[C2] reducing centrifugaal advance
#1
Melting Slicks
Thread Starter
reducing centrifugaal advance
My centrifugal on a standard AC distributor adds about 28°. What is the best way to reduce that?
#2
Le Mans Master
Spring strength
The distributor will have built in limiter to 36 deg centrifugal . You control the timing with the vac can and initial advance so that too much timing is not coming in too soon. You vac can may be putting in too much...I use an adjustable one to dial in my advance...and then use the springs too control total advance at all speeds.
My car is happy at 21-25 at idle...with VC and Int.....in.....very little centrifugal at idle....10* int plus about 12-14 VC....in an L-79....
At 3,000 rpm I am about 48-50 total * 10 + 12 + 30 ish centrifugal + 48-52, with VC dropping as rpms increase....allowing full 30+* centrifugal....I think.....lol
Jack
Last edited by Jackfit; 03-30-2018 at 09:21 AM.
#3
Melting Slicks
Thread Starter
I have a very low CR crate (8.5-9), and those (according to spec sheet) require only 22°. Just want to try that...
#4
Le Mans Master
Total Reading at 3,000 - 6* I think for your engine..
Jack
Last edited by Jackfit; 03-30-2018 at 09:26 AM.
#6
Melting Slicks
Thread Starter
that does screw up the rpm when total gets in, so I really want to reduce centrifugal impact. You can't resist trying to stop me working on my car , I just love it
I just discovered there is a bushing for that...(I was typing this while L78Racer was posting ;-) )
I just discovered there is a bushing for that...(I was typing this while L78Racer was posting ;-) )
Last edited by alexandervdr; 03-30-2018 at 09:27 AM.
#7
Le Mans Master
Have fun.....I take the car out of the oil tank next week....first time in decades that I have not use it during the winter.
Jack
#8
Le Mans Master
Jack
#9
Race Director
The bushing is the best approach on a GM although it will only do so much. But if you don't have a bushing now, it may take enough out to satisfy you. After that a bit of light welding to close up the slot in the shaft plate can limit it further but takes someone with a deft touch with a welder to not make a mess of it (unlike me).
#10
Team Owner
Those 'spec sheets' are usually quite conservative to cover a variety of driving styles, available fuels, altitudes and traffic conditions. I wouldn't take that as gospel for one minute, they can almost invariably be improved on.....if you're not having problems now (trailer hitching/detonation) why would you 'detune' your car ?
#11
Melting Slicks
Thread Starter
Those 'spec sheets' are usually quite conservative to cover a variety of driving styles, available fuels, altitudes and traffic conditions. I wouldn't take that as gospel for one minute, they can almost invariably be improved on.....if you're not having problems now (trailer hitching/detonation) why would you 'detune' your car ?
Last edited by alexandervdr; 03-30-2018 at 02:59 PM.
#12
Melting Slicks
Thread Starter
I am at 38° (no Vac) mechanical and 10 initial advance.
#13
Melting Slicks
Thread Starter
The bushing is the best approach on a GM although it will only do so much. But if you don't have a bushing now, it may take enough out to satisfy you. After that a bit of light welding to close up the slot in the shaft plate can limit it further but takes someone with a deft touch with a welder to not make a mess of it (unlike me).
#14
Team Owner
Lars and Duke are the 'guys' for this effort....
My experience is that with initial and centrifugal 'all in' at about 36*-38* as quick as your engine can take it (2500 RPM -3000 RPM) is about ideal. With vacuum advance on top of that 48* is good but I've pushed some cars to 52*.
My experience is that with initial and centrifugal 'all in' at about 36*-38* as quick as your engine can take it (2500 RPM -3000 RPM) is about ideal. With vacuum advance on top of that 48* is good but I've pushed some cars to 52*.
#16
Melting Slicks
Thread Starter
Lars and Duke are the 'guys' for this effort....
My experience is that with initial and centrifugal 'all in' at about 36*-38* as quick as your engine can take it (2500 RPM -3000 RPM) is about ideal. With vacuum advance on top of that 48* is good but I've pushed some cars to 52*.
My experience is that with initial and centrifugal 'all in' at about 36*-38* as quick as your engine can take it (2500 RPM -3000 RPM) is about ideal. With vacuum advance on top of that 48* is good but I've pushed some cars to 52*.
#17
Team Owner
Member Since: Oct 2000
Location: Washington Michigan
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Remember that in the real world, under most normal driving situations, initial and centrifugal maximum advance are not additive. At high rpm and WOT, the vacuum advance is inoperative, so the engine's only working at 38* under those conditions.
#18
Race Director
Go ahead and install the largest metal bushing that will fit and slide in the slot - it will make at least a bit of difference over the rubber one.
#19
Melting Slicks
Thread Starter
I know, still, what is then the relevance of arguing total advance (it's used all the time in discussions...)
#20
Le Mans Master
Now, all I said could be wrong, but I sure have my car running...but again, it’s good to be in the garage . Maybe something is lost in translation....lol...my hello to the sane one in the family.
Jack
Jack
Last edited by Jackfit; 03-30-2018 at 07:31 PM.