rocker arms and performance
11-14-2003, 10:27 PM
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rocker arms and performance
ok, someone please school me on this. when you change your rocker arm ratio, you change the lift and duration of a camshaft right? if so, if you go larger on the rocker arms, shouldn't that help you out all around or is the duration change on the cam hurting performance? that is until you change cam to match the rocker arms? if changing rocker arms does in fact change the cam lift, you will lose performance down low but gain top end? is this right. if so, would it be wise to hold off on the rocker arms until a aftermarket cam is installed?
11-15-2003, 12:40 AM
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Whoa .. that was an eye full. Here's the info I got on it ..
Adding 1.8:1 rocker arms will add roughly 9% lift. More importantly it will increase the ramp rate which is the time it takes the rocker to open the valve. The increased ramp rate makes the valve open quicker and a hair sooner, so I guess it would increase duration by a very small amount. I think some of the f-body guys looked at Yella-Terra's 1.8 over stock and saw about a 5-7 hp gain but said getting rid of the stock rockers made it worth it since they are known to bust a needle bearing from time to time.
Adding 1.8:1 rocker arms will add roughly 9% lift. More importantly it will increase the ramp rate which is the time it takes the rocker to open the valve. The increased ramp rate makes the valve open quicker and a hair sooner, so I guess it would increase duration by a very small amount. I think some of the f-body guys looked at Yella-Terra's 1.8 over stock and saw about a 5-7 hp gain but said getting rid of the stock rockers made it worth it since they are known to bust a needle bearing from time to time.
11-15-2003, 10:22 AM
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hey goshawk is this what you read?
"qoute from another site"
As you can tell in my sig i have the Comp Cam 1.85 ratio rocker arms.
Stock i do believe is 1.75, correct me if im wrong on that one, but anyways on to my question.
I was reading an article in a magazine called Power and Performance, that i recieved from the Thunder Shootout last weekend. In it it said that by me installing these 1.85 rocker arms, that i have changed the degree of the cam. This to me would explain to some degree why my motor feels dead.
the article goes something like this......
Question: What are the real effects of adding rocker ratio to an engine?
--- from the tech lines of Comp Cams
Answer: when people talk about changing ratios, the most common and noticable effect is the change made to the valve lift. Any time you change rocker ratio, it's a direct mathematical change to the existing lift of a given camshaft.
The new ratio times the camshaft lobe lift is the new net valve lift. For example, a 1.5 ratio multiplied by .300" lobe lift equals a .450" valve lift. A 1.6 ratio multiplied by the same .300" lobe lift equals .480" valve lift. Thats an increase of .030" net valve lift.
Thats an obvious and significant change. Going up in ratio primarily helps the engine breathe better at higher rpm's. However, what many don't fully understand is that a change in rocker ratio also produces a change in the duration of the existing camshaft. It is not readily noticeable and is hard to measure, but if the rocker ratio goes up, so too does the cam duration.
A rule of thumb is, for every half-point of rocker arm added; it will yeild 1 degree of cam duration at fifty-thousandths.
For instance if you have a 1.6 rocker arm, and you go to a 1.65 ratio the duration increases one degree. if the cam duration was at 250* at .050" the new duration is 251* at .050".
Whats interesting is that because this procedure is a pure direct mathematical calculation, it does the opposite if you take ratio away. In other words if you step back in rocker arm ratio, you lose valve lift, and then the opposite occurs to the cam duration by the same increments.
Although ratio reduction is not the most common method that's used in engine tuning it can provide aolutions to some problems. For instance, in an oval track situation rocker arm ratio reduction may be desirable to overcome concerns like spinning the tires coming out of a turn; or a driver that's over agressive on the pedal.
So when you look at rocker ratio, it's evident that rockers provide a vital engine tuning tool. Armed with this knowlwdge, engines can be more precisely tailored to a specific performance application.
In short, the rocker arm is every bit as valuable as ignition timing, or valve lash in tuning an engine.
----Darrel Miles, Technical Consulatant, Comp Cams P&P
Is there anyway with edit to be able to correct this problem untill i can get a cam and springs installed?
Thanks,
Daniel
"qoute from another site"
As you can tell in my sig i have the Comp Cam 1.85 ratio rocker arms.
Stock i do believe is 1.75, correct me if im wrong on that one, but anyways on to my question.
