Ignition tuning question

[Al]

After replacing the stock 906 heads and stock cam on my 383 with the lunati 60303 cam (http://www.summitracing.com/parts/LUN-60303LK/) and the Edelbrock Performer RPM aluminum heads ( 84cc), I started to fine tune my ignition timing after the cam break in. My ignition system consists of the MSD 6 box and MSD blaster coil with new Mopar dizzy. My Champion plugs are gapped at .45.

Strangely I cannot get the initial advance lower than 18@880 ! If I go lower, the engine shudders. If I listen to the engine, I could even give it more initial advance: it picks up RPM till I advance the base timing to around 27 degrees. The vacuum also increases (from 10 inch. of vacuum in D at 880rpm with 18 deg. initial. and 15 inch. in N) to 18 inch. at 27 deg. in N  

The engine seems to like a lot of ignition advance but isn't 24 to 27 too much for base timing? There is NO pinging whatsoever even at higher RPM.

This is the ignition curve with 18 deg. initial timing.
18@880
21@1000
24@1200
26@1400
31@1600
35@1800
38@2000
40@2200
43@2400
From 2400 the 43 remain constant till 5000. Seems a bit much or am I mistaken?

Your ideas are welcome.

Al

[frederick]

Check if the balancer has spun.
43 is too much, generally 36 is ok.

This is all without the vacuum attached, right?

[Al]

Balancer looks ok, no visual sign of spinning, inspected it while it was off. No vacuum attached.

[aifilaw]

Total timing is a product of the cam, the airflow through the heads, the bore, stroke, and the type of fuel. I have had a couple engines that likes low 40's total timing. and one in particular that greatly appreciated 48 degree's of total timing. If that's where you are making good power and it runs fine, go with it. A dyno run will give you the final say-so though.

[Rayzor]

I to am dealing with a similar problem on a small block build. Without vac hooked it flat will fall on its face with less then 14 degrees at idle. And it will still bark threw the carb if the throttle is stabbed. My time marks are dead on and I have checked 4 times. I am begining to think spun balancer. Gonna try jumping the dist. ahead one tooth to see if that makes the difference.

[R2]

I would use the vacuum reading to get your initial your searching for....not the RPM...

There is a point of minimal return on vacuum as you keep bumping up the initial timing.....ie,,,too much initial,,,and you could develop some cranking / starting issues,,etc.
I think 18* would be ok,,,,maybe leave it there......but..............

Its the TOTAL timing that is off,,,,I think it's too high,,,,
Should be around 35-38

You need to modify the PLATE in the distributor,,,and weld up the slot a bit,,,and experiment with it,,,i did mine,,,and it was pretty easy,,,just some trial and error, this was you can keep you 18* initial,,,and get a better total timing,

I do NOT run the vacuum advance on mine,,,it's plugged off,,,,more performance orientated for me....(my opinion)

What springs are in it now ? My timing is ALL IN by 2400,,,, I put a light and moderate sized springs in mine instead of two light springs,,,

I found if the springs were too light,,,the timing would "wander" a bit,,,,and hunt around as the idle came down,,,,they were not strong enough to pull the timing back to baseline........

It's alot of trial and error...........

good luck,,,

Doug

[Al]

I would use the vacuum reading to get your initial your searching for....not the RPM...

There is a point of minimal return on vacuum as you keep bumping up the initial timing.....ie,,,too much initial,,,and you could develop some cranking / starting issues,,etc.
I think 18* would be ok,,,,maybe leave it there......but..............

Its the TOTAL timing that is off,,,,I think it's too high,,,,
Should be around 35-38

You need to modify the PLATE in the distributor,,,and weld up the slot a bit,,,and experiment with it,,,i did mine,,,and it was pretty easy,,,just some trial and error, this was you can keep you 18* initial,,,and get a better total timing,

I do NOT run the vacuum advance on mine,,,it's plugged off,,,,more performance orientated for me....(my opinion)

What springs are in it now ? My timing is ALL IN by 2400,,,, I put a light and moderate sized springs in mine instead of two light springs,,,

I found if the springs were too light,,,the timing would "wander" a bit,,,,and hunt around as the idle came down,,,,they were not strong enough to pull the timing back to baseline........

It's alot of trial and error...........

good luck,,,

Doug

I got a Mopar distributor where the total advance can be changed with 2 bolts that change the length of the slot in the base plate. So changing that should be an easy one. I'll try to get it down to 36-38 total.

My total advance is also all in at 2400. By the way your triple black R/T looks great. 

Al

[Al]

Total timing is a product of the cam, the airflow through the heads, the bore, stroke, and the type of fuel. I have had a couple engines that likes low 40's total timing. and one in particular that greatly appreciated 48 degree's of total timing. If that's where you are making good power and it runs fine, go with it. A dyno run will give you the final say-so though.

Unfortunately I have no access to a dyno facilty in the region I live. The nearest one is a 400 mile drive away.

[firefighter3931]

I got a Mopar distributor where the total advance can be changed with 2 bolts that change the length of the slot in the base plate. So changing that should be an easy one. I'll try to get it down to 36-38 total.

My total advance is also all in at 2400. By the way your triple black R/T looks great. 

Al

Hi Al 

Try setting the idle timing at 25* for now and try to start the car after it's warmed up. If it doesn't kick back on you then leave the base timing at 25* and dial in 10-12* of mechanical advance using the adjustable stops on your MP distributor. You don't need any more than 35-37* total with the closed chamber e-heads and there's no reason to risk detonation. The full advance coming in at 2400 is perfect so you don't need to mess with the springs.

