……
Corvair DiagramCorvair Photo
Corvair Center
home forum corvairs calendar links Corvair Podcast
California Corvairs
Clarks Corvair
Clarks Corvair
“CORSA"



Chevy Corvair License Plate
Chevy Corvair Chrome Wheel
Corvair Center Forum :  Corvair Center Phorum - presented by CORSA The fastest message board... ever.
Corvair Center 
Pages: Previous123
Current Page: 3 of 3
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: v8vair ()
Date: January 16, 2023 05:23PM

wittsend Wrote:
-------------------------------------------------------
> I was looking on the Isky site today for other reasons..., but came across this Isky Cam Install Instructions (scroll down to "checking at the valve"):
>
> "Another reason for never checking at the valve is that a rocker arm's theoretical ratio, usually 1.5:1, is true only at approximately mid (1/2) valve lift. The ratio varies from slightly more to slightly less than 1.5:1 through the lifting cycle, because the rocker arm continually varies its point of contact on the valve stem."
>
> A number of posts above I asked the question: "Could it be as someone noted earlier the arcing rocker to the stationary valve isn't a constant LIFT ratio. And as such the 1.50 might be the "average" lift and 1.56 being the gross lift???"

>
> Perhaps this is the answer to that question.
Norman Latullipe does his geometry check at mid lift and I think he does his gross valve lift calculations from mid.
But for me why does everything jive on my V8 but not on the Corvair ???

1964 Bill Thomas Monza Replica Racer
1964 Spyder Street Car
1998 Honda Prelude Dirt track car
1967 Crown V8 under construction
Mike Levine
Cumming Georgia
North of Atlanta

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: erco ()
Date: January 16, 2023 05:50PM

Who the heck is LOUIS?

The Louis Tool is a discontinued little metal jig that helps you elongate the pushrod slot in your guideplate since 1.6 rockers move the pushrod ~7% closer to the pivot ball.

[garage.grumpysperformance.com]

Attachments:
Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: zarfnober ()
Date: January 17, 2023 06:18AM

erco Wrote:
-------------------------------------------------------
> Who the heck is LOUIS?
>
> The Louis Tool is a discontinued little metal jig that helps you elongate the pushrod slot in your guideplate since 1.6 rockers move the pushrod ~7% closer to the pivot ball.
>
> [garage.grumpysperformance.com]

Now I’m curious, did GM make a different guide for the 140 heads, and not tell us, or is the difference in valve angles small enough for the rocker arms to make up the difference? I’m assuming it is.

Rocco

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: Wagon Master ()
Date: January 17, 2023 09:40AM

I wasn't thinking the center distance of the valve stems themselves changed. But I've been wrong a lot lately.

Friends Don't Let Friends Drive Stock
Been Aircooled Since 1973
Northwest Ohio 45840

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: erco ()
Date: January 17, 2023 12:12PM

Ah, Louis Tool inventor Louis Fry. Last post at [www.hotrodders.com]

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: JimBrandberg ()
Date: January 18, 2023 04:52AM

63turbo wrote

"...there was a large number of different recommended lash settings in the manual over the years also..."

--------------------------------------------------------------------------------

After reading what Bob Helt had to say about the different lifters, I am under the assumption that the earliest, like 60-61 lifters have more travel so need more than 1 turn down from zero lash. I am under the assumption that they were pretty much the same from about 62 on as far as adjustment is concerned, although the external may look a little different through the years.
I generally use 3/4 turn for most applications, maybe 1 turn on a 60 and 1/2 turn on something like an Isky 280, maybe 1/4 turn on my own Isky 280 since I can monitor it.

I never really received a definitive answer to my earlier question.
So absolutely positively stock rocker arms are 1.5 ratio and 1.57 was initially a misprint that still shows up on some cam cards and such?

Jim Brandberg
Isanti, MN
CorvairRepair.com



Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: tgould ()
Date: January 18, 2023 06:17AM

Jim,

When I received my 95 hp cam from Lunati Cams back in 1976, I multiplied the lift by 1. 57 and said whoops too much lift, won't pass NHRA tech. I called Lunati, talked to Tech. He said let me ask Joe. Came back. "Joe said they are all 1.5"

Tom Gould
Beaufort SC, 29906

1966 Monza Coupe 110 4spd

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: erco ()
Date: January 18, 2023 09:05AM

@Tom Gould: IMPRESSIVE wheelstand photo, you da man!

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: Seth Emerson ()
Date: January 18, 2023 11:02AM

Before you shuffle other rocker arms onto the Corvair, remember that a "1.5 to 1" or a "1.6 to one" is only a ratio. The distance from the rotating center of the pivot/rocker ball to the rotating center of the pushrod and the distance from the rotating center of the ball to the valve tip must be correct. The pushrod can adapt a bit, but the valve stem cannot. The rocker tip must be designed for the Corvair number (not necessarily for the Corvair, but for the Corvair number) Competition cams told me their 1.6 Ford rocker was the closest to the Corvair. If you can get the correct pattern on the valve tip, without binding at the pushrod guide, that is all that counts.

Seth Emerson

Check my new Performance Corvair Web site: [www.perfvair.com]

Located in lovely San Jose, California

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: wittsend ()
Date: January 18, 2023 12:43PM

I ran the 1.5 vs 1.57 ratio numbers for the following cam lift (rounded at the 4th digit) for the following:

.275 1.5=.413 vs 1.57=.432 for a +.019 difference

.300 1.5=.450 vs 1.57=.471 for a +.021 difference

.325 1.5=.488 vs 1.57=.510 for a +.022 difference

I don't want to say that lift counts for nothing but I'm wondering the significant gain for roughly .020 extra lift?

