Don't buy the 'import' product and these days your usually O.K. You get what you pay for!

Scott.

 

that goes for any vette part....most repops are junk. Stay away from cheap heads too....it will cost you more in the end

 

Great job with the DDyno sim! @Fly skids up!

This was all tested by Engine Masters, I USED to have a subscription and I wrote some basic notes on that episode but I didnt grab the dynograph screen-shot, it did look basically like Fly Skids up!'s Dyno sim, though from memory. -The 1.6 ratio rocker was up 2.7 ft lbs and 17.3hp, but my notes suck enough that I'm not sure if that was directly compared to the 1.5 ratio roller rocker or the roller-tipped 1.5 rocker that they also tested that episode... The 1.6 had an hp peak 100 rpm higher. The hp peak was way up at 6,700 rpm with the 1.6 rocker and 6,600 rpm with the 1.5.

The valve events stay the same so the DCR stays the same, it's not like when you move to a cam with a bigger adv / seat-to-seat duration and you're lowering the DCR/ trapped air volume in the cylinder. You're increasing the VE with the higher ratio and keeping the valve in the "good air" longer, so the torque peak and area around it (where max VE is made) goes up. You're making the cam lobe act like it's a more aggressive lobe than it is.

For @4-vettes look at this exaggerated diagram of the valve motion changes when increasing rocker ratio and you can actually SEE how the durations-at-the-valve change at .050" and up (obviously the seat-to-seat durations don't/can't change), but that diagram IS super exaggerated. I've got a pretty aggressive hyd roller cam and with some rough estimate math, I think it estimated that moving from 1.5-1.6 would gain me around 2 deg @ .050" but to actually tell you need the durations at every lift and a cam designer / mfgr won't give it to you; you'd have to steal it from cam doctoring your cam to have enough info to actually calculate it.



On the different ACTUAL ratios of SBC rockers, there was a great comparison of MANY, MANY SBC rockers that was included in a big test by Hot Rod magazine in 2013 that included measuring the ACTUAL rocker ratios of each rocker. I took that article, turned it into a spreadsheet and then turned that into an image here:

The prices from 2013 are obviously WAY off, but most of those rockers don't seem to have been changed at all.
1.6:1 Rocker-Arm Comparo (motortrend.com)

A lot of dyno operators will say that 3/4 or 4/5ths of the gain with increasing rocker ratio will also come from just the intake side, and increasing the ratio on the exhaust will do almost nothing, too. (A lot of very new cams (ones that have actual designed exhaust lobes and aren't just using the next size up intake lobe as the exhaust lobe) have less exhaust lift than the intake because exhaust lift doesn't really matter that much on an NA app.)

If those are upgraded 7/16" rocker studs (they look beefy), I say go-for-it on the 1.6 ratio rockers, personally.

Like others said get an upgraded TC to get into the RPM where the torque is quickly.
A small long-tube header with good velocity OR a set of Reeds Custom's TRI-Y headers (Reeds Customs FB page, brewscustoms@gmail.com, OR call and leave a message at 253-334-1694) will help support the bottom-end and make good bottom-end torque, too.

Adam

 

Adam that is an excellent graph that demonstrates visually what I've been saying.
Not only can you see the difference in valve lift for each increment of cam rotation which illustrates how the valve will be open further and therefore longer (all cam events and thereby valve events are measured in crank degrees of rotation) at any specific increased lift of 1.6 vs 1.5.
Also notice what happens to the overlap triangle. It also is larger, similar to what a greater duration cam would do.
The overlap triangle is critical to each new intake phase as it is this time in which the action of the exhaust exiting that the most depression is created to draw in the fresh charge. Also where excessive reversion can occur if it's too big for the application.
It also dictates much of the "personality" of the cam. the rumpity-rump and/or lack there of.
This overlap triangle size significantly influences just how much torque it can create below peak torque. And how much RPM can be developed above peak torque.

 

Agreed, but, if we’re only increasing the durations down at 0.050” by 1 or 2 degrees (and less than that at all higher lifts), then the intake lobe only contributes half that much towards overlap and the exhaust lobe (if it’s identical) only contributes half that much, so we’re only talking about a 1-2 degree increase in overlap.

Less aggressive lobes will see even less increase in durations and overlap, so these are very minor changes compared to the lift still.

The biggest change is just more time spent in the greater flowing air that exists at higher lifts with VERY minor changes in duration and overlap.
Adam

 

Warren Johnson said, " don't worry about it kid " .

 

The graphs show me the duration hasnt changed..lift does and where lift is in the rotaion but it doesnt show the valves are open any longer...that is all the same at the bottom of the chart....duration is length of time from open to close. Openning faster and peaking out at a greater valve lift is not duration

 

But anywhere in the process that the valve is off the seat, from that point of opening to that point in closing, the "duration" is greater.

Not to mention the greater gross lift sum achieved.

Scott.

 

the duration doesnt change. It physically cannot change. the ramp speed increases as the lift increases and the time at peak decreases therefor the dwell time at each point of the ramp decreases. Im not arguing you will gain some power as the amount of air fuel mixture is increased because the time amount the valve is opened has increased, but it cant stay open any longer than the cam ramp dictates. As David Frieburger eloquently explains it, its a doorway and you can open it a little, leave it open a moment then shut it. What you are doing is you are opening it a bit faster and a bit wider but it is open the same amount of time.

 

Wow, a whole lot of discussion here. I'm surprised no one mentioned how much more horsepower it takes to turn a camshaft with 1.6 rockers?

