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 Too much advance at light throttle? 
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Joined: Wed Feb 13, 2013 4:04 pm
Posts: 65
Yep thats the same mech advance my Mallory's have. Both have the YH series advance

I noticed in mallory's instruction sheet it states:
http://documents.holley.com/mallory_instructions_yh_series_mechanical_advance_kit_29014.pdf

Quote:
Two Stage Advance Curves:
Figure 1 shows the different two stage advance curves. All
two stage curves are obtained by using one purple spring and
one other color spring. (DO NOT USE TWO PURPLE
SPRINGS: This will cause erratic timing at low RPM). These
curves are called two stage because the slope of the curve
changes at about 1500 RPM. This is because the purple
spring is loose when installed and doesn’t become a factor
until after about 1500 RPM. Two stage curves are usually preferred
for street driven vehicles (especially V8s) because the
quicker advance at low RPM provides good throttle response,
while the slower advance at mid RPM helps prevent detonation.
Full advance is in no later than 3500 RPM for good top
end power.


And Chryslers Instructions seem to imply having the timing all in by 2000 in the Ignition Kit Instructions.
Page 7 section 8
http://www.dippy.org/upgrade/ignition.pdf

Quote:
For Max performance this distributer becomes fully advanced at 2000 rpm. At that point, the total mechanical advance - sum of the initial adavance and centrifical advance - should equal the number shown on page 5 or 6 for your specific engine. This is the max performance setting


Also chrysler sells an advance spring set which looks to be 2 matching light springs which would bring the advance in pretty quick like Mallorys matched paired spring chart fig 2 on page 3.

In Mallory's advance curve kit it has the Purple spring BUT both my Mallory's have a very stiff silver spring also shown in the picture you posted which isn't shown in any instructions so I'm wondering if its chrysler specific?

I tested the different springs and I found the Purple spring begins to engage at 6 degrees of mechanical distributer degrees where as the silver springs which came with the dizzy's didn't until 7 and 7.5 distributer degrees. All were tested with the light pink spring.

I hope all this makes sense........

Hysteric


Sun May 01, 2016 5:09 am
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Hysteric wrote:
...
I noticed in mallory's instruction sheet it states:

Quote:
Two Stage Advance Curves:
... These curves are called two stage because the slope of the curve
changes at about 1500 RPM. This is because the purple
spring is loose when installed and doesn’t become a factor
until after about 1500 RPM...

I was disappointed to see this misleading description in there. As you describe, the second stage starts whenever the advance hits x degrees depending on the loop length.

Quote:
And Chryslers Instructions seem to imply having the timing all in by 2000 in the Ignition Kit Instructions.
Page 7 section 8
http://www.dippy.org/upgrade/ignition.pdf

Quote:
For Max performance this distributer becomes fully advanced at 2000 rpm. At that point, the total mechanical advance - sum of the initial adavance and centrifical advance - should equal the number shown on page 5 or 6 for your specific engine. This is the max performance setting


Yup, and the graph in the Engine Book ('Speed Secrets' version) also shows that. But edit: Checking the older instruction sheet, it says set timing at 2600 to 2800 rpm andwhen I tested the MP distributor that came in that kit (Chrysler built) it clearly was still advancing at 2000 rpm. This was done on the engine, and I didn't know enough then how to get it to idle at lower rpm, but that wouldn't change the shape of the curve.
Test started at Timing 17 degrees BTDC at 900rpm (Idle).
Attachment:
P3690430-advance.jpg
P3690430-advance.jpg [ 63.97 KiB | Viewed 295 times ]

There must have been an editing error that kept getting repeated or there was a change in parts. MP was highly unimpressive when I was getting into this. No one I spoke with knew any tech about the parts or cared about problems. I think the people who really knew stuff and the files of test data were gone. Larry Shepard may have still been there, but he comes across as pig-headed. I think Larry misapplied answers that had worked in the pinch or for a specific problem decades earlier. For example that would explain the ridiculous advance in Mallory made Mopar Performance distributors (as described here http://www.moparts.org/Tech/Archive/elec/29.html). This worked for the tach drive distributors if establishing stable idle was not very important at the same time achieving easy starting. MP produced some good items and sometimes had good deals, but I felt it was, and is, legacy from a decade or two earlier.

Quote:
Also chrysler sells an advance spring set which looks to be 2 matching light springs which would bring the advance in pretty quick like Mallory's matched paired spring chart fig 2 on page 3.

