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Discussion in 'Thumpers' started by DisTech, Nov 27, 2009.
do you know what mods where done to the rockers ? and do you have the cam specs you used ?
Thanks for all the input guys. I'm going to roll the dice and go with the way it's set up now. Jesse has the same setup with just two .5mm base gaskets. If it won't run right because the compression is to low, I'll remove one of the .5mm gaskets.
40.0cc combustion chamber
3.14 ⋅ (90.0 / 2)² ⋅ 0.5 = 3180 (3.18cc) 0.5mm gasket volume
3.14 ⋅ (90.0 / 2)² ⋅ 71.2 = 452954 (453cc) displacement
(40.00 + 453) / 40.00 = 12.325:1
(43.18 + 453) / 43.18 = 11.491:1 one added 0.5mm gasket
(46.36 + 453) / 46.36 = 11.009:1 two added 0.5mm gaskets
Edit: Bad assumptions, see #336.
Oh I think it'll run, you'll just be losing some power/torque.
You are cruel John. You got me thinking about it.
I know, I know...
You can feel better knowing that I'm having problems with my FZ1 right now so you're not alone.
how thick is your head gasket?
'bout an inch and a half, I think.
unless i am missing something ,the piston would have to be a flattop piston and would have to touch the bottom of the head to get the #S you have.
Not sure I follow. For doing a compression ratio comparison with different base gasket thicknesses my only unknown value was the "combustion chamber" (includes combustion chamber, deck height volume and head gasket space volume).
90.0mm piston (standard drz400)
71.2mm stroke (from the manual)
455cc displacement (from Jesse, 453 in calc)
12+:1 compression ratio (from Jesse, 12.325:1 in calc as starting point)
Solve for "combustion chamber":
(x + 453) / x = 12.325
1 + (453 / x) = 12.325
453 / x = 11.325
x = 40
If the compression ratio used as a starting point is off, the comparison values would slide up or down as well.
I asked this question in thumpers a while back and got a good answer from an inmate from Aussie.
Link to actual thread, http://www.advrider.com/forums/showthread.php?t=646691
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.
Ahh, true. Was just using the numbers Jesse gave me. Maybe it's time to try and cc the head.
Bigger valves may have changed the volume of the combustion chamber for me.
How far do the valves actually stick down below the head?
The exhaust valves protrude 5 mm below the head. :eek1
The intake valves stick down 6.5 mm. :eek1 :eek1
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.
DRZ400 piston with DR350 exhaust valve reliefs.
Thanks BSR-1 and slowsuki1 for the pushing me this direction.
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:
Flat plastic large enough to cover the top of the cylinder and combustion chamber.
Some kind of oil to fill the voids.
A way to accurately measure the oil.
Things learned from first attempt at ccing head:
The plastic must be rigid, like plexiglass.
You can use any oil, canola was used so I could wash out the giant syringe from the first attempt.
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.
<iframe width='1070' height='630' frameborder='0' src='https://spreadsheets.google.com/pub?hl=en_US&hl=en_US&key=0AncxB1ueKB3AdHNlWHFscmR4bWVMdGdxeU9RUTRQd1E&output=html&widget=true'></iframe>
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.
Awesome job on the cutting and the calcs!
Looks like you'll soon be in business!
Impressive work, doctor.
looking good man keep up the good work
love the getto mill
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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.
Sounds amazing! Good work!