Hello all
I am wondering what a ballpark ideal timing curve would be for my setup? Its a near stock 225 with HEI, bored .40 over, oversized main bearings, an RV10M camshaft, lash is .22 intake & .24 exhaust, head is stock except for gasket matching with a dremel on the intake and exhaust ports, carb is a 1964 BBS, stock tourque converter, 904 3spd automatic, and a 7-1/4 with 2.76 ratio. Right now I have a VC208 vac can that comes on at 4 inhg. Initial timing is 10 deg and looks like i get about 20 deg mechanical timing for a total of 30deg that is all in at about 2000rpm. The dizzy always has had two light springs in it. Im thinking the the mech and vac is all in to early. Im wondering if my dizzy weights are slightly engaging at idle (currently 690 rpm) i get a slight movement with the timing light (maybe 2 degrees) and also on the vac gauge at idle, almost 3/4 inhg. But if I slow the idle down to 500 or less the gauge is rock steady. Im sure the carb is set properly with tan spark plugs as proof. I am shooting for max fuel economy without a huge sacrifice to performance. My thoughts are slow down when the mech is all in to about 2800rpm and let the vac can take care of the rest. Thanks in advance. Any thoughts/input would be greatly appreciated.

-Josh

I did some more tinkering tonight. Pulled the distributor, cleaned and lubed everything. Discovered that the governor is a 15L type. Which if i recall means that the dizzy is a cardone reman Found that one of the springs were sticking due to rust. Oil seemed to help that issue. Made some pulls with the tach and timing light hooked up and heres what i have so far. With the can plugged i get About 11 deg initial at 700 and about 30 total at about 2500. For some reason one of the weight posts (I think) was catching the bottom of the advance plate and shifting it slightly. Disassembly cleaning and lubrication seemed to resolve the issue. Timing no longer jumps at idle or through the rpm ranges. I still get about 1/2inhg stutter at idle only. Maybe my valves are to loose? Not a lot of clatter more like a loud sewing machine. About a month ago i loosened my valves and this helped steady the idle, before i loped like a hot cam. I played with the vac can a bit and got it set to kick in at 6” off the ported vac nipple. But that is before the tach reads 1000. I have less than an inch of vac on the ported line at idle. Seems right to me. Time to call it a night.
-Josh

Certainly sounds like you've got it about where you want to be. I like my mechanical advance to be in slightly sooner than 2500, but that's just my personal preference.

How much advance are you getting with full vacuum to the can? How much advance total are you getting holding steady 2500?

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

THOR- I still need to plot my curve. I seem to be having a little bit of difficulty holding the timing light, watching the tach and balancer, while manipulating the throttle plate at the same time lol. I plan on plotting in 500rpm increments so i can stop and write down my findings. With the can (vc208) it gives me an additional 22degs so that puts me at 52degs total. Im using the poor man’s method of marking the balancer wheel in 10deg increments because i dont have a dial back timing light. After I get off work tonight im going to start plotting my curve on paper. Thanks for the questions, I will have answers later tonight. I ordered a spring kit from Bigslant6fan hopefully they are still available. What affect does having a load have on the ignition timing? For example going up a hill at 2000rpm vs in park at 2000rpm? I havent yet heard any pinging (that im aware of!) will post later. Thanks!
-Josh

Hi Josh,

The difference between loaded at 2000 vs unloaded at 2000 is vacuum advance.

At 2000 in park/neutral, I would imagine you are pulling somewhere in the neighborhood of 18+"hg based on a basically stock engine so you have full vacuum advance. (Noting that your mechanical advance isn't completely "all in" yet if the springs are set to 2500rpm)

At 2000 with a fair load (such as climbing a hill) your vacuum signal to the canister will be less, to the tune of perhaps 10"hg. This reduces the amount of advance provided by the can to prevent pinging. (Same note as above)

DusterIdiot is the awesome guy I learned a lot of this from, aside from my own experiments with advance curves on engines.

I will say 52 degrees of advance is quite a lot when spinning at low rpm, but if the mixture is good and it doesn't ping, then that's fantastic.

A dial back timing gun is probably one of the best $100 I have ever spent for getting a car tuned properly. Mine is digital and has an RPM readout built into it, so there's no fussing with looking around at a tachometer while holding the gun and trying to focus on which 10 degree increment is marked on the balancer.

I'm keen to see what your advance curve looks like on a graph. If you are unable to make a graph, I could do that for ya if you give me all the values on a table.

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

THOR-

Thanks for the explanations! It makes perfect sense.

I have read most of DusterIdiots topics and posts over the past few months. He really know his distributors and ignition timing (among other topics im sure!). This is all a first for me before inwould set initial timing by ear at idle and if it pings at WOT then back it down.

I think I am going to hold off for a few days until i got a dial back light. I have been down this road before in a sense. Not realizing my DMM battery was almost dead while trying to diagnose a charging issue. A lot of head scratching lol.

I appreciate the offer to make a graph for me. I will take you up on that offer. Im not very computer savvy but assume i would need excel at least (which i dont have). Thanks again for taking the time to help me through this.

