LIL SS

iTrader: (9)

I’m interested in cam design and maximizing power under the curve and only reving to say 6,800.

Currently I have a 223/228 XER 108/108 in my truck (63 P/U LS6). I came up with this cam as I didn’t want to rev more than 6,800 and I wanted good TQ down low due to the truck weighing over 4k lbs. I came up with the above profile by looking at a 02 Z06 cam’s IVC point at .050 (39.5 ABDC) and using that as a starting point. With a SCR at 10.89 this cam keeps DCR up at 8.68 with a .006 IVC at 68.5 ABDC and I think it will peak around 6,300-6,400 (going to a dyno in the next couple weeks).

I was up thinking last night about IVC points, DCR, EVO and valve clearences. If I kept the IVC at .006 right around 65* ABDC but maximize the duration just missing P/V issues, I could pack more air in the cyl, netting more power under the curve.

So I know a TREX will fit in a stock short block (given mines not having Eagle rods and diamond pistons with reliefs) but until I can put a degree wheel on the motor and pull a rocker to see P/V clearences, I will use the TREX info I found.

I believe I need to stay with in these limits to avoid P/V issues
IVO .006 is 37.4 BTDC
IVO .050 is 13.5 BTDC
EVC .050 is 13.2 ATDC
EVC .006 is 39.8 ATDC

A XER 234/242 104/106 allows me to stay in those limits with keeping the DCR at 8.61 with a IVC of 65.5* ABDC. But moves the IVC at .050 to 41* vs the 39.5*. I think that will still keep it in the mid 6k rpm peak.

IVO .006 is 37.5 BTDC
IVO .050 is 13 BTDC
EVC .050 is 13 ATDC
EVC .006 is 37.5 ATDC

I’m using XER lobes as the example just to get talking about it but I’m sure and LSK or some other lobe could be used.


Now I keep hearing thing like the LS6 intake doesn’t like narrow ICL/LSA’s. So before I go have comp grind a cam what issues are seen with Narrow ICL/LSA’s? Have you actually tried using a cam such as mentioned? The Grand Am cam is like 24x/25x on a 106 so I am curious to see what is said here.

What other input, thought, ideas, suggestions do others have?


Thanks

Old SStroker

You need to get everything working together. The LS6 manifold will determine where tuning peaks occur, and your primary header length can be used to perhaps fill in the torque holes.

I believe you still have stock LS6 heads. IMO, you should have a custom cam designed to work with the converter stall, gears. etc. you have or plan to have.

I don't think you should be choosing you own valve events. A couple of guys I know could do or have done similar truck cams. Unfortunately they don't post here anymore. They are elsewhere.

LIL SS

iTrader: (9)

Yes I agree that the LS6 intake would like to force a HP peak at 6,300ish RPM. However, many have pushed it over that with larger cams ect. Perhaps I should have said I don't want to shift passed 6,800 rpm, there for keeping the peak around 6,300-6,400.

A lot of these things will be changing. The truck will more than likely be seeing different heads in a couple months. That's probably when I'll have the cam ground. I will also be swaping out the stall then as well but still keeping it mild in the 2400rpm range. I'm trying to discuss theorey here to learn more. Knowledge is key.

You wouldn't be refering to EC would you?

What's wrong with choosing your own valve events? As long as I'm paying the bill, why should I not be learning from it? Everyone had to start some where and if no bady has actually tried what I'm talking about, then how do we know if it does/doesn't work.

Things I have not heard argued and seem to be true:

IVC dictates where peak will be (Obviously to a point such as intake restrictions ect) Seems that 39.5 + tend to want to peak at 6,300-6,400 with the LS6 intake.

Higher DCR wil help power under the curve.

Correct overlap helps to pull fresh air in vs causing reversion.


So those 3 things alone tel me if your going to run an LS6 intake and want to get the most out of it shifting by 6,800 rpm, to find the IVC point that best suits the LS6 intakes 6,300-6,400 peak. Get that intake valve as far open as possible before TDC as we all know heads are not flowing a ton of air before .200 lift. Also keeping the IVC point as low as possible on the compression stroke will aid the DCR. Next would be to figure out the EVO/EVC, bleeding off the combustion to early looses TQ but opening it too late and too long might polute the intake charge.


So let me ask this.

What is the IVC point that should be considered when looking at the 6,300ish peak? .006 .050 or .200? I'm going to guess it's somewhere between the .050 and .200 mark but not sure.

Old SStroker

You say you want area under the curve, but seem to be most concerned about power peak. Especially with a 2400 stall do you really want to trade torque from 2400 to say 4500 for power above 6000?

Actually one of the cam guys I'm referring too said this about this thead...

"Typical LS1tech thinking that only one valve event counts. You are talking about AVERAGE TQ but aren't doing anything regarding the IVO, EVC and EVO to help that out, just the IVC and DCR. Exhaust events DON'T BLEED OFF COMPRESSION!!!! So you are someone who needs to study the valve event diagram again. The exhaust valve will start opening 180° after the fuse is lit. As for opening the valve as much before TDC, all depends on your heads in terms of low lift flow.... the more they flow the less lift you want before TDC. Almost nobody realizes the relationship between flow and pressure is the key when the piston is moving towards the valve. Basically it sounds like you just know enough to be dangerous!"

It looks like you really don't want help or even advice, but rather agreement with your line of thinking. Sorry, not from me, either.

I don't think you would be happy geting a cam from someone else, especially if you weren't give all the specs. You probably should spec your own cam, try it and if you are not satisfied, try again, and again. It's only your money and time invested.

Good luck.


