Hemi cam lobes

When selecting a cam for a Hemi, 12:1 572 street/strip Hemi, would the straight lobe pattern on duration be what is used or are the Hemi guys still using a split lobe pattern? Here is a street Hemi cam pattern i found, 276/280 and here is a race pattern 281/281 both at .050". I understand the Hemi head flows much better than a wedge head, so not certain what is needed in that aspect. Also the lobe sep, i have seen 106, 108, 110 and 112 used in this app. What works best in this app? 3400# 727/8" 5500 stall. Thanks

Hey Dave from what I've seen the bigger inch, street /strip Hemis all seem to be cammed around 112, mine included.

Typically intake lift is more than exh lift as the exh is so efficient, and usually see with intake durations in the 270s and exh in the lo/mid 280s.

The Bullet roller I'm running is on a 112 LSA, due to this the idle great and relatively "mild" given the size of the cam. Most race Hemis seem to run 108 LSAs or tighter ie 106...providing a narrower power band.

What car is it going in and what's it weigh ?

Same here!

IMG_8495 by Greg Ault, on Flickr

and the idle:

https://rumble.com/vfcpz1-cars-and-coffee-march-2021.html

I was told years ago to be very careful on selecting LSA on all 426 hemi motors due to the overlap affecting the intake and exhaust valves possibly hitting each other, I had one cam, customer furnished it and wanted to run it, which did that I had to have the valves cut down, narrow the O.D., and sink the seats also
108 to 112 should work fine on most grinds
Always degree the cam and check the valve to valve clearances with one piston out on the overlap Dang them Hemiroid motors anyways

Thanks for the great info. I don’t know enough about the over lap event to understand why large engines need wider lobe sep angles. Can someone explain how this works?

I was taught that the lobe separation angles affect the power band, close LSA make more power below 6000 to 7000 RPM and wider affects it above 5000 RPM on N/A motors.
Also 4 speed cars wider and automatic cars closer works well for me, Pro Stock are suppose to be using 118 to 120 LSA, maybe not

Ok, but where does the cubic inch come into play? I don’t understand why larger cubic inch motors want wider lob seps.

Probably to help them not spin the tires as hard as they would with a closer LSA
I use to use Isky 590-616 solid lifter grind cams in my BB M.W. motors back in the mid 1970s, it was ground on a 104 LSA and I would installed it between 99 and 101 ILC
I like that cam a lot but isky took it out of their catalogs and made it a "custom grind"and wanted to charge $30.00 more for the "custom grind"
I quit buying direct from Isky as a "dealer" about that time and switch to become a dealer for Comp Cams, went faster too

Lots of reading here. But it might answer some questions.

www.hotrod.com/articles/0805phr-engine-masters-challenge

Well you would start with picking the valve events.

Large displacement generally results in more duration so as duration increases, lobe separation usually does as well to keep overlap in check.

If you just keep increasing duration without ever widening lsa you end up with a ton of overlap.

Ok, I understand.

I've heard from a few guys that the Hemi chamber design allows the fuel/air flow to go straight out the exhaust on overlap. If you look through the intake port of a Hemi head without valves you can see a little daylight on the exhaust side of the head. I would think a wider LSA would help kill some of the overlap and keep the fuel in the chamber. Also the a/f mixture just tumbles out the intake valve and doesn't seem to spread to the sides of the pistons. The pistons get a carbon track between the valves and the quench areas are fairly free of carbon.

Another problem is valve to valve interference on overlap on tight lobe centers. They used to clip the exhaust valve to gain clearance. I have a CC roller that had valve to valve contact with my valve gear. I ended up with a Bullet custom roller on a 113 center to get correct valve to valve clearance.

What was you lobe sep before the 113?

That kind of what I had invisioned.

110° it was a comp cam grind# crh 1393-1395-R110

Thanks

i have a solid roller custom crower cam out of my pumpgas 12.2 to one 605 cuin it ran 9.60s at 142 mph on motor !!! i have a procharger on it now had to change the cam !!