-Josh

I agree you sound like you have a handle on the variables. I also want to add that it is virtually impossible to map a spark advance curve without a dial-back timing light. I have a $30 harbor freight gun that works. Also, I use the idle speed screw to control engine RPM when mapping a spark curve. I don't hold the throttle open by hand. Using the idle speed screw frees you up to hold the timing gun and take notes.

_________________
Casually looking for a Clifford hyperpak intake for cheap.

^^^This^^^

Good thought on the idle screw Reed! Why haven't I done that yet? lol

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing

I also think the dialback timing light is the best way. I use a combo of the dial on the light and watching the flash/mark relative to the timing tab (marked 0-10 at least on most tabs) and that makes mapping much faster. Since the mark can jump around due to slip in the timing chain and dist/gears, I do not think anything more precise than about +/-2 deg is meaningful.

Lou

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Home of Slant6-powered fun machines since 1988

Since I have decided to wait to plot my spark curve until i get a dial back timing light I went ahead and hooked up the vac gauge to my ported vacuum outlet on the carb and ran it through the rpm range and this is what I came up with in 500 rpm increments.

At idle (700rpm) - 1/2”hg
1000rpm - 15 &1/2”hg
1500rpm - 17 &1/2”hg
2000rpm - 21”hg
25000rpm - 22 &1/2”hg

22&1/2 seemed to be about its max any higher rpm didnt increase the vac significantly and eventually (guessing above 4000) the needle became jumpy between 21 and 23inhg. Also from 700 to 1000 rpm is not a smooth transition on the vac gauge; it goes from 1/2 to 5 at about 850rpm and from 5 to 11-12 at about 925ish then up to the above numbers. After 1000 it seemed to be very smooth from 15&1/2 all the way to 22&1/2.

According to SSD’s vac can list the vc208 starts at 6” and maxs at 9-11” it is stamped 11R for a total of 22deg advance. So if I understand that correctly my vacuum advance would be all in before 1000rpm? That doesnt seem right to me, but im new to this!

I also have a vc239 which starts at 7” and maxs at 11.5” with 8.5 stamped on the arm giving me 17 total deg vac advance if I need to dial my total timing down.

I dont recall any other posts with ported vacuum data at different rpms. Maybe this info will help somebody else. Or maybe I wasted my time, but I sure enjoyed it Also it will give me a better understanding of what the vac can is doing when I do plot my baseline curve.

Also Im still thinking that my valves maybe too loose. It seems a littler loud during the fast idle warm up period. After it gets to operating temp it quiets down a bit. Im pulling almost 21&1/2inhg of full vacuum (not ported) during fast idle warm up but at idle its right under 20inhg. When fully warm at idle it bounces from 19.5 to 20 almost randomly. Possible im being nitpicky? What do you guys think?

I want to say thanks again for the help so far. Great tip about using the idle screw I used it tonight. I should have joined years ago when I started stalking the forum but there was never a question that couldnt be answered by using the search button and some reading!

Let me know what you guys think. I plan on getting a timing light this weekend then I work on the curve.

-Josh

Ok, I got a dial back timing light and here is the how the timing is setup. All numbers are with the vac can hooked up, curb idle is 700rpm with inital advance set at 10degs:

1000rpm - 32degs
1500rpm - 42degs
2000rpm - 49degs
2500rpm- 58degs
3000rpm - 65degs

I did the test twice to verify my numbers. There was no aduible pinging. I get about 2 degrees of throw on my timing mark. I assume this is from timing chain/dist gear slop. I thought that since my governor is a 15L (30 crankshaft degrees) and the vac can gives me a total of 22 degrees that I would not be able to go past 52 degrees? Should I put a lighter primary spring in it to give me more sooner since it didnt ping?

Should I give it more advance? I have had it closer to 15 degrees in the past but it seemed sluggish past 35mph. But that was before I adjusted the vac can.

In my initial post I said the distributor had two light springs in it but honestly I have nothing to compare these too yet. They are both identical so maybe they are medium springs?

Any thoughts and suggestions would be greatly appreciated.

-Josh

Disconnect vacuum line to vacuum advance, and plot mechanical advance from idle to highest advance obtained (probably below 3000 rpm). This will simulate engine under load, or in other words, a low vacuum condition which deactivates vacuum advance when driving such as at WOT. Base timing plus mechanical should be at or below 30 degrees max for a car."Vacuum can" can be tuned using an allen wrench to top out at all in advance (base + mechanical + vacuum) total of 50 or 51 degrees when under high vacuum conditions such as cruising at constant throttle opening on flat ground to deliver better fuel mileage.

_________________
67' Dart GT Convertible; the old Chrysler Corp.
82' LeBaron Convertible; the new Chrysler Corp
07' 300 C AWD; Now by Fiat, the old new Chrysler LLC

Thanks Wjajr,

Last night i adjusted my valves again and lowered my idle to 650rpm (seemed to be hunting at 750 with almost 70rpm variation) I think it was starting to dip into the power curcuit. This helped smooth the idle out a bunch. I T-ed my gauge into my ported vac line so i could plug it and hook up the vac can at will. Here is my baseline: intial timing is 9degs at 650rpm.

