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Old 07-02-2010, 12:08 PM   #16
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Originally Posted by Roelof View Post
Yes. if you say the 10% part of the fuel is 100% oil then you go to 120%....
ah ok. got it.
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Old 07-02-2010, 12:17 PM   #17
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Yep, that is correct. The issue is the higher oil content reduces the amount of methanol in the fuel. Methanol vaporizes in the combustion chamber at a relatively low temperature and when it does so it has a heat wicking effect which cools the combustion chamber. This means that the operating temperature of the engine is reduced so you can lean the engine out for additional power/run time. An additional benefit of the increase in methanol content (in addition to the reduction in combustion chamber temperature mentioned above) that is not often talked about is that methanol has a really high effective octane rating or anti knock index give you the ability to safely run a lower deck height hence increasing your engines compression ratio with less likelyhood of pre-detonation.

Regards,

Ron
Great info! Here's what I'm got so far.

1. more oil=less methanol=richer to get the same fuel/air mixture
2. more oil=less methanol=richer because the fuel is thicker and harder to pump the fuel through the motor.
3. more oil=less methanol=richer because there's less methanol to get the cooling effect of methanol and less anti knock properties of methanol

Keep the info coming... What about how the engine idles. Would more oil and less methanol not idle as well?
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Old 07-02-2010, 02:54 PM   #18
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So if I switch from 30% nitro with 11% oil to 20% nitro with 16% oil, would I have to richen or lean the settings on the carb?
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Old 07-02-2010, 03:29 PM   #19
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So if I switch from 30% nitro with 11% oil to 20% nitro with 16% oil, would I have to richen or lean the settings on the carb?
The topic was assuming the nitro % stayed the same I think. I think you can lean it out because even though there's more oil, there's also more methanol... We'll wait for the experienced guys to confirm that. I'm not sure...
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Old 07-04-2010, 12:03 PM   #20
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You add more oil (5%) so you must richen

You add more nitro (10%) so you must lean....

I think you should lean it a bit.

But before you lean it... Run your engine, let it warm before you start tuning it. The LEAN/RICH discussion that we have in the previous posts is only to guide you if you need to lean or rich the setting
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Old 07-04-2010, 12:23 PM   #21
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Originally Posted by Sylvain View Post
You add more oil (5%) so you must richen

You add more nitro (10%) so you must lean....

I think you should lean it a bit.

But before you lean it... Run your engine, let it warm before you start tuning it. The LEAN/RICH discussion that we have in the previous posts is only to guide you if you need to lean or rich the setting
As mentioned before, learn how to read your engine and adjust what he is telling you to do. Adjusting an engine only by this list will not work.
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Old 07-04-2010, 12:49 PM   #22
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That's mentioned in the article too
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Old 07-05-2010, 11:35 PM   #23
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Looked the list over and looks pretty good,

Only thing I saw that was questionable to me was the lean/rich setting for high and low temps. When the weather temps go up, Ive always had to richen the top needle to keep it from going too lean in the heat of the day. I would think that the high/low temps work hand in hand with the high/low Bar. pressure. Could be wrong though.
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Old 07-06-2010, 04:18 AM   #24
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Originally Posted by Teufel Racing View Post
Looked the list over and looks pretty good,

Only thing I saw that was questionable to me was the lean/rich setting for high and low temps. When the weather temps go up, Ive always had to richen the top needle to keep it from going too lean in the heat of the day. I would think that the high/low temps work hand in hand with the high/low Bar. pressure. Could be wrong though.
The colder air is more dense so you need more fuel to keep the fuel/air ratio the same.
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Old 07-06-2010, 04:27 AM   #25
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Originally Posted by Teufel Racing View Post
Looked the list over and looks pretty good,

Only thing I saw that was questionable to me was the lean/rich setting for high and low temps. When the weather temps go up, Ive always had to richen the top needle to keep it from going too lean in the heat of the day. I would think that the high/low temps work hand in hand with the high/low Bar. pressure. Could be wrong though.
As I mentioned before, a high temperature does not say anything about the other factors like humidity, airpressure etc. Good hot weather mostly comes with a high pressure but the humidity can go both ways....
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Old 07-06-2010, 10:24 AM   #26
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Re: Air Temps

Think about air temps this way.

