Advancing timing???

[bluelancer200283]

Im new to tune ecus and such and i was wondering the more you advance timing the higher octane is needed???? B/c my car is tuned for 87 but I want to tune for 93.

[Accord2nrz]

Not necessarily it depends on your overall tune and what your VE is. If i understand your question right think of it like it. Your using a new chemical that has more potential for creating energy with each spark event. With more energy created per spark the pistons are going to travel down ward at faster rate causing another cylinder to compress at a faster rate as well. Without advancing your timing you are running the risk of pre-ignition as your creating a spark ahead of the piston being at its optimal position to transfer the energy from that spark event to the crankshaft.

Care to confirm tguy? Im not sure if i understood the question right.

[Turbineguy]

Timing can be advanced up to just short of the detonation threshold for your particular engine and setup. Different engines have different detonation properties. Octane rating on fuel is the fuels resistance to detonation and also the fuels burn rate. Higher octane will be more detonation resistant and will also have slower flame front propagation thus allowing more timing to be run with the associated power gains. If you are tuned on 87 and then go to 93 you may be able to advance the timing only a few degrees or quite a bit. The best way to determine this is with a knock light and small adjustments to the advance. If it's a distributor type ignition then the advance will be across the board and you are limited to the timing you can run at the highest VE point which is usually where the engine is most knock sensitive. If you have the ability to change the timing based on RPM, load, and throttle position then you have alot more options as far as when and where to advance or retard it. It's usually a good idea to leave some headroom between the actual timing and the detonation threshold to allow for various atmospheric conditions, heatsoak, and fluctuations in fuel quality.

The short answer is that 93 will allow more advance over 87.

[bluelancer200283]

thanks for the help so basicly get knocklite, run 93, adjust timing a lil at the time, and then back it up a lil to run it safely. i understanding what both you are saying. I just wanna make sure the way to go about doing this b/c this is my only ride and i want a lil more power but i want the power in a safe range. Accord2nrz I got the 1g eclipse 60mm tb i needed for my car.:)

[Dzaster]

And doesn't lowered compression ratio also have its role in the detonation threshold?

I realize that bluelancer may not have lowered compression, but I raise the question just to cover a little more ground on the "timing and detonation" topic.

[Accord2nrz]

Lowering the compression has it's role in lowering the detonation threshold becuase your increasing the amount of empty space in the firing chamber. Without increasing the amount of airflow your chances of detonating decrease I think. However you definitely need to adjust your timing. after doing such a thing. tguy can definetly elab on this one.

[bluelancer200283]

i havnt lowered comp and go question about that too. I know my stock comp is 9:5.

[bluesnowgt]

ooooooooh good question ......that kinda worries me now.... i was thinking about getting some 11:1 pistons and i didnt think i had to adjust my timing... i have found some 272/272 cams to go along with it also. wat would happen if i installed them and not touch timing?:confused:

[Accord2nrz]

Throwing in a cam is going to seriously throw your entire curve off. If you don't have much knowledge into cam theory I would seriously send it off to have your ecu reflashed for the cam. Without messing with the timing and air/fuel curves your car would run like crap.

[bluelancer200283]

i thought that would change a lot if you added a cam but i wasnt sure. I looked into it about my car and all i saw was "rough idle" lol. Im glad i know now. Blues I might need a lil help here soon. I dont have the tools to do my entire tb swap myself and i was wondering if you could help?

[Accord2nrz]

ask the company if it's safe for a stock ecu aside from the rough idle. and get it in writing that way if something happens you can hold them liable.

[Turbineguy]

i havnt lowered comp and go question about that too. I know my stock comp is 9:5.

Unless you plan on doing a rebuild that will be forced induction specific lowering the CR on an NA engine will have some pretty negative effects on power and throttle response.

ooooooooh good question ......that kinda worries me now.... i was thinking about getting some 11:1 pistons and i didnt think i had to adjust my timing... i have found some 272/272 cams to go along with it also. wat would happen if i installed them and not touch timing?:confused:

If you have an iron block and heads this will require you to run higher octane than you can get from a pump (i.e. racegas). Typically you can run half to a full point higher on CR with aluminum heads due to the thermal transfer properties of aluminum versus iron. For iron heads you need to stick to no more than about 9.5 or so. You can run 10:1 on pump but you'll have to be careful with timing. However this may not directly translate into an FI setup since the CR will be based on how much boost is planned. Regardless of the boost level CR is almost always lower on a purpose built FI engine than an NA.

And doesn't lowered compression ratio also have its role in the detonation threshold?

I realize that bluelancer may not have lowered compression, but I raise the question just to cover a little more ground on the "timing and detonation" topic.

Lower CR will have a positive effect on the detonation properties but create other issues. As the cylinder charge is compresses it heats up and if CR is too high it will ignite on it's own without a spark. This is how a diesel works. Where the timing is set determines when the charge is ignited. The charge is ignited at some point prior to TDC to allow time for flame front propagation and develop maximum cylinder pressure for the power stroke. If the timing is advanced too much and the charge is ignited the pressure begins to build too high from a combination of charge expansion and the piston still on the compression stroke on the way up. This can cause pockets of unburned fuel air charge to ignite ahead of the flame front. The result is very high spikes in cylinder pressure that are unevenly distributed as well as pressure waves that collide from different directions. This will cause piston slap from rocking in the bore, very high stresses on the piston crown and rods, holes in the tops of pistons, broken ringlands, valve damage, and various other possibilities.