Rpm. Advance w/o vac. Advance w/vac. Ported vac line “hg
650———— 9.—————————— 9——————————1/2”
800.———— 9.—————————— 31.————————— 13”
1000.———-12.————————— 40.—————————15-1/2”
1200.———-14.————————— 42.—————————16”
1400.———-18.————————— 48.—————————17”
1600.———-23.————————— 51.—————————18”
1800.———-26.————————— 51.—————————19.5”
2000.———-27.————————— 52.—————————20”
2200.———-29.————————— 54.—————————20-1/2”
2400.———-33.————————— 58.—————————21”
2600.———-37.————————— 62.—————————21-1/2”
2800.———-39.————————— 64.—————————21-1/2”
3000.———-39.————————— 64.—————————21-1/2”

Again no aduible ping was heard during this test. So according to this test all of my mechancal is “in” at 2800rpm. According to what you said “Base timing plus mechanical should be at or below 30 degrees max for a car." Seems like my options are to lower my base timing to closer to zero, or weld up one of the governor slots to limit my total mechanical advance.

I would like to see my mechanical come “all in” earlier (before 2500). My cruise speed currently is 2600-2800 but that will change as I am going to install taller tires 26” vs 22” that should (theoretically) lower my cruise speed to 2300-2500.

Even though the vc208 can is rated for 22deg max it appears to have more. This is smoke and mirrors i assume because; By hooking up the can say at 1400 rpm this raised it to 1650 thus giving me the full 22degs plus 10 more mechanical due to the raised rpm? Am I correct in that thought?

So as of now my total advance is 9deg initial, 30deg mechanical, and 22deg vacuum advance for a total of 61 degs.

Later tonight I will see about lowering my initial and how the engine responds to it. I tried this before but to keep the idle up my throttle plate was opened to much and was letting the vac can kick in at idle. So I willll play with lowering my initial and adjusting the can to keep it “off” at idle.

Thanks wjajr for your response I was reading your adventures in recurves last night before I fell asleep. Sorry to all if it seems like I need a certain amount of “hand holding” on this I really appreciate all the advice!

-Josh

Hello all, I wanted to update the progress thus far:

I have played with the timing a lot the last few days and have found that 15* initial is what my motor likes the best. Highest vacuum reading without any pinging, the motor will start up with half a crank of the starter. I also tore into the carb and cleaned out the low speed circuit and discovered one of my floats was slightly lower than the other after re-adjusting the floats and the cleaning it idles much happier and the low speed throttle response has greatly improved.

At 10* initial the motor produces slightly over 20” of vacuum and the motor required more cranking to fire up. At 15* initial it produced almost 21-3/4” of vacuum and fires as soon as the key hits the run position. I have a slightly lean condition right now that i will address next time I wrench on the car. Before the carb cleaning and adjustment I would get 40-60rpm fluctuation at idle now it is 4-8rpm fluctuation. Needless to say I am quit happy

With all that being said I think the best route to proceed with my ignition curve is to weld up my govenor slot to give me a total mechanical advance of 15 degrees. Currently it gives me 30 degrees of mechanical advance once its all in. I received the distributor springs earlier this week so once the gov is welded and filed to the correct length I will be swapping springs and recording the results.

So to get my ducks in a row before I completly dive into the recurve:

1. I want the mechanical to be “all in” before 2400- 2500 rpm?

2. Should the mechanical curve have a steady increase until it is all in? Or is it more favorable for the mechanical to start at say 1500-1700 and be all in before 2400-2500? In other words: how long (in rpms) is the 15 degrees of initial favorable for the combustion ignition process before it is igniting “late”? I know I can test this question with different spring combos and see when it pings. For example say it pings from the mechanical advance coming in to quick at 1200 then I would know to use a stiffer spring. I dont have a distributor machine so all test will be on the engine l, but I was hoping to glean a little knowledge from thos who have been down this road before.

At this point i am going to focus only on the mechanical aspect of my curve and will move to vacuum after the mechanical is dialed in. Of course recording my results so I have references.

-Josh

Sounds like you are making good progress.

I am a bit confused as to how you are getting 30 degrees of mechanical advance, but the timing light does not lie.

15 deg of initial is about spot on. I run all my stuff at about that point.

With regard to how the mechanical advance works, there is a relationship using many many maths which will tell you all you need to know about what amount of mechanical advance you get at a certain rpm. Since you have the table numbers for mechanical, I can make you a graph which will illustrate what that relationship is currently. If you have light spring in it, that will make the mechanical advance come in sooner (lower RPM) and heavier springs will make it all come in later (higher RPM).

I wouldn't go welding up governor slots just yet. I'm going to make a graph here shortly and post it for ya.

Another question, are you absolutely sure the balancer ring hasn't slipped at all? It's not uncommon on these old cars for the rubber insulating ring between the v-belt groove and the center hub to move thus throwing the timing mark off a bit.

~THOR~

_________________
1984 D100 Shorty Custom
Certified Auto Appraiser - RevItUp Classic Appraisals
President - Cherry City Bombers CC
Part of Tyrde-Browne Racing