s346k

iTrader: (4)

lsk lobes on both intake and exhaust?

speak more of this

Dom

iTrader: (2)

One more thing. How long do you expect those springs to last on the LSK lobes?

Beast96Z

iTrader: (21)

True, your maximizing duration area, but you have alot of lift you don't neccasarilly need on the exaust. When I started looking at numbers for my cam, I was gunna go big duration (259/263 LSK) with a 106 LSA+4 to raise DCR. Later, many told me that using a narrow LSA and big advance is a bad way to go about upping DCR beause of the huge overlap that is a by product of a cam of this size. With as good as the intake setup of mine is gunna be flowing, many have reccomended smaller durations(low 240's) with about a 10 degree split. Basically just wondering if I should be looking for another exaust lobe with a nice curtain area and less lift (which I think I've found) or just get a LSK exaust and be done.

Phil99vette

iTrader: (11)

I like the cam specs but I would run 8-10 degree split on the exhaust.

CNB

iTrader: (4)

What's your reasoning?

Phil99vette

iTrader: (11)

CNB,
The 8-10 degree split is what we have feel will eventually be the best route for the big cc ET heads. Our computer modeling and real world data has said that the big flowing heads need a larger exhaust duration to maximize performance. We consulted with 3 cam grinders and they all said the same thing.
Phil

Beast96Z

iTrader: (21)

Exactly the same responses I got too. I was told not to be as focused on the 10 at .200, but more on the 10 at .050" and .006". I agree that the high intake flow and the somewhat normal exaust flow of these heads will require more of a split than the normal LSX based cams.

CNB

iTrader: (4)

Interesting. Will you elaborate more please.

CNB

iTrader: (4)

That seems right in line with my cam. 12 at .050 and 11 at .006.

J-Rod

Intake to exhaust ratio is one of the keys for determining exhaust split. On something with a good I/E ratio you don't need 8-10 degrees of exhaust split. Now, when you look at something like the LS7 head which is a 60% I/E ratio, then yes you start looking at bigger splits.

But, I definitely don't think you need 8-10 degrees on AFR heads.

As for a big cam witha narrow lobe sep. You don't necessarily need to advance those cams. Even with all the overlap, they often make big power. Look at my buddies in Australia.

Pete dyno tested his 408" Ysi at 12 psi of boost with a big cam and a narrow lobe sep day before yesterday (the cam was optimized for a N/A setup). Anyway, he ran out of injector at ~6500 & 12 psi of boost... 920 HP time to move up from 60lb injectors.. The cam they used most folks would not consider as a blower cam. But it still makes crazy power....

Patrick G

iTrader: (14)

J-Rod is right as usual...it's all about the combo that's in your car and your goals. I can understand in theory why certain cam grinders would want a 10 degree split between intake and exhaust, but theory ain't reality. Consider the fact that most of us are saddled with an intake manifold (FAST 90/90) that is known to knock down the flow of even the most spectactular heads, and your intake/exhaust ratio changes dramatically. Now your 320 cfm heads only flow 285. With an exhaust port that flows in the 230-240 cfm range, your exhaust is flowing well over 80% of the intake. There is no need for a 10 degree split when running a FAST intake. Now swap to a sheet metal intake or a well-ported single plane and that 10 degree split would probably make more sense.

My goal was to keep overlap reasonable while maximizing the DCR and power under the curve. By adding an exhaust lobe with a 10 degree split, I would have had to either run a smaller intake lobe or widen my LSA to keep the overlap the same. Both are recipes for decreasing area under the curve IMO. The 4 degree split with similar curtain area for intake/exhaust was a prudent approach to achieve my goals in my view.

Phil99vette

iTrader: (11)

Didn't tony do some testing and conclude that 4-6 degrees was money on the AFR heads?

ninobrn99

iTrader: (8)

well those are the durations Tony recommends for the afrs and what he runs. not sure what the specs are at .06 and. 200.

ls6jimmy

iTrader: (2)

Great stuff hp is cute but torque gets you moving.

Tony Mamo @ AFR

iTrader: (13)

Most AFR headed LS applications would be best served with that scenario of exhaust split, but not every situation. If in doubt however, 4 degrees will almost always provide good results with our cylinder heads.

Tony M.

PS...I know its been touched on but some of the "big flowing" intake ports aren't as big as you think in their actual application (think restrictive manifold designs)....making a blanket statement like they always need 10+ degrees of split might just needlessly give up bottom end TQ with no appreciable gains in peak #'s. Most of the cam guys you are polling are purely looking at flownumbers with a radius plate on a flowbench....not too many of us are actually running our engines that way.....LOL

King James

iTrader: (13)

God I love threads like this!

Patrick G

iTrader: (14)

Chris, to pass emissions, you need to keep your overlap at .050" at -7 degrees or less and your overlap at .006" at 45 degrees or less. To make tons of power under the curve, you'd want your dynamic compression in the 8.7-8.8:1 range and your intake closing point above 40 degrees ABDC at .050". Here's a cam that meets that criteria:

................................ 0.006 0.050 0.200
Intake Duration..... - ID 265 215 142 2124 LSK .629 lift
Exhaust Duration... - ED 273 223 153 2127 LSK .636 lift
Lobe Center Angle - LSA 113 113 113
Intake Centerline.. - ICL 113 113 113

Intake Valve opens.. - IVO 19.5 -5.5 -42 BTDC
Intake Valve closes.. - IVC 65.5 40.5 4 ABDC
Exhaust Valve Opens - EVO 69.5 44.5 9.5 BBDC
Exhaust Valve Closes - EVC 23.5 -1.5 -36.5 ATDC
Exhaust Centerline... - ECL 113 113 113
Overlap........................ 43 -7 -78.5 degrees

It's probably better suited for headers than manifolds (because of the later EVO) but it will make TONS of power under the curve.

LSK lobes on intake and exhaust: 215/223 .629/.636 113LSA (+0)

Based on your specs: static compression = 11.15:1, dynamic compression with this cam = 8.82:1

cantdrv65

iTrader: (3)

The cam recommendations Im seeing in this thread make ALOT of sense...

Beast96Z

iTrader: (21)

I'll probablly flow it before install, but I believe the Harrop 55mm will allow my ET's to flow rather well. I'll probablly make my cam decision after the flowing of the heads with the intake on and a pipe on the exaust.

Patrick G

iTrader: (14)

The cam would work just fine on stock heads. All that is needed are good springs shimmed to within .050" of coil bind, light retainers and 7.450" chrome moly pushrods. Even though stock heads don't flow much more over .600 lift, they don't back up either.

The beauty of the LSK lobes is cramming more duration at .200" lift (which is .340" at the valve). You'd have to admit that more duration at .200" (with the same duration at .050") will make you more power. Add the extra lift and it's a bonus. And I'm not sure where you pulled the .615 max lift number from, but you have to understand, going from .615" lift to .633" is not a huge step. Once you have the correct spring setup, it's all academic.