Slant Six Forum :: Understanding The Curve

Pat,

I have several Suns. Each has proven to be off re. rpm as read from the machine tach. Just as with the need to calibrate a variable rheostat scale against a good voltmeter for accurate output curves, you will find it useful to calibrate your Sun's tachometer against a standard. I borrowed one of the optical tachs that read a mark on the dizzy shaft while it spins. You can also use a hand tach that has the rubber tip on it and put the hand tach on the shaft where the rotor goes and plot a curve while the dizzy spins. I did mine every 500 rpm. Just match accurate readings from a good tach to those on your machine's tach. The variance is cause by almost anything in the path from the motor armature through the belts and pulleys and the chuck shaft.

rock
'64d100

Author:	polara pat [ Wed Apr 29, 2009 4:25 pm ]
Post subject:	Understanding The Curve
I had a chance on the weekend to use a Sun distributor machine for my newly curved distributor. We didn't have a lot of time so I just got a base line for now, I'll have more time next visit to swap some springs. Here's my combo: 1964 V-100 wagon that probably weighs 3400#; 3.23:1 open gears; re-built and broken-in 225 with 9.5:1 compression and ported head...anything else? The dizzy: 1975 core with 440 secondary spring and stock primary; R-13 governor; 11.0R vac pod. Here's how it went. 800rpm mech. starts 1000rpm 4* 1500rpm 10* 1750rpm 15* 2000rpm 16* all in Vac advance came in around 7" and the total mech + vac came to 38* Keep in mind that I am a rank novice at this, so if my figures are out of whack then it's because I was trying to scribble as fast as possible while still following what was happening. My next step is to assemble my new (old) vacuum guage (gage) and tach so I can start coming up with some cruising speed RPMs and Vac #s. Feel free to criticize and make useful suggestions.

Author:	emsvitil [ Wed Apr 29, 2009 4:50 pm ]
Post subject:
A R-13 governor should give you 26 degrees of mechanical advance.......

Author:	DusterIdiot [ Wed Apr 29, 2009 7:17 pm ]
Post subject:	Not necessarily...
Quote: A R-13 governor should give you 26 degrees of mechanical advance....... It would if he had the whole swing to use...using a heavy spring it will actually limit the advance... I test my 'long slot' distributors at 'max' rpm on my Sun (just crank until it pins the tach which is over 2500 distributor rpm) just to see if the heavy spring will allow it to go farther... I've been able to get 13/15 R slots to limit out using short slot heavy springs and the top end lays in nicely, unlike using a short slot with light springs which can cause the pins to slap off the end of the governor... He should run that combo at 5BTDC and see if it ping with the vacc. advance, if it doesn't work your way up to see if you can get to about 48 degrees vacc.+mech+base and check your plugs... -D.Idiot

Author:	polara pat [ Wed Apr 29, 2009 7:28 pm ]
Post subject:
Interesting, I was thinking that my mechanical seems to be all in too soon (2000rpm). What do you guys think? If my cruising (highway)rpm is around 3200rpm (currently guessing) shouldn't I still be advancing to this point and a little beyond?

Author:	emsvitil [ Wed Apr 29, 2009 8:49 pm ]
Post subject:
It seems the curve should continue.... 22 at 2500 26 at 2833 You want 28-30 at 3000. So 2-4 degrees BTDC with the 26 would be just about right. Try removing the heavy spring.

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Understanding The Curve https://www.slantsix.org/forum/viewtopic.php?t=35115	Page 1 of 1

Author:	Aggressive Ted [ Thu Apr 30, 2009 10:56 am ]
Post subject:
It really depends how fast you drive. Let us know how the car feels first before you change anything.

Author:	polara pat [ Thu Apr 30, 2009 7:57 pm ]
Post subject:
Quote: It really depends how fast you drive. Let us know how the car feels first before you change anything. I'll be honest, I would way rather get a ball park base line before I start doing any in car testing. Once my car is on the road it is driven hard, daily. So where do you think I am in terms of progress? I think I should be getting more mechanical and it should not run out so soon but again, I'm the novice. I still have the opportunity to tweak it some and hit the Sun machine again.

Author:	rock [ Fri May 01, 2009 6:00 am ]
Post subject:	Pat, check the machine, too
Pat, I have several Suns. Each has proven to be off re. rpm as read from the machine tach. Just as with the need to calibrate a variable rheostat scale against a good voltmeter for accurate output curves, you will find it useful to calibrate your Sun's tachometer against a standard. I borrowed one of the optical tachs that read a mark on the dizzy shaft while it spins. You can also use a hand tach that has the rubber tip on it and put the hand tach on the shaft where the rotor goes and plot a curve while the dizzy spins. I did mine every 500 rpm. Just match accurate readings from a good tach to those on your machine's tach. The variance is cause by almost anything in the path from the motor armature through the belts and pulleys and the chuck shaft. rock '64d100

Author:	polara pat [ Fri May 01, 2009 8:52 am ]
Post subject:	Re: Pat, check the machine, too
Quote: Pat, I have several Suns. Each has proven to be off re. rpm as read from the machine tach. Just as with the need to calibrate a variable rheostat scale against a good voltmeter for accurate output curves, you will find it useful to calibrate your Sun's tachometer against a standard. I borrowed one of the optical tachs that read a mark on the dizzy shaft while it spins. You can also use a hand tach that has the rubber tip on it and put the hand tach on the shaft where the rotor goes and plot a curve while the dizzy spins. I did mine every 500 rpm. Just match accurate readings from a good tach to those on your machine's tach. The variance is cause by almost anything in the path from the motor armature through the belts and pulleys and the chuck shaft. rock '64d100 Thanks Rock, that's good to know. I'll mention it to the guy, he'll be up to the task of calibrating it.

Author:	Aggressive Ted [ Fri May 01, 2009 10:10 pm ]
Post subject:
Pat, I would drive it first. It might be better than the machine shows, especially if the machine is off a little.

Author:	polara pat [ Sat May 02, 2009 11:30 am ]
Post subject:
Quote: Pat, I would drive it first. It might be better than the machine shows, especially if the machine is off a little. Good plan. I will be hooking up a tach and vacuum guage for testing purposes. What sort of range should I be looking for?

Author:	Aggressive Ted [ Sun May 03, 2009 7:05 am ]
Post subject:
Pat, I am thinking it all 16 degrees mechanical might be in by 2500 rpm. Maybe another 4 degrees by 3000 rpm. I would start with 10 degrees initial. You should feel allot more spunk out of the engine. I t should not feel sluggish at all.

Author:	convx4 [ Mon May 25, 2009 8:27 pm ]
Post subject:
I have Some 1960's Sun info spec sheets if they are neeed. Convx4@yahoo.com

Author:	Rug_Trucker [ Tue May 26, 2009 5:03 am ]
Post subject:
Anyone seen the distributor phase thread on Moparts right now? Talk about a cat fight! Back on task......3:23's is 2100 on my Duster @55mph 205/70/14's I had the original distributor off my 383 on a Sun machine. It wouldn't fire on 3 cylinders until it hit 1500! 3 of the lobes were gone........single points. The MP electronic was a fantastic cure!

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