More distributor/advance questions

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NukeBass

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You guys are probably getting tired of my questions on all of this, but I hope to be finished with this soon.

As (a short) background for those who haven't seen my numerous posts, I had my car restored and motor changed from a /6 to a 340 and now I am in the process of learning how to tune it (the shop didn't do any distributor advance adjustments except for the vacuum). Based on various threads here, I took the distributor out and was going to change the centripetal advance (weights and springs...centrifugal isn't a real force ;) ), but found that the distributor didn't have an adjustable advance. The receipt from the shop said Mopar Performance distributor, so I was surprised that it wasn't adjustable. Maybe it was an old model that whomever sold it had on the shelf or something. Since I have no welding skills to change the advance plate, I bought the kit from FBO (as an aside, the tuning booklet that comes with it is quite interesting...) that has precut slots to use to limit the advance.

So, the question is what advance curve would you recommend? I've seen a few different numbers in different posts, but I'm guessing it can be application specific. I still haven't asked to find out what my compression ratio is, but the camshaft is a XE274H, I have a 5 speed TKO-500 transmission, and the rear gear is 3.23. This is strictly going to be a daily driver type car so I probably won't get into high RPM very often. Based on what everyone here has said, and
Don at FBO when I ordered the part, I am going set my initial timing around 18-20 degrees advance and use the 14 degree distributor advance slot on the plate, for a total around 32-34, depending on slop in the plates and all. The kit lists the approximate curves for their springs, and the options look like using just the distributor spring where the advance comes in around 1000 RPM and is at 14 degrees around 1750. Another option is to use the stock and the light kit spring, but the chart indicates the advance won't come in until around 1700 RPM and will be full in by 2500 RPM. Another spring option comes in around 1700 RPM and is full in around 3000 RPM. I do plan on running vacuum advance, so what sort of mechanical advance curve should I aim for?

Another corollary question is what distributor should I get if I wind up breaking this one? :) I would like one with a more accessible adjustment setup, but it is hard to tell from the descriptions which ones are adjustable (summit said the MP distributors aren't adjustable and another one from Mancini didn't seem to be either).

Thanks for your help!! I am learning a lot about this stuff as I go from all of the info here.
 
First, what do you have NOW? There is normally a number stamped, usually on the bottom of the Mopar advance:

http://image.moparmusclemagazine.co..._electronic_ignition_system+advance_plate.jpg

The number 15 above is DISTRIBUTOR degrees which means that you are getting THIRTY (30) at the crank. This is a VERY long and would have been slow "smog" advance

Somewhere I read (cannot confirm) that the Mopar adjustable weights actually gave trouble, something about being twitchy because of the construction of the mechanism............I can't confirm or deny

There are TONS of articles,

http://www.forabodiesonly.com/mopar/showthread.php?t=64449

http://www.forabodiesonly.com/mopar/showthread.php?t=178584

http://www.moparmusclemagazine.com/techarticles/engine/mopp_0301_mopar_electronic_ignition_system/

Ideally you want to determine what the engine wants for total.

Dyno, G-tech, or other instrumentation, or the "old way......" strip times

And determine what the engine wants for initial.

Those two points will determine your curve LENGTH

Springs are "in the middle" IE too much advance too soon will cause knock / ping at low/ med RPM too slow won't give you the power you want. I'd start about 2500 for "all in" but you'll likely get a whole range of answers.
 
I was hoping to set this once and be done. Sounds like the answer isn't quite that simple. I didn't pull the plate down that far, but when I was measuring it a couple of weeks ago 30 sounds about like what I was getting from the distributor without the vacuum advance. Thanks 67!
 
As mentioned.....What are you starting with ?
You need to install this distributor,set the initial,and find out when it is all in.
On a DD/Street car, 12-14 initial 32-34 all in (2200-2500) should be adequate.
Remember, this isn't a clapped out drag car,so tune it accordingly.
After you get your initial timing set,then you can play with the vacuum advance.
 
I set it to 12 degrees advanced a few weeks ago and by 3000 RPM it was well over 40 without the vacuum hooked up. With the vacuum it was well over 50. Right now it is set around 5 initial and the throttle plates on the carb are open at idle to keep it at 800 RPM (the ported vacuum has 10 in Hg) so the recommendation was to increase initial to around 18-20 because of the cam and adjust total from there.
 
Initial is more important on a street car than a hopped up race car. You spend most of the time in low rpm ranges, where the initial is a bigger player, especially at idle.

DO NOT concern yourself with vac adv at this point. Plug it off until you get the other items squared away.

The progression you should work through is this:

1. Initial - IMO, the 18-20 range is likely going to be pretty close.
2. Total - shorten up slots use the plate
3. Curve - Springs
4. Vac adv - different can (more/less added), more vac to initiate, etc.

I run stock 318's at low double digit initial timing. No way a XE274 is going to like that timing setting.
 
Ok, I have a simple way to set this up.

1st, with the car warm and the vacuum advance disconnected and plugged and a vacuum gauge hooked up, find the timing with the highest idle speed and vacuum and note this.