I was reading an article in a magazine called Power and Performance, that i recieved from the Thunder Shootout last weekend. In it it said that by me installing these 1.85 rocker arms, that i have changed the degree of the cam. This to me would explain to some degree why my motor feels dead.
the article goes something like this......
Question: What are the real effects of adding rocker ratio to an engine?
--- from the tech lines of Comp Cams
Answer: when people talk about changing ratios, the most common and noticable effect is the change made to the valve lift. Any time you change rocker ratio, it's a direct mathematical change to the existing lift of a given camshaft.
The new ratio times the camshaft lobe lift is the new net valve lift. For example, a 1.5 ratio multiplied by .300" lobe lift equals a .450" valve lift. A 1.6 ratio multiplied by the same .300" lobe lift equals .480" valve lift. Thats an increase of .030" net valve lift.
Thats an obvious and significant change. Going up in ratio primarily helps the engine breathe better at higher rpm's. However, what many don't fully understand is that a change in rocker ratio also produces a change in the duration of the existing camshaft. It is not readily noticeable and is hard to measure, but if the rocker ratio goes up, so too does the cam duration.
A rule of thumb is, for every half-point of rocker arm added; it will yeild 1 degree of cam duration at fifty-thousandths.
For instance if you have a 1.6 rocker arm, and you go to a 1.65 ratio the duration increases one degree. if the cam duration was at 250* at .050" the new duration is 251* at .050".
Whats interesting is that because this procedure is a pure direct mathematical calculation, it does the opposite if you take ratio away. In other words if you step back in rocker arm ratio, you lose valve lift, and then the opposite occurs to the cam duration by the same increments.
Although ratio reduction is not the most common method that's used in engine tuning it can provide aolutions to some problems. For instance, in an oval track situation rocker arm ratio reduction may be desirable to overcome concerns like spinning the tires coming out of a turn; or a driver that's over agressive on the pedal.
So when you look at rocker ratio, it's evident that rockers provide a vital engine tuning tool. Armed with this knowlwdge, engines can be more precisely tailored to a specific performance application.
In short, the rocker arm is every bit as valuable as ignition timing, or valve lash in tuning an engine.
----Darrel Miles, Technical Consulatant, Comp Cams P&P
Is there anyway with edit to be able to correct this problem untill i can get a cam and springs installed?
Thanks,
Daniel
11-15-2003, 02:14 PM
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yea 01, i was reading up trying to figure out if the rocker arms are hurting you down low. that was the article i was referring too when i spoke with you. in my thinking, the rocker arms are going to help you but only up top. not down low because the cam duration stuff was changed. i know rocker arms are a good thing to add to reduce friction and all that good stuff.
01, have you spoken to anyone local about this to see what they say?
01, have you spoken to anyone local about this to see what they say?
11-15-2003, 02:51 PM
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Hey! 01 Thunder...do you have any valve float?? I mean you have 1.85:1 rockers with stock springs. I once had a vehicle I failed to change springs on it after a certain RPM it just didn't make any more power.
What are the stock valve springs good to lift wise?
Remember full roller rockers with roller tip and fulcrum free up power by reducing friction too.
What are the stock valve springs good to lift wise?
Remember full roller rockers with roller tip and fulcrum free up power by reducing friction too.
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11-15-2003, 04:07 PM
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Stock springs are good for around .525 best I remember. I think the ls6 springs are good to about .565 or something aroung there. It's been a while since I seen it, but that's what my memory tells me.
I once had an old s15 with a 2.8 v6 in it. I nailed it once open header, yes, headers, and it didn't stop pulling until around 7k on the tack. I was shocked. When it hit that though .. it like cut out all at once. That was a prime example of valve float. I couldn't believe the thing held together that long. I thought I messed something up, as any other time it would only pull to around 5500 or so.
I once had an old s15 with a 2.8 v6 in it. I nailed it once open header, yes, headers, and it didn't stop pulling until around 7k on the tack. I was shocked. When it hit that though .. it like cut out all at once. That was a prime example of valve float. I couldn't believe the thing held together that long. I thought I messed something up, as any other time it would only pull to around 5500 or so.
11-15-2003, 04:36 PM
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yeah my secong gear runs out around 5600 rpms, kinda goes flat then shifts into third and pics up again. also the same in 1st. really noticeable since the transmission is not slipping anymore.guess im gonna have to go ahead and get some springs before i get the cam.
