setting timing question

[grumpyvette]

"I am trying to figure out the best way to set up my ignition timing and posted a question there, where someone else was asking about BBC timing too. I understand the manifold vacuum to the distributor advance, but what should the settings be? Right now, I have 12 initial, 24 mechanical, and 14 vacuum advance. So at idle I have 26, and I was concerned that was too high. Any advice you can give me? Get an adjustable vacuum advance and lower the amount to, say, 10?"
watch video
http://www.youtube.com/watch?v=UYGU7mTw ... r_embedded

Ok lets start with the basics, you need to verify the TOP DEAD CENTER on the damper is correct and the timing tabs correctly located.
you don,t really care where the timing IS as long as its correct and you don,t get into detonation which will damage the engine.
ideally your take the distributor to a decent ignition specialty shop to have it curved, ideally youll want the ignition to be someplace in the 8-12 degrees advanced at idle speed (800rpm-1000rpm, )Im most cases,and smoothly advance to about 35-37 degrees total advance at about 3200rpm, ignition spark should be bright blue and impressive, if its, weak,narrow, yellow or red theres a problem so research the cause, verify the coil and voltage

the following linked info will help, and yes reading thru the sub-linked info is very useful

http://www.gmhightechperformance.com/te ... index.html

http://www.youtube.com/watch?v=YdIGZ-tV ... re=related

viewtopic.php?f=70&t=1135

viewtopic.php?f=70&t=875

viewtopic.php?f=70&t=232

viewtopic.php?f=70&t=1015

viewtopic.php?f=70&t=967

viewtopic.php?f=70&t=232&p=277#p277

http://www.centuryperformance.com/ignit ... g-219.html

viewtopic.php?f=70&t=1809

watch the video

http://www.youtube.com/watch?v=YdIGZ-tV ... re=related

short answer
once your TDC is correct and youve installed the correct timing tape, you bring the engine rpms up to 3200rpm on the tach and set the timing at about 36 degrees advanced, them drop it back down to idle and see where you are at idle speed, this virtually eliminates alot of calculating and mistakes that get introduced if your trying to set the ignition timing advance from the timing at idle.
obviously an LT1 regulates its own ignition timing and uses knock sensor, and programmable CPU input and the crank sensor unlike the L98 with it HEI but both system need you to check /verify they are operating correctly.

link to more info on finding TDC and seating a distributor
http://forum.grumpysperformance.com/viewtopic.php?f=70&t=967

links may help

http://garage.grumpysperformance.com/index.php?threads/finding-top-dead-center.967/

http://garage.grumpysperformance.com/index.php?threads/timing-tabs-and-indicators.1015/

http://garage.grumpysperformance.co...ying-your-real-advance-curve.4683/#post-12672

http://garage.grumpysperformance.com/index.php?threads/shiming-a-distributor.251/

http://garage.grumpysperformance.co...ouble-shooting-rebuilding-hei-ignitions.2798/

http://garage.grumpysperformance.com/index.php?threads/distrib-won-t-seat-correctly.9231/

step one, pull the #1 plug and place the tip of your finger over the plug hole and rotate the engine until you feel COMPRESSION build as the number one cylinder, piston starts its compression stroke as the mark on the damper gets close to the timing tab, then remove your finger and continue turning the engine until the timing line on the damper aligns with the timing tab (0) TDC
once thats done the engine should not rotate any more until the distributor is seated correctly.
once thats lined up you drop the distributor into the engine so the rotor on the distributor points at the #1 cylinder when it seats and you install and lightly tighten the clamp and connect the wires, connect the timing light and set the timing at about 6-8 degrees BTDC at idle as a start point., if the distributor won,t fully seat the oil pump drive shaft needs to be turned a few degrees with a long large flat blade screw driver and re-try seating it while, it might take several tries until it lines up, it will seat into the distributor base gear once the oil pump drive aligns with the oil pump slot in the distributor gear base

 

[myraley]

Thanks!

 

[myraley]

Sorry - another question. Since I have an aftermarket distributor, my settings are 12 BTDC initial, 24 mechanical from 1000 rpm to 3200 rpm, and 14 vacuum advance connected to manifold vacuum. But I read that the original distributors - the HEI - had 20 mechanical and 22 vacuum advance. Should I change my initial timing back to stock (8 BTDC) and put an HEI (which I have lying around) back in with the 20 mechanical and 22 vacuum advance? And if I did, should I then run manifold or ported vacuum to the HEI distributor (in other words, were the HEI only designed to run ported vacuum to the vacuum advance, and those settings wont work for manifold vacuum)?
Thanks!
Eric

 

[grumpyvette]

When your dealing with ignition timing its always critical to verify your working with the correct reference points first.
stock timing marks are very limited in the extent of timing changes that can be indicated

obviously you need to have a consistent base line advance curve to work with,
on most Chevy v8 engines that run cams designed for street/strip use Ive generally found a advance that goes from about 8 degrees at idle speed (800-900rpm in most cases) and smoothly advances the ignition to about 36 degrees or about 28 degrees advance from where it started at to reach 36 degrees at about 3200rpm , is generally a good place to start, or about 82 rpm increase per degree of ignition advance , up to about 3200rpm, where increase turbulence and squish tends to speed the burn process, you can then play with the engine and determine what changes MIGHT be require

standard vacuum connections

manifold to power brake booster
manifold to distrib vacuum advance
pvc to carb or air cleaner assembly

viewtopic.php?f=70&t=1809&p=4671#p4671

step one is always verify the damper and timing tab really do indicate TDC and its a very good idea to have two timing lights to check against each other, adding a timing tape
your ignition timing has a huge effect on the cylinder heat, total engine heat,oil and coolant temps,and the engines power curve and its tendency to detonate when it gets hot. get it too retarded and power drops, the exhaust tends to run very hot and plugs foul, get it to advanced, power falls off, detonation can destroy pistons and plugs look excessively hot.

to the damper or use of a factory marked damper

with the degrees clearly marked is a huge plus to getting the timing correct.

