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What is your timing curve?

Kern Dog

Life is full of turns. Build your car to handle.
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I'll admit...I'm not all that skilled on this topic. I'm willing to learn though.
Drag racers may be inclined to run their engines with locked out timing since they run their cars at WIDE open throttle the length of the race.
I don't drag race. My cars are more aimed toward all around performance where acceleration is as important as handling and braking.
Until 2001, I hadn't owned anything making more than 250 HP. For those cars, stock ignition systems were adequate. I never had to learn about tuning engines to account for radical camshafts, 800+ CFM carburetors or high compression.
I had to get acquainted with it once I built my first 440.
Here I am now and I have a 440 based 495 with 9.8 to 1 compression and a rowdy cam. I currently have a curve that starts at 20 degrees initial at a 1000 rpm idle and maxes at 34 degrees around 2200. The car doesn't detonate at all but I am just wondering if this rate of curve is too fast.
This distributor is from Mopar Performance circa 2001 and is one of those that had those tiny weights and springs, two things that cause unstable timing. I can attest to that. Sometimes I can see the timing mark move around even with the engine at a steady rpm. I have a NEW distributor I'm going to try but I want to see what others here have for timing curves.
 
Your jumpy timing can be caused by a loose timing chain, a slipped outer ring on the crank damper or a worn bearing or bushing in the distributor.

If you have a dizzy from 2001 I would keep it...today's ChiCom distributors are poor quality IMHO.

34* is a good place to be for your engine. That lumpy cam isn't helping timing stability at an idle but it will smooth out at speed.

Generally speaking you will want all the timing is at 2500...faster timing usually gives you better driveability... but your cam doesn't help.
 
The engine has 650 miles on it. The timing chain is fine. There is nothing wrong with the engine, nothing worn out either.
The problem with this distributor is the design itself.
The Mopar Performance distributors from 2000-2014 were based on a GM HEI design, scaled down to fit inside a Mopar housing. To do this, they used really flimsy and light weights and even lighter springs. Rick Ehrenberg has written about this numerous times in Mopar Action magazine. The light weights and springs don't have enough mass to them to operate smoothly.
Oddly, the timing is pretty stable at idle but jumps around as rpms increase.
I sure don't know it all but I do know that if it isn't detonating, a quick advance curve can be beneficial for power. Back when I had detonation problems 10 years ago, I thought about trying a distributor that I could modify to extend the curve so the full advance didn't come in until later. I just didn't get around to it....instead I worked to lower the compression ratio.
 
I would say that if you are not getting any detonation, your timing curve is just fine. You could experiment slowing it down a bit, but I doubt it will get you any better performance. If you are looking at trying a different distributor, I have Firecores on 2 of my cars and like them. They use a factory Mopar cap and rotor. I have the motor from my Bee at a shop right now having it gone through. Those guys prefer MSD over everything else, so that is what we are using on that one.
 
I'll admit...I'm not all that skilled on this topic. I'm willing to learn though.
Drag racers may be inclined to run their engines with locked out timing since they run their cars at WIDE open throttle the length of the race.
I don't drag race. My cars are more aimed toward all around performance where acceleration is as important as handling and braking.
Until 2001, I hadn't owned anything making more than 250 HP. For those cars, stock ignition systems were adequate. I never had to learn about tuning engines to account for radical camshafts, 800+ CFM carburetors or high compression.
I had to get acquainted with it once I built my first 440.
Here I am now and I have a 440 based 495 with 9.8 to 1 compression and a rowdy cam. I currently have a curve that starts at 20 degrees initial at a 1000 rpm idle and maxes at 34 degrees around 2200. The car doesn't detonate at all but I am just wondering if this rate of curve is too fast.
This distributor is from Mopar Performance circa 2001 and is one of those that had those tiny weights and springs, two things that cause unstable timing. I can attest to that. Sometimes I can see the timing mark move around even with the engine at a steady rpm. I have a NEW distributor I'm going to try but I want to see what others here have for timing curves.
How many different websites have you asked this question at?

Curious, as I suspect the results may vary.
 
Following as I have the same jumpy timing at higher rpms.
Im thinking about the shaft on the Dist not fitting the oil pump drive? I can grab the rotor and rotate it back and forth quit a lot.
(Timing gear/chain is new).

I have the heavy spring on and my max timing is far beoynd 3000 rpm, so will do some more testing with springs this summer.
 
I use the Mopar distributors because they have a vacuum advance. On my one car (stock stroke 440, moderate mech cam, alum heads, headers, bunch of carb) I modify the basic design. I use a 9 degree plate, a light primary spring and heavier secondary spring with the loop, and a limited vacuum advance. The springs I use are old factory stuff that I have an assortment of. I use 18 degrees initial and the light spring allows for 22 degrees at 900rpm. The light spring by itself will allow about 28 degrees total below 2000rpm. The heavier spring will allow 36 degrees total at around 2500rpm. The 9 degree vacuum advance has a small washer "glued" between the housing and notch in the arm. It limits the vacuum advance to about 6 or 7 degrees now. I keep total with the vacuum advance to 48-50 degrees. I built a bunch of curves and just trailed and errored my way thru this. For my car and the way I drive this set up is darn near perfect.
 
