I'm just starting to learn about DCR and i'm building a high compression LS1 setup (5.3 heads, Agostino Racing Stage 2) for myself, and trying to find a good cam and make sure i can run on pump gas. Now i see plenty of setups with 5.3 heads and MS4 cams so i'm confident it works, but i just want to be sure i'm utilizing all the power without needing to use any gas higher than 91 octane.

I'm coming up with a Static Compression Ratio of ~11.4:1 and using the calculator on the bottom of this (http://members.uia.net/pkelley2/DynamicCR.html) page and MS4 (at 115 LSA, 115 ICL) cam, i get a DCR of 9.57:1, which seems ridiculously high. Even the stock cam gets me 10.34:1. I'm shooting for 8.0:1 DCR because it's my understanding that between 7.5-8.5 is good for a street driven car (ie. higher needs higher octane fuel, better designed for strip/track).

Something seems way off. I believe it's because i have the wrong numbers for intake and exhaust duration on the MS4. I'm using 239/242 115LSA because i can't find anything else on TSP's site. Is that correct? Any and all help is appreciated!


Edit: Just FYI, the other numbers i'm using:
Bore: 3.898
Stroke: 3.622
Rod length: 6.125
Chamber Volume: 61cc
Head Gasket bore: 4.000
Head Gasket thickness: 0.041
Piston To Deck Clearance: -0.008
Piston relief/dome volume: 0cc

I found a thread on here saying the pistons normally come out of the deck ~0.008. Is that correct?

 

are you going to flycut? Im not so sure you can run a cam that size unless those heads are made with sunk valves or whatever to help clearance a bigger cam. Also where did you get those cam specs from? A cam that bit with that high of lsa might not be your best choice unless you have spray in your future or something.

 

I'm not stuck on using the MS4 cam. I'm totally willing to change that up. I just wanted to get an idea of the size cam i could use. If i need to flycut, so be it, but i'd like to avoid it.

I should note i only have the stock cam on hand. I will purchase a new cam once i determine the size.

 

Those duration numbers, although not labeled, are presumably the figures @0.0500 lift.

 

I got somewhere around 8.35, give or take..

If you use the figures at .500 lift you have to add 20-25 or so to the final number...Again, just a rough estimate.

 

@Darkman: I should edit that. The calculator does not include lift numbers to determine DCR, which seems odd to me. Here's what i'm going by: 239/242 .649/.609 115 (only using 115 as a guide, because it's my understanding stocker is 155.5)

@FlamingTA: I see what you're saying. Thanks! 8.35 sounds good to me.

 

Doesn't the MS4 usually come in 111 lsa?

 

Yes. You can get it anywhere from 111-115. Again, i was just trying to get an idea with that cam.

 

I have an MS4 with a 111 LSA and I am coming up with 11.438:1 Static and 8.141:1 Dynamic utilizing 77* ABDC which is what I used when determining these figures.

EDIT: This is the SCR/DCR Calculator I use

 

@1SlwLS1: Beautiful. Now, how did you come up with 77* ABDC?

Here's what i'm getting at. 239/242 durations, plus 25 on both assuming duration is listed at 0.050, gives 264/267, using 111 LSA 111 ICL gets me 63* ABDC, plus 15* nets me 78*. I would like to get a full grasp on what i'm doing lol.

Edit: Got 77 after dicking around with the ICL. I changed it to 110, and then i was spot on. But i kinda just guessed at 110. How can i determine that with confidence?

 

LOL, I am and have been trying to remember since I read this thread. I did it a while back and found an old post with lobe profile ramp rates from Pat G and extruded the information to what you see. Although, my cam is installed 1* advanced on a 110 ICL so that's why I come up with 77* vs 78*

 

Right on!

