old motorhead

iTrader: (10)

Why do just about all of the "shelf" LS cams have less lift on the exhaust side? The way I look at it is more lift and less duration = less overlap with maybe similar flow? Less overlap usually leads to better manners. What am I missing?

NAVYBLUE210

According to Darin Morgan I believe, since the diameter of the exhaust valve is smaller it needs correspondingly less amount of lift
vs the larger intake valve. it has to do with curtain area if I am understanding correctly.

grubinski

I've never heard anything like that, but it *could* be believable. Once you lift the valve high enough, the curtain area is greater than the valve area. This happens at pi*d*lift > pi*((d/2)^2), which means any lift > d/4 is sufficient that the curtain area is less restrictive than the valve area. For a 1.60" exhaust valve, that only takes .400" of lift. For a 2.08" intake, it'd be at .502" lift. So even if the exhaust valve has less lift than the intake, *relative to it's diameter*, it has more lift than the intake valve, and so the lift is less of a restriction on the exhaust side than the intake side.

I could be wrong, but it's an interesting question, and that's my speculation given the post from NAVYBLUE210.

Darth_V8r

iTrader: (4)

Also--

Throat area is even less than the valve diameter.

And the exhaust gets the benefit of a piston pushing the air out.

I remember seeing some testing a long time ago that involved Brian Tooley showing more power produced with slightly less exhaust lift.

old motorhead

iTrader: (10)

Not disagreeing or arguing with any of you guys. I've read enough of all three of y'all's posts to know that you know what you're talking about. Just wanting to educate my pea brain a little.

My 226/234 115+4 cam has .620 lift on both sides. Engine is an LS3 in a C6 with GM LS3 heads ported by Tx Speed. I'm very pleased with the combo. I didn't want to go over .620 lift in deference to valve train reliability. Pat G recommended a similar cam with .629 lift on both sides and a narrower LSA.

Asked this because I'm about to take the knife to the wife's LS2 powered SSR. Similar to the LS3 build, I'm wanting all I can get with little to no compromises to drivability. Wife handles my M6 shifted Vette just fine and the SSR also has an M6 tranny. The LS2 will have ported and maybe milled 243 heads. Ported Trailblazer SS intake mani and a cam something like a 226/230 115+? depending on milling and head gasket used. Where would you put the lift on a combo like this? I'll probably use stock rocker arms with maybe a trunion upgrade. BTR Platinum duals for springs.

Corona

Correct as with Rowdy I was concerned about the 1.55 exhaust valve same as with using a lower lift. Crazy part is even with the smaller exhaust valve & using lower lift on the same side wouldn't be crazy.

ER answer"ed my question on the use of the smaller valve or lower exhaust lift when I came up with idea he had already done. Darin said the same thing.

I know it's real coming from either. Having both just makes it like it came from Heaven. When 2 or more agree He's in da Mist. 😆

Corona

Build up of pressure makes power the Exhaust
doesn't require anything as its the result of combustion.

It being Forced out regard less.

NAVYBLUE210

My .02
I would use a Cam Motion .365 lobe for a .620" lift intake, and a .360 lobe for a .612" lift on the exhaust with the above situation.
I like the 115* LSA for the heavier vehicle as well....

But then I am the knuckle head that would use the PAC .625" Bee Hive Springs.
LOL

Double06

iTrader: (1)

I think the 629 vs 620 lift is not that much to warrant that - but many times it is a totally different lobe design so that maybe why the lift is not the same as it is from a different lobe family. Like I run an LXL lobe - in the catalog description of that lobe they say this is a good exhaust lobe (good valve control with 1.8 rockers etc.) and people usually run the LSL as the intake lobe. From what I read there, is the exhaust lobe here is softer than the intake for some of the reasons mentioned above.

old motorhead

iTrader: (10)

I can go with your lift figures, but I'm scarred for life from using single springs. I know they're better now, but the experience of ruining an engine with Comp's 918 behives still pisses me off. And that was the better part of 20 years ago. All the "help" they offered was a new set of the same crappy springs. Damn big of them, don't you think? Richard at West Coast Cylinder Heads even told me exactly where it broke before I could tell him.

While I'm on a valve spring rant, I broke a Tx Speed dual spring stortly after install. And Tx Speed installed them on a new long block put together by them. The cam used was a mild blower cam with Comp's LXL lobes on intake and exhaust. As Double06 mentioned, those lobes are supposed to be easy on the valve train. Tx Speed was nice enough to give me one (1) spring and sell me the rest of the set at a discount. Damn big of them, don't you think? The inner spring held the valve up so no engine damage. That wasn't that long ago and that's what led me to Tooley's platinum duals. I've had three sets of those with no issues

grinder11

iTrader: (1)

It seems Comp has lost some measure of quality AND customer service since Crane went under.......My .02........

grubinski

I have Manley Nextek in my engine, which is what Tony Mamo selected. If I was building another engine, even without his input, I'd go with those springs. If they're good enough for him, they'd be good enough for me, too.

old motorhead

iTrader: (10)

Dual of beehive? There's not much I'd argue about with Mr. Mamo.

grubinski

Dual spring.