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LS3 heads wide split camshafts

 
Old 05-21-2019, 11:29 AM
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Default LS3 heads wide split camshafts

I'm just curious what you all think about camshaft specifications for LS3 heads.
There are a lot of differences of opinion whether 6-8 or 12 -17 degree splits work best.
There was an interesting post by jakefusion saying you need 1.5 degrees of split per percent of difference from the intake to exhaust flow.
On an LS3 heads according to a calculation this works out to a 15 degrees split.
Pat G, Ed Curtis: the camshafts I have purchased from them both used an 8 degree split.
Comp cams uses 15+ splits, cam motion 12+ degree splits here in Australia crow cams uses 16-17 degree splits.
Brian Tooley uses 15-17 degree splits too.
I know wider splits hang on better after peak power and extend the rpm range but does anyone know for a fact if the LS3 does in fact need a wide split to work optimally?
According to Brian Tooley's testing, he found that camshafts with 15 degrees splits, made more power and torque from 3500rpm+ compared to cams with less exhaust duration.
Would really like to read other opinions and thoughts on this.
Go ahead, Darth, Smokey, Jake, GTasma etc!
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Old 05-21-2019, 12:22 PM
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16* here and she runs pretty good (SBE 6.0).
What CI motor are we talking here?
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Old 05-21-2019, 12:34 PM
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The THEORY is that because of the wide disparity between intake and exhaust port size, exhaust duration needs "more time" to properly exhaust ALL the spent gases those humongous intake ports let in.
I've always wondered why the exhaust ports weren't enlarged more than they were to account for this.
Having said that, I've wondered why GM didn't use a cam other than the 204/211, .551/.525 one that they did use.
They already had a 204/218, .555/.551 cam they used in the late LS6.
To me, that would have been a far better fit with the wider split AND more lift on the exhaust.
That's my take on this.....
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Old 05-21-2019, 01:10 PM
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Im running a 229/244 from Tooley. It runs hard and sounds great.
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Old 05-21-2019, 01:12 PM
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Originally Posted by Tuskyz28 View Post
Im running a 229/244 from Tooley. It runs hard and sounds great.
That 15-degree split is likely just what it needs to run like that.
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Old 05-21-2019, 01:32 PM
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Originally Posted by ragtopz28 View Post
16* here and she runs pretty good (SBE 6.0).
What CI motor are we talking here?
Let's say for a 408
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Old 05-21-2019, 01:40 PM
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Originally Posted by G Atsma View Post
The THEORY is that because of the wide disparity between intake and exhaust port size, exhaust duration needs "more time" to properly exhaust ALL the spent gases those humongous intake ports let in.
I've always wondered why the exhaust ports weren't enlarged more than they were to account for this.
Having said that, I've wondered why GM didn't use a cam other than the 204/211, .551/.525 one that they did use.
They already had a 204/218, .555/.551 cam they used in the late LS6.
To me, that would have been a far better fit with the wider split AND more lift on the exhaust.
That's my take on this.....
I agree the LS6 cam would have been more ideal.
However I was reading when gm designed the ls3 they had to meet emissions and a power goal.
The spec they chose was the same as the LS2 except the lsa was at 117 which I'm betting is to account for the larger displacement and so it hangs on where it's meant to.
If they put the LS6 cam it would make more power than what they were wanting.
Also I wonder why they didn't make the intake and exhaust close to the same size so we could run single pattern camshafts.
Maybe if the square port design had a smaller intake it would not flow as well and therefore GM had no choice but to have that imbalance . Just a guess.
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Old 05-21-2019, 01:43 PM
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Originally Posted by Tuskyz28 View Post
Im running a 229/244 from Tooley. It runs hard and sounds great.
I bet it does.
If I had an LS3 that would be the camshaft of choice for me too.
It's a good compromise between streetability and power.
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Old 05-21-2019, 01:53 PM
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Originally Posted by bortous View Post
Let's say for a 408
235ish/251ish @ .62xish would more than likely rock!
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Old 05-21-2019, 03:01 PM
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My non professional .02..
Split is heavily influenced by Exhaust/Intake Ratio and Peak HP/ RPM Goal Range.
OE LS3 heads ~60% E/I ratio +12-16* Split
Aftermarket or Ported OE Castings, W/ ~70% E/I ratio +8-12*
Aftermarket Cathedral W/75+% +0-6*
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Old 05-21-2019, 03:39 PM
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Originally Posted by NAVYBLUE210 View Post
My non professional .02..
Split is heavily influenced by Exhaust/Intake Ratio and Peak HP/ RPM Goal Range.
OE LS3 heads ~60% E/I ratio +12-16* Split
Aftermarket or Ported OE Castings, W/ ~70% E/I ratio +8-12*
Aftermarket Cathedral W/75+% +0-6*
That sure makes a lot of sense! Kinda how it looks like it's done in most cases, the better running ones anyway.
The above is why I thought the late LS6 cam would be a winner in the LS3 with its 14 degree split and higher exhaust lift.
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Old 05-21-2019, 04:46 PM
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To your point G, GM used a 230* exhaust lobe on the ls7 which is almost unheard of duration for a factory car with fixed cam timing and lift. In their other cars with smaller engines it wouldn't have met emissions and driveability requirements. Hell, it probably wouldn't fly with today's requirements at all and that's why everything big power is FI.

