Ported vacuum advance or manifold. Let's debate!

[Kern Dog]

Geoff, I usually respect your opinions but you're wrong here.
Vacuum advance whether ported or manifold does help. I'd trust Rich Ehrenberg over most anyone on this forum.
I got 2 mpg better when I ran with it.
While gas mileage isn't the reason to own and drive these cars, it sure helps to keep costs down and make the plugs last longer.

 

[HawkRod]

Geoff, I usually respect your opinions but you're wrong here.
Vacuum advance whether ported or manifold does help. I'd trust Rich Ehrenberg over most anyone on this forum.
I got 2 mpg better when I ran without, then with it.
While gas mileage isn't the reason to own and drive these cars, it sure helps to keep costs down and make the plugs last longer.

Kern,

1) I think you meant you got 2 MPG better with vacuum advance.

2) I think @Geoff 2 was just making a comment about locked distributors, but I'll let him chime in if he feels like it.

3) What I will say is a street car should have vacuum advance. A true race car doesn't need vacuum advance because it never cruises - it basically only idles and goes full throttle. But, if you drive a car on the street without vacuum advance, you are reducing how effectively the car runs. Period. Will it run on the street without vacuum advance? Of course it will. And properly set up, it will accelerate great. But it won't cruise effectively.

 

[Geoff 2]

Kern,
No I am not wrong & Hawk Rod got what I was saying........You misread my post.

Which was......if you are using a locked dist, you may not need VA because locking the dist provides a lot of timing that VA would normally provide.

 

[Geoff 2]

It is not correct to say race cars cannot benefit from VA. Some combos can benefit from manifold VA because it adds timing at idle. This keeps the engine cooler, allows for a lower idle speed & less chance of plugs fouling with big cams.

 

[Kern Dog]

Kern,
No I am not wrong & Hawk Rod got what I was saying........You misread my post.

Which was......if you are using a locked dist, you may not need VA because locking the dist provides a lot of timing that VA would normally provide.

Are you going to lock your distributor out at 55 degrees?
No.
The total timing advance can often reach 55 degrees with centrifugal and vacuum advance combined. You'll get better mileage as a result.

 

[Geoff 2]

Increase the timing from 35* to 55* & see much your fuel economy increases. Most likely immeasurable because the bulk of the timing is already in.
I don't know what Ehrenberg said about VA but I presume it was in the context of using it on stock or mildly hopped up engines, not race engines, but some race engines can benefit from MVA. It all depends on the combo.
I have just picked a random year from my Motors Manual, 1974 Dodge & Ply engines. All engines reach max centri timing at 4000rpm or higher. VA would be a big benefit cruising at 2-3000 rpm & I would guess that this type of combo is where Ehrenbergs comments were directed.

And I NEVER said VA does NOT help. [ Second line post #181 ]. Just the opposite. Read what I said before you criticise.

I have used over 60* of total timing occasionally, on low compression big cammed engines. Like I said, it all depends on the combo....

 

[Wietse]

What i am kind of missing here is that there is no mentioning at all about the AFR.
You can advance/retard timing, but the AFR must follow to suit.
You cannot expect an engine to run efficient with a rich mixture to run wit 50* of advance, it needs to be leaned out.
Same counts for the opposite side of the story.

 

[Geoff 2]

OK. But what IS the correct AFR for a cruise mixture????

It is well known that engine will tolerate leaner mixtures at cruise. How much leaner is going to depend on individual engines.

I don't see that aiming for a specific AFR number is that useful in this situation.

 

[Photon440]

OK. But what IS the correct AFR for a cruise mixture????

It is well known that engine will tolerate leaner mixtures at cruise. How much leaner is going to depend on individual engines.

I don't see that aiming for a specific AFR number is that useful in this situation.

Every engine is different. While it is often accepted that 16:1 - 16.5:1 is a good cruise mixture, and misfiring will start if you go leaner than 18:1, that can vary by things like compression or type of cam. For instance, a high overlap cam can allow increased exhaust residuals in the mix and will need a little more fuel to keep the flame lit.

Experimentation will be needed in each case. You may find that a very lean mixture still runs smoothly, but it may also drop torque enough that increased throttle is required to maintain speed, which will negate the lean fuel savings.

 

[Geoff 2]

My thoughts exactly. Hence not much to be gained by selecting a pre-determined AFR & sticking to it.

 

[Wietse]

My thoughts exactly. Hence not much to be gained by selecting a pre-determined AFR & sticking to it.

Did i say to select a pre-determined AFR?
We know an ideal WOT AFR is about 12.8 - 13.0, Photon440 also mentions the very lean (+14.7) mixtures engines can be cruising on. This is very variable and engine by engine as we all know and the right numbers need to be found by trial and error.
Your common advise to people to throw in a ton of advance could help but without even knowing the engine idles rich or lean you can't simply add a lot of advance when the AFR is rich.