 

I just rewatched the engine masters show on this subject. All the real power gained started above 5200 rpm. 1.6 gained 17 hp over the 1.5 at 6700 rpm....they did mention lift a lot, never mentioned duration, and they love to talk duration
how many of you guys drive above 5700 rpm and how often...

 

I think there is confusion on the word "duration"
The "duration" were talking about is how many crankshaft degrees was the valve open at "X" inches of lift...or greater.
All valve events are measured in crankshaft degrees.
IE 270/270 refers to crankshaft degrees open from .006" valve lift back to .006" valve lift.
Yes with one cam it opens and closes at the same point if that point is 0.0" of valve lift, but it's not, is it.

It's measured at .006" of valve lift. This is the industry standard where flow is recognized to have begun or stopped. And flow is what we are concerned with.
When .006" of valve lift occurs in relation to the crank shaft degrees could be drastically different if we could change the RR drastically.

Since we can't, the point at which .006" of lift occurs going from 1.5" to 1.6" ratio in relation to crankshaft degrees has changed, albeit just a little, it still has changed.

Therefore the "duration", or the number of crankshaft degrees, in which the valve was open .006" or more has increased. Therefore giving the effect of a greater duration cam.

The cam after all is just the tool we use to get desired valve events, and lift.
We don't directly refer to the valve events when talking about a cam for simplicity of discussion. It is the valve events we are after in the long run and the RR used can and will have an effect on these events.

 

If you look at that Engine Analyzer Valve lift diagram showing the 1.5 and 1.72 ratio rockers' valve motion, and look at the DISTANCE between the 1.5 ratio lines -that distance in degrees IS the duration. It clearly shows that there's more degrees of duration at .400" lift for the green line representing the 1.72 ratio rocker vs. the red line representing the 1.5 ratio rocker's valve motion. In that chart the valve with a 1.5 ratio rocker will spend VERY FEW degrees @ .500" of lift, but it clearly spends quite a few degrees @ .500" lift or more with the 1.72 ratio rocker.

Let's say with the 1.5 ratio rocker the max lift was .501" and with the 1.72 ratio rocker, the max lift was .575" -then clearly with the 1.72 ratio rocker the durations from 5.02" increased, right? -The rocker doesn't just suddenly teleport from the former .501" lift to .575", the speed at which the valve is opening and closing is increased, it's adding more "meat" to the valve curve to get to that lift, so the durations that the valve is open have to go up at every lift >.000".

-The same number of seat-to-seat degrees and actual time passes regardless of the rocker ratio, but because the acceleration is faster the valve is traveling farther with each degree of crank/cam rotation, so it gets to every lift >.000" sooner on the open side of the lobe, and gets to every lift slighly later on the closing side, which means it has more time spent at or above the lifts as before (more duration).

The distance between the same-colored lines in the diagram at each lift IS the duration at the valve and it's clearly larger with more lift.

Adam

 

you would have to change the cut on the cam to change the duration of the valve events. I believe you have an inaccuracy in your graph. the ratio is the lift ratio, nothing else.

 

It IS the exact same amount of time from when the door starts closed (seat) to when it returns to closed (seat) -seat-to-seat duration is the same.
But as soon as that door cracks open a little bit -say 6" -it has to open WIDER than before in the same amount of time -it has to get flung open faster and slammed close faster so it spends a slightly greater percentage of it's time at 6" open or more than it did before (more .006" / advertised duration), it spends more time 2' open than it did before, too if it has to both open MORE than before AND open and close within the same amount of time -so the duration of time that it spends open 2' or more (.200") has also gone up -.200" duration goes up vs. before.

David Freiburger's analogy is failed in that way, which might be why he was perplexed at why the RPM went up 100 rpm when switching to the 1.6 ratio rocker.


Adam

 

No. All you have to do is open the valve FURTHER in the same amount of time. In order to do that, by definition you're spending a more time at greater "door openings".

That's not my graph that's from Performance Trends, the maker of Engine Analyzer Pro high-end engine simulator and I think also the owner of the Super Flow dynos.


Adam

 

There seems to be a misunderstanding between cam events vs valve events and the correlation between the two and how that correlation can vary.
This would only be true if the valves were directly actuated by the cam. In a pushrod engine you have rockers whose ratio can be changed.

If you said that the CAM events can only be changed by changing the cut on the cam, then it would be a true statement.

 

If you race 1,320 feet in 11 seconds, and then increase your engine HP and can race to 1,500 feet in that same 11 seconds, of course you’ll find that your 60’ time was lower, your 200’ time was lower, your time to reach 300’ from the start line was lower, etc… when the car covered the longer distance in the same amount of time.

Now if you did something incredibly confusing and created a metric called “60 foot duration” that was measured by counting the amount of time in your pass that was spent beyond the 60 foot mark, and you tracked your “200 foot duration” my measuring how much time you spent further away from the start line than 200 feet, you’d find that all of your “durations” were larger with the faster car that covered more distance in the same amount of time and that you actually spent more time in seconds further from every point from the start line.

-IMO, this is why it’s confusing, because the concept of duration, from the perspective of the valve is confusing and about how long it spends >x distance away from the seat. It’s a weird measurement from the perspective of the valve.

A higher rocker ratio makes the valve travel further in the same amount of time, so it spends less time in crank degrees further from every point of the lift curve in the same way.


Adam

 

A 2* increase in overlap is relevant. It's not like duration where 2* is very little change. The overlap has a large effect for very little change in degrees.

 

Almost every single time I drive my vette....so I would say often.