Shut the car off and immediately try to re-start it. If it starts normally, this is your initial timing...it will probably be between 18 and 22 degrees BTDC. Retard a bit if there's a problem cranking and try again

Total timing, the car will probably want 32-36. I'd shoot for 34. Adjust your plates accordingly. If you had a welder, you would have been able to do this easily with some ratios.

For springs, I found my car liked using only the factory light spring, but with one coil removed.

My car is extra touchy...9.7:1 340, 228/[email protected] roller cam, 750 DP, 4-speed, 3.23's. Driveabilty is seamless. I don't have the vacuum advance connected because the car seems to run worse with it connected.
 
I tried some JB WELD on my slots the last time and it worked well for me. Listen to crackedback, it may take you a couple times andactually gets to be fun after awhile. Good luck.
 
I thought about using JB Weld last week when I had the distributor apart, but I didn't know at the time how to get the advance plate off (at the time I was expecting an adjustable mechanism).

A buddy of mine came over this evening and we took the distributor apart and put in the FBO plate at 14 degrees. The hardest part was finding the clip holding the plate in place under all of the grease and figuring out that we were squeezing the clip when it should have been expanded for removal. The plate didn't have any numbers on it, so I don't know what it was supposed to be, but we went with the 14 degrees and tried the light spring in the kit (so now there are two light springs). It got late and we didn't get a chance to set the timing, but hopefully that will be done Sunday or Monday. We did check and the car at least cranked after we put the distributor back in, so it appears we didn't break anything too bad.
 
Those little spring clips sometimes are easy and sometimes not, Lets us no how that plate works.
 
Alright, so I got it all started again today. I reset initial timing to around 18 degrees (it jumps around a lot, so I'm pretty sure I'm between 15 and 20 leaning towards the 20 side). It looked like it was full in between 2000 and 3000 RPMs (my tachometer stops at 2k, but my REVNNATOR blinks for 1000 RPM increments) and was around 35 degrees max (or so, I think), so the plate looks like it did its job within a few degrees assuming various tolerances and all of that. Then I hooked up the vacuum and, around 3 or 4k RPM got over 50 degrees, so I'm going to take a few degrees out of the vacuum canister.

I was able to get my ported vacuum down to around 1 or 2 in HG (probably the low end of my gauge) so that is good, and my idle is around 750 RPM. However, I am now getting no vacuum on the manifold side of the carburetor. This might not be an issue if I keep my vacuum advance hooked up to the ported side, but I still think the carburetor may not be built right (wait, that was a question from a different topic in the fuel section. I have too many questions! ).

So, then I get paranoid and have to ask what detonation/pinging sounds like? I have a book that describes it as a can of marbles, and I don't hear anything right now out of the ordinary in my motor, but I haven't driven it on the street yet and it could be I am missing it. Is it something obvious I will notice? In my garage, the motor sounds don't change as I run it up into 3000 RPM, but I'm worried I may be missing something.

I also should have worn ear plugs. It gets loud under that hood!
 
"Pink" "spark knock" "detonation" sounds like rocks pepples "in there." The sound is directly connected to engine load and throttle position, IE more load, more throttle, more ping. If you google around you should be able to find photos of "plug readings" that show signs of knock.

I doubt you can duplicate it in the garage. Worst ping is usually at low/ med RPM with a lot of load and "more throttle." It depends on compression, timing, cam timing, engine temperature, and fuel quality.

"Back in the day" when I had the 340 in the RR, I got "a little broke" before payday. I had a half tank of premium, and thought, "hell" I can put regular on top of the high test, and "take it easy" until payday. That thing pinged so bad it wasn't funny. This was a 71, high compression 340. You did NOT have trouble hearing it ping.
 
Yep, the ping sounds like the valves are adjusted loose if you can imagine what that sounds like. You may be able to get it if you load it against the brake (brake and the gas at the same time) but that can be hard on transmissions and can cause you to drive through the back side of your garage. If you idle along and mash the gas if it is going to ping that's when it will do it. Sounds like you are getting closer. tmm
 
I drove it up to the store and hit the gas hard a few times and didn't hear anything, so that is good. I'm not sure I got my air mixture screws on the carb correct since one of them didn't seem to do a whole lot and my tach was bouncing a bit with the motor (the Edelbrock instructions say to lean it up 20 RPM after finding the maximum RPM, but that is too fine a measurement for my tach). I think I got close, but I'll leave it like it is and keep driving it and see how it does. I'm pretty sure the throttle plates are as closed as they will be, but it still seems to want to diesel (it kept going for a second or so after one of the times it was shutoff, but not nearly as bad as before). If I cut the idle down much lower, it'll probably get really rough.

All in all, I have learned a lot from this tuning project (and it's probably not finished). I was hoping not to have to do it since I paid tons of money for the car to be put together, but, in the end, this is something I need to learn how to do on my own (and all of the help from this forum!!).

Thanks!!!
 
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