I'm building a 408 lq4 and am looking for a few suggestions on my setup. Its a fully forged bottom end with weiseco -3cc pistons bought from tsp, and assembled with all arp studs (already complete). I plan on going with gm cnc ls3 heads with hollow intake valves but will upgrade the springs with prc .650 double springs with titanium retainers. I will be going with an edelbrock victor jr intake with a 4 barrel throttle body retaining the fuel rails on the intake. I will be going with 1 7/8 full length headers and already have a full 3" exhaust with x-pipe and slp loudmouth 2 mufflers and tail pipes. The car is a 72 Chevy Nova setup for roadracing/street. The car sees more street but is driven very hard and the motor will be backed with a t56. The heads have a 68cc chamber so I think that comes out to about 11:1 compression ratio (help me if I'm wrong here). I'm hoping for a little over 500hp at the wheels but it needs to be usable, I'm not sure what cam I should be looking at or if I should go with a custom grind. Any help or thoughts are greatly appreciated since I do not have the top end completely finalized and I am currently deployed to Kuwait.

I sent this to tsp and they replied with a custom grind of 239/247 .624/.624 on a 113 degree+3 degree lsa. Wanted to see what your guys opinions are.

 

I'm not a cam expert by any means but I've done A LOT of reading lately as we're going to go H/C in our C5 this year. Call Martin @ Tick Performance. He is very much in the know on cams and is also extremely friendly and will listen to all of your needs. Lots of guys running quick out there with their cams.

Good luck!

Scott

 

I sent an email to Tick, hopefully they can figure something out

 

Here are my thoughts on this matter.

Single plane intake has a shorter intake runner length than a Fast, LS1, LS6, LS3, LS7 etc. etc. etc does. Air has mass to it. As port velocity increases in the intake runner, so does inertia. When mass gains inertia(momentum) it doesn't stop instantly. As the piston passes top dead center and travels down the bore on the intake stroke, velocity in the intake port increases. This is where cylinder fill begins.

Of course the piston has to come back up to TDC as well. This is called the compression stroke as this is where compression takes place. Cylinder fill still occurs on the compression stroke though.

Remember:

"An object in motion stays in motion until an equal or opposite force acts upon it."

You would think that as soon as the piston starts to travel back up the bore it would push that air mass in the cylinder back out immediately through the still open intake valve. Because that air mass has gained inertia(momentum) it does not. It continues to fill the cylinder even after the piston begins to travel upwards.

A longer runner manifold allows more length for air mass to gain momentum AND lose momentum. Because of that we can take advantage of cylinder fill later on the compression stroke than a short runner intake and make more top end power than if we closed the intake valve earlier.

With a short runner intake, air speed will decrease much sooner after the piston begins its path back to TDC. If you try to close the intake valve later like you would with a long runner intake (Fast/OEM intake) you actually push air mass back out the cylinder and you lose a lot of torque. This is why I close the intake valve much sooner with single plane intakes than long runner intakes. The short runner by its own design will make more top end by itself due to shifting the torque curve. There is no need to continue to attempt closing the intake valve that late with this style manifold.

Now on to I/E flow %.

When you have an intake to exhaust flow % that is low, the relationship of how air enters the engine and exhaust exits the engine changes from that of a cylinder head with a good intake to exhaust flow %.

I have tested many different theories on this. From little to no split, to lots of split. I will say that after nearly two years I have found that more split makes more power and runs faster at the track and on he street every single time. These are my findings. Others I'm sure will disagree. I am always open to learn, but I've tried it a couple different ways with the same results.

Physics are simple and this relates 100% to physics. Just like I discussed early about inertia and momentum and air having mass. It works in the same way with I/E flow %. You have the ability to cram more air mass in the cylinder than the exhaust port can exhaust at high rpm without giving that exhaust port more time to blow down and evacuate.

Some might say torque is lost by opening the exhaust valve too early, but I have yet to lose torque with LS3 heads by having large amounts of split. If you can't get spent exhaust gas out of the combustion chamber/cylinder and keep trying to cram more fresh air in with more intake duration and less exhaust duration you're just making the situation even worse.

Look at all the GM OEM square port cams and the GMPP square port cams. They have huge I/E duration splits. The COPO LS7 and 396 cams have HUGE amounts of split. I think with the amount of testing the general has at its disposal they wouldn't of chosen those grinds for no reason.

With all of that said and barring something unseen in your specs, here is what I'd spec:

235/250 .621/.595 110lsa

 

Thanks so much for the info!