Thread: Got Time? (Part 1)

Tweet

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.

Got Time? (Part 2)


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.

Got Time? (Part 3)


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.

Got Time? (Part 4 - Fini)

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 flow increases 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 reasonably 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

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Nice article, lots of good info. It brings up one question, however: If manifold vacuum is the real deal, why do the instructions for just about every Chevy crate motor on the market recommend connecting to ported vacuum?

I am not disputing your method or reasoning, just wondering . . .

Is that a artical or a book!!!


~ Vegas ~

Great information there C9x, and wonderful reading. Very informative. Henry, I have noticed the same thing about most crate motors but have had better luck with full time vacuum also. Don't know why, read it somewhere once but don't remember why.

My question lies with the initial stabbing of the distributor, can you do the same thing somehow with an HEI? That is, make the light go off and on by moving the dizzy to determine you best spot to set initial timing? Just interested to know. I am going to copy and paste this into some of my own stuff to use for future reference. Great stuff.

Originally posted by urotu
My question lies with the initial stabbing of the distributor, can you do the same thing somehow with an HEI? That is, make the light go off and on by moving the dizzy to determine you best spot to set initial timing? Just interested to know. I am going to copy and paste this into some of my own stuff to use for future reference. Great stuff.

my answer is simple, pull plug number one, and keep the wire connected with cap on, turn distributor slowly til plug sparks, then back it up just a hair.... its not as accurate, but its the best you can do with hei, btw coil must be connected and getting power as well

as for the vaccuum, i believe the ported is more of a fuel smog type thing

and thanks for the info, its great great info.... a lot of which i knew already even more that i didn't consider

Originally posted by Henry Rifle
Nice article, lots of good info. It brings up one question, however: If manifold vacuum is the real deal, why do the instructions for just about every Chevy crate motor on the market recommend connecting to ported vacuum?

I am not disputing your method or reasoning, just wondering . . .

I didn't know the Chevy crate motors came with that recommendation, but where part of the confusion (I think) comes from is that the Carter and Edelbrock instruction/install sheets recommend using the ported side.

The part I don't like about using ported vacuum - aside from the overheating problems it sets up in most cars - it keeps adding advance as air flow - pressure differential - through the venturi increases due to engine speed.
The pressure differential can be altered due to throttle settings as well.


I ran some interesting tests on my roadster as pertains to vacuum levels from each source.
Had a vacuum gauge connected to full time vacuum and another connected to ported.vacuum.
If I can find it, I'll post it.
Reason I say "if" is that I think it's in my old computer which seems to have a mind of it's own as far as giving up info goes....

Originally posted by urotu

My question lies with the initial stabbing of the distributor, can you do the same thing somehow with an HEI? That is, make the light go off and on by moving the dizzy to determine you best spot to set initial timing? Just interested to know. I am going to copy and paste this into some of my own stuff to use for future reference. Great stuff.

I do very much what DennyW and thesals do with HEI.

I usually know where true TDC (Top Dead Center) - and I'm sure they do as well - is and I set the engine at the initial timing mark and not zero.
For my 462" Buick it's set at 8 degrees BTDC. (Before Top Dead Center).

For timing I like to use a spare spark plug plugged into the #1 plug wire.
The plug has a grounded 14 gage test lead clamped around the hex or threads and the plug either hanging in plain view or lying where it's not going to interfere with V-belt or fan.
In either case, the electrodes are set so I can see the arc.

Since the Buicks rotate CW (Clockwise) I like to turn (retarding timing) the distributor CW about 20 degrees.
This takes the play out of the distributor drive stuff going one way.

With ignition on, turn the distributor CCW (Counter Clock Wise) advancing the ignition until you see an arc at the spare spark plug.
Stop there and bolt the distributor lock bolt down.

This sets up the timing very accurately and when you start turning the distributor CCW you'll take the distributor play out of the picture going in the direction it will be - mechanically loaded - when it's running.

After that, double check with a timing light when the engine is running and you're in business.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

I see a lot of talk about timing an engine with a vacuum gauge or by ear.
Some guys do that and their cars run ok.
I do see them turn the distributor quite a ways in most cases and my opinion is the timing can be off at least 5 degrees one way or the other.
Dyno - and the dragstrip - testing show gains or losses in performance when the timing is just a couple of degrees off.

Using a timing light or changing timing statically as described above is the only way you're gonna know exactly where you're at as far as initial timing goes.

Close enough is not good enough and to my way of thinking if you don't use a timing light you're depriving yourself of a lot of important information.

Originally posted by vara4
Is that a artical or a book!!!


