Looking at one of these two cam options (TB-SS, stock 'verter):

212/218 115LSA +3 advance -or- 212/218 114LSA +2 advance

How will these two minor "changes" on the Lobe-separation & Advance affect the cam's behavior?

212/218 115+3
---------------
IVC = 38
EVO = 47
Overlap = -15


212/218 114+2
---------------
IVC = 38
EVO = 45
Overlap = -13


The 115LSA will idle slightly better (-15 overlap), but how much in the RPM range will the peak HP/Tq shift between the two?

The truck will have AFR205s & longtube headers to complement the cam. Staying with the stock converter, and retaining/improving low/mid rpm torque is definitely a must. (stock cam is 204/211 116LSA) Looking for as smooth of an idle as possible, and I don't want to spin the motor past 6500rpm.

 

The IVC of the stock LS2 cam is much later than 38 degrees ABDC. It's more like 42-43 degrees since the cam is retarded a degree or two. Although your cams have more intake duration, they're going to peak earlier and run out of breath very quickly. You may want to consider running the 114LSA cam with 0 advance. With an IVC of 40 degrees ABDC, you will make more power under the curve and have much more robust power above 5000 rpm (while maintaining solid low-end grunt).

 

PatrickG - Thank you for the response.... I was hoping you would see this and chime in. I have gotten advice also from Tony M, and he recommended a 214/218 112LSA +2 or +4... BUT he was also trying to maximize low-end tq from ~2k-4500rpm for me. Although I am sure it would be a stump puller, I was/am concerned that his recommendation would run completely out of steam above 5000rpm (Tony, don't get me wrong, you have been a TREMENDOUS help with my cam selection to complement your AFR205's). Knowing that I want to run the truck no higher than 6300-6400 rpm (somewhere in that range, 6500 absolute max) to keep A4 longevity, I figured there is a lot of upper RPM that the truck just wouldn't pull well with that cam choice. Likewise, I'm scared of the 112LSA & idle quality (-8 overlap)....its a DD, and usually by my wife so I need to keep it smooooth.

Thus, I have then been looking at the two cams I had mentioned in my first posting above....and I appreciate the additional feedback you've given.

With your comments then, what do you think of this:

212/218 116+2
---------------
Overlap: -17 (good idle!)
IVC: 40
EVO: 47

How will this cam compare to the stock LS2 cam in terms of what rpm HP & Tq peak are made at? This gives an IVC of 40 (like the 114 +0), but the EVO is 47 (114+0's EVO is 43). Which is better suited for stock manifolds exhaust, and which is better for longtube headers dumping into the stock catback? Heck I can even split the difference, and do a 115+1 for an IVC of 40, EVO of 45, and a -15 overlap.... But how much am I really splitting hairs, here?

212/218 is the biggest I want to go while still using the stock stall converter, so now I'm into the details of what specs that 212/218 needs to have in order to give me a good boost of low/mid torque, but not die-off too early in the upper RPMs...and thus trying to figure out what specs will give me a good compromise of both. (since I know I can't have my cake and eat it too...) Bear in mind that I don't want this to only have gains in the upper RPMs like many LS1s typically have (including my own...nothing down low, but BIG gains up top). Its a big, heavy truck and it needs a healthy dose of low/mid torque at the expense of some of that 6200+rpm HP....and I especially can't lose any low-end torque; that would be a huge no-no in this 4700# SUV. KnowwhutImean?

Yours (and others!!) thoughts and comments are very much appreciated.

 

Patrick is putting you in the right direction. If you want to shift around 6300/6400 then your cam should peak around 6000/6100.
That translates into 40/41 IVC
If you want to keep low-midrange trq then keep your EVO around 45* or so the more you increase the more it shifts upward.
In general you want the IVO/EVC as equidistant from TDC as possible, 1 or 2* intake biased will carry well, exhaust biased will die off sooner.
Anything above -10* overlap will be hard to trace with a quiet muff and more so with cats.

Look at my Vette cam in sig.
This one peaks at 5900, very exhaust biased for stock manifolds, shifts 6100 (but it will go a little further), midrange trq is good.
Basically it worked as designed and I gained ~ 30rwhp while there is no way to detect there is a cam (still stock exhaust). Idle is stock.

 

My car is a A4 with stock converter and my 218/222-115+4 works great

 

Great info to have, thanks P-Z.

When you say that with the IVO/EVC is 1-2* intake biased it will "carry well" - what exactly do you mean...? In other words, the power curve won't be nearly as peaky?

And since low/mid torque is highly important for my application, I want to keep my EVO ~45 or less?

