Originally Posted by booz

Currently I am in 470rwhp with
12.03cc
Tea stage 1 243
Cam with 1.8
1 7/8 with true dual
Ls6 intake tpis ported
And the usual bolt ons

Originally Posted by Nick Rutledge

I have a 2000 Silverado with a 5.3, 1 7/8 headers, TBSS intake, Wilkes Performance ported 862 heads, and a D1sc procharger on 16lbs. The current cam is a 224/228 .604/.604 110+2 and the truck made 732/611.

It does great 1/8-1/4 mile but roll racing it just gets walked by alot of lower powered cars. I ordered a new Cam for it and I'm hoping I went in the right direction. Without losing too much low end.

The new cam is a 224/240 .604/.595 116+5. Anybody have any input on this? Will I lose power with the new cam? Should I have gone a different route??

Originally Posted by Che70velle

Interesting that your getting walked. What trans and rear gear are you running?

Originally Posted by Darth_V8r

Wait... I mean Weight...

You're in a truck, and they're in cars? Takes a lot of power to make up that kind of weight difference, unless your truck is very light. Also, what's your stall.

If you don't plan to rev, the new cam is probably going to feel soft compared to the old one. I'd be more in the 224/230-112 territory.

Originally Posted by JakeFusion

So, I decided to write a little something on cam valve events as I've been thinking about it over the last couple of days.

As a general rule of thumb, very late IVC will contribute to terrible low end. So will opening the exhaust valve too early and allowing the charge to escape. And as will excessive overlap. You can't build cylinder pressure if all the intake charge is being pulled through the exhaust at idle or reverting burnt fuel back into the intake manifold.

For anybody looking to make torque... in a 5.3L keep the IVC around 36-38 degrees to build cylinder pressure and bring the overall peak HP down a few hundred RPM (same stroke as a 346, but you have to offset the missing displacement and bore). And the 346 would be around 40 or so. Then you set your EVO properly to carry power past peak or to enhance the torque peak. And that relies on the cylinder head exhaust efficiency, the exhaust valve size, the headers, and exhaust itself. As a good rule of thumb for most street engines is if the I/E ratio is 75% you need a single pattern cam at .050". If for every % below that you need about 1.5 degrees of split favoring the exhaust. For every % above that you need to add 1.5 Degrees to the intake.

The intake is fairly well set with the long-runner plastic manifolds. Their harmonics create a 4800 peak torque and 6300 peak HP number. So trying to push the valve events too far away from those ends up with dog turd performance. In either direction.

But let's take a balanced set of cam events for a 347. That peaks at 4800 with torque and 6300 with power. Carries it out nicely, but generates a lot of off-idle torque. What would that look like?

Well an IVC of around 45 in a 347 creates that 6300/4800 peak with an EVO of 55 carrying it out another 500 or so RPM while maximizing torque as an example of creating a profile that makes power everywhere. If you set your EVO at 53 or 51, it'll build more torque at the expense of carry past peak. And there's many ways to get there to create the total overlap wanted (which affect drivability and total performance). More overlap means more power at the expense of being able to drive the car but increasing the efficiency in the upper RPM range. But all of the profiles below would generate similar cylinder pressures with the same compression.

The overlap and the IVO/EVC tell us where those cylinder pressures occur: higher overlap and overlap that biases toward the intake makes power later (but may not move the peak - just carry better), whereas lower overlap that biases it toward the exhaust will make a little more torque down low (but retains similar peak torque and peak HP RPM areas, but would fall off up top faster). And if you center your overlap you'll make good power everywhere without enhancing or exaggerating either end of the powerband. But then the trick is to get the overlap right for the power and drivability desired.

So what about the 45 IVC and 55 EVO combo? Here are 5 cams that produce the same valve events. We now can play with IVO and EVC to get the duration/LSA needed to achieve a stated goal.

240/248 108+3 28 degrees of overlap biased toward the intake - monster cam that produces explosive topend
234/242 111+3 16 degrees of overlap biased toward the intake - top end screamer
230/242 112+3 12 degrees of overlap biased toward the exhaust - explosive midrange
226/234 115+3 0 degrees of overlap balanced - excellent street manners and good power everywhere
224/224 118+5 -12 degrees of overlap biased toward the exhaust - stealthy with a lot of torque

All would work best with 11.5:1 CR assuming using the same lobe (50 degree .005 to .050" ramp rate).

That's the best way for me to describe how you can affect torque and drivability using different cam profiles. And all would peak around the same 6300/4800 range in the same motor. But would drive differently and either carry the power out longer as with the two bigger cams or generate more explosive midrange or lowend grunt with the smaller cams. But again, that's with the same IVC/EVO. You can play with those to get huge swings in performance too.

So as the last example, a 42 IVC cam would need less compression. So it may not make more torque than the smaller cam above with more compression. So it comes down to what you want. Maybe you want a chop in the idle and don't want to run high compression? Or you have a 5.3L? Then move the IVC down to get the cylinder pressure building early. And go through the same exercise again to set overlap how you want it to achieve the outcome you'd like in terms of drivability and where the power comes on the hardest.