Project LSZ: Building Heads

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Update by Tom Suddard to the Nissan 350Z project car
Mar 19, 2018

We’ve been down this road once before: We ordered a set of 799-code heads from eBay, but they were cracked when they arrived. Our early LS1 still needed a better set of heads.

Fortunately, the world still has physical swap meets. While walking around the Daytona Beach Turkey Rod Run, we spotted the perfect heads: 243-code heads, which would have originally come on 2001 or newer LS2 and LS6 engines. They have larger intake and exhaust runners and a smaller chamber, meaning more compression and better airflow. The price? Just $300, though we had to carry them about a mile back to the car. Worth it! They were crack-free and in good shape, but we decided to replace the valves anyway. LS6 heads have hollow-stem intake valves and sodium-filled exhaust valves, and they have a bit of a reputation for breaking. Is that deserved? We couldn’t quite discern whether that was internet rumor or a real risk, but we weren’t willing to leave it up to chance.

We ordered a set of OEM-sized Manley valves from Summit Racing, then lapped them in by hand. The original valve guides were in great shape, so we reused them. After a thorough cleaning, we assembled the heads with the Manley heads, Fel-Pro seals, and new springs, seats, and retainers from Crane Cams. The valve springs were matched to our cam and rockers, ensuring our valvetrain would be able to handle our cam’s higher lift.

Then, we tried to put it all together: oops! We’re using 1.8:1 ratio rocker arms from Scorpion Racing Products. Compared to the OEM LS1 rocker arms (ratio 1.7:1), these lift the valves higher. That’s not as critical as it once was, since our 243-code heads flow so well compared to a vintage small-block Chevy head (260 CFM according to our research), but every little bit helps. To change the ratio, aftermarket rocker arms move the pushrod closer to the pivot, since the valves can’t be moved without custom heads. Why does this matter? In order for our newly-inboard pushrods to clear their openings in the heads, we needed to enlarge the holes slightly.

So, we took the heads back apart. And, after a few minutes with a die-grinder, we had plenty of room for our pushrods. After a thorough cleaning and another new set of Fel-Pro valve stem seals, we finally had a set of heads for our LS1.

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View comments on the GRM forums
deaconblue New Reader
3/20/18 9:50 a.m.

The beauty of the 1.80:1 roller rockers is that not only are they stronger than the factory, plus you do not have to install the Comp trunion upgrade kit #13702, but they allow you to run a "smaller" camshaft like the stock '02-04 LS6 camshaft and get some very nice gains. Keep in mind that the 1.80:1 ratio adds about 2 degrees to the duration numbers compared to the 1.70 rocker as well as boosts the lift numbers while maintaining the wide LSA. The net sum is a cam that works better at higher RPM, extend the excellent torque curve and keeps most of the low end grunt. There are stock '02-04 LS6 out there with nothing more than long tube headers, high flow catted X-pipe and 1.80 rockers that make 385 rwHP and 380 ft-lbs of torque in C5 Z06. True it will not have any cool sounding lumpy idle or peaky top end scream, but it may yield more area under the torque curve with can help eliminate a shift or two during a lap which is way more important.

I know you are using Crane parts and we used Comp parts in our LS engine but here is what we did. Most folks tend to be a bit conservative and run shifter springs due to issues they have had with the factory Blue '01 LS6 and Yellow '02-05 LS6 springs. With the net lift numbers approaching 0.600" I would recommend setting up to the Comp #29618 springs with 125 lbs seat load @ 1.800" install height. I personally run the Comp #26926 dual spring with my cam which has well over 0.600" lift and I used Comp 7 degree tool Ti locks #779, as they are lighter than factory of after market steel locks.  The Manley valves can handle the higher spring seat pressures better than the more delicate light weight factory LS6 valves, so that was a smart choice. Also remember that those light weight factory valves were only found in 243 heads that were installed on LS6 engines in the '02-04 C5 Z06. The 243 castings with the light weight valve and Yellow springs had they own assembly number from GM #12564824.  All the other 243 heads on LS6 engines that were installed in the GTO and CTS-V as well as on the LS2 engines did not use the light weight valves.

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