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Discussion Starter #1
just wondering if i would benfit from going to a 1.6 rocker on my engine. i dont have any to borrow so id have to buy them. maybe just on the intake?...

383, 10.5:1 220 pro toplne heads, 6" rod, strip dominator intake, cam is 626/626 262/271 @50 in at 106. i have plenty of pv clearance.
 

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On the Pro Topline heads, and pretty much all 23 degree type sbc heads I have always had to make additional pushrod clearence, so you will likely run into this as well with the 1.6 rockers...so the are not just a bolt on item...I wouldnt try grinding on my heads when they are on the motor either.
 

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Thought you switched intakes? I would say not worth the money for the 1.6 if you have to buy new but if you can get a good deal on some might be worth a try.
 

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I presume you have 1.5 rockers now?

.626/1.5= .417 lobe lift

.417*1.6= .667 lift

Might make a small difference but not much.
 

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Discussion Starter #5
Thought you switched intakes? I would say not worth the money for the 1.6 if you have to buy new but if you can get a good deal on some might be worth a try.
i did go from the vic jr to the strip dominator and it made a diff.
 

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Butch
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just wondering if i would benfit from going to a 1.6 rocker on my engine. i dont have any to borrow so id have to buy them. maybe just on the intake?...

383, 10.5:1 220 pro toplne heads, 6" rod, strip dominator intake, cam is 626/626 262/271 @50 in at 106. i have plenty of pv clearance.
Tighten the lash up first and see if the engine responds to the added duration ;)

Here is a post where I posted the seat duration at the valve

I have had a couple people ask about adjusting lash, so today while I was doing a 355 and was done setting the camshaft in I checked opening/closing points @ .0005" tappet lift and .0005" valve lift with the rockers mounted (Shaft mounted I used as the stud rockers are not here yet for this engine, I used my spare shafts)

Timing @ Camshaft .020"" tappet lift to .020"" tappet lift, spec on the lobe was dead on the money (Crane custom lobe)
IVO 51.5° btdc IVC 75.5° abdc
EVO 86.5° bbdc EVC 46.5° atdc

Thats what it was at the lifter, so we will compute the seat duration as follows
Intake - 51.5° + 75.5° + 180° = 307° seat duration
Exhaust - 86.5° + 46.5° + 180° = 313° seat duration

With cast iron heads and block, you set the lash cold .002" larger and the hot lash will be .002" tighter (with in .001"). This camshaft calls for .020"/.022" hot so I set them @ .022"/.024",,, here are the opening and closing points @ the valve @ .0005" valve lift
IVO 57° btdc IVC 82.5° abdc
EVO 90.5° bbdc EVC 51° atdc

Now we can compute the seat duration at the valve with .022"/.024" lash to give us .020"/.022" hot lash
Intake - 57° + 82.5° + 180° = 319.5° seat duration
Exhaust - 90.5° + 51° + 180° = 321.5° seat duration

Now many people ask how lash effects it and rockers, I checked lash, I will check different rockers when I have time (Which I don't at this moment). This camshaft is safe to run @ .012"/.012" lash, but how much do we really gain from just tightening up the lash .008"-.010"????? See below

Here are the timing specs with lash set @ .014" on both intake and exhaust, The opening points are taken at .0005" valve lift, thats as close as a human can get
IVO 60.5° btdc IVC 86.5° abdc
EVO 95° bbdc EVC 54° atdc

Now lets compute our seat duration and how much we gained
Intake - 60.5° + 86.5° + 180° = 327° seat duration
Exhaust - 95° + 54° + 180° = 329° seat duration

We tightened up the lash on the intake .008" and .010" on the exhaust. As you can see we gained a good amount of seat duration at the valves, see below

Original seat duration @ .022"/.024" cold lash 319.5°/321.5° @ the valve
Our new seat duration @ .014"/.014" cold lash 327°/329° @ the valve

Now every rocker and every lobe will be different (between different lobe profiles, different brand rockers and/or ratios, but this gives you an idea as to what can be there)

By tightening up lash .008" on the intake we gained 7.5° seat duration and on the exhaust by tightening up the lash .010" we gained 7.5° duration

I hope this gives those interested an idea or example to look at. You can also check this yourself too after you degree your camshaft

Also this will effect valve lift a little too, if you have say 1.5 rockers and a .450" lobe lift, you will have .675" at the valve before lash, now you have to minus the lash from that number

I understand this is not your every day street camshaft here, but its a good example
 

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Butch
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very intresting trmnatr! have you had time to do the tests with different rocker ratio yet?
Yes but it makes a huge difference between stud and shaft, mainly due to the lash, see below for a copy of a post I made. There are a few parts at the end that don't have anything to do with what you asked, I just copied my post and data

A major design area is the lash, a few examples below.

