360 Tune Up
You will refine your testing program the more you do it.
Lets break this down:
72 B-body with a/c. automatic transmission, 5.9 magnum with the distributor from original application. Goal street use mainly or only?
>> It would certainly be helpful to find out the initial and advance specs from the original application. Additionally if the original application used a A/C switch actived solenoid to increase idle rpm with the A/C on. This would provide a baseline. (Your 72 B-body may have had an throttle solenoid tied to A/C - its not a new idea).
>> If the engine was originally a 2 bbl or standard performance, note if you've made changes that would effect combustion. Typically we see increase in efficiency at high mid to high rpm, wide open throttle, with things like going from a 2 bbl to a 4 bbl.
Above is for establishing a baseline off of all the engineering and testing done by the factory - unless you think they're a bunch of dummies and didn't know what they were doing.
Testing
>> Do steady state testing first, transitions afterwords. Steady state tests make it easier to isolate and change one variable. Transistions will often take require nothing if the steady conditions are tuned in.
>> Accelerating at part throttle, especially from low rpm, is an example of a transitory test. The throttle opening is changing at the same time the rpm is changing, and the load is changing. If you have a dash mounted vacuum gage you will see the changing load reflected in the changing vacuum. It is possible to do a part throttle acceleration where one 'crowds' or holds the vacuum stready. The throttle will not be steady when crowding, but needs to be squeezed further open to maintain the crowd. I've posted a data log of that.
>> Steady state tests that you can do.
a. Idle in drive. The least drop in rpm and/or manifold vacuum when going from neutral into gear will be the strongest. This is a good foundation and will also be immediately useful for at least driving around town.
b. Idle in drive with A/C on. This will be a higher load test. It will give you an idea as to whether a solenoid that bumps up idle rpm may be needed. I would test with a/c on only after the battery is recharged (as shown on the ammeter) so as not to also have a high alternator load on the engine.
c. Full load tests at higher rpm. Ideally this is a 1/4 mile drag strip run so the engine is at wide open throttle (max power) in third gear (max gearing load) under highest resistance from air etc. in the power band.
c1. If no access to a drag strip, or your not ready for that yet, then pick a place you can consistantly do a heavy load full throttle test. If you hear gurgling at full or near full throttle, back off!!! The test has to been done with so much load that the vacuum advance is out of the picture, and the power valve or step up circuits are enrichening the mixture. In other words at or near full throttle.
c2. Judgement of performance on max load will be higher mph through the lights (drag strip) as an indicator of top end timing, and lower rpm timing curve can be judged by e/t, 60' and so forth for engine acceleration.
c3. An indicator of too much advance will be any sounds of pinging (back off throttle !!!) and specs of aluminum on the spark plug porcelain.
Vacuum advance
Set so the vacuum advance on moderate to intestate highway cruising is close to factory recommendations. See the MP instructions linked earlier. If its pings on part throttle or light acceleration, make a small adjustment to reduce the advance at that vacuum or limit the toal which ever is applicable for that condition. (A little gurgle under light throttle is not the highly destructive condition that it will be under full or near full throttle.)
This is in the ball park.
make small changes to tune.
For example.
Do the in gear at idle tests. Then adjust timing 2* and fiddle with idle speed and mix to get back to the same rpm (700 if thats what it is) and retest. Write down the resutls and compare.
You know how to adjust initial.
Earlier in the thread there are instructions on how to get the advance to being at lower or higher rpm. Similarly you can get the secondary spring to engage at a little lower rpm. The latter may be useful with this engine.
Performance tuning is the opposite of plug and play.
Its low dollar and high on time.
Good luck.
Fair enough.
You will refine your testing program the more you do it.
Lets break this down:
72 B-body with a/c. automatic transmission, 5.9 magnum with the distributor from original application. Goal street use mainly or only?
>> It would certainly be helpful to find out the initial and advance specs from the original application. Additionally if the original application used a A/C switch actived solenoid to increase idle rpm with the A/C on. This would provide a baseline. (Your 72 B-body may have had an throttle solenoid tied to A/C - its not a new idea).
>> If the engine was originally a 2 bbl or standard performance, note if you've made changes that would effect combustion. Typically we see increase in efficiency at high mid to high rpm, wide open throttle, with things like going from a 2 bbl to a 4 bbl.
Above is for establishing a baseline off of all the engineering and testing done by the factory - unless you think they're a bunch of dummies and didn't know what they were doing.
Testing
>> Do steady state testing first, transitions afterwords. Steady state tests make it easier to isolate and change one variable. Transistions will often take require nothing if the steady conditions are tuned in.
>> Accelerating at part throttle, especially from low rpm, is an example of a transitory test. The throttle opening is changing at the same time the rpm is changing, and the load is changing. If you have a dash mounted vacuum gage you will see the changing load reflected in the changing vacuum. It is possible to do a part throttle acceleration where one 'crowds' or holds the vacuum stready. The throttle will not be steady when crowding, but needs to be squeezed further open to maintain the crowd. I've posted a data log of that.
>> Steady state tests that you can do.
a. Idle in drive. The least drop in rpm and/or manifold vacuum when going from neutral into gear will be the strongest. This is a good foundation and will also be immediately useful for at least driving around town.
b. Idle in drive with A/C on. This will be a higher load test. It will give you an idea as to whether a solenoid that bumps up idle rpm may be needed. I would test with a/c on only after the battery is recharged (as shown on the ammeter) so as not to also have a high alternator load on the engine.
c. Full load tests at higher rpm. Ideally this is a 1/4 mile drag strip run so the engine is at wide open throttle (max power) in third gear (max gearing load) under highest resistance from air etc. in the power band.
c1. If no access to a drag strip, or your not ready for that yet, then pick a place you can consistantly do a heavy load full throttle test. If you hear gurgling at full or near full throttle, back off!!! The test has to been done with so much load that the vacuum advance is out of the picture, and the power valve or step up circuits are enrichening the mixture. In other words at or near full throttle.
c2. Judgement of performance on max load will be higher mph through the lights (drag strip) as an indicator of top end timing, and lower rpm timing curve can be judged by e/t, 60' and so forth for engine acceleration.
c3. An indicator of too much advance will be any sounds of pinging (back off throttle !!!) and specs of aluminum on the spark plug porcelain.
Vacuum advance
Set so the vacuum advance on moderate to intestate highway cruising is close to factory recommendations. See the MP instructions linked earlier. If its pings on part throttle or light acceleration, make a small adjustment to reduce the advance at that vacuum or limit the toal which ever is applicable for that condition. (A little gurgle under light throttle is not the highly destructive condition that it will be under full or near full throttle.)
This is in the ball park.
make small changes to tune.
For example.
Do the in gear at idle tests. Then adjust timing 2* and fiddle with idle speed and mix to get back to the same rpm (700 if thats what it is) and retest. Write down the resutls and compare.
You know how to adjust initial.
Earlier in the thread there are instructions on how to get the advance to being at lower or higher rpm. Similarly you can get the secondary spring to engage at a little lower rpm. The latter may be useful with this engine.
Performance tuning is the opposite of plug and play.
Its low dollar and high on time.
Good luck.
