j200pruf

iTrader: (1)

So I have been doing a lot more research on selecting cams and I just want to make sure that I am going down the right path for my 5.3

So when it comes to cam specs for emission is the over lap the only thing to be worried about, or duration, or a blend of both? Adn does ICL play any part either?

It appears that the biggest people have said to pass is a 224/224 on a 114 LSA and the overlap on that is going to be -4 degrees

I have been reading throught predatorz's post about a reverse split cam and how it is helpful with a cam that uses a stock head and intake with a free flowing exhaust. That got me thinking, I have a 5.3 that will be going through 1 5/8 headers but using stock heads and a ls1 intake. Sounds like a good canidate for my situation. I am trying to get a cam that will have a good mid to upper rpm band, I don't mind to much if its a little peaky as my car is fairly light and stuck using 4.10 gears.

I was thinking about using a 227/224 from TR. It comes with a 114 LSA giving it -2.5 degrees of over lap. I was thinking of having it done on a 115LSA giving us -4.5 degrees of over lap, just a bit better than a 224. Now upping the LSA is going to make the power band a little narrower/peaky correct? Now is there any chance that will go through a sniffer(not as strict as CA) or is the extra intake duration making that impossible?

WeathermanShawn

iTrader: (1)

Overlap is your primary concern.

-4.5 degrees overlap will be borderline doable. If you have an 'emissions' tune available, increasing desired idle speed may also help you.

Having it ground on a 115 LSA will help (less overlap). Should be a nice smooth idle with an occasional burble. Performance wise vs the 114 LSA might be a 100-200 higher rpm HP peak (later IVC).

I have previously passed emissions in Colorado with a -6 degree overlap. Always felt if you were borderline passable to go with a -6 overlap or more, or have access to some 'creative' tuning.

Hope that helps.

..WeathermanShawn..

12secSS

iTrader: (30)

Pretty much what the Weatherman posted. I have had customer cars that I tuned pass smog on 228 cams with a 114. Anymore then zero overlap and you start to pollute the combustion process, which is nto good for emissions numbers. This is talking strictly in regards to cam specs. Other factors cam affect emissions as well, like high compression ratios (promotes high HC numbers).

j200pruf

iTrader: (1)

So does insceasing the LSA narrow the power band or move it up?

I know that my test you know have to pass at idle or 2500rpm, with no load, and your idle can be fairly high.

So with a good tune even -2 degrees is do able, especially if I am willing to take "drastic" measures.

Any other things to look out for other than the cam? I know that the compression thing wont be an issue since I am running a truck engine and am not going to mill the heads.

WeathermanShawn

iTrader: (1)

Without exceeding my expertise in cam science, here is my understanding.

1). With the 227/224 114+4 LSA the Intake Valve closes (IVC) at 43.5 degrees.
2). With a 227/224 115+4 LSA IVC is at 44.5 degrees..

In case (1) the cam's HP peak will be at ~6300 rpm (estimate).
In case (2) the cam would peak at ~6400-6500 rpm (estimate).

Theoretically the cam that peaks at an earlier IVC (case 1) would begin to build its cylinder pressure earlier in the 'power curve'..I.E. a few hundred rpm's sooner than in case (2).

This is a greatly simplified explanation. Some have successfully demonstrated that while a cam such as in case (2) peaks later, it may hold its 'peak' longer than the cam in case (1).

In your case -6 degrees of overlap will virtually guarantee that you will pass emissions. As you get closer to -2 or zero overlap, you are gambling. With -4.5 degrees of overlap it is probably a >75% chance you will pass.

As a general suggestion, my best advice is to get some reputable reading material or solicit the advice of some highly respected cam experts. There are several who frequent this board.

Valve events can be fairly complicated, and can be subject to a lot of debate.

Let us know how it goes.

Good luck.

..WeathermanShawn..

j200pruf

iTrader: (1)

I just wanted to say thanks weatherman and 12secss, I asked a similar ? on the truck forum and everyone says just go with the 224/224, but I feel confident I will get this to pass, and not a whole lot of people seem to use the reverse split cams on the 5.3 so I am interested in what I will find.

WeathermanShawn

iTrader: (1)

Your more than welcome.

Hope our advice works out.

Glad to see someone has the aptitude and interest to try something others might not consider (reverse-split cam).

Let us know how it goes.

Later.

..WeathermanShawn..