Why Air Density Is Important In Engine Tuning.

[Jeffmaturo]

Do most of you pay attention to this or is it over rated? Just wondering if it really effects a nitro engine as much as it would say a full size car engine?

On a side note, do many of you read the water when you are racing? I was amazed when I finally started to pay attention just how much trouble I could avoid by reading the water.

 

[Grimracer]

back when I was testing each day.. altitude density was more important then density

Grim

 

[Alan Elzer]

Mike

Thnx for all your input & ideas on new threads! It's a pleasure visiting with you at races & your help is appreciated!!

Sent from my SM-N920V using Tapatalk

 

[Lennard Cuenco]

kinda nice to know what props your motor can spin prior to your heat.....

 

[Wally Marsh]

To expand on Mike Zs comment, air density is affected by both air temp and current air pressure (similar to altitude pressure). Air density gauges, such as Kinsler and other QUALITY AND CALIBRATED gauges account for both in their air density value, stated as per cent. There is an international standard for calibration at 100%, Id have to look it up. I check mine (almost) every year and it seldom needs adjustment. Bottom line, our nitro fueled motors are very sensitive to small changes in AD, due to the stoichiometric ratio, ie high fuel/air ratio. What air density does not account for is relative humidity in the air, water doesnt burn and high humidity screws with performance of our motors. Just sharing what Ive learned from others before me.

Wallster

 

[Wayne Johnstone]

So the higher the humidity, the richer the motor will run? Meaning reduce the fuel a little?

 

[Tom Foley]

Think of your grade school model of an air molecule . The less humidity , the less of the actual molecule is taken up by H2O , making room for more O2 thus requiring more fuel to obtain the optimum ratio of air to fuel ratio .So the actual amount of "air " your engine breathes with each cycle is more efficient with high air density than less . Fuel needs Oxygen to burn , the more oxygen the more theoretical power . I just use ol' seat of the pants tuning but by keeping records of air temp and density and needle stiing from the flow meter you can be more consistent .

 

[Ray Sametz]

Think of your grade school model of an air molecule . The less humidity , the less of the actual molecule is taken up by H2O , making room for more O2 thus requiring more fuel to obtain the optimum ratio of air to fuel ratio .So the actual amount of "air " your engine breathes with each cycle is more efficient with high air density than less . Fuel needs Oxygen to burn , the more oxygen the more theoretical power . I just use ol' seat of the pants tuning but by keeping records of air temp and density and needle stiing from the flow meter you can be more consistent .

Dilly Dilly, O2 in the air is the key. Good post Fast.

 

[Michael Costanzo]

So the higher the humidity, the richer the motor will run? Meaning reduce the fuel a little?

you can also add timing..hotter plug or pull a coil out. motor is a air pump,it is only going to take in a poop out so much.you will never make as much power on a hot and humid day as is a cooler/dense day. density altitude or corrected altitude/or as close to sea level or lower is ideal.i drag race a Top Sportsman car and have a hand held weather machine that takes air sample's and give me a **** load of info.as far as these little motor's,like tom Foley said,get a ball park and learn how to read the glow plug wire and color.DO NOT OVER THINK THIS!! i have a flow meter and it is still in the box.when the motor is on the pipe,check the plug after some run time and you will learn what the motor like's and what it does not,mike.

 

[Jeffmaturo]

So the higher the humidity, the richer the motor will run? Meaning reduce the fuel a little?

you can also add timing..hotter plug or pull a coil out. motor is a air pump,it is only going to take in a poop out so much.you will never make as much power on a hot and humid day as is a cooler/dense day. density altitude or corrected altitude/or as close to sea level or lower is ideal.i drag race a Top Sportsman car and have a hand held weather machine that takes air sample's and give me a **** load of info.as far as these little motor's,like tom Foley said,get a ball park and learn how to read the glow plug wire and color.DO NOT OVER THINK THIS!! i have a flow meter and it is still in the box.when the motor is on the pipe,check the plug after some run time and you will learn what the motor like's and what it does not,mike.

Good info thanks.

 

[Mike Hughes]

I have an altimeter and a barometer in my trailer. You can watch things change as the day goes by. I never change the barometer setting on the altimeter. At home Im around 200-250. air is getting good as altitude is dropping.

 

[Samuel Hagan JR]

So the higher the humidity, the richer the motor will run? Meaning reduce the fuel a little?

Bingo!

 

[Mike Cathey]

Since nitro fuel also carries oxygen right in the fuel you can compensate for low air density by bumping the nitro percentage. If the air really thins out on a really hot day I have went from 60% to 65% and the high end performance will pick up some because you can richen up the mixture. It's not any kind of huge advantage, but is noticeable and with the competition so evenly matched throughout most of the field even a little help is worthwhile.

I used to fall into the trap on hot summer days when the air is thin because I thought my boat is really slow today and start over adjusting everything because I would think there's a problem with the boat. Now I take the time to look around on those occasions and usually see that everyone else is down on power/speed as well.

I eyeball my Kinsler all day long. The correlation is evident on the flow meter numbers when the density changes. Big air density changes means the more I have to adjust to get back to where I need to be on the flow meter and then minor tweaks on the 3rd channel on the mill. I always lay down a couple of fast laps on the mill to make sure the boats isn't going to sag off the turns and it will come out of the hole at the start.

 

[LohringMiller]

If you really want to know the difference air density makes, race in Colorado or Montana. Because 60% nitro carries a lot of oxygen, the nitro engines only need minor adjustments and a little smaller props at 5,000 feet. My stock outboards only needed a little needle adjustment from sea level, but gas engines are a different story. They won't pull sea level props at 2500 feet and need a lot smaller props on a summer day at 5,000 feet. The needle settings are a lot leaner.

Lohring Miller

 

[Terry Keeley]

If you really want to know the difference air density makes, race in Colorado or Montana. Because 60% nitro carries a lot of oxygen, the nitro engines only need minor adjustments and a little smaller props at 5,000 feet. My stock outboards only needed a little needle adjustment from sea level, but gas engines are a different story. They won't pull sea level props at 2500 feet and need a lot smaller props on a summer day at 5,000 feet. The needle settings are a lot leaner.

Lohring Miller

Or try going from Canada to Alabama! The air density drops but the big killer is the water grains, I saw 120 gpp last June in Huntsville which I've never seen anywhere.

On a humid day up north we might see 70. It doesn't effect the air density much but it sure changes how the motors run!

 

[ace]

why do i have to richen when it rains ??

 

[David Ashcroft]

Delete

 

[Terry Keeley]

Getting too technical ...

Just use the guidline when its cool,short and fat when its hot long and lean and tune from there.

air density is good where i am year round 93-100%.

If you're running your 93% set up at 100% you're leaving a bunch on the table!

 

[David Ashcroft]

Delete

 

[Brandon Atwell]

Is there a relative ratio/ percentage between a change in air density and the required change in our needle flow? Or is that where the tune it by ear aspect comes into play?