Time to go stage II with A/C!

[kidglok]

You would run 22 degrees at 30# of boost. What's the benefit of idling at such a low timing? If you don't have enough timing in the motor you aren't burning all the fuel which will result in it burning in the headers. This will not give you a real sample of actual a/f ratio.

Are talking strictly race gas? Or is that irrelevant to idle timing?

 

[Alky V6]

You might want to ask what size cylinder he's referring to, also.

 

[kidglok]

You might want to ask what size cylinder he's referring to, also.

Good point!

 

[turbobitt]

Good point!

I use high idle timing on a 272 pump gas tune 9:1 engine but with large cam and low vacuum.

Allan G.

 

[kidglok]

I use high idle timing on a 272 pump gas tune 9:1 engine but with large cam and low vacuum.

Allan G.

So smaller cam/CID/ and higher vacuum would require less timing?

 

[Alky V6]

A simple method to find optimum idle timing is to increase timing until you find a point of maximum vacuum. You can certainly continue to add timing and you might get a very small increase in vacuum with that, but all you're really doing is preheating your cylinder, unless that is what you're trying to do. Can't think of a reason why you would want to do that.
I wouldn't necessarily recommend that you preheat your cylinder to a higher than necessary level before making a run with a drag engine. Especially if your combination is already on the edge of detonation.

 

[Alky V6]

Too much timing and you heat the cylinder. Too little timing and you heat the exhaust. The trick is to find the happy medium.

 

[kidglok]

Very interesting Donnie

 

[Dusty Bradford]

So smaller cam/CID/ and higher vacuum would require less timing?

Optimum timing is influenced by several variables. Bore size, stroke, piston design, cam design, chamber design. But I only worry about this at WOT under boost. Like many other things......people can over analyze and complicate everything. Today it must be idle timing. lol.

You read the plugs to determine what the engine wants at WOT. My 22 degree example was just a ballpark range. Some engine may want 19, others may want 24. Reading the plugs will tell you what it wants. As for idle. I have never....never had an engine that didn't clean up from running over 30 degrees of timing. You can hear it in the way it idles, you can see the a/f change. If your trying to light off a catalytic converter running a low timing may help but how many of us are worried about a cat converter.

 

[kidglok]

Optimum timing is influenced by several variables. Bore size, stroke, piston design, cam design, chamber design. But I only worry about this at WOT under boost. Like many other things......people can over analyze and complicate everything. Today it must be idle timing. lol.

You read the plugs to determine what the engine wants at WOT. My 22 degree example was just a ballpark range. Some engine may want 19, others may want 24. Reading the plugs will tell you what it wants. As for idle. I have never....never had an engine that didn't clean up from running over 30 degrees of timing. You can hear it in the way it idles, you can see the a/f change. If your trying to light off a catalytic converter running a low timing may help but how many of us are worried about a cat converter.

The guy who inspected my car said "where's the catalytic converter? In the junkyard?" I said yes!

 

[Alky V6]

Not complicated at all, Dusty. Just watch your MAP reading as you play with the timing. For instance, start at 15 degrees at idle and notice your MAP reading. Increase the timing by 2 degrees. Notice the MAP reading decrease (assuming kPa reading). Starting from 15 degrees and increasing the timing from there, you will notice large decreases in MAP as you're adding timing. You'll reach a point where as you increase timing further the decrease in MAP begins to slow down and level out. I would consider that point to be your minimum idle timing number. You can increase the timing from there if you wish. Like I already stated, you will reach a point where as you increase timing further, all you're doing is heating the cylinders more. Like Dusty stated, you can reach a point where the burn is cleaner too. That means you are burning more of the fuel that has been trapped in the cylinder. When you burn more fuel, you create more heat. More of that increase in heat is transferred to more exposed cylinder wall due to the ignition process starting earlier in the compression stroke. Great for emission standards. Not so good for a racing engine that is already tuned to the limits of detonation.
Another thing that helps you burn cleaner. Run your engine temp at 195 degree F. Another parameter that's great for emission standards. Not so good for a racing engine that is already tuned to the limits of detonation.
When you're detonation limited, you want your cylinders to retain as much heat sink capacity as possible. That's why gasoline racers tend to want to start a race with their engine closer to 160 degrees rather than 195 degrees F.
From an emissions stand point, an engine running at 160 F is not ideal for emissions. 195 is preferred. For racing, it is commonly the opposite. Although, some engines will make more power at the hotter temperature, it's just more dangerous with a detonation limited tune.

 

[Dusty Bradford]

You do a burnout, you build boost to stage.....the motor already has alot of heat in it before you ever launch. Idling at 24 or 38 isn't going to be the difference in blowing head gaskets from detonation.

 

[Alky V6]

You do a burnout, you build boost to stage.....the motor already has alot of heat in it before you ever launch. Idling at 24 or 38 isn't going to be the difference in blowing head gaskets from detonation.

That's a good point. But if you're idling a lot in the staging lanes, you will have moved you temp ranges higher overall with all the pre-staging stuff.

 

[Alky V6]

Burning pure methanol, you can actually control what temperature your engine runs at if you choose to sit in the staging lanes with the engine idling away. A lot of that control is done with the a/f ratio, since a methanol engine won't foul the plugs from being overly rich. Timing also plays a role in that controlling of the engine temperature during idling.
I could tune the idle to have the engine run at a stable 155 degrees F while I sit idling in the staging lanes, waiting my turn, or I could change up the tuning to have it on the verge of overheating when I drive into the burnout box.
If I drive into the burnout box already at a temperature that I want to leave the line at, where will that put me after I do my burnout?
The answer is, it will put me in an unfavorable position.

 

[norbs]

I want the turbo hot as possible at low speeds....and by making the motor less efficient you need more fuel at idle and more PW to get the injector in its operating range. I'm being told on the FAST board I need saturated drivers for these injectors to work at low PW's..could this be my issue? But 1st I'm going to take the volt booster out of the system see if its the problem. I may have to go back to smaller inj, i'm thinking with higher fuel pressure.

 

[Alky V6]

I want the turbo hot as possible at low speeds....and by making the motor less efficient you need more fuel at idle and more PW to get the injector in its operating range. I'm being told on the FAST board I need saturated drivers for these injectors to work at low PW's..could this be my issue? But 1st I'm going to take the volt booster out of the system see if its the problem. I may have to go back to smaller inj, i'm thinking with higher fuel pressure.

what do you mean by making the engine less efficient?

 

[norbs]

what do you mean by making the engine less efficient?

Burning more fuel at idle in the header..

 

[HighPSI]

I'm being told on the FAST board I need saturated drivers for these injectors to work at low PW's..could this be my issue?

Ask five people and you will get five diferent opinions. I would fix your other problems first before I changed anything.

 

[kidglok]

i thought the xfi uses saturated drivers??

 

[Alky V6]

Burning more fuel at idle in the header..

I want to make this very clear. I am not suggesting that someone should run so little timing that you have fuel burning in the exhaust system at idle. Good grief. At 28 degrees timing, you are not burning fuel in the exhaust system.