I am seriously considering the TR227/224 .569/.563 114LSA cam for my car and just cant understand how opening the intake side of the valvetrain longer than the exhaust side is any better than just leaving them open the same amount of time?

Lets say I were to get a 227/227 .569/.569 cam. Would the numbers be the same? Is there a benefit to having the exhaust side close sooner?

What if I were to flip flop the TR227 cam and made it 224/227 .563/.569 114LSA? How would that effect it?

If anyone has any theories on why the reverse split is a good idea, please let me know.

 

I know very little about camshaft design or theory or but it is not surprising to me that intake and exhaust may have different lobe profiles. Everything is different. Valve sizes are different and gas temperatures and pressures are different. With all the differences, it is surprising that symmetrical cams work as well as they do. I assume that the main reason for having identical intake and exhaust lobes is to reduce cost.

 

I was wondering same thing? What are the theories/advantages behind the reverse split or traditional split cams? Not only the split duration numbers but also the split lift numbers.
Maybe Lou could chime in and give us his explanation since he said he would never put out a reverse split cam.
Basically how does changing the splits affect things?

 

From an email that I got from Geoff @ TR earlier today:

The intake on an LS1 is a significant restriction, if you are using a decent set of long tube headers you will have a great flowing exhaust but an intake that really doesn't keep up in spite of the fact that the ports in the heads show big numbers on the flow bench. Understand? In a nutshell part of the tactic of the reverse split is to crutch the intake.

(end paste)

You can have a set of 335 cfm LS6 heads (with no intake)... Bolt on an LS6 intake, you now get 280-285 cfm. That's the reason for the theory behind the reverse split.

-Andrew

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Camaroholic:
<strong> From an email that I got from Geoff @ TR earlier today:

The intake on an LS1 is a significant restriction, if you are using a decent set of long tube headers you will have a great flowing exhaust but an intake that really doesn't keep up in spite of the fact that the ports in the heads show big numbers on the flow bench. Understand? In a nutshell part of the tactic of the reverse split is to crutch the intake.

(end paste)

You can have a set of 335 cfm LS6 heads (with no intake)... Bolt on an LS6 intake, you now get 280-285 cfm. That's the reason for the theory behind the reverse split.

-Andrew </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">See, that makes sense to me, but that doesn't answer my question. I can understand wanting to leave the intake valve open longer to compensate for the lesser flowing intake, but what does closing the exhaust valve sooner have to do with anything. If opening up the intake valve more allows more air in, how does closing the exhaust valve sooner help HP?

Wouldnt a 227/224 cam and a 227/227 cam put out the exact same numbers?

 

i agree with no juice, i would like Lou to come on here and give us his professional explanation because he doesnt seem to be too crazy about the reverse splits. however, i have heard of guys makin some nuts numbers with 5.3 heads and a good reverse split cam. and i also totally agree and understand what camaroholic said, hell, it makes sense to me. so things seem to be contradicting: Lou, who is very respected and really knows his **** says they're crap, but guys are puttin out awesome numbers <img border="0" title="" alt="[Confused]" src="images/icons/confused.gif" /> .

PS. first post on this board <img border="0" alt="[cheers]" title="" src="graemlins/gr_cheers.gif" /> . maybe some of you guys might recognize me from the other 3 boards im a member of <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" /> .

 

Part of the reasoning behind it, from what I understand, was to keep emissions,idle, and drivability better. Why add the extra exhaust duration if the car doesnt need it, all that'll do is affect the things listed above. I believe thunder tried a 227/224, 227/227, and 227/230 and they nearly made the exact same (the 227/224 may have even made the most, but geoff @ TR would be best to comment on that).

Mine idles great, drives great, and makes good power. Smells a lot better than the 230/230 I had too.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by jmX:
<strong> Part of the reasoning behind it, from what I understand, was to keep emissions,idle, and drivability better. Why add the extra exhaust duration if the car doesnt need it, all that'll do is affect the things listed above. I believe thunder tried a 227/224, 227/227, and 227/230 and they nearly made the exact same (the 227/224 may have even made the most, but geoff @ TR would be best to comment on that).

Mine idles great, drives great, and makes good power. Smells a lot better than the 230/230 I had too. </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">BINGO!!! Jon hit the nail on the head.

 

Hey Paul have you received any of the emails that I have sent you?

 

Andrew posted my e-mail to him from this morning...that was one way of looking at it. Another way of explaining it is like this: If you take a 350 CID motor operating under 7000 RPM, it typically has a certain diameter header tube that is optimum (typically 1 5/8" to 1 7/8" depending on application). What do you think would happen if you put on a header with a 2 1/2" primary tube and a 4" collector? More than likely the engine is going to make less power than before. Again there are several schools of thought on why you would lose power but it is generally accepted that you will lose.

