Don Terrill’s Speed-Talk

1. How long have they been around ?
2. What was/were the reason/reasons for it's development ? (tight lash cams)
3. In what engine applications (use of engine,type of racing) can they be used ?
4. What are the positive results of tight lash cams ?
5. Are there and negative aspects of tight lash cam's ?

These questions are asked with V-8 solid roller type camshafts in mind, however facts about other types of camshafts relating to tight lash would be ok as well.
Thanks for any answers in advance!! Mark H.

At what lash would you call a cam tight lash?

In the mid '60s I had a SBC Engle solid roller cam which had 0.012" Intake lash and 0.014" Exhaust lash.

Stan

Wasn’t the -097 Duntov in the FI 283’s like .012”/.018”? They have been around a while

Didn't this start/become popular when solid lifters were used on hydraulic cams?

Currently I'm running solids on a hydraulic cam and set them at 0.006 - 0.008". Iron block, heads and rockers.
I know when the lash grows to around 0.010" because that's when I start to hear them.
Any tighter than .006 and valves don't close securely anymore and the engine's idle suffers a bit when warm.

Thanks Stan for getting this topic started. To answer your question in my mind i would consider lash less than .016" to be getting tight. I was hoping for Camking to answer. Mark H.

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

Early slant six Mopars were .008" & .012".

I was under the impression the lash ramp can be ground into the cam pretty much where ever you want it.
"Tight Lash" does sound like a good marketing term and inflates the numbers a bit.

Goes back pretty far... flathead Fords .013in .015ex

swampbuggy wrote: ↑Sun Sep 08, 2019 9:11 am 1. How long have they been around ?

Longer then I have

2. What was/were the reason/reasons for it's development ?

Mostly for marketing, because the shorter the lash ramp, the more aggressive the cam looks, when looking at the distance between .020" and .050", even though it's no more aggressive.
The only performance gain for for going with a tighter lash, is in a restricted class that restricts you to a max duration, or max gross lift.

3. In what engine applications (use of engine,type of racing) can they be used ?

They can be used in any type, as long as the valve lash growth between cold and hot, is less then the recommended Hot Lash

4. What are the positive results of tight lash cams ?

There are none. When we design a profile, we design the valve action(above the lash point), and then add whatever height lash ramp we want. For a given valve lift profile, a .006" lash ramp will have the same velocity and acceleration at the lash point, as a .020" lash ramp.

5. Are there and negative aspects of tight lash cam's ?

As long as the recommended Hot lash for the tight lash cam, doesn't cause the valve to open when it's cold, there's no negative issues.

In short, most of the "tight Lash" cams you know see being marketed, are not about any type of performance or reliability gains. They're pushing them, so people who look at "Major Intensity" will think they're buying a more aggressive cam. They're also pushing them, so they can take all their hydr roller profiles they've been making for decades, and re-brand them as "Tight Lash" mechanical rollers.

I see them being marketed for the street guys. Doesnt the tighter lash make for more lifter life at idle? They say idle is harder on lifters part due to oiling and part i thought was from taking up that initial clearance

Orr89rocz wrote: ↑Mon Sep 09, 2019 11:40 am Doesnt the tighter lash make for more lifter life at idle? They say idle is harder on lifters part due to oiling and part i thought was from taking up that initial clearance

No. When the valve is closed, and there's lash in the valvetrain, there's almost no force being applied to the roller wheel.
The force to the roller wheel/axle, is applied at the lash point, where tie lifter has to work against the forces of the spring and valve mass.
Since the velocity/acceleration at the lash point will be the same, no matter what lash ramp height I make, the force will be the same.

When designing a lobe profile, you first design the lift curve above the lash points, then you add a lash ramp to both sides, matching the velocity/acceleration curves above the the lash points. It doesn't matter the height of the lash ramp you make, because it's still going to have the same velocity/acceleration at the lash point.

Mike, what lash do your cams have for the most part?

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.

Thank you Mike Jones for answering my questions!!! Mark H.

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?