Technical ELECTRICAL, Initial timing, vacuum ports, breasts, total...?

So, I saved all this good info the last time it was posted all in one post... and that document is currently sitting in the computer with the fried system board... which isnt gonna get fixed until AFTER the truck is put together, as a further incentive.

So, heres my old setup (on a 327 with camel heads) 2 bbl holley, HEI with stock egr vac advance. set at 8 deg btdc, I BELEIVE, not sure, but I think it was on the vacuum tap that didn't give you any vacuum until the rpms go up...

IS THIS timed or ported vacuum? which one is like tapping in directly to the intake manifold vacuum???

So, heres the new setup, same engine, same heads, same HEI, except that I got an adjustable vacuum advance. new Edel. 600 cfm 4bbl. I assume I'll use my same 8 deg btdc initial setting...

WHICH vacuum should I use, ported or timed? Now, when I adjust that adjustable advance, what should my total vac advance be? (degreewise, I'm gonna hafta borrow my buddy's adj. timing light, mine isnt advanceable)

See, with the old setup, I pinged even with 91 octane going up a hill. I got fed up with that setup cause Dr. J says he uses 87 in his big ol' truck and gets MAAAD gas mileage and never pings... so something was definately amiss with this thing...

Truck MUST run this weekend, dammitt, its been down since 2 days b4 haloween.... suckage.

Thanks for tolerating a repeat question, but perhaps some of the new crop of newbies need to be schooled as well...

Oh, and sorry, there truly were no breasts in this post, but add some if you feel so inclined! (')(')

-J

 

I think one of us is confused, I refer to that one as the timed port, and the other as the manifold port.
For better streetability you are supposed to use the manifold vacuum signal, on a Holley, it is the one underneath the primary bowl. I can NEVER remember which one is which on an Edelbrock. Put it on one port, then drive a bit, then swith to the other one. Which ever one runs better, keep it on there. Make sure you romp on it and back off the throttle to see how that reacts.

 

Manifold vacuum on a GM motor...Fords used to run "ported" vacuum...but manifold vacuum improves driveability and helps smooth the idle.

Start at about 6 degrees BTDC as your initial setting with the vacuum advance disconected, (and re-connect it before ya drive!) and work from there tuning by ear and listening for spark knock.

As for the breasts....get your own!

 

A re-post from a while back....

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Got Time?


Seems like there’s a whole lot of confusion over this timing an engine stuff.
That said, here’s what works for me.
At least what works for me on the GM engines, but the information is pretty much applicable to the other brands as well if they are modified.
If the other brands are stock, you would do well to use the stock timing curves and advance methods.

We’ll go over initial advance, vacuum advance, centrifugal - or as some call it, mechanical - advance, full time vacuum and ported vacuum.
Other than noting that camshaft advance or retard is something completely different from ignition advance or retard I’ll just point out that camshafts are set to place the torque curve peak in a particular place as well as for smog requirements on some engines.

Low end - rpm wise - torque requires the camshaft advanced.
In most cases no more than 4 degrees BTDC. (Before Top Dead Center)
The great majority of cams, both hot and stock are installed straight up as the saying goes.
Retarded cams are usually found on smog motors.
Retardation due to the indexing on the timing gears.

Degreeing in a camshaft is a requisite for building serious engines and it doesn’t hurt to do it with engines that are not so serious.
A not so serious engine perhaps exemplified by a stock compression 350 SBC with modest cam, modest carburetor size and a reasonable for the street intake manifold and at the least duals and better yet, small primary tube headers.

For the not so serious engines, simply installing the cam on the marks will suffice.
I’ve done more than a few of these, degreed them to boot and found that at the most they were off 1 - 1 1/2 degrees. Entirely reasonable for a street engine and indicative of the quality work that cam grinders do.
Play in the timing chain is more than likely the reason why the cam doesn’t degree in right on the money.

In fact, even if you want to run a cam “straight-up” on the street, it’s probably a good idea to advance it a couple of degrees to start with.
Timing chains stretch to a certain point right away and stretch even more over time.
My thinking being, if you start straight-up when the chain stretches, the cam timing is going away.
With the cam advanced to start with the engine will remain in an overall better state of tune for a longer period of time.

One big caveat here: Don’t confuse cam timing with ignition timing.
They are entirely separate.
If you find an ignition timing point that your engine likes, you can always return to it regardless of where the cam is dialed in.
Reason being, the cam and the ignition are separately adjusted devices.

