My engine builder strongly suggests a mechanical advance rather than a vacuum advance for my new 408w stroker. As I will be buying a new distributor any suggestions on what to get? I would like a electronic ignition but with out having to install a box, just something simple.
distributor
po51
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My engine builder strongly suggests a mechanical advance rather than a vacuum advance for my new 408w stroker. As I will be buying a new distributor any suggestions on what to get? I would like a electronic ignition but with out having to install a box, just something simple.
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So what are the advantages for running a mechanical advance distributor on a race engine? Did he give you the reasons why or just make the strong suggestion?
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My question was somewhat rhetorical. However, it would be interesting to hear what his engine builder gave him for his reasoning. Here is one of the best articles I have read in the past.
Mechanical advance vs. vacuum advance article
Mechanical advance vs. vacuum advance article
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I read a lot on this and this is this well known write - up that attempts to makes a definitive statement that manifold vacuum is the way to go. A lot of people think it's gospel and it's quoted everywhere.
I say bull. Why do you need additional advance at idle? I don't see any advantage. I did discover a big disadvantage though.
I was having trouble where the car would drop idle speed very quickly, and even stall if I let it, when idling and turning the steering wheel or pushing the hydroboost brake. It made for problems when off the gas while braking and turning a corner, or parking.
Tried a lot of things to fix it, but it was just weird. The problem turned out to be manifold vacuum advance. Although it seemed like I had a good strong 800 rpm idle in neutral or with the clutch in, it was what I guess I would term a "weak" idle. My theory is that timing was so advanced at idle that it couldn't handle any load from the steering pump, because it was firing so early it was fighting itself similar to how too much initial timing makes for hard starts.
I moved to ported timing, and now the idle doesn't drop at all when steering pump is working. Not at all. I can move it back to manifold, adjust it to 800 and it will stall under steering pump load, and move it back to ported and reset idle to 800 and it has no problem with steering pump load. Easily repeatable.
This also might help folks with automatics whose idle drops too much when put in drive.
So, my vote is ported because manifold is all con and no pro I can figure out.
Bob
Dizzy
When I asked the builder this is the response I got "mechanical adv only to avoid detonation which these engine are highly prone to". I regards to my driving it will be used for around town cruising, a car show now and then. Nothing track or race related.
When I asked the builder this is the response I got "mechanical adv only to avoid detonation which these engine are highly prone to". I regards to my driving it will be used for around town cruising, a car show now and then. Nothing track or race related.
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They're only highly prone to detonation if they're BUILT to be prone to detonation. Running a properly tuned vacuum advance shouldn't have an adverse effect. You're going to be adding spark advance primarily at closed throttle no-load or deceleration-load situations where it is needed to properly burn the lean mixture.
I'd buy a mid-to-late seventies DurasparkII distributor with an adjustable vacuum advance unit. You can cap it to begin with and once you know what kind of vacuum your engine produces during various types of operation you can adjust it to provide advance only under those circumstances when it's advantageous.
I'd buy a mid-to-late seventies DurasparkII distributor with an adjustable vacuum advance unit. You can cap it to begin with and once you know what kind of vacuum your engine produces during various types of operation you can adjust it to provide advance only under those circumstances when it's advantageous.
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If the vacuum advance is properly adjusted, that should not be an issue. The BOSS 302 had vacuum advance, does that mean it was prone to detonation? Is your engine more radical than the track-ready BOSS?
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I have found that engine builders have opinions (not necessarily correct) like everyone else. My engine builder insisted on a single plane manifold for my mildly built 302, his reasoning was dyno testing they had done, temperatures in the cylinders bla bla bla. I finally replaced it with a dual plane air gap and the car is much more responsive on the lower end. If I lost some top end so what, it's a street car not a Nascar. He builds a lot of circle track race engines
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po51,
For a street engine for all around best performance over a wide range of operating conditions the best setup is a combination of mechanical (centrifugal) and vacuum advance properly set up (ie 'curved') to work with the particulars of your engine/trans/ axle set up.
Good luck
Paul
For a street engine for all around best performance over a wide range of operating conditions the best setup is a combination of mechanical (centrifugal) and vacuum advance properly set up (ie 'curved') to work with the particulars of your engine/trans/ axle set up.
Good luck
Paul
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That's right, the single plane will give better dyno numbers at top end. Question you have to ask, how often will your engine BE at top end. If it's once a week, or even once a day, use a dual plane.
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whats wrong with just using a plain ole stock autolite and have it set up and repaired and rebushed as necessary
if properly set up and curved theyre good to 6K and very reliable for the street and even mild track and will give yrs of trouble free service
if Ford got one thing right it was the dizzys of that era and 2100 carbs. you cant kill them.
if properly set up and curved theyre good to 6K and very reliable for the street and even mild track and will give yrs of trouble free service
if Ford got one thing right it was the dizzys of that era and 2100 carbs. you cant kill them.
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So did the builder say all these engines or HIS engines are prone to detonation,lol
Thats the problems with building an engine with the heart of a stallion but only using it to pull a cart around with. Asking for more problems than its worth.
Thats the problems with building an engine with the heart of a stallion but only using it to pull a cart around with. Asking for more problems than its worth.
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