Buying ceramic Bearings

alvin l nunley

Premium User
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.
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.
 

arc100

Member
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.

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 assume the air density gauge corrects altitude as well? Never used one but when I played with outrigger model boats a guy had a big gauge that he used to adjust and record his mixture strength with, He would plug a hose onto the fuel fitting from the gauge and check the main jet flow. I was wondering if there is some way of doing the same thing with a diaphram carb.
 

alvin l nunley

Premium User
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.
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.
 

alvin l nunley

Premium User
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.
Comments, compliments, criticisms and questions always welcome.
 

alvin l nunley

Premium User
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.
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.

These were the Pros.
 
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.

Thats a very old article youre referring to and was written when there was ONLY the flattie for 4 cycles. Times have changed. Also, the Pros i know, and myself, havent changed any jet in any of our more modern motors( clones/animals) from sea level to the mountains of the Carolinas....still winning races at both places.
Maybe its time you actually learn about 4 cycles instead of hanging on others coattails and telling everyone what they should do, when in fact you havent a clue.
 

Freezeman

Premium User
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.
 
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.

Sorry you feel this way, but ive never seen Tod, Kevin, Michael, Tim, or any of the other TOP builders in the country tell me or anyone to change the jet. Im not a builder, but i deal with and know some of the best in the business. Ill go by what they say, they do it for a living, and do pretty well at it too.
 
What kind of power may be gained from changing the jets to match the air density better? Me and my green plate driver have made good progress this year. I'm always listening for places I may be leaving something on the table set up wise. I guess if no one else is changing jets we haven't been at a disadvantage. I personally don't have the ability to try this out but would love to hear from folks who do.
 
Then we went to the front when we changed to SoCo Preps....Like you can read here on 1000 different posts "It's all in the Tires"
 

Freezeman

Premium User
SoCo, I do find your experience on the coat tails of professional motor builders interesting and think that there is a reason for them to not recommend a jet change. Humm A few reasons for that I am going to post here to see and hope to learn as to why that may be the case with our limited knowledge of how air density effects our use of an internal combustion engine.
1. Maybe the density of the air hasn't changed enough to make a full .001" change in the limited sizes of jets that are used in our application. Like in Als example of utilizing smaller stepped jets.
2. The effects of jetting with the use of methanol has a much wider window in which the air fuel ratio is "near" perfect. So a small change in density would yield a small gain or loss if the perfect jet size was being used to begin with.
3. Air density goes hand in hand with the amount of maximum power output that is available of any specific naturally aspirated power plant so when the density of the air is reduced the amount of power is reduced which in karting would mean that a gear change may be recommended rather than a jet change.
4. Restrictors used after the emulsion tube and main jet reduces air flow across the fuel metering devices which in turn causes the need to expose more fuel at the fuel pick up point in order to obtain the correct mixture of air and fuel being delivered after the restriction. Just thinking about this example....... It could cause situations where a reduction in air density may merit a need for an even larger main jet as air flow is reduced.
5. Faster lap times can be achieved even with a reduction in power if you can find the perfect forever changing set up that allows for faster corner speeds which causes less need for better acceleration and the perfect air/fuel ratio. But if you have the ability and time to perfect all the above you will become even faster and I guess that would be when ceramic bearings could be utilized to try and beat the other guy that has it all figured out too. LOL
 
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