I've been wanting to cam my LT4 for a while now, and finally have all the details ironed out. It will take place over this Christmas break, and here are my current mods:

-LT headers
-RT cats
-Corsa exhaust
-k&n cut filter lid


And here is what I'm doing:

-CNC ported LT4 heads and intake purchased from forum member, with springs and valves
-Transfer my pushrods and rocker arms from my stock heads over to the new ones
-Comp Cams 503 cam
-new GM Opti since I'll be in there anyway. I haven't heard good enough things about the MSD unit to warrant the price differential.
-Meziere electric WP
-All associated little parts


Whadya think?

 

Should scream. LT4 heads are capable of a lot. Just hope it's a good port job and not a bubba job.

You'll love the electric water pump.

Do you know the specs on that cam?

 

Nathan!

Nice seeing you back on the forum!

 

Nice to see you back.

 

I had to post a football question over on OT. Figured I'd jump in and see how many fights I could get into.

 

hey Nathan! Your website was definitely one of the first I read when learning about the LT-motors. Very informative.

The CC503 specs are:

Duration@0.50: 224/230*
Valve lift: 0.503/0.51
overlap: 112*

http://www.compcams.com/Cam_Specs/Ca...csid=1107&sb=2

Basically, a little bigger than the HotCam. I've heard it doesn't lose anything on the bottom end, but makes as much as 30hp on the top (compared to the HotCam).

I'm hoping the port job is good. The guy I'm buying from says his combo, with a slightly different cam, put down 408rwhp.

 

I'd run 1.6 rockers for sure and go with 110lsa version for more power and still have decent idle. That should make a good bit of power over LT4 hotcam but the hotcam isnt that far behind most cc503 cam combos i've seen. The tighter lsa will help boost midrange to upper rpm torque/power over the hotcam. LT motors seem to love tigher LSA's

 

What are LSA's? The stock rockers on the LT4 are Crane 1.6 roller-rockers, so I'm good there.

 

lsa = lobe seperation angle. 503 cam is 112, i think 110 would fit a LT motor better but both are good stuff

 

A tighter lsa would help top-end? I would think just the opposite; tighter lsa = better low-end torque, but doesnt provide the scavenging effect needed to fill the cylinders at upper rpms. Hmm. I'll look into it.

 

no sheet...I had to look at the date on the post.

 

well tighter lsa is said to help low end but in reality it shouldnt as i will explain. But it will help at higher rpms more so because tighter lsa has more overlap, meaning exhaust valve and intake valve are open at the same time longer than the same duration cam with a wider lsa.

overlap combined with duration is what really determines rpm range and where the motor will make power. Not just duration alone. More overlap means it will support higher rpms and suffer on the low end
Higher rpms, the timing events are happening sooo fast that you need to keep valves open a touch longer to help draw in more air and expel air out the exhaust. higher rpms have fast piston speeds and thus faster opening/closing rates on the valves. So in order to get air in and out of the cylinder the valves have to be open at the same time to allow enough time for new intake air to get in and old exhaust gas to get out

Low end suffers because with lower rpm, the timing events are happening slower because slower rpm means slower piston speeds and thus slower valve open/close rates. When you keep valves open longer, cylinder pressure bleeds off since exhaust valve is open longer than what is optimal.

Same applies with duration since duration has an influence on overlap. More duration, longer valve is open, more air gets in, more air gets out.

That is why large cams hurt low end and small cams hurt top end, not just because of duration but the overlap from how the LSA is setup. Small duration wider lsa is less overlap so more cylinder pressure at low rpms, meaning great low end power. vice versus for larger duration/tighter lsa



You can have a smaller duration cam and make it act "larger" than what it shows on paper because you can tighten lsa up to make overlap the same as a larger duration cam.

Thats why custom grinds like some LE2 or similar for instance is claiming to make more power than 'similar' off shelf grinds like cc306 all the while making more power in the midrange with alittle less duration.

The duration on the LE2 is usually around 230 intake/234 exhaust but it will vary from cam to cam from what i've seen. A older version i have seen is around 230/234. Advertised duration at .006 (something around 280-282 intake/284-286 exhaust) is less than the CC306 (290/306) but same duration on intake lobe at .050". LE2 lobes are more aggressive ramp rate meaning valve opens higher in less time/degrees rotation. LE2 is on a tight 107-109 lsa depending on version usually. cc306 is on a 112 lsa

So what we have in the end is the LE2 cam making 68-70 degrees overlap total, and 18 degrees at .050". CC306 is larger at 74.5 degree total and like 13.5 at .050"

So the LE2 even with less advertised duration is still able to keep total overlap up near the cc306 due to the tight LSA, but the big thing is it has more overlap at .050 than the larger duration cc306. This will further help boost top end performance all the while keeping the bottom end strong.
So what they did was improve top end over CC306 without increasing duration at .050". The less advertised duration for more aggressive ramps was able to keep mid/low range torque/power up and has shown to make more power than the cc306. Less duration split of the LE2 as well helps boost that low end. Even tho the cc306 has less .050" overlap, its larger exhaust duration bleeds off low end. The smaller 234 degree lobe on the LE2 will keep that pressure up so low end comes up.

Thats why custom grinds are nice to invest in. They can accomplish everything with little sacrifices everywhere else.

For some of those reasons i like the 110 lsa over the 112 so you can really feed that LT4 up top where those heads WANT to go, yet you dont increase duration too much so low end is still there.

But then again i dont know how much there is to gain from 2 degree tighter lsa. overlap goes from 54 / 3 to 58 / 7 at .006/.050. 4 degrees could really help make some good stuff up top. For comparison, comp's 230/236 on a 112, the next size up is 59/9, so the 224/230 on a 110 is inbetween those cams.

 

You might want to consider optimizing the lift to your heads. I gained 17 RWHP and torque clean across the board by going with 1.7 ratio rockers over 1.6's on my Hot Cam combo.

LT4 heads flow better across the board, but what's the point of having a head that flows killer at .600 lift if your cam only goes to .500? A higher rocker ratio will get the valves open quicker, effectively to any given lift at a shorter period of time. This will maximize the "area under the curve" if you will.

 

good solid info there Orr89rocz, i agree....and i also agree with Nathan's reply considering lift....that's why custom cams are so much better...one thing to consider too is once the cam gets more aggressive you really need to ditch the stock LT4 rockers and pushrods, and choose good valvesprings and (to a lesser extent) lifters

also, don't forget to budget for a timing set, gaskets, fluids, and tuning