What rocker arm ratios do people see? Options

[nathansnathan]

It sounds to me like you are doing something wrong. I could be wrong of course but the valve lift looks like it should be .368". That factors in the stock rocker ratio. I talked to the people at webcam and they confirmed this to be the case. I forget what it was 1.3 or 1.4 that they said they used. They are pretty versed on this stuff. The secretary was explaining the difference between cam lift and valve lift to me. (IMG:style_emoticons/default/smile.gif)

[stugray]

(IMG:style_emoticons/default/confused24.gif)

[ChrisFoley]

It is not possible that you are the first to discover the rocker ratio is different than what everyone has believed for 40 years.
There is only one remaining possibility - the camshaft is fubar.

[stugray]

Stu,

Nobody will try to help you if you continue with your argumentative attitude.

MY Raby cam card shows the peak cam lift and peak valve lift based on 1.3 rocker ratios. I would think your card shows the same.

All factory Type IV lifters regardless of 1.7, 1.8 or 2.0 have a 1.3 ratio. Go with 1.3, stop trying to re-evaluate a known value.

Jake's article explains that shims and pushrod lengths will affect total lift.
Look at the value for peak lift valve on your cam card and shoot for that.

Bob, now that we have established that these rockers tend to be 1.4, I suggest you re-evaluate your statement above. I have now measured 5 sets of 1.8L Intake rockers and found them to be almost exactly 1.4 Ratio. So should I just ignore reality or "stop trying to re-evaluate a known value"? What is that "known" value again?

Stu

[stugray]

It is not possible that you are the first to discover the rocker ratio is different than what everyone has believed for 40 years.

Chris - I had three reputable machine heads sit and watch the dial indicator "go-round and round" and measured .520 on two different cylinders and after swapping out the rockers from two different engines. (more than FIVE separate measurements). The cam lift is .368 per Jakes cam card and measurement ....

I have two complete sets of 1.4 Intake rockers. Exhaust rockers measure closer to 1.3.

Stu

[ChrisFoley]

The cam card says the valve lift is .368".
Your posted measurement of cam lift was .384".

[stugray]

Chris,

That's right. I need to remeasure the cam lift now that I have full spring tension on the lifters. I'll do that today.

Stu

[worn]

Chris,

That's right. I need to remeasure the cam lift now that I have full spring tension on the lifters. I'll do that today.

Stu

I have followed this with interest, for a while now. It seems like you can safely draw a few conclusions.

1. The rockers are what they are.

2. The valve lift is the goal, and apparently for you, it is too high.

3. The cam causes the valve lift.

So, with all of that in mind, I respectfully submit that the cam you have may not be able to produce the goals you have set. Your diagram about changing the height of the rocker pedestals isn't going to cure this. For one thing, while you showed the arm length changing on the push rod side, you didn't take into account the change in moment arm on the valve side, so the impact on ratio is not as big as you think.

It may be that the cam is designed for people who want a great deal more lift than you or most people want to run.

Good luck - My next project is (IMG:style_emoticons/default/w00t.gif) cutting push rods to length .

[stugray]

I just spoke with one of the Type-IV experts at Fat Performance.

After explaining that I bought a "Raby Cam package.." His exact quote was "Oh not another Raby Victim!".

He said that these engines never came with 1.3 Intake rockers and that the 1.4 I am measuring is essentially textbook.

He said that you can get rockers for almost any ratio you want for a TYPE-I, but not a type IV.

So for all of those out there telling me "All factory Type IV lifters regardless of 1.7, 1.8 or 2.0 have a 1.3 ratio. Go with 1.3, stop trying to re-evaluate a known value."

Try measuring one yourself instead of using hearsay to build an engine.

I will now determine which WEBCAM to buy or send my raby cam to Steve Long to fix it.

I have measured 5 separate Intake rockers and they are ALL ~1.4.

worn - I totally agree with your assesment above - " I am attached to another object by an inclined plane, wrapped helically around an axis" (Leonard Big Bang Theory)

Stu

[bobhasissues]

Bob, now that we have established that these rockers tend to be 1.4, I suggest you re-evaluate your statement above. I have now measured 5 sets of 1.8L Intake rockers and found them to be almost exactly 1.4 Ratio. So should I just ignore reality or "stop trying to re-evaluate a known value"? What is that "known" value again?

