Agreed, 80% of intake flow is damn good, especially compared to old school "muscle car" heads from back in the day. But, the fact remains that what goes into the cylinder must be expelled from the cylinder. And, as you mentioned, since the exhaust valves are smaller and the exhaust ports don't flow quite as well as the intakes, the exhaust cam lobes can and should be configured to help out. The last thing we want is for the piston to needlessly wiz away horse power pushing the exhaust gasses out of the cylinder, when a little extra exhaust duration can significantly benefit cylinder evacuation, thereby reducing parasitic pumping losses. How much extra duration is appropriate, is obviously determined by the specific heads being used.
Honestly, I think that we are largely in agreement here, given the head/cam combinations (and accompanying explanations) that you cite. Even your cathedral 225's called for a little extra exhaust duration, despite the comparatively excellent performance of those exhaust ports.

 

This is the flow chart for his LS2 heads.


This is the cam specs:

 

I was traveling a lot recently (Europe and Brazil) for work and did not have much time post. I see you have a pro involved and the tuner which is a really good idea to involve them both. Look at this guidance, some very sound advice here:
http://www.ls1howto.com/index.php?article=1

There is a Lot of "while you are there" cost of things that will add significantly to the cost of your project. These are the things that I focused on:

• I was freaking out about the steering rack and that was really one of the easier things (Tie down the steering wheel with ratchet straps or something!).
• I bought a Quick Jack set-up, While not an absolute necessity, it sure is nice to get the car where you need it by pressing a button. Doing this on jack stands, I would consider that a young mans game. I am not young anymore sooo...
• Centering of the front crank seal. Install cover on with dabs of RTV in the corners of the front cover. Leave the bolts loose, less than sung. Lubricate the seal and the HB where the seal rides. Install the HB and torque. Spin the engine over a few revolutions, by hand, to center the seal on the HB. Now, Tighten cover the bolts, don't forget the two on the bottom of the oil pan.
• If you install a new oil pump, it is very easy to prime. There is a fitting on the side of the block you can thread rubber hose into. Use a funnel and run a quart of engine oil into your new pump and put the plug back in the side of the block. Easy.
• I had a few OEM TTY bolts that came out on the tight side (stalled my air ratchet) and I was worried the threads were boogered in the block. You need an air nozzle that can get down into the bottom threads in the block. Blast out the coolant and mung, covering the opening with a shop rag, spray the threaded hole with brake clean, repeat over and over again as needed. Lastly, I cut some slots into a known good head bolt that came out easily upon disassembly. You will be amazed at the amount of debris this will generate. Again clean threaded holes with brake clean and compressed air. I used ARP studs. They are the best way to fasten a head to a block, best clamping action. Not cheap however $400... Whatever fastener you decide on the threaded holes in the block must be clean to achieve proper torque and/or stud installation.
• Couple thing that you'll likely need a helper for:
  • Getting the hood off and on
  • The headers.
• Take pictures as you dis-assemble and label everything.
• Take your time and think through your next step so you do not have to go back.
• Its all about attention to detail.

I am by no means an expert. I would willfully do this again if I have the time off of work to do this to another car. I would also be willing to help (also lend tools needed ) to someone else close to me capable and wanting to perform this job. I found the project extremely rewarding and I learned a lot about these cars. My only regret has been why didn't I buy a C5 sooner in life? Great car, especially now with the HC and clutch done. Here is a link to my HC swap and there is a spread sheet with PN's and money's near the end. Start thinking about a clutch with your new found power...
https://www.corvetteforum.com/forums...-coupe-m6.html
IMO That LS1how to HC swap link should be a sticky. Also if my HC post would fit into that category, I could clean up the non-relevant content. I'm not sure how to address that with a moderator?
I'm off to KRFD airport to turn money into noise in the Piper and put another 100 miles or so on my Coupe. If I think of other pitfalls while I'm driving I'll ad an edit.

 

Intake flows also factors in on cam selection, in the days before the FAST intake, reverse split cams were not uncommon.

Fortunately for cathedral port heads, the price to be paid for missing the perfect cam timing is not as high as it is for other heads/engines (which is not to say there isn't a price to be paid).

IMO for most street cars, 228 at .050 on the intake is about the limit before you start trading off the broad torque curve for a narrower high RPM power band as well giving up street manors. Which is best depends on your goals and overall setup.

A friend and I tuned in my nephew's 04 LS1 GTO with 243s valve job with a back cut on the intake valves no porting, decked only for clean up, factory intake, tb, and air box with a full SLP exhaust, 1 3/4 headers. He's running a Summit 226/238 and turned 380/380 very broad curve after a dozen pulls over an hour and 15 minutes or so. The curve was very much the same as my old Futral F11 228/230 and my friend CamMotion Titan 228/232. Also duration only tells you so much, the overall lobe design has an impact as well. I'd be interested in more info on how they designed the lobes on the track weapon compared to their Titan cams. Stapleton42 on youtube interviewed a CompCams cam designer and gave a good breakdown of the lobe design ramps rates, intial energy off the seats, and closing the valve. Interesting stuff if you nerd out on this type of thing.

