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Tight lash camshaft questions

General engine tech -- Drag Racing to Circle Track

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swampbuggy
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Re: Tight lash camshaft questions

Post by swampbuggy » Mon Sep 09, 2019 10:23 pm

Bill i think you are correct in what you said. ^^^^^^^ Mark H. :-k

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Re: Tight lash camshaft questions

Post by David Redszus » Tue Sep 10, 2019 1:47 pm

CamKing wrote:
Mon Sep 09, 2019 12:46 pm
novafornow wrote:
Mon Sep 09, 2019 12:33 pm
Mike, what lash do your cams have for the most part?
We use a .012" Lash ramp on most of our roller profiles, so Hot Lash would be .012" x Rocker Ratio.
We chose .012", because if you go down to a .010" ramp, with an Aluminum block and Aluminum heads, the lash growth from cold to hot, would be more then the Hot Lash setting.

We have a series of rollers with .010" ramps, but we recommend them for iron block engines.
We have made roller cams with lash ramps as small as .004", but they're for restricted classes, and have to run with iron blocks and heads.
Mike, thanks for sharing so much useful information.

Do you use the same ramp slope for all cams? What slope do you use, if you feel comfortable sharing that info.

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Re: Tight lash camshaft questions

Post by Truckedup » Tue Sep 10, 2019 2:17 pm

About 15 year ago I had a tight lash cam reground on a new stock core for a vintage GMC 302 inline powered 37 Chevy PU street truck I had...It was done by the late Lazer Cams owner supposedly to get as much duration as possible from a regrind..It was .005 and .007 hot lash I believe ,stock was about .012 and .016 with long ramps..It was faster than the other vintage lumps........
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Re: Tight lash camshaft questions

Post by CamKing » Tue Sep 10, 2019 2:42 pm

David Redszus wrote:
Tue Sep 10, 2019 1:47 pm
Do you use the same ramp slope for all cams? What slope do you use, if you feel comfortable sharing that info.
No. The ramps are matched to each cam.
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Re: Tight lash camshaft questions

Post by Krooser » Tue Sep 10, 2019 10:56 pm

travis wrote:
Mon Sep 09, 2019 2:09 am
Wasn’t the -097 Duntov in the FI 283’s like .012”/.018”? They have been around a while
Nope...they were called "30-30" 's for a reason.

The valve noise was enough to drive off most street racers...if it's that loud it must be fast.
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Re: Tight lash camshaft questions

Post by Stan Weiss » Tue Sep 10, 2019 11:19 pm

MadBill wrote:
Mon Sep 09, 2019 12:55 pm
I guess a tight lash lobe would be a constraint for someone who wanted to experiment with changing lash as a signpost re the benefit of more/less duration?
Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
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Re: Tight lash camshaft questions

Post by travis » Wed Sep 11, 2019 12:50 am

Krooser wrote:
Tue Sep 10, 2019 10:56 pm
travis wrote:
Mon Sep 09, 2019 2:09 am
Wasn’t the -097 Duntov in the FI 283’s like .012”/.018”? They have been around a while
Nope...they were called "30-30" 's for a reason.

The valve noise was enough to drive off most street racers...if it's that loud it must be fast.
The 097 is nothing like the 30/30. The 097 was something like 228/230@.050, about .400” lift. The 30/30 was 254@.050, .485 lift

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Re: Tight lash camshaft questions

Post by David Redszus » Wed Sep 11, 2019 1:47 am

Stan Weiss wrote:
Tue Sep 10, 2019 11:19 pm
MadBill wrote:
Mon Sep 09, 2019 12:55 pm
I guess a tight lash lobe would be a constraint for someone who wanted to experiment with changing lash as a signpost re the benefit of more/less duration?
Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
A constant velocity ramp would consist of a slope (rise over run) for a certain number of degrees.
If the lash is set to a value greater than the ramp height, the follower will crash into the flank of the cam producing a substantial increase in valve acceleration and very often rocker breakage.

Knowing the ramp height and duration in degrees allows one to adjust seat to seat valve timing.
While cams for mechanical lifters may have a ramp duration of 30 deg or more, cams for hydraulic lifters have very limited ramp duration, if any at all.

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Re: Tight lash camshaft questions

Post by Stan Weiss » Wed Sep 11, 2019 9:01 am

David Redszus wrote:
Wed Sep 11, 2019 1:47 am
Stan Weiss wrote:
Tue Sep 10, 2019 11:19 pm
MadBill wrote:
Mon Sep 09, 2019 12:55 pm
I guess a tight lash lobe would be a constraint for someone who wanted to experiment with changing lash as a signpost re the benefit of more/less duration?
Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
A constant velocity ramp would consist of a slope (rise over run) for a certain number of degrees.
If the lash is set to a value greater than the ramp height, the follower will crash into the flank of the cam producing a substantial increase in valve acceleration and very often rocker breakage.

Knowing the ramp height and duration in degrees allows one to adjust seat to seat valve timing.
While cams for mechanical lifters may have a ramp duration of 30 deg or more, cams for hydraulic lifters have very limited ramp duration, if any at all.
David,
How does any of that change between a tight and loose lash cam and being able to do lash loops?

