Re: Full advance
[Re: B1MAXX]
#2934594
06/18/21 02:42 PM
06/18/21 02:42 PM
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Joined: Jan 2004
Posts: 8,240 fredericksburg,va
cudaman1969
master
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master
Joined: Jan 2004
Posts: 8,240
fredericksburg,va
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I used one light spring to make it close on start up, then bang it’s wide open. Didn’t need a spring with points because friction on the rubbing block would pull it back, electronic needs the spring. Never bothered with the slots, just the stock dist in every race car. Trying to set idle with light spring is tough. In my experience they will move your idle timing around, causing erratic idle rpm. Are you idling below 400 rpm? Just guessing on that rpm because when I check at 600 rpm it’s at 37 degrees and steady. Maybe we talking different springs?
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Re: Full advance
[Re: cudaman1969]
#2934615
06/18/21 04:12 PM
06/18/21 04:12 PM
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Joined: May 2005
Posts: 1,966 Apollo, PA.
B1MAXX
top fuel
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top fuel
Joined: May 2005
Posts: 1,966
Apollo, PA.
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Must be talking different springs. Most of the light springs I've messed with are full in around 1200rpm. So when you set the timing at say 23* at 900 idling in neutral then drop it in gear it takes timing away making it want to stall, at the timing is all over the place.I guess if your idling at or near 1200 in this case it would be a wash. So you are saying with light springs installed you have no curve? From 600 all the way up?
Last edited by B1MAXX; 06/18/21 04:12 PM.
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Re: Full advance
[Re: B1MAXX]
#2934635
06/18/21 05:32 PM
06/18/21 05:32 PM
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Joined: Jun 2008
Posts: 3,916 usa
lewtot184
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master
Joined: Jun 2008
Posts: 3,916
usa
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Must be talking different springs. Most of the light springs I've messed with are full in around 1200rpm. So when you set the timing at say 23* at 900 idling in neutral then drop it in gear it takes timing away making it want to stall, at the timing is all over the place.I guess if your idling at or near 1200 in this case it would be a wash. So you are saying with light springs installed you have no curve? From 600 all the way up? all the light race springs i've ever used will bring the full centrifugal in at 1100-1200rpm using a 9 degree plate. so if you set the total centrifugal at 36 degrees there will be 36 degrees at 1100-1200rpm. naturally below that rpm advance will reduce. there is a point were the springs can be too light and not let the weights fully retard when the engine is shut off but that would only happen if someone tries to use only one of the race springs. i've found erratic timing to be other issues than springs.
Last edited by lewtot184; 06/18/21 05:33 PM.
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Re: Full advance
[Re: lewtot184]
#2934657
06/18/21 06:56 PM
06/18/21 06:56 PM
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Joined: Jan 2004
Posts: 8,240 fredericksburg,va
cudaman1969
master
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master
Joined: Jan 2004
Posts: 8,240
fredericksburg,va
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Spring was made for the Chevy dist, looked like the size of hair, almost to light to rotate it back to zero. Also no grease on those pivots or slots (center shaft too) dry lube only. We used one of those Sun machines to set it up but lost track of the dude, don’t know where him or machine moved to.
Last edited by cudaman1969; 06/18/21 07:05 PM.
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Re: Full advance
[Re: mopar dave]
#2934668
06/18/21 07:45 PM
06/18/21 07:45 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
master
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master
Joined: Apr 2006
Posts: 4,220
West Plains, MO
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After sitting for hours, I can see it being able to start at 29 degrees. But will it start hot? My 451 starts to buck at 26 hot. The current setup I'm running to avoid the hot start problem is one light spring, one heavy spring with loop, and a 22/11 degree plate. This allows me to crank at 16 degrees, the light spring is all in at 27 degrees (the loop on the heavy spring holds it from going higher) as soon as it starts and idles at 1100-1200. The advance starts coming in around 1500 or so. I've measured 35 degrees at 4000 but I won't stand next to it and rev it any higher! The plate will limit the advance at any speed to 38, less the inevitable retard in the ignition box, so that should be about 35-36 at high rpm. Plus vacuum advance that does nothing at idle (8" Hg.) but is fully engaged at cruise (15" Hg.) Don't remember how many degrees. Haven't heard it ping yet on pump premium, 10.3:1, iron heads for now. 272@.050, .652 gross lift, .018 lash. After reading this thread, I'm tempted to just put two light springs in so it's all-in at idle, and try it out...
