Using two stock light springs in distributor advance, good idea?

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LivewireBlanco

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So I'm upgrading my points ignition on my '71 318 Dart to factory electronic ignition. I know that the factory distributors have quite a long advance. Would taking the light spring from my old distributor and putting it in place of my heavy spring in the new distributor give me a fairly good advance curve? I know total advance won't be affected. Anyone try this before?
 
It will go to full advance in a hurry. That's the reason for the bigger spring to buffer it to full mech advance. Get them in as cores all the time. That's why guys sell me the cores!
 
Also they as so weak timing can bounce around a bit at idle.
 
So ya'll would say leave the factory springs in there? I say this because I have an after market camshaft, 4bbl carb, headers, and high stall converter. I've been reading about having full mechanical advance in by about 2,500 RPM and that ordering the Mr. Gasket springs and only switching the heavy one out is the way to achieve this. I just was wondering if the same could be achieved by using the light spring from the old distributor.
 
Really depends on what spring you have in there. Tons of different oem ones. Also what is the advance cam that is in there now. Should be marked say 10R or so. They are all over the place in those years. seen 8 and 18! Got a distributor number I can get the specs. Those Mr. G springs slam right in say at 1500 or lower.
 
Really depends on what spring you have in there. Tons of different oem ones. Also what is the advance cam that is in there now. Should be marked say 10R or so. They are all over the place in those years. seen 8 and 18! Got a distributor number I can get the specs. Those Mr. G springs slam right in say at 1500 or lower.
That's what I've heard and why people only use one spring from the kit. I'll have to take apart the new distributor and look at the plate. My old one had about 35 degrees of advance built in so I'm looking forward to this new one plus not having to mess with the points anymore.
 
They are nice with almost no maintenance. Pretty easy to curve also.
 
Those numbers are distributor degrees double them for crank degrees.
 
I used to light springs but originally had a 13 degree (26 degree at crank) advance cam, I shortened the slots by running a bead of mig wire on the shaft side of the slots and filed down evenly for a total of 10 degrees at distributor. It works out to 20 degrees mechanical at crank and 14 degrees of static timing. One of my light springs is lighter than the other but I am all the way in at full advance of 34 degrees all in at 2600 rpm. Your combination with proper gearing would probably run better with more static and a little less mechanical, but at what rpm is dependent on how much compression/cam/gear/stall speed. The goal is as much advance as early the engine will take without running into detonation. I am close to the ragged edge with 10:1 and 2.76 gears with 340 regrind camshaft.
 
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I used to light springs but originally had a 13 degree (26 degree at crank) advance cam, I shortened the slots by running a bead of mig wire on the shaft side of the slots and filed down evenly for a total of 10 degrees at distributor. It works out to 20 degrees mechanical at crank and 14 degrees of static timing. One of my light springs is lighter than the other but I am all the way in at full advance at 2600 degrees rpm. Your combination with proper gearing would probably run better with more static and a little less mechanical, but at what rpm is dependent on how much compression/cam/gear/stall speed. The goal is as much advance as early the engine will take without running into detonation. I am close to the ragged edge with 10:1 and 2.76 gears with 340 regrind camshaft.
Just clarifying, you used two stock Mopar light springs and not aftermarket? If so, that's pretty much dead on what I'm aiming for.
 
The Mr. G are super light just like the MP ones they still sell.
 
yes, two stock light springs that were in stock distributors... Got rid of the two ramp advance curve that the heavy spring gives, it wasn't getting all the timing in until 4500 rpm beforehand, not good when you run out of intake at 4800!
 
Highly suggest getting this spring kit and drop in limiter plate combo (J685S) from 4secondsflat.com

kit.jpg
 
I had originally seperated a spring coil on my heavier spring but had to tie it back together with safety wire, I immediately lost 4 degrees of advance at idle with the seperated spring coil. Would have worked great on a drag car for start retard.
 
Also if you call Don on the phone, he will actually stop what he is doing, and give his suggestion on how to set up everything up based on what you have. There is a lot to say about a guy that will go over your setup, and spend time helping you dial it in, after spending only $40 on his website..
 
I must agree! if you have someone that you are able to talk to about your specific combination and they understand tuning enough to set you up with an accurate baseline, $40 is a real bargain... You will spend that that much in aggravation alone figuring out for yourself!
 
I've seen that plate and spring kit. If the new distributor has a advance plate over 13 then I'll probably go with that kit. I'm not looking for every tenth down the drag strip but I definitely would like to wake up my 318!
 
Also if you call Don on the phone, he will actually stop what he is doing, and give his suggestion on how to set up everything up based on what you have. There is a lot to say about a guy that will go over your setup, and spend time helping you dial it in, after spending only $40 on his website..
Don gave me some FREE advice once or twice as well...I didn't even buy anything at that point. I emailed a list of my problems and the specs I had, he responded with a fair explanation of what I should do. This is a rare thing, to get FREE help from a trusted professional.
 
I've been reading about having full mechanical advance in by about 2,500 RPM
Halifaxhops is giving you the real info.
Start here for ballparking an initial timing for your engine combo.
Distributor starting point for a curve

How emissions changed timing curves and why 318-2 bbl timing was different than 273 4 bbl in the middle of this post:
Rich Idle AFR reading

'All in by 2500' is misleading.
Even on a hot rodded engine, the two stage setup is very useful, especially with electronic ignitions. The switching in electronic amplifiers takes time, and that time shows up as retarding advance that becomes noticible between 3000 and 6000 rpm. There are faster electronic boxes and slower ones and even units that are designed to offset that internally - I think pertronics III may do that and FBOs box might too. The revenator patent suggests it sortof does that as well - but I haven't studied and its probably over my head.

For drag racing using a distributor with no vacuum advance, the heavy spring can be used to hold the WOT steady or even better, a very slow increase with rpm. That's what the Direct Connection 'tach drive' distributors do. Detailed discusion here: P4120701 Small Block Mech Tach drive Its drivable on the street - I've done it. Its just not ideal.

Both those distributors and the regular Mopar Performance distributors with vacuum advance were best setup at an rpm near 'full advance'. By 2600 - 2800 they are usually at or close to full advance and pretty stable. Instructions for those vac advance equiped MP distributors here:How to determine the RPM for all in?
Trying to set them at idle can be difficult because its advancing quickly at low rpm. However that can be adjusted if you know what to do. It's all about the initial spring tension.
 
Usually not. Most people have the best luck leaving the stock light spring in and coupling it with whichever aftermarket spring works best. Sometimes it's the lightest aftermarket spring, sometimes not. It's all combination dependent. I leave the factory light spring in and replace that big battleship factory spring with the lightest aftermarket spring as a start. So far, that's what I always end up with. Probably because None of my hot rods have been heavy like a B body. My 75 F250 I used the lightest and heaviest aftermarket springs and got the best result. 99 times out of 100 you will end up with a mismatched pair of springs to get the best result. I know I always have.
 
Why are we "guessing" at what works? Put your combo on a distributer machine and know how much advance you have. Also it will show you the rate of advance at any RPM. Use the machine and know what you got and tailor the advance to meet your needs.
 
yes the 6 spring kit pictured
 
Well, I guess best case scenario is to use a distributor machine if you can get access to one. Your baseline based on your combination is still a "guess" being that you are going to get "close" as far as how much static, and how much mechanical all in by what rpm. You are still going to have to fine tune in what is "optimal to your combination" with some seat of the pants, chassis dyno, or preferably, drag strip tuning.
 
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