I think this is a legacy from pre-magnetic pickup/amp box or possibly some other specific application. The think its in the 1969 MTSC High Performance Tips, they suggest removing the heavy spring for racing. That would be a dual points distributor though - no slew rate losses at high rpm. I have one of those spring sets - calculates to 0.6 lbs/in. Might be good for a fast advance in a mallory YH..* Just guessing here.
Quote:
In Mallory's advance curve kit it has the Purple spring BUT both my Mallory's have a very stiff silver spring also shown in the picture you posted which isn't shown in any instructions so I'm wondering if its chrysler specific?
I've wondered the same thing.
Attachment:
Springs-for-MP-YH.jpg
Springs-for-MP-YH.jpg [ 57.79 KiB | Viewed 295 times ]

Quote:
I tested the different springs and I found the Purple spring begins to engage at 6 degrees of mechanical distributer degrees where as the silver springs which came with the dizzy's didn't until 7 and 7.5 distributer degrees. All were tested with the light pink spring.


That is good info.
It explains a problem I ran into with the YH in the mopar housing. After adjusting to limit advance to 16 engine degrees, the long loops were barely engaging. That matches what you measured- the silver spring wouldn't engage until 15 degrees advance. :(
______________________________________________________________________________________
*Mopar Perfomance superlight spring set part number P 2932675; 0.6 lb/in, Spring loops are 0.7" apart.
Mallory YH Pink springs calculated at 1.1 lb/in, and 2.11 lb/in. and avg .55" loop to loop.
Information that came with the MP version of the spring kit states the Pink springs are 1.7 lb/in and presumable more accurate than my calcs.


Last edited by Mattax on Fri May 06, 2016 9:46 am, edited 1 time in total.



Thu May 05, 2016 11:32 am
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Joined: Wed Feb 13, 2013 4:04 pm
Posts: 65
The benefit of the Mallory advance mechanism is you can bend the tab to change when the spring begins.

Also I noticed in the last graph you posted titled "Centrifical Advance P3690430 the MP Tested curve is close to what Tuner recommended in his 1st reply to this thread:

Quote:
The lower of the two green curves is about what I would do, except above 3000 the slope should be flatter and extend to 8000+ RPM. 18 initial until 1200-1400 RPM, then to 30-32 @3000, then 35°@5500, 38°@ 8000, near 1 degree per 1000 RPM.


Is that the curve the MP Unit actually produced when you tested it, and if so what springs did it use?

Hysteric


Fri May 06, 2016 3:32 am
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Hysteric,
That graph above is for the MP small block distributor with Chrysler internals - no modifications. That's one reason I'm now modifying the one with Chrysler guts instead of the easier to work with YH style advance.

But, I may have messed up the part numbers. I found my receipt from 2006 for the MP distributor with the YH advance - part number is 3690430. I need to double check the tag on the older version with the Chrysler advance - is it the same part number??? Ugh. I assumed the part number changed. I hope that's true... more to follow.

Also, while in the files, I looked at the instructions that came with the older MP electronic ignition kit (which included the chrysler built MP distributor). Get this. It says to set the engine rpm between 2600 and 2800 rpm!. Then set timing to specs on chart. That makes sense given the curve. I'll scan and post as pdf when I get a chance, its Instruction Sheet DCF-194 (no date). For distributors with vacuum advance, p/n P3690426 P3690427 and P3690428.

Quote:
The benefit of the Mallory advance mechanism is you can bend the tab to change when the spring begins.

Ya. And looking at my notes, toward the end of my experimentation I did bend them a little. But with the advance set at 16 degrees, I was afraid to bend the tab not knowing what was needed or how it would effect the curve. Now with a better understanding of both, I'll take another look at it when I swap it out (its in the car now). Another option might be to install a screw in the tab to take up some of the slack.


Fri May 06, 2016 11:11 am
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Joined: Wed Feb 13, 2013 4:04 pm
Posts: 65
Hey Mattax,

I've been digging around and found on another forum (moparts) where it was mentioned the Mallory made MP distributors with the YH advance had problems. Is this the case for the YH advance mech in general including mallory made dizzy's?

Hysteric


Thu May 12, 2016 6:37 am
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Joined: Sun Jun 23, 2013 1:41 pm
Posts: 375
Location: Phila. Penn.
Hysteric,
I'm not really sure what 'the problems' on the Mallory made MP distributors, other than it may not be possible to get the long slow curves without serious modification.
I would guess this is the same on Mallory distributors. But maybe the spring angles or advance plate shape is different.
Do any of the moparts posts state what the (alleged) problems were/are?

PS. It does look like Mopar Performance used the same part number for both versions of their vacuum advance distributor. :( :roll:

- Matt


Tue May 17, 2016 9:51 pm
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Joined: Wed Feb 13, 2013 4:04 pm
Posts: 65
Quote:
Do any of the moparts posts state what the (alleged) problems were/are?


This thread:

http://board.moparts.org/ubbthreads/ubbthreads.php/topics/1655018/re-mp-distrubutor-schooling-needed.html


He mentions the mallory weights as being too light.


Thu Jun 02, 2016 5:58 am
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