We have documented cases of LS1's (with normal split pattern cams)dynoing with a closed exhaust and then dynoing with open headers and seriously losing power and torque with no particular change in AFR or timing. We have never seen an LS1 lose power with a reverse split using open headers.

I guess the message that I'm trying to send is that in a perfect world an engine that has perfectly balanced Intake and Exhaust characteristics a single pattern cam would be perfect. If you have an exhaust that doesn't properly scavenge or is inefficient then a crutch is needed with the cam in the way of a bigger lobe. Most old school Small Block Chevys are limited in their exhaust system as compared to their intake system. Logically it only makes sense that if your exhaust is more efficient than your intake that you must increase the intake side of the cam in order to keep the intake and exhaust flow potentials balanced.

We may be totally out in left field with this line of thinking, but I guarantee that if you look in the motors of certain LS1 stock eliminator racers you will find a reverse split cam. Also just because GM only sells normal split pattern cams for the LS1 doesn't convey much. Think about this: If you are a winning pro racer your aren't going to be selling your cam specs. The cams that GM sells to the public and what winning racers use aren't necessarily the same thing.

 

I think reverse split is working more on a principle that has to do with the ram effect of the long runner intake.

It does nothing to help the fact that you have a head that flow 335CFM and an intake that does 280. Head and intake should always be ported and flowed together for most power anyway.

On a side note, maybe getting the extra flow without the manifold attached is costing flow when it is attached, happens all the time.

In anycase, I think the long runner intake does not need as much help from the exhaust system. So no need for the duration there. Exhaust is going to get out, has nothing to do with flow of exhaust port @ 28", since there is greater pressure differential across there due to intense pressure and heat in the cyllinder.

The larger duration cam allows the intake to pile air into the cyllinder to a longer.

The reverse splits are working very well on fords with long runner intakes.

 

HP GURU,

Good post. One thing on the exhaust boosting the intake: IMHO the boost if you will is going to happen during the overlap period. It seems to me that in a normal (Non Long Runner) application more overlap is always a good thing as long as we aren't blowing raw gas out of the tail pipes. With the long runner intake maybe the amount of overlap needed is the same just biased towards the intake because the intake needs the help (at engine speeds that are out of the design parameters of the intake). Basically I agree with what you are saying, I am just looking for a better way to help others understand what is going on here.

 

I guess I was trying to say in short that the biased intake lobe has a lot more to do than head and intake flows.

Also I hope that the porters do so with the intake manifold in mind. The entry of the port should match the exit of the manifold, and not just the height and width. This should form a continous cross section. The angle of the runner should not change at the head and manifold interface, worst case of this was the old Torker carb intakes, a 45 angle would be formed at the head and intake interface.

It is possible to take a head that flows 330 and an intake that flows 280, and have this combination flow less than a head that flows 270 and an intake that flows 280.

They are a system. I'm definately not a know it all, but I love reading about high power N/A setups.

The LS1 combinations are putting out some serious power.

I think if someone tightens down the LSA's some, run the tuned length headers, perhaps a solid cam, we will see 500rwhp before 6500 on a 346.

LSA needs to be tightened down so the intake can work in the range where it boosts power. Seems to do this very well up to 6000 rpm, so we need to build alot of TQ before 6000 and hold onto it.

Think the big strokers can benefit from tightening down the LSA so they don't fight against the manifold as much, plus the exhaust system will be allowed to help out a little more.

 

</font><blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr /><font size="2" face="Verdana, Helvetica, sans-serif">Originally posted by Liquidnutz:
<strong> Hey Paul have you received any of the emails that I have sent you? </strong></font><hr /></blockquote><font size="2" face="Verdana, Helvetica, sans-serif">Yes I have. We've been very short handed this week. You should have a reply back tomorrow. Sorry for the delay...


Paul

 

Just curious...

If a reverse pattern works because of runner length, would just degreeing a symetrical (or exhaust biased) cam so the intake opens 3 deg earlier have the same effect?

 

<img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" /> Paul @ Thunder
<img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" /> Geoff
<img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" /> HP-GURU
<img border="0" alt="[worship]" title="" src="graemlins/gr_hail.gif" /> jmX

WOW! <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" /> This is really good stuff. This thread should be archived here because I've never seen such a detailed explanation behind the theory of reverse split. My mind is made up more than ever to get the TR227/224. I cant wait til I get my tax return!

A big thanks to everyone who replied in this thread! <img border="0" title="" alt="[Big Grin]" src="gr_grin.gif" />

 

In my opinion, reverse split cams are a gimmick (unless we're talking turbos).

227/224 cam would open the exhaust 1.5 deg later and close it 1.5deg earlier than if it was 227/227.

If the reasoning behind why a reverse split is needed was true, we would see cams with a more substantial split like 227/217. (but we don't).

I think that most of the time, single pattern is a good choice for a naturally aspirated engine. I also think that a 'standard' split duration cam is a good idea with smaller (less than 218 @.050) cams.

