Stiffer springs in 243 heads with factory hollow stem valves?
12-06-2011, 11:44 AM
#1
Stiffer springs in 243 heads with factory hollow stem valves? The factory yellow springs have 90lbs seat pressure and are noted for 0.570" max lift. Are there any reliability issues with the factory hollow stem valves if you were to switch to say a stiffer spring such as the Comp 915 with a 105 lbs seat load and .600" max lift? I was thinking of setting up the engine with a fresh set of heads and either the GT2-3 cam (0.573"/0.578") or the factory '02-04 cam with 1.80 rockers (0.583"/0.579"). I am installing the Comp Ti retainers to help reduce the valve train mass as well.
TIA
TIA
Last edited by DeaconBlue; 12-08-2011 at 01:16 PM.
12-06-2011, 12:56 PM
#2
If those heads are off a 2002 or 2003, I'd recommend getting rid of those OEM yellow springs anyway as they are known to fail.
12-06-2011, 01:37 PM
#3
Okay I have a set of fresh Comp 918 springs with 125 lbs of seat pressure and I was thinking that those would be too much for the factory hollow stem valves (very thin 0.8mm walls). Since I am not going over 0.600" lift, I think I will just drop down to the 915 springs to be on the safe side.
12-06-2011, 04:40 PM
#5
Okay I have a set of fresh Comp 918 springs with 125 lbs of seat pressure and I was thinking that those would be too much for the factory hollow stem valves (very thin 0.8mm walls). Since I am not going over 0.600" lift, I think I will just drop down to the 915 springs to be on the safe side.
12-06-2011, 04:53 PM
#6
Ive seen 918s, with hollow stems run 8500rpm on the Spintron on a .620+ lift cam. Its a good combo, just add a set of pushrods.
Although thats with 1.7 stock rockers, aftermarket rockers are nose heavy and can cause valvetrain instability. Id stock with the stock rockers w/ the Comp trunion upgrade
Although thats with 1.7 stock rockers, aftermarket rockers are nose heavy and can cause valvetrain instability. Id stock with the stock rockers w/ the Comp trunion upgrade
12-07-2011, 12:21 PM
#7
The 12564824 heads came in today - the last two new in the box '02-04 Z06 LS6 heads that were in the GMPP network. Date on the box is Jan '06. They are fitted with the LS2 orange 12586484 springs, not the earlier LS6 yellow 12565313 springs.
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12-07-2011, 03:49 PM
#8
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12-07-2011, 09:09 PM
#13
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The factory yellow springs have 90lbs seat pressure and are noted for 0.570" max lift. Are there any reliability issues with the factory hollow stem valves if you were to switch to say a stiffer spring such as the Comp 915 with a 105 lbs seat load and .600" max lift? I was thinking of setting up the engine with a fresh set of heads and either the GT2-3 cam (0.573"/0.578") or the factory '02-04 cam with 1.80 rockers (0.583"/0.589"). I am installing the Comp Ti retainers to help reduce the valve train mass as well.
TIA
TIA
12-08-2011, 12:10 AM
#15
Ive seen 918s, with hollow stems run 8500rpm on the Spintron on a .620+ lift cam. Its a good combo, just add a set of pushrods.
Although thats with 1.7 stock rockers, aftermarket rockers are nose heavy and can cause valvetrain instability. Id stock with the stock rockers w/ the Comp trunion upgrade
Although thats with 1.7 stock rockers, aftermarket rockers are nose heavy and can cause valvetrain instability. Id stock with the stock rockers w/ the Comp trunion upgrade
8500 RPM...That's awesome. Did the engine use .105" wall pushrods, stock walled hardened pushrods, or other?
12-08-2011, 01:16 PM
#16
Well that is sort of what I am looking for, the shorter duration and wide lube separation of the stock cams, but with more lift. Plus I would have to do the trunion upgrade to the stock rocker anyways. When I priced out my options the best deal for me was the '02-4 LS6 cam with the 1.80 rockers. I would have loved to do the GT2-3 cam with the trunion upgraded stock 1.70 rockers. The numbers are fairly close. Plus this engine is going into an older street car and I where live we have the chassis dyno emissions testing to deal with.
12-08-2011, 01:30 PM
#18
Well that is sort of what I am looking for, the shorter duration and wide lube separation of the stock cams, but with more lift. Plus I would have to do the trunion upgrade to the stock rocker anyways. When I priced out my options the best deal for me was the '02-4 LS6 cam with the 1.80 rockers. I would have loved to do the GT2-3 cam with the trunion upgraded stock 1.70 rockers. The numbers are fairly close. Plus this engine is going into an older street car and I where live we have the chassis dyno emissions testing to deal with.
OK, that works, LS6 Cam + 1.8 rockers. Just be sure to get centered valve wipe pattern from the proper pushrod length. Hate to see you not get everything out of the hollow stem valves though. They're really good for high RPM...larger cams that make power through higher RPM's.
12-08-2011, 04:51 PM
#19
The pre-load on the PAC springs gives them the higher closed seat (installed height) force.
12-08-2011, 05:06 PM
#20
If you are looking at numbers, then you would prob want to check your installed height then make your calculations from there. All those places have the lb per inch layed out afaik or at least a calculation for you to use.
