Russ95Z28

Quick history: 8 years and 50,000 miles ago I put a cc305 cam in my 95 Z28. Engine now has 140k on it. At the time I put in LT4 springs and used the stock 1.5 rockers due to budget constraints. I chose this cam because I wanted something with a power band under 6000. I do not rev it over 6100. Heads are stock. Now I’ve decided to finish that project and install full roller rockers. So far I’ve purchased a set of PAC1218 springs and comp retainers, 7 degree. The installed height will likely be stock which I think is 1.780. That leaves me with 3 choices as I see it:

1. Comp Ultra Pro Mag 1.6 SA (either 3/8 or 7/16 stud)
2. Scorpion 1.65 non-SA (either 3/8 or 7/16 stud)
3. Comp Ultra Pro Mag 1.7 or Scorpion non-SA (either 3/8 or 7/16 stud)

The 1.6 SA are the easiest of course, but I’m debating if a little additional lift and associated gains from the 1.65 or 1.7 will be worth $150 or so for guide plates and pushrods. Also unsure if the 1.7 with .578 lift would reduce the lifespan of the springs. I know the lobes on the 305 are very mild compared to newer XE designs but I’m not sure how that plays into rocker arm choice. Let me know your thoughts.

KW Baraka

The Scorpion rockers ain't even in the same league as the Ultra pro-Mags .....

If it were my car, I'd get the 1.6 CC Ultras.....self aligned.....for stock (3/8") studs.

You'll be able to use mild springs with those rockers (the Pac-1218 beehives will do nicely), no stud change requirements, won't even have to get a fresh PCM tune.....although doing so wouldn't hurt .

Going with higher than 1.6 ratio rockers with stock heads will certainly result in no benefit....given the flow limitations of the stock heads once you get into the .550" range.

Best of luck

KW

Bersaglieri

I'm simply not a fan of beehive springs. They'll probably live an easy life on CC305 lobes, but the failures I've seen over the years have turned me off to them. The only time I've used them was because of a spring pocket limitation where a double spring could not be used. Spring wear isn't based solely on lift; lobe design, spring material, spring design, RPM, and many other factors effect spring life. Make sure you have tediously installed, measured and calculated those springs, improper install height is a contributing factor to their failure as well as valve float in many setups. Remember the installed heights can vary valve to valve, the valve pockets aren't all the same depth.

That being said the CC305 can isn't the worst cam, but your right those lobes are pretty tame compared to the newer HR cam technology. One of my biggest issues with the CC305 is many were ground on a 114LSA. If you've got one of those their is definite room for improvement with a different cam, without revving too high for power.

Increasing rocker arm ratio will increase lift at the valve, but, without getting too technical, it will effectively increase the aggressiveness of the cam lobe at the valve as well. If you plan on running that cam for a long period of time I say get as much lift as you can out of it, that's the only way to overcome it's handicaps. I've run 1.65 ratio rockers on a few smaller cams to give them a little bump. In this case I'll disagree with Baraka and claim there will be results with more lift. You'll also be setup for ported head in the next evolution of the motor. Only down fall is if you run a modern HR lobe later, they usually have alot of lift at the lobe and 1.65 or 1.7 rocker may give you more than you want.

I always like extra security in the motor and that's what guide plates and 7/16 rocker studs can provide. They're is a decent chance you might need a pushrod change with the rocker swap anyways.

Injuneer

Depends on the head characteristics. I thing the stock heads will stall above 0.55 lift and actually flow less with more lift.

Bersaglieri

Think it would wash out gain from the added duration and valve movement?

Injuneer

Depends how bad they stall. I haven't seen a table of stock head flows in years. Gain at the bottom, lose at the top... who knows.

Russ95Z28

I did a search for stock flow numbers and found a variety of information but all had a common trend for the .500 and .600 cfm. They were either the same or within 1 or 2 cfm of each other. The link below has numbers for .500 and .550, the .550 being only 2cfm lower than .500.

LT1 vs LT4 vs LS1 stock vs ported head flow

So it seems as though there is no additional flow but it does not drop off very much either. Although not the greatest cam, the cc305 is sufficient for my needs. I’m leaning toward the Ultra Mag 1.7s to get .578 lift. The only other mod I can see doing down the road would be mild ported heads and the additional lift would be more beneficial.