------------------------------------------------------------------------------

***'61 Lakewood, a "Freebie" in hibernation for 27 years - In the process of applying CPR.***

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: American Mel ()
Date: January 18, 2023 12:58PM

Witt, it is so much the insignificant height, but the additional intake volume one gets, when you take in the total circumference the tiny amount of lift entails.

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
WA. state, 1 mile south of the Canadian border, I am not at the end of the world, but you can see it from here.

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: Wagon Master ()
Date: January 19, 2023 09:39AM

Would not additional lift, even slight, not also increase duration and overlap.

I said slight.

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: American Mel ()
Date: January 19, 2023 02:38PM

"In Theory", that makes some sense to me, WM.
But my wife says I don't think along logical lines hot smiley

-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
WA. state, 1 mile south of the Canadian border, I am not at the end of the world, but you can see it from here.

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: wittsend ()
Date: January 19, 2023 06:43PM

Wagon Master Wrote:
-------------------------------------------------------
> Would not additional lift, even slight, not also increase duration and overlap.
>
> I said slight.


In theory the total duration would be the same because the lifter is still only reacting to the cam. HOWEVER, the valve is opening faster (and thus higher) with a greater ratio rocker at any given comparison point to a lesser ratio rocker.

Not sure of the current rules but NHRA Stock classes use to require cams with factory lift and duration numbers. But to "cheat" the rules the cams would be ground with a ramp to get to the maximum lift as fast as possible and stay there as long as possible. Thus imagine the lobe of the cam being more shaped like and egg than a triangle.

To some lesser extent a greater ratio rocker does the same thing except it does increase total lift more in the process. As to overlap the height of the valve is greater through the overlap and having a slightly similar effect to an increase in overlap. But again theoretically the overlap is still the same due to the lifter being at the same no lift state at the same time regardless of the rocker ratio.

------------------------------------------------------------------------------

***'61 Lakewood, a "Freebie" in hibernation for 27 years - In the process of applying CPR.***

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: tgould ()
Date: January 20, 2023 04:16PM

This was not the only specification change for 1966. The deck spec was changed from .0005 below (64/65) to .004 above (66-69). I wonder what triggered these changes???

Tom Gould
Beaufort SC, 29906

1966 Monza Coupe 110 4spd

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: 63turbo ()
Date: January 20, 2023 06:06PM

Something kind of interesting relates to the GM stock engine tests that I have.

As part of the tests, they measured the actual lift and came up with a rocker arm ratio.

For the 1963 Spyder, the max lift on the intake is: .375", .378" exhaust
the rocker arm ratio: 1.51:1 (intake) 1.52:1 (exhaust)

For the 1965 140, the max lift on the intake is .402", .389" exhaust
the rocker arm ratio: 1.52:1 (intake) 1.53:1 (exhaust)

Notice that theres always a slight difference in rocker arm ratio between the intake and exhaust, but Chevy did not ever offer intake rocker arms and exhaust rocker arms, nor was there supposed to be a change in rocker arm ratio.

Its really hard to see how these ARENT actual measured values and the rocker arm ratio is a simple RESULT of cam lift vs valve lift.

------------------------------------

Kevin Nash
Friday Harbor Washington
63 Spyder, Daily driver, EFI read about my project here: [corvaircenter.com]
first test start on EFI here:[www.youtube.com]
first official EFI boost test here:[www.youtube.com]
My new fan! [corvaircenter.com]
engine less 62 Spyder
Canadian 64 Monza Parts car
Test Start#2 [www.youtube.com]



Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: erco ()
Date: January 22, 2023 08:20PM

My Elgin RK-508SP SBC 1.6 LS Rocker Arms arrived. I installed one and no surprise, the pushrod rubs the guideplate. I didn't do a valve lift test as a result.

Photos show one new silver 1.6 intake rocker on the end vs. a browner 1.5 rocker on the exhaust. Last pic shows the silver 1.6 rocker tip is shorter.

Trying to decide if I really want to modify the guideplates or just stick with 1.5 rockers. I've checked valve geometry made custom length pushrods for the 1.5 rockers.

Over the years, my 140 heads have worn out exhaust valve guides only, intakes were always fine. I may decide to use 1.6 rockers on the intake valves only. What's a girl to do? smiling smiley



Edited 1 time(s). Last edit at 01/22/2023 08:22PM by erco.

Attachments:


Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: Wagon Master ()
Date: January 23, 2023 05:41AM

tgould Wrote:
-------------------------------------------------------
> This was not the only specification change for 1966. The deck spec was changed from .0005 below (64/65) to .004 above (66-69). I wonder what triggered these changes???


I had heard this before too. Just like "Special" 140hp rocker arms and guide plates. Never seen any, just heard they exist. I wonder if GM changed the deck height with different base gaskets. Or was it just another backroom skunk works myth that never saw production?

Friends Don't Let Friends Drive Stock
Been Aircooled Since 1973
Northwest Ohio 45840

Options: ReplyQuote
Re: Is the 1.57:1 Rocker Arm Ratio another Corvair Myth?
Posted by: erco ()
Date: January 23, 2023 08:34PM

Jeez those work great.

Options: ReplyQuote
Pages: Previous123
Current Page: 3 of 3


Sorry, only registered users may post in this forum.
This forum powered by Phorum.