Learn me on some timing
Originally Posted by DirtyJohn
Excellent analogy. Thanks!
Do we want to throw cylinder temperature vs. RPM into the mix and see how that effects timing/knock aswell?
I think heat plays a big part in knock/preignition, so I'm guessing you have to find a happy medium between enough advance in the upper RPM's to get the spark at just the right time, while avoiding preignition from the higher temps due to higher revs?
Do we want to throw cylinder temperature vs. RPM into the mix and see how that effects timing/knock aswell?
I think heat plays a big part in knock/preignition, so I'm guessing you have to find a happy medium between enough advance in the upper RPM's to get the spark at just the right time, while avoiding preignition from the higher temps due to higher revs?
Originally Posted by SSpdDmon
...Rather the time from when the PCM commands the spark, the plug fires (which is virtually instantaneously), and the time the mixture takes to burn. Electricity moves a lot faster than the burn rate of the mixture in the cylinders....
Google for "spark advance crank angle burn"
turns up some nice material.
http://omni.cc.purdue.edu/~tlrobert/...nd%20knock.ppt
turns up some nice material.
http://omni.cc.purdue.edu/~tlrobert/...nd%20knock.ppt
Originally Posted by jimmyblue
Google for "spark advance crank angle burn"
turns up some nice material.
http://omni.cc.purdue.edu/~tlrobert/...nd%20knock.ppt
turns up some nice material.
http://omni.cc.purdue.edu/~tlrobert/...nd%20knock.ppt
Thread Starter
Joined: Jun 2004
Posts: 5,125
Likes: 4
From: Alexandria, VA
I'm sure that link tells the whole story, but the fact that I suck at physics and have never tuned anything prevents me from understanding 90% of those terms and equations. I already did google on timing/knock/kr/etc but wanted it explained from the LS1's point of view, but not necessarily biased towards it. I'm not quite sure how to say that. I was basically asking how our cars like timing, what causes knock, and how you figure out the timing you need, but then to generalize it. Brad and others have done a good job thus far on enlightening me. I'll take as much info as I can though.
Do you think spark plug indexing can play a crucial role in allowing you to run more timing with the heads available for our cars? Or would that be a minimal factor that should only be considered in all out race apps?
Do you think spark plug indexing can play a crucial role in allowing you to run more timing with the heads available for our cars? Or would that be a minimal factor that should only be considered in all out race apps?
Originally Posted by ArcticZ28
Do you think spark plug indexing can play a crucial role in allowing you to run more timing with the heads available for our cars? Or would that be a minimal factor that should only be considered in all out race apps?
The general idea is to adjust timing so that you get knock and then back off a degree or 2, that will put your cylinder combustion right about at TDC. If it knocks you know that it combusted before dead center, when you back off till it doesnt knock you are damn close to TDC combustion.
Thread Starter
Joined: Jun 2004
Posts: 5,125
Likes: 4
From: Alexandria, VA
So is it fair to say you want to run the most amount of timing possible for the most power, or the least amount of timing possible for the most power. Say, you get knock at 30, back it off to 28 and get 430 peak hp then back it off to 26 and get 429 peak hp. Would it be better to run at the higher timing or the lower timing, or does it not matter (or just not work that way)?
run as little timing as possible for power, if you make the same power at 26* as you do at 30*, there's no since in runnin extra, head design, cam design and fueling also play and a part in timin needs of an engine, a real shitty set up make take 32* of timing for power, but a well thought out setup may only need 24* to make the same power
LS1 Tech Stories
The Best V8 Stories One Small Block at Time
6 Common C5 Corvette Failures and What's Involved In Repairing Them
Pouria Savadkouei
Retro Modern Bandit Pontiac Trans AM Comes With Burt Reynolds' Autograph
Verdad Gallardo
Top 10 Greatest Cadillac V Series Performance Models Ever, Ranked
Pouria Savadkouei
Top 10 Most Powerful Chevy Trucks Ever Made!
Hennessey's New Supercharged Silverado ZR2 Has 700 HP
Verdad Gallardo
Coachbuilt N2A Anteros Is an LS2-Powered C6 Corvette In Italian Clothes
Verdad Gallardo
Awesome K5 Blazer Restomod Comes With C7 Corvette Power
Verdad Gallardo
10 Camaros You Should Never Buy
10 LS Engine Myths That Refuse to Die
Verdad Gallardo
Originally Posted by oange ss
run as little timing as possible for power, if you make the same power at 26* as you do at 30*, there's no since in runnin extra, head design, cam design and fueling also play and a part in timin needs of an engine, a real shitty set up make take 32* of timing for power, but a well thought out setup may only need 24* to make the same power
i agree Thread Starter
Joined: Jun 2004
Posts: 5,125
Likes: 4
From: Alexandria, VA
Can you explain the reasoning behind that running less timing when possible? Is it just to stave off possible knock? B/c from what I understand, if it's making the same power at both 26 and say 30 degrees, then that would say to me that the same forces are acting on the pistons at both setups and that neither one is necessarily better or worse. So, I don't understand why less timing is better.
Originally Posted by ArcticZ28
Can you explain the reasoning behind that running less timing when possible? Is it just to stave off possible knock? B/c from what I understand, if it's making the same power at both 26 and say 30 degrees, then that would say to me that the same forces are acting on the pistons at both setups and that neither one is necessarily better or worse. So, I don't understand why less timing is better.
Originally Posted by ArcticZ28
I understand the advance a bit more now, but am I wrong in thinking that retarding the timing allows for more compression of the mixture making it more vulnerable to being spontaneously combusted or is that just totally wrong?
Originally Posted by ArcticZ28
Can you explain the reasoning behind that running less timing when possible? Is it just to stave off possible knock? B/c from what I understand, if it's making the same power at both 26 and say 30 degrees, then that would say to me that the same forces are acting on the pistons at both setups and that neither one is necessarily better or worse. So, I don't understand why less timing is better.
Originally Posted by SSpdDmon
To get the most out of your motor, you ideally want to find the point where you can run the most timing and fuel while making the most power. Just because you see knock retard doesn't mean the motor can't take more timing. You first need to increase the amount of fuel delivered and check to see (on a dyno) if it makes a little more power and the KR goes away. There's a specific term for this, but I can't remember it off the top of my head. I must be losing it...
TECH Resident
iTrader: (3)
Joined: Nov 2001
Posts: 979
Likes: 0
From: Richmond, VA Where fast cars, well......are hard to come by.
Just to clarify, detonation is too much advance causing the burning force to hit the piston before it passes TDC, and pre-ignition is basically the mix lighting on it's own before the plug fires due to heat/pressure? So changing timing wouldn't affect pre-ignition (unless it was advanced so far it happened before the mix lights itself), and all you can do is add fuel/octane or reduce pressure/heat? And reducing timing or adding fuel/octane should help in fighting detonation?
Colder range plugs will definitely help with preignition. One problem with that is the colder ones all are made to have smaller gaps, and you can't adjust them beyond a certain range, probably not more than .050 (which works fine though).
Thread Starter
Joined: Jun 2004
Posts: 5,125
Likes: 4
From: Alexandria, VA
I have tried it, but at the same time it was my first time on cam install a while back, so the motor only lasted about 10 miles before a valve embedded itself in a piston 
I fubar'ed that one up pretty bad, so no results yet.
I fubar'ed that one up pretty bad, so no results yet. 