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lash change to duratioin
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DRR S/Pro
Picture of wideopen231
posted
I know there's no set number here, looking for general or rule of thumb. How much valve lash change to duration change. For instance .010 valve lash looser on a 290* at .050 roughly how much change in duration. Something I was asked and have never investigated,so figured maybe someone here has done while degreeing cam or just curious.Figure curious thing has to effect others too. LOL


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Chris McBride

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Posts: 1341 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post
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the spec lash has nothing to do with the cam's .050 duration and everything to do with the lobe design, specifically it's ramps which is why when setting lash, it's critical you position the lifter on the lash ramp, using the EO/IC method.

That said, .024 hot lash is a safe bet for 99% of roller cam's used in bracket engines discussed here.
 
Posts: 8547 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
DRR S/Pro
Picture of wideopen231
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Ed thanks for reply.

Maybe its how I stated it. What I was wanting to know is how much duration would change with a lash change of ___(.010 was just example as was the duration at .050). More Knowledge thing then a going out and run right off thing. Using Ed's .024 lash how much duration would you gain if going to .014?


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Posts: 1341 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post
DRR Sportsman
Picture of CURTIS REED
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quote:
Originally posted by wideopen231:
Ed thanks for reply.

Maybe its how I stated it. What I was wanting to know is how much duration would change with a lash change of ___(.010 was just example as was the duration at .050). More Knowledge thing then a going out and run right off thing. Using Ed's .024 lash how much duration would you gain if going to .014?


Would depend on the ramp design.


2017 Osage Casinos Tulsa Raceway Park No-Box Champion
 
Posts: 760 | Location: KIEFER, OK. | Registered: August 17, 2007Reply With QuoteReport This Post
DRR Sportsman
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I can never remember. EO/IC do I check intake when exhaust starts to open and check exhaust when intake starts to close?

ep-I usually phone a friend to verify I not screwing up
 
Posts: 208 | Location: dodging double wides... | Registered: November 28, 2007Reply With QuoteReport This Post
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when the exhaust valve just starts to open set the intake lash. When the intake valve fully opens and is almost closed, set the exhaust lash.
 
Posts: 8547 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
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quote:
Originally posted by wideopen231:
Using Ed's .024 lash how much duration would you gain if going to .014?


a few numbers. The advantage of tighter valve lash than spec up to the minimum which for 99% of the cams in the bracket engines discussed here is .010 tighter than spec is everything is happier especially the lifters. Looser than spec just beats up the valve train.

Also keep in mind that the lash spec on your cam card isn't the number where your car will ET/MPH the best, it's just a safe starting point.

Running lash loops to find the best on track performance pays big dividends providing your cam is in the ballpark and not out to lunch.

But hey, I don't know anything and I'm just a check writer who never turns a wrench nor gets his hands dirty according to the haters here but somehow my door cars, both my Chevelle and Firebird have and do piss all over similar cars with more of everything. Uncontrollable Laugh
 
Posts: 8547 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
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Hey ...... next time you're writing out checks ......

Me too



Razz



.


NHRA Pro Stock..........now on a no CARB diet.
 
Posts: 3184 | Location: ohio | Registered: February 21, 2006Reply With QuoteReport This Post
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Laughing very hard who writes checks anymore, I pay everything electronically via the internet including 2 college tuitions. Blue Man
 
Posts: 8547 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
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Picture of "The Bender"
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quote:
Originally posted by 1320racer:
when the exhaust valve just starts to open set the intake lash. When the intake valve fully opens and is almost closed, set the exhaust lash.


^^^^This is a good method^^^^

You can also mark your dampner/hub at TDC, 90°, 180° and 270° (every 90°) and just start with #1 on TDC, then turn 90° and go to the next cylinder in the firing order, then just go through the firing order from there, of course turning the crank 90° for each cylinder in the firing order.


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DRR Sportsman
Picture of CURTIS REED
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Note to self. Don't park beside Ed's cars. Don't want any pee on my stuff. Help


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Posts: 760 | Location: KIEFER, OK. | Registered: August 17, 2007Reply With QuoteReport This Post
DRR Sportsman
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quote:
Originally posted by 1320racer:
when the exhaust valve just starts to open set the intake lash. When the intake valve fully opens and is almost closed, set the exhaust lash.


thanks 1290. I can remember exhaust starts to open check intake. but have trouble remember when intake is almost closed check exhaust. I forget and try to set when intake starts to close.

ep-im on it now

This message has been edited. Last edited by: pauley,
 
Posts: 208 | Location: dodging double wides... | Registered: November 28, 2007Reply With QuoteReport This Post
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quote:
Originally posted by 1320racer:
Laughing very hard who writes checks anymore, I pay everything electronically via the internet including 2 college tuitions. Blue Man




Gotcha ....... so you're wanting my routing number ..... ok


In keeping with the thread....duration.....what's the duration of your college expenses?

