408 L92 valve float ? HELP
408 L92 valve float ? HELP I have a 2000 408 camaro and just freshened the engine with new cam comp 244/252 @ .050" with 1.7 rockers L92 intake and 1.8 exhaust LS7. Patriot dual extreme springs and the heads are WCH ported L92 with a ported carb intake and a 92mm TB and 4" exhaust just dynoed the car 468 rwhp TH350 and 4200 converter and ET street tires 28"x12.5.
The problem I have is at 6500RPM like clock work the hp and TQ drops about 30 each and it will not spin 7000RPM even. The power curve is straight up at 6500rpm and then straight down at 6600rpm
I am wondering if anyone has encountered this ? I am assuming its either the 1.8 exhaust rockers causing some kind of lifter problem or just plain valve float I have Ferrea 6000 valves both intake and exhaust Patriot says those should be enough spring I checked them on a remac spring tester when i got them they are all 158PSI @ 1.800" so I have no idea I have never encountered this it does not seem to break up like typical float so ??
The problem I have is at 6500RPM like clock work the hp and TQ drops about 30 each and it will not spin 7000RPM even. The power curve is straight up at 6500rpm and then straight down at 6600rpm
I am wondering if anyone has encountered this ? I am assuming its either the 1.8 exhaust rockers causing some kind of lifter problem or just plain valve float I have Ferrea 6000 valves both intake and exhaust Patriot says those should be enough spring I checked them on a remac spring tester when i got them they are all 158PSI @ 1.800" so I have no idea I have never encountered this it does not seem to break up like typical float so ??
Post up a dyno chart. You can usually see the characteristics of float on the chart. Not a big fan of the Patriots. I ran Comp 921's on my L92 setup shimmed to .050 and I run 1.7 YT Ultralights and .110 Trend PR's. For my new cam even the 921's weren't enough. I went with PAC 1521's...nitrited and good for .700 lift.
Last edited by WKMCD; Aug 12, 2008 at 06:14 AM.
The dyno graph does not look like typical valve float I know what your refering too... I have dynoed all 5 cars i built including 3 friends and 1 of them had float and you could see it in the chart fluctuating as it got higher RPM's. I compared it to my other cars and the pulls look identical unitl 6500 it drops like a rock. The car drives fine and at the track I have been shifting at 6500rpm instead of my normal 7100rpm to avoid problems. But it does seem to break up above 6800rpm on the top end it has done that 2 times more when the car is hotter so I am assuming the springs are hotter and that effects them Im sure especially duals with no dampner. I know the patriots have horrible harmonic problems too. I am searching for a spring package now to switch too I dont see any comps with what seems enough pressure ? maybe PAC 1518's ? it has .630 lift so that limits the springs available quite a bit.
Well when I built this engine I called 5 different places and all said the LS7 exhaust rockers would work ? so against my better judgment I am using them ? I know the LS7 has a 12 degree valve angle compared to the LS1 15 degree. I am changing the exhaust rockers and re dynoing tomorow to see what happens ?
Well when I built this engine I called 5 different places and all said the LS7 exhaust rockers would work ? so against my better judgment I am using them ? I know the LS7 has a 12 degree valve angle compared to the LS1 15 degree. I am changing the exhaust rockers and re dynoing tomorow to see what happens ?
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Decent power considering the drive train. Change all the LS7 rockers to proper L92 units. There is a significant geometry problem fitting the LS7 rockers to L92 heads. Arm lengths are very, very different. More than likely this is your issue.
BTW we sell a significant number of Patriot's Extreme dual spring assemblies and have not encountered a problem with any of them. I'm not sure what harmonic problem they have but we have seen them used with a wide variety of cams without valve train issues.
Good luck,
Richard
BTW we sell a significant number of Patriot's Extreme dual spring assemblies and have not encountered a problem with any of them. I'm not sure what harmonic problem they have but we have seen them used with a wide variety of cams without valve train issues.
Good luck,
Richard
You could try the LS3 hollow valves, those would take some mass out of the equation if valve float is your issue. Other than the higher ratio's, I don't see why you can't use LS7 on the exhaust only. I thought the L92 heads had pretty much the same exhaust valve and runner as all the other LS heads, but I could be wrong.
-Geoff
-Geoff
The L92's have 15* valve angles, the LS7 has 12*. That makes the distance from the center of the rocker fulcrum to the tip different. That is throwing off your geometry.
Thanks for all the help I just changed out the LS7 rockers today for the normal L92 rockers. I am back on the dyno friday. Also I only have .020" thou of lifter preload someone told me this could cause the same problems ? not enough preload will let the lifter pump up easier and cause Float ? and I should have more like .080"-.100" I thought less was better in high rpm application ?
I have the stock "L92" heads and stock rockers. Lifters are caddy. Springs are Lunati duals. Preload is .045. I have turned mine 7200 rpms with out any problems. Just from my exprience with my 4 engines before this one, I had some issue with valve bounce coming in at 6200-6400 rpms. I found that when I used shorter pushrods (less preload) it corrected my problems with valve bounce (real noticeable on 1-2 shift).
I ran thoes exact springs on my l92 heads (patriot golds), the dyno showed a nose dive at 6200 rpm I was reccommended by grannyshifting to use stronger springs, I believe they are close to 200 PSI on the seat. I havnt had it back on the dyno yet but she pulls hard all the way to the rev limit (6800RPM) in 3rd gear without letting up any.
I ran thoes exact springs on my l92 heads (patriot golds), the dyno showed a nose dive at 6200 rpm I was reccommended by grannyshifting to use stronger springs, I believe they are close to 200 PSI on the seat. I havnt had it back on the dyno yet but she pulls hard all the way to the rev limit (6800RPM) in 3rd gear without letting up any.
My preload is .020" I have been told maybe too little and letting the lifter pump up at high RPM ? I always thoutght less preload prevent that problem not too little ? The springs are patriot golds 130lbs @ 1.800" and 350 open @.1.20" all my other builds have been solid rollers with 200+ seat and 500-600 open so I have no idea on this new stuff ? I know ussually when valve float occurrs it will pop or backfire this doesnt do that ? I am going to switch the exhaust rockers from the LS7 to the regular L92 to see if that helps if not ? I am going to a stiffer spring, But the problem is I cannot find anything for the stock pockets with more pressure ? I want around 170 seat 1.80" and 450 open 1.20" My friend has the same setup with those springs and he shifts at 7200rpm and it still makes power up there on the dyno he peaks at 7000rpm.
If you have lift of .630 and you are using 1.8 exhaust rockers, then your actually having a lift of .667. As gas as I know unless you shim the springs you are overworking them. I have the same springs in my 427 stroker and a similar cam, 632/632 250/266 112lsa and I can rev up to 7500rpms and it's still pulling hard.