The timing advance set at idle is of very low importance, its the rate of advance and the total timing advance that can be far more critical to the engines durrability
Ive always found that verifying that total ignition advance is all in and stable by about 3200rpm in most cases was a good idea, so I set the timing at about 3200rpm at about 34-38 degrees full advance as a starting point then adjust it as necessary for each indicated application,and let it retard back to where ever it falls at isdle then take note as a reference point for later, but I continue to verify the full advance occasionally.
now if that falls at 6 or 8 or 12 degrees that's not super critical unless its causing a problem, (detonation, hard starting ETC)

the links in the thread above answer most questions

now I generally run manifold vacuum to the distributor and verify the advance curve falls within the engines needs by either taking the car to a shop with an oscilloscope or just watching the timing light on the damper as I play with setting the advance, like I said setting the timing at idle will get you close but KNOWING whats going on by watching the timing change on the damper with the timing light has more info than a semi random guess based on what you hopes correct by setting the timing only at idle.

theres also damper covers that are marked

read thru the links above for more info

BTW too much total ignition advance or to fast of an ignition advance curve tends to raise NOX & at times HC emissions in the exhaust

viewtopic.php?f=70&t=1015&p=1864#p1864


when your breaking in a new engine or cam, one common problem indicator is the headers running excessively hot

due to the effective delay in the ignition process because the ignition is not advancing to compensate for the lower time frame between ignition and the power stroke as the rpms increase as the rpms increase a greater percentage of the fuel/air mix thats being burn exits the exhaust still burning, greatly increasing the exhaust temps in the heads and exhaust manifolds


viewtopic.php?f=70&t=4683

viewtopic.php?f=70&t=1809

viewtopic.php?f=70&t=3438

viewtopic.php?f=57&t=4701
EXAMPLE

btw notice the front header tube seems to be a bit cooler and each header tube as you move to the rear looks a bit hotter, thats because the engine compartment air flow cools the headers less effectively as its heated as it moves from the radiator rear ward

the picture above is commonly the result of having Your ignition timing too retarded for the 2500rpm-3500rpm your supposed to be lapping a new cam in at for the first few minutes,or the ignition advance curve rpm is to slow with a light load. Under a light load combustion is a slower process. Some of the combustion is still taking place after the exhaust valve opens which will make the headers glow.
if your running a LEAN due to either jetting, tuning issues or a large vacuum leak....the overly lean fuel/air mix tends to raise the exhaust temps, obviously an IR temp gun can be very useful in spotting this condition early, but its even more useful because it can easily tell you if only one or two headers are running significantly hotter, usually indicating a vacuum leak or tuning issue rather than ignition timing where all the header tubes tend to run hot.
now obviously you should have verified the correct oil and coolant levels and verified your ignition timing and advance and firing order before starting it , or seeing the headers glow before letting the engine run very long

 

[myraley]

Thanks, then I am on track with the initial and the mechanical - they are right where you said. I guess my only confusion remaining is with the vacuum advance. It is currently 14 crankshaft degrees, and to change it requires changing to the crane adjustable vacuum advance or something similar. I know other people have said the vacuum advance should only be 8 degrees at the crank and not 14, but the original HEI was 20 or so. Is 14 ok or is it too much?

 

[grumpyvette]

http://garage.grumpysperformance.com/index.php?threads/timing-advance.3438/

http://garage.grumpysperformance.com/index.php?threads/shiming-a-distributor.251/#post-1366

Engine Firing Order

Firing Order is the order in which the ignition system will fire the spark plugs after the starting point of Top Dead Center for the No.#1 piston.

Distributor Rotation is the direction that the rotor (located underneath the distributor cap) will spin as the engine runs.
Firing Order
AMC Most V8
1-8-4-3-6-5-7-2
Distributor Rotation: Clockwise
Buick Most V8 except HEI
1-8-4-3-6-5-7-2
Distributor Rotation: Clockwise
Chevrolet Small Block V8 267, 305, 327, 350, 400
1-8-4-3-6-5-7-2
Distributor Rotation: Clockwise
Chevrolet Big Block V8 396-454
1-8-4-3-6-5-7-2
Distributor Rotation: Clockwise
Chrysler Small Block V8 273, 318, 340, 360 A
1-8-4-3-6-5-7-2
Distributor Rotation: Counter Clockwise
Chrysler Big Block V8 361, 383, 400, 413, 426W, 440, B/RB, 426 Hemi
1-8-4-3-6-5-7-2 (All Big Blocks and 426 Hemi)
Distributor Rotation: Counter Clockwise
Ford V8 260, 289, 302 (5.0L)
1-5-4-2-6-3-7-8 (289, 302 Non H.O.)
1-3-7-2-6-5-4-8 (5.0L H.O. (302), 351M, 351W, 400)
Distributor Rotation: Counter Clockwise
Oldsmobile
1-8-4-3-6-5-7-2 (V8s '67-up)
Distributor Rotation: Counter Clockwise
Plymouth V8 A Engine 277, 301, 303, 313, 318, 326
1-8-4-3-6-5-7-2
Distributor Rotation: Clockwise
Pontiac 265, 301, 307*, 326, 350, 389, 400, 421, 428, 455
1-8-4-3-6-5-7-2
Distributor Rotation: Counter Clockwise
*Distributor Rotation: Clockwise (307 V8)