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Author
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Topic: Carb jetting from 5,800ft to 1,000ft
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JJonesy99
Gearhead Posts: 203
From: Lakewood, CO USA
Registered: Jan 2005
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posted 11-22-2006 02:39 PM
 
I live in Denver and the elevation at bandimer is 5800 ft. I will going to Vegas and Fontana to race next weekend. I wanna how many steps show I re-jet? I'm drawing a blank today.... for instance if I need to jet up 4 steps: I'd go from 80 to 84, correct?Thanks
Jason ------------------
66' stang
408W, C4, 4.11 gears
11.94 1/4 @113mph @ 5,800 elevation
367 RWHP & 373 RWTQ
DAILY DRIVER
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Moneymaker
Administrator Posts: 29200
From: Lyons, IL, USA
Registered: May 99
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posted 11-22-2006 03:00 PM
All of my altitude class racer friends tell me that they use the 5&5 method when they come to sea level.
Up 5 jet sizes and down 5 degrees of timing.
Don't forget that Vegas is 2000 above sea level.------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First NHRA & IHRA 289 automatic Superstock Mustang in the TENS 06-99
First SS/MA in the TENS 04-03
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
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JJonesy99
Gearhead Posts: 203
From: Lakewood, CO USA
Registered: Jan 2005
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posted 11-23-2006 03:02 PM
Alex, so your saying I should jet up 4 steps (6000-2000)? And why do I decrease the timing? This will be my first time racing at a lower altitude.Jason ------------------
66' stang
408W, C4, 4.11 gears
11.94 1/4 @113mph @ 5,800 elevation
367 RWHP & 373 RWTQ
DAILY DRIVER
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Moneymaker
Administrator Posts: 29200
From: Lyons, IL, USA
Registered: May 99
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posted 11-23-2006 03:31 PM
I don't know about you Jason, but every motor that I tune the higher the altitude, the more timing advance it responds to.
Based on that experiance, I assume that you would run quite a bit of advance.
We always lean the fuel and advance the timing when we go high.------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First NHRA & IHRA 289 automatic Superstock Mustang in the TENS 06-99
First SS/MA in the TENS 04-03
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
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JJonesy99
Gearhead Posts: 203
From: Lakewood, CO USA
Registered: Jan 2005
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posted 11-24-2006 02:13 AM
Alex, I'm new to this racing thing and tuning my motor. So what you say to me is like GOLD. Your the master and i'm the kid learning. My total timing now is 34 degres. So what may be a good starting place for my timing? 30 degrees? And thank you again for all the helpful advice. I would really be lost if it wasnt for you. Jason ------------------
66' stang
408W, C4, 4.11 gears
11.94 1/4 @113mph @ 5,800 elevation
367 RWHP & 373 RWTQ
DAILY DRIVER
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JCQuinn@work
Gearhead Posts: 998
From: Lakewood, CO, USA
Registered: Jun 2001
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posted 11-24-2006 06:03 PM
Have you ever noticed that when you are at Bandimere's you are looking down at Denver?People I have know who brought altimiters to the track have reported altitudes from 6300 to near 7000 ft. When I was traveling around racing we changed the jets but not the timing when going to lower altitudes. If you do not change the jets you should advance the timing when moving to Denver so I guess the reverse would be true going downhill. You could probably do combinations of timing and jetting changes but I did a bunch of test runs before I settled on jetting only. I'm not arguing with Alex, he knows what he is doing, I just had different results but I raced a lighter car with a more modified engine so maybe that made a difference. John
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Moneymaker
Administrator Posts: 29200
From: Lyons, IL, USA
Registered: May 99
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posted 11-24-2006 08:07 PM
John and I are both correct.
Carb size has a lot to do with it.
The bigger the carb, the less you have to adjust for altitude.
I would start out at Vegas with the timing the same and jet up two sized for a baseline.
If it is happy there you can come down another two at Fontana.
With our little carb we need to both jet down and timing up at altitude.
Others I know with large carbs (750 and up) manage with mostly with just jet changes.
We do a lot of other little things for altitude too like longer collectors and more gear. Things that I would have already done to your car if I lived where you do. Then going down would be easy.
 ------------------
Alex Denysenko
Co-Administrator and Moderator NHRA/SRA member and licensed Superstock driver
NHRA and IHRA SS/LA & SS/MA National Record Holder '00,'01,'02,'03,'04 &'05
First NHRA & IHRA 289 automatic Superstock Mustang in the TENS 06-99
First SS/MA in the TENS 04-03
IHRA division 5 Superstock Champion
Fleet of FoMoCo products including 88 ASC McLaren Mustang #28 The Barry of BarrysGrrl Quote #1: "I never met a magazine mechanic I liked."
Quote #2: "Make sure brain is in gear before engaging mouth!"
Quote #3: "If you can't run with the big dogs, stay on the porch!"
www.moneymakerracing.com
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