Hot air rises..............why? Because it weighs less than cold air.
This would mean the air has less oxygen molecules per cubic foot/liter when warm. Air/fuel mixture ratios are actually measured by weight.
Your carb flows (x) number of cubic feet/min. Therefore at the same flow rate, warmer air provides less oxygen, thus requiring less fuel (leaner) to achieve the same mixture ratio.

Going richer in warm temps and leaner in cold temps just to keep the engine at a preferred temp is an incorrect method.
Use foil or airflow (bigger body openings or a small scoop) to adjust temps.
Using the correct mixture is NEVER wrong! Just remember that the correct
air/fuel mixture and all the other variables may not give you that "perfect" temp. The "perfect" temp simply doesn't exist.

Doesn't it make sense that at warmer air temps an engine would run hotter with the correct air fuel mixture? So many people richen their mixture in hot weather to keep temps down. Doesn't your engine run hotter when you use a heat gun during break-in? Hot air simply isn't going to transfer as much heat from your engine as cooler air.

Ask a top fuel dragster mechanic if their engines always run at the same temp.
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Old 07-13-2010, 10:23 PM   #27
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Originally Posted by mrcdub View Post
So if I switch from 30% nitro with 11% oil to 20% nitro with 16% oil, would I have to richen or lean the settings on the carb?
Hi.

Great thread

If you reduce the nitro percent, you will need to lean the HSN. Eg: You need to lean the HSN almost ˝ turn, when going from 25% nitro to 0%!

I've made some tests with my boys Hyper 7/Power Racing engine car:

Take a look from from 0:38
+ YouTube Video
ERROR: If you can see this, then YouTube is down or you don't have Flash installed.


You need more oil, if you go down in nitro percent:
Nitro needs A LOT more oxygen to explode compared to methanol (that is why you need a richer HSN with high nitro percent). When you lean the HSN due to less nitro, you don't get enough oil through the engine.

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Old 07-13-2010, 10:32 PM   #28
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so when you go from 20% to 30% there isnt a big difference? A lot of people run 30% sayin it makes more power but does it really make that big of a difference?
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Old 07-13-2010, 11:05 PM   #29
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Originally Posted by rcdude236 View Post
so when you go from 20% to 30% there isnt a big difference? A lot of people run 30% sayin it makes more power but does it really make that big of a difference?
Hi.

I can't meassure any changes with different nitro percents (even though there must be some (better gas respons???)).
Any engine needs a certain amount of nitro to run well: If you use too little nitro the middlearea will fatten up like crasy no matter what you do.
I found that my NOSRAM engine runs great with 16% nitro, my Novarossi min. 25% (EDIT: perhaps less but haven´t tried it yet) and the Power Racing engine (modified combustion chamber to get higher compression ratio) approximate 7% nitro.
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Old 07-14-2010, 08:59 AM   #30
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Quote:
Originally Posted by motomatt View Post
Re: Air Temps

Think about air temps this way.

Hot air rises..............why? Because it weighs less than cold air.
This would mean the air has less oxygen molecules per cubic foot/liter when warm. Air/fuel mixture ratios are actually measured by weight.
Your carb flows (x) number of cubic feet/min. Therefore at the same flow rate, warmer air provides less oxygen, thus requiring less fuel (leaner) to achieve the same mixture ratio.

Going richer in warm temps and leaner in cold temps just to keep the engine at a preferred temp is an incorrect method.
Use foil or airflow (bigger body openings or a small scoop) to adjust temps.
Using the correct mixture is NEVER wrong! Just remember that the correct
air/fuel mixture and all the other variables may not give you that "perfect" temp. The "perfect" temp simply doesn't exist.

Doesn't it make sense that at warmer air temps an engine would run hotter with the correct air fuel mixture? So many people richen their mixture in hot weather to keep temps down. Doesn't your engine run hotter when you use a heat gun during break-in? Hot air simply isn't going to transfer as much heat from your engine as cooler air.

Ask a top fuel dragster mechanic if their engines always run at the same temp.

So when cold you need to run rich and when hot you need to run lean, basicly for performance not for temps but also you don't want to run the motor too hot or to cold. So when running in the winter your motor may be running 200* and in the summer 240* and the adjustments on the needle is to get the same performance not for running the same tempeture which will be impossible because of the different climate.

Is this correct?
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