Cam advice? Split, reverse split or equal?
Here are some stock spec's on a Honda GSR:
Stock Specs from GSR Advertised Int-274 mid Exh-276 mid @ .050" Int-230 mid Exh-216 mid Int-.423 mid Exh-.378 mid
Note not much difference at seat duration, but when it comes to .050" numbers, it has 14 degrees more duration. This is OEM cam. Now for the power these 4 bangers put out per CC, reverse splits must correlate to something and this redneck southerner is sure it is flow percentage.
Chris
Stock Specs from GSR Advertised Int-274 mid Exh-276 mid @ .050" Int-230 mid Exh-216 mid Int-.423 mid Exh-.378 mid
Note not much difference at seat duration, but when it comes to .050" numbers, it has 14 degrees more duration. This is OEM cam. Now for the power these 4 bangers put out per CC, reverse splits must correlate to something and this redneck southerner is sure it is flow percentage.
Chris
I got another one for you.
Why is there such fluctuation of flow percentages at different lift?
I got a 5.3 head flow percentages here:
.100 = 85.7%
.200 = 72.6%
.300 = 67.6%
.400 = 69%
.500 = 74.7%
.550 = 76%
.600 = 76.9%
------------
The head flow numbers I used to calculate these percentages, I'm guessing weren't with a stub pipe and some sort of exhaust manifold.
Why is there such fluctuation of flow percentages at different lift?
I got a 5.3 head flow percentages here:
.100 = 85.7%
.200 = 72.6%
.300 = 67.6%
.400 = 69%
.500 = 74.7%
.550 = 76%
.600 = 76.9%
------------
The head flow numbers I used to calculate these percentages, I'm guessing weren't with a stub pipe and some sort of exhaust manifold.
Originally Posted by SportSide 5.3
Any more information on that? I think some get a brain fart when they hear we are intake restricted.
Originally Posted by Cstraub
If an engine has a very good exhaust port, in the 80% range of the intake, then a reverse split is the best option. Reverse splits are common in the foreign cars where some exhaust ports flow as much as 90% of the intake. Duration difference in these cases can be 15 degrees more favoring the intake side.Chris
Originally Posted by gomer
No problem man! I agree with your thinking on reverse splits.. BUT only when running open headers. The extra intake duration helps our "crippled" intake, but I think trying to exhaust 6,500rpms worth of combusted gasses out a single 3inch exhaust is what hurts reverse splits on the top end in our cars.
Last edited by mrr23; Oct 17, 2004 at 09:42 AM.
Originally Posted by SportSide 5.3
I got another one for you.
Why is there such fluctuation of flow percentages at different lift?
I got a 5.3 head flow percentages here:
.100 = 85.7%
.200 = 72.6%
.300 = 67.6%
.400 = 69%
.500 = 74.7%
.550 = 76%
.600 = 76.9%
------------
The head flow numbers I used to calculate these percentages, I'm guessing weren't with a stub pipe and some sort of exhaust manifold.
Why is there such fluctuation of flow percentages at different lift?
I got a 5.3 head flow percentages here:
.100 = 85.7%
.200 = 72.6%
.300 = 67.6%
.400 = 69%
.500 = 74.7%
.550 = 76%
.600 = 76.9%
------------
The head flow numbers I used to calculate these percentages, I'm guessing weren't with a stub pipe and some sort of exhaust manifold.
Originally Posted by SportSide 5.3
For CID under 400, 75% exh ratio to intake dictates a single pattern cam. For every % point over you need to crutch the intake 1/2 degree of duration
and when we talked about this you insisted on a reverse split cam even though the old theory you posted up told you not to.
Originally Posted by NoseUpChromeDown
I've been wondering the same thing. The first person I've heard of that complained about the LS intake system being restricted...
Originally Posted by mrr23
read above. gomer says the intake is crippled. just want to understand the basis of this thought.
