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1100 rocker arm ratio   General Discussion

Started Jul-14 by Ed (VeryNorCalEd); 312 views.
LordRamiro

From: LordRamiro

Jul-23

Like I said, I`m fairly new to all this Bike Mechanics, but after searching as to what it was exactly you were looking for

I remembered a video I watched on the valves adjustements.

Hope this helps

https://www.youtube.com/watch?v=RbypV3OCz4Q

Ed (VeryNorCalEd)

From: Ed (VeryNorCalEd)

Jul-23

LordRamiro,

thumbsupthumbsupthumbsup

Thank you for the reply.relaxed “Retro Tech & Electronics, J C Rubin” has made some very informative YouTube V Star 1100 videos. Thank you for the link.

Everything I’m about to write is my best educated guess and should NOT be considered “Definitive” or used to calculate valve train clearances. For informational purposes only.

From poking around on the web it would seem that the stock 1100 valve springs and  valve to piston clearance can take up to .450 “ of lift.

So lets say you called up Web Cams or Schneider Cams and asked them to make you a set of custom cams with .450” of of total cam lift and you put them in your 1100 you would have catastrophic engine failure or at least or best? bent or broken rocker arms and shafts, valves and springs.flushed Bummer.

Whatever is available out there from a vendor advertising a “Drop in cam” has been already tried and tested and you can use with confidence that they will improve the performance of your 1100 and not cause catastrophic failure.thumbsup

I just needed to mess with the numbers to prove things to myself. Also with some custom cam computer programs you can tweek the horse power and torque curves by applying different cam profiles and total cam lift, different durations of valve over lap and with different rocker ratios.
 

Then the work starts with the actual dyno work to prove out your computer expectations. Again all this has been done.

The reason I am going to post some numbers and calculations is because I have not been able to find anything out there giving me a definitive answer to the original (question) “what is the ratio of the rocker arms on the 1100 and are they both the same?”

1.41 to 1 is the ratio and yes both rockers are the same. Again not definitive. Ratio was calculated using known values found on the internet which may or may not be correct because the info was not from Yamaha  but applied to the 1100 and then applying math forwards and backwards.stuck_out_tongue_winking_eye

If a rocker arm was made like a childs see saw or a balance beam scale it would be a 1to 1 ratio. One side would go down as much as the other side went up.

Engine engineers use a rocker that is not equal or centered and can achieve more down (valve lift) than is applied to up (cam lift) if the longer side is on the valve side.

In the air cooled VW world they have used different ratio rockers to achieve the desired valve lift for a performance gain without having to change cams. You may or may not know but you have to completely tear an air cooled VW engine apart to change a cam. So ratio rockers are an easier way to gain some performance keeping in mind that the valve spring can only compress so much and there is valve to piston clearances to consider as well. The same considerations for the 1100.

So a stock 1100 cam, specs provided to me from Web Cams, has a total cam lift of .284 intake and .280 exhaust.

The aftermarket cams seem to all have the same profiles for the intake and exhaust.

So we will just use the intake to find total valve lift to compare a drop in performance cam and to a stock Yamaha TT 500 cam in a bit.

Stock cam

.284 (stock total cam lift) x 1.41(the ratio of the rocker)= .40044 or .400 inches of total valve lift.

Drop in performance cam

A cam on the internet for the 1100 advertises a total valve lift of .438 so using the same math backwards .438 divided by 1.41= .31063 or total cam lift of .310” Stock is .284

The differences between the total cam lift, in these two examples a stock cam verses an aftermarket performance drop in cam, is .026”

“Drop in” definition is just change out cams the rest of the valve train is stock.

The difference between the total valve lift is .038”

.038” total valve lift - .026” total cam lift = .012 of difference between total cam lift and total valve lift because of the ratio rocker arms.

A total of .012 more total valve lift over total cam lift thanks to a ratio rocker of 1.41” neatothumbsup

More lift means more cylinder filling of fuel and air which means bigger bang, more power.

I mentioned a Yamaha TT 500 cam. Kinda half of an 1100 and also Yamaha engineered.


What happens to be the stock cam profile of Yamaha’s hopped up TT 500 dirt bike cam from 1976 with very similar head design as the 1100?

TT 500;

Total cam lift .312 and duration @ .010” is 292 degrees of rotation. 


Duration is a whole other discussion but for now we will use the number as a base of drivability. The 292 degrees of rotation provides the engine enough vacuum for smooth idle and off throttle increase of RPM.

So the TT 500 cam having .312” of total cam lift x the ratio of the rocker arm of 1.41= .4399 you could call that .440” of total valve lift!!!! thumbsup I like moregrin Remember stock 1100 valves (springs and piston to valve clearance) can handle up to .450” of total valve lift.

The previously mentioned performance aftermarket cam offered on the internet advertised .438” of total valve lift compared to the TT 500 cam of .4399/.440. Only .002” difference and I can only assume the duration would have to be similar to the TT 500 cam or the desired drivability would be affected perhaps in a negative way, maybe not.

TT 500 single cylinder

Vstar 1100 twin cylinders

If you understand exhaust and “scavenging effect” then more degrees of duration can be very beneficial over the 292 degrees of the single cylinder TT 500.

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