TBucket Engine Project (Dart SHP)

I made another video of the ignition timing stability since the last one was blurry. But first the
video with instability in post #2929 .....


In the next video I did not disconnect the vacuum advance, so the actually timing is different,
but the stability is solid.


The only things that I can remember changing is the harmonic balancer and the addition of the
valve stud girdle. Looks like the harmonic balancer made the difference, don't see how the stud
girdle could make that much of a change.
.
 
I think a stud girdle would have an affect on timing stability. I think it keeps the valve timing more stable, so it would indirectly affect the ignition timing.
 
I think a stud girdle would have an affect on timing stability. I think it keeps the valve timing more stable, so it would indirectly affect the ignition timing.
I think it more about 12°.

Ok, but how does the stud girdle affect the ignition timing. I'm trying to make sense of this in a scientific way.
.
 
I think a stud girdle would have an affect on timing stability. I think it keeps the valve timing more stable, so it would indirectly affect the ignition timing.

How this could be? It make no sense to me from logical point. The distributors connection is the camshaft and than via timing chain to the crankshaft, this would be the only parts for tolerance issues on the mechanical side (I leave the distributor internal parts aside). The stud girdle stabilized the rocker arm stud and rocker arm, ok the rocker arm has contact to the camshaft via lifter and pushrod but if there is "flexing or whobbeling" how this would have a effect on the teeth on the camshaft to distributor?
I don't think that the camshaft is "shaking" or so when the stud girdle is not installed, it would have an effect to the rocker arms and then to the valves. I think the lifter would work as an "damper" in this situation, except if it is a mechanical lifter.

I hope you can understand what I'm trying to write, sometimes it is not easy to translate my german in english words when it goes to technical stuff.
 
You can only Run 13.5 ET 1/4 mile at the Track with the T-bucket NHRA Rules.
Need a Full Rollcage to Run Faster.

Ready to run and see if you can hit 13.5 ET.
 
I hope you can understand what I'm trying to write, sometimes it is not easy to translate my german in english words when it goes to technical stuff.
Made sense to me. I think what you are saying is the effects of the stud girdle are too far
removed to make a difference in the ignition timing.
 
I think it more about 12°.

Ok, but how does the stud girdle affect the ignition timing. I'm trying to make sense of this in a scientific way.
.
I think they are indirectly related! They are all hooked together physically, I am not saying its going to have a drastic affect, but I believe it will aide in the stability of not only the valvetrain but also the timing.
 
There is no mechanical faults with the T engine.
It's overbuilt for its low and medium range engine operations ( compared to high rpm drag race ) .

It's all Electronic going on.
Design engineering faults in ignition.
 
I have two goals, 1.) a more stable idle and 2.) better performance.

First Goal, Stable Idle
Wondering where you guys think the initial timing should be to have a good stable idle. I have been
setting it at 12° until now, I just bumped it up to 16°. The idle is higher when I come in off the highway,
compared to when I'm just cruising around town and come to a stop light.

Second Goal, Performance
By moving the timing curve from all in at 3500 rpm, then changing the Advance Stop Bushing from
Silver
to Blue (Mechanical 25°/21°) this should bring the total mechanical advance to 35° again after
increasing the initial t0 16. Previously the total mechanical advance is 35° - 12° = 23°, then I increased
the initial to 16° and total to 39° total. Basically adding 4° to the initial and subtracting 4° from the total.

IgnitionAdvanceStopBushing.JPG

My current ignition timing curve is shown below. Vacuum is plugged and initial set to 12°, now 16°. After
changing the initial to 16°, I checked the total timing with vacuum attached and it's 34° at 875 rpm.

Initial set to 12° for the curve below.

IgnitionTimingCurve.JPG
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Is your vacuum advance connected to manifold or ported vacuum, and what are your thoughts on this?
 
Grumpy,
I still need to change the springs and stop bushing. The stop bushing will be much easier if I pull
the distributor. Right now it's supposed to be rainy for the next 2-3 days. I really need to test when
it's above 90°F, to see if my detonation problem comes back after retarding the cam timing.

Love302Chevy,
I'm using the manifold vacuum, not worried about emissions. The manifold vacuum should help
with getting a smoother idle. If I change things too much, the transition slot on the carb will be
out of whack.
 
I have found Vacuum advance to be detrimental when tuning any engine with a camshaft profile advertised duration greater than 262 Hydraulic.
Nothing but fighting detonation issues with Vacuum advance ported of manifold direct constant source.
Mechanical advance I dial in all by 900-1200 rpm.
 
If the car has a hot cam then the distributor should be connected to engine vacuum. Because hot cams like a lot of timing at idle. But too much base timing makes the starter struggle. So we set the base timing to like 8 or 10 degrees advance and when the engine starts it comes up 11 more degrees to ~20 which is right where hot cams like to idle. If we have a stock cam from a factory somewhere it is meant to be really efficient at idle and will need less timing there so with a stock cam we always like to goto ported vacuum.
 
Welcome AutoWiz. With a hot cam, I personally prefer ported vacuum advance for a more stable idle. With a hot cam, you (should) have a faster rate of mechanical advance - meaning lighter springs. Lighter springs have a harder time keeping the timing steady, especially with a lumpy cam and the carb usually being adjusted right at the edge of the idle/off idle transition. I find that ported vacuum advance gives a bigger "window" for a more steady idle.
If using an MSD ignition, it's nice that it retards the timing 20 degrees during cranking to help with easier starting of the engine (less kickback).
 
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