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Re: Full advance
[Re: oldtimer5151]
#2934684
06/18/21 08:44 PM
06/18/21 08:44 PM
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Joined: Apr 2006
Posts: 4,220 West Plains, MO
DrCharles
master
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master
Joined: Apr 2006
Posts: 4,220
West Plains, MO
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But - at partial throttle and low load, the lean, less-dense mixture requires MORE time to burn and reach maximum pressure at 15(?) ATDC. Sometimes much more time. That's why vacuum advance is so useful on an engine that doesn't run only at wide-open... light throttle cruise well into the 50's advance is not unusual. The reason for having variable centrifugal advance is that at low rpm there is already more time for the mixture to burn so less total advance is needed. As the rpm climbs, so does the need for advance - up to a point... that point is usually 34-36 degrees for most big-blocks, maybe a few degrees more for small-blocks. Depends on the combustion chamber design, of course. You're right that 38 may be too much at low rpm and wide-open throttle. Except that my cam has a lot of overlap so it needs more low-speed advance... My engine won't see 38 degrees. Every ignition box has some retard, because a finite amount of time is required to read the trigger signal and fire the coil. At higher RPM the crank turns more degrees in that same time interval. Somewhere I saw (maybe on FABO) a test of several boxes and many were retarding 1 degree per 1000 rpm, or even more
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Re: Full advance
[Re: mopar dave]
#2934749
06/19/21 01:32 AM
06/19/21 01:32 AM
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Joined: Sep 2014
Posts: 4,457 Washington
madscientist
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master
Joined: Sep 2014
Posts: 4,457
Washington
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All ignition boxes retard with RPM. If you lock out a distributor you haven’t a clue where the timing is once the box starts retarding. And it WILL retard.
Just because you think it won't make it true. Horsepower is KING. To dispute this is stupid. C. Alston
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Re: Full advance
[Re: B1MAXX]
#2935204
06/21/21 08:23 AM
06/21/21 08:23 AM
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Joined: Jan 2003
Posts: 13,357 Marion, South Carolina [><]
an8sec70cuda
I Live Here
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I Live Here
Joined: Jan 2003
Posts: 13,357
Marion, South Carolina [><]
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Big cams always idle better w/ full timing in my experience. The only thing I wouldn't lock out is a near stock build. Like some others have said, we don't use a start retard on anything.
CHIP '70 hemicuda, 575" Hemi, 727, Dana 60 '69 road runner, 440-6, 18 spline 4 speed, Dana 60 '71 Demon, 340, low gear 904, 8.75 '73 Chrysler New Yorker, 440, 727, 8.75 '90 Chevy 454SS Silverado, 476" BBC, TH400, 14 bolt '06 GMC 2500HD LBZ Duramax
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Re: Full advance
[Re: an8sec70cuda]
#2936336
06/24/21 09:37 AM
06/24/21 09:37 AM
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Joined: Jan 2003
Posts: 8,163 Plymouth, MI
Blusmbl
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master
Joined: Jan 2003
Posts: 8,163
Plymouth, MI
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Based on this thread I bought the Mr. Gasket 925B spring kit and put it in my .590 cammed 440. The distributor had one heavier spring in it already but changing it out was a noticeable improvement in idle quality and off idle response, definitely snappier/crisper now and the idle speed picked up by a couple hundred rpm with no other changes. My drive idle is just below full advance so it still might lead to some hunting but I'll live with it.
'18 Ford Raptor, random motorcycles, 1968 Plymouth Fury III - 11.37 @ 118
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