What's up with these "reverse split"cams?
Thread Starter
On The Tree
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From: St. Louis, MO
What's up with these "reverse split"cams? Typically you would want more lift and duration on the exhaust side because of a smaller valve and less port flow. What is the point of increasing lift and duration on the intake side? The intake side already flows better than the exhaust??? If you can't get the burnt gasses out as fast as they are coming in, you can't make more power. Someone enlighten me please. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
Re: What's up with these "reverse split"cams? J99Frc has a reverse split cam in his vette. He explained to me once the advantage of it but I did not pick up on it well. All I know is that that vette runs like a raped ape.
Re: What's up with these "reverse split"cams? while most will say it has to do with poor intake design, it has to do with the intake manifold restriction. by allowing the intake valves to stay up longer it allows for more air in, but since the exhaust ports are soooo good in these ls1 heads, we can get away with smaller exhaust duration. it does NOT have to do with exhaust manifolds/headers. it also allows for a smoother idle since you dont hold the exhaust valves up as long. now if we could get a great flowing intake manifold then we would not benefit from a large intake duration. lots of turbo cars do this too for different reasons.
Thread Starter
On The Tree
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From: St. Louis, MO
Re: What's up with these "reverse split"cams? I have never heard of any make/model of engine that had exhaust ports that would outflow the intake ports. So did GM just royally F**K up, or is this just a sales gimmick?
TECH Apprentice
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From: san antonio/college station tx
Re: What's up with these "reverse split"cams? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by nthnwbr:
<strong>I have never heard of any make/model of engine that had exhaust ports that would outflow the intake ports. So did GM just royally F**K up, or is this just a sales gimmick?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">FWIW, the 3800 II V6 motor in the V6 F Bodies is the same way. Exhaust flows alot better than the intake. At least that is what we believe it to be, but no one is entirely certain. <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
Scott
<strong>I have never heard of any make/model of engine that had exhaust ports that would outflow the intake ports. So did GM just royally F**K up, or is this just a sales gimmick?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">FWIW, the 3800 II V6 motor in the V6 F Bodies is the same way. Exhaust flows alot better than the intake. At least that is what we believe it to be, but no one is entirely certain. <img border="0" title="" alt="[Sad]" src="gr_sad.gif" />
Scott
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From: Louisiana
Re: What's up with these "reverse split"cams? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by nthnwbr:
<strong>I have never heard of any make/model of engine that had exhaust ports that would outflow the intake ports. So did GM just royally F**K up, or is this just a sales gimmick?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Intake manifold is the restriction
<strong>I have never heard of any make/model of engine that had exhaust ports that would outflow the intake ports. So did GM just royally F**K up, or is this just a sales gimmick?</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Intake manifold is the restriction
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On The Tree
Joined: Jan 2002
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From: Carrollton, TX
Re: What's up with these "reverse split"cams? Exhaust gasses are hot and under intense pressure.
They force their way out of the exhaust port.
Intake charge is cool and under low pressure.
The pressure differential that the exhaust see's during exhaust evacuation is going to be much greater than a measurement @ 28" of water.
They force their way out of the exhaust port.
Intake charge is cool and under low pressure.
The pressure differential that the exhaust see's during exhaust evacuation is going to be much greater than a measurement @ 28" of water.
Re: What's up with these "reverse split"cams? the ls1 head intake outflows the exhaust ofcourse! LOL!!! if you have an exhaust the outflows the intake, you have problems! <img border="0" title="" alt="[Wink]" src="gr_images/icons/wink.gif" />
TECH Senior Member
Joined: Nov 2001
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From: Troy, AL
Re: What's up with these "reverse split"cams? It doesn't matter that the intake port outflows the exhaust port if the intake manifold sucks ***. As said before, reverse splits work with the LS1 NOT because the exhaust ports outflow the intake ports (they don't) but because the intake manifold is so restrictive.
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From: St. Louis, MO
Re: What's up with these "reverse split"cams? So, if the intake is so restrictive that it warrants a special cam, then we should see MAJOR improvements with JUST an intake swap. But that doesn't seem to be the case.
Re: What's up with these "reverse split"cams? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by nthnwbr:
<strong>So, if the intake is so restrictive that it warrants a special cam, then we should see MAJOR improvements with JUST an intake swap. But that doesn't seem to be the case.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">so what intake are you talking about sir genius? put a well designed sheet metal intake and you will see incredible gains.
<strong>So, if the intake is so restrictive that it warrants a special cam, then we should see MAJOR improvements with JUST an intake swap. But that doesn't seem to be the case.</strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">so what intake are you talking about sir genius? put a well designed sheet metal intake and you will see incredible gains.
FormerVendor
Joined: Nov 2001
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From: Houston, Tx.
Re: What's up with these "reverse split"cams? Gator,
What intake are you talking about? The LS1 has a 15 degree exhaust port that has tremendous flow for such a small valve and is even better than it seems on the flow bench since it is so much straighter than a normal SBC or SBF exhaust. It's so efficient that it's almost "oversized" in stock form and as a result the exhaust duration can be shortened up a bit in relation to the intake which is also quite good actually. At higher and higher RPM the exhaust IS needed and the reverse split pattern won't pull as far but within the tuning and stock mainifolds rpm band they work pretty well.
I agree that a truly great manifold will beat an LS6 intake but no one's really come up with that yet. Even on SAM's 418, the sheet metal intake just extended the power on out further but didn't really pick it up tremendously. We didn't design that intake however but rather were just testing it. For a stock intake the LS6 is simply incredible. Jud ran 10.0s with it at that first NFRA shootout and took all the marbles including N/A AND King of the Hill!