Stu,
Here are the known values:
1) You are a mentally ill idiot who insists on having the last word. I don't think you have established a thing other than you are an asshole. A lot of people tried to politely point that out to you in your Raby rant thread but nobody seems to have gotten through to you.
2) You will build a grenade, that's why I follow this thread.
3) Nobody really wants you to fail (but you are such a douche I can't wait for it)


The geometry of your set-up will effect your ratio. You have already stated that shimming the rockers has changed your ratio. Have you tried shortening your pushrods? Pushrod length will also have an effect on the ratio because you will have to re-adjust the swivel foot to compensate for the shortened pushrod which will change the centerline of the rocker and effect the ratio. Also, you've read it in Raby's instructions and it has been repeated here, at 50% of whatever your lift is you need to make sure your adjusters and valves are in a straight line, otherwise the geometry is wrong and everything else you are doing is a waste of time.

[stugray]

Bob I " will build a grenade, that's why I follow this thread" only if I listen to your advice.

You told me ignore the measurements and go with it.

If I did that I would have .550 Intake valve lift and about MINUS .030 clearance.

[stugray]

Ok, so I decided to go with a webcam 86b instead of the other.

I measured it prior to installation.
The wecam 86b has an advertised "Valve Lift" of .500/.500 Int/Exh.
http://www.webcamshafts.com/pages/automobi...691_001095.html

So I measure the cam and get: .365/.365 lift at the cam.

.365 * 1.37 = .500 valve lift.

So apparently Webcam knows that these rockers are closer to 1.4 than 1.3, but I must just be a "mentally ill idiot" just like webcam.....

So based on the advice above (Type-IV rockers are always 1.3), I need to adjust these rockers until I get a valve lift of .365*1.3 = .474 instead of the advertised valve lift of .500.

So which is it? Both webcam and I must be "off our rockers"

I now have just what I needed. Valve lift of less than .510 on both int & exh. and I can dial my deck height to get a close as possible valve clearance whie maximizing CR.

Thank you webcam.
Stu

[worn]

Ok, so I decided to go with a webcam 86b instead of the other.

I measured it prior to installation.
The wecam 86b has an advertised "Valve Lift" of .500/.500 Int/Exh.
http://www.webcamshafts.com/pages/automobi...691_001095.html

So I measure the cam and get: .365/.365 lift at the cam.

.365 * 1.37 = .500 valve lift.

So apparently Webcam knows that these rockers are closer to 1.4 than 1.3, but I must just be a "mentally ill idiot" just like webcam.....

So based on the advice above (Type-IV rockers are always 1.3), I need to adjust these rockers until I get a valve lift of .365*1.3 = .474 instead of the advertised valve lift of .500.

So which is it? Both webcam and I must be "off our rockers"

I now have just what I needed. Valve lift of less than .510 on both int & exh. and I can dial my deck height to get a close as possible valve clearance whie maximizing CR.

Thank you webcam.
Stu

Hi Stu,
When I got the head on for a trial run I got the exact valve lift that web cam advertises. I added shims under the pedestals so that the end of the elephant foot screw (inside the foot) was lined up at the mid point of the rocker shaft at mid lift. That is the starting point. After that, the screws do not alter valve geometry very much. Then I cut the push rods so that they also contacted the rockers at centerline height at mid valve lift. In both cases you draw the line at right angle to the valve stem or pushrod through the rocker shaft center line.

OK, I miss cut the chromemoly pushrods, so now I have to shorten them by 1.5 mm. They will be in my case 2 mm shorter than stock. I strongly endorse this link to help solve things:
http://www.crankshaftcoalition.com/wiki/im...ER_GEOMETRY.pdf
This has a lot of info about SBCs, but at the bottom it discusses our type of rockers. It is a fantastic article. Good luck with the build. Ice may melt eventually here.

[nathansnathan]

So apparently Webcam knows that these rockers are closer to 1.4 than 1.3, but I must just be a "mentally ill idiot" just like webcam.....

So based on the advice above (Type-IV rockers are always 1.3), I need to adjust these rockers until I get a valve lift of .365*1.3 = .474 instead of the advertised valve lift of .500.

So which is it? Both webcam and I must be "off our rockers"

I called webcam again last week about another issue. I had posted before that I couldn't remember if they said 1.3 or 1.4, but this time, remembering this thread, I said 1.4 and she corrected me that they are using 1.3.