Just making sure I understand your notes....!

 

Correct, "carry well" means it will hold the peak power for a longer time through the rpms before starting to dip downward.
On stock cubes, good lo-midrange trq is relative to the longer stroke BBDC. so 44-45-46 will be really good 47-48-50 good and above 50 will start to suffer in that area.

 

How would the cheater cam work in this application?

 

The CheaTR would work great in this application if its LSA was narrowed some and it was advanced 2 degrees. Stock, it has an intake valve closing point of 43 degrees ABDC which would make it too much of a top-end cam for this application. Narrowing LSA 2 degrees and adding 2 degrees of advance would make it ideal for a Trailblazer SS.

215/230 .600/.578 115LSA +2.

 

Wow, how much idle vacuum to do want? I'd go much, much lower in LSA with that small of a duration because you will still have a nice idle. Otherwise you are just giving a ton of average power away.

Bret

 

Hi Bret

I don't know about that; I have heard more than a few soundclips of the 212/218 cam in 114 and 115 LSAs, and they already have a noticable lope to them. Not much, but you can tell its there, even on a stock exhaust. Hearing a distinct lope with your ears not next to the tailpipe isn't what I'm going for, unfortunately - and I think that is what I'd get if I went with something less than a 114LSA.

 

I'm not talking about lope, I'm talking about TQ. It doesn't make much sense to me to take that little of duration and then just cripple it with such a high LSA. Even if you get SOME lope the thing is never going to sound evil and it will still drive awesome.

Bret

 

Its entirely possible that I am missing something still, but my understanding is that this would screw up the valve events - and thus then go against what P-G and P-Z had to offer in terms of what the "optimal" IVC and EVOs should be for best tq/power & a shift point of ~6300. Which, in turn, I would then need to run a bigger duration.

Yes, I would agree that a lower LSA will make some killer torque on the low-end, but I don't think I could rev it to 6k+ & still have good power. (??) I could totally be wrong, as I will never profess myself as being an astute mind in this subject of cams.... I know just enough to 'ask the proper questions'... I appreciate your input.

 

Well you might get the IVC point where you need it for that RPM, but I don't base that point for where you produce max power. Curtain area (namely valve lift) have much more to do with it.

What you are doing with the valve events with the wide LSA is jacking them up something serious in terms of the IVO and EVC points, along with the EVO being way to early.

You can spend to much attention on that IVC and jack up the rest of the specs if you are stuck with a certain LSA or certain duration.

I'd look more at a 218/218 setup and start dropping the LSA a lot. You would have to get down to a 102 LSA to equal the overlap of a MS3.

Bret

 

He wants DD, with almost no lope (meaning nice amount of negative overlap)

I see what stroker is pointing at, but at 218/218 111+0 it is only a -4 overlap, which will have a definite lope, peak around 6000, good carry, but very early trq and it will pull on the stock verter.

There could be a 220/220, .581/.581 113+0 XE-R, 6200 peak (43 IVC), shitload of low-mid trq (43 EVO), will carry to 6500 no problema and -6 overlap (really tiny lope)
Like a Mini Stealth

 

Interesting stuff

I'm listening

 

Obviously not eveyone is....

I'm talking about keeping the IVC around the same spot, but not killing TQ by opening the exhaust valve so early #1 and #2 opening the intake valve sooner as well.

We are talking about two cams with either 19" of vacuum or 14" of vacuum but they will drive the same.

Bret

 

Ok, Stroker, how about some numerical exemple so we can see the light.

 

Z,

Try basing the IVC off of what I gave you "keeping the IVC around the same spot"

"212/218 114+2
---------------
IVC = 38"

"I'd look more at a 218/218 setup and start dropping the LSA a lot."

"but not killing TQ by opening the exhaust valve so early #1 and #2 opening the intake valve sooner as well."


Right there is all the info you need.

Bret

 

0.050
218>int DUR
218>ext DUR
110>LSA
109>ICL


0>IVO
38>IVC
40>EVO
-2>EVC
111>ECL
-2>Overlap

OR (for less overlap)

0.050
218>int DUR
218>ext DUR
112>LSA
109>ICL


0>IVO
38>IVC
44>EVO
-6>EVC
115>ECL
-6>Overlap

But those will run out of breath quicly after peak (make shitload of early trq though).
BTW 38 IVC is ~ 5800 peak.

I'm trying to see your logic (38 IVC and carry till 6500 will have to be intake biased close to TDC). I fail to recognise how a negative overlap will do that on tight LSA with this 218 you are talking about.

218/218- 109+0 ??? But 0 overlap is not stock idling ?