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| Which Grade of Regular Unleaded? https://www.slantsix.org/forum/viewtopic.php?t=15157 |
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| Author: | DusterIdiot [ Sun Nov 27, 2005 6:23 pm ] |
| Post subject: | Hmmmm... |
Quote: 1.5 deg to 3.5 deg @ 650 RPM
so you have in 'crank' degrees:2.0 deg to 4.0 deg @ 900 RPM 3.5 deg to 5.5 deg @ 2200 RPM Vacuum Advance: 1.5 deg to 6.5 deg @ 7 in. vacuum 10.0 deg to 12.0 deg @ 12 in vacuum 11 @ 2200 rpm mechanical and 24 @12" vaccuum for a grand total of 35 at cruise if 2200 rpm.... there's more in there, somewhere... what are your shift points for the truck? what is your idle, cruise and WOT vaccuum readings... off the bat: you could try more initial (technically 30 minus 11 = 19 would be OK, but if the vacuum gauge gets 'peaky' or rattle sets in...back off...BUT you also have to contend with 50 minus 24 = 26 minus 11 = 15...) Try the initial at 14 or 15 and see what happens...you're still under the typical performance numbers... if it's hard to crank over, plan B comes into formulation... -D.Idiot |
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| Author: | bwhitejr [ Sat Dec 03, 2005 3:49 pm ] |
| Post subject: | Which Grade of Regular Unleaded? |
Ian a previous post I quoted from the service manual Centrifugal Advance: 1.5 deg to 3.5 deg @ 650 RPM 2.0 deg to 4.0 deg @ 900 RPM 3.5 deg to 5.5 deg @ 2200 RPM Vacuum Advance: 1.5 deg to 6.5 deg @ 7 in. vacuum 10.0 deg to 12.0 deg @ 12 in. vacuum I just noticed it says Distributor degrees @ Distributor RPM. With 12 deg BTDC Initial Timing Does that mean 12 deg @ 650 RPM 15 deg to 19 deg @ 1300 RPM 16 deg to 20 deg @ 1800 RPM 19 deg to 23 deg @ 4400 RPM In crank degrees? With the vacuum advance added at cruise. My idle vacuum number is 20 in. vacuum. That must make it fully advanced at idle. So with vacuum attached to distributor. I would get 24 deg advanced? bwhitejr |
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| Author: | emsvitil [ Sat Dec 03, 2005 4:21 pm ] |
| Post subject: | |
Yep you got it right except for the vacuum advance at idle..... The vacuum port is just above the throttle plate and doesn't get any vacuum until the throttle starts to open. i.e. no vacuum advance at idle. |
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| Author: | bwhitejr [ Sat Dec 03, 2005 4:51 pm ] |
| Post subject: | Which Grade of Regular Unleaded? |
I think the advance is cumulative and which case it would be: 12 deg @ 650 RPM 15 to 19 degs @ 1300 RPM 19 to 27 degs @ 1800 RPM 26 to 38 degs @ 4400 RPM This seems to match the "smog curve" of the 1970's. Have I got this right. I am trying to figure out what to do about my distributor curve. Right now, I have no vacuum advance hooked up because it pulls the advance so far it fires on the next cylinder! |
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| Author: | emsvitil [ Sat Dec 03, 2005 5:03 pm ] |
| Post subject: | you're thinking too much...... |
you were right the first time...... The centrifugal advance specs are total (plus initial) for a given rpm. vacuum is added to centrifugal. See http://www.slantsix.org/forum/viewtopic.php?t=13264 where I went thru curving a distributor........ |
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| Author: | bwhitejr [ Sat Dec 03, 2005 5:20 pm ] |
| Post subject: | Which Grade of Regular Unleaded? |
Many Thanks emsvitil! It looks like you have done some very extensive work. Great job! It will take a day or two to digest it. In the meantime, I am looking at the recurve springs from Mopar (P2932675). They appear almost identical except that one has a loop that is 90 deg rotated. I thought you were supposed to leave the original light spring and replace the heavy spring with one of these in the recurve spring kit. Since they are almost identical do you replace the two springs in your distributor with the ones in the kit? bwhitejr |
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| Author: | emsvitil [ Sat Dec 03, 2005 5:32 pm ] |
| Post subject: | Re: Which Grade of Regular Unleaded? |
Quote: Many Thanks emsvitil!
