Anyone Interested in a Reverse Split Discussion
Anyone Interested in a Reverse Split Discussion So I was reading the reverse cam theory sticky and it has me wondering how many degrees reverse split is too much. Would a 229/222 on a 108 -1 be to large at 7* split? At my calculations the 9.5* overlap seems ideal for the reverse split remaining streetable and making great power under the curve and keeping peak. Should this cam be better at 227/222 on a 107-1 at 10.5* overlap or 226/222 on a 107-1 for exactly 10* overlap?
Last edited by TurbopigB4C; Sep 8, 2013 at 10:12 PM.
So from my understanding when using an ls6 intake you take 10% off the intake flow numbers for the cylinder head you are using and then do your i/e ratio calculation. From my understanding the higher the ratio the more a reverse split makes sense correct? Is there any general idea regarding how many degrees are acceptable for the reverse split based on how much higher the I/E ratio is than 80%. For example what I mean is 82.5% good for a 3 degree split while 85% may be good for 5 and 87.5% would be good for 7 and so on?
Are you taking the entire exhaust into account too? I thought this worked good for guys without an intake, but with intake was better to go single or conventional split... You just trying to spec something yourself?
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From: BFE
OP, the split is decided by the valve events values you are tying to design.
Personally I do not like going much over 4 degrees difference. Sometimes just 2 degrees (like 230/228) or mine 238/236 (actually mine specs as a 236/236 XFI/XER but once ground it comes out usually 238/236); because XFI mostly grinds 2* bigger than advertised.
From my personal experience there are a lot of myths that people believe like the bible and RS cams have their share.
1- A lot of folks believe that if you want to use an aftermarket intake (like FAST) the RS cam is then no good. That is completely false and what you'll see is that the gain will not be as much as a traditional split of same duration but there will be gains nonetheless. Same scenario with heads, different head specs will react differently.
2- To spec RS cams one need to step out of the box a bit and not apply 100% traditional split design in the specs. They are 2 different animals and should be understood to make them more successful. Example TR230/224 is advanced and produces awesome low to mid-range push; however it dies rapidly after peak, so not for those high rpm lovers. (I remedied that in my cam by delaying IVC while keeping EVO,EVC more or less equidistant from TDC).
Bottom line, RS cams have their 'niche' of users, I like them because I like to get a jump on a quick 60' at the track, RS are not big mph pushers but it takes a LOT of power for someone to reel you in on the back half even if you finish 2 mph slower, you are already there, lol the race is over.
Trq is what I play with and RS cams are good on trq production in LS1/LS6 platforms.
Personally I do not like going much over 4 degrees difference. Sometimes just 2 degrees (like 230/228) or mine 238/236 (actually mine specs as a 236/236 XFI/XER but once ground it comes out usually 238/236); because XFI mostly grinds 2* bigger than advertised.
From my personal experience there are a lot of myths that people believe like the bible and RS cams have their share.
1- A lot of folks believe that if you want to use an aftermarket intake (like FAST) the RS cam is then no good. That is completely false and what you'll see is that the gain will not be as much as a traditional split of same duration but there will be gains nonetheless. Same scenario with heads, different head specs will react differently.
2- To spec RS cams one need to step out of the box a bit and not apply 100% traditional split design in the specs. They are 2 different animals and should be understood to make them more successful. Example TR230/224 is advanced and produces awesome low to mid-range push; however it dies rapidly after peak, so not for those high rpm lovers. (I remedied that in my cam by delaying IVC while keeping EVO,EVC more or less equidistant from TDC).
Bottom line, RS cams have their 'niche' of users, I like them because I like to get a jump on a quick 60' at the track, RS are not big mph pushers but it takes a LOT of power for someone to reel you in on the back half even if you finish 2 mph slower, you are already there, lol the race is over.
Trq is what I play with and RS cams are good on trq production in LS1/LS6 platforms.
Example TR230/224 is advanced and produces awesome low to mid-range push; however it dies rapidly after peak, so not for those high rpm lovers.
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From: BFE
Question here...how is a reverse split cam like that going to produce more low end torque than a traditional split like a 224/230? I always thought that short intake duration builds more compression and makes more torque early on, but falls on its face in the high RPMs due to not keeping the intake open long enough to fill a cylinder at those engine speeds.
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so bigger duration fills cylinder better=bigger bang=more powa=more trq.