So I can look forward to that "heads up" build.


Razz



.


NHRA Pro Stock..........now on a no CARB diet.
 
Posts: 3184 | Location: ohio | Registered: February 21, 2006Reply With QuoteReport This Post
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3 more years and another $250,000 undergraduate then the big $ years start. Holy Moly
 
Posts: 8547 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
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quote:
Originally posted by 1320racer:
3 more years and another $250,000 undergraduate then the big $ years start. Holy Moly



AWESOME .......good Dad !



Not worthy




Bought my kid a carbon fiber body ......... screwed him up for life !


Big Grin



.


NHRA Pro Stock..........now on a no CARB diet.
 
Posts: 3184 | Location: ohio | Registered: February 21, 2006Reply With QuoteReport This Post
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Uncontrollable Laugh
 
Posts: 8547 | Location: NJ | Registered: August 20, 2000Reply With QuoteReport This Post
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The events on your camshaft, intake and exhaust, do not change, although let's say that your current running hot lash is .026/.026. If you take that lash down to .016/.016, then your valve in relation to the valves seat, events start earlier and close later, which in turn alters the valves duration (extended/increased) of which will reduce cylinder pressure, and provide for different hp results. Now, whether those results will be for the positive or negative, no one really knows, and it all depends on how the combination was originally designed. In most cases, many camshafts that are chosen for the end user, do not have enough exhaust side scavenge, and therefore by leaving the hot lash at .024 or .026 on the intake, and lashing down hard on the exhaust, such as .016 or .018, makes for nice down track improvements. This method actually allows for a stronger signal on the carbs booster, and idle circuit which in turn allows for the fuel shear to be better, and it also reduces the reversion, of which is more common that not, with incorrect primary length, incorrect collector length and incorrect camshaft events, of which is commonly found in the industry.


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Posts: 1650 | Location: Suffern, NY | Registered: November 03, 2001Reply With QuoteReport This Post
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Picture of wideopen231
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Thanks for replys. Not to be butt hole but non have given info asked about. How to adjust valve lash was not question. Running valves every run for years, almost always in hurry,I have that one pretty down pat.
EO/IC is method I have used for 30 years(damn I am getting old).Running one side at time and working thru all 8, not cylinder by cylinder.Having adjuster loosened makes sure you don't miss one. Quickest way for me anyway. Then most are not doing between rounds after putting motor back together as regular between rounds.Yea wasn't bracket racing at the time.


What I was asking is there rule of thumb that says for every .005 lash change duration changes roughly 2* or----(just example). Actually I know there is one I was told it 30 plus years ago by old fuel racer just can't remember what it was.

Guess throwing degree wheel on motor is best bet and run few test to see what answer is. Probably should have done in first place.

Strange magic stay away from carbs they are bad for you.My diabetic Dr. said as bad for me as sugars.


http://www.schooledbyscotty.com/
Only the stupid know too much to learn something new.
Chris McBride

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Posts: 1341 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post
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Picture of Lenny5160
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quote:
Originally posted by CURTIS REED:
Would depend on the ramp design.


This is the correct answer to your question.

I did some calculating using the cam from my old 565. This would assume that the cam lobe is shaped like a triangle. It also assumes that the "duration at .050" is based on valve lift and not lobe lift using my 1.8 rockers and .024" lash.

Anyway, I come up with .0055" of valve movement for every 1 degree of cam rotation for the intake, and .00494" on the exhaust.

That would suggest that roughly .005" tighter on the lash would add 1 degree of duration @ .050, and .005" looser on lash would subtract 1 degree of duration.

Again, I'm no cam guru and this is "Holiday Inn Express" math, but that's what I have for you.


Tony Leonard
 
Posts: 2414 | Location: Inver Grove Heights, MN | Registered: March 18, 2004Reply With QuoteReport This Post
DRR S/Pro
Picture of wideopen231
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Lenny thanks! was thinking 1 to 2 per .005 either was hard to get much change. Was hoping I was way off.
Guessing that would equal 2* change in piston to valve movement.Now how much is that worth in real world performance? Don't you love how one answer leads to another question. LOL

Sometimes holiday inn is good enough.


http://www.schooledbyscotty.com/
Only the stupid know too much to learn something new.
Chris McBride

deplorables saving america one vote at a time
 
Posts: 1341 | Location: Greensboro NC | Registered: May 24, 2011Reply With QuoteReport This Post



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