In the meantime, I am looking at the recurve springs from Mopar (P2932675). They appear almost identical except that one has a loop that is 90 deg rotated. I thought you were supposed to leave the original light spring and replace the heavy spring with one of these in the recurve spring kit. Since they are almost identical do you replace the two springs in your distributor with the ones in the kit? bwhitejr You're welcome. I think the recurve springs are for setups with more mods and higher stall converters than trying to get a good curve on a mainly stock setup. I ended up making my own springs to get what I wanted...... |
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| Author: | bwhitejr [ Sat Dec 03, 2005 5:49 pm ] |
| Post subject: | Which Grade of Regular Unleaded? |
Mine is not exactly stock. I am running (allegedly 9.69:1), ported and polished 390 cfm carb and an admitedly mild cam with moderate lift. It is a truck and weighs 4800 GVWR so I guess the distibutor curve is pretty flat. bwhitejr |
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| Author: | bwhitejr [ Sun Dec 04, 2005 11:31 am ] |
| Post subject: | Which Grade of Regular Unleaded? |
Does anyone have the centrifugal and vacuum timing data for the MP Performance distributor (P3690788)? I assume it may have come with the instructions for installation. bwhitejr |
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| Author: | SlantSixDan [ Sun Dec 04, 2005 11:55 am ] |
| Post subject: | Re: Which Grade of Regular Unleaded? |
Quote: Does anyone have the centrifugal and vacuum timing data for the MP Performance distributor (P3690788)?
Centrifugal advance "curve" is actually a straight line: All the advance gets dumped-in all at once, because this distributor has only one lightweight spring.The vacuum advance is adjustable. |
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| Author: | bwhitejr [ Sun Dec 04, 2005 12:19 pm ] |
| Post subject: | Which Grade of Regular Unleaded? |
SSDan, Do you have any numbers? Like when does it kick-in and what is the maximum advance and the RPM it reaches it? Would it be better to experiment with centrifugal advance springs and vacuum on a stock 3874876 then buy a P3690788? bwhitejr |
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| Author: | DusterIdiot [ Sun Dec 04, 2005 4:58 pm ] |
| Post subject: | Search... |
Quote: Does anyone have the centrifugal and vacuum timing data for the MP Performance distributor (P3690788)?
it's been posted on one of the "advance" posts... Specs are easy: 10BTDC initial mandatory 20 deg. mech. advance "all in by 1200"...your timing will bounce badly at anything less than 1000 rpm (like +/- 6 degrees on the timing light) 20 degrees of vac. adv...you dial it in with the allen wrench as to when it's to come in...(I think the one I played with was something like 12 or 14")... this is a "drag only" distributor... I use a small block med. spring for 'car' street use to modify this curve to become: 10 initial 20 degrees mech advance "all in" by 2300 rpm (picked by shift and 'cruise' rpm)... Before recurving I get two of the same distributors, so I have a benchmark/stock one to get me to work (and I know runs)...then I do the swaps to the other one... One of the posts has the 'slot' welding measurements if you end up with one of those pesky early 70's 15R governors (set @ no initial and 30 degrees of mechanical advance)... -D.Idiot |
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| Author: | emsvitil [ Sun Dec 04, 2005 5:14 pm ] |
| Post subject: | Re: Search... |
Quote:
One of the posts has the 'slot' welding measurements if you end up with one of those pesky early 70's 15R governors (set @ no initial and 30 degrees of mechanical advance)...
-D.Idiot I wrapped some wire around/thru the outside of the opening to limit the travel on the centrifugal slot....... |
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| Author: | bwhitejr [ Sun Dec 18, 2005 1:39 pm ] |
| Post subject: | Which Grade of Regular Unleaded? |
If the specifications from the FSM are : Quote: With 12 deg BTDC Initial Timing I get: 12 deg @ 650 RPM 15 deg to 19 deg @ 1300 RPM 16 deg to 20 deg @ 1800 RPM 19 deg to 23 deg @ 4400 RPM bwhitejr bwhitejr |
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| Author: | emsvitil [ Sun Dec 18, 2005 2:58 pm ] |
| Post subject: | |
Looks like you have a 5.5R in there (23-12)/2 |
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