No Quarter
New Member
- Joined
- Oct 12, 2002
Could someone explain timing to me. What exactly it is and how it affects how the motor performs. Also how adding it and taking it can affect things.
This is going to soubd bad i know - timing question.
- Thread starter No Quarter
- Start date
Oh boy! That's a big question. Let me see if I can give you the basics.
Combustion is not an instantaneous process. After you ignite the air/fuel mixture, it takes a little bit of time for the combustion to happen. The goal of timing is to time the combustion so that it creates the highest pressure on the piston at the optimal time.
Envision the piston at exactly top dead center, not moving- the connecting rod is pointed directly up and down. Now, create enormous downward pressure on the piston. What will happen? Nothing- the piston won't move. You will just smash the bearing into the crankshaft (ouch!). That's kinda what happens if you fire too early.
Ideally, you'd like the highest cylinder pressure when the crankshaft is maybe 45-60 degrees from vertical. However this isn't really possible either- since the piston would be further down in the cylinder, you've lost a lot of the compression that helps improve combustion.
In the real world, generally speaking you want the spark as early as possible, without being so early that the combustion is pushing the piston down while the crankshaft is trying to push the piston up- this will cause knocking and severe damage. Rapidly worn bearings, broken pistons or rings, etc- it's just not good.
Now every car likes a slightly different timing curve- based on cam design, compression ratio, and a few more subtle things. A typical timing curve would be set up like this-
Idle timing- 15 degrees
Highway cruising (light load, a few thousand RPM) will be very high, like 40-50 degrees.
Wide-open Throttle- maybe 28-38 degrees (NA vs. boosted vs. nitrous etc. makes a big difference on this one.
If you don't have enough timing, you will lose a lot of power. If you have too much advance (i.e. start the spark too early), you will get knock and big-time engine damage.
It's a bigger topic than I've covered, but digest that and see what you think.
-Bob Cunningham
Combustion is not an instantaneous process. After you ignite the air/fuel mixture, it takes a little bit of time for the combustion to happen. The goal of timing is to time the combustion so that it creates the highest pressure on the piston at the optimal time.
Envision the piston at exactly top dead center, not moving- the connecting rod is pointed directly up and down. Now, create enormous downward pressure on the piston. What will happen? Nothing- the piston won't move. You will just smash the bearing into the crankshaft (ouch!). That's kinda what happens if you fire too early.
Ideally, you'd like the highest cylinder pressure when the crankshaft is maybe 45-60 degrees from vertical. However this isn't really possible either- since the piston would be further down in the cylinder, you've lost a lot of the compression that helps improve combustion.
In the real world, generally speaking you want the spark as early as possible, without being so early that the combustion is pushing the piston down while the crankshaft is trying to push the piston up- this will cause knocking and severe damage. Rapidly worn bearings, broken pistons or rings, etc- it's just not good.
Now every car likes a slightly different timing curve- based on cam design, compression ratio, and a few more subtle things. A typical timing curve would be set up like this-
Idle timing- 15 degrees
Highway cruising (light load, a few thousand RPM) will be very high, like 40-50 degrees.
Wide-open Throttle- maybe 28-38 degrees (NA vs. boosted vs. nitrous etc. makes a big difference on this one.
If you don't have enough timing, you will lose a lot of power. If you have too much advance (i.e. start the spark too early), you will get knock and big-time engine damage.
It's a bigger topic than I've covered, but digest that and see what you think.
-Bob Cunningham
No Quarter
New Member
- Joined
- Oct 12, 2002
I don't have a real concrete idea behind timing and I'm trying to get the timing curves smoothed out in the FAST. How should the timing corralate to boost?
No Quarter
New Member
- Joined
- Oct 12, 2002
These are the adjustments to make in the spark advance vs. RPM vs. MAP - are there any other spark controls to be set? Such as a base or curve setting?
I'm still getting familiar with the FAST. Someone should wrtie a FAST System 4 Dummies publication
I'm still getting familiar with the FAST. Someone should wrtie a FAST System 4 Dummies publication
Originally posted by No Quarter
Someone should wrtie a FAST System 4 Dummies publication
No,
There are a few mini-tutorials around, like the one that norbs has.
To answer your question, your spark advance kPa vs. RPM is 97% of the timing tuning. Besides that you only have "timing trim" (which you should just zero out, at least for starters IMO), crank reference angle, and ESC parameters to set up.
However judging from your question, you don't need "FAST for dummies", you need more of a "basics of engine tuning" book. The FAST is really only a way to implement the tune that your car needs, but it assumes you already have a pretty good idea about most aspects of engine tuning. The beauty of FAST is how easily you can change engine tuning parameters- without knowing what you are tuning, you are losing a big benefit of the FAST.
My opinion is that FAST can probably still help you make your car go faster- a local guy here just put one in and picked up 3 tenths of a second (with better drivability, etc.) even though it's exactly the same hardware under the hood (except no MAF). In your case, however, I would recommend that you bring it to a knowledgable FAST tuner to get it running right- it may cost several hundred dollars, but a few hours on the dyno and driving around and they can usually give you a car that runs better than it ever has. Then, over the next few months, learn more about engine tuning and you can grasp even more control over the tune by yourself.
-Bob Cunningham
