gs850 cam degrees; just need a second, third or more opinions

[redahtamn]

Hey all, I am in the process of calculating the ideal intake manifold length and was just looking for a second opinion here.

the picture below is what is in my repair manual on the degrees of my intake and exhaust valves


so what I needed to do was calculate how long the intake valve was open and closed.

calculating open intake in degrees: 276
I got this value by adding 28, 180 and 68 together

calculating closed intake in degrees: 456
since I already had the amount of time that the valve was open I began to calculate the time closed by simply subtracting 276 from 720 degrees; 456

anyone have obligations to these numbers? im going off of what the diagram was telling me, but thats all the info i have so I am hoping that it is correct.

 

[rockcitycafe]

dunno, I think it's going to be a little more complex, what are those open and close numbers at as far as lift? how are you going about calculating intake length?

 

[Sonreir]

dunno, I think it's going to be a little more complex, what are those open and close numbers at as far as lift? how are you going about calculating intake length?

OP is talking about wave tuning.

Also, your intake closed numbers are off.

If the intake valve is open 276° of the cam, then it's closed 84° (360 - 276 = 84). Double it if you want degrees of crank rotation instead of cam rotation.

 

[redahtamn]

yes I am doing some wave tuning theory for my 850. I also believe i understand what your saying about my numbers being off.

what I am hearing is the following

camshaft specs state:
inlet open- 276 degrees
inlet closed- 84 degrees

crank rotation
inlet open- 552 degrees
inlet closed- 168 degrees

with that info I have derived the following

I have decided to start to "tune" my rpm range for 6000rpm, this is 2/3 the 850's redline

I take my rpm and divide by 60 to get revolutions per second; 6000/60= 100

then multiply by 360 to get degrees per second; 100*360= 36000 degrees per second

now i calculate how long the valve is closed; 168/ 36000 = .0046

now i can calculate the required intake length by multiplying by 90% the speed of sound and dividing it all by 2

.0046(306.3m)/2= .714 m (28.11 in)

3rd pulse= 28.11 in/3= 9.37 in
4th pulse=28.11 in/4= 7 in
5th pulse=28.11 in/5= 5.6 inch
6th pulse=28.11 in/6= 4.65 inch

this is the "total" length of the air intake system; including the intake port, tunnel, carb and stacks

a question; do you measure from the rear edge of the intake port, or the most inward part of the dome.

thanks all!

 

[Sonreir]

It's not an exact science since you're approximating the speed of sound anyway. I doubt there's much difference between the inside of the intake valve or the inside of the combustion chamber.

Also, wave tuning is only good for a couple of percentage points of power. I'm not saying don't do it, but let's say your GS850 is putting out 50 horsepower at 6000 RPM. 2% increase nets you one pony. You're not going to be able to tell the difference.

 

[redahtamn]

honestly the only reason why i was trying it was to rough calculate a proper intake length for the bike. im not into horsepower gains on the 850, the thing is a rolling tank.

thanks for the help sir