Landracing Forum Home
November 21, 2017, 08:51:04 AM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with username, password and session length
News:
BACK TO LANDRACING.COM HOMEPAGE
 
   Home   Help Search Calendar Login Register  


(Note: Donations are not tax deductible)







Live Audio Streaming and Archives of Past Events
Next Live Event: TBD
Pages: 1 ... 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 [196] 197   Go Down
  Print  
Author Topic: Team Go Dog, Go! Modified Partial Streamliners  (Read 519459 times)
salt27 and 1 Guest are viewing this topic.
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2925 on: November 03, 2017, 12:14:37 AM »

Now I am figuring out the timing settings with no valve lash so I can time the cams.  IO, IE, etc.

The cam card lists a 17 BTDC intake opening with no lash at 0.050 lift.  It lists the duration at 0.050 as 258 at .050.  Using the formula for a cam with the lobe centered between the ramps, the intake centerline is (258/2) - 17 = 112.  This is the intake centerline listed on the cam card.

These cams were digitized by Kibblewhite and the file is input into the "D" program.  Note that the intake centerline is entered as 112 just like on the cam card.  The intake duration at 0.050 is 258.8 degrees using the IE + 180 + IO formula.  This is very close to the value on the cam card.

The lobe tip should be centered between the ramps according to the cam card.  The intake centerline based on the opening and closing values from the digital model are (258.8/2) - 20 = 109 degrees.  This is not the 112 value.  This cam is ground funny, or it is ground correct and the cam card is goofy.  I can't win.

That table made last night is based on the digitized cam profiles in the "D" program.  It looks like these settings work best.  103-111 when the cams are installed with a new chain, this will go to 105-109 when the chain is half worn, and 107-107 when the chain is worn out.  It gives the best trapped mass at lower rpm with only a small loss on top.  Keep in mind, these cams with their dingbat profiles might act like ones with wider lobe centers.   


* 2018 Build 020.JPG (277.21 KB, 960x720 - viewed 29 times.)
Logged
RansomT
Sr. Member
****
Offline Offline

Age: 58
Location: Georgetown, KY
Posts: 472





Ignore
« Reply #2926 on: November 03, 2017, 08:38:52 AM »

From the screen capture...I get intake at 111 and exhaust at 111.5 so that's close enough....goofy cam ground maybe..



* cam capture.JPG (34.81 KB, 318x290 - viewed 32 times.)
« Last Edit: November 03, 2017, 08:50:41 AM by RansomT » Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2927 on: November 03, 2017, 07:42:51 PM »

By hand using data from the screen shot for 0.050:  intake duration = 20 + 180 + 58.8 = 258.8  exhaust duration = 60.6 + 180 + 17.6 = 258.2  overlap = 20 + 17.6 = 37.6  intake centerline = (258.8/2) - 20 = 109.4  exhaust centerline = (258.2/2) - 17.6 = 111.5  LSA = (109.4 + 111.5) / 2 = 110.45  This input was entered into the RB Racing cam calculator during lunch and I got similar results.

The lobe centers are set in the "D" program at 112 intake and 111 exhaust and it is using the digital profiles  This is what I think is happening.  The exhaust has a typical profile with the front and back faces symmetrical.  The opening and closing is what one would expect from the simple math equations.  The intake cam is ground with a more convex front face and a less convex rear.  It is opening and shutting the intakes like a symmetrical cam would with a 109.4 lobe center angle.

This hypothesis will be tested using a degree wheel on the cam and a dial indicator on a lifter.  The initial modeling in the "D" program used 10-point data based on cam card values.  The card data is based on symmetrical lobes.  Later modeling used digitized profiles.  There was a significant difference in the results.  This might explain why this happened.

   
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2928 on: November 04, 2017, 09:20:27 AM »

What is the formula to alter static compression ratio to simulate change in air density between SAE conditions and the climate at the salt flats?  I am aware that the actual ratio does not change.   
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2929 on: November 05, 2017, 02:54:03 PM »

This is the worksheet for peak cylinder pressure using 13 to 1 static compression ratio and SAE atmosphere.  The highest pressures are boxed.  The most boxes are in the 107 to 108 range.  This corresponds exactly to the value recommend by a chart in one of Vizard's books.


* 2018 Build 021.png (465.68 KB, 713x1080 - viewed 14 times.)
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2930 on: November 05, 2017, 03:10:37 PM »

The compression ratio is lowered to 11.1 to 1 to simulate the atmosphere at the salt flats.  The chart was redone with the same results.  The 107 and 108 angles give the best pressures.  The valve timing will be set using 107.5 LCA.  The lobe centers will be set at 105.5 and 109.5.  This is 2 degrees advanced.