And at the same time, a 230/234 should make the same torque as a 230/224 since it's the same duration to fill the cylinder. But the first one has more exhaust duration than the second one to get the spent gases out. So you get the same cylinder fill, but with the benefit of clearing out the cylinder better. So how is a 230/224 better than a 230/234 when it fills in the cylinder the same thus same bang thus same powa thus same torque?
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Verdad Gallardo TECH Senior Member
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From: BFE
So how is a 230/224 better than a 230/234 when it fills in the cylinder the same thus same bang thus same powa thus same torque?
Anyway, though you have done a great job explaining some elements of RS cams, could you perhaps explain why a RS cam might work well in a heavy car like a CTS-V or a GTO? Or would it not?
It seems like you're saying they build a lot of torque, but fall flat faster, so would be better for heavy rides that don't spin high. Does the torque build faster and lower in the RPMs? Is that the advantage over a traditional split? It builds faster, but at the expense of falling off faster?
And who said 230/224 is better, it depends on the application and rest of combo. Please avoid dealing in absolutes, there is no such thing.
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From: BFE
It builds faster and if traditionally advanced it will fall off quickly after peak. That is one reason that got me to play around with the events to see if I could keep that early power all the way to 6500>6600 rpm. As I mentioned before, I achieved that by delaying IVC and keep IVO, EVC equidistant from TDC. This made the cam carry well after peak and an earlier EVO. Now give it the right amount of overlap and you have a good street/strip cam. I prefer them with autos.
A critical part of an RS combo is the exhaust. LT + X + true duals being the best I've used them on. On f-bodies, LTs + Y with good merge + cutout works well.
A critical part of an RS combo is the exhaust. LT + X + true duals being the best I've used them on. On f-bodies, LTs + Y with good merge + cutout works well.
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Joined: Mar 2004
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From: BFE
I'm probably going to bore some people but here is a good example of what an RS cam can achieve in stock cubes:
It builds faster and if traditionally advanced it will fall off quickly after peak. That is one reason that got me to play around with the events to see if I could keep that early power all the way to 6500>6600 rpm. As I mentioned before, I achieved that by delaying IVC and keep IVO, EVC equidistant from TDC. This made the cam carry well after peak and an earlier EVO. Now give it the right amount of overlap and you have a good street/strip cam. I prefer them with autos.
A critical part of an RS combo is the exhaust. LT + X + true duals being the best I've used them on. On f-bodies, LTs + Y with good merge + cutout works well.
A critical part of an RS combo is the exhaust. LT + X + true duals being the best I've used them on. On f-bodies, LTs + Y with good merge + cutout works well.
Since someone was asking for a more modern or practical example I think using the discussion related to the difference between a tr224/224 camshaft at 112 lsa and 218/218 at 109 lsa. From how I understand the discussion the 218 will make superior trq and horsepower to 6200 rpm because that is where the ls6 intake likes to have power fall off with the same driveability, valve events and overlap. So the 224 essentially is wasting the extra duration by what it gives up down low because what it gains up top is not better than the 218 everywhere else.
Using the same kind of idea with new cam technology something could be done with a 219 LSL or EHI intake lobe and then depending on how free flowing the entire exhaust is compared to intake manifold and head design you would either choose a 214 LXL or 218 LXL exhaust lobe and go with a 109 LSA. This would be the better choice for a DD or torque car when compared to the Comp off the shelf grind using the 219 LSL lobe that uses a traditional 219/227 split on a 112 LSA. The powerband would peak on the reverse split around 6200-6400 but pull harder than the traditional split everywhere before it.
The RS theory largely has the intake manifold in as part of it. A truck intake, ls1 intake and ls6 intake are the only one that makes sense with a reverse split since they flow less than the intake runners on most small port cathedral heads.
For example take the AFR 210 head that flows 302 on the intake and 237 on the exhaust. You have long tube headers with true duals or a high flowing 4" or larger single exhaust with no cats. You choose for whatever reason to stick with a factory gen 3 composite intake and this would lower intake flow on the 302 cfm intake runner by 10 % or more. The I/E ratio on the AFR head with the 10% loss factored in from ls6 intake makes the ratio 87.4% making it make sense to use a reverse split. If you were using a ported fast 102/102 with these heads you likely would not use the 10% intake reduction making I/E ratio 78.5% favoring a slight traditional split.