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Internal combustion design

 
ex_isp
I love my Chevy Chevette!
Posts: 4
Joined: 10/13
Posted: 10/29/13 06:50 PM

This might be a bit offbeat, but I'm looking to find a definitive answer and I figured here would be the best source!

I'm having a debate with my brother over engine design/theory.

I believe that internal combustion engines, with a given throttle
setting will seek a given rpm.  IE, if 1/8 throttle on a particular engine results in say, 5000 rpm in neutral, that engine will attempt to
reach 5000 rpm in any gear.  It may not be successful due to load which can be described with gear ratio, wind resistance, incline, etc.  All of these "load" factors are variables and are introduced into the formula.
They are also more affected in vehicles with lower power to weight ratios.  An example... Suzuki 1000cc bike.  High power to weight ratio.
On said vehicle, 1/8th throttle makes ~5000 rpm in neutral.  In first gear, 1/8th throttle results in 5K rpm, but take a couple seconds longer
to achieve due to load/gear ratio.  2nd gear will still reach 5K rpm but
take an additional couple seconds, etc.  

My stance is again, that load is an external, artificially induced variable and that ANY internal combustion will seek (perhaps not achieve due to load) a consistent rpm.

My brothers stance is that I'm totally out to lunch with this line of thinking.

Any light you can shed on this would be hugely appreciated!

Highest regards,

Ex  

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68scott385
I mow my lawn and find Chevys
Posts: 1994
Joined: 10/09
Posted: 10/29/13 11:36 PM

I say instead of asking others for answers, you and your brother should take your vehicles and do some scientific testing to find answers you both will believe to settle the dispute.  
68scott385 68scott385 68scott385

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 10/30/13 01:03 PM

You are right in one sense. Unloaded any engine be it gas, electric, etc. will seek the rpm it is set at, the example given is 5000 but it can be anything from 5 rpm to 50,000. As soon as any load is put on it it will never reach that rpm again because of the drag put on it by whatever it is pushing or turning, even if it a very tiny load. It may get very close to it if the load is very light however.  
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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 10/30/13 04:04 PM

Hi Dave,
 Yes, Put it on the road with all things being equal.
 Record EVERYTHING!!.
 
 Off the post...Where is Pepsi Bottle??.  
skyeking

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ex_isp
I love my Chevy Chevette!
Posts: 4
Joined: 10/13
Posted: 10/30/13 04:45 PM

Scott,

Agreed but not practical for either my brother or myself.  Time and 1000 miles separate us.  That and resources which is why I posted here.

If forums are not for sharing info and concepts, what good are they except for BSing?  

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ex_isp
I love my Chevy Chevette!
Posts: 4
Joined: 10/13
Posted: 10/30/13 04:52 PM

Dave,

Good answer!  This is the kind of input I'm seeking!  Do you agree that load is in this example, an externally applied factor? Separate from, but affecting the nature of the engine to try and reach it's design spec whether it be higher or lower rpm as you stated?

Thanks  

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 10/30/13 07:59 PM

Yes, I agree that any load put on the motor will slow it's approach to the limit  and it will try to seek that limit. It may never get there however due to the load.
Of course the bigger the load the slower it will move up the RPM range.  
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wayne712222
My first time was in a Chevy
Posts: 245
Joined: 10/13
Posted: 10/30/13 08:03 PM

i am confused..  but let me do some putting here...


at a Stable 5,000 RPMs in neutral...

the air flow thru the carb is pulling the most fuel and air for that very limited load..

when you add load by putting it into gear...   the engine requires more air and fuel to maintain the same RPM...

....

this is confusing because of the variables.

a 350 cubic inch motor idling at 15 inches of vacuum.. is only moving half of the displacement volume of air thru..  because there is 15 inches of vacuum out of a possible 30 inches of vacuum  that's roughly half the volume of air.

now... more air and more fuel.. more rpms and more power..   when you add load.. the vacuum drops as you increase throttle lowering the air pressure that increases air flow thru the motor.. more air.. more power..

if you have a fixed throttle at 1/8.. you add load the engine will slow down in proportion to the load..  depending on the load and how much power the engine is making at that point... which ever.. the engine when load is applied.. will be reduced..


want to have some fun... build a motor that builds 18 to 20 inches of idle vacuum... and you will have a motor that can get decent MPG..  its all in the cam grind ..  hint.. look at the H230 grind.. a cam grinder will know what you are talking about..  

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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 10/31/13 05:14 PM

Hi Wayne,
 This is why my Jag Mechanic tunes my ZZ4 with a Vacuum gauge
 and nothing else...I think he was born with 32inches of Mercury
 in him and THAT is REAL *** to the rookies.
 Stay safe people. Nothing like a good verbal grapple....Noel.  
skyeking

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ex_isp
I love my Chevy Chevette!
Posts: 4
Joined: 10/13
Posted: 11/03/13 01:22 PM

Thanks all for the input!

Dave, your answers show me that you best understood the question and you have given the best explanations!

Wayne, your answer also demonstrates that you understood my question and gave correct and requested info!  I like your vacuum gauge analogy.  Also right.  

Root of my question having been that load is an external factor.  The engine will always try to reach it's rpm/throttle setting but will not always be successful due to load.

Again, thanks to all!

Ex  

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Dave632
I mow my lawn and find Chevys
Posts: 2253
Joined: 07/08
Posted: 11/03/13 06:29 PM

I went to school when Dinosaurs ruled the earth. So my memory has faded thru time, and those hits by asteroids, but I still remember some of the teachings of Leonardo my tutor.  
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skyeking
I mow my lawn and find Chevys
Posts: 2738
Joined: 08/09
Posted: 11/07/13 08:32 PM

Metaphorically>> THE XMAS TREE STILL REPRESENTS " SWORD OF DAMOCLES."
 No hyothetical grey area..You is or you're Ain't..  
skyeking

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