|02-20-2006 07:57 PM|
Chevy 383 - I set my timing to give me a total advance of about 36* at about 2800 rpm. This is with vacuum disconnected, and using aftermarket distributor springs. Once I set total advance, I don't care were initial is.
I know I am getting some centrifugal advance at idle due to the softer springs, but it doesn't matter.
I then check what the maximum vacuum advance @what ". This is best done using an outside vacuum source - MitiVav is what I use. Check your engine vacuum at idle. For performance, vacuum can should bring in all vacuum advance about 2" less than idle vacuum. Total advance from the vacuum can only should be about 14* to give a total of about 50*. Don't believe me, check Vizards books.
With the right can, I hook the vacuum up to manifold vacuum. Initial advance on the timing light is in the 30+* range beause of the full 14* vacuum + the initial = the amount of centrifugal I am pulling in.
Engine is 10.25CR aluminum heads, CC XE274 cam, and runs on 89 octane gas without ping. May even run on 87, but I have no guts to try it.
No problem starting, as starting only sees initial timing + any little centrifugal it sees at cranking speed.
|02-18-2006 08:54 PM|
If you had your e/mail address accessable for others here on the board, I would have already sent info for you on the distributor.
If this is a crate 502 using a carb, and the STOCK CRATE HEI DISTRIBUTOR, then please contact me, I have 6 pics of how to make the stock dist work the right way.
If not, I can help you do it the right way, no mater the distributor type.
In the subject box for the e/mail, please use "pics, HEI redo". Disregard the spam filter message, when I send pics to you, e/mail won't be spam blocked again
|08-28-2003 12:59 PM|
You are using the 'full' vacuum port. This is why the timing and the idle RPM increases when you hook the hose back up and is normal. Just lower the idle speed with the stop screw on the carb throttle linkage to the RPM you want the engine to idle at. If you have an automatic trans, set the idle RPM with the trans in gear. The idle speed will be higher when the trans is in Park.
i.e. My vacuum line is also hooked to the full vacuum port. Idle in Park is 850 RPM. Idle in gear is just under 700 RPM.
Some will suggest that you hook the vacuum line to the 'ported' vacuum fitting. Try it. Then switch it to the full port and try it. Decide which one works best for your combo. What you are looking for is the best take off from a stop.
|08-28-2003 12:44 PM|
I set the initial timing at 16 and changed the springs in the dist. to give me a total timing of 34 degrees. now when I hooked the vacume adv. back up it bump up the timing a consider amount.
do I need to adjust the vacume adv. so that it does not pull that much out or what does it have to be so that I can set it corectly.
I'm learning how to do this so please be understanding.
|08-26-2003 08:03 AM|
Try setting your initial timing to 16-18 degrees with the vacuum advance line disconnected and plugged. After you have set the timing, hook the vacuum advance line back up.
|08-26-2003 07:40 AM|
when you set the timing to to 22 degrees did you have a hard cranking start or did it start easily?
I have the vacume adv hooked up to the frt of carb (which would be intake manifold). I use the the car for just street use but
occasionally use it for the strip.
|08-25-2003 05:01 PM|
|firstname.lastname@example.org||I've mentioned this in a few other threads and I got it originally from a thread on this board. Once you modify your engine, the book advance values are useless. The best way I have found to set initial timing on a modified engine (for lowest temp., highest power, no ping, etc.) is with a vacuum gauge. Disconnect your vacuum advance and attach a vacuum gauge to manifold vacuum. Then start and warm your engine and advance the timing @ idle until the vacuum is maximized. Back it down a couple of degrees of advance from this peak and you are set! If you get a little ping, back it down a degree at a time 'til the ping goes away. Works for me every time.|
|08-25-2003 04:41 PM|
AHA!!! DMMorris we do agree at last!!!
Increasing your initial timing can lower your operating temps. Experiment to see. Increase in 2 degree increments until you get 'ping' under a light to moderate load. Then back off two degrees.