The engine is telling you it likes lots of initial timing so just do it. Every engine combination is different and there's no set rule. This is what tuning for maximum performance is all about. 

Let us know how it works out 



Ron

[Al]

Hi Al  

Try setting the idle timing at 25* for now and try to start the car after it's warmed up. If it doesn't kick back on you then leave the base timing at 25* and dial in 10-12* of mechanical advance using the adjustable stops on your MP distributor. You don't need any more than 35-37* total with the closed chamber e-heads and there's no reason to risk detonation. The full advance coming in at 2400 is perfect so you don't need to mess with the springs.

The engine is telling you it likes lots of initial timing so just do it. Every engine combination is different and there's no set rule. This is what tuning for maximum performance is all about.  

Let us know how it works out  



Ron
[/quote]

Hello Ron

Thanks for your input. I'll do as you said and report back.  

Al

[Al]

I got a Mopar distributor where the total advance can be changed with 2 bolts that change the length of the slot in the base plate. So changing that should be an easy one. I'll try to get it down to 36-38 total.

My total advance is also all in at 2400. By the way your triple black R/T looks great. 

Al

Hi Al 

Try setting the idle timing at 25* for now and try to start the car after it's warmed up. If it doesn't kick back on you then leave the base timing at 25* and dial in 10-12* of mechanical advance using the adjustable stops on your MP distributor. You don't need any more than 35-37* total with the closed chamber e-heads and there's no reason to risk detonation. The full advance coming in at 2400 is perfect so you don't need to mess with the springs.

The engine is telling you it likes lots of initial timing so just do it. Every engine combination is different and there's no set rule. This is what tuning for maximum performance is all about. 

Let us know how it works out 



Ron

Hi again

I opened the distributor to check the mechanical advance. The slots were completely open thus giving me a total of 25 degrees of mechanical advance. Too much as you said. So I blocked the slots in the middle via the 2 Allen screws. Normally this should give me half as much total advance.

Then I set the initial timing to 25@900. The total advance is now 38 degrees total, just as you said.

However the 38 total are all in at 1600!  At bit early or ...?

What I noticed when I set the advance, was that there are 2 springs of different width, a thin one and a bigger one. The thin one does all the job, the big one seems to me a bit too long, there is free play at rest and when the advance is at the max it barely stretches the width of a hair. So to my understanding, it's only the small, thin spring that extends. Note that the distributor is a brand new one, no modifications except the one I did today.

The car drives fine, starts at a quarter turn when hot, without gas pedal and doesn't kick back. The vacuum at 25@900 is around 13,5 (Lunati 268 cam).

Should I leave the ignition as it is ? However the 38 coming in @1600 intrigues me.

By the way, I get the highest vacuum reading (17) with 35 deg. initial timing!!!

aL

[R2]

I would change the "bigger" spring,,,,,and put a "medium" sized spring in it,,,,this might slow the curve down a bit,,,,so you dont bring the timing in so fast.

You are going to have to experiment a bit,,,,

Sounds like you have the "plate" dialed in ok,,,,, now just need to work on the curve,,,,

Wayne Smothers,,,usually recomends running as heavy of springs as you can,,,,,,

I ended up with one "light" and one "medium" spring in mine,,,,, ( 2 of the light springs didnt work for me ),,,,( 1 light and one "bigger" stock spring also didnt work for me)


Doug

[Al]

I would change the "bigger" spring,,,,,and put a "medium" sized spring in it,,,,this might slow the curve down a bit,,,,so you dont bring the timing in so fast.

You are going to have to experiment a bit,,,,

Sounds like you have the "plate" dialed in ok,,,,, now just need to work on the curve,,,,

Wayne Smothers,,,usually recomends running as heavy of springs as you can,,,,,,

I ended up with one "light" and one "medium" spring in mine,,,,, ( 2 of the light springs didnt work for me ),,,,( 1 light and one "bigger" stock spring also didnt work for me)


Doug

Doug,

What kind of spring kit do you use? I got the Mr. Gasket kit, there are only two springs in it and they seem pretty light.

Al

[firefighter3931]

Hi again

I opened the distributor to check the mechanical advance. The slots were completely open thus giving me a total of 25 degrees of mechanical advance. Too much as you said. So I blocked the slots in the middle via the 2 Allen screws. Normally this should give me half as much total advance.

Then I set the initial timing to 25@900. The total advance is now 38 degrees total, just as you said.

Good work Al....that is perfect 

If the car starts fine and runs strong there's no need to worry about where the advance is coming in. Slowing the advance curve down is usually done to correct problems with detonation which you don't have. The aluminum heads with their efficient closed chambers are keeping those problems away. 

I'd leave it alone and call it good.   


Ron

[Al]

Hi again

I opened the distributor to check the mechanical advance. The slots were completely open thus giving me a total of 25 degrees of mechanical advance. Too much as you said. So I blocked the slots in the middle via the 2 Allen screws. Normally this should give me half as much total advance.

Then I set the initial timing to 25@900. The total advance is now 38 degrees total, just as you said.

Good work Al....that is perfect 

If the car starts fine and runs strong there's no need to worry about where the advance is coming in. Slowing the advance curve down is usually done to correct problems with detonation which you don't have. The aluminum heads with their efficient closed chambers are keeping those problems away. 

I'd leave it alone and call it good.   


Ron

Hello Ron

That's good news. Thanks for your help. 

Al

[Al]

Thanks also to all of you for sharing.  
Al

[Al]

UPDATE

The base timinig is at 25@900. I replaced the bigger spring, that does strictly nothing, with one lighter spring from the Mr Gasket kit.

The total advance of 38 is now @1850. However the light wobbling of the timing mark, when seen with the timing light, is now firm.