Percent of lost lift due to 58 degree lifter angle?
- Thread starter gregsdart
- Start date
-
It can affect both, but most people only notice the net lift numbers. If it has the correct net lift, the geometry must be right, right????? ......Nope!
C130 Chief
Mechanical Genius
The loss of lift is not due to the lifters angle with the cam, but the pushrod's angle with the lifter. So to calculate, take the lobe lift times the inverse cosine of the angle of the pushrod relative to the lifter at mid lift. Then multiply by the rocker ratio to estimate lift at the valve. Note that this is a slight oversimplification because the angle changes as the lifter rises. Keep in mind also that the pushrod is at an angle both along and across the cam axis, so you would need to calculate the resultant vector. If you wanted to go nuts, lift could be calculated over a range of lobe lifts and a curve then plotted showing the variation of valve lift relative to lobe lift. Fun with trigonometry.
The slightly odd pushrod angle is why you can't just multiply the lobe lift by the rocker ratio to get valve lift, even though that's how cams are advertised. The early hemi had the pushrods basically inline with the lifter. When the A (poly) engine came out, the lifter angle carried over so both engines could be built on the same tooling, same story with the LA and Magnum variants. Each time it got a little worse (Magnum worse than LA due to taller lifter).
The slightly odd pushrod angle is why you can't just multiply the lobe lift by the rocker ratio to get valve lift, even though that's how cams are advertised. The early hemi had the pushrods basically inline with the lifter. When the A (poly) engine came out, the lifter angle carried over so both engines could be built on the same tooling, same story with the LA and Magnum variants. Each time it got a little worse (Magnum worse than LA due to taller lifter).
moper
Well-Known Member
There is nothing fun about trigonometry...lol.
C130 Chief
Mechanical Genius
I didn't think this was true until I took Multi-variable and Vector Calculus. Perhaps there IS such thing as too much of a good thing.
Great thread. Thanks for starting it gregsdart.
Yea! chocolate ! Toco bell after heavy drinking, viagra in one doseage (10 hour stiffies!)
Yes, that’s good to know. Thanks. By the way, the Harland Sharp tech said they make their 1.6 closer to 1.7 to account for that.
Newbomb Turk
Well-Known Member
That’s at best a fib. All rocker arms flex. If you build the rocker to whatever the nominal ratio it will be less when loaded.
So they do build their rockers with a higher than nominal ratio but not to account for pushrod angles.
How do I know that as a fact? Because every HS rocker I’ve checked has been a higher than nominal ratio. That includes GM rockers.
And every Jesel and T&D rocker is the same.
Like I said, that’s a fun at best.
Everybody worries about the 58* angle but nobody looks at the rocker brand/design which can greatly affect lift. A difference of 0.068" in total lift between the best & the worst of these alum rockers....
mopowers
Well-Known Member
I think your decimal is in the wrong place. I'm seeing a difference of 0.016" for the roller rocker from shortest to longest pushrod.
Honestly, I'd just say run the strongest components you can afford and don't overthink it.
If you're really worried about that 30 thou, just go one size up in the cam.
Next time you're looking at a ruler look how small the 1/32 increment is. I'm not saying it doesn't make a difference in flow and/or power output, but honestly it probably wouldn't be much.
If you're really worried about that 30 thou, just go one size up in the cam.
Next time you're looking at a ruler look how small the 1/32 increment is. I'm not saying it doesn't make a difference in flow and/or power output, but honestly it probably wouldn't be much.
B3422w5
Well-Known Member
Agree.
I have 1.5 Harland Sharp rockers and a smallish cam for what I have.
I asked Dwayne if it was worthwhile to put 1.6 rockers on, and he said unlikely to be worth doing, so I didn’t.
Yeah and a handful of tests out there support this also. It's a bit counterintuitive but at least in some cases the extra lift doesn't do anything at all.
Everybody's favorite dude Richard holdener did a 5.3 test with a BTR cam one was rated for stock springs and the other one higher lift and required spring upgrade. Otherwise basically the same cam timing events. Guess what....Just about zero....nada.... difference between the two in terms of power output.
harrisonm
Well-Known Member
Ah, a closet mathematician. I always liked math. I used it a lot for most of my adult life. I think it is hilarious when I see people with T-shirts that say something like "ANOTHER DAY WITHOUT USING ALGEBRA"
A lot of that is also the parameters of the test engine and the cylinder heads. What Rich showed was really good IMO and probably saved a lot of guys some money. But it is not always the case.
Much of it is in how the cylinder head flows and where it stops flowing more at higher and higher lifts. Also small duration cams really don’t allow much time for air to get in. So if the extra lift is there and the time is short with not so great flowing ports beyond what cam number 1 lifted to, then there really is no point of f getting the high lift cam.