I was trying to index a cam using a harbor freight indicator on a lifter. I tried going back and forth between the intake and exhaust on #1 for like 2 hours and couldn't get a decent consistent reading - was getting variations of like .035". The tip kept moving up the cone of the lifter and the indicator itself was giving me some slop to like +/- .005, so measurement was really hard to get at the cam in my experience. Add to this that any error there will be multiplied by the rocker ratio.

I would measure at the valve and be happy with coming within whatever recommended percentage of advertised lift. It sounds like the difference you are getting is within 5% of advertised which I think is acceptable.

[stugray]

My plan is to set the intake right at the "advertised" lift of 0.500.
Knowing full well, that I will not be able to get that at the Exhaust.

I expect to see the following:
0.500 Intake with 1.37 Rocker Ratio (0.365*1.37)
0.475 Exhaust lift with 1.3 Rocker Ratio (0.365*1.3)

The point I was making is that if this cam has an advertised valve lift of 0.500 and both valves have a lobe lift of 0.365, then whoever designed the cam was using 1.37 for the rocker ratio.

If they assumed 1.3 (like the person on the phone said), then the lobe lift would need to be: 0.500/1.3 = .385
So apparently not everyone uses 1.3

I measured all 4 lobes and all measurements were within .001, so I am positive that I am not off by .020.

Stu

[worn]

My plan is to set the intake right at the "advertised" lift of 0.500.
Knowing full well, that I will not be able to get that at the Exhaust.

I expect to see the following:
0.500 Intake with 1.37 Rocker Ratio (0.365*1.37)
0.475 Exhaust lift with 1.3 Rocker Ratio (0.365*1.3)

The point I was making is that if this cam has an advertised valve lift of 0.500 and both valves have a lobe lift of 0.365, then whoever designed the cam was using 1.37 for the rocker ratio.

If they assumed 1.3 (like the person on the phone said), then the lobe lift would need to be: 0.500/1.3 = .385
So apparently not everyone uses 1.3

I measured all 4 lobes and all measurements were within .001, so I am positive that I am not off by .020.

Stu

From what you say, it sounds like you will be seeing 0.500 lift at both valves. The lobes sound the same - am I understanding that? If the lobes are the same, the lift must also be the same, unless you have found the rockers with the 1.3 ratio I know that you were seeking. Did you find rockers with different ratios? If so, can you comment on how you did it?

[stugray]

I have found (after testing 8 sets of rockers) that the Intakes tend to be ~1.36-1.38 while the Exhausts are 1.3-1.32.

Now of course you can adjust SOME via pushrod length or rocker spacers (I have both), so we shall see. I expect to break down and remove the other cam and insert the webcam this weekend.

I used every adjustment technique suggested above and could not get my Intake vale Lift to less than .520 with that cam (without ridiculous rocker spacers).
It was just not the right cam for my engine.

This is why we measure (per Jakes recommendations) instead of just accepting myth & "internet expert's" advice.
If I had just accepted "on faith" that the Intake rocker was OK based on the 1.3 value & my calculations, I should have been fine.
But after measuring with the valve travel/dial indicator, and the "clay on the piston" method I would have broken an intake valve during the cam break in period.

We are all good now while still using Jake's recommended valve train geometry adjustment instructions.

I will try to take a lot of pics the second time through.

Stu

[stugray]

So I put in the new webcam 86b.

Advertised lift is: .500/.500

And I get .504/.475. Funny how that is within .005 of what I predicted above using rocker ratios of 1.37/1.32.

And the 50% lift adjustment left me with a pushrod length of 269.5mm very close to what Jake says to start with.
No shims required (even though I already had them;-(

Stu

[stugray]

Just finished the "Clay on the Piston" test and get:

Intake Valve to Piston clearance: .100
Exhaust Valve to Piston clearance: .130

Deck height with no shims or head gasket is .025-.034 (cyl1-cyl2)

Just for future comparisons.

Stu

[stugray]

One observation that I made:

When measuring the webcam with a micrometer, the smooth face of the mike easily marred the black oxide coating on the cam with just one delicate measurement.

After removing Jakes cam (that went through HUNDREDS of full engine rotations with pushrods & springs) there is absolutely zero noticeable wear of his coatings. I even measured the cam with the same Mike method as I measured the webcam with and not a single noticeable scratch.

So whatever Jake has done to his cams for a coating is NOT the same as a stock webcam.

Not sure if it makes a difference in the long run or not.

Stu