Jon

LIL SS

iTrader: (9)

You are reading in to what I am saying all wrong. I agree with EC's statement you put in here that EVO/EVC and IVO points do matter. But I believe IVC should be looked at first. But have Ed put on his glasses and read the thread a little better. I was reffering to the hot gasses bleeding off after combustion by opening the EV to early.

Think about this for a second. EC says that "As for opening the valve as much before TDC, all depends on your heads in terms of low lift flow.... the more they flow the less lift you want before TDC. Almost nobody realizes the relationship between flow and pressure is the key when the piston is moving towards the valve."

Now, I am totally agreeing here. But where are heads really starting to flow? .006, I think not. .050 still not a whole lot. In between .050 and .200? Yes.

So for arguement sake, lets say .150 is where the head I am using starts to shine on the intake. If the IVO point for .150 was at TDC you are now utilizing the whole intake stroke to jam the air in to the cyl. You are able to move more air because you are in the "sweet" spot of the head (.150" - .550") This to me is how to determine a cams IVO point. Get the most lift you can with out P/V issues early on in the intake stroke. Obviously you need to be concerned about P/V at all points and that is why I used the TREX as a model for IVO points at .006 .050 and .200 as to not exceed them. Hopefully that clears my IVO thinking.


Personally my thought on TQ is that both the IVC and EVO points help dictate TQ.

IVC has a lot to do with the TQ you can achieve. If you were to compare 2 cams of the same size, lobes in the same motor and moved the IVC point farther away from BBDC and in to the compression stroke, would that TQ not reduce and move further up in RPM.

EVO point also has a lot to do with TQ. Open it too early and you loose power by bleeding off the hot gasses. But open it too late and/or too long and you could polute the intake charge due to the highpressure exhaust and the low pressure vacum on the intake side. But to me, these come after figuring out the IVC and IVO.


Does that clear up a little bit of my thinking?



BTW, I don't take offense to EC calling this some thing like typical LS1tech stuff. Cam theorey is just that, A theorey. Not all Cam grinders agree on what is most important either. I don't think Elgin's thoughts are spot on to Ed's, nor others out there. Theorey's are meant to evolve and not stay in one spot in the past.

Old SStroker

Excuse me, but I was not quoting EC. Don't make assumptions about what I say. I'm not sure of which EC you meant, BTW.

Actually, Mother Nature determines what is going to happen. Explaining her actions and trying to work with her is what you are calling "Cam Theory". I agree that different people have differing ideas as to what valve events should be. You can choose whomever's ideas you want, or go your own way. Ma Nature doesn't care what you or anyone else thinks about how she works. If you choose good valve events she smiles on you; if you choose less good ones she laughs. You can't change her mind. I think that's why we've given her a female name.

I know something about how engines work, but I let others do the cams as well as port heads. You seem to be making up numbers as you go along. Every head/port acts differently depending on what is attached to it on either end. If you want to choose valve events the Ma Nature likes for a particular engine, you need to know how She moves air. I'm not talking just flowbench numbers, but rather the mechanism that is moving the air in a particular engine at a particular rpm/throttle opening. Many cam folks lose track of how that works, IMO.

I won't get into your thinking about valve events, except to say the unsteady flow gas dynamics is way more complex that I think you realize.

Patrick G

iTrader: (14)

It's very easy to get schooled by people who've made building engine's their life's work. What makes threads like this worthwhile is when you walk away with something that will work for your application. So without getting into any advanced theory, let me give my two cents on how to get that two ton beast moving.

First off, with only a 2400 stall and a two ton weight, you're going to want want to limit your overlap to 10 degrees at .050". Otherwise, it's going to be somwhat of a turd below that. My experience with the LS6 intake and LS6 heads has shown me that the sweet spot for hitting the 6300 rpm power peak is with an IVC between 44-46 degrees ABDC at .050". Obviously, you can cheat that a little by how you position your overlap. By centering your overlap over TDC or slightly to the intake side of TDC, you can still make a power peak of 6300 rpm with a 42 degree ABDC at .050" IVC.

If you're trying to maximize your power under the curve on motor (think heavy vehicle with a tight converter here), you're going to want to have more of your available power at lower rpm. This means not opening your intake valve too early and not opening your exhaust valve too early...both will make your low and mid-range power worse. Also, since the flow of the LS6 exhaust valve coupled to a properly sized exhaust header (like you have), you won't need to close it too late. In your case, you won't need much of a split to the exhaust to strike a happy balance with your more flow-limited LS6 intake/heads.

Here's what I come up with (don't be surprised if it looks familiar).
226/228 .585/.588 109LSA +0
This would work well on motor. 4 degree BTDC IVO, 42 degree ABDC IVC, 43 degree BBDC EVO, 5 degree ATDC EVC. 9 degrees of overlap (all at .050"). 8.54:1 DCR

But if you're still going to run a 200 shot, then this changes things some. Your intake valve events and overlap are still fine, as is your exhaust valve close, but since nitrous speeds combustion a great deal, you'll need to open the exhaust valve much earlier (to avoid pumping losses and get the much larger volume of exhaust out of there). Keeping the same IVO,IVC, EVC and overlap of the NA cam, we would need to open the exhaust valve about 8 degrees earlier for a 200 shot (51 degrees BBDC vs 43 degrees).

226/236 .585/.602 111LSA +2
This would work better with a 200 shot and wouldn't be too shabby on motor. 4 degree BTDC IVO, 42 degree ABDC IVC, 51 degree BBDC EVO, 5 degree ATDC EVC. 9 degrees of overlap (all at .050"). 8.54:1 DCR

While the Engine Masters may be able to shoot holes in my recommendations, they will work very well for your mods and goals.