Why increase rocker ratio ?
Thread Starter
Le Mans Master
Joined: Apr 2000
Posts: 7,562
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From: B'Ville NY
Cruise-In III Veteran
St. Jude Donor '05
Why increase rocker ratio ?
I don't see what advantages there are by inceasing your rocker ratio to increase cam lift :confused: . Why not just buy a cam with more lift ? Is this a route usually taken by people that want more lift but don't want to go through installing another cam ?
Help me see the reasoning behind rocker ratios :crazy: .
[Modified by SmokedTires, 6:28 PM 1/6/2003]
Help me see the reasoning behind rocker ratios :crazy: .
[Modified by SmokedTires, 6:28 PM 1/6/2003]
Le Mans Master
Joined: Mar 2002
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From: Castro Valley Calif.
St. Jude Donor '03 thru '26
Re: Why increase rocker ratio ? (SmokedTires)
Because of the geometry. I've always been told the higher the profile of the lobe itself, the longer the duration to get over the ramp. (Does that make sense?)
If the multiplication of the rocker is all we're talking about, you achieve a higher lift at the top of the lobe only without increasing the duration of the ramp.
Now this is goin' back to the 60s mind you so I could be full of prunes too :lol:
If the multiplication of the rocker is all we're talking about, you achieve a higher lift at the top of the lobe only without increasing the duration of the ramp.
Now this is goin' back to the 60s mind you so I could be full of prunes too :lol:
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Re: Why increase rocker ratio ? (Caboboy)
It's just a littlel trick commonly used to increase lift without affecting duration much and your right it is easy to do :D
Race Director
Joined: May 2000
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Re: Why increase rocker ratio ? (MotorHead)
Based on the research I've done with the DD2000 and Engine Analyser simulation programs I've concluded that aftermarket "high ratio" rocker arms are not a very cost effective way to improve engine performance.
The key is to buy a cam that give you reasonalbe low end torque and then work the heads, inlet, and exhaust system to the limit of your budget to get peak power.
Duke
Duke
The key is to buy a cam that give you reasonalbe low end torque and then work the heads, inlet, and exhaust system to the limit of your budget to get peak power.
Duke
Duke
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Re: Why increase rocker ratio ? (SmokedTires)
Going from 1.5 to 1.6 rockers will give you an increase in lift w/min increase in duration. A .450 cam w/1.5 will be .480 w/1.6. The higher ratio will add about 1.5-2.0 degrees of duration. If you got a bigger cam, you would have to add 15-20 degrees of duration to get the same lift. A side benifit is the reduction in temps form the full rollers. When I added 1.6 rrs to my 74 the temps went down 10-15 degrees and the engines "sweet spot" was raised about 200 rpm. Just my .02! The increased lift will not help after "valve saturation" = the point where more lift does not get more CFM.
Thread Starter
Le Mans Master
Joined: Apr 2000
Posts: 7,562
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From: B'Ville NY
Cruise-In III Veteran
St. Jude Donor '05
Re: Why increase rocker ratio ? (Taijutsu)
Ok, so basically for more lift without much increase in duration. Thanks, I'm always learning something here :D !
Le Mans Master
Joined: Feb 2001
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From: The problem is all inside your head she said to me.
Re: Why increase rocker ratio ? (SmokedTires)
Don't want to spin this thread off course but, I was wondering if most of you would say that a set of roller rockers is worth having or necessary? I guess they are not all that expensive. There are claimed bennifits to them but are do they really help in the real world. I guess you would need tall valve covers if roller rockers are installed. My engine is just your basic 355 4bolt forged crank, CC280 230@.050 .488,.488, 041 GM heads, flat tops with one valve relief grove, performer ,650DP, 1 5/8 headers and 2.5 EX. 4sp car with 3.70's With this build would roller rockers add anything to the motor, power or longer valve guide life. Could this motor benifit from increased ratio if buying the rockers anyway? What would this motor DD2000 at? In my dreams I would love to have a good set of heads for this, how much would this motor benifit from AFR 195's???????? :D
Drifting
Joined: Apr 2002
Posts: 1,736
Likes: 37
From: Stockton Ca
Re: Why increase rocker ratio ? (INMYBLOOD)
You need to check the flow rates for your heads. If they flow better at .515 that .488, tes I would get them. Most stk engines gain 10-15 hp & tq. In your case, I can't be sure. The better heads will make far more difference that the rollers. Just my .02.
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