TBucket Engine Project (Dart SHP)

Maniacmechanic1

solid fixture here in the forum
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).
Most of the Trans Am Pontiac V8 Street guys use ported vacuum for advance Mike.
Does not work out with a True Race cam to spin 7000-8000 Drag.
 

Loves302Chevy

"One test is worth a thousand expert opinions."
Yes, I was talking about the older (not digital) 6A and 6AL boxes. But I can't find anything on them retarding the timing during cranking.
I guess I will have to dig out my old paperwork. I am sure of it.
 

Loves302Chevy

"One test is worth a thousand expert opinions."
Most of the Trans Am Pontiac V8 Street guys use ported vacuum for advance Mike.
Does not work out with a True Race cam to spin 7000-8000 Drag.

True. My 302 Chevy (8000 rpm) has the distributor locked out and the timing set to 36 degrees.
But it has no problems starting because of the MSD 6AL ignition and it's built-in timing retard during cranking.
Or so I thought. I will have to verify this.
 

Maniacmechanic1

solid fixture here in the forum
Yes, I was talking about the older (not digital) 6A and 6AL boxes. But I can't find anything on them retarding the timing during cranking.
I guess I will have to dig out my old paperwork. I am sure of it.
They had alot of options and still do.
I think start retard standard on higher end models like MSD 7AL & 8AL.
Have 2 step boxes that piggyback for drag race launches .
 

Maniacmechanic1

solid fixture here in the forum
True. My 302 Chevy (8000 rpm) has the distributor locked out and the timing set to 36 degrees.
But it has no problems starting because of the MSD 6AL ignition and it's built-in timing retard during cranking.
Or so I thought. I will have to verify this.
I had the 6AL on the TA a long time ago.
Pro Billet distributor.
That old timing control knob.
I set it so I could retard timing for 100 LL Avation gas.
Drop down to 32 BTDC from 36.
36 I used with 110 Race Gas.
 

AutoWiz

Well-Known Member
I have two goals, 1.) a more stable idle and 2.) better performance.

You might have retarded ignition timing. You need more timing at idle. 16-20 degrees total. to start. And your motor will run cooler also as you bring the combustion process back into the combustion chamber. 20 degrees of base timing will not crank nice, so you need to have the distributor canister connected to full engine vacuum.

Whenever we hear someone describe or define something so specific as a proper engine calibration as a thing of opinion or preferences, we should run from that source of information. If you want to say the parts you use to build with are subjective to what you are looking for then great. But once all the pieces are bolted together there is most definitely a correct rod angle to be firing the spark plugs at and there is most definitely a specific afr we should be chasing. Calibrating engines is very much an exact science. Or at least it is to those of us with a dyno, anyways.
 
Last edited:

AutoWiz

Well-Known Member
I have found that 1 light silver, 1 light blue spring and the green stop bushing work great for most or all sbc/bbc oem or crate applications And as well with most of the cam swaps I have done and motors I have installed in sbc/bbc. And using the factory base timing settings from there. The manufacturer notoriously likes things in a safe place. That is why so many jack that base timing on the bone stock 350 to 12 or 15 instead of 6 or 8. So there is a touch of leeway here. Using these base and known good settings for the distributor, If we add the hot cam we should move ported timing to full engine vacuum and re assess where we are at. Very likely in most applications at this point we will be able to find a happy sweet spot where the car seems to run good all over even if it could do better if only Dyno Tuned.
 

Indycars

Administrator
Staff member
I have found that 1 light silver, 1 light blue spring and the green stop bushing work great for most or all sbc/bbc oem or crate applications.
Thanks for the suggestions AutoWiz!!!

I don't have a Green bushing, did you mean the Blue bushing by chance. It's the one I'm using now with 2 light blue springs.

MSD_StopBushings.JPG

You might have retarded ignition timing. You need more timing at idle. 16-20 degrees total.

How do you mean .... retarded timing? My initial is setting at 16° advanced now and 34° total.
 

AutoWiz

Well-Known Member
I mean green. https://www.jegs.com/i/MSD/121/8464...d-g8tvbWvmEYJHPmIjYaAhQ0EALw_wcB&gclsrc=aw.ds

If you don't have green I guess blue is ok.

My point just that if you are hunting a better idle quality then you can try setting your base timing somewhere it is meant to be, like 8 or 10 and use full time vacuum to pull the timing up to 20 degrees. Do you know why manufacturers don't set base timing that high? Because there are times at or near wide open throttle and at low engine RPM when the cylinder is full of fuel and air and we want the spark to come closer to TDC. But when the base timing is set to 16 base and we stab the gas pedal to the floor from a 5 or 600rpm idle we can only detonate. Because no engine needs 16 degrees of timing at wide open throttle just coming off of idle. For that we need vacuum timing that can go away.

Try setting your base timing to 8-10 degrees and connecting the distributor to full time vacuum. See how it runs. You might like it.
 
Last edited:

AutoWiz

Well-Known Member
The stop bushing will be much easier if I pull
the distributor.

