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Old 05-15-2011, 08:05 AM   #331
shearboy2004
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I asked this question in thumpers a while back and got a good answer from an inmate from Aussie.


Quote:
Calculating Compression Ratio
No maths guy here so asking for help .

I have a DR350 now bored out to 450 nothing else has been done to increase squish area so I can imagine that the compression ratio is now fairly high?

DR350 Bore and Stroke is 79 - 71.2

DR450 Bore and Stroke is 89.5 - 71.2

The compression ratio on the DR350 IS 9.5 ; 1

Gotta be someone clever here that could help out .
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Quote:
Somewhere around 11.8:1.

Assumptions. 9.5:1 is accurate. I have used 350cc and 450cc as the actual displacements - fine tune it yourself :) . 1mm squish height. Flat top pistons with valve reliefs that have not changed volume. If the pistons have a dome or dish that differs from the original the new volume must be taken into account.

1. Calculate chamber and squish volume of the 350 using C=Vs/Vc ie. Vc=Vs/C = 350/9.5 = 36.8cc

2. Calculate the difference in volume of the squish area using V=pi.r^2.h. ie V2-V1 = (pi. (8.95/2)^2. 0.1) - (pi. (7.9/2)^2. 0.1) = 1.38cc

3. Add volume to the chamber/squish volume calculated in 1. to the volume in 2. then calculate the new compression ratio.
C = 450 / (36.8+1.38) = 11.77
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Link to actual thread, http://www.advrider.com/forums/showthread.php?t=646691
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shearboy2004 screwed with this post 05-15-2011 at 08:10 AM
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Old 05-15-2011, 08:33 AM   #332
slowsuki1
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the problem is the dr piston is a flat top, the drz piston is dished, the drz piston would have more volume and less compression. dr big bore is 10.5 to 1 compression, so i can't see how the drz would be 12 to 1.
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Old 05-15-2011, 08:48 AM   #333
shearboy2004
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Quote:
Originally Posted by slowsuki1 View Post
the problem is the dr piston is a flat top, the drz piston is dished, the drz piston would have more volume and less compression. dr big bore is 10.5 to 1 compression, so i can't see how the drz would be 12 to 1.
The piston I used was a flat top.
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Old 05-15-2011, 09:24 AM   #334
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Quote:
Originally Posted by slowsuki1 View Post
the problem is the dr piston is a flat top, the drz piston is dished, the drz piston would have more volume and less compression. dr big bore is 10.5 to 1 compression, so i can't see how the drz would be 12 to 1.
Ahh, true. Was just using the numbers Jesse gave me. Maybe it's time to try and cc the head.

Quote:
Originally Posted by shearboy2004 View Post
The piston I used was a flat top.
Bigger valves may have changed the volume of the combustion chamber for me.
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Old 05-21-2011, 04:42 PM   #335
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DR455 - Valve clearance

How far do the valves actually stick down below the head?

The exhaust valves protrude 5 mm below the head.


The intake valves stick down 6.5 mm.


If I understand the cam timing card, it says that at TDC the valves should only be only about 11% into opening or from closing. With that the 3 mm (below deck) exhaust divots in the piston and the 4.5 mm (below deck) intake divots plus 1 mm for the head gasket there should be plenty of clearance. The problem is the exhaust divots in the DRZ400 piston are in the wrong place for the DR350 exhaust valves.

Ghetto "mill".


DRZ400 piston with DR350 exhaust valve reliefs.


Thanks BSR-1 and slowsuki1 for the pushing me this direction.
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Old 05-21-2011, 05:56 PM   #336
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DR455 - Ccing the head and compression ratio

I called Jesse to find out if I was crazy about the 12+:1 compression ratio that I thought he said he had and... I was. He has stock valves and something close to 11:1. Slowsuki1 is correct, 12+:1 would require different hardware than what I've got.

Ok then, how the hell do I figure out the real compression ratio? Need the true volumes to do the calc, so that means ccing the head.

Items for ccing head:
  1. Flat plastic large enough to cover the top of the cylinder and combustion chamber.
  2. Some kind of oil to fill the voids.
  3. A way to accurately measure the oil.

Things learned from first attempt at ccing head:
  1. The plastic must be rigid, like plexiglass.
  2. You can use any oil, canola was used so I could wash out the giant syringe from the first attempt.
  3. A smaller 10 mL syringe is much easier to control and that's important when you only need one more mL!

Spread a film of grease around the rim of the combustion chamber for the plexiglass to seal to (pretty much holds it in place too). Fill the syringe to 10 mL and start filling the combustion chamber through the hole in the plexiglass.


Combustion chamber: (3 * 10) + 4.6 = 34.6 mL


Since my piston is not flat on top the deck void will also have to be cc'd. TDC with 0.45 mm base gasket. Same deal, grease and fill!


Deck volume: 6.8 mL


This is the first time I've used a Google spreadsheet and I must say that is one impressive web control.



If I put it back together right now, it would have 'compression ratio C' 10.36:1. A 0.032" base gasket like slowsuki1 has would put it at 'compression ratio A' 10.73:1. Have to see if the clearance issues are resolved.
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Old 05-21-2011, 07:22 PM   #337
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Awesome job on the cutting and the calcs!
Looks like you'll soon be in business!
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Old 05-21-2011, 07:47 PM   #338
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Impressive work, doctor.
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Old 05-24-2011, 06:50 PM   #339
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looking good man keep up the good work
love the getto mill
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Old 05-27-2011, 04:17 PM   #340
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She lives!

Thanks guys!



Gonna do a post on jetting the FCR-MX37, but I'd like to thank slowsuki1 right now for really putting me in the ballpark to start with.
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Old 05-27-2011, 04:21 PM   #341
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Sounds amazing! Good work!
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Old 05-27-2011, 05:13 PM   #342
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After playing with the base gaskets and deck height I'd check the cam timing - Suzuki isn't especially careful in getting it right to start with and it will have changed if deck height changed.

Glad its running
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Old 05-27-2011, 08:25 PM   #343
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Quote:
Originally Posted by DisTech View Post
Thanks guys!Gonna do a post on jetting the FCR-MX37, but I'd like to thank slowsuki1 right now for really putting me in the ballpark to start with.
Looks and sounds great.
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Old 05-27-2011, 10:53 PM   #344
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Hey man sounds great !!! You must be gagging to ride it ?
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Old 05-28-2011, 01:15 PM   #345
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Ever want to sell it, name your price, I'll take it off your hands. Beautiful bike.
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