The issue with these old fueling systems is that you cannot specifically see what you are doing all the time, modern injection system are constantly monitoring AFR and adjust the fueling to suit and advance timing until the knock sensor provides "knock" feedback and it will dial it back.
A carburated engine should behave in a similar manner, but does not have all those fancy electronics to do it for you.
Instead you need to go by adjusting timing advance, listen for ping while driving and read off your plugs to see it runs rich or lean under different circumstances.
You could increase timing advance in the cruising speed area and find it does not like it at all, an adjustment on the fueling could get it to work.
That is what i tried to say by mentioning the AFR being missed out.

 

[Geoff 2]

Well why bother with AFR numbers at all if you are going to set mixture by listening for ping, checking plugs & timing adv/ret? This is how I do it.
Once satisfied that the engine is happy with the adjustments that have been made, THEN check the AFR & record it for reference.
So at the end of the day, the AFR becomes just as number & plays no part in achieving in the actual tuning. This was my point.....

 

[Wietse]

So, for what do you check the spark plugs for then? Tire pressure?
Don't you agree the plugs will tell a story about the fueling?

 

[Hemirunner]

So, for what do you check the spark plugs for then? Tire pressure?
Don't you agree the plugs will tell a story about the fueling?

If you’re referring to drag race tuning, yes they tell a story if you know how to read. If there’s a lot of varying conditions driving on them you won’t get much from them, especially with the USA pump fuels and the black sludge left from additives. E85 or race fuel tuning is a whole other chapter as well. Those fuels all run different AFRs and each will tolerate different timing.

 

[Geoff 2]

Wietse.
'Checking plugs', post #192.

 

[Wietse]

If you’re referring to drag race tuning, yes they tell a story if you know how to read. If there’s a lot of varying conditions driving on them you won’t get much from them, especially with the USA pump fuels and the black sludge left from additives. E85 or race fuel tuning is a whole other chapter as well. Those fuels all run different AFRs and each will tolerate different timing.

I agree on that.
But when starting on dialing in an engine from fresh (carb/ignition) you would (at least I would) start with a new set of plugs.
After some dialing in and test driving you will get some feedback of them about the combustion process, being rich or lean is easy to spot.
And if, lets say your carb is jetted too big, you will mostly run rich, which will be visible on the plugs. Same for the idle mixture.
All i am saying is that when advancing the timing, the fueling ratio must be in the ballpark fueling wise to benefit from it.
As we know, a rich mixture burns fast, lighting it up too early causes the peak cylinder pressure to be too early and the engine is fighting itself.

Regarding the fueling, i think we are more lucky with that in Europe compared to the US.
Our pumps provide RON95 (E10) as minimum and still a lot of petrol stations have RON98 (E5), I always use the E5.
And i always use an additive (Millers) that boosts the octane (they advertise 2 points but you can't know for sure), and it helps to avoid issues with the bio fuel which is my main reason to use it.
(The E10 will have up to 10% bio fuel and the E5 up to 5% bio fuel)

Wietse.
'Checking plugs', post #192.

Yes? You said that in reaction on my post.

 

[Photon440]

I agree on that.
But when starting on dialing in an engine from fresh (carb/ignition) you would (at least I would) start with a new set of plugs.
After some dialing in and test driving you will get some feedback of them about the combustion process, being rich or lean is easy to spot.
And if, lets say your carb is jetted too big, you will mostly run rich, which will be visible on the plugs. Same for the idle mixture.
All i am saying is that when advancing the timing, the fueling ratio must be in the ballpark fueling wise to benefit from it.
As we know, a rich mixture burns fast, lighting it up too early causes the peak cylinder pressure to be too early and the engine is fighting itself.

Regarding the fueling, i think we are more lucky with that in Europe compared to the US.
Our pumps provide RON95 (E10) as minimum and still a lot of petrol stations have RON98 (E5), I always use the E5.
And i always use an additive (Millers) that boosts the octane (they advertise 2 points but you can't know for sure), and it helps to avoid issues with the bio fuel which is my main reason to use it.
(The E10 will have up to 10% bio fuel and the E5 up to 5% bio fuel)


Yes? You said that in reaction on my post.

If your country is still measuring octane in RON, that would make a difference in numbers compared to the USA, Canada or Mexico. We use the RON/MON combination, listed as R+M/2, which is about 4 to 6 numbers lower than a RON rating. So if I go to a Chevron and buy our 94 octane, it would be rated a few numbers higher in Europe.

Most octane boosters that use "points" are showing little value, it take ten points to make 1%.

 

[BSB67]

US 93 octane (R+M)/2 = 98 RON.

 

[Geoff 2]

No, Wietse, I was agreeing with your comments.

It was you, not me, that introduced plug reading into this thread.

 

[ignition1]

I have found success in which vacuum advance setup is best depends on the outcome I want to achieve:

- simplicity
- least emissions
- best mpg
- off idle response
- hot/cold start
- originality
- drivability
- dieseling
- idle quality

Sometimes it is Ported, Most times it is Manifold, Sometimes No Vacuum.

Sometimes only 7 cylinders when idling into the car meet