For the street, which includes most of us here, you need to run a distributor with vacuum advance and it needs to have the proper vacuum source.
It’s as simple as that.
If you’re running a centrifugal advance only “racing” distributor, you’re just fooling yourself and creating problems as far as driving the car in traffic on hot summer days.
Running the engine at idle without the extra advance provided by the vacuum advance system will have the engine running hot in almost all cases.
The engine needs quite a bit of advance at idle since the fuel/air mixture is lean and it takes longer to burn the mix at a low engine rpm.

Run a vacuum advance distributor selected to the proper vacuum source and you can run your hot rod in heavy traffic on the hottest days with no problems.
Assuming you have fan of adequate cfm capability and a properly sized radiator in reasonably good condition.

For GM engines the vacuum advance deeds to be selected to full-time manifold vacuum
Do not, do not source the vacuum advance from ported vacuum.

Here’s why you want a vacuum advance distributor for the street and also why you want it sourced to full time vacuum.
Full time vacuum as vs. ported vacuum, but we’ll get to that in a bit.
The number one main reason you want full time vacuum is that you need to run a considerable amount of advance at idle.

Since you need the timing retarded to make starting the engine reasonably easy, vacuum advance - and maybe it should be called vacuum retard - is one way to do it.
The centrifugal advance is part of the equation as well.
With the engine at rest or at the least cranking slowly centrifugal advance doesn’t come into play and the spark is timed right for easy starting.

Initial advance is a compromise between being retarded enough for easy starting and the amount of advance required for an engine at part or full throttle and low rpm.
Initial timing is usually set from 0 degrees to12 degrees BTDC. (Before Top Dead Center)
The setting dependent on the compression ratio, cam timing and a host of other factors.
Not the least of which is that timing figure we’ve all seen that’s called “All-In.”
All-in meaning that the centrifugal advance mechanism has advanced the timing as far as it’s going to go.

Centrifugal advance is entirely dependent on engine rpm and no other factor.
Vacuum advance is entirely dependent on the vacuum applied and it will be affected due to -
engine rpm. ( This is especially noticeable if you’re running a big cam which varies the vacuum level considerably as a function of rpm with the engine in a no-load state. No-load other than overcoming friction and pumping losses associated with retaining a particular idle speed.)

Note that a typical engine with stock or very modest cam will idle at 17-19" of vacuum.
That same engine with a big cam - 280 degrees advertised duration - will idle at about 10-12" of vacuum.
The 10-12" figure due to some engines idle faster than others and as the idle speed comes up, the vacuum levels raise.
Run the big cam engine up to 1000-1200 rpm or so and you’ll find the vacuum levels at 17-19".
Assuming the engine is well sealed.
Well sealed defined as good rings, good valves, good head gaskets and no intake vacuum leaks.

A lot of guys and maybe even a few gals think that you have to suffer with a high idle when running a big cam.
In most cases you can get the big cam engine to idle at a reasonable rate.
Part of that depends on the lobe center of the cam in question.
The basic rule is, wide lobe centers calm things down a bit and allows a reasonable idle.
Wide lobe centers defined as 112-118 degrees.
As a matter of interest, cams oriented toward racing are generally set at 108 degrees lobe centers with some running 104 and others 110.
We’re not gonna get into the whole camshaft thing here, but the information is noted to help you decide where you’re at and where you can go as far as obtaining a decent idle.

Fwiw - I was able to get the 462" Buick in my 32 roadster to idle at 600 rpm.
This with a dual quad medium riser setup running two 500 cfm Carters with straight linkage and a couple of different big cams.
Both cams with 284-290 intake and exhaust duration, 112 degree lobe centers on one and 118 degree lobe centers on the other and virtually identical lift.

So here’s the deal on timing the engine.
And I’m gonna assume you do have the camshaft timed right and you do know where True Top Dead Center is on the harmonic dampener. (The harmonic dampener called the balancer by some.)
In most cases if the cam timing is really off, you’ll have mechanical damage if you try to fire the engine with the cam improperly installed.
Proper installation includes, among other things, proper orientation with the crankshaft, sufficient clearance between coils of the valve springs as well as proper adjustment of valve clearances.
Improper adjustment hardly ever a problem on startup, but you may as well have it right before the engine is lit off.

