vacuum gauge for the past two weeks, I knew what vacuum the advance had to be all gone by, so I just set it that way.
Now that everything is set I'm pretty happy with it. Only real issue is the cruise mixture is pretty lean. There's no surging or anything, but it might be too lean for maximum economy. I may end up slimming down the rods to 41s. But other than that I'm pretty happy with it as is. Too bad there's only so much performance you can get out of the factory cam!
Incidently, as the original carb was an E4ME, I can't tell you how much of a change in the primary jetting. However, I can tell you the secondaries were originally CN rods on an N hanger. After the non-ECM swap, the secondaries were so lean it was scary. I'm not quite sure why it wants so much more fuel but I'm not complaining
Oh and one other thing: For anyone who thinks the 3.8L doesn't need a Qjet... look at the last spec posted in the vacuum section. Yep, that's right, on primaries alone my 3.8L is pulling a vacuum at WOT at the top of each gear.
