[64speed]

Engine builder set the timing and carburetor for me today. He found that engine seemed to run best with 27 degrees of total timing with the vacuum disconnected. It seemed strange to me but he says it’s optimal tune and not to mess with. Engine cranks easily and sounds great. How does 27 with no vacuum sound to y’all.

[Gach]

No surprise mine is best at 29 degrees total

[Kenth]

On par with the 1970 455 specs and about where my 462 runs best.

[64speed]

Originally Posted by Kenth

On par with the 1970 455 specs and about where my 462 runs best.

Do you run vacuum advance

[Kenth]

Originally Posted by 64speed

Do you run vacuum advance

Yes, the correct "365" 20 degree vacuum advance.
Running full manifold vacuum because the fairly mild 744 cam allows it.
Have found no need to reduce the amount.

9-27-20.
27 @ 4400 rpm WOT.

[25stevem]

Let’s get the terminology right here for your benefit.

The builder told you that 27 degrees of total mechanical advance works best, not total timing which would include vacuum advance.

It’s fine to just run 27 degrees if that’s what works best in terms of power while also being safe for different weather conditions.

So now you just need to run ported vacuum to bring in another 8 to 12 degrees above idle.

This you will need to determine on your own by driving the vehicle to see how much the motor will accept without pinging at part throttle and under changing ( hills and such ) road conditions

[Formulajones]

Sounds like it's going to get terrible gas mileage.

You'll want that vacuum advance hooked up and dialed in properly if you plan to put a lot of street miles on it and want at least a semi efficient engine on gas.

As far as total mechanical timing there is no absolute way to know what is best unless you either run it on a dyno or hit the dragstrip. Otherwise it's just a guess.

[Nyairguard]

I’ve always tried to run some vac advance either ported (off idle) or straight from the intake (always on) but some cans have way too much, I normally end up with about 10 degrees additional. Adjustable can or by a can for your style distributor hei or point style or even tack weld a stop in the arm movement slot . The last Pontiacs I worked on were 14 initial 19 from my mechanical all In by 2800 and 10 from my vac .


Sent from my iPhone using Tapatalk

[64speed]

My machinist is a hardcore racer and I don’t think MPG ever enter his mind

[Formulajones]

Originally Posted by 64speed

My machinist is a hardcore racer and I don’t think MPG ever enter his mind

That's not surprising given the amount of people I run into that still don't have an idea how the vacuum advance works or why it's beneficial and choose to just run without it rather than learn or spend the time dialing it in.

I'm a racer too, but that doesn't mean I won't run a vacuum advance. While racing it has no influence but it's beneficial with everything else the engine does.

[geeteeohguy]

Originally Posted by 64speed

My machinist is a hardcore racer and I don’t think MPG ever enter his mind

This is concerning. Your car is a street car. The only cars that run locked in timing with no vacuum advance that I know of are drag cars. If your initial timing is 27, be prepared to knock the nose off your starter and break flywheel teeth on a hot start if you have ignition connected.

ALL street driven cars should run vacuum advance for fuel economy, power, engine cooling, and overall performance.

How much and manifold or ported depends on what your engine wants.

Optimal timing can't be determined on a run-in stand. Your machinist is blowing smoke.

[chuckies76ta]

Originally Posted by geeteeohguy

This is concerning. Your car is a street car. The only cars that run locked in timing with no vacuum advance that I know of are drag cars. If your initial timing is 27, be prepared to knock the nose off your starter and break flywheel teeth on a hot start if you have ignition connected.

ALL street driven cars should run vacuum advance for fuel economy, power, engine cooling, and overall performance.

How much and manifold or ported depends on what your engine wants.

Optimal timing can't be determined on a run-in stand. Your machinist is blowing smoke.

He did not say his initial timing was 27 degrees.

[Half-Inch Stud]

Total Advance, while under load:
27* indicates both an optimal fuel atomization and optimal combustion chamber. Vaccum signal providing ZERO*.

Adding Vacuum Advance would be for partial load, like cruising, so i wonder what an optimal Vac Adv* value would be for combined mileage and part-throttle power?

Supposing a Highway eval can occur with Mech control of the vac pod (which i tried awhile back), with or without the help of cruise control.

[dataway]

People need to come up with a uniform way to express their timing numbers ... something like.

Initial - mechanical - vacuum .. in my case 9-24-15

Then maybe two numbers for start - end rpm of Mechanical like (800-2900)

So my engine (YS-400) would be 9-24-15 (800-2900) ... doesn't tell the whole story by a long shot, but gives a basic idea.

Sorry, back to the OP's question.

[srmmmm]

Originally Posted by dataway

People need to come up with a uniform way to express their timing numbers ... something like.