IMO, I like to take advantage of the cylinder heads flow capability. Not so much for the daily driver or mild hot rod, but more so for the heavy street hitter or race car.
B3422w5
Well-Known Member
What Dwayne said regards adding more lift to an existing cam via going from 1.5 to 1,6 rockers was that virtually nothing he had ever tried showed anything worthwhile, no matter what he has seen it tried on.
That said, every cam I know of running heads like mine has shown way more power( granted they are rollers) but the reason I asked him in the first place is because the heads climb up past 650 lift, so I thought seeing more of that might be worth it.
My home ported J iron heads peaked at 260 cfm at 500 and didn’t increase from there. I wanted all of it so I went to 1.6 rockers to get me to 500. Cam is 280 duration, I believe 234 at 50.
B3422w5
Well-Known Member
See any gain?
Is some of the loss in flex? I have to wonder. There has to by some loss dynamically compared to a "static" measurement.
New build, don’t know what I’ll get.
M_Body_Coupe
Active Member
A bit late to the discussion, but since I've done all of this measuring when I was blueprinting my W2 408 stroker build, I thought I would share.
So here is the combo:
1) comp cams hydraulic roller cam XR292 and their roller lifters
2) Harland Sharp 1.6 ratio rocker arms
3) two different lash caps: CAP1 = 0.0.79" thick, CAP2 = 0.87" thick
Take a look at the attached charts, here is what they show:
1) @1.6 - this is the theoretical lift at valve
2) AS-IS - is the uncorrected lift, bad the geometry was really bad here (my W2 heads were the long valve Econo castings)
3) CORRECTED - this is the lift with Mike's (B3) correction package
4) LASH CAP1 - this is the lift while using CAP1
5) CORRECTED TO AS-IS DIFF - this is the actual valve lift loss/gain comparison between the AS-IS setup and B3 kit corrected setup, see RIGHT side of the chart for scale
6) LASH CAP1 TO AS-IS DIFF - same as #5 above, but comparing the CAP1 lift
7) LASH CAP2 - valve lift with CAP2
8) LASH CAP2 TO AS-IS DIFF - same as #5 above, but comparing the CAP2 lift
Mike and I discussed, he concurred that what I was seeing was correct with the use of the kit, however the benefits would stem from the actual geometry corrections.
To better understand the true contribution of the cam=>lifter=>pushrod=>rocker arm=>valve geometry to the final lift I re-did all of these measurements with 3 threads showing on the rocker arm adjuster. If you visualize this you can tell how that causes pivot to be moved, and therefore by extension the effective rocker arm ratio.
I must say that I've regularly spun that motor up to the 6500 RPM redline, and you can't tell this is a hydraulic roller cam setup. The thing buzzes up in no time, if I'd let it, it would readily pull right past that 6500 mark! ...which leads me to believe that the valvetrain geometry here is NOT an issue.
So here is the combo:
1) comp cams hydraulic roller cam XR292 and their roller lifters
2) Harland Sharp 1.6 ratio rocker arms
3) two different lash caps: CAP1 = 0.0.79" thick, CAP2 = 0.87" thick
Take a look at the attached charts, here is what they show:
1) @1.6 - this is the theoretical lift at valve
2) AS-IS - is the uncorrected lift, bad the geometry was really bad here (my W2 heads were the long valve Econo castings)
3) CORRECTED - this is the lift with Mike's (B3) correction package
4) LASH CAP1 - this is the lift while using CAP1
5) CORRECTED TO AS-IS DIFF - this is the actual valve lift loss/gain comparison between the AS-IS setup and B3 kit corrected setup, see RIGHT side of the chart for scale
6) LASH CAP1 TO AS-IS DIFF - same as #5 above, but comparing the CAP1 lift
7) LASH CAP2 - valve lift with CAP2
8) LASH CAP2 TO AS-IS DIFF - same as #5 above, but comparing the CAP2 lift
Mike and I discussed, he concurred that what I was seeing was correct with the use of the kit, however the benefits would stem from the actual geometry corrections.
To better understand the true contribution of the cam=>lifter=>pushrod=>rocker arm=>valve geometry to the final lift I re-did all of these measurements with 3 threads showing on the rocker arm adjuster. If you visualize this you can tell how that causes pivot to be moved, and therefore by extension the effective rocker arm ratio.
I must say that I've regularly spun that motor up to the 6500 RPM redline, and you can't tell this is a hydraulic roller cam setup. The thing buzzes up in no time, if I'd let it, it would readily pull right past that 6500 mark! ...which leads me to believe that the valvetrain geometry here is NOT an issue.
-
