Roller vs. Flat-Tappet Cams! - Engine Masters Ep. 16 Motor Trend Channel

[plovett]

Yes, I am talking about the original poster's question and the Engine Masters video link in it.

The guys in the video aren't dumb.  If they used 224@0.050" cams the difference would be different.  if they used 212@0.050" cams I doubt you'd see anything.   On the other hand if they went much bigger than 244@0.050" (and 7000 rpm), then they might start getting into valve train control issues.  They picked the right cams to prove the point.

Now, as to Engine Masters Challenge, I don't know if I would ever make a general statement.  That's because a lot of those guys are so good that they could make you eat your words with their creativity within the rules.  Tell somebody like that they can't do something and it just might happen.

JMO,

paulie

[andyf]

To the OP - for a fairly mild 500 hp engine just save your money and use a flat tappet cam. The only reason not to use a flat tappet cam on an engine like that is if you are really concerned about lobe life. In that case you could run a street friendly hyd roller. The hyd roller setup is very reliable but it will add some expense to the engine build. Leave the solid rollers to the race guys. No need to use one in a mild build, especially if you are on a budget.

[ACHiPo]

At the risk of asking a stupid question, how do flat hydraulic lifters compare to solid flat tappets or hydraulic roller lifters?  I originally wanted hydraulic roller lifters (seems to be the popular thing to do) in a mild 482 FE side-oiler (BBM block), but my engine builder claims to have had a lot of issues with hydraulic rollers in FEs so he put in hydraulic flat tappets.

[plovett]

At the risk of asking a stupid question, how do flat hydraulic lifters compare to solid flat tappets or hydraulic roller lifters?  I originally wanted hydraulic roller lifters (seems to be the popular thing to do) in a mild 482 FE side-oiler (BBM block), but my engine builder claims to have had a lot of issues with hydraulic rollers in FEs so he put in hydraulic flat tappets.

Here's my take.  In general hydraulic flat tappet cams are less "aggressive" than solid flat tappets and hydraulic rollers.  By aggressive I mean the steepness of the lobe, how fast the cam moves the pushrod up as the cam lobe turns.  I have to say in general because there are all sorts of cam grinds in each type of lifter.  There are some pretty aggressive hydraulic flat tappet grinds and there are some very mild solid lifter and hydraulic roller cam grinds. 

I don't know what issues your engine builder had with hydraulic rollers, but they're used all the time.  Maybe he had valve control problems at higher rpm?  If you're under 6000 rpm it doesn't seem to be a problem.

My opinion is that on a big engine like a 482 you're probably going to have a cam with a good amount of duration, even if it is a fairly mild build, just because of the cubic inches.  In that case I would think a hydraulic roller could make some significant gains over a hydraulic flat tappet.  The greater duration gives the roller cam more time to blast by the flat tappet and create more area under the curve.   It can hold the valve open further for longer, even if the 0.50" duration is similar.

JMO,

paulie

[plovett]

The point, which you know very well, is the duration of a cam significantly affects how much advantage a roller tappet has. 

Ehhhhhhh..................may want to rethink that statement.   

That's like saying long stroke engines won't rev.....

Well, I won't say long stroke, or big inch engines, won't rev.  I've never believed that.  What I am getting at with the cams is if you have a 205 degree @0.050" cam.  The roller version is not going to have a lot more area under the curve than a modern flat tappet version.  Again, speaking in generalities because either type can be ground an infinite amount of ways.  If you have two 260 degree @0.050" cams the roller has more time(duration) to use it's higher velocity, to create more area under the curve.  I think with big cams the difference can be dramatic.  With small cams, not so much.  I think it's even conceivable that a flat tappet could outperform a roller if the cams are very small. 

JMO,

paulie

[blykins]

I think we're talking in circles.....

Seems like we're thinking along the same lines but there's too many variables to be making comparisons between the two lifter designs.  I wouldn't even say that duration affects the advantage. 

[plovett]

I think we're talking in circles.....

Seems like we're thinking along the same lines but there's too many variables to be making comparisons between the two lifter designs.  I wouldn't even say that duration affects the advantage.

We might be talking in circles.  I'm not a great communicator.     But I maintain that duration affects the advantage of a roller cam.  And yes, you're right, there are lots of variables.   That's what makes it fun!  Thanks for the conversation.  I enjoy it. 

[Barry_R]

The point, which you know very well, is the duration of a cam significantly affects how much advantage a roller tappet has. 

Ehhhhhhh..................may want to rethink that statement.   

That's like saying long stroke engines won't rev.....

Well, I won't say long stroke, or big inch engines, won't rev.  I've never believed that.  What I am getting at with the cams is if you have a 205 degree @0.050" cam.  The roller version is not going to have a lot more area under the curve than a modern flat tappet version.  Again, speaking in generalities because either type can be ground an infinite amount of ways.  If you have two 260 degree @0.050" cams the roller has more time(duration) to use it's higher velocity, to create more area under the curve.  I think with big cams the difference can be dramatic.  With small cams, not so much.  I think it's even conceivable that a flat tappet could outperform a roller if the cams are very small. 

JMO,

paulie

We wish it were that simple....

A flat tappet can actually out accelerate a roller for a small increment of time as it starts on its way up the ramp.  Think about the way and the angle in which the flat tappet attacks the lobe compared to the roller.  Now look at the rollers axle as a pivot point - its potentially being pushed sideways for a short while more so than its going up on a radical ramp.  Pressure angle... part of the reason its hard to do a real comparison based on .050 numbers.  You would really need to do a valve motion trace on one and reverse engineer the other to match to isolate the frictional gain - and the impact on idle characteristics would be interesting at that point.  Every OEM went that way despite the expense multiplied by millions of vehicles.  Probably not an accident.

