Take-up ramps and Valve Lash (with graph)

n2omike · Post by **n2omike** » Sun Sep 21, 2008 12:13 pm

There is a guy on the FE ford forum by the name of Jay Brown who deals a LOT with the Ford SOHC engine. He's won HotRod's drag week a couple times, but had rocker arm troubles this year.

He has a cam analyzer and posted the chart below. It measures lift every 2º.

He's been running the stock valve lash of 0.016" and 0.024" on his new Comp cam lobes.

What would the ideal valve lash be based on the below design? I'm thinking the current lash completely by-passes the take-up ramp, and may be contributing to his problems.

Thanks!

Post by **CamKing** » Sun Sep 21, 2008 12:26 pm

It's not the lash, it's the cam design.
It looks like the opening and seating velocity's are triple the stock cam.

It also looks like those profiles were not designed for that follower system.
Look at how the exhaust lobe is offset to the left, and the intake is offset to the right. It looks like they used some profiles for another follower system that didn't move as far off center at max lift.

Wolfplace · Post by **Wolfplace** » Sun Sep 21, 2008 12:52 pm

CamKing wrote:It's not the lash, it's the cam design.
It looks like the opening and seating velocity's are triple the stock cam.

It also looks like those profiles were not designed for that follower system.
Look at how the exhaust lobe is offset to the left, and the intake is offset to the right. It looks like they used some profiles for another follower system that didn't move as far off center at max lift.

=
Mike
You confused me which ain't that hard but doesn't the lobe centers in that graph just show a wider LSA?

Other Mike
Tell him to grab the screen & blow up the opening & closing points but to me the opening sides of the Comp lobes look more like I would expect in a very "tight lash" or even hyd lobe

I am not a cam expert by any stretch but I just can't see how you could make the stock lash live with those lobes unless I am missing something.
It looks more like you would need 010 or less to me.
I would expect the valvetrain to get the crap beaten out of it at 16 & 24

My427stang · Post by **My427stang** » Sun Sep 21, 2008 1:05 pm

Mike, I am glad you brought this over.

Like we both discussed on the FE Forum, the RAS caged bearings were bad for the application, but I think its an uphill battle until the lash ramp is changed to something a bit more gentle.

Post by **CamKing** » Sun Sep 21, 2008 1:07 pm

Wolfplace wrote: Mike
You confused me which ain't that hard but doesn't the lobe centers in that graph just show a wider LSA?

To me, it looks like the lobes are off more at the top then they are at the seat. If he can measure the centerline ever .050" lift, we can tell for sure.
I suspect it'll change as it goes up in lift.

Wolfplace · Post by **Wolfplace** » Sun Sep 21, 2008 1:21 pm

CamKing wrote:
Wolfplace wrote: Mike
You confused me which ain't that hard but doesn't the lobe centers in that graph just show a wider LSA?
To me, it looks like the lobes are off more at the top then they are at the seat. If he can measure the centerline ever .050" lift, we can tell for sure.
I suspect it'll change as it goes up in lift.

=
Thanks Mike
Now I see what you are looking at
Is this a bad thing or could it be the opening side is "faster" than the closing
Obviously the open & close ramps are different but it looks like the curve is different over the nose,, especially the ex lobe

That or my eyes are crossed,,,,

Post by **CamKing** » Sun Sep 21, 2008 2:59 pm

Wolfplace wrote: Is this a bad thing or could it be the opening side is "faster" than the closing
Obviously the open & close ramps are different but it looks like the curve is different over the nose,, especially the ex lobe

Without looking at the numbers, it's really hard to tell what's going on.
It looks like the exhaust opens faster then it closes. This can cause the acceleration at valve opening to be higher, and cause damage to the valvetrain..
The intake looks like it closes faster then it opens. This could cause the seating velocity to be higher, and cause seat bounce.

It's hard to tell from that graph, but that's what it looks like to me.

n2omike · Post by **n2omike** » Sun Sep 21, 2008 8:54 pm

Tell me something....

The rockers got their bearings pounded out when the lash was set at 0.016" intake and 0.024" exhaust. Would the rockers be more likely to last, and the cam be more servicable with a tighter lash? If so, what's a ballpark lash that you would recommend?

Can you, or do you know anybody that can grind appropriate lobes for the Ford SOHC FE?

Thanks!

David Redszus · Post by **David Redszus** » Sun Sep 21, 2008 8:58 pm

Is it possible to post the actual data?

Post by **CamKing** » Sun Sep 21, 2008 9:16 pm

n2omike wrote:Tell me something....