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Verdad Gallardo but to say this. sportside, in the most basic sense of the question, yes the intake is restricted. i will grant you this. after our last conversation, it came to me. i was thinking past the basic question. like a doctor when asked if he saw someone laying on the ground not breathing. what do you do. most doctors fail that question. the answer is perform CPR. but they get analytical. they start asking is the person bleeding? has an arm be torn off? and so on.
but, i will still hold my ground on telling you that it's not. in the bigger picture, it's not. in your scenario you asked me about, i said the exhaust still was the restriction. because the head still doesn't flow more on the exhaust side than 75%.
but, i will still hold my ground on telling you that it's not. in the bigger picture, it's not. in your scenario you asked me about, i said the exhaust still was the restriction. because the head still doesn't flow more on the exhaust side than 75%.
Originally Posted by SportSide 5.3
Example:
-stock heads
-stock intake manifold
-cold air intake
-long tube headers
-aftermarket exhaust
-no cats
With that there, which side would you consider the restriction? The intake or the exhaust?
-stock heads
-stock intake manifold
-cold air intake
-long tube headers
-aftermarket exhaust
-no cats
With that there, which side would you consider the restriction? The intake or the exhaust?
I too was swayed by theory of reverse split cams. I flowed my heads and spec'd my cam based on the low flowing intake and high flowing exhaust. Cam was spec'd at 234/228 with the intake cut on a XER lobe and the exhaust on a XE lobe. Lift was 595/571. Theoritically this should have evened out the "crippled" intake and excessive exhaust to prevent reversion. Wow, I thought, I feel good because this is how you are supposed to do it for optimum results.
Well, the dyno numbers just sucked. No doubt because of the heads. But I felt the reverse split cam was at least part of the problem. So I went against theory (and my tuners hard advice) and ordered up a 232/232 .595/.595 cam cut on XER lobes. I was told I would lose power and torque. Well I picked up 16 rwhp and 23 rwtq just from the cam swap. The car pulled better from down low all the way up to 6500 rpms (could easily go to 7K if I had a forged bottom end). I felt somewhat vindicated and promised myself I would never run a reverse split cam.
Well, the dyno numbers just sucked. No doubt because of the heads. But I felt the reverse split cam was at least part of the problem. So I went against theory (and my tuners hard advice) and ordered up a 232/232 .595/.595 cam cut on XER lobes. I was told I would lose power and torque. Well I picked up 16 rwhp and 23 rwtq just from the cam swap. The car pulled better from down low all the way up to 6500 rpms (could easily go to 7K if I had a forged bottom end). I felt somewhat vindicated and promised myself I would never run a reverse split cam.
like a doctor when asked if he saw someone laying on the ground not breathing. what do you do. most doctors fail that question. the answer is perform CPR. but they get analytical. they start asking is the person bleeding? has an arm be torn off? and so on.
Thanks for the lovely example
Anyways,
Sorry that I make it sound like reverse splits rule all. My whole point was just that off the shelf cams (which you were defending at Vinci), like the ASP KICKER with 8 degrees favoring the exhaust wasn't very well matched with the average guys head flow characteristics.
no prob. it's all in the sake of learning.
VHP cams aren't off the shelf. there are many many hours of testing done to achieve what these cams cans do. same with comp and all the other major cam manufacturers out there. in their test vette, they are still on stock heads when they installed both the 047 and 062 cams. heads are soon.
but anyways, we've all got opinions and some facts. all we can do is point them in a direction. people will make up their own mind eventually. me, the heads are going on the wife's car next. then the 047 cam. then we'll know what it can do with stock heads and ported heads.
VHP cams aren't off the shelf. there are many many hours of testing done to achieve what these cams cans do. same with comp and all the other major cam manufacturers out there. in their test vette, they are still on stock heads when they installed both the 047 and 062 cams. heads are soon.
but anyways, we've all got opinions and some facts. all we can do is point them in a direction. people will make up their own mind eventually. me, the heads are going on the wife's car next. then the 047 cam. then we'll know what it can do with stock heads and ported heads.
You know, someone could easily end all this garbage by having only the exhaust side of a set of heads ported. That'd get you the 90% exhaust to intake to test a reverse split cam.
Though yes, it would be a more in-depth, this is my take: The more the exhaust side flows, the less exhaust duration is needed. 80% is where I'd go single pattern. I wouldn't personally go near a reverse-split cam until about 85%-maybe 2* less exhaust. I think @ 90% is where a larger reverse-split would shine. Maybe even 6* less exhaust.
I'm going by heads though. The actual intake and exhaust systems would obviously also have to match the head charactoristics.
