Best AFR for consistency

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Archeryguy02

Archeryguy02

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For those that track it, what is your experience as to what air fuel ratio you have experienced the best consistency when bracket racing.
 
For serious chasers and competitors at the track, the tune changes everyday. Getting a perfect and reliable AFR?
Call me pessimistic but I don’t think that is possible all the time between the two.
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rumblefish360 said:
For serious chasers and competitors at the track, the tune changes everyday. Getting a perfect and reliable AFR?
Call me pessimistic but I don’t think that is possible all the time between the two.
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I would agree with it not being possible all the time especially with only getting one or two time trials, but surely those that track have some idea about what it is and how consistent the car is that day.
 
I think RF360 is spot on, very weather dependent. A baseline is just that, a starting point for the day. As weather and track conditions change thru out the day a tweak here and there may need to be applied. Example: a good AFR in the cool dense air morning may not be optimum if you make it to finals at six pm with blister butt heat and humidity. Just my .02
 
Sublime one said:
I think RF360 is spot on, very weather dependent. A baseline is just that, a starting point for the day. As weather and track conditions change thru out the day a tweak here and there may need to be applied. Example: a good AFR in the cool dense air morning may not be optimum if you make it to finals at six pm with blister butt heat and humidity. Just my .02
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Yah thats my whole point. Trying to figure out if anyone has noticed a base AFR reading that varies the ET least with given weather changes on an average day.
 
Most (bracket) racers I know have a good tune in the carb and leave it alone. They adjust their dial as the weather changes. Guys that run heads up stuff may do things differently.
 
Archeryguy02 said:
Yah thats my whole point. Trying to figure out if anyone has noticed a base AFR reading that varies the ET least with given weather changes on an average day.
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Air/Fuel ratio is just that. It the ratio of air to fuel. It doesn’t matter what the weather is. If your engine makes the most power at 12.8 then you need to tune for that A/F ratio.
 
Ideally you want the same AF ratio. For bracket racing you want consistency and predictability. As others have said, once the tune-up on the car is settled, most racers will leave it alone and keep notes on how their car runs compared to density altitude. That way dial-in numbers can be changed based on past performance.
 
C130 Chief said:
Ideally you want the same AF ratio. For bracket racing you want consistency and predictability. As others have said, once the tune-up on the car is settled, most racers will leave it alone and keep notes on how their car runs compared to density altitude. That way dial-in numbers can be changed based on past performance.
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Would you not want to have a tune up that made the car the most consistent? Is it possible AFR is a key factor in a consistent set up that changes less with weather making the car easier and more predictable to dial? I am trying to flatten the trajectory similar to predicting vertical hold when shooting a bow vs shooting a rifle, the flatter trajectory is much more forgiving to hit the target.
 
Archeryguy02 said:
Would you not want to have a tune up that made the car the most consistent? Is it possible AFR is a key factor in a consistent set up that changes less with weather making the car easier and more predictable to dial? I am trying to flatten the trajectory similar to predicting vertical hold when shooting a bow vs shooting a rifle, the flatter trajectory is much more forgiving to hit the target.
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What makes you think the A/R curve should be flat?
 
Rat Bastid said:
What makes you think the A/R curve should be flat?
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What makes you think I think it should be flat? The trajectory example was not intended convey the desire for a flat for A/F curve, but to make the weather changes less extreme making them easier to predict and more forgiving if you predict incorrectly.
 
Archeryguy02 said:
Would you not want to have a tune up that made the car the most consistent?
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That’s what was described to you above. Most racers will have 1 tune and not touch it but learn how it runs in the varying weather conditions. The AFR IS te key factor. If you wan to constantly change your tune up for what ever ratio works best then by all means do so. That doesn’t mean it will run consistently over and over again at the last and best slip shows.

Chasing what makes your car the most consistent also doesn’t mean it will be the fastest it can be. That changes on an hourly basis at the track.
 
Archeryguy02 said:
What makes you think I think it should be flat? The trajectory example was not intended convey the desire for a flat for A/F curve, but to make the weather changes less extreme making them easier to predict and more forgiving if you predict incorrectly.
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See post 10. You compared an A/F curve to ballistics. I didn’t do that.
 
We put an oxygen sensor in the kids Duster. Dialed in the 650 DP for 12.7 to 1 at WOT. The car ran a tight 0.2 mph difference . It used to jump around. Now it was always at its best mph. The ets were very consistent. Left it alone after that.
 
rumblefish360 said:
That’s what was described to you above. Most racers will have 1 tune and not touch it but learn how it runs in the varying weather conditions. The AFR IS te key factor. If you wan to constantly change your tune up for what ever ratio works best then by all means do so. That doesn’t mean it will run consistently over and over again at the last and best slip shows.

Chasing what makes your car the most consistent also doesn’t mean it will be the fastest it can be. That changes on an hourly basis at the track.
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Most serious bracket racers I talk to will rejet at least a few times a year and some much more often. I have and would again trade a tenth or two for more consistent.
 
Archeryguy02 said:
Most serious bracket racers I talk to will rejet at least a few times a year and some much more often. I have and would again trade a tenth or two for more consistent.
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Unless you lose 1500 feet of air you shouldn’t need to change anything.

Warren Johnson said a couple of decades ago when he went to Denver he didn’t change a jet. That should speak volumes.
 
Rat Bastid said:
Unless you lose 1500 feet of air you shouldn’t need to change anything.

Warren Johnson said a couple of decades ago when he went to Denver he didn’t change a jet. That should speak volumes.
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Density altitude will change 1,000 to 1,500 feet throughout a day of racing for me just about everyday.

So you are saying Warren Johnson said proper jetting at a mile high is the same jetting as sea level? Do you think he was compensating in other ways? I don't think you can find any reputable tuning people in the business now that will tell you optimum Jetting wont change at 5,000 feet.
 
Archeryguy02 said:
Most serious bracket racers I talk to will rejet at least a few times a year and some much more often. I have and would again trade a tenth or two for more consistent.
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Agreed. Operative word, “serious.”
 
Archeryguy02 said:
Density altitude will change 1,000 to 1,500 feet throughout a day of racing for me just about everyday.

So you are saying Warren Johnson said proper jetting at a mile high is the same jetting as sea level? Do you think he was compensating in other ways? I don't think you can find any reputable tuning people in the business now that will tell you optimum Jetting wont change at 5,000 feet.
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He was compensating in other ways, but from my understanding he wasn’t opening the carbs. That doesn’t mean he wasn’t changing air bleeds though. And I know they change both axle and transmission gearing, raise compression and probably a couple of other things I’m forgetting.
 
Archeryguy02 said:
Density altitude will change 1,000 to 1,500 feet throughout a day of racing for me just about everyday.

So you are saying Warren Johnson said proper jetting at a mile high is the same jetting as sea level? Do you think he was compensating in other ways? I don't think you can find any reputable tuning people in the business now that will tell you optimum Jetting wont change at 5,000 feet.
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Is David Reher, of Reher-Morrison Racing Engines, reputable?

Tech Talk #44 – Summertime Blues: How to Live with Bad Air
 
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