Boost question

Missed my tune up guy today and I'm imatient, so I'll run it by you guys. We normally run about 600 ft altitude. We are racing at 2900 ft in 2 weeks. Assuming the same overdrive and only altitude change, would the boost decrease, or just the amount of oxygen going into the engine.

 

The boost will likely go down a couple of psi. I find that I have to adjust the hat nozzles to keep the fuel pressure consistent. I think you'll find that you need close to 1 gallon per minute less at the increased altitude.

 

example : on my deal 3000ft. 100 pill in the main
2000ft 90
example : on my deal 1000ft 80 pill in the main
500ft 75
with my waterman pump i go up are down 1 number per 100ft

with my enderly pump i would go up are down 2 numbers per 100ft

remember this is a example but its what i run according to the dens alt. formula will change depending on what the plugs look like

hope this helps

 

Are you limited in OD? Why wouldn't you turn up the air and leave the fuel/performance where it is?

 

I can turn the blower up. I'm just curious if there is actually a difference in boost with an elevation change of 2300 ft or a way to determine approximately what it would be. i have all my tuneup info I need.

 

i wouldn't mess with the overdrive danny. i would just adjust the main jet accordingly to the altitude for at least the first run. do you use any altitude correction computer program. I use a davenport program religiously and it has never let me down when it comes to altitude changes. if you make the first run after leaning the motor accordingly and still aren't happy then you could put a little more overdrive on it. i always played it safe for the first run in a different area or altitude . a wise man told me you can always fix a rich condition with a 9/16 wrench and straight screwdriver.

 

That's what i'm planning on doing, just wanted to see if anyone had any hard data on effect on altitude vs boost. i know theres less oxygen at altitude which means less fuel needed, but the blower still pumps the same amount of air though, so the boost should be the same?
by the way, the motor is working great, had to correct a few small things, but overall it beats the hell out of the old chevy deal. We went faster on the very first pass with a new car than we ever went with the chevy motor.

 

Update

Just an update on this. I lost about 6-7 lbs of boost and another racer also lost the same amount. This was with the same overdrive for both of us. Altitude was 2900 ft and DA was 4500 ft copared to 600 ft and DA of 2000 ft

 

Great info I'm reading here, is there anybody out there that gives classes, or a real 'for dummies' book on how all this ties together, altitude, boost, fuel, ect... I'm still learning, and would really like to understand this at a deep level before I start playing with stuff, so far I've just been going by plug readings. (hope I'm not jacking thread, just asking for more info sources on your topic)

 

Bob Szabo's books are awesome. I own both. www.racecarbook.com

 

anyone watching grains of water? Dave