Cam/Rocker Ratio Question?
Thread Starter
Le Mans Master
Joined: Oct 2001
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From: Paradise City
Cam/Rocker Ratio Question?
I've been entertaining a cam swap for some time, but it's been suggested that I just swap my rocker arms instead. I have the L-82 cam, which I believe has specs of .450/.460 222/222 duration w/ a 114 degree LSA. Stock rocker arms are 1.5, correct? So to get the actual valve lift, I multiply the cam lobe height by 1.5 (1.5x450)to get .675-this would be my actual valve movement. So If I were to swap to a set of 1.6 rockers, I would get (1.6x.450) =.720" of lift-which would be the equivilant of sticking w/ 1.5 ratio rockers and a cam w/ a lift of .475". Is my math correct, or am I approaching this the wrong way? Thanks guys :cheers:
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Joined: Apr 2002
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From: Worcester MA
Re: Cam/Rocker Ratio Question? (79Corvette02)
With either a cam or a rocker arm change, always make sure to keep your valve clearances in mind. If your max stock lift was .460, any time you increase that with a cam or otherwise the original valve clearance is decreased. This could be a problem if you increase the lift significantly.
Thread Starter
Le Mans Master
Joined: Oct 2001
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From: Paradise City
Re: Cam/Rocker Ratio Question? (schrecke)
How can I determine what my allowable clearance is? I don't know about the pistons, deck height, or anything like that. I'm assuming my math was right, that I just multiply the ratio of the rocker by the lobe height of the cam. In that case, does everyone feel that .7" is too much lift and I would end up w/ clearance issues? If I swapped rockers, would I also need to change to new springs and retainers too?
Race Director
Joined: Jan 2003
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From: State of Confusion
Re: Cam/Rocker Ratio Question? (79Corvette02)
Your lift 'at the lobe' is the advertised lift DIVIDED BY the rockerv ratio. If your valve lift is .450", and you're running 1.5:1 rockers, the lobe lift is .300" (.450" div/by 1.5 = .300"). The easy way to figure lift after swapping ratio-rockers is take current lift div/by current ratio mult/by 'next' ratio; if you have .450" lift w/ 1.5s, and are considering 1.6s, your lift will then be .480" (are you SURE a stock L-82 has that stout a cam? {.450"/220* @ .050"???}). :chevy
Thread Starter
Le Mans Master
Joined: Oct 2001
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From: Paradise City
Re: Cam/Rocker Ratio Question? (Glensgages)
Glensgages-thanks for straightening my math out :cheers: . As for the cam, I was under the impression (wrongly, now I'm assuming) that the L-82 cam was .450/.460. Now that you mention it, it does sound rather meaty for the anemic late 70's cams that had golf ***** for lobe profiles. Any idea what the specs for the L48/L82 cams were?
Race Director
Joined: Jan 2003
Posts: 15,176
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From: State of Confusion
Re: Cam/Rocker Ratio Question? (79Corvette02)
My '79 Z28 cam was .390"/.410", and duration was BARELY 200* @ .050" lift, too. L-82 might be SLIGHTLY better, but ONLY slightly. As for your other questions, I think w/ stock internals (pistons, rods, etc.) and proper valve springs, you'd be A-OK to go as high as .480"/.500" lift w/ no problems. I ran a cam at .450"/224* @ .050" (single-pattern) in my other-wise stock X28; it ran great!!! If you need help with '79 hop-up ideas, gimme an E-mail; the Z28 (I still own it) ran a best of 14.29 @ 97 MPH with fairly simple (cam, headers, intake, carb, 'camel-hump' heads, etc.) mods, on pump gas, with the stock converter & 3.42 gearing :thumbs: :chevy :chevy :chevy
Drifting
Joined: Oct 2000
Posts: 1,825
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From: Shawano WI
Re: Cam/Rocker Ratio Question? (79Corvette02)
Any idea what the specs for the L48/L82 cams were?
The cam is different in an L-48 and an L-82. The L-82 specs are .450/.460 lift with 1.5 rockers .222/.222 duration at .050 on a 114° lobe center
With 1.6 rockers that would give you .480/.491 lift
Safety Car
Joined: Aug 2001
Posts: 3,685
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From: Waterford Mi
Re: Cam/Rocker Ratio Question? (Pete79L82)
Which ever way you go you should up-grade the valve springs and rockers. More tarvel and old springs can lead to valve float. The rockers you have now will have worn to the travel so if you put in a new cam they will fail. I learned this the hard way (Had one break). The cam would be the right way to do what you want. Then ypou can choose a cam with the grind you want for best performance. The 1.6 rockers will increase the hiegth and it will also affect duration. That may not be good for the cam you have in there.
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Advanced
Joined: Apr 2002
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From: Worcester MA
Re: Cam/Rocker Ratio Question? (79Corvette02)
The GM P/N for the L-82 cam is 3896962 with a C/N of 3896964. If you type the P/N into any search engine, you'll find the stock specs. They were stated correctly earlier as .450/.460 222/222
Drifting
Joined: Jun 2001
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Re: Cam/Rocker Ratio Question? (79Corvette02)
Food for though but your duration looks good at 222@50 but what would really be nice is to get your lift in the 500. However I don't know if you can use 1.7 on a small block or not hopefully one of the cam guys will chime in.
I currently have a cam similar to what your trying to get 222@50 and .470 lift and 1.6 rockers. I think I would like some more lift.
I currently have a cam similar to what your trying to get 222@50 and .470 lift and 1.6 rockers. I think I would like some more lift.
Thread Starter
Le Mans Master
Joined: Oct 2001
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From: Paradise City
Re: Cam/Rocker Ratio Question? (Tominator)
Hmmm. This is pretty interesting. I guess the L82 cam has a little umph to it. I think I'm going to swap the rockers-I think it'll be easier than taking apart the top end. Any suggestions on which company to use? Am I going to need to get self-adjusting rockers?