 

Adding, the lobe design will dictate how long a valve is open at a given lift point. For example, lift may spend more time at 75% open than at 100% open. This factors in midrange power vs. top end, and this is where ramp speed play a major role.

This is where a conversation with the cam guy will go a long way in developing the best combination of components.

 

Always measure pushrod length, also tell whoever you order pushrods from how you measured them. Some such as Manton do not meassure tip to top. BTR and I believe Summit have 11/32 diameter pushrods which I and most engine builders prefer. Manton has custom length 11/32 pushrods but they are expensive and likely overkill, IMO. When you pull the rockers off look at the tip which pushes down on the valve as well as the cup that the pushrod pushes on for wear. Feel the pushrod tips, cups on the rockers and push rod tip for anything that is not smooth. Keep the parts in order in case you notice something.


Pittsburgh 8" calipers work fine to measure the pushrod length. IMO measure all 16 to verify measurements are consistant.

It is a very good idea to check piston to valve clearance.

SAC city and others have allignment tools for the covers. If the front cover isn't alligned properly, the front seal can fail.

For the balancer, I very much recommend an ARP bolt, good install tool like a pro form, and torque to ARPs specs. Use ARP lube for their hardware. I used an Amazon crank stop which goes in place of the starter to engage the flywheel when I torqued the balancer down.

 

This is all great stuff. Thank you kindly @Prop Joe , Polo and others. I have taken a look at prop Joe's build thread. Lots of excellent info in there. For the most part what I was asking in regards to what to pay extra attention to you all answered. Thank you. I'm gathering all the parts now and from time to time I just get hung up on for example what brand of gaskets to get and what thickness etc. What oil pump, high pressure or high volume... which fasteners and so on and so on as you all know I'm sure. That's why I like to throw questions out there to those who have been there done that. I have some good resources to get this job done correctly myself and all the tools I need with my father and brother owning and operating a small car repair shop for decades. We all love cars....me personally, I like driving them more than fixing them. But this time I'd like to take this on myself. Looking for that rewarding feeling that Joe mentioned above. These cars are fun to mess around with. A good combination of the new and old technologies. My shopping for parts continues...

 

Agreed. My 225s did need 4° more, and lift was also .006" more.....

 

High pressure oil pump

 

These arrived today. I put together some of the other parts for this. Balancer with ARP bolt, new rockers with the BTR trunnions, timing chain and dampener, cam retainer plate with the ARP bolts. Still need the oil pump, head gaskets and all the other gaskets. I'll get the pushrods last after i check for the proper length. I know I'm missing something... just can't think of it right now. Should i replace the cam sprocket??? Car has 60k. I was going to get it but held off.

 

I would get the thread chasers from ARP to clean the head bolt holes and an actual balancer install tool for putting the balancer back on

 

Got the ARP hardware for the balancer, heads and cam retainer plate. Also was able to locate a SAC city alignment tool. I have a decent micrometer. Just recently got the 10295 pump as well.

Thanks @93Polo I have a question about the Summit 11/32 pushrods. They come in both .120 and .105 thick walls. The heads I'm using are LS2 243's from Advanced Induction. They will retain the factory valves with the PAC double spring kit, titanium retainers etc. I have new factory rocker arms with the BTR trunnions and Johnson 2110 short travel lifters. Mild cam that's going to be under .600 lift on I and E. Do I really need .120 think walls on the pushrods? Is it ideal to go as strong as possible in this area? I'm just trying to think ahead.

 

hard pressed to hit 400 i would say

 

I would speak to the vendors, the idea is to get as stiff as possible. However oil must also flow in the pushrod. The Summit 11/32 .120 wall should be a good option for a street car. I believe my nephew is running those. I am on 3/8 but my aftermarket heads have the clearance needed for 3/8.

A little more reading on this topic.
https://ls1tech.com/forums/generatio...0-12-wall.html

 

One other note, there are 2 cam retainer plate versions. The early version uses standard bolts, the newer counter sunk. The torque spec for the counter sunk version is less.

Cam and crank sprockets? Good idea to replace, many haven't. A mechanic friend who I talk to when I run into things used to run BMX bikes. He always prefer to replace as a set.

 

Thanks, Im sure the .120 will probably work well. I'll call and check to be sure.

 

 

I have put together every piece for my build but I'm still patiently waiting for AI to send me the cam and heads.

 

Got em!

 

They're beautiful. Hope they run as good as they look!