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Canucker
Dodge Dakota
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10/16/2002
13:29:55
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 Subject: Lift vs Duration
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So here's a question. What are the advantages/disadvantages of changing the lift of a cam (say with rockers), or changing the lift AND duration with a new camshaft?
i.e. take a 208/.470 cam (lets say only intake). what would be the advantages/disadvantages of putting rockers on there to get more lift ... to say .56 but keep the same duration versus swapping it out with a cam that was 218/.560???
did that make sense?
I'm just pulling numbers outta you know where so don't get too technical on how realistic they are.
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CW
GenIII
10/16/2002
14:31:23
|  RE: Lift vs Duration
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The rockers change the duration some as well because the valve comes off the seat sooner due to the increased ratio.
4.7 HO, CW style
2001 4.7 5sp 3.92 LSD
Ported 68mm TB, IAT adjuster, 3" flowmaster cat back, TPS @ .76V, 4" Z-tube, Roadmaster active suspention, Removed Third cat, Electric fan Convertion, HO cams, Robert shaw 180 therm, HO intake manifold.
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Anthony G
Dodge Dakota
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10/16/2002
16:01:31
|  RE: Lift vs Duration
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Try to keep the cam lift near the max flow rate for your heads. For example, your cam lift is .500 and your max flow rate is 300 cfm @.550 on your heads. So you would want to increase your cam lift to match your max flow rate or a little higher due to the valve having a wide range of lift. Almost like increasing your rev limiter past your peak, so when you hit second, it's back into it's power range agian. :)
Now duration is the amount of time that your valve stays open, the longer the time the more air enters the combustion chamber, it helps move air at high rpms speeds, due to valves opening and closing at a fast rate, a longer duration is needed to keep air moving. Down side, the higher the duration the less low end power you have, due to keeping the valve open too long at slow speeds, that why they invented VVT :) eat your cake and pie too. Since we don't have VVT you'll have to pick the lesser evil :). Hope that helps.
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MikeD
*R/T*
10/16/2002
16:26:00
| RE: Lift vs Duration
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Hey Anthony....haven't seen U around in awhile. Did you get your truck running like you wanted it? If so how do you like the extra power, I know I can't get enough of mine :)
~Mike~
Get In...Sit Down...Shutup...& Hangon
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Anthony G
Dodge Dakota
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10/16/2002
16:49:54
| RE: Lift vs Duration
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It's been very powerful :) I bet It will do 13's once I can get myself a PP3 so I can change my rev limiter. Have you tried a large turtle yet? It made a good amount of torque increase after the computer learned the new air flow. I hope to hit the track soon :) Right now I've been busy getting another car, so I can work on the R/T any time I want. The second car is nice, it's has a 1.8L 20valve Turbo :) with a 5 speed. Got to have a car that seats more than two people or three.
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MikeD
*R/T*
10/17/2002
11:36:10
| RE: Lift vs Duration
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My buddy got the turtle and he has about the same mods as me and I thought I'd wait and see and he thought he coudln't tell much difference. So I didn't spring for the turtle.
I thought about gettin a 4banger daily driver but I'd miss driving my R/T too much.
~Mike~
Get In...Sit Down...Shutup...& Hangon
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Anthony G
Dodge Dakota
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10/17/2002
12:24:35
|  RE: Lift vs Duration
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With my heavy food, I need something that doesn't suck fuel down faster than 18 wheeler.
I took my neighbor for a ride two days ago, first we took my 40k loaner car out :) It pretty peppy with a Turbo and all. We gave it hell, the turbo was glowing. He was impressed with it then I said, let take a ride in my truck now, lol. I did a burnout from a start, man was the truck loud! (.543 exhaust lift) even with two mufflers on a single side pipe. Then I headed for the highway on ramp. I floored it so it shifted into first, then barks into second. He then say's If I can pass that other Dakota on the highway already going no less than 70, due to the speed limit being 70. Mind you this on ramp is uphill and I was only going 30 mph starting out. To make a long story short, by the time I hit the end of the on ramp which is not long maybe 1/8mile I was already getting close to reaching my speed limiter! Boy was he impressed, so was I :) I don't normally do this, but it was safe enough. I just don't have a get out of jail card. Next time I hit 110+ will be at the track.
Yea he was impressed when the truck was stock and it could melt tires, but now he was speech less due to the raw power it had in the upper end vs stock. Not only does my RC have a bed liner and a fiberglass cover, we both added about 440lbs to the truck with our weight. I would love to have this engine in a leight weight car. Oyea I did pass the other Dakota a few feet after the on ramp, I bet he was saying, why can't my Dakota do that. LOL
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Mgiuzkvf
Dodge Dakota
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12/06/2009
10:51:43
| iUhSLUoWEXGy
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comment3,
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