bufmatmuslepants

iTrader: (3)

I noticed a lot of people doing 228/236ish cams with 112-116 lsa in LS engines and most LT builds with a similar duration go with 107-110, why is that? The cam for my LT is a 230/240 on a 107.5, which caused my brothers jaw to drop since his is a streetsweeper HT 228/232 on a 111 in his LS. Mine has 20 degrees of overlap and his has 8 degrees. Is it head design with the cathedral ports? My cam was specced for a 383 with 11.5:1 and dart 180cc heads for fuel economy and midrange power, I am putting it in a 350 with heavily ported stock castings with 2.02/1.6 valves.

Exidous

iTrader: (11)

I'm pretty sure it's the head design. The Cathedral port was a vast improvement over the LT heads. The less overlap needed is a byproduct of the better flowing heads. Just a guess though. A fuel economy head for the LS1 is the AFR 205 which is the smallest port available.

Rise of the Phoenix

iTrader: (27)

Yep, LS head design is better so you don't need as much overlap. With that said, I've seen a lot of LS builds with quite a bit of overlap put down some killer ET's and dyno numbers.

Exidous

iTrader: (11)

They certainly can run them it's just not usually necessary. :-)

Rise of the Phoenix

iTrader: (27)

I believe that's why the AFR heads have always done so well with very low duration, or even cams like 224/224 114 LSA.

Exidous

iTrader: (11)

Aye, I'm on a 225/227 with Tony's 220's(AFR casting) and I'm really happy. No numbers yet but it's DEFINITELY faster than what I had before and that was about 420whp. That setup had a FAST 102 on it and I'm on an LS2 intake atm....just to give you an idea.

JakeFusion

iTrader: (7)

My current cam has 16 degrees. You can keep throwing overlap at cathedral ports and they just keep making power.

My next cam has 33 degrees of overlap...

Exidous

iTrader: (11)

I've got -2* overlap. I know I'm leaving a lot of power on the table but the street manners are just hard to beat.

How does that 16* run on the street? Where does it surge if at all?

A.R. Shale Targa

iTrader: (2)

The short runner intake liked overlap to pull more cylinder filling charge. The long runner column of the LS continues to fill with less HELP from the high velocity exhaust side. Which is what oberlap really is
Also since the cathedral design is so much better (ex/in ratio) it can make great power with less duration (224) while still trapping a lot of cylinder pressure (TQ) and then a wide lobe separation can smooth out the manners;maintain fuel efficiency AND carry further up the rpm scale due to the delayed exhaust event. In a world of compromises; the LS architecture is such a win/win !!!!!

redtan

iTrader: (5)

As others have said, it's the head design not the block itself.

And it's the same reason why LS3 rectangular heads like even less overlap, the more efficient the port is the less overlap is needed to make the same kind of power.

ERockZab

Probly a stupid question but... Is overlap the biggest cause of surge? I've been reading a lot on what cam to go with and I see a lot of the same lobe configurations but with different overlap and it seems the less overlap the more "streetable" it is.

Exidous

iTrader: (11)

Overlap and timing are your biggest components. Less overlap means better street manners, yes. A stock cam has in the neighborhood of -30 to -45* overlap.

gtfoxy

When considering the stock cams, or emissions legal ones, in the aspect of more overlap, not necessarily performance related, is emissions output. A bunch of raw fuel igniting in the exhaust doesn't play well with the smog checker.

Darth_V8r

iTrader: (4)

My understanding is that it isn't "like" so much as "need".

Like others have said, the cathedral head flows very well and has very good port velocity, so you don't need as much cam to make power. I sort of think of a stock LS as a "heads-only" chevy small block.

Then, you have the lS3-style rectangle ports, which flow even better, requiring even less cam.

Like gtfoxy said, if you can generate the torque with less cam, then emissions will naturally drop.

Like JakeFusion said, the cathedrals will take high overlap cams quite well. They just aren't as necessary in general compared to the SBC/LT1 heads

svede1212

iTrader: (3)

Kind of. Fueling and timing fine tuned can eliminate a lot of it. A lot of tuners take the easy way and tell the customer "That's how a cam works" but many times it can be greatly mitigated.

i.e. I had a 10.5* overlap cam that wasn't huge but still pretty good sized. After playing with the tune could drive 1,200 rpm in 6th with no surging.