S4 10:1 C/R, the big lie?
01-05-2004, 03:51 AM
#47
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this is what 6.2cc's looks like in relation to the piston and its surface area.
On an initial look at some used pistons i just recieved, i dont think there should be a problem machining out this amount of volume. This is just my simple opinion, im taking the idea to a few machine shops soon. Im having one of the pistons cut up so i can get a better look at its cross section (along the pin axis and perendicular to it) The 6.2cc is based on an earlier post on this thread using Adams numbers for volume and CR. I figured and extra 6.2cc on the piston would yeild appz 8.5:1...from a 10:1 stock setup.
To achieve a 8.52:1 CR you would have to add 6.2cc of piston volume (machine out 6.2cc)
695/(75.3+6.2)= 8.52
Using http://www.sciencemadesimple.net/EASYvolume.html to put it in perspective..
6.2 Cubic centimeters equals 0.419294 Tablespoon (that’s not even half a tablespoon!)
To get 8.79:1 remove 3.7cc from piston
To get 8.90:1 remove 2.7cc from piston
To get 9.00.1 remove 1.7cc from piston
Looking at it closely i think material can be removed from the piston and still retain the same "dish"...perimeter and depth. The material would be removed from the wall of the dish making a slightly deeper slope.
Anyway, to put a max of 6.2 cc in a bit of perspective...
On an initial look at some used pistons i just recieved, i dont think there should be a problem machining out this amount of volume. This is just my simple opinion, im taking the idea to a few machine shops soon. Im having one of the pistons cut up so i can get a better look at its cross section (along the pin axis and perendicular to it) The 6.2cc is based on an earlier post on this thread using Adams numbers for volume and CR. I figured and extra 6.2cc on the piston would yeild appz 8.5:1...from a 10:1 stock setup.
To achieve a 8.52:1 CR you would have to add 6.2cc of piston volume (machine out 6.2cc)
695/(75.3+6.2)= 8.52
Using http://www.sciencemadesimple.net/EASYvolume.html to put it in perspective..
6.2 Cubic centimeters equals 0.419294 Tablespoon (that’s not even half a tablespoon!)
To get 8.79:1 remove 3.7cc from piston
To get 8.90:1 remove 2.7cc from piston
To get 9.00.1 remove 1.7cc from piston
Looking at it closely i think material can be removed from the piston and still retain the same "dish"...perimeter and depth. The material would be removed from the wall of the dish making a slightly deeper slope.
Anyway, to put a max of 6.2 cc in a bit of perspective...
01-05-2004, 03:56 PM
#49
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Tony,
When I modified GTS pistons for the 1000 twin turbo, I cut into, but not eliminated the "sloped" area and made it considerably steeper to increase piston volume....and never touched the "center area". I removed almost 8 cc!
Of course, I massaged the heads appropriately.
I sold both the heads and pistons, but I might still have a "dummy" psiton for a pic.
Marc
DEVEK
When I modified GTS pistons for the 1000 twin turbo, I cut into, but not eliminated the "sloped" area and made it considerably steeper to increase piston volume....and never touched the "center area". I removed almost 8 cc!
Of course, I massaged the heads appropriately.
I sold both the heads and pistons, but I might still have a "dummy" psiton for a pic.
Marc
DEVEK
01-05-2004, 04:52 PM
#50
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A picture would be litterally worth a 1000 words Marc. If you have one that would be great.
I took my pistons down to Carl here in Vegas (Carls Place) and he was pretty intreged by the idea and gave me some phone numbers. Ive got it in my head of exactly how it can be done, its just getting it across to the places/machine shops i visit of what i want...but not knowing there capabilities.
Did you do the machining yourself Marc or was it farmed out?
Id think that to do it by hand raises the error of inconstant machining. It looks as if the pistons could be turned on a lathe but id much rather have them stationary and a CNC type milling maching do the work. I have this image in my head of a piston anchored down and a machine whipping around it with alloy shavings flying and in 20 minutes a newly shaped piston in my hand with a computer generated 6.0cc removed....NNNNEXT. With computer machining once the "practice" piston is dialed in, it could be duplicated very easiliy for 8 more.
Thing is, im not in the maching business, i only know what ive watched on TV or read about....my 1st stop today was pretty eye opening and gave me some more food for thought.
I saw the thread earlier on open road racing ...Carl has a new Twin Turbo now, identical to the one he and his wife were darn near was killed in 2yrs ago. Im pretty sure hes getting back in the saddle again so to speak... just not as fast. Then again, speed doesnt win open road racing (except in one category) the "fraction of second hand" does.
I took my pistons down to Carl here in Vegas (Carls Place) and he was pretty intreged by the idea and gave me some phone numbers. Ive got it in my head of exactly how it can be done, its just getting it across to the places/machine shops i visit of what i want...but not knowing there capabilities.
Did you do the machining yourself Marc or was it farmed out?
Id think that to do it by hand raises the error of inconstant machining. It looks as if the pistons could be turned on a lathe but id much rather have them stationary and a CNC type milling maching do the work. I have this image in my head of a piston anchored down and a machine whipping around it with alloy shavings flying and in 20 minutes a newly shaped piston in my hand with a computer generated 6.0cc removed....NNNNEXT. With computer machining once the "practice" piston is dialed in, it could be duplicated very easiliy for 8 more.
Thing is, im not in the maching business, i only know what ive watched on TV or read about....my 1st stop today was pretty eye opening and gave me some more food for thought.
I saw the thread earlier on open road racing ...Carl has a new Twin Turbo now, identical to the one he and his wife were darn near was killed in 2yrs ago. Im pretty sure hes getting back in the saddle again so to speak... just not as fast. Then again, speed doesnt win open road racing (except in one category) the "fraction of second hand" does.
