| Author |
Message |
    
Robert Chapman
Prolific User
Username: shadow
Post Number: 76
Registered: 5-2003
| | Posted on Wednesday, 15 September, 2004 - 10:56 pm: |    |
Hi Pat,
I believe I quote your position on comp/ratio correctly when I say you believe it to be FIXED.
The result of calculating the static dimensions of the cylinder volume and the combustion chamber volume.
Just to refresh your memory on the topic,I suggested that in fact this was only the theoretical comp/ratio and that in fact the comp/ratio varied during engine running,to which you answered that this was impossible.
I take it you have not changed this veiw since you made the statement so unequivocally on the swamelstein site. |
Patrick Lockyer.
Frequent User
Username: pat_lockyer
Post Number: 11
Registered: 9-2004
| | Posted on Thursday, 16 September, 2004 - 03:59 am: | |
Robert Chapman,Do not take me as a fool.
Remember DYNAMIC.My word.
Remember HIGH PERFORMANCE CAMSHAFT WILL INCREASE THE COMPRESSION RATIO.Your words.
Hey we will all see you on the Swammelstein site. |
James Aitken
New User
Username: james_a
Post Number: 4
Registered: 7-2004
| | Posted on Thursday, 16 September, 2004 - 07:57 am: | |
I am a little confused (and bemused) here.
From the point of view of an Engineer, the term "Compression Ratio" is the mathematical ratio of the cylinder volume at BDC to the volume at TDC. Unless we are dealing with one of those "rocking block" designs from Saab, this ratio is mechanically fixed.
However, the actual pressure achieved in the cylinder at TDC depends on the amount of air/fuel charge inducted during the intake stroke. This varies depending on many factors like (but not limited to) throttle position, valve timing, engine RPM, manifold losses and residual pressure from the exhause cycle.
Is it possible we are arguing about terminology rather than the actual functions of an internal combustion engine? |
David Gore
Moderator
Username: david_gore
Post Number: 306
Registered: 4-2003
| | Posted on Thursday, 16 September, 2004 - 04:34 pm: | |
Thank you James - I think your observations correspond to the collective outcome of the Swammelstein thread. |
Robert Chapman
Prolific User
Username: shadow
Post Number: 77
Registered: 5-2003
| | Posted on Thursday, 16 September, 2004 - 07:53 pm: | |
Hi James,from my view point as an engineer.
The mathmatical ratio you discribe of course is the (theoretical) ratio and a very defferent thing to effective or dynamic comp/ratio.
As you have correctly pointed out this varies according to valve timing ,throttle opening and engine speed,in short Volumetric efficiency.
My contention all along has been that "camshaft timing effects comp ratio"I said a change of camshaft could effect the comp ratio and I was howled down by "experts" who said that was impossible because the volume of the cylinder and combustion chamber could not alter,but of cource the amount of air inducted and also the effective volume of the cylinder do, when the engine is runing.
I stick to my original position that comp/ratio is not FIXED,the dimension of the cylinder bore and the combustion chamber certainly are,but the comp/ratio is not.
I would suggest those "experts" read The High Speed Internal Combustion Engine by Sir Harry Ricardo first published in 1924,they might gain something from it. |
Robert Chapman
Prolific User
Username: shadow
Post Number: 78
Registered: 5-2003
| | Posted on Thursday, 16 September, 2004 - 10:41 pm: | |
Hi Pat,
My sincere apologies if my quoting your stated position on this subject in any way makes you feel foolish.
The word DYNAMIC was certainly used by you,and as you yourself have posted on swamelstein in discribing "dynamic compression PRESSURE" not compression ratio.
Whilst CP is directly related and proportional to CR and volumetric efficiency it is not the same thing.It is the result.
As I recall when BOB UK told you that he estimated the CR on his Shadow at idle was about 2:1 you did not agree.(Not everyone agreed with you).
The original statement I made that you so vigorously and vocally took me to task over was indeed that a change of camshaft would increase the CR,AND I STILL maintain that position.
You said "thats a new one on me tell us all how that's possible".You headlined this INCORRECT.
The very fact that you simply proclaim me wrong over and over does not prove your case ,what is needed from you is technical argument to support you case,this is something that has been conspicuous by its absence to date.
