I want to make sure I have a firm grasp on all this timing stuff before I order my new cams and cam gears. First, could someone tell me whether the following statement is correct:

Advancing ignition timing is moving the spark further into the compression stroke. Retarding ignition timing is moving the spark farther back in time, sparking earlier in the compression stroke. Do I have that right?

My first question is with respect to cam timing. A cam gear allows you to change the cam timing .. but when you change the cam timing, you're leaving the ignition timing the same relative to the compression cycles, right? If your ignition was at 14deg, say, it will still be at 14deg, you're just adjusting when the valves are opened with respect to that?

When you adjust cam timing, what are the benefits to advancing/retarding? I assume one is better for top-end and one is better for bottom-end?

What is the stock ignition & cam timing on a D16Y8?

When I add a more aggressive aftermarket cam, is it best to advance or retard spark timing, or just leave it?

If I were to step up to a higher octane gas, would that allow me to run slightly more advanced ignition timing, and make a bit more power?

Know that's a lot of questions. Thanks.

 

no. timing is based on BTDC, but actual ignition and fuel burn happens AFTER TDC otherwise you have the pistons being forced down on the upstroke. advancing the ignition timing sets the ignition to spark when the piston is closer to TDC, immediately after TDC. retarding sets the ignition to spark later than stock, when the piston has passed TDC and is further on it's downstroke than stock. basically can be summed up as "dynamic compression", as the static compression is the same, but by retarding the ignition, the compression is less than at TDC where static compression is measured as the piston has gone further beyond TDC before ignition compared to stock. advancing slightly raises compression as the piston is closer to TDC at ignition, thusresulting in more squish at ignition... but of course no matter how much advance you have, you can never exceed static compression.

that is correct to a point. you're more or less changing valve timing in comparison to the crank's angle/piston position during it's revolution. only valve timing is changed, to either open your valves earlier (advance) or later (retard). think about this in your head. one piston goes up and down...
step 1. ignition occurred, piston begins downward draw.
step 2. after BDC, the piston moves upward, and the cam opens the exhaust valve while the piston pushes exhaust gas out.
step 3. upon TDC, the intake valves begin to open, the exhaust valves are almost closed. this is called OVERLAP. as the piston hits TDC, having the intake valves open up assists in blowing exhaust gas out, giving you a less residual exhaust gas trapped into the fuel mix. adjusting for advance on the cam gear will obviously open the intake valves slightly sooner. the longer the intake valve is open, the more draw you get when the piston starts it's downward stroke.
step4. piston hits BDC as the intake valves close.
step5. piston goes on upward stroke as all valves are now closed, and combustion happens near TDC and repeats at step 1.

advancing the cam will open all valves sooner on an SOHC motor. if timed properly, you'll get the most efficient draw of intake air combined with optimum timing for exhaust valves opening to push all of the burnt gases out.

refer to www.howstuffworks.com if you cannot visualize all of this.

dont know offhand

leave it until you can tune it on a dyno. only a dynamometer can tell you if what you're doing is producing any useable power, or if you're even losing power.

the gas alone wont really make more power, but if the degree of advance combined results in significantly increased compression, it could result in detonation. this is where higher octane gas will burn more controlled, preventing detonation, and allowing you to safely run with the timing advanced, which is bringing you more power.

 

Thanks a lot man.. I appreciate all the answers. More...

How does retarding ignition timing help to reduce detonation? Logically, you would think that if the mixture is going to detonate, it would do so at the point of greatest compression (exact TDC) .. so why does moving the spark later after TDC reduce detonation?

Regarding the valve timing: Understaning that since it's a SOHC, and I can't change the intake/exhaust timing relative to eachother, what would be the effects of advancing or retarding valve timing? I understand what you were saying about the benefits of opening the intake valves earlier .. however that also means you're closing them earlier, and opening the exhaust valves earlier too. What overall effect does this have versus opening everything later? I understand that a dyno is really the only way to properly tell, but are there any general rules of thumb?

 

right now on my Y8 i have a crower stage 1 cam advanced 8' crank. you basically move your torque curve when you advance/retard your cam timing. i advanced my cam simply because i have a 4-2-1 header, which is more for low-mid range, if i had 4-1 then i would have either left it at 0 or maybe retard it 4' crank. BTW when vtec kicks in it will scream, not bad or anything sounds awesome but just giving you a heads up...lol

at 5500 at WOT when vtec kicks in people say it sounds like im redlining

 

When you say 4' or 8' crank, you mean advanced or retarded 4 or 8 degrees with respect to the crank angle, right?

So if you advance your cam timing, you're moving your torque curve more into the low end, and if you retard it, more into the high end? Is that right, or do I have it backwards?

So stock cam timing for the Y8 is 0', then?

 

Stock Y8 ignition timing is 12degrees +/- 2

 

So stock ignition timing is 12 degrees AFTER TDC, and you can advance it to 10 degrees, or retard it to 14 degrees. Do I have that right now?

 

spark ALWAYS happens after TDC. when you set your ignition to 12 degrees before top dead center, by the time fuel ignites, the piston has passed TDC. i stated that in my post.

if you retard the spark, the piston has moved away from TDC... therefore being less compression on the mixture compared to when the piston is at TDC. if you have less compression, you have less chance of detonation. when air is compressed, it heats up due to friction in the air molecules. if you over compress it, it will auto-ignite. this is how a diesel engine works... they have no spark plugs as they rely on auto-ignition for combustion.

so, if there's less compression due to the location of the piston during ignition, then your octane requirement is lowered. advancing your ignition increases your chances of pre-ignition, so octane levels must be higher to control the combustibility of the mixture as it's compressed.

for single cam motors, advance for more power. retard if you're retarded or boosting.

 

Thanks .. I'm still not totally getting it though... or not communicating it well enough. Lemme try it this way .. you said:

You said the spark always happens AFTER TDC, but in the next sentence you said you set it to 12deg BEFORE TDC. That's what's sorta confusing me. Are you saying that the physical spark occurs BEFORE TDC, but that the mixture doesn't fully ignite until AFTER TDC? What am I missing?

I totally get this .. my question was just the following: whether the spark happens at 12 or 14 degrees AFTER TDC, you're still PASSED TDC. If the mixture were going to detonate, wouldn't it detonate at EXACTLY TDC, where compression is the greatest? I don't understand why a mixture would detonate at 13' after TDC, for example, but not have detonated at exactly TDC? Think of it this way .. (1) you start before TDC. Compression is low. (2) You move on to TDC, and compression increases. (3) You hit TDC, and move away, and compression starts to DECREASE again. And NOW it detonates? Why didn't it detonate at TDC? Does that make any sense?

 

ignition timing is based at the degree stated before top dead center. actual combustion happens a few degrees later. in a normally functioning engine, true combustion happens afer TDC, even when the igntion is set to a timing before TDC. you're not missing.

like i said in my first post... if ignition and combustion happened before TDC, that means the piston is trying to go up, while the combustion causes downward force... the crank wouldnt revolve... it would go up counterclockwise, then be pushed back down clockwise, resulting in no crank revolutions and extreme rod stress.



compression is not always the catalyst for detonation. spark is usually the catalyst for detonation... but it comes at the wrong time, or the charge burns too quickly to controlled, or just plain explodes uncontrollably.

so at TDC, there's still not enough compression to detonate, but wen a catalyst is introduced, like a spark, the mixture is still more volatile than a proper charge, resulting in uncontrolled burn, higher temps, and destruction of internal parts.