And Yes, I discovered this when breaking in a cam in the past. I set the distibutor at a point where I knew the engine would start immediately. I then increased the RPM to about 2800 RPM and began to go over the engine looking for any leaks. After about ten minutes of run time I noticed the headers were glowing red at the junction of the individual pipes and the collector. The water temp was about 225. I almost panicked. Without lowering the RPM, I hooked up the timing light, dis-connected the vacuum hose and plugged it and set the timing to 36 degrees. It was about 22 degrees to start. Pipes immediately cooled down, water temp slowly went down to 185.
|08-25-2003 02:20 PM|
|08-25-2003 02:08 PM|
|Dave E Shank||I would like to chim in with a further question... my sbc 350 runs hot at idle in traffic, about 230 degrees. Local hot rod supplier is telling me the cure is to advance distributor until rattle and ping under load, back off a little and engine will run a lot cooler??? Have any of you seen this in action?. Right now I am running about 8 degrees BTDC. But this sounds so off the wall to me. Any comments would be appreciated.....THANKS....DAVE|
|08-25-2003 01:59 PM|
|08-25-2003 01:45 PM|
|Frisco||Unfortunately; while you and I are debating what 'Total Timing' is, BAD502 would like to know what and how to set up his timing. I have stated what I feel is the correct way to do it. What do you have as a suggestion for him?|
|08-25-2003 01:38 PM|
Well it looks to me like you just confirmed my statement and you even copied it for us. "This "can" also include your vacuum advance". As you even stated, depending on how your system is set up the vacuum advance plays a big role in your engines total advance. I, as well as many others, use ported vacuum as a source for my timing advance. My Ford has no problem handling as much advance as both vacuum+mechanical can provide. Depending on how you hook up your advance, full or ported, obviously as you stated affects the engines total timing under different load conditions. So again I say your original statement that " The vacuum advance is NOT added to these figures" you are incorrect. You even posted this yourself here...
|08-25-2003 01:24 PM|
What is Initial Timing and Total Timing?
Initial timing is that setting you make while your engine is idling with a timing light. This is typically between 4° ATDC (After Top Dead Center) to 16° BTDC (Before Top Dead Center). For performance applications "in most cases" you want as much initial timing as the starter can handle (the more timing the more cylinder pressure that the starter must overcome to crank the engine). Too much initial timing, besides the starter load, can also run the HC (Hydrocarbon) emission levels beyond legal or breathable levels <hint to the smog machine as a tuning tool above>.
Total timing is the calculation of the combined initial and mechanical advance timing settings (max). This "can" also include your vacuum advance though, I like to describe it as "total timing plus vacuum advance". Since vacuum advance is a nearly inconsistent value I like to use it after I have set up the correct mechanical values in the distributor. At times I must use the vacuum advance to generate the timing values I require, but I try to only use it as an "economy" tool to give a street driven vehicle more efficiency and throttle response by this addition.
There are two types of vacuum advance functions available:
One uses a PORTED vacuum source that as RPM increases, so does
the vacuum to the port .... this is a BAD connection in Racing, especially
since we typically retard our timing at the upper RPM levels. But it can be
used as a tuning tool so long as you do not exceed the MAX total timing
figure you need. In this case you will be using the vacuum advance as part
of your total timing.
The second uses FULL MANIFOLD vacuum, which is how I prefer to
use vacuum advance (street cars only). Some may disagree, but it works for
me! To do full manifold mandates an adjustable vacuum canister on the
distributor. The way this system works is when you smash the throttle and
vacuum levels go to atmospheric the vacuum advance is stopped. No ping, no
excess unneeded timing that is only good for street car efficiency anyway.
The above is from the article you linked to.
|08-25-2003 01:14 PM|
so your saying that I should leave the vac adv. hooked up
when I set the initial timing? Should I leave it at 15 deg.
or should I change it.
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