Its funny i seen 2 different people win $10,000 last weekend, qualifying during the day in about 50 degree weather, racing at night in about 30 degree weather, and neither 1 changed a jet. Something to ponder.Not that I think ceramic bearings are no good, but they are for sure a waste of money if you’re buying them in hopes of going faster.
Spend that money on an air density gauge and some good jets, (not the drilled kind, reamed only) in in-between sizes and then you’re spending your money on something that really can get you going faster.
Comments, compliments, criticisms and questions always welcome.
Not that I think ceramic bearings are no good, but they are for sure a waste of money if you’re buying them in hopes of going faster.
Spend that money on an air density gauge and some good jets, (not the drilled kind, reamed only) in in-between sizes and then you’re spending your money on something that really can get you going faster.
Comments, compliments, criticisms and questions always welcome.
I don’t doubt you for a moment. People do the dumbest things. But I will go with the pros, and if they’re changing jets with a change in air density, I have to believe they know what they’re doing.Its funny i seen 2 different people win $10,000 last weekend, qualifying during the day in about 50 degree weather, racing at night in about 30 degree weather, and neither 1 changed a jet. Something to ponder.
Never raced a carb with changeable jets, but we certainly did see a change in needle postion with a change in air density with a 2 cycle.Just on the air density gauge, I know you're pretty crazy about that stuff. Did you find a direct relationship between air density and jet sizes.
Never raced a carb with changeable jets, but we certainly did see a change in needle postion with a change in air density with a 2 cycle.Just on the air density gauge, I know you're pretty crazy about that stuff. Did you find a direct relationship between air density and jet sizes.
I don’t doubt you for a moment. People do the dumbest things. But I will go with the pros, and if they’re changing jets with a change in air density, I have to believe they know what they’re doing.
It’s not secret stuff, it’s mostly common knowledge. If the air density goes up, that means more air in the engine and with more air you need more fuel.
It’s always surprised me that 4 cycle people drill jets. And they use .001 step sizes. Did you know that the difference in area between a .039” jet and a .040” inch jet is 5.188%?
Longacre, who sells air density gauges, says a 1% change in air density calls for a 1% change in jet area. To get a 1% (close) change in jet area, starting with a .039” jet. would call for a .0392” jet. Of course nobody has that size jet, but you can buy reamers, (which you should be using in any case) near that close.
In any case, the jets should be flow tested if you want to do it right. We did this at a place where I use to work and found a big difference in flow with rocket engine jets, (very similar to kart jets) that were made on a Swiss CNC lath.
Now people spend all kinds of money for the trick this and the trick that but really their not paying attention to the really important stuff.
Now I don’t know what the air density did at this race you speak of, but you would think the air density went up with the colder air, but that is not a given. Air density is a measure of the effects of air temp as it is affected by the barometric pressure. Air density would be higher in colder weather, if, the barometric pressure stayed the same, but it could be that the lower temp was brought on by a drop in the barometric pressure. It could go either way.
I’m pretty sure that the people that know, like Longacre, know what they are talking about, and they say, “As the air density goes up, you need more fuel.”
If not, why do people that race at higher altitudes use smaller jets than the people that race at sea level?
This air density stuff is not my idea; I’m just passing it on.
Comments, compliments, criticisms and questions always welcome.
I don’t doubt you for a moment. People do the dumbest things. But I will go with the pros, and if they’re changing jets with a change in air density, I have to believe they know what they’re doing.
It’s not secret stuff, it’s mostly common knowledge. If the air density goes up, that means more air in the engine and with more air you need more fuel.
It’s always surprised me that 4 cycle people drill jets. And they use .001 step sizes. Did you know that the difference in area between a .039” jet and a .040” inch jet is 5.188%?
Longacre, who sells air density gauges, says a 1% change in air density calls for a 1% change in jet area. To get a 1% (close) change in jet area, starting with a .039” jet. would call for a .0392” jet. Of course nobody has that size jet, but you can buy reamers, (which you should be using in any case) near that close.
In any case, the jets should be flow tested if you want to do it right. We did this at a place where I use to work and found a big difference in flow with rocket engine jets, (very similar to kart jets) that were made on a Swiss CNC lath.
Now people spend all kinds of money for the trick this and the trick that but really their not paying attention to the really important stuff.
Now I don’t know what the air density did at this race you speak of, but you would think the air density went up with the colder air, but that is not a given. Air density is a measure of the effects of air temp as it is affected by the barometric pressure. Air density would be higher in colder weather, if, the barometric pressure stayed the same, but it could be that the lower temp was brought on by a drop in the barometric pressure. It could go either way.
I’m pretty sure that the people that know, like Longacre, know what they are talking about, and they say, “As the air density goes up, you need more fuel.”
If not, why do people that race at higher altitudes use smaller jets than the people that race at sea level?
This air density stuff is not my idea; I’m just passing it on.
Comments, compliments, criticisms and questions always welcome.
SoCo Tire Treatments, Nothing has changed with what you call "Modern Motors" when it comes to reading the air density. You are way off base slamming Als post of information which is as true as the sun coming up in the morning. You are very sorry in so many ways.