We’re going to use the timing figures for a points distributor SBC engine - a 1966 210 HP 327 in this case - but the technique will work for any other non-computerized engine if you just give it a little thought.

One small caveat here, note that the timing figures in many manuals show the advance figures in distributor degrees.
If so, you’ll have to double the timing figures to get crankshaft degrees and you may have to double the listed rpm.
Pay attention to the notes in the engine manual.

Note too that the figures referenced below are in crankshaft degrees.

Roll the engine over - manually - so it is at True Top Dead Center (TTDC from here on out).
Most times, if you have the stock timing cover and dampener you can simply line the dampener’s zero mark/factory scribed line up with the zero mark on the timing pointer.
(Other engines will have the degree marks engraved on the dampener and the timing pointer is just that, a simple pointer.)

Some guys and gals will install the distributor with the rotor pointed at number one, fire it and shoot the timing with a light and that’s an ok way to do it.
Here’s a little better way and it will get you a leg up on having accurate timing right at the start.
Especially important when you’re firing the engine for the first time and proper camshaft break-in is on the agenda.

The initial timing figure for our sample engine is 2 degrees BTDC. (Before Top Dead Center.)
BTDC is an important consideration as some engines are listed with an ATDC initial timing setting. (After Top Dead Center.)
All of which means, check the figures and pay attention to which side of zero you want to end up on.

With that said, instead of rolling the engine - again manually - to zero, roll it to 2 degrees BTDC with #1 cylinder having both valves closed and ready to fire.

Disconnect the condenser from the points.
Make sure the points are set correctly.
Usually .016 to .018.

Install the distributor with the rotor pointing at the #1 distributor cap terminal.
Make sure you’ve engaged the oil pump properly and don’t force things.
If it doesn’t go all the way down, pull the distributor, note the orientation of the oil pump drive bar inside the bottom of the distributor and if necessary, insert a long screwdriver into the distributor receptacle and orient the oil pump distributor drive slot to match where the distributor should be when it’s properly installed.
Sounds complex, but it’s not.
This will get you very close to where the distributor gear is meshed with the cam gear and you end up with the rotor pointing at the #1 terminal allowing the distributor to slide onto the oil pump shaft and ready to be locked down.

Install the distributor hold-down so that vertical play is out, but loose enough so the distributor can be turned smoothly by hand.

Connect a volt/ohm meter - also called a multi-tester - set for continuity across the points.
A test light across the points works just as well if not better.
What you’re doing here is using the points as a switch to tell you exactly where you’re at when you come up to the timing point that you want. (2 degrees BTDC in this case.)

Since the distributor rotates in a clockwise (CW) direction, turn the body of the distributor in a CW direction for about twenty degrees or so.
You should see continuity - or the test light, light.
This sets things up to take the play or backlash out of the distributor when you bring it back to the firing point.
Which adds to the accuracy of what you’re doing.

Then, very slowly, rotate the distributor body counter clockwise (CCW) until continuity breaks or the test light goes out.
That indicates the points have opened which also tells you the point at which the cylinder fires.

Tighten the hold-down bolt locking the distributor in place.

Reconnect the condenser, install cap and wiring, connect the distributor’s primary wire (the small one) to the coil, install spark plug wiring, coil wire and you are ready to start the engine.

Done correctly, there will be no backfires from the ignition source.
The engine will light right off and provided the centrifugal and vacuum advances are working ok it will run fine.
If you are doing the “breaking in the cam bit” this will get usually get you through the 20 minute break-in period just fine.
Some like to shoot the timing right after start-up and all that’s required there is to have the vacuum advance disconnected.

In fact, if there’s one golden rule about dynamic engine timing and the checking of same it is to have the vacuum advance disconnected.
Pull the hose at the distributor and plug it so you don’t have a self induced vacuum leak.
Golf tees work well as small vacuum line plugs.

So, now that the cam is broken in or if you’re just dealing with a tune-up on an already broken in engine, here’s the drill on timing.

The book figures for the engine we’re dealing with here - the 210 HP 327 - shows the timing figures as follows:
Initial = 2 degrees BTDC.
Centrifugal = 32 degrees BTDC at 1975 rpm.
All-in = 34 degrees BTDC. (All-in equals Initial timing plus full Centrifugal timing.)
Vacuum = 16 degrees BTDC at 15" of vacuum.

