I’ m at another crossroad with my build. We took the engine out last Wednesday and started tearing the motor down yesterday after work. My mod list is: LS1 intake with adapter, rockers/rods/springs, cam, headers and N2O wet kit. Money is tight (school teacher), still need to spend money on: gaskets, exhaust shop (new flex pipe and hooking headers to cat back) and professional tune. So here are my questions: should I do anything to my heads? I am staying with an ls4 tb so what is the point of porting if the choke point is before the port? Are there different degrees of porting? What is the average cost of a port? I looked around last night and saw a few ported 5.3 heads from the truck community for sale. Thanks guys

 

It's quite a bit in labor to replace them. Texas speed has the prc 5.3 ones in various ported stages with flow numbers on their website if you want to look at that.

 

I'd shave the heads to compensate for the overlap in the cam and leave it at that.

 

Just have them freashed up. I had had mine hot tanked, decked, and had the valves and seats restored back to stock specs. The only upgrades added were viton valve seals and new LS7 springs with titanium retainers. The valves were back cut too.
Make sure you clean out the engine block head bolt holes with a ARP chaser, or grind three vertical slots into a stock bolt. Very important.
I bought all of my gaskets and bolts from http://www.gmpartsgiant.com/ Great pricing!

 

You could port them, but I would just mill them for a bump in compression and call it a day. Keep in mind that means you pretty much have to run 93 or 91 (for the Californa people ) all the time if you don't do so already.

 

Yep, going to a cam with any amount of overlap will rob you of some power without bumping the compession by other means...

 

Truth. You'll get some power from porting too if it is done correctly, but you can have ports that are too large. Matching the intake/exhaust ports to your manifold/headers is a good place to start. If you measure the dynamic compression, you'll see that the cam change will cause you to build less pressure in each cylinder. You can compensate by increasing static compression. The tendency to knock is more closely related to dynamic compression. I've seen a couple builds in Hot Rod where they ran 12-13:1 static compression on pump gas using Rhodes lifters or a really big cam. They were obviously built more for the strip than the street, but you get my point.

 

I hear you guys. I am moving really slow on this issue. Talked to a couple of shops, they all have different opinions, kind of like you guys. A few days ago I meet up with this guy who has been building engines for decades and he took a look at the heads, intake and headers. He has made a few statements but he is holding off until he gets some more info on the exhaust side of the head. One thing I do know is that whatever course I take, it’s going to cost money and time. We've been a one car family now for 15 days

 

The headers being 1 7/8" is going to be kind of weird. I wonder if we could use a cam with less exhaust duration?

 

A single pattern cam with more overlap would be the key. The two most important phases in a camshaft, is the Intake closing point (compression stroke) and the Exhaust opening point (power stroke). These events are controlled by duration and Lobe seperation or Lobe centerline angles wich can be altered thru cam degreeing. Most cams have advacement ground into them cam to protect people from over caming, and to comp for timing chain strech. Generally, restrictive exhaust systems need a dual pattern cam with more exhaust duration with little overlap. Intake closing events have the biggest impact on peak hp numbers, and the exhaust opening events determine peak tq rpm.
Bamma, is right I just wanted to point a few things out. 1 7/8" headers are overkill and I think that they might be hurting performance with are stock cam and intake.

Please excuse my spelling I'm on my phone lol

 

What about a reverse split? We're far more intake limited (especially with a LS4/1 intake) than we are on the exhaust side with the huge headers.

LSx motors are seeing really good numbers even with huge reverse splits...

 

Just freshen up your heads man... no need to get to crazy. Im sitting at 10.25:1 now with milled heads and it has made a huge difference!

 

Rule of thumb is generally 15hp/full point in compression. Definitely SOTP difference right there.

 

This is due to LSX heads. They are super resonsive!

 

So I guess picked up about 4hp across the power band.

 

Probably had more to do with the port work. lol

 

Shh.... Very mild port work