It's not that bad. You need a Philips head screw driver to remove the cap and rotor. And then 11/32 wrench and a pen magnet and pick to retrieve anything you drop. Once apart you can slide the new bushing up on its shaft and the springs and weights will keep load on the bushing so it doesn't drop while you get the washer on and nut started. Just with the cap off bump the starter until the bushing is in a position you can get to and not directly over the pick up coil.
 

Indycars

Administrator
Staff member
Something does not match. The pic in your link shows green and 6 bushings, but the instructions
on Jegs only shows the ones (4) I posted above.
 

AutoWiz

Well-Known Member
Something does not match. The pic in your link shows green and 6 bushings, but the instructions
on Jegs only shows the ones (4) I posted above.

It is close to blue. Use your blue. I do not order separate kits for bushings. All the MSD distributors we get and install for sbc and bbc even for the older tach drive all come with the green bushing. The way you will tune that stop bushing size is by winding out second gear with the gas pedal on the floor. Third if you are brave. If the car pulled hard and the motor sounded good. Then you can go down a size on the stop bushing and this will allow 1 or 2 more degrees of timing. And go make that pull again. One size at a time. And when you just begin to hear change rattle you can either go back to the last bushing installed or you can change to a heavier spring and slow down how fast that total timing comes in.

To tune against retarded ignition timing without a dyno we can use the engine's coolant temp. As we advance timing the engine will run cooler all the way up to detonation. This is because all of the combustion process is done before the exhaust valve opens and the coolant is only trying to cool the cylinder. When we have our ignition timing set too late the fuel is still burning as the exhaust valve is opening and we are letting the fire creep out to the cylinder head ports and into the exhaust header. Late timing make engines run hot. So how are your temps after 20 or 30 minutes of idling? Do you have to work to keep it cool on a hot day?
 

Maniacmechanic1

solid fixture here in the forum
I like the way Grumpy taught us to graph put the advance curve Vs Crank Rpm on engineering graph paper.
I can do most of the time in my head with my Snap On Timing digital advance timing light.
Any good timing light will work.

Look for a SUN DT400 distributor machine Rick. Accurate most affordable on market used..what I have at home to spin test my Mags.
$200 a good price used.
You get to Tinker again
What you Love to do.

Out of here Rick.
Later.
 

Indycars

Administrator
Staff member
The way you will tune that stop bushing size is by winding out second gear with the gas pedal on the floor. Third if you are brave. If the car pulled hard and the motor sounded good. Then you can go down a size on the stop bushing and this will allow 1 or 2 more degrees of timing.
Your right, it's hard to stay in the throttle in such a light car and no roll bar, then there is the police. Wheel spin thru 2nd gear is always exciting.

To tune against retarded ignition timing without a dyno we can use the engine's coolant temp. As we advance timing the engine will run cooler all the way up to detonation. This is because all of the combustion process is done before the exhaust valve opens and the coolant is only trying to cool the cylinder. When we have our ignition timing set too late the fuel is still burning as the exhaust valve is opening and we are letting the fire creep out to the cylinder head ports and into the exhaust header. Late timing make engines run hot. So how are your temps after 20 or 30 minutes of idling? Do you have to work to keep it cool on a hot day?
I've never had a cooling problem. I'm using a 180°F thermostat and until it gets to 90°F ambient, the temps will be less than the 180°F thermostat. That's moving down the road, but parked in the driveway the temps will exceed 185°F until the electric fan comes on. Then the fan cycles on/off to maintain the temps at 195°F. Using a Flexalite fan controller. I don't hear any detonation idling in the driveway.

Detonation only happens when I eased into the throttle trying to climb a small hill on the highway at 70 mph and ambients are 90°F plus. NOTE: It has not happened since I retard the cam timing by 4°, reducing the DCR. Now I have not had a chance to test at these kind of conditions since changing the cam timing.
 

AutoWiz

Well-Known Member
Detonation only happens when I eased into the throttle trying to climb a small hill on the highway at 70 mph and ambients are 90°F plus. NOTE: It has not happened since I retard the cam timing by 4°, reducing the DCR. Now I have not had a chance to test at these kind of conditions since changing the cam timing.

With whatever you have in your distributor now, just taking it from 16 degrees base and setting it to 8-10 degrees base and connecting the vacuum canister on the distributor to the full time vacuum port on your carb you will get all this extra timing at idle, but right there in that space you just pointed out, you will be at less timing. Without ever pulling the cap off of your distributor.

Because everywhere but idle will now have 6 degrees less timing.
 
Last edited:

Indycars

Administrator
Staff member
Are you referring to the first plugs or the last plugs???

These are the last plugs just before I changed them about a month ago.

DSC01218.JPG
 
Last edited:

Maniacmechanic1

solid fixture here in the forum
I think You and Bob can build fab up a roll cage Rick that bolts in and can be removed.
You have your Nice MIG welder now.
Takes alot of planning but you can do it.
Going to start covering Race Fab work with my Bud Ed like I did on DC.
Stuff to help everyone.
Need to be safe at the track.
Get home unbolt it.
 

AutoWiz

Well-Known Member
Well those look a lot better. I meant on page 11 of the thread you linked to me. Your post #214. Those plugs looked gnarly. and you were complaining of oil consumption.
 
Top