1) With a stud rocker, and a solid flat tappet, lets say it calls for a .026" lash, you put the feeler gauge between the valve tip and roller, and adjust the .026" lash. When you remove the feeler gauge the whole rocker falls straight down the rocker stud WITHOUT pivoting, now when the rocker pivots, it works at its ratio, say in this example a 1.5.

So with a .026" lash, the pushrod has to LIFT the rocker up .026" before the rockers fulcrum can JAM against the adjustment nut, remember when the rocker is moving up and down the rocker stud it IS NOT pivoting just sliding up and down the shank of the stud (look at the wear marks), so the pushrod has to move .026" which means the effective duration of the camshaft is .026" tappet lift on the opening side to .026" tappet lift on the closing side, the lash, to lift the rockers fulcrum into the adjusting nut THEN the rocker can start pivoting

2) If the same example above was a shaft rocker, a shaft rocker DOES NOT move up and down, a shaft rocker PIVOTS ONLY, so a shaft rocker pivots at its designed ratio, in this example 1.5

So for .026" lash, with a 1.5 shaft rocker, the pushrod only has to to have .0175" tappet lift to take up the lash because for every .001" the pushrod is lifted by the lifter the valve side see's .0015" lift, so .0175" tappet lift lash will be taken up with a 1.5 shaft rocker

Now if you look at the 400 we ran for example, you will see in every post the lash was set at .018"/.018" lash with the stud rockers.

The camshaft acts much larger with the 1.5 shaft rocker due to the fact the shaft rocker PIVOTS only. This camshaft in this example gets lashed at .018"/.018" with 1.5 stud rockers and .026"/.026" with 1.5 shaft rockers

So as you can see above, a lash of .018" with a stud rocker will have the lash taken up at .018" tappet lift, where a .026" lash with a stud rocker will have the lash taken up at .0175" tappet lift

3) In general, Most cams will gain 1° seat duration for every .001" you tighten up the lash. I did an example a while ago measured on the degree wheel, .010" lash gained 9° or 10° seat duration. This can be used to help provide stability in the design, if you start on the small side and use the lash loop to tune the engine

4) A major issue with flat tappets going out is the pushrods are not going straight down to the lifter, like they do with GM heads. Another issue is, stud rockers ALREADY have up and down movement, and have a lever motion (Where it works at its ratio), and side to side motion IN MOST APPLICATIONS, If you see shiny threads at the top of the rocker stud shank, YOU HAVE TOO MUCH SIDE TO SIDE MOTION and are putting more tension on the cam/lifters

The rocker stud is 7/16" or 3/8" for example, the fulcrum is designed to fit and BE STABLE on the rocker studs SHANK. That rocker SHOULD NEVER, NEVER ride up and down off the shank, it should be on the shank 100% of the time. A common issue in almost every engine I have ever touched.

Maybe that is how we are making 530hp from a stock block, GM nodular iron crank, GM 291 heads with no intake runner porting, 2975 intake, and running 6500rpm where most people claim to run out of power with aftermarket heads on 406 engines (??)

5) A shock to some people, a 7/16" rocker is WEAKER than a 3/8" rocker. Some may ignore this, but it is a fact. See below,,,

You can NOT make a rocker stronger (in this case 7/16" rocker), however you can make the studs stronger with a girdle, so IMO it is smarter to use a 3/8" rocker that has a THICK fulcrum compared to 7/16" rockers, and strengthen what you can,,, THE ROCKER STUDS WITH A STUD GIRDLE
You can verify everything here with a degree wheel and a dial indicator
 

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Yes and dont think twice about it.
 

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Valve acceleration.

For a given piston position on the intake stroke the valve will be open farther allowing more air in.... More air in sooner in the cycle makes for more complete cylinder filling. This means better VE and usually more power. Going to a higher ratio isnt always about increasing the max lift value. This also goes inconjuction with port designs that emphisize mid lift flow. When you can put more air in sooner, torque and midrange power will increase. These style port designs work extremely well on hobby level race/street cars whos sole intention isnt going down the strip but to get driven too. Ill take a port that flows more at .3 .4 and .5 and noses over at .7 versus a port thats down at those lifts and flows to 1.000.