~ Vegas ~

Most of the books I do are longer....

Here's something I discovered after quite a bit of research on Chevy crate motors over the last few days. I posted part of it on another thread.

It seems that the vacuum can Chevy supplies with the crate motors has too much advance (20 deg.) and the spring is way too soft. That brings the advance in too quickly. It's easy to get 52 -56 degrees in some situations. At the same time, the newer, more efficient heads (like the Fast Burn) don't like a lot of timing.

Many of the folks reporting good results with these motors either disconnect the vacuum advance, which has an effect on idle, engine heating and gas mileage, or they get a replacement vacuum can (either fixed or adjustable) with 10 degrees or less and a stiffer spring.

Of course, after that, they still have the debate about manifold or ported vacuum.

On my new crate motor, I'm taking this approach:

- I ordered a vacuum can recommended by Sallee Chevrolet's performance department - PN 1973681

- Install the new vacuum can, tune the motor, set the timing, then see what happens on the tach (idle), temp gauge, fuel gauge and the "seat-of-the-pants power gauge" with both ported and manifold vacuum.

- Disconnect the vacuum can, then take a look at the same four gauges.

Experimenting. Isn't that what hot rodding is all about?

Here's my guess on the results:

I didn't believe I'd ever say this, but . . . new vacuum can connected to manifold vacuum. (Don't have a heart attack on me, Denny)

Bear in mind that this is coming from a dinosaur (Vacuumus Nixis) who never used anything but a full mechanical advance distributor in ANY hot rod.

Originally posted by Henry Rifle
Here's something I discovered after quite a bit of research on Chevy crate motors over the last few days. I posted part of it on another thread.

It seems that the vacuum can Chevy supplies with the crate motors has too much advance (20 deg.) and the spring is way too soft. That brings the advance in too quickly. It's easy to get 52 -56 degrees in some situations. At the same time, the newer, more efficient heads (like the Fast Burn) don't like a lot of timing.

Many of the folks reporting good results with these motors either disconnect the vacuum advance, which has an effect on idle, engine heating and gas mileage, or they get a replacement vacuum can (either fixed or adjustable) with 10 degrees or less and a stiffer spring.

Of course, after that, they still have the debate about manifold or ported vacuum.

On my new crate motor, I'm taking this approach:

- I ordered a vacuum can recommended by Sallee Chevrolet's performance department - PN 1973681

- Install the new vacuum can, tune the motor, set the timing, then see what happens on the tach (idle), temp gauge, fuel gauge and the "seat-of-the-pants power gauge" with both ported and manifold vacuum.

- Disconnect the vacuum can, then take a look at the same four gauges.

Experimenting. Isn't that what hot rodding is all about?

Here's my guess on the results:

I didn't believe I'd ever say this, but . . . new vacuum can connected to manifold vacuum. (Don't have a heart attack on me, Denny)

Bear in mind that this is coming from a dinosaur (Vacuumus Nixis) who never used anything but a full mechanical advance distributor in ANY hot rod.

Very interesting Henry.
Especially about the fast burn heads.

Does the new vacuum can have an adjustable advance?

(I'm sure you know, but adjustable vacuum cans can be ID'd by looking inside the hose bib.
If you see a slot headed screw in there, it's adjustable.)

I believe Accel makes an adjustable vac adv can.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

"Experimenting. Isn't that what hot rodding is all about?"

Yes indeed. Seems there's a lot of cars running around out there that haven't come as close to their potential as I think they could.

Hard to tell sometimes when you're running a lightweight car with a strong engine, but once you get the timing and jetting right on it's a whole other world.

Just getting it running is not enough....

Does the new vacuum can have an adjustable advance?

C9,

No, it does not, but it's cheap, and the performance guys at Sallee Chevrolet have tested it pretty thoroughly. If that doesn't work, I may get a Crane Adjustable.

Right now, I just want to get the dang car painted, wired and on the road.

I hate bodywork . . .

Oh, and you're right. When you've got a 2400 lb car with a fairly radical big block, the difference between 400 and 450 hp is pretty hard to feel - particularly on street tires.

Denny,

I used to take my mechanical distributors to a guy like you, and tell him to "make it run with this combination." I gave him ALL of the car specs from engine setup to weight to gearing, etc. I didn't have to experiment too much because Charley Sussman at Charley's Speed and Machine in Blair, NE set 'em up right every time. Old Charley's passed, but he was a hell of a hot rodder.

One other good thing about setting up a dis. or recurving is it seems to slow chain stretch. Something, at least fords do.