Here is my opinion on timing curves for street cars, for what it is worth:
1) They are super important. A poor timing setup can make a great engine run like crap!

2) Vacuum advance is important if you are ever going to run with light throttle, (i.e. you drive it on the street).

3) A big bore engine (don't care about the stroke) needs more advance than a small bore. This is a factor of flame wave propagation. Basically, the big bore make the flame take longer to burn across the cylinder so you need to light it off sooner.

4) Some rules of thumb for mechanical advance:
* Max timing 36 - 38 degrees. I run 37* on my 70 Road Runner 400 based 500 stroker
* Mechanical timing should start coming in at around 1000 RPM
* Timing should be all in by 2700 - 3000 RPM
* Set static timing more than 10*. Mid teens is probably better.
 
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Here is my opinion on timing curves for street cars, for what it is worth:
1) They are super important. A poor timing setup can make a great engine run like crap!

2) Vacuum advance is important if you are ever going to run with light throttle, (i.e. you drive it on the street).

3) A big bore engine (don't care about the stroke) needs more advance than a small bore. This is a factor of flame wave propagation. Basically, the big bore make the flame take longer to burn across the cylinder so you need to light if off sooner.

4) Some rules of thumb for mechanical advance:
* Max timing 36 - 38 degrees. I run 37* on my 70 Road Runner 400 based 500 stroker
* Mechanical timing should start coming in at around 1000 RPM
* Timing should be all in by 2700 - 3000 RPM
* Set static timing more than 10*. Mid teens is probably better.
Basically nailed it Hawk,
 
Lots have the timing jumping around and cure it with a lock color on the distributor shaft. It keeps the drive gear seated in the cam gear.
 
Watch those collars I have seen the set screws come out. Usually masks a worn tower bushing really. MP or Mr Gasket springs are super light and will cause it also at idle. On a points system if it is a bad ground the timing will walk also.

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Lock collar?
How about adding a small weld on the Dist shaft key for better fit?
 
To build the tab up, I think. If it is in decent shape think about this when it rotates it will not walk back at all just because of the rotation. Another one of those things.
 
Yes, though I have red many posts that fixed a jumping timing with tab build up.
Though the drive shaft bushing is a bigger suspect...
 
I used to do the collar thing. It doesn't work on a b engine. The intermediate shaft thrust is down due to the helix cut on the camshaft and intermediate shaft gears. All you have to do is look at the wear pattern on the bushing thrust flange. I've found that sloppy timing is more of a loose timing chain or more often than not a loose intermediate shaft bushing. Sloppy distributor shaft bushings are a player too. I also think heavy roller cam springs can effect this issue too at low rpm and loose components.
 
I used to do the collar thing. It doesn't work on a b engine. The intermediate shaft thrust is down due to the helix cut on the camshaft and intermediate shaft gears. All you have to do is look at the wear pattern on the bushing thrust flange. I've found that sloppy timing is more of a loose timing chain or more often than not a loose intermediate shaft bushing. Sloppy distributor shaft bushings are a player too. I also think heavy roller cam springs can effect this issue too at low rpm and loose components.
There is a lot of guys running a collar on the B/RB-Hemi that claim it works. Might be more critical with roller cams. Myself i have never used one.
 
How many different websites have you asked this question at?

Curious, as I suspect the results may vary.
This is the only site where I have asked about timing curves.
I do run vacuum advance. It makes a difference in fuel economy. I'm no hyper-miler but it is nice to be surprised at a better mpg number than I expected. Getting 15 instead of 13 can make the difference between making it to a gas station at 1/8 tank or having to fill up at a 1/2 tank just to be safe.
 
This is the only site where I have asked about timing curves.
I do run vacuum advance. It makes a difference in fuel economy. I'm no hyper-miler but it is nice to be surprised at a better mpg number than I expected. Getting 15 instead of 13 can make the difference between making it to a gas station at 1/8 tank or having to fill up at a 1/2 tank just to be safe.
both of my cars actually run/drive worse with full centrifugal distributors than vacuum advance distributors. to think all i'd run back in the day was full centrifugal makes wonder if i used my brain back then. long term the cylinders last longer, plugs burn cleaner, and mpg can be a noticeable factor with a vacuum advance.
 
How many different websites have you asked this question at?

Curious, as I suspect the results may vary.
This question had been asked and answered at least 250 times, on this site alone yet, as well as the FABO & FCBO sites ....almost as many times as: which spark plugs are best, which cam is best for my _______ (fill in the blank) engine, which carb is best: Holley, Carter oem, Edelbrock (Eddie), EFI, fuel pressure, oil, wax, radio station, beer consumed, air in the tires, coolant, etc. Perhaps the Moderators should conduct a class in HOW TO USE THE SEARCH FUNCTION by subject....it seems it's just easier to keep on asking the same question rather than searching the data base for the answer or subject Sooner or later the FBBO servers will explode from overload. Just my opinion of course.....(now comes the barrage of insults and expletives.....).
BOB RENTON
 
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