Though yes, it would be a more in-depth, this is my take: The more the exhaust side flows, the less exhaust duration is needed. 80% is where I'd go single pattern. I wouldn't personally go near a reverse-split cam until about 85%-maybe 2* less exhaust. I think @ 90% is where a larger reverse-split would shine. Maybe even 6* less exhaust.
I'm going by heads though. The actual intake and exhaust systems would obviously also have to match the head charactoristics.
Originally Posted by Cstraub
Here are some stock spec's on a Honda GSR:
Stock Specs from GSR Advertised Int-274 mid Exh-276 mid @ .050" Int-230 mid Exh-216 mid Int-.423 mid Exh-.378 mid
Note not much difference at seat duration, but when it comes to .050" numbers, it has 14 degrees more duration. This is OEM cam. Now for the power these 4 bangers put out per CC, reverse splits must correlate to something and this redneck southerner is sure it is flow percentage.
Chris
Stock Specs from GSR Advertised Int-274 mid Exh-276 mid @ .050" Int-230 mid Exh-216 mid Int-.423 mid Exh-.378 mid
Note not much difference at seat duration, but when it comes to .050" numbers, it has 14 degrees more duration. This is OEM cam. Now for the power these 4 bangers put out per CC, reverse splits must correlate to something and this redneck southerner is sure it is flow percentage.
Chris
BTW I wish ls1's had vtec
TECH Senior Member
Joined: Mar 2004
Posts: 14,620
Likes: 17
From: BFE
Look at the picture in more Lehman terms, as I ran into these reverse split discussions when favor them for nitrous applications below 150 shot.
Longer intake duration=bigger charge= bigger bang=higher cylinder pressures=faster exit through exhaust.
This of course is true and tested through a series of matching parameters, (intake flow, head intake runner flow, exhaust)
I still get shot at when I mention I like a close reverse split cam on a tight lsa to shoot 150 or less N20.
Expl: 228/226, .57x/.57x 110+0 lsa
Longer intake duration=bigger charge= bigger bang=higher cylinder pressures=faster exit through exhaust.
This of course is true and tested through a series of matching parameters, (intake flow, head intake runner flow, exhaust)
I still get shot at when I mention I like a close reverse split cam on a tight lsa to shoot 150 or less N20.
Expl: 228/226, .57x/.57x 110+0 lsa
I don't know about the whole nitrous deal...You're pulling more in, therefore you're having to push more out as well. I feel that with all things being equal with the addition of just N20, you wouldn't want to change the split in either direction, just maybe the LSA. With N20 responding well when accompanied by larger or stepped tube headers, maybe bumping up the exhaust duration a bit would be the advantage. Again, just my take...
when talking power adders, you're in a different field. the discussion is about using a reverse split in a NA motor. for years turbos use a reverse split. same when using n2o and SC. you have another way of getting the air/fuel in. the motor isn't doing it all by itself.
with power adders, by all means a reverse split might be the better way to go. but in a n2o situation, unless it's a drag only car, driving around NA, the performance will suffer.
with power adders, by all means a reverse split might be the better way to go. but in a n2o situation, unless it's a drag only car, driving around NA, the performance will suffer.
Originally Posted by SportSide 5.3
I read somewhere, every percent over, you crutch the intake 1/2 degrees.
In fact, I think I got that from Chris. He used 75% as the median though, not 80%.
In fact, I think I got that from Chris. He used 75% as the median though, not 80%.
and on the whole flow numbers for heads with an intake and exhaust pipe on thing. how long are the runners in an intake vs the length of the exhaust pipe they use when flowing heads. just look a the head itself. the intake ports are longer than the exhaust ports. by adding a pipe to the exhaust side, you have extended the length of the exhaust port by doing it. maybe one day someone will add a 30" long tube to the exhaust port for testing. this would simulate a long tube header. then watch what happens to that wonderful exhaust flow.
sometimes, theory needs to be thrown out the window. and have real world testing be the norm. theory is just that theory. a bunch of people guessing what's going to happen. then real world steps in and either confirms theory or disputes it.
i'm glad people are starting new theories with the reverse split cam ideas. but, at this point, there isn't enough evidence to support that it works in moderate applications.
Last edited by mrr23; Oct 9, 2004 at 01:41 PM.