* 2018 Build 022.png (236.08 KB, 521x720 - viewed 23 times.)
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2931 on: November 05, 2017, 11:46:34 PM »

Some background information.  The cylinder head has good low lift flow and this is typical of a professionally ported four valve head.  It is very effective at dropping cylinder pressure when the exhaust valve opens at the bottom of the compression stroke.  The head is also good at bleeding off pressure when the piston rises before a the intake valve closes.  The result is they need shorter duration cams than would be expected.  The cam in this bike is tall in relation to the diameter of the tappet cap.  A narrow profile cam will not push the cap down enough far enough to stay on the tappet when the lobe tip crosses it.  Some convex profile is needed near the lobe tip to depress the tappet enough so the tip will stay on top of the bucket when it passes over it.  This gives the cams more duration than is desired.

"Set cam timing so excess duration is thrown toward the overlap" is what I remember being told, and "This maintains the best cylinder pressures."  This is what the computer program says, too.  It results in a tighter than expected optimum LSA.   
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2932 on: November 10, 2017, 11:24:50 AM »

Intake valve head to piston crown clearances are measured.  The minimum clearance recommended by Arias is 0.090 inches.

The first trial is for the 107.5 lobe separation angle recommended by the program and Vizard's book.  The cams are set at 4 degrees advanced with a new cam chain.  The cam advance is expected to be optimal at 2 degrees after the chain beds in.  No cam advance is expected when the chain wears out.  The piston gives 11.7 to 1 compression with the measured combustion chamber volume.

The smallest piston to valve clearance is 0.100 at 4 degrees advance.  This shows me that this is the tightest intake angle that can be had with these pistons using the valve pockets they have.  Raising the compression ratio to 13:1 will require raising the crown, only.  No depth can be removed from the valve pockets.  They are just deep enough for this separation angle.

Next, the 110 degree separation angle recommended by Ransom T will be checked with 106-114, 108-112, and 110-110.  That larger angle might be needed to give enough clearance for a compression raise.
Logged
RansomT
Sr. Member
****
Offline Offline

Age: 58
Location: Georgetown, KY
Posts: 472





Ignore
« Reply #2933 on: November 10, 2017, 01:39:17 PM »

Intake valve head to piston crown clearances are measured.  The minimum clearance recommended by Arias is 0.090 inches.


0.090" seems a little on the conservative side for the intake.  0.060" IN , 0.090" EX is what I check against.  It all depends on piston manufacture, rods, combustion design, etc...  But if Arias recommends it, I would stick with it..also could be valve to valve clearance if it gets tighter than 0.090"..
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2934 on: November 11, 2017, 01:08:46 AM »

It is an air cooled engine and the pistons are wide and short.  They rock in the bores before they get warm and expand to a tighter fit in the cylinders.  That 0.090 recommendation seems to be valid based on experience, too.

The RB Racing dynamic compression calculator gives combustion chamber volumes.  The volume now with 11.7 to 1 compression is 46.50 CC.  The volume for 13 to 1 compression is 41.46 CC.  The difference is 46.50 - 41.46 = 5.04 CC.  The deck height and head gasket thickness are at minimums now.  The only way to get compression is to add metal to the combustion chamber or to the piston crown.  Reworking the chamber is far to mental for this guy.  New pistons with higher crowns are the way to go.

The top of the existing crown is 1.5 CM by 7 CM.  The top of a higher crown would be 0.5 CM by 6.5 CM  The crown would be 0.163 CM higher.  This gives a crown addition volume of 1.06 CC.  This leaves 5.04 - 1.06 = 3.98 CC that needs to be added to the pistons.  The only way to do this is to raise the valve pocket floors.

The valve pocket floor area is 34 square centimeters.  The rise in pocket height is 3.98 CC / 34 SQ CM = 0.12 CM or 0.046 inches.

My calculations are not rocket science precision.  A minimum 0.100 inch clearance will be used between the valve head and the piston crown.  This is slightly higher than the 0.090 recommended by Arias.  Intake valve clearance at 107.5 degrees lobe separation is checked first.  The smallest clearance is 0.119 inches at 10 degrees ATDC.  The valve pockets can be raised 0.019 inches.  This is not enough.

The minimum clearance at 110 LSA is 0.123 inches at 10 degrees ATDC.  This is not enough, either.  It needs to be at least 0.146 inches.  The clearances will be checked at 112 and 114 LSA tomorrow.
   
