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Old 09-30-2003, 01:17 PM   #61
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Hey Ragman,

What is this "crew" maintaining?
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Old 09-30-2003, 01:32 PM   #62
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Pitcrew, my dad used to race oval back in the 70's. Running a 1600 Xflow with IIRC a 9lb flywheel, it wouldn't idle at anything less than 2000rpm.

TurnNBurn, nothing I have to rely on thankfully. One of the blokes is OK, he used to work on industrial Diesel engines so me and him can have nice long chats(arguements) about all things IC. He doesn't speak very good English though so at times it can get "interesting".

//Stu
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Old 09-30-2003, 02:08 PM   #63
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guys i posted before that the flywheel cand be used to make the engine smoother at idle.
rag the everytime the piston goes down is not a power stroke like you said only on a 2stroke. it fires on the 3 stroke of compresion then on that down motion is power stroke in a four stroke engine.
also an engine will not stall with a light flywheel because that is where ignition timing and idle speed comes into place.
for example in a vw beetle drag motor that runs 11's in the quarter mile we would use a 9 lbs flywheel and a factory wheel was around 18 lbs the reason we didnt use a heavier fly wheel is because the car was extreemly light at 1500 lbs and had 190 hspower it didnt need the extra flywheel wieght it was a 2.2 liter engine but when i dcreased the displacement to 1.8 liters i had to increase the flywheel wieght to make it launch harder. the wieght has nothing to do to increase compresion or power it makes all it does is smooth the engine out for better idle an for of the line drivability the engine does not need a flywheel to run guys its actually there to make it more drivable!but added benift we can tune it to make the egine behave different (feel different).
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Old 09-30-2003, 02:16 PM   #64
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allright.

I am wrong. But hey, it was a GUESS

LOL
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Old 09-30-2003, 02:26 PM   #65
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pit crew you were pretty close just remember a few of us do this for a living! we are only trying to help those that dont understand how it works just get some basic auto tech books and it'll explain to you some theory which will actually help with r/c.
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Old 09-30-2003, 05:57 PM   #66
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Sweet. Its fun to have mental sparing once in awhile.
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Old 09-30-2003, 11:22 PM   #67
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i need gatorade!
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Old 10-01-2003, 09:52 AM   #68
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pitcrew i can appreciate the mental sparing
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Old 10-01-2003, 11:29 AM   #69
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I am glad we all made up.
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Old 10-01-2003, 11:56 AM   #70
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I have a masters in mechanical engineering and have been around both RC cars and real race cars all my life, so I know what I'm talking about.

Incorrect. Race cars have lightened fly wheels, sometimes no flywheel, just the mass of the clutch/torque converter to improve the responsiveness of the throttle, both going up the RPM band and down. Going up, to improve acceleration of the car and increase the speed of downshifts. Going down the RPM band to make upshifts faster. Most street cars with a manual shifter are limited on the speed of gear changes, not by operator skill, but by waiting for the RPMs to rise or fall to the right speed so you don't run your clutch. Most race engines operate in the upper 1/3rd of the rpm range so low speed lumpyness is not an issue that comes with light or no flywheel.

Higher intertia of the rotating parts will only decrease the ability of the drivetrain to react to changes in speed. This is bad.

A ratio that is used in real cars is 4 lbs of rotating mass is worth 1 lb of static mass.

The rotational interia of the parts also matters. Two parts that weight the same can have difference charateristics under rotational acceleration. More mass toward the center of rotation is better. (look up polar moment of interia) (somebody else already pointed this out on this thread)

Since most competition oriented rc cars are under or at weight with good rc gear, concentrate on reducing the rotating mass and unsprung mass of the car. Add static weight to the chassis at the center of the car to bring it up to mass. Lighter diff balls, prop shafts, turned pinions and spur gears, drilled diff plates (check out niftech's stuff), all are good ideas to reduce rotating mass. Composite/graphite arms and hubs are good for unsprung mass.

Quote:
Originally posted by BigDogRacing
In fact, there is only one reason for tuning a 1:1 race car with flywheel weight- because the stored energy in a rotating flywheel is what the car uses to accelerate it from a standing start and on gear changes.
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Old 10-01-2003, 12:07 PM   #71
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Quote:
Originally posted by sands
A ratio that is used in real cars is 4 lbs of rotating mass is worth 1 lb of static mass.
Can I assume a typo there, did you not mean 1lb of rotating mass is worth 4lb of static?

Know what you all mean about mental sparing. I just decided one day I wanted to understand how engines work so I went out and bought the Bosch Automotive design reference book(my new bible). Some serious calculations and stuff in it but a quality way of making my head swell.

//Stu
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Old 10-01-2003, 12:23 PM   #72
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ragman i have that blue book too its actually a recommended reading material by vw of america and m.benz to their techs! so if i give any info here on this stuff its because i reaserched it or know from first hand experiance!
i guess a few of us have that little blue book huh, i like the chapter were they explain structural strengths in materials.
makes you wonder about the claims some of the r/c manufactures make on their cheep products! well thats another subject.
its nice to see that someone can agree with me that there is no need for a flywheel and that it is a tuning aid for drivability! i didnt even have to look it up!
thanks sandman!
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Old 10-01-2003, 03:11 PM   #73
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Removing one pound of rotating mass is as good as removing four pounds of statif mass, yes I made a typo. Thanks for catching that.

Quote:
Originally posted by Ragman
Can I assume a typo there, did you not mean 1lb of rotating mass is worth 4lb of static?

Know what you all mean about mental sparing. I just decided one day I wanted to understand how engines work so I went out and bought the Bosch Automotive design reference book(my new bible). Some serious calculations and stuff in it but a quality way of making my head swell.

//Stu
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Old 10-01-2003, 05:36 PM   #74
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Speed: you just had to throw that in there huh...
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Old 10-02-2003, 09:13 AM   #75
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speedxl what is this refference manual you have?where do you get it? it is something i would like to see.i am a certified tech as well. but its Mercruiser marine engines and sterndrives,so as i am also aware that engines do not need flywheels,nor do flywhees have anything to do with compresion(i couldnt resist Pitcrew ) but as far as structural strengths and other automotive topics i dont know all that much. so this book sounds interesting.
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