01-05-2004, 04:52 PM
#51
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Thread Starter
Marc wrote:
Marc, are you refering to relieving the peak between the valve cut outs and the main dish?
It seems like this would be an easy way to gauge material removal, by running a cutter a specified depth onto the valve cut out in such a manner that opens the cut out to the dish.
Maybe even wind up with a non-interference engine in the process?
I cut into, but not eliminated the "sloped" area and made it considerably steeper to increase piston volume....and never touched the "center area". I removed almost 8 cc!
It seems like this would be an easy way to gauge material removal, by running a cutter a specified depth onto the valve cut out in such a manner that opens the cut out to the dish.
Maybe even wind up with a non-interference engine in the process?
01-08-2004, 02:03 AM
#53
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From a cool little program at www.smokemup.com
I inputed all the data i had......
I think 10:1 on these motor is definitley on the high side!
Bore(Inches)=3.9370
Stroke(Inches)=3.1063
Connecting Rod Length(Inches)=5.9055
Cylinder Head Volume(cc)=40
Deck Height(Inches)=.003
Head Gasket Bore(Inches)=4.01575
Head Gasket Thickness(Inches)=.035
Piston to Cylinder Wall Clearance(Inches).00984
Top Ring Land Height(Inches)=.33464
Piston Dish Volume(cc)=24
Positive number is dished piston. Negative number is a domed piston.
------------------------------------------
Bore / Stroke Ratio: 1.267 : 1
Rod / Stroke Ratio: 1.901 : 1
Total volume: 691.972 cc's
Compressed volume: 72.184 cc's
Compression Ratio: 9.586 : 1
time for another too many numbers today!
I just edited this AGIAN!!..the new CR is above...for some odd reason the program gave me a different value the 2nd time around?????i ran it 3 frikn times now and that, Regis, is my final answer...9.586:1!! <sigh>
Compression Ratio: 9.586 : 1
I inputed all the data i had......
I think 10:1 on these motor is definitley on the high side!
Bore(Inches)=3.9370
Stroke(Inches)=3.1063
Connecting Rod Length(Inches)=5.9055
Cylinder Head Volume(cc)=40
Deck Height(Inches)=.003
Head Gasket Bore(Inches)=4.01575
Head Gasket Thickness(Inches)=.035
Piston to Cylinder Wall Clearance(Inches).00984
Top Ring Land Height(Inches)=.33464
Piston Dish Volume(cc)=24
Positive number is dished piston. Negative number is a domed piston.
------------------------------------------
Bore / Stroke Ratio: 1.267 : 1
Rod / Stroke Ratio: 1.901 : 1
Total volume: 691.972 cc's
Compressed volume: 72.184 cc's
Compression Ratio: 9.586 : 1
time for another too many numbers today!
I just edited this AGIAN!!..the new CR is above...for some odd reason the program gave me a different value the 2nd time around?????i ran it 3 frikn times now and that, Regis, is my final answer...9.586:1!! <sigh>
Compression Ratio: 9.586 : 1
Last edited by Tony; 01-08-2004 at 02:36 AM.
01-08-2004, 01:48 PM
#54
All this CR talk has forced me to look at my 89GT service info technik....I'm sure this has been posted before, but here is some additional info..
The CR spec for the M28/47 is given at 10.0
The CR spec for the M28/41 and 42 is given at 10.0 (-.6)..so range of 9.4 to 10.0
Comment on Pistons
" Pistons for M 28/47 engines have a smaller well between the valve pockets. This guarantees that there is always a compression ratio of at least 10.0 to 1 in all cylinders. (In comparision: compression ratio of 10.0 (-.6) fro M28/41 and M28/42 engines).
The principle design and designations on the pistons have not been changed"
So..question is....the well between the valve pockets????..is that the center dish area?..if so...then machining this area deeper (evenly across) is probably a good way to lower the CR?
Later,
Tom
The CR spec for the M28/47 is given at 10.0
The CR spec for the M28/41 and 42 is given at 10.0 (-.6)..so range of 9.4 to 10.0
Comment on Pistons
" Pistons for M 28/47 engines have a smaller well between the valve pockets. This guarantees that there is always a compression ratio of at least 10.0 to 1 in all cylinders. (In comparision: compression ratio of 10.0 (-.6) fro M28/41 and M28/42 engines).
The principle design and designations on the pistons have not been changed"
So..question is....the well between the valve pockets????..is that the center dish area?..if so...then machining this area deeper (evenly across) is probably a good way to lower the CR?
Later,
Tom
12-14-2006, 04:37 PM
#55
Trying to continue this very informative thread to keep this organized when people search.
The S4 Piston, stock then, is 24cc.
The S3 piston is 8cc or 6.5cc. 8cc is the going number from what I can see.
That makes the S3 pistons in block + heads 11.5 compression.
Per: This
Very informative!
A bit of relieving on the S4 head may work to lower the compression, but here it is:
Will the flycuts in the 86 pistons hit the valves in the S4?
John V in this thread thinks it may be an issue that needs to be addressed.
The S4 Piston, stock then, is 24cc.
The S3 piston is 8cc or 6.5cc. 8cc is the going number from what I can see.
That makes the S3 pistons in block + heads 11.5 compression.
Per: This
Very informative!
A bit of relieving on the S4 head may work to lower the compression, but here it is:
Will the flycuts in the 86 pistons hit the valves in the S4?
John V in this thread thinks it may be an issue that needs to be addressed.
02-02-2009, 02:42 PM
#57
Nordschleife Master