Logged
jacksoni
Sr. Member
****
Offline Offline

Age: 73
Location: Annapolis, Maryland
Posts: 964




Ignore
« Reply #2935 on: November 11, 2017, 06:33:55 AM »

You should check your P-V at additional spots besides the "magic" 10* before and after  (EX and IN) TDC. Each engine is different. On mine the closest on the intake valve was closer to 20*after TDC and was a lot closer than at 10*. I start checking each at 20 before and go until it starts getting bigger after, every 5*. And that may be too big a jump if you are running really tight (you  are being generous and safe at .100".) I think you can get away, some engines, with a lot less on the intake- I have run under .030"- but you better be sure of your valve control in that sort of setting and with your cam advance changing so much with chain wear, what you are doing is wise.
Logged

Jack Iliff
 G/BGS-250.235 1987
 G/GC- 169.741  2009
 G/GMS-178.835 2010
RansomT
Sr. Member
****
Offline Offline

Age: 58
Location: Georgetown, KY
Posts: 472





Ignore
« Reply #2936 on: November 11, 2017, 09:55:12 AM »

Just a thought: Sometimes folks forget the interaction of the spark plug into combustion chamber, especially when using the assumptions of computer generated chamber sizes.

And: I've heard stories of drag race engine builders from a couple of decades ago, that would incrementally reduce the quench area to the point that the pistons would scruff the head and call it perfect!  But, when the rod bearings would wear, you had a big boom!


Of course, you know that sometimes 1 degree of cam timing movement frees up a lot of PTV clearance.
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2937 on: November 11, 2017, 10:13:11 AM »

That is what I did.  It was to check the clearances every two degrees on either side of the tightest.  It was tightest at the usual 10 degrees.  It looks like big LCA is needed to give as much as 0.090 clearances.  This will cancel out the advantages of using higher static compression.  The wider angles kill the dynamic.  There is another solution.  

The intake valves are 2mm larger than standard and new seats were installed.  The removal of cylinder head material to accommodate those seats and to reduce the shrouding around the bigger valves is causing the bigger chamber volume.

The exhaust valves are 1mm larger than standard and the existing seats and ports are reworked to get better flow.  There is no loss in combustion chamber volume.  The compression would be 13 to 1 if I had done similar with the intake valves.

Mach number calculations show the 2mm larger valves are not needed.  Computer modeling shows that a slight loss in intake flow at low lifts does no harm at all.  There is an almost new cylinder head in the junk pile.  Right now I will go with the pistons I have and redo that newer head when I get the time.  That will give me good flow, 13 to 1 compression with the pistons I have, and allow a tight LCA.  There is a new set of pistons and rings just like the ones in the bike now with thermal and friction coating in the junk pile.  This is incentive to work on the newer head.

    
Logged
RansomT
Sr. Member
****
Offline Offline

Age: 58
Location: Georgetown, KY
Posts: 472





Ignore
« Reply #2938 on: November 11, 2017, 10:38:12 AM »

That is what I did.  It was to check the clearances every two degrees on either side of the tightest.  It was tightest at the usual 10 degrees.  It looks like big LCA is needed to give as much as 0.090 clearances.  This will cancel out the advantages of using higher static compression.  The wider angles kill the dynamic.  There is another solution.  

The intake valves are 2mm larger than standard and new seats were installed.  The removal of cylinder head material to accommodate those seats and to reduce the shrouding around the bigger valves is causing the bigger chamber volume.

The exhaust valves are 1mm larger than standard and the existing seats and ports are reworked to get better flow.  There is no loss in combustion chamber volume.  The compression would be 13 to 1 if I had done similar with the intake valves.

Mach number calculations show the 2mm larger valves are not needed.  Computer modeling shows that a slight loss in intake flow at low lifts does no harm at all.  There is an almost new cylinder head in the junk pile.  Right now I will go with the pistons I have and redo that newer head when I get the time.  That will give me good flow, 13 to 1 compression with the pistons I have, and allow a tight LCA.  There is a new set of pistons and rings just like the ones in the bike now with thermal and friction coating in the junk pile.  This is incentive to work on the newer head.

 cheers  The best option by far!
Logged
wobblywalrus
Hero Member
*****
Offline Offline

Age: 64
Location: backwoods Oregon
Posts: 4443





Ignore
« Reply #2939 on: November 11, 2017, 03:17:12 PM »

The exhaust valves were checked this morning.  The tightest clearance is 0.164   This can be reduced 0.064 inches.  This, the taller crown, and the small reduction in valve pocket depth on the intakes gives enough volume reduction.  This is using the tight 107.5 lobe separation with a four degree lead.  This is the best setup using 'puter modeling.  An e-mail will go to Arias.  Life is looking good again.  I retire on 30 June next year and I want to get this motor done while there is some cash flow.

An extra set will be made.  This way, if I build a new head in future years with a small volume combustion chamber, a pair of these slugs can be used to give real high compression.  An alky motor in the future?
Logged
Pages: 1 ... 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 [196] 197   Go Up
  Print  
 
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines
Simple Audio Video Embedder
Valid XHTML 1.0! Valid CSS!


Google visited last this page November 11, 2017, 11:52:48 PM