Another thing i want to work out:

Using MS4 specs, 111 LSA, 110 ICL, 78* ABDC, SCR = 11.438, DCR = 8.141
Stocker, 115 LSA, 118 ICL (random guess on ICL), 70* ABDC, SCR = 11.438, DCR = 8.660
Stocker, 115 LSA, 110 ICL (random guess again), 62* ABDC, SCR = 11.438, DCR = 8.925
Stock durations, 111 LSA, 110 ICL (random guess again), 62* ABDC, SCR = 11.438, DCR = 8.925

So using the stocker with 5.3 heads would be outside the "average" DCR for a street car, thus suggesting the use for >91 octane fuel? But using the bigger MS4 cam brings the DCR down into the "average" DCR, allowing 91 octane to be used? This suggests to me that the stock cam would be more preferential over the MS4 for strip use while using 5.3 heads. This seems very odd to me, but like i said, i'm just scratching the surface of my cam knowledge.

It's becoming very apparent to me that ICL plays the biggest role in DCR.

 

The MS4 and other high duration cams bring the DCR back down because they bleed off pressure closing later in the lower RPMs (loss of TQ down low) but since cylinder filling has a lot to do with engine speed and air velocity, will allow the cylinder to "over-fill" in the higher RPM range permitting the other limiting factors allow it.

 

To roughly figure it's actually (239/2)+ICL-180 and then add either 20-25 depending how the ramp rate of the cam. And it's ICL not LSA, not sure how much the MS4 is advanced. So in this case it would be:
(239/2)+111-180=50.5(assuming no advance). Add say 22(MS4 seems pretty aggressive)= @72.5 ABDC

 

MS4 is advanced 1º in the cam itself

 

Looking at the duration and lift I'm guessing it's running a LSK intake lobe. If we know that then we can look it up and see that the advertised duration of the 239@.050 LSK lobe is 289. Plug that in and you get 74.5 ABDC, bring you to about 8.3 DCR.

 

With that kind of duration (239/242), you would need to flycut.

 

Is this going to be a track car, DD, fun street toy?

Now I could be wrong and I know ppl do have them, but it seems like the MS4 is really huge for a street 346ci car. I had a SNL VX cam that was pretty close to this except the intake duration was a touch smaller, and in a 6.0 GTO it was pretty big cam for street use.

It seems these days that more and more ppl are over camming their cars for their intended purpose. I will be the 1st to admit that I love the sound and feel of a big nasty loping cammed car. But you have to look at how you are going to use your car. A huge cam is going to have very little bottom end and midrange might suffer too. It might have better top end HP numbers but I will tell you, it's won't be very much fun to drive alot of the times on the street.

Take my case, I am building a 421 stroker for my Goat. Now with that many cubes, I could have gone with something like a 252/259 or 255/263 but instead I took some advice and went with a 243/247. Not alot bigger then the MS4 despite having 75 more cubic inches. Why? The car's intended purpose and were it will spend 95% of it's time, a fun street car. I wanted more low and midrange torque. I wanted better part throttle response, better tip in/roll on. If I'm rolling down the street at 3K and want to play or a mustang comes by, I can just nail it and I'm gone. In a overly cammed car I would have to shift to get it to 4.5 or 5K to get a good punch out of it. Sorry for the wall of text, just my thoughts on "street' cars these days.

 

Ideally, it'll be DD/fun street toy. I say DD but i feel like i would be hard pressed to find tires to handle the Michigan snow, especially considering i'd like to see 400rwhp. Having said that, i'm more concerned with having a well-built engine and sacrificing hp to do that is fine. Plus i can always buy a winter beater for like $500 and keep the Camaro for the warmer times.

And i completely agree. I'm also a sucker for that lopey idle that sounds like the car is backfiring, but i do realize that my intended use would be better with a smaller cam. So maybe a custom grind is in my future! Is there any way to determine power band based on cam specs? I think a cam where it starts to really pick up after 2500-3000 would be great for me, so you're right, something like the MS4 picking up at 4500 or so would be entirely too big.

 

I think i've got this nailed. I'm trying to get as many opinions as possible on my final cam choice. 230/234 .600/.600 115lsa+0.

Also will stock pushrods and rockers suffice?

Full setup, stock unless noted:
Stock bore LS1
Agostino Racing stage 2 5.3 heads
K-Motion 750 springs (good for .610 lift)
1 3/4" long tube headers (planning on grabbing 1 7/8" but i first want to get this thing running), x-pipe, straight tubes
3.23 gears (again planning on upping to 4.10)