Initial - mechanical - vacuum .. in my case 9-24-15

Then maybe two numbers for start - end rpm of Mechanical like (800-2900)

So my engine (YS-400) would be 9-24-15 (800-2900) ... doesn't tell the whole story by a long shot, but gives a basic idea.

Sorry, back to the OP's question.

I like this thought. It would be great to build a small database with members' settings, adding block, stroke, Head Casting & CR. So mine would be:

12-21-10 (1000-3000) 1970 model 350, 4.25" Stroke, 6X-4 Heads, 9.13CR

[LKLusza]

Originally Posted by dataway

People need to come up with a uniform way to express their timing numbers ... something like.

Initial - mechanical - vacuum .. in my case 9-24-15

Then maybe two numbers for start - end rpm of Mechanical like (800-2900)

So my engine (YS-400) would be 9-24-15 (800-2900) ... doesn't tell the whole story by a long shot, but gives a basic idea.

Sorry, back to the OP's question.

Your notation suggestion is similar to what I use now. I have one of those Progession Ignition Bluetooth distributors. I store various "tunes" on my iPhone using their app.

I usually list the initial timing first, followed by vacuum (with a "V"), then the mechanical (with an "M"), followed by the "all in" engine speed for the initial + mechanical. Here's an example:

initial= 14deg.
mechanical= 20deg
vacuum=12deg
"all in": initial+mech (14+20) at 3200rpm
so, on the list it looks like this: 14-20m-12v_34@32k

It's easily distinguishable from any other tune I keep on the app and makes choosing easy.

[Half-Inch Stud]

We 455 engined folks just might have a complete disregard for Initial Advance. 6* thru 18* being a broad window after having Dial-In the Total ADV for ET.

Whereas the 400 and 350 engine folks really got to optimise Initial ADV after learning the optimal Total ADV.

Well, then again the initial can be optimized, and should be, which involves changing the Mech ADV to set the Initial and sustain the desired Total ADV. This is called "Tuning", that which is a lost effort for many folks across the hobby.

[Half-Inch Stud]

Hmmmm. For those 1/4 mile folks that run best with 38*+ Total Adv; Aside from declaring the Head Combustion chambers as grossly inferior, i wonder if trials on carb emulsion changes, ( atomization changes ) would bring the Total ADV down, perhaps to 27*.

Afterall, the lower Total ADV combined with optimal power assures least compression loss ( - HP), perhaps even least Octane requirement, oh and least Starter motor stress.

Low Octane "kernel" taking less time to "burn to pressure" whereas High Octane "kernal" takes longer to "burn to peak pressure" will also factor in to the Total ADV under load, needed for optimal ET.

All that fuel chemistry considered to get with Ping-Free power for a set Total ADV and Compression also begets getting the CYL pressure aligned/optimal over the Stroke's "Torque-arm efficiency" range.

Reminds me that the 4.21" Stroke has the earliest TQ-Arm eff crank angle, compared with 4.00", 3.75", and lesser Strokes. Should provide cause to have least Total ADV for big Strokes.

In conclusion, there ought be a Sticky chart made from compiling the MOTOR's manuals for optimal Initial and Total ADV vs Stroke and Compression (all Iron Head Data), along with notable modern (Aluminum) head Initial and Total ADV included for these Stroke and Compression spreads. THAT would be a great aid, and revealing.

Coffee was good this AM.

[Lee]

Originally Posted by Half-Inch Stud

Hmmmm. For those 1/4 mile folks that run best with 38*+ Total Adv; Aside from declaring the Head Combustion chambers as grossly inferior, i wonder if trials on carb emulsion changes, ( atomization changes ) would bring the Total ADV down, perhaps to 27*.

I have an ECU that controls fuel and spark on my 455, "66" casting Dports, zero mods to ports or chambers, 8.3:1. I have a timing table, in lieu of a vacuum advance or advance weights & springs, and can put the timing anywhere I want at any part of the table. For BEST performance on a chassis dyno, my motor performs best with 37 degrees timing.

[Formulajones]

The only engines I've ever been involved with that only like 26-28 degrees of timing on pump gas are LS engines. They generally came with factory timing in the 22 degree range but dyno testing showed they really responded to 26-28 degrees and a rare occasion 30.

All the old dinosaur engines I've built and tuned, including engines that have had more modern chamber cylinder heads, has never responded very well to timing as low as 28 degrees. I always shoot for zero deck and tight quench engines and as much compression as I can get away with on pump gas and the camshaft being used. Even with modern heart shaped combustion chambers it's been rare from my experience that they made best power on the dyno any lower than 32 degrees, and most of them are always up around 34-36 as the norm, sometimes 38-40. There is no rhyme or reason, but the engine would have to be dyno'd or track tested if you really want to find out what it wants.

Honestly it sounds to me your engine builder is being extremely cautious and erroring on the light side for timing not knowing how you're going to treat the engine. Can't say I blame him, when you're in that sort of business.