[blykins]

I think we're talking in circles.....

Seems like we're thinking along the same lines but there's too many variables to be making comparisons between the two lifter designs.  I wouldn't even say that duration affects the advantage.

  But I maintain that duration affects the advantage of a roller cam.

Based on what data?

I'm trying to think if I've ever done two engines with the only difference being flat tappet/roller.   

My point is that duration can't be a constraint because the effect of duration is based on displacement and head flow, among other things.  You're saying that duration affects the advantage of a roller cam, but what if the cams were in a 1000 cube engine where something like a 260-280° @ .050" camshaft only produced peak hp at 2500 rpm? 

I'm getting ready to do a 428CJ that is almost identical to one that I did a little while back.  The difference will be in the camshaft.  Oddly enough, the first CJ was a 227/233 @ .050" hydraulic roller on a 112 LSA.  The one I'm working on now is a hydraulic flat tappet, with almost identical .050" durations and LSA.  Obviously, there's more to a camshaft than that, but it's basically impossible to grind a hydraulic flat tappet and a hydraulic roller exactly the same.   Advertised durations will be different, .200" durations will be different, and lift will be a little different.    It will be good data as the first engine peaked at 5500 and I expect that this one will as well. 

[plovett]

My assertion is based on the fact that flat tappets are limited in their maximum velocity while roller cams are not.  A flat tappet can only move up so much per amount of cam rotation before the lifter digs into the lobe.  A wider lifter affects this maximum rate.  A Chrysler/AMC 0.904" lifter has a higher maximum velocity  than a Ford 0.875" lifter which is better than a GM 0.842" lifter.

A roller cam is not limited in this way.  It's velocity is not limited by the lifter diameter, though bigger diameter lifters have advantages for rollers, as well.  My understanding is that a roller lifter is limited in acceleration.  This has to do with the physical parts.  Flat tappet lifters are not limited in this way as they are just metal on metal.  I suppose hydraulic flat tappets are limited by their hydraulic mechanism, but not by the actual lifter/cam interface.

So a flat tappet lifter can accelerate faster, but reaches a top speed that it cannot exceed without digging into the cam.  The roller accelerates slower, but is not limited in top speed.  Well, valve train control will limit the speeds eventually, but not strictly because it's a roller.  Time and duration are the same thing here.  With a very small cam the cam is moving the lifter for less time (duration) so the initial fast start of the flat tappet is important.  With more duration (time) the higher peak velocity of the roller allows it to catch up and pass  the flat tappet.   The more duration the more time there is to gain advantage in area.

An analogy would be the sprinter vs distance runner.  A flat tappet cam is like a 100 meter runner.  It takes off fast, but that's all he's got.  A long distance runner will be behind at first, but will eventually catch up and pass him.   The longer the race the more the difference in times will be.   A longer cam duration is a longer race.  The longer race favors the roller cam.

I don't think this is a controversial issue.  But like I said, maybe I just can't communicate it well.

I guess we could look at 0.200" duration numbers vs. 0.050" and advertised.  Compare small cams to big cams.  I'm not sure how to quantify it, though.

JMO,

paulie

[scott foxwell]

Again,
Lets think about this from the valve point of view.
A cam is designed to give the valve a certain path.
Roller lifter, flat tappet lifter, mushroom lifter, no lifter...
It's all about the valve path and events.
If either roller or FT can provide the same valve path, there is no difference in performance. There is no performance advantage from one to the other. You're achieving the same goal, achieving the same performance. The lobe may be shaped differently, have different "numbers", but the end result is the same. Then, the choice becomes cost, maintenance, noise, or other non-performance attributes that may sway the decision. Up to the point where either can meet the goals of the build, I really don't see a way to compare them. They're different. Apple and an orange. Also, there is no benefit to opening the valve faster than needed. If the FT can do that (open the valve fast enough), the fact that a roller can have "more area" is meaningless. Once a FT can not open the valve as quickly and provide the area (duration) needed, then the roller becomes beneficial but if it's not designed right, a FT still might make more power. There are aggressive FT lobes that can make some serious power. Iv'e seen some that look like roller lobes, and there are roller lobes that are worthless. It's all about the valve path. The FT has limitations. That's just simple physics. The roller does too, but that boundary keeps getting pushed further and further with BIG lifter wheels and cam cores, but that's not what this discussion is about. At 4-500 hp (maybe more) and even up to 7000rpm, flip a coin. One is cheaper but has more risk. IMO that's about it.
Least that's how I see it.

[blykins]

My hypothesis is that it would be more rpm based.  If that 400 in the Engine Masters video needed 244 @ .050" to get to a 5000 rpm peak, I think the difference would have been less noticeable. 

 

[Barry_R]

I agree with Scott on his major point.  That being the concept of valve motion being the main deal here.  Once you get past that you only have some incremental friction component and the risk versus reward on cost and break in.  On a ten grand build the insurance might easily justify the cost..

[mike7570]

I'm more of a visual guy so I found this explanation on Isky's web site beneficial. If I have to use a flat tappet (for rules) how could a lifter be configured to be used on steeper roller style ramps?
Would the roller profile make more hp than the flat tappet at the same lift (lets say it's limited to .525)

[stroked67]

Back to the original question for me! I wish I knew as much about cams as some of you guys!  But my 463 is a solid roller, and I love it, I'm young, so I don't mind adjusting lash 3-4 times a year, I actually enjoy it. I also love the "sewing machine" sound at about 3500 rpm cruising down the highway. And at gas stations when I pull in to grab a red bull, people ask "what's wrong with your car, why does it sound like that. I tell them "solid roller", and they look at me like a deer in the headlights.