The rockers got their bearings pounded out when the lash was set at 0.016" intake and 0.024" exhaust. Would the rockers be more likely to last, and the cam be more servicable with a tighter lash? If so, what's a ballpark lash that you would recommend?

Withjout having all the data, I can't give an exact lash, but it looks like tightening it up will help. If he's got a degree wheel and an indicator on the retainer, he can move the lash by .002" and measure how much the actual seat duration grows. Keep tightening it by .002" and re-checking. At some point, the duration change per .002" lash will about double. That's where I'd set the lash.

Can you, or do you know anybody that can grind appropriate lobes for the Ford SOHC FE?

If I can get the rocker follower geometry, I can grind what ever he needs.

Lasher... · Post by **Lasher...** » Sun Sep 21, 2008 11:42 pm

I know this wont help any with this thread but I have a 1967 Crane Cams catalog and they list several lobes for the SOHC 427.Crane was very involved with Ford on the SOHC program.... Just as a comparison to what was available back in their heyday in 1967 if anyone is intrested.

Please note the durations below.... Crane rated them @ .066 lift at the VALVE.....I have no idea where the timing figures were measured at.

32124...Hi Torque..41-77 / 77-41 , 240 dur , .022/.024 lash , .562 Lift.

32126 .. S/S & FX ..62-84 /84-62 ,270 dur , .016 /.018 lash , .600 Lift

32128.. FX / FC ....70-90 / 92-68 , 280 dur , .016/.018 lash , .612 Lift

32130.. Fuel Drag, 80-100 - 100-80, 300 dur, .016/.020 lash ,.618 Lift

32132.. Lite FC .... 66-86 / 90-62 , ..275 dur , .016 /.020 Lash , .640 Lift

trmnatr · Post by **trmnatr** » Mon Sep 22, 2008 10:01 pm

Cam King,

I have seen where with a small block V8 when you look at the seat timing @.020" on a certain grind the intake opening numbers reflect 105° lobe seperation with a 105° intake centerline

BUT

The @.050" numbers reflect a 106° lobe seperation with the ICL @ 104°

Its a cam i have used alot in the past, makes great tq and hp in small engines. Take a look at the timing numbers @.020" and .050". By .020 it is 105°/105° but @.050" its 106°/104° ///// Now put it on a degree wheel and its 102° ICL - This first one we did degree many times, and looked at the cam card and computed it and thats how it is - Can you give thoughts to what and how they do this? It makes great TQ
.020" numbers reflect 105 lobe center/105icl
IVO 40 IVC 70
EVO 78 EVC 48

.050" numbers reflect 104 ICL but its actually 102
IVO 26 IVC 54
EVO 62 EVC 26

It works great, any thoughts

Post by **CamKing** » Mon Sep 22, 2008 11:01 pm

That's just an asymmetrical profile with a quicker opening then closing.
Most other cam companies do this by designing the opening side without a clearance ramp.
It gives the engine that quick valve opening it likes, but it's hard on parts.
It's like hitting the valve open with a hammer.

dacaman12 · Post by **dacaman12** » Tue Sep 23, 2008 8:14 am

CamKing wrote:That's just an asymmetrical profile with a quicker opening then closing.
Most other cam companies do this by designing the opening side without a clearance ramp.
It gives the engine that quick valve opening it likes, but it's hard on parts.
It's like hitting the valve open with a hammer.

FWIW, all cams have a "clearance ramp". In other words, the values for velocity, accel., and jerk at the lash point are precisely controlled. We just don't use a value of "0" anymore. We use rather high accel. values on the opening in order to keep the peak accel. down. Even the most aggressive opening ramps in the industry aren't "hard" enough on parts to actually break them or wear them out.

This is NOT true for the closing side. We use substantially lower velocity and accel. values for the closing lash point, although we don't use "0" here either.

Here is an example accel. curve with no "traditional" clearance ramp. We've raced these ramps in our craftsman truck engines, and also ran them in street motors that get the lash checked(and maybe adjusted) once a year. No failures, EVER.

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As for the original question, can't you simply call Comp and ask for the correct lash figures? Only the designer knows what the seating values should be and were they are located.

Post by **CamKing** » Tue Sep 23, 2008 1:34 pm

Harold told me back in the 80's
" You can't float the valve on the opening"

You can call it a ramp if you want, but when it's got 3-4 times the velocity at the opening lash point as it does the closing lash point, I don't call it a ramp.
You may not see the effects it has, but I've seen it in many cases, from many different cam companies.

I'm glad you're having success with it.
From what I've seen over the last 25 years, I'll stick with my way.