All-in timing refers to centrifugal timing only and as mentioned is derived from the rpm level of the engine.
Centrifugal timing is zero (don’t be confused by the 2 degrees initial here, we’re talking only about how much timing the centrifugal advance mechanism puts in) until 450 rpm.
The 450 rpm level is where centrifugal advance starts advancing the timing.
The timing is all-in (hence the term) at 1975 rpm for this particular engine.
The book shows the idle rpm for the engine to be 500 rpm so idle speed will have to be backed down to 450 rpm to double check the initial setting.
If you can’t get there, but you do get it to idle at 500-600 rpm or so and assuming it’s a smooth idle - even with a hot cam, although the engine specs we’re quoting here are for a stock cammed engine - you can do a little extrapolation.
Extrapolation being a big word that in effect means to just think about it a bit and make an estimate as to where you should be with the information you do have.

The other way around this is to check the all-in figure at say 2000-2200 rpm.
Provided the dampener or timing tag is marked for that point.
You can mark the dampener for the all-in timing figure of 34 degrees and match it up to the zero point on the timing tag.
This necessary if the timing tag is marked off in degrees and the dampener just has a scribed line at the zero point.

With the vacuum advance disconnected as mentioned above, fire the engine - and making absolutely sure to stay out of the plane of the fan blades - run the engine up to 2000-2200 rpm and note the reading.
At these rpm levels it’s much safer to shut the engine down, change the distributors orientation if desired - only small adjustments in distributor orientation is required - fire it up and check again.

If the timing light shows no change in the centrifugal timing when engine rpm is changed, then you have a problem in the centrifugal advance mechanism.
Centrifugal advance problems are fairly rare.
At least the ones where it doesn’t advance at all.
The usual problem is when you have a distributor that’s been tinkered with a bit.
Most times by novice hot rodders who change weights and springs without realizing what they are trying to do.

As a small side note, when fan blades come off they can do considerable damage.
Two that I’ve seen, one in person and the other after the fact; a 53 Chevy, stock six cylinder lost a blade. It went through the hood and partway through the garage roof.
The other, a guy I knew had a fan come unglued, the blade hit his left forearm and the resulting scar tissue made it look like a hand grenade went off in his pocket. A more than serious injury and he was lucky to regain full use of his arm.

Now that the centrifugal timing is where you want it to be and operating correctly, all that remains to be done is to check the vacuum advance timing.

Couple of things to know beforehand is where the vacuum source comes from.
Not always as easy as you may think although the general rule is: ported vacuum comes from above the throttle blades and full time manifold vacuum comes from below the throttle blades.

Note that some Holley carbs have a full time vacuum bib above the throttle blades and others use a bib in the same general area for ported vacuum.
Carter carbs and their twin, the Edelbrock - they both come off the same production line - many times have two bibs below the throttle blades.
One reason for the confusion in selecting a vacuum source as far as Carters go and perhaps for the Edelbrocks as well is that the instructions point to the passenger side bib as the one to use for vacuum advance.
This is incorrect for GM engines and in fact the passenger side bib is ported vacuum.
The drivers side bib is what you want and it is full time manifold vacuum.

You can source full time manifold vacuum from several other places as well.
Any fitting that taps into the manifold proper.
Even those in just one intake runner.
The large and sometimes medium sized bibs at the front and rear of the Carter carb base.
As well as the small hex shaped vacuum manifolds usually found at the rear of GM engines.
These are hex shaped as mentioned, have several bibs of varying sizes and you can either T into one or if you have an unused bib, use that.
Be careful you don’t tap vacuum from a thermostatically controlled vacuum switch because you may end up with no vacuum at all due to the engine temperature not being sufficiently high.
T’ing into the power brake vacuum line also works well.

Now that you’ve sourced your vacuum advance properly, checking it for proper operation is easy.
With the distributor vacuum can connected or re-connected as the case may be, fire the engine, let it idle and take note of the amount of advance.
It will be quite a ways above the initial setting of 2 degrees BTDC at idle.
Assuming you have 17-19" of vacuum you should show the full vacuum setting.
IE: 16 degrees BTDC plus the 2 degrees initial making a total of 18 degrees BTDC.
You’ll probably show a bit more than the 18 degrees BTDC because the advanced timing causes the engine to speed up and once the rpm raises the centrifugal adds it’s little bit to the mix.
Which means you may have to re-adjust the idle rpm once the vacuum advance is connected.