 

Scavenging is what most companies refer to when talking about reverse split cams, to a few they believe that with a larger exhaust duration and intake staying open longer that it helps draw more of the burnt gasses out of the combustion chamber. Hope this may shed some light on what has been said about these cams.

 

tell me, physically why is a single pattern any better than a split. You have two entirely different systems working, that work in different ways.

On some very high power N/A setups, you have more duration on the intake and others you have more on the exhaust.

If they really wanted to get "jiggy" with it, I bet someone could come up with a lobe that does .600" on intake with 230@.05" and .500" on the exhaust with 220@.05, however the exhaust might have more advertised than the intake side.

The right lobe is not something that you can conceptualize in your mind, just depends on what the motor wants.

Like I said, the reverse splits have been working very well on the mustangs that run long runner intakes. Seems to keep bottom end power and torque boosted while raising the rpm levels.

They are tightening them down to 109 LSA or so on that side.

 

While TR and others have had good success with the reverse split, I think that is the wrong direction to go. While many folks get good exhaust flow numbers percentages I to E (80%). Most folks can pretty much bank on around a 70% relationship. If you look many folks are running a single pattern (like Cartek). I look at the GM cams.GM uses a standard split lik it has on its SBC cams of all 3 generations of SBC motors for the last 50 yrs. GM has more R&D dollars than anyone on the face of the planet when it comes to developing cams for the SBC. If you look at Lou's cam they are heavier on the exhaust profile, just like GM.

Look at the Z06 cam,
LS6 2002 Z06, 204/218 Duration @ 0.050. Hydraulic Roller Camshaft
Price: $185.00 Part # 12565308
Advertised Duration Int.: 270
Advertised Duration Exh.: 282
Duration @ 0.050" (I/E): 204/218
Lift (I/E): 0.551"/0.541"
Lobe Separation: 117.5
RPM Range: 2000 - 6200
Cam Type: Hydraulic Roller


the HOT cam,
LS1 Hot Cam, 219/228 Duration @ 0.050, Hydraulic Roller Camshaft Kit
Price: $399.50 Part # 12480033
Advertised Duration Int.: 279°
Advertised Duration Exh.: 287°
Duration @ 0.050" (I/E): 219°/228°
Lift (I/E): 0.525"/0.525"
Lobe Separation: 112°
RPM Range: 2200 - 6500
Cam Type: Hydraulic Roller


the ASA cam,
LS1 ASA, 223/236 Duration @ 0.050, Hydraulic Roller Camshaft
Price: $345.75 Part # 12480110
Advertised Duration Int.:
Advertised Duration Exh.:
Duration @ 0.050" (I/E): 226/236
Lift (I/E): 0.525"/0.525"
Lobe Separation: 110
RPM Range: 2500 - 6500
Cam Type: Hydraulic Roller


the Grand-Am cam.
LS1 Grand-Am Cup, 239/251 Duration @ 0.050, Racing Camshaft
Price: $439.95 Part # 88958606
Advertised Duration Int.: 294
Advertised Duration Exh.: 306
Duration @ 0.050" (I/E): 239 / 251
Lift (I/E): 0.570 / 0.570
Lobe Separation: 106
RPM Range: 4000-7000
Cam Type: Hydraulic Roller


All bigger on the exhaust side.
Gm spent into the 6 figure range developing the Gran-Am cam just in dyno time. They tried over 30 grinds to find the best profile. That is the Grand Am cam. How many "tuner" shop have those kinds of R&D dollars. Not even comp is spending that kind of time and money on just the LS1 platform.
I don't argue that folks make power with reverse splits. I think there is more power to be found going the other way, and has been the case with most SBC motors since 1955. One thing though , drivability may suffer somewhat on a big exhaust side. The smaller exhaust side hides a lot of the lope, but it will make bigger HP and more TQ. I think this ios one of the reasons the reverse spilt cams have been so popular also, they remove some of the raggedness of the standard split cams, they also make the car idle better, and I would imagine they make tuning a bit easier.
I think that is one of the things that has appealed to folks is quieting down the cam while making similar HP numbers to a bigger exhaust profile. But if you want the best power and TQ look at what 50 yrs of cam design has taught us....


It not all about raw numbers though. Its about area under the curve. There are folks out there who are developing their own lobes. While an XE-R is an agressive lobe, I have the feeling that there are even more agresive lobes out there. Two that come to mind are the intake lobe on the "Old Man" cam from TR, and the Cartek cams. The numbers Cartek has been throwing out are 228/.580 113LSA if memory serves me.

How can they do that with that cam? Well, if the lobe has as much area under the curve as say a cam with 7^-10^ more duration with a "lazier" lobe that would be easy to understand.

Like I said, there is much to be said for reverse splits. But, I think if you want the best no compromise power, a standard split is probably the way to go.

<small>[ March 07, 2003, 07:06 AM: Message edited by: J-Rod ]</small>