|12-07-2012 03:37 AM|
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.
|12-06-2012 06:14 PM|
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?
|12-06-2012 05:44 PM|
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.
|12-06-2012 05:42 PM|
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.
|12-06-2012 04:58 PM|
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)
|11-16-2006 06:22 PM|
|1972warship||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...|
|11-16-2006 08:13 AM|
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
Made 373 hp @ 5200 RPM
427 ft lbs @ 3700 RPM
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
|11-16-2006 07:47 AM|
Here's a comparison of two similar cams switching from flat tappet to roller. It's not a clinical test, but the results are interesting.
|11-16-2006 07:19 AM|
I re ran the numbers the morning, checking everything over.
Somehow when I ran the flat tappet yesterday the SCR got changed to 10.6 . Ihave no idea how that happened, but that's what scewed the results.
Tried it again today to see if I could prove myself wrong: Used the same specs at .050, same LSA, same ICL, just changed the type from mild flat tappet to aggresive hyd. roller (which should be maximum benefit) to see what would happen. The roller returned with a little less torque on the bottom end at up to 4000 RPM, but then the roller started to shine 557HP at 6000 RPM versus the flat tappet's 541 HP at 5500RPM (after which Engine analyzer said the lifters were pumped up). At 6000 RPM the flat was only making 483 HP, which is due to lifter pump up - I don't think that is represented correctly, but oh well.
So then, just for fun, I jacked the flat tappet duration until the @ .200" duration was the same and reran it. It got closer to the same peak HP (as expected), but the torque in the lower end was way down, and the idle vacuum would be 9" Hg. So it would be really too hot for the street I think.
Someone suggested I try running the roller with an extra 10 deg. of duration - so I tried that too. Unfortunately, my SCR doesn't support that very well, but I still came up with 565 HP at 6000 RPM, while loosing torque up to 5.5K. Idle vacuum dropped to 9.9 (the flat was 11.8 which suggests more street friendly). Clearly the first roller was better in almost every aspect at this SCR of 9.9.
SO there you have it - the roller reigns supreme if you want to be streetable and have enough cam to make those big heads breathe. Sorry for posting inaccurate data - I should have been paying more attention.
If budget is an issue, the street racer would do the flat tappet and then use the "extra" money for nitrous. Or else build a mild big block 496
|11-16-2006 05:13 AM|
Yes roller lifter failure is something that can happen, but in the mild hyd roller cams i think it's a none issue...I would bet you can't find 5 guys on this site that lost a roller on a mild hyd roller cam,,,but you can find 10 times that amount that lost a flat tappet lobe...IMO the odds are against you on that one...
Now a solid roller with 1000 lbs over the nose,,,thats another story!!!
|11-15-2006 11:30 PM|
To do the calcuation correctly you need to confirm either off a Cam Doctor test or via the cam manufacturer what the .200 duration numbers are for the compared camshafts.
Again, of course if you simulate two camshafts that have basically the same lobe profile they are going to A) look exactly the same to the valve they are lifting, and B) basically make the same power.
It's as simple as that. Unless your going to take advantage of the benefits of the roller within the lobe profile there really is no reason to go roller. For the exact reasons you mentioned. Taking advantage of the roller design and lifting the valve off the seat quickly and to a high lift is where you gain the power.
|11-15-2006 11:24 PM|
|lust4speed||Roller cams act like a hydraulic cam 10 degrees smaller in manners. I can run a mechanical roller with 246/252 @ .050 and still have plenty of vacume for the power brakes. Same with the hydraulic roller having manners like a much smaller flat tappet hydraulic. Since you can run a cam 10 degrees larger and have the same street manners, it seems that it would be fair to run the test with 10 a degree larger roller cam.|
|11-15-2006 10:03 PM|
As far as inputting the right info - when the computer spits out the result it gives you a duration @ .200" lift as well - and when I change the cam type (mild hyd roller, agg roller, mild flat, aggr flat) you can see that the numbers change. That suggests to me that the program is in fact taking into account more and less aggresive lobe profiles.
What I'm suggesting here is that all the money spent on going roller (which I thought was going to be worth every penny) was perhaps not spent in the right spot for me.
I did input real data for the cams. Actually tried to get a "best" run from each type, (which of course meant choosing different adv. durations), but when it was all said and done - I could have chosen the right flat tappet cam and been within 10 or so HP throughout the powerband. When you change the type of cam in the program, it just simulates a more aggresive lobe - which allows a comparison of two cams with the same @ .050" durations.
If one is looking for a more radical valvetrain, the roller (hyd. or especially solid) would be the way to go - however, on a street vehicle with any manners, that sort of cam is not necessary so I'd say the flat tappet is just near as good at that point.
If my 406 was 12.0:1, I could run that 306/314 in there on pump gas - DCR would be close to 8:1 - and she would fly. However, there are -20cc reverse dome pistons in it that give me 9.9:1. The 306/314 is just tooooo big.
I would have been better off buying an LM-1 and tuning the engine properly - you can gain way more than 10 HP and probably several MPG too. Course I bought one anyway. I have learned SOOO much from mine. LOVE IT!
|11-15-2006 09:45 PM|
|11-15-2006 08:48 PM|
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