Here’s how you check the vacuum advance for proper operation.
It’s not enough to show full vacuum advance, you want to make sure the vacuum advance is operating freely and retarding when it should.
Retardation coming in when the throttle is depressed putting the engine under load which makes vacuum levels drop.

Paying attention and once again staying out of the plane of the fan blades, wing the throttle lightly and watch to see if the vacuum advance is backing off.
Don’t be fooled by the centrifugal advance coming up as rpms increase.
Winging the throttle in this case simply means cracking it open quickly, which drops the vacuum levels and then letting the throttle return to idle without much gaining much rpm at all.
You should see the timing back off when you do this.

If the engine stumbles when you wing it, run it up to 1000-1200 rpm, take note of where the advance settles out and then wing the throttle.
You’ll have a little more advance on with the rpm spun up a bit and added to the full vacuum advance, but the vacuum advance will retard just as it should when winging the throttle.

If you run the engine up past the 1975 rpm mark the total timing will be 50 degrees BTDC.
That due to the centrifugal advance has reached it’s maximum due to the rpm level and the vacuum advance has reached it’s maximum as well due to the high 19" or so vacuum level as well as the 2 degrees initial timing.
It’s not a problem.
There is no detonation because the load on the engine is light and just like at idle the fuel/air mixture is lean and takes while to burn.

Aside from just paying attention to where your vacuum source is, you can double check it with a vacuum gauge, timing light or tachometer.

A vacuum gauge will show 17-19" vacuum at idle with a stock cam indicating full time vacuum.
Spinning the engine up with light throttle settings under no-load conditions will have the gauge indicating the same 17-19" of vacuum regardless of rpm.

The vacuum gauge will show zero to 2" or so on the same engine at idle which indicates ported vacuum.
Raise the rpm levels and you will see the vacuum levels raise in coordination with the rpm.
This because the ported vacuum is tapped into the venturi and as air flows through the venturi there is a pressure drop.

Pulling the vacuum line to the vacuum can on an idling engine will retard ignition timing as shown by the timing light if - the vacuum line is connected to full time vacuum.
There will be no change if the vacuum line is connected to ported vacuum.

Very much the same thing happens when a tachometer is utilized.
Pull the vacuum line from a full time vacuum source and rpm drops.
No rpm drop is realized when pulling the line from ported vacuum.

In lieu of either the timing light or tachometer, simply listening the engine and noting whether the rpm drops will tell you what you want to know.

You can easily see that connecting the distributor to ported vacuum will increase the timing considerably past what is optimum for an engine under load once the rpm comes up.
With detonation resulting in most cases.
Keep in mind that the vacuum advance system is also a vacuum retard system depending on engine load.

To strike off on a short tangent here, pinging, which some call detonation - and it is - is usually caused by two things.
Assuming a reasonable compression ratio for the street and an adequate gasoline octane figure for the engines requirements.
Pre-ignition is one and it’s caused most times by a piece of carbon glowing red hot in the combustion chamber or a sharp edge somewhere in the combustion chamber.
Many times these sharp edges can become hot enough to ignite the fuel/air mix early - as does the hot carbon piece - and pre-ignition results.
Detonation is initiated by firing the fuel/air mix too early.
In both cases - pre-ignition and detonation - with the fuel/air mix ignited early, the piston still rising and compressing the fuel/air mix in the combustion chamber creates very high pressures which will ignite the remaining fuel mix in the chamber very much like a diesel engine does.
The sharp metallic ping you hear is from the collision of the two flame fronts and is the result of a very high and potentially damaging pressure spike.
Nuff said there.

Distributor curve or curves is much bandied about.
What it boils down to is simply the amount of advance vs. a particular engine rpm.
Once you have it laid down on graph paper with say, engine rpm at 200 rpm steps and the distributor advance having one degree steps you can see the resulting curve on the paper and that’s where the name comes from.

One last little note and that on the style of timing light you use.
The newer dial-back timing lights have their advantages, but if you’re running an MSD - or similar - ignition amplifier box you’ll end up with the timing considerably retarded.
With a multiple spark ignition box use a standard timing light.

