Ignition Timing and Webers

[Rick Parker]

Those of you with Small Blocks (289/302) that have gone with Webers, what about the Ignition Timing. How much did you change it from your Holley set up? How did it respond or change things? I've read some information about it, but nothing confirming results with dyno or seat of the pants results etc?

Anyone????

[*13*]

Did you ever get an answer on this, Rick?

[Rick Parker]

Oh yes, 18-20 initial at 950 36 all in by 2600. Crisper than a bag of Doritos.

[PoppyMod]

Originally Posted by Rick Parker

Oh yes, 18-20 initial at 950 36 all in by 2600. Crisper than a bag of Doritos.

Hi
It seems these carbs like a lot initial timing. I'm running dual 40 DCOEs on my 333 and are working very well. It responds very well with initial of 16-18 deg. Mine's all in by 3K.
What me distributor are you running and what is the mechanical?
Ken

[*13*]

I set mine at 18 a couple weeks ago. Waiting for a chance to give her a good breathe.

[jhirasak]

I set mine at 16 degrees initial and all in (36 degrees) at 3000. This is the same mechanical advance distributor timing that I used with the 715 Holly.

[j_b]

38 degrees total advance all in around 2000rpm, and initial timing means next to nothing, per Jim Inglese.

[cab]

38 deg. all in @2000 on my 289.

[wolf k]

Yes, initial timing means next to nothing if you rarely run your engine below 2000 rpm.
But for those that do, 20 deg initial, 38 deg total by 2600 rpm works great for me. I did try a stock setting of 12-14 deg initial and 38 total and it sure did not run well in the lower rpm ranges, may have been able to tune it out with jetting, but when I went back to 20 initial, it ran like it was injected car. I do not know why weber IR carbs like a lot of initial timing. Anybody have a theory? I have zero pre ignition with 10.5 compression and 87 octane fuel

[olddog]

Originally Posted by wolf k

I did try a stock setting of 12-14 deg initial and 38 total and it sure did not run well in the lower rpm ranges, may have been able to tune it out with jetting, but when I went back to 20 initial, it ran like it was injected car. I do not know why weber IR carbs like a lot of initial timing. Anybody have a theory? I have zero pre ignition with 10.5 compression and 87 octane fuel

My guess is that you are not running vacuum advance. Correct?

[wolf k]

Correct

[Gaz64]

Originally Posted by olddog

My guess is that you are not running vacuum advance. Correct?

There is the answer.

It's the difference between a 2D ignition map and a 3D map.

Vacuum advance should be utilised whenever possible, especially for a street car.

Race cars don't need it, it gets taken out to have one less part failure.

[wolf k]

It's the difference between a 2D ignition map and a 3D map.

Understood

Plumbing a IR manifold for a vacuum source can be complicated, always wondered if you could use just one runner for the vacuum signal to the distributor. Anybody done this?

[olddog]

600 rpm = 10 rev/sec = 5 intake strokes per second. Put a vacuum gauge on a single port and see how much pulsation you see. You might be able to dampen the pulsations by adding a vacuum canister in the line. However it will add lag time between when the vacuum changes at the engine and when you see the change on the other side.

Some guys on here have posted pictures of plumbing under the intake with stack injection. I have to assume the pulsation is a problem or they wouldn't go to all the trouble. I would say that EFI would be more sensitive to pulsations and lag time than timing would be.

[Rick Parker]

I believe to do so would cause that single cylinder to run lean and be less responsive to tuning.?? JMO

[*13*]

That is a good point, Rick. In fact, wouldn't it effect all of tuning, even with a under manifold system? These carbs are very sensitive & the runners are very short. It's also not a big plenum that you are drawing from. It's a bunch of small lines

[wolf k]

A vacuum actuator on a distributor I would assume does not consume much vacuum(for a lack of better terms). Those guys that plumbed the runners together for a vacuum source did so perhaps to run power brakes, or maybe they needed a pcv valve connection, just guessing. I will try the vacuum gauge test as suggested. IDF carbs have a vacuum source tap.

[*13*]

Let us know what you come up with

[Gaz64]

If you plumb all the runners with 1/8 line into a "log" then tap off with 3/16 to the advance diaphragm, you'll still get near equivalent average manifold vacuum to that of a single plane manifold.

The small lines don't make that much difference to carburettor balance.

[wolf k]

Connected a vacuum gauge to the tap on the IDF carb, turns out that it is a ported tap. Had a nice steady needle, it was low at 7 in.hg at 1500 rpm, but only drawing from one cylinder. I do have a mild camshaft.