Hydraulic cams - flat versus roller - revisited - Page 2 - Hot Rod Forum : Hotrodders Bulletin Board
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  #16 (permalink)  
Old 11-16-2006, 08:13 AM
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Here is another comparason. These are the same motor except the cam used. To me, this seems like a good way to compare the two cams. The common factor in each cam in the duration @.050. Recommended powerband is also very similar. 1600-5800 for the hyd flat tappet and 1900-5600 for the hyd roller. both cams have 224 230 @.050 duration.

Hyd flat tappet.

made 342 hp @ 5000 RPM
413 ft lbs @ 3800 RPM
http://www.compcams.com/Technical/Dy...68H-10_001.asp


Hyd roller

Made 373 hp @ 5200 RPM
427 ft lbs @ 3700 RPM
http://www.compcams.com/Technical/Dy...6HR-10_001.asp

The two cams performed in very similar powerbands, which I would expect with the same duration @.050, but the roller made more hp and more torque.

Here is the list of all the dyno tests on the comp site
http://www.compcams.com/Technical/DynoSheets/

Adam
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Old 11-16-2006, 06:22 PM
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don't remember, but I read somewhere that some big engine builder guru like David Vizor(spelling?) said a roller cam was not worth it with anything under 270 advertised duration cams.....just a vague memory though...
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  #18 (permalink)  
Old 12-06-2012, 04:58 PM
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Resurrecting this old thread, as I'm looking at both cams types right now and have read and searched all kinds of old posts without really finding the answer I'm looking for.
Two posts up there's an A vs B comparison.. but it's not quite the apples/oranges, as the roller has more lift.
I've found roller cams that have the desired lift and duration that I'm looking for, but can't seem to transfer that same setup into a flat tappet cam. Like the above comparison... it seems that every flat tappet cam I find with the desired duration @ .050 has less lift than I want.
If you want higher lift in the flat tappet... you have to have the longer duration too it seems. Is there a reason for that? Will a similiar profile in a flat tappet cam not work properly due to the ramps or something?

(Just to be specific... the roller cam I'm trying to duplicate is 0.510 int./0.525 exh. and 219 int./225 exh. @ .050)
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Old 12-06-2012, 05:42 PM
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You'll need 1.7 rockers with a hydraulic grind to get that lift at such a short duration.

Comp has a bunch of standard lobes. I just custom ordered a mild roller myself using the grinds available. I checked different lobes on my Engine Analyzer.

Very pleased with my results. Everything from the EA was bang on.

Check the PDF on the link below of lobes available. Plug in the numbers and see how that goes for you.

http://www.compcams.com/Technical/Ca...obeCatalog.pdf
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Old 12-06-2012, 05:44 PM
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You need to look at this a little differently. The flat tappet design by its nature is limited to the rate of lift (as you have verified). Apply lift too quickly and at worse the edge of the lifter contacts the lobe and digs a trench.

The best thing about roller cams is the additional lift without sacrificing idle quality or low RPM drivability. Long term durability on the street for a flat tappet dictates maximum lifts around .500", while the roller will yield the same life with maximum lift around .600". Even if you don't utilize the additional lift of the roller, the roller is opening the valve much faster and keeping it open longer. It is also doing this with the same amount of closed time on the valve. Except for the initial cost, it is definitely a win-win situation with the roller.

edit: As 123pugsy pointed out, you can use a higher ratio rocker, but this is still no where near the area under the curve available with the roller -- and the high ratio rockers also extend the duration of the FT cam you are using. For that matter, you can use a high ratio rocker with a HR, and have even more area under the curve if you desire.
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Old 12-06-2012, 06:12 PM
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Most apps rollers work better. but a lot of flat cams make big power and most max racing applications use flat solid lift cams. Nascar uses flat with extra large lifters to give large lift ratios.

Rollers are good but heavy and not good for max rpm applications. motorcyle and many twin cams apps use solid lift cams.

really only good for v8 applications and low rpm car engines.

But if you got the bucks and a v8 go roller for sure. Nothing better for engines running below 7K rpm.
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Old 12-06-2012, 06:14 PM
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Believe me, I'de rather go roller. It's literally the difference in money that has me looking at the FT cams. The actual HP difference is hard to justify for the extra dollars spent.
I've found an FT cam that would be close in lift if I use a 1.6 rocker. How much does the 1.6 rocker change the duration though?
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Old 12-06-2012, 07:29 PM
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Quote:
Originally Posted by Motochris View Post
Believe me, I'de rather go roller. It's literally the difference in money that has me looking at the FT cams. The actual HP difference is hard to justify for the extra dollars spent.
I've found an FT cam that would be close in lift if I use a 1.6 rocker. How much does the 1.6 rocker change the duration though?
Rollers and flats can build the same power but roller will have smoother idle and wider power band. And can get a little more lift with the same give and take as flat.
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Old 12-07-2012, 03:37 AM
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Quote:
Originally Posted by Motochris View Post
Believe me, I'de rather go roller. It's literally the difference in money that has me looking at the FT cams. The actual HP difference is hard to justify for the extra dollars spent.
I've found an FT cam that would be close in lift if I use a 1.6 rocker. How much does the 1.6 rocker change the duration though?
I can't see duration being affected by a roller cam. The ramp opens and closes the valve the same no matter what the rocker ratio is.

The roller just pops it open sooner giving the effect of more duration.

As for price, I changed mine out for better performance. Even with a mild cam, my lifters had a very slight concave starting. Not worth the risk to me at any cost to use a flat tappet. Then again, I'm not the type to go find the additive needed at every oil change either.
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