What intake are you talking about? The LS1 has a 15 degree exhaust port that has tremendous flow for such a small valve and is even better than it seems on the flow bench since it is so much straighter than a normal SBC or SBF exhaust. It's so efficient that it's almost "oversized" in stock form and as a result the exhaust duration can be shortened up a bit in relation to the intake which is also quite good actually. At higher and higher RPM the exhaust IS needed and the reverse split pattern won't pull as far but within the tuning and stock mainifolds rpm band they work pretty well.
I agree that a truly great manifold will beat an LS6 intake but no one's really come up with that yet. Even on SAM's 418, the sheet metal intake just extended the power on out further but didn't really pick it up tremendously. We didn't design that intake however but rather were just testing it. For a stock intake the LS6 is simply incredible. Jud ran 10.0s with it at that first NFRA shootout and took all the marbles including N/A AND King of the Hill!
Thread Starter
On The Tree
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From: St. Louis, MO
Re: What's up with these "reverse split"cams? Gator...I you can't have a serious tech conversation without getting ignorant, please keep it to yourself. Especially if you have no real information. Posts like vince's and racer's are helpfull. I was simply trying to figure out if/why LS1's resond to this unusual cam pattern.
Re: What's up with these "reverse split"cams? The 'sir genius' comment adds no value this is a tech forum keep it tech or don't post.
I have to say, the LS6 intake is pretty darn good. To go 133-136mph NA with an OEM out of the box intake is pretty sharp. Compare with other 400-440ci setups at a similar raceweight.
So far the sheetmetal intakes out there just extend the power range, create a little more peak rwhp, but at the expense of midrange torque. So far I don't think anyone is going to plunk one on and pick up 2-3mph, especially if you end up needing more gear and more converter to make it work. Gains of 10 peak rwhp is not unusual.
Can anyone explain the value in the reverse split, I am still not getting it but I'd like to understand, is it better because you fill up the cylinders more and build more compression?
I have to say, the LS6 intake is pretty darn good. To go 133-136mph NA with an OEM out of the box intake is pretty sharp. Compare with other 400-440ci setups at a similar raceweight.
So far the sheetmetal intakes out there just extend the power range, create a little more peak rwhp, but at the expense of midrange torque. So far I don't think anyone is going to plunk one on and pick up 2-3mph, especially if you end up needing more gear and more converter to make it work. Gains of 10 peak rwhp is not unusual.
Can anyone explain the value in the reverse split, I am still not getting it but I'd like to understand, is it better because you fill up the cylinders more and build more compression?
Thread Starter
On The Tree
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From: St. Louis, MO
Re: What's up with these "reverse split"cams? </font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">is it better because you fill up the cylinders more and build more compression?
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You may be on to something there, it would not increase the compression ratio, but combustion pressures would go up. That makes sense, but along with an increase in the air/fuel volume, comes an increase in exhaust gas volume after the power stroke. Which, in turn, would need more lift and duration on the exhaust valve to effectively rid the cylinder of these gasses. which brings us back to a "straight" cam pattern. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
<small>[ September 20, 2002, 10:50 AM: Message edited by: nthnwbr ]</small>
</font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">You may be on to something there, it would not increase the compression ratio, but combustion pressures would go up. That makes sense, but along with an increase in the air/fuel volume, comes an increase in exhaust gas volume after the power stroke. Which, in turn, would need more lift and duration on the exhaust valve to effectively rid the cylinder of these gasses. which brings us back to a "straight" cam pattern. <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" />
<small>[ September 20, 2002, 10:50 AM: Message edited by: nthnwbr ]</small>
Launching!
Joined: Dec 2001
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From: Houston
Re: What's up with these "reverse split"cams? Hey Eric what's going on dude.. long time no talk.
anyways for all you guys that belive this reverse patter thing is because of the intake.. answer me this.
NASCAR do not run a reverse pattern cam on there restrictor plate motors.
The C5R and the Viper GTS don't run a Reverse patter cam on there motors... there bouth run Intake restrictors.
The reason the reverse patter cam works is The car likes the bigger Intake lobe that all these revers patter cams are running.
The smaller exhuast just manage too keep the RPM down. So the big cam stay in the 6400-6800 where every one likes it.
later
Brent
anyways for all you guys that belive this reverse patter thing is because of the intake.. answer me this.
NASCAR do not run a reverse pattern cam on there restrictor plate motors.
The C5R and the Viper GTS don't run a Reverse patter cam on there motors... there bouth run Intake restrictors.
The reason the reverse patter cam works is The car likes the bigger Intake lobe that all these revers patter cams are running.
The smaller exhuast just manage too keep the RPM down. So the big cam stay in the 6400-6800 where every one likes it.
later
Brent
FormerVendor
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From: Mpls., MN
Re: What's up with these "reverse split"cams? The reason the LS1 likes the reverse split cam is due to the great exhaust port, the minor restrictiveness of the intake and MOSTLY due to the length of the intake runner. The characteristics of a long column of intake air require different valve TIMING points as opposed to a shorter runner intake, i.e. single plane carb intake (Victor, etc.). The longer column of air has more mass, therefore more inertia. This means it takes more energy to get it moving from a standstill, and, once it gets moving, it takes more energy to stop it. Because of this, a later valve closing allows the runner to 'inertia ram' the cylinder when the same valve closing on a short runner setup (LT1) would cause the air to be blown back out of the cylinder (intake reversion). When matching the intake and exhaust port valve events to a particular RPM range on the LS1 so that they work together, the valve timing on the intake side winds up being longer than the exhaust.
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