förtändnig

[Lars-Henrik]

hej jag har en ny 355á jag undrar vad jag skall ställa tändningen på för grader hur har ni det??

m.v.h henke

[GETWET]

hej jag har en ny 355á jag undrar vad jag skall ställa tändningen på för grader hur har ni det??

m.v.h henke

Uj, svårsvarat men det brukar röra sig om 8-12 grader vid ca 800-1000varv.
Börja där någonstans och se om det går bra.

[Lars-Henrik]

tackar skall prova att skälla upp den till 12 grader nu i helgen.Skall jag ta bort mitt vacum till min fördelare när jag gör detta???? ??....Hade lite förgasarsmällar nu när den stog på 8 grader

m.v.h henke

[jompa]

hej jag har en ny 355á jag undrar vad jag skall ställa tändningen på för grader hur har ni det??

m.v.h henke

Hoppas du kan engelska bra, för denna text av Norrmannen Lars som bor i Denver beskriver en hel del. Ett bra grej att ha är en stroboscopelampa med gradinställning, så att du kan ställa t.ex. 36 grader på lampan och sedan titta efter 0-linjen.


How to Set the Timing

When you think about it, setting the timing at idle speed makes no sense at all: You don't operate your car at idle, and timing changes as the rpm changes. Fact is, the timing spec at idle speed is provided as a simple way for most people to set the timing, and is not a good procedure for optimum performance.

Small block Chevys (and most other GM performance V8 engines) perform best when the total timing (full centrifugal advance plus the initial timing setting with vacuum advance disconnected) is all in by 2,500 - 2,800 rpm and is set to 36 - 38 degrees. If you have an adjustable timing light, this is very easy to check. If you don't, you need to scribe a 36-degree mark on your harmonic balancer. Here's how:

Measure the circumference of your harmonic balancer using a sewing tape measure (or other flexible tape measure). Get it as accurate as you can. Take this measurement and divide by 10. The number you get is the distance to 36 degrees. Measure this distance CLOCKWISE from your existing harmonic balancer timing mark and place a clear mark on the balancer.

Remove your distributor cap and rotor.

Remove the 2 centrifugal advance springs.

Install the rotor and the cap (without the springs). Disconnect the vacuum advance.

Start the engine. It may kick back a little due to the advance coming in immediately without the springs. If you're using an adjustable timing light, set the light to 36 degrees advanced. Now rev the engine just a little while observing the timing marks with the light. It shouldn't take much rpm to peg out the advance without the springs installed. With an adjustable light set at 36 degrees, align the stock timing marks with "0" when the timing is "pegged out." With the non-adjustable light, align your new 36-degree mark with "0." Rev the engine a little to make sure the timing will not advance any further. Shut it down.

Pop the cap and rotor and re-install the springs. Put everything back together, but leave the vacuum disconnected. Start it up. For future reference, make a note of the timing setting at idle. This is your new curb idle timing spec. Now give the engine a few quick rev's past 3,000 rpm and verify that the full timing (36 degrees) is coming in. If it's not, you need to change to a softer set of springs until you get full 36-degree advance before 3000 rpm. (NOTE: A stock set of springs will usually not allow full centrifugal advance to come in before redline rpm. If you have stock springs installed, don't rev the engine beyond its limits to try to force full advance in.)

Shut it down and hook up the vacuum. Now do a road test.

The 36-degree 2500 rpm advance curve is optimum for performance, but may require premium fuel. Lug the car around, and punch the throttle at low rpm while listening for detonation ("engine knock"). If you're getting any audible knock, you MUST retard the timing. Retard the timing in 2-degree increments until engine knock stops. Engine knock will seriously damage engine components if not corrected. If you get no knock, you may see slightly improved performance at 38 degrees total timing. This is particularly true if you're running at high altitude.