Come to the technical forum and put forward verifiable technical argument not just rhetoric.
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Robert Chapman
Prolific User
Username: shadow
Post Number: 85
Registered: 5-2003
| | Posted on Monday, 20 September, 2004 - 10:01 pm: | |
Pat Lockyer,
You have quoted a book to me by Harry Ricardo ,please advise chapter and page . |
Patrick Lockyer.
Frequent User
Username: pat_lockyer
Post Number: 18
Registered: 9-2004
| | Posted on Tuesday, 21 September, 2004 - 04:37 am: | |
Robert Chapman.
Warning whatever you do read it very very slowly or you may not grasp it.
Some of it is not out of date.re 1941.
Chapter V111 226-259 inclusive.
specialy the graphs.I will help you no more. |
Patrick Lockyer.
Frequent User
Username: pat_lockyer
Post Number: 19
Registered: 9-2004
| | Posted on Tuesday, 21 September, 2004 - 10:12 pm: | |
apologise last post should be under the heading :cut oil consumption v8 valve stem seals. |
Patrick Lockyer.
Prolific User
Username: pat_lockyer
Post Number: 31
Registered: 9-2004
| | Posted on Saturday, 30 October, 2004 - 10:30 am: | |
Robert as it was you who put the posting up for debate, compression ratio,as you are now proved to be incorrect i thought you may like to know that rumour has it that you are not the only person to get compressions ratios and compression pressures muddled up,for it has i am told been done by Dr Radolf Diesel with his early experiments causing him almost death by the engine blowing up.
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Robert Chapman
Prolific User
Username: shadow
Post Number: 97
Registered: 5-2003
| | Posted on Sunday, 31 October, 2004 - 08:05 pm: | |
Pat Lockyer,
At the risk of boring other readers(I apologise in advance).
I have never had any problem understanding the difference between C/Ratio and C/Pressure as you obviously do.
For your benefit,C/R is simply the calculation of how many times the swept volume plus the clearence volume is compressed into the clearence volume.At this point Pressure is unknown.
Compression pressure is dependent on, and the result of the amount of air inducted(VOLUMETRIC EFFICIENCY) and the amount/ratio by which the air is compressed(COMPRESSION RATIO)and also the density and temperature of the air.
This is why not suprisingly to most ,it is called COMPRESSION PRESSURE.
Let me remind you that your statement that started this discussion was "A CHANGE OF CAMSHAFT CANNOT CHANGE THE DYNAMIC COMP/RATIO".
I would suggest that I have with the use of maths and geometry in my post proved beyond doubt that in fact your statement was incorrect and that a change of the inlet valve closure timing will alter the effective length of the compression stroke and therefore the comp/ratio and by the way, the resulting Compression Pressure.
Your post (so articulately written by your daughter may I say) was to use the naval vernacular just, making smoke.
Since you like to quote reference books here is a reference that really exists and whats more I will not be deliberately evasive about where in the book the reference is.
The book is titled ADVANCED ENGINE TECHNOLOGY the author is Heinz Heisler, REF PAGE 4, this book is used as reference material for CGLI.BTEC and DIPLOMA OF MOTOR VEHICLE ENG.
Your obstinate refusal to except that this is just another one of your " incorrect facts" as you refer to them , in the face of documented proof to the contrary is quite honestly pathetic. |
Patrick Lockyer.
Prolific User
Username: pat_lockyer
Post Number: 36
Registered: 9-2004
| | Posted on Tuesday, 02 November, 2004 - 02:23 am: | |
Robert Chapman.
So everyone including myself is wrong i think not.
Your begining to look silly. |
Patrick Lockyer.
Prolific User
Username: pat_lockyer
Post Number: 37
Registered: 9-2004
| | Posted on Tuesday, 02 November, 2004 - 06:24 am: | |
Robert Chapman.
As i have stated, compression ratio is calculated and fixed Camshaft will alter the compression pressures.
Read the previous postings in the General dicussion postings.
If still not sure re read the many postings on the SWAMMELSTEIN SITE.Confirmed by the many more professional folk than yourself.
I will not waste any more time on this matter.
Unless you want to be argumentative!
I do not.
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