I ran across this little bit last summer when I had a little extra coin and figured a dial-back timing light would have some real advantages.
Especially so on engines that didn’t have the maximum all-in timing figure marked on the dampener.
I shot the timing on the roadsters MSD equipped Buick engine and found the timing showed about 12-15 degrees or so too far advanced.
This was with the light set at zero.
Shooting it again with the old faithful standard timing light showed the timing right on the money.
Easy to see there would have been a lot of lost performance if I would have reset the timing using information supplied with the dial-back light.

Ya know, dad was right when he said that running a stock engine I needed to stick to what the manual said.
He said too, I couldn’t go far wrong in using the manual figures with a mildly modified street engine as well.
My experience bears out what he told me and I find with mildly cammed and reasonable carbureted not too high a compression ratio street engine that the factory figures work quite well.

Once you get into the serious engines - and that doesn’t mean a low comp SBC 350 with killer cam - that you need to do some experimenting with ignition as well as fuel curves to get where you want to go.

In fact, most of us need to listen to what the cam manufacturers are telling us when they make cam recommendations.
You can’t go far wrong in either following their recommendations to the letter or at the very least deciding on what you need for a cam and selecting a cam one step milder than what you thought you needed.

I find that most guys select a cam and stick with it come hell or high water.
It’s interesting to realize how few have run more than one cam in a particular street engine.
Racing engines, another story, lots of experimentation needed there, but trying two or more cams in a street engine can tell you a whole lot.

Part of it has to do with vehicle weight and gearing, no doubt about that, but for me the aim is to have a strong engine with good mid-range torque that runs crisply.

About four cams, three intake systems and a couple of ignition set ups later I think I’ve succeeded.
The Buick engine in the roadster is a bored out 455 now measuring 462".
It’s an easy starting, strong running, quick responding dependable cool running engine that runs on 87 octane and will idle all day in hot summer traffic with nary a whimper.
It’s civilized, easy to drive and when called upon it’s just hell on the on-ramps.

Sort of a Jekyll and Hyde kinda deal.

As it should be I think.

Hot rods are all about performance in my book and looks are secondary.

If not, why bother?

C9

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Burndup - now that I made you read all the way through this, here’s the figures for 1967 275HP 327.
8 degrees initial.
26 degrees centrifugal, all in @2050 rpm.
16 degrees vacuum @ 15" of vacuum....

 

Great read, as usual, C9.

I remember seeing you post this before, but lost it before I realized I needed to save it. It's saved now. It's amazing how we can get so good at the hard stuff like building motors, porting heads, fabbing brackets, and pounding metal back into shape, but forget things like the fundamentals of tuning.

Thanks.

 

Crane makes an adjustable vacuum advance cannister you can use to fine tune your curve,about $23.i got lucky and found one on ebay for $5.now i'm gonna go back and reread C9's post,then maybe i can get my car dialed in finally,thanks Jay-george

 

I am a proponent of mechanical advance - that vacuum shit always acts different depending on what day it is. Plus it is one less hose to look at.

 

Some fine reading there C9. Heavy going for the ininitiated, but that is where you learn this stuff, by reading and taking note of other peoples knowledge.

Something I've run across is checking that TDC centre, as marked on the crank damper, is the REAL TDC on cyl 1. Friend of mine spent an age setting up his SBC 400, couldn't get it right, until he checked the damper and found the outer ring had 'slipped' a half inch!!
Paul

 

I clicked this post... I don't know why... but I did...

damn subliminal messaging. (*)(*)
sam.

 

where's the boobs?????????????

 

If I said anything at all it would never get read because C9 covered about everything anyone ever wanted to know about uh just about everything.

Never the less about breasts
Did anyone ever read that little pamphlet that the Govt put out in the late '60s early '70s about pot. It said something to the effect that pot smoking would cause breasts to grow on men. I don't know I'm still waiting.

 

THANKS C9!!!!

Yep I thought it was you that wrote the definitive guide... I had that post saved on the dead computer, which hopefully regains consciousness tomorrow....

If that method were true for cultivating extraneous mammary tissue, I'd know a bunch of girls that'd need a serious miracle of mechanical engineering to support.... naw, fuckit, their backs woulda snapped years ago.

Thanks again!

-J

 

[ QUOTE ]
I am a proponent of mechanical advance - that vacuum shit always acts different depending on what day it is. Plus it is one less hose to look at.

[/ QUOTE ]

Is this the smiley face for a polite question?