If you have no engine knock under acceleration, but the car "chugs" or "jerks" at cruising speed (light throttle application), you are getting too much vacuum advance on top of the mechanical advance. You may need to change out the vacuum advance diaphragm with an adjustable unit available from aftermarket sources. Adjust these units so that you get the most vacuum advance possible without any "chugging" or "jerking" at cruise speed.

Your timing is now set for best possible performance. Make note of the new setting, and use this for your future tune-up work.

Ytterligare en text från honom:

Most GM V8s, including small block and big block Chevys, will produce peak torque (and power) when the TOTAL mechanical timing (full centrifugal timing is slammed all the way in without the vacuum advance contributing) is at or about 36 degrees at 2500-or-so rpm. The 36-degree spec is a general spec that is a good starting point to do some final fine-tuning from: you can optimize it in one of two ways:

1. If you have access to a track or to a performance computer (G-Tech or Vericom, etc.), starting from the 36-degree total spec, advance or retard timing in 2-degree increments until trap speed (speed at end of a fixed distance) is maximized. You will find in virtually all cases that trap speed will be maximized when the TOTAL timing is set somewhere between 34-38 degrees. The new "fast-burn" style heads require less total timing. Higher elevations require more total timing.

2. You can advance your timing until you just barely get audible detonation ("engine knock") while lugging the car under load and wide open throttle. I usually check for this by putting the car in 2nd gear at about 1500 rpm and flooring it up through about 3500 rpm. If any audible detonation occurs (which sounds like putting a bunch of marbles in a blender), retard the timing in 2-degree increments until all detonation stops. Likewise, if there is no detonation under this test, you can advance the timing in 2-degree increments until you hit detonation, then back off 2 degrees. This procedure is commonly known as "power timing." You are setting up the timing to produce the maximum amount of cylinder pressure that your engine/fuel will support.

A critical note on power timing, however: Power timing only works if you use the grade (octane) of fuel that is recommended for your engine. If you use high-octane fuel in a low-compression engine, detonation will be fully suppressed, and you will obtain an over-advanced ignition condition before you ever hit detonation. The over-advanced condition will result in a power loss. If you are doing the power timing method, always check to see what total timing spec you end up with: if you end up with much more than 38 degrees total timing, I would question the validity of the spec you ended up with...
Finally, there are two terms relating to "engine knocking" that are commonly interchanged. Pre-ignition and detonation.

Pre-ignition occurs when the air/fuel mixture in the cylinder ignites before the spark plug lights the mixture. It can be caused by hot-spots in the cylinders, or by high volatility of the fuel causing the fuel to explode from engine compression prior to spark plug ignition. The early ignition of the fuel causes excessive cylinder pressures and temperatures before the piston hits top center.
Detonation occurs when the fuel is ignited by the spark plug, but instead of the fuel burning at a nice, steady pace across the combustion chamber and across the face of the piston (fuel, when buring properly, does not "explode" - it burns at a steady, although very rapid, pace from one side of the combustion chamber to the other, this producing a predictable steady "push" on the top of the piston), the fuel suddenly explodes all at once. This produces a massive and sudden impact on the top of the piston, much like hitting the piston with a sledge hammer instead of pushing the piston with a steady force.

Both pre-ignition and detonation are audible as a "rattling sound" in the engine, as if the engine were full of marbles. Both pre-ignition and detonation cause a masive power loss, since the fuel is not being burned properly in the engine. And both pre-ignition and detonation can cause massive engine damage due to melting and errosion of the tops of the pistons, and impact damage to wrist pins and rod bearings. Higher octane fuel has a resistance to detonation. High octane fuel will not solve a pre-ignition problem caused by hot or glowing points in the cylinder. High-octane fuel does not have any more energy than low-octane fuel. However, high-octane fuel can allow you to produce more power by eliminating the power-robbing symptoms of detonation and by allowing you to set your timing for 36 degrees total without getting into detonation. If you can obtain the 36-or-so degree total spec without detonation on low-octane fuel, you will not gain more power by using high-octane.
I know, I'm rambling off subject now... I better quit.
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