Remember Peps thread? (gmhg70) he tested a rocker change back to back... Car was quicker but slower mph wise( due to being at different tracks) but it picked up .09 to the 60. Thats a tenth. Thats not from a gain at peak horsepower.... Thats a torque and mid range gain result.

Do it and dont think twice about it. If you do it based on what ive explained and it doesnt pick up, ill pay for half the cost of the rockers you bought.
 

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Butch
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Valve acceleration.

For a given piston position on the intake stroke the valve will be open farther allowing more air in.... More air in sooner in the cycle makes for more complete cylinder filling. This means better VE and usually more power. Going to a higher ratio isnt always about increasing the max lift value. This also goes inconjuction with port designs that emphisize mid lift flow. When you can put more air in sooner, torque and midrange power will increase. These style port designs work extremely well on hobby level race/street cars whos sole intention isnt going down the strip but to get driven too. Ill take a port that flows more at .3 .4 and .5 and noses over at .7 versus a port thats down at those lifts and flows to 1.000.

Remember Peps thread? (gmhg70) he tested a rocker change back to back... Car was quicker but slower mph wise( due to being at different tracks) but it picked up .09 to the 60. Thats a tenth. Thats not from a gain at peak horsepower.... Thats a torque and mid range gain result.

Do it and dont think twice about it. If you do it based on what ive explained and it doesnt pick up, ill pay for half the cost of the rockers you bought.
He can still test with lash too, and a 1.6 with that cam should 60 foot faster as that lobe is kinda slow compared to some Crane, Comp and other stuff out there. Heck I bet the cam below would pick him up another tenth, maybe more combined with 1.6/1.5's
290/306 @.020"
260/268 @.050"
184/183 @.200"
.715"/.625" with 1.6/1.5
106° lobe center
.012"/.018" lash
.960" base circle
 

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He can still test with lash too, and a 1.6 with that cam should 60 foot faster as that lobe is kinda slow compared to some Crane, Comp and other stuff out there. Heck I bet the cam below would pick him up another tenth, maybe more combined with 1.6/1.5's
290/306 @.020"
260/268 @.050"
184/183 @.200"
.715"/.625" with 1.6/1.5
106° lobe center
.012"/.018" lash
.960" base circle
Butch Moffat didn't you get called out on that over on speedtalk
http://www.speedtalk.com/forum/viewtopic.php?f=1&t=25644
 

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Butch
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Butch Moffat didn't you get called out on that over on speedtalk
http://www.speedtalk.com/forum/viewtopic.php?f=1&t=25644
Use a degree wheel instead of running your mouth Carl Hinkson. What is funny is 10 people have asked and verified it their self, except for the GOD'S in your circle that believe they know everything

I stick to what the degree wheel and dial indicator shows, anyone who wants to debate it, LEARN HOW TO READ A DEGREE WHEEL, yes that includes YOU.
 

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What seems to work wonders for us with the pro topline heads is an offset rocker from scorpion(nicest stud mount alum rocker ive ever seen) and an isky adjustable guide plate. Lets me get the valve train to a nats ass.
 

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Butch
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What seems to work wonders for us with the pro topline heads is an offset rocker from scorpion(nicest stud mount alum rocker ive ever seen) and an isky adjustable guide plate. Lets me get the valve train to a nats ass.
Comp has the guide plates out now too, just are a little easier to get for east coast people than the Isky's
 

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EH... not a big Comp fan. They seem to be into selling shelf shit instead of the right part. Isky has flat told me "we don't make that" and they told me who did.
 

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Yea playing with the lash will tell him if itll work.... Never said not to try it if he wanted... Id just skip the step and go for the rockers.

I dont know that going down in duration would pick him up. I like the cam. The durations are right for the heads. They are right for the car being a stick. The one place i feel like the combo is lacking is compression. Think it aught to be 11.2 or 11.3, which is still pump gas friendly. Id venture a guess and say his cranking compression is probably about 185 now.... He could approach 200 without a problem and some tuning. If anything... Id find someone who could do me a cam with the same durations and a .450 lobe on the intake and a .440 on the exhaust..... Grind it on a 108-109 and put it in on a 105-106. Spin the bitch to 7000-7200 and not worry about what it does below 3200-3400 Then pray the tranny holds.
 
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