You are aware that a vacuum advance distributor - in most cases today - also has a centrifugal mechanism within?
It's an overlapping deal ... load vs. rpm.

Racers don't need a vac advance, but street runners do.

 

[ QUOTE ]

where's the boobs?????????????



[/ QUOTE ]

No boobs, but a small bit of trivia that's somewhat related.

Didja know a Double D bra fits Dietz headlight buckets perfectly?

Don't ask me how I know.

Better yet, don't ask me how I figured it out....

 

"...and $10,000 to build my robot....my GIRL robot..."

C9, was that YOU???

 

[ QUOTE ]
Don't ask me how I know.

Better yet, don't ask me how I figured it out....

[/ QUOTE ]


AWW, C'MON!

This sounds like the beginnings to another epic...

 

[ QUOTE ]
AWW, C'MON!

This sounds like the beginnings to another epic...



[/ QUOTE ]


No epic, all I'm gonna say is, sometimes ballerina's grow up....

 

With those specifications, that ballerina would have tipped over!

 

too much advance, ported is "timed vacuum" off idle, manifold is straight to manifold (vacuum at idle). sbc don't use vacuum at idle. run vacuum to a ported nipple (also use a regular advance), run total advance at 28 deg (32 if you want to be ricky racer) or run 10 deg at idle (inital)........ or just get a mech advance dist.

 

Hey Burndup not to jump the post but what ever happened to your Caddy? Just wanted to check up and see that my shop manual is still in good hands...Ted

 

too much advance, not at idle rpms.

ported is "timed vacuum" off idle, correct except for the "off idle" comment, vacuum is present at all rpm levels, higher as engine speed increases due to pressure drop in the carbs venturi.

manifold is straight to manifold (vacuum at idle), correct again, although vacuum is present at varying levels according to rpm and load.

. sbc don't use vacuum at idle. Yes they do.

run vacuum to a ported nipple, wrong. If you do that once the engine speed is up there is quite a pressure differential within the venturi and you will have excessive advance for an under load condition. using the last figures supplied, 8 degrees initial, 26 degrees centrifugal and 16 degrees vacuum you'll have 50 degrees of advance once you get over the all-in timing point of the centrifugal mechanism with enough rpm up to pull the vacuum advance all the way in.

(also use a regular advance), ???

run total advance at 28 deg (32 if you want to be ricky racer) or run 10 deg at idle (inital), you can run either. it's all about what the engine wants, not what you think it wants.

........ or just get a mech advance dist. and look racy and have a street driven car that doesn't run as well as it should.

<font color="red"> One really big thing people need to think about is; factory engineers know a lot more about this stuff than we do. The other thing to think about is cost. Factories wouldn't spend the money on a vac advance setup unless they thought it was totally necessary. </font>

 

too much advance, not at idle rpms... he wasn't pinging at idle.

ported is "timed vacuum" off idle, correct except for the "off idle" comment, vacuum is present at all rpm levels, higher as engine speed increases due to pressure drop in the carbs venturi... was meant as it GETS vacuum above idle.


sbc don't use vacuum at idle. Yes they do.... to the vacuum advance ??? they (most of the point type) are hook to a ported nipple on the left lower side of the quad (from the factory).


run vacuum to a ported nipple, wrong. If you do that once the engine speed is up there is quite a pressure differential within the venturi and you will have excessive advance for an under load condition. using the last figures supplied, 8 degrees initial, 26 degrees centrifugal and 16 degrees vacuum you'll have 50 degrees of advance once you get over the all-in timing point of the centrifugal mechanism with enough rpm up to pull the vacuum advance all the way in........... the factory is set-up that way and only gets to 26-28 at full throttle, even on a 3x2 set-up the total advance is 28 at the balancer....i've run serveral mech advance dist on street cars, they perform great and have great drivability.


(also use a regular advance), ???..... stock vacuum advance not a adjustable one.

run total advance at 28 deg (32 if you want to be ricky racer) or run 10 deg at idle (inital), you can run either. it's all about what the engine wants, not what you think it wants........ that's why i said "OR" and both of those setting are a good place to start tuning.


factory engineers know a lot more about this stuff than we do..........if that were 100% true then there would be no calling for aftermarket parts. the vacuum advance is there to "fill" the gap before centrifugal kicks in on factory distributors.