Stan
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Do you use engine simulation software that uses cylinder head flow files?
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Re: Tight lash camshaft questions

Post by David Redszus » Wed Sep 11, 2019 10:23 am

Stan Weiss wrote:
Wed Sep 11, 2019 9:01 am
David Redszus wrote:
Wed Sep 11, 2019 1:47 am
Stan Weiss wrote:
Tue Sep 10, 2019 11:19 pm


Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
A constant velocity ramp would consist of a slope (rise over run) for a certain number of degrees.
If the lash is set to a value greater than the ramp height, the follower will crash into the flank of the cam producing a substantial increase in valve acceleration and very often rocker breakage.

Knowing the ramp height and duration in degrees allows one to adjust seat to seat valve timing.
While cams for mechanical lifters may have a ramp duration of 30 deg or more, cams for hydraulic lifters have very limited ramp duration, if any at all.
David,
How does any of that change between a tight and loose lash cam and being able to do lash loops?

Stan
Stan
How would you define a tight and loose lash cam?

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Re: Tight lash camshaft questions

Post by MadBill » Wed Sep 11, 2019 9:18 pm

Stan Weiss wrote:
Tue Sep 10, 2019 11:19 pm
MadBill wrote:
Mon Sep 09, 2019 12:55 pm
I guess a tight lash lobe would be a constraint for someone who wanted to experiment with changing lash as a signpost re the benefit of more/less duration?
Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
A lobe designed for say 0.012" lash will have a far shorter ramp than one meant for 0.030", thus a narrower range between running off the end of the ramp as per David's post and encountering zero/negative cold lash. (Speaking of which, I read of a well-known West coast Porsche specialist that was running a series of lash loops on an air-cooled engine. Power was improving with each lash reduction, but after they broke for lunch the engine wouldn't start... #-o)
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Re: Tight lash camshaft questions

Post by David Redszus » Thu Sep 12, 2019 12:22 pm

MadBill wrote:
Wed Sep 11, 2019 9:18 pm
Stan Weiss wrote:
Tue Sep 10, 2019 11:19 pm
MadBill wrote:
Mon Sep 09, 2019 12:55 pm
I guess a tight lash lobe would be a constraint for someone who wanted to experiment with changing lash as a signpost re the benefit of more/less duration?
Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
A lobe designed for say 0.012" lash will have a far shorter ramp than one meant for 0.030", thus a narrower range between running off the end of the ramp as per David's post and encountering zero/negative cold lash. (Speaking of which, I read of a well-known West coast Porsche specialist that was running a series of lash loops on an air-cooled engine. Power was improving with each lash reduction, but after they broke for lunch the engine wouldn't start... #-o)
Reviewing about a dozen Cam Dr files for various camshaft types, some consistencies seem to appear which can be easily confirmed.

A ramp height of .020" over 40 deg would produce a slope of 2 deg/.001". That is to say a change in lash of .001" would result in a duration change of 2 deg. Valve train flex and compliance not being considered here.

The same ramp slope could apply no matter what the actual ramp height might be. Or the slope might be steeper or more shallow. I feel much more comfortable knowing the actual ramp height and slope for the cam; actually it is the valve position that must be considered, not the only the cam.

If lash is set larger than the maximum ramp height, we have a problem waiting for us. The impact of excessively large lash settings becomes more severe as the engine rpms increase due to the emergence of valve acceleration spikes.

It is not uncommon, upon CamDr measurement, to find significant variance in duration from valve to valve. Some compensation can be accomplished by setting each valve lash to a different value. In total angle area, it may make little difference, but it does have an affect on overlap and event locations.

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Re: Tight lash camshaft questions

Post by CamKing » Thu Sep 12, 2019 12:48 pm

David Redszus wrote:
Thu Sep 12, 2019 12:22 pm
A ramp height of .020" over 40 deg would produce a slope of 2 deg/.001". That is to say a change in lash of .001" would result in a duration change of 2 deg.
Actually, it would change 4 degrees, because you would be changing each side 2 degrees.
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Re: Tight lash camshaft questions

Post by Stan Weiss » Thu Sep 12, 2019 3:01 pm

MadBill wrote:
Wed Sep 11, 2019 9:18 pm
Stan Weiss wrote:
Tue Sep 10, 2019 11:19 pm
MadBill wrote:
Mon Sep 09, 2019 12:55 pm
I guess a tight lash lobe would be a constraint for someone who wanted to experiment with changing lash as a signpost re the benefit of more/less duration?
Bill,
I don't see why trying the lash looser would be any different between a tight and loose lash cams. Now if you want to try a tighter lash setting then you would probable have to set the valves hot on the dyno.

Stan
A lobe designed for say 0.012" lash will have a far shorter ramp than one meant for 0.030", thus a narrower range between running off the end of the ramp as per David's post and encountering zero/negative cold lash. (Speaking of which, I read of a well-known West coast Porsche specialist that was running a series of lash loops on an air-cooled engine. Power was improving with each lash reduction, but after they broke for lunch the engine wouldn't start... #-o)
Bill,
I knew someone years ago that happened to. Luckily his was water cooled and he was able to run some hot water into it and was off and running again.

Stan
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We have a package of more than 3025 DFW or FLW Files

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Re: Tight lash camshaft questions

Post by Stan Weiss » Thu Sep 12, 2019 3:04 pm

Still not sure what the lash ramp height has to do with lash loops.

I don't know what style lash ramp is being used now, but I have not seen many constant velocity ones lately, although they do make the calculations very easy. For illustration this is a 40 degree 0.020" constant velocity and constant acceleration ramp one side.

Stan

ab-lash-ramp.gif
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Do you use engine simulation software that uses cylinder head flow files?
We have a package of more than 3025 DFW or FLW Files

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