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#1
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what effect will 1.6 rockers have on cam?
Hello all. I purchased a set of 1.6 roller rockers for my 440 and was wondering what effect these will have on my motor. I am running an mp 4452993 so called "street hemi" grind cam now. advertised duration is 280 for intake and exh, gross lift is 474 for intake and exh, lobe sep is 110.
I am running 346 '71 iron heads. 2.14/1.81 valves, 3 angle valve job w/ minor bowl blending (no gasket match) holley 900 cfm projection, performer rpm manifold,10:1 comp,1 3/4" hedmans w/3"collector, full 2.5" dual exh w/two chamber flomasters. 2800 stall conv w/3.55's out back. all in my 68 charger. my question is, how will these rockers change the characteristics of the cam? I spoke to the rep at comp cams and he says that it will change the valve lift. he told me to take my current lift of .474 and divide by 1.5, then take that number and multiply by 1.6 and that will be new valve lift spec. from that I get 505. is this right? I have no clue will it have any effect on any other characteristics of the cam? I realize that I should get the benefit of less friction due to roller tips and needle bearings in new rockers, so that's good, just wondering if, with my relatively mild combo, I will feel any "seat of the pants" difference. thanks as always,Kevin |
#2
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Your numbers are correct, you will have .5056 lift, you should have a little bit better top end horsepower, may lose a little low end torque, but every engine behaves differently, it depends on how correct the current cam is for your engine combination, 1.6 rockers also put more load on the cam and pushrods, but usually not enough to hurt anything.
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#3
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I talked to a rep from Comp Cams (in person) and he told me that changing rocker arm ratio to a higher one will usually increase torque without changing horsepower output, rpm band, etc.--USUALLY. That is not to say that your engine will not react differently. Just like DartByU says, you can't ever tell. The only way to know for sure is to dyno before and after. Remember to change your valve springs to accept the higher lift when you swap everything, and have fun!
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#4
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I don't know about seat of the plants feel, but, the larger ratio rocker will raise the valve off the seat quicker. This quicker rise to the max lift will make the cam seem bigger.
How much bigger? I couldn't say. The bowl job on your heads sounds like it will make use of your new lift. In general, that type port work , works well with lifts up to and around .500. |
#5
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BTW--roller tips don't usually do enough to even show up much on a dyno, maybe 2 or 3 horsepower. Your bigger ratio, however will do SOMETHING for the better.
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#6
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to be safe I would check the valve to piston clearance and the valve springs to make sure they dont bind because the valves will be opening .0316" more, just to be sure that nothing gets screwed up
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#7
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thanks for the great responses. I do have new valve springs and pushrods to go with these. the springs are comp cams p/n 911-16 (comp cams rep recommended them for the XE274H cam they sell which I believe has similar lift to what I will end up with)
The pushrods are crane stock length but have a "cup" end to accomodate adjusters on new rockers. My piston-to-valve clearance shoud be ok. My pistons have pretty deep valve reliefs and my machine shop assured me I would have clearance for up to .600 lift they put together the long block for me. Deadhorse, I had always heard that roller rockers were beneficial because of less friction in valvetrain due to roller tips and needle bearings where rockers ride on the rocker shafts. is there anything to that? or is it just something that "they" say. |
#8
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We built a SBC in school and ran it with stamped rockers and then with roller fulcrom, roller tip Comp rockers. We picked up 3 horsepower. They do help valvetrain friction, but it's only real benefit is that it is less likely to bind/float at extreme high rpm. Where did you get roller fulcrom rockers for your 440? I know that several companies make them, but I also know that they are usually pretty high dollar. Do you mind divulging the make and price?
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#9
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well.....I hesitate to say, because of the inevitable backlash, but I got them from a company called CAT. they were only $175.00. they are extruded aluminum alloy. hardened roller tips, fulcrum needle bearings. Polylocks included. I was a little suspect of the price, but , they appear to be nice quality. They are also warrantied.
I realize that they are not as mainstream a brand as harland sharp or crane, but those other guys want something like 500 bucks. My motor is kind of mild and does not see a ton of track time or real high rpm's, so I decided to roll the dice a bit. I will keep you guys posted on this, these could turn out to be a killer deal, or I could end up cleaning up engine parts with a broom. |
#10
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Quote:
You might as well give them a shot, though I can't figure out why they're so cheap... Maybe made in China? Anyways, you could pay more for Crane Gold rockers, but there have been a number of posts here about problems with them, so paying more isn't always a guarantee of performance. The Harland Sharps are real nice, but overkill on your average street motor. I'm running Erson-brand ductile iron adjustable rockers, and they've been just great. Let us know where you got 'em and how they work for you. |
#11
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Quote:
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#12
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I got them from dyno-flo. www.dyno-flo.com
they are in Las Vegas, NV phone is 702-597-0106. It was through an auction on ebay, though I think they sell for that price every day. I first heard about them on this site. if you search dyno-flo, I believe there is a thread on these. CAT's direct number is: 626-330-1999. I actually spoke with them when I realized that my stock pushrods would not work (balls on both ends) these require the aforementioned "cup" on one end. They were very helpful, and while they do not sell the needed pushrods, they turned me onto who did and gave part #'s. |
#13
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D'oh!!!! I just searched the site, and yes there is a thread on these- turns out I posted on this thread about 4 times- bad memory!
anyway, looks like lee pritchard and 70aarcuda both used them and had no problems. |
#14
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Coil bind is a result of not enough intalled hiegth on the valve, incorrect wire diameter combined with TOO MUCH lift.
Install one and measure for coil bind. CAT rockers...ya they'll probably work OK......My objection to Chinese product is the deceptive advertising and packaging, plagerizm, and what they do with our money......but I'm not gonna start this again you all know my feelings on this topic. |
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