The LS7 and LS3 have very similar camming requirements, with the LS7 often getting even larger splits than LS3 cams.
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Old 05-21-2019, 06:25 PM
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Originally Posted by spanks13 View Post
To your point G, GM used a 230* exhaust lobe on the ls7 which is almost unheard of duration for a factory car with fixed cam timing and lift. In their other cars with smaller engines it wouldn't have met emissions and driveability requirements. Hell, it probably wouldn't fly with today's requirements at all and that's why everything big power is FI.

The LS7 and LS3 have very similar camming requirements, with the LS7 often getting even larger splits than LS3 cams.
What's funny is the NA LS7 and blown LS9 have NEARLY identical cam specs- 211/230, with the LS7 @ 121 LSA having 1.5 degrees less LSA than the LS9. It shows that sort of timing does work in certain apps!
In testing, those cams in an early 5.3 lost tons of power in the low end. They need displacement and good heads to run right.
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Old 05-21-2019, 06:48 PM
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Originally Posted by G Atsma
What's funny is the NA LS7 and blown LS9 have NEARLY identical cam specs- 211/230, with the LS7 @ 121 LSA having 1.5 degrees less LSA than the LS9. It shows that sort of timing does work in certain apps!
In testing, those cams in an early 5.3 lost tons of power in the low end. They need displacement and good heads to run right.
The reason for the loss of low end has nothing to do with the duration or split. Its a cam with a 47 degree IVC. A 5.3 likes a 41 degree IVC. If you advance the ls7 cam six degrees in a 5.3 it gains torque.

By comparison a 427 makes torque on accident. You do not need to can for torque. So GM relaxed the IVC and let it rev. Although on a 427 I like 52 degrees IVC.
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Old 05-21-2019, 09:18 PM
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What intake you plan on running ?
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Old 05-21-2019, 10:03 PM
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I’ve built three 6 liter builds with LS3 heads. First one had 14 degree split. Second one had 9 degrees split. Third one had 11 degree split. Each build had a different purpose, and completely different valve events, so I can’t really compare split only in this situation making a difference one way or another.
I’ll say this however. The second build used the WS6Store high lift ASA camshaft, and when talking with those guys about duration and events, and exactly what I was doing with the build, I was told by them that square port heads don’t need the split, and that it was pretty much a myth. I paraphrased that statement, but that’s pretty much what I was told by them. That engine, of the 3, runs out the best on top. The latter engine, with 11 degrees split makes the most torque, seat of the pants dyno testing. First one, with 14 degrees was a VVT build, and was the most fun to drive.
The exhaust side of a square port head, LS3 or LS7, does need more duration to aid in getting the air out, because of the imbalance of the I/E ratio, but as to how much I feel totally depends on the combination and what your doing with the vehicle.
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Old 05-21-2019, 11:51 PM
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Originally Posted by ragtopz28 View Post
235ish/251ish @ .62xish would more than likely rock!
Something like a 236/252 115 LSA +3 would be a good cam for a 408 and drive pretty good.
Unfortunately I had a 236/244 114 LSA +2 cam and this drive good in the low and mid range but not that great in the top end.
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Old 05-21-2019, 11:56 PM
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Originally Posted by Darth_V8r View Post
The reason for the loss of low end has nothing to do with the duration or split. Its a cam with a 47 degree IVC. A 5.3 likes a 41 degree IVC. If you advance the ls7 cam six degrees in a 5.3 it gains torque.

By comparison a 427 makes torque on accident. You do not need to can for torque. So GM relaxed the IVC and let it rev. Although on a 427 I like 52 degrees IVC.
Darth, thank you so much for explaining that! I have so much to learn about cam timing.
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Old 05-22-2019, 12:02 AM
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246/262 @.050 here. Geoff at eps specced llsr from cam motion
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Old 05-22-2019, 12:02 AM
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Originally Posted by Che70velle View Post
Iíve built three 6 liter builds with LS3 heads. First one had 14 degree split. Second one had 9 degrees split. Third one had 11 degree split. Each build had a different purpose, and completely different valve events, so I canít really compare split only in this situation making a difference one way or another.
Iíll say this however. The second build used the WS6Store high lift ASA camshaft, and when talking with those guys about duration and events, and exactly what I was doing with the build, I was told by them that square port heads donít need the split, and that it was pretty much a myth. I paraphrased that statement, but thatís pretty much what I was told by them. That engine, of the 3, runs out the best on top. The latter engine, with 11 degrees split makes the most torque, seat of the pants dyno testing. First one, with 14 degrees was a VVT build, and was the most fun to drive.
The exhaust side of a square port head, LS3 or LS7, does need more duration to aid in getting the air out, because of the imbalance of the I/E ratio, but as to how much I feel totally depends on the combination and what your doing with the vehicle.
Interesting observations.
Could you list the cam specs of each if you can recall?
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