He is saying the same basic thing. The reason for increased lift is to maximize duration at your peak flow lift. I use .550, because that number came from Darin as to when the short side radius on a cathedral head starts getting screwy.

 

Right. Looks like that happens on the 706 head right around .500. The flow graph looked weird to my untrained eye.

 

Not all short side radii on cathedral heads are the same, though. A 241 is basically a cliff compared to the short side on a 243, for instance.

So... how much different is the 5.3 head short side radius from other heads?

 

If you are only comparing @.050 but you know better than that. You can make a lobe with higher lift that isnt as aggressive or even less aggressive than a lobe with less lift.
The tsp lobes are definitely not lsk at all.
Speculation isnt helping and, when searched by some novice etc and see this, will paint a bad picture in their mind also and give them false info to then parrot to others.
Their 212 .600 lobe is no more aggressive than quite a few other lobes out there with less lift
More lobe area is the good part there also. As well as their precision.

Talking about valve events and how important they are then speculation on the tsp lobes? Yall know better. Thats a no no..

 

So freaking true.....I asked for a 800 lift lobe that's as soft as some 750'ish aggressive lobes .....it's all about the Ramp. Darin said the heads would love 800 ..so 🤨
I found springs

 

You asked for a .800 lobe or you asked for .800 lift? .800 lift with an 1.8 rocker is a .444 lobe using a 1.8 rocker.
You are correct about the ramp rate.

 

Lol. Was a poorly written post. I was not trying to say tsp lobes were like lsk. If it came off that way it was not my intention.

 

You should also think less about the "peak lift" number, and more about the effect of having the valve open a bit more at all times.

The valve spends very little of its time at full lift. Emphasis on VERY LITTLE. All of this about "port stall" and similar effects is only meaningful for a VERY aggressive cam that snaps the valve open to nearly full lift, holds it there for most of the cycle, then drops it back onto the seat quickly. A street cam isn't going to do that. It's going to open the valve more gradually, hold it fully open for only a short time, then begin lowering it early and drop it gently. (relatively speaking) Violent valve action isn't real good for longevity... after all, a single commute to work probably puts more open/close cycles on your valve train, than an ENTIRE ENGINE LIFETIME of pro racing, where things like "port stall" really matter.

Lobes tend to have a specific shape, a particular kind of curve. Darth's football example is a good analogy for the type of curve often used for the majority of the lobe shape except near the seats, which is a mathematical form known as a "catenary". Try thinking about the football's motion like this: imagine throwing the ball exactly 40 yards, first as flat as possible, then make it go 40' into the air, 60' into the air, then 75' into the air, etc., but still, exactly 40 yards. Then look at the curve that the ball moves through. That curve actually looks alot like a cam lobe. The 40 yards down the field corresponds to the lobe duration especially the .050" part, and the peak height the ball reaches corresponds to peak lift. If you throw the ball 40 yards 75' into the air, it will be higher off the ground AT ALL POINTS ON THE CURVE than one thrown 40 yards but 60' into the air, not just at the peak. That's really what a higher lift cam of the same duration does: the additional flow at the peak is almost irrelevant; rather, the fact that the valve is open a little bit more ALL THE TIME is where the benefit comes from.

 

Well said. That is why the benefit to increased lift is not increased peak flow. It's increased duration at .500 lift.

 

I was just going to mention duration till you beat me to it.

 

And .100", .200", .300", and .400"; and every point in between. The valve simply spends more time open farther, even though the contribution to the total engine package created by the "peak" lift, is minimal.

 

True. I tend to focus on duration at 500 lift on a cathedral head. On ls7 heads, I look at duration at 700 lift

 

Low Lash solid roller.
263/279 Duration @ .050’’
113 lobe separation 109 intake centerline
.810’’/.810’’ lift with 1.8 rocker
the lobe is Soft as butter...

 

Even with 1.8 rockers, that is still a huge lobe lift number...

 

It's for a street engine that was the key part when I filled out the cam recommendation sheet. Had to find springs ...& Reasoning in Bushed lifters.

JHE SPRINGS- MADE BY PSI

Part # Type Application
PSI JHE-15 Circle Track = Endurance springs🤫🤨😉
OD (in) 1.310 Outer ID 0.900
​​​​​​Seat pressure Load (in) 0.615 Open pressure load 750 Rate (lbs/in) 690
Max lift 0.840

 

What would the best point be for an ls3 head?

 

.650 imo. I can see wide opinions on this one. Especially ported or AM ls3 heads.

 

600 to 650 generally with the Ls3. 700+ kinda tells how much bigger the port is if flow continues to climb and lower lifts are compromised.

 

Ls7 head has more port Volume yet a smaller MCSA & CSA and is smaller in size VS the same Ls3 head. Flow is wish - wash. Both heads flow around the same at different lift points 360's vs 370's - ls7. Lower lifts is where the Ls7 kills the Ls3 with a smaller raised runner.

 

All lifts the ls7 flow kills ls3