Mighty Whitey

here lately I've noticed quite a few cars-regardless of camshaft- have been peaking quite a bit higher in the RPM range when running stock-ratio rockers (1.5:1).

I'm beginning to think the 1.6's on my car are somewhat hindering it's top-end performance. my dyno-graphs seem to slope off rather quickly when cranked beyond 6300 or 6400 RPM.

my valvetrain consists of this: comp 503, stock lifters, comp welded pushrods, SA 1.6:1 pro-mags, Comp 918's, 787-16 retainers, 601-16 locks. stock studs.

my car peaks HP at 5780RPM and is totally out of breath at 6400. 6500, and the car just seems to nose-down.

is there a possibilty that the ramp-rates of the comp 503 (224*/230*, .503"/.510", 112LSA) are too fast to work properly with a 1.6:1 rocker ratio? if the loss of lift means I lose SOME low-end grunt, but gain top-end power, it is well worth it. when crossing the line at 6500rpm in 4th, it's definately running out of breath- and fast!

my friend bluecat is purchasing a dynojet 224 dyno on saturday, so I guess I'll 100% know for sure.

anyone else pondered about this? or noticed any similar trend? if so I guess the truck is getting a set of comp pro-mags, and the car is getting some shaft-mount 1.5's!

GIZMO

iTrader: (8)

How did you adjust your valves?

jmill96Z

iTrader: (3)

Sounds to me like they're floating like a boat.

Mighty Whitey

well... without trying to explain a long drawn out process, on TDC-compression of each cylinder, and preloaded the lifter roughly a 1/4 of a turn, roughly .010" preload.

I was thinking the same thing you are (I believe). in thinking that there could be too much preload on the lifter, and high rpm could be experiencing some valve "float" issues.

I'm not sure if it's the fact that the lifter can't stay on the lobe of the cam, (valve float) as it is the extreme ramp rate of the cam on 1.6's that actually collapses the plunger in the lifter, effectively killing off the lift/duration up top.
could this be possible? 6% more load is being put on the plunger or cup of the lifter when using 1.6 rockers over 1.5's.

I know I ran in to a problem with cheap Sealed Power lifters and the 918's- they bleed of horribly, made my car sound like a powerstroke when you started it (yeah, no exageration either!) my stock lifters currently have 90k miles on them could this be a problem?

GIZMO

iTrader: (8)

Your problem might actually be not enough pre-load. It might be worth experimenting with as much as one full turn (factory spec.). When I first started running Stock Eliminator I ran un-modified stock lifters at the factory spec. with zero failures (7000+ rpm).

Good Luck,

Daren

Mighty Whitey

I'll give that a try and see what happens. I know the less you pre-load, theoretically, the less space there is to "float" but I still think the factory set the pre-load at 3/4 to 1 turn for a reason...

Formula_LT1

iTrader: (2)

To add more to Mighty Whiteys theory, its not just his car that has this issue. It seems like all of the 1.6 roller rocker guys with aftermarket cams (all different cams) have the exact same issue. The same guy (bluecat as mentioned before) has tuned them all so it wouldn't be tune related.
They all seem to fall off at the exact same RPM no matter wht kind of setup? It seems to be a common trate that all of the guys in our area with aftermarket cams with stock 1.5 rockers ar twist them to 7k without a problem and still make pover above the 6300-6400 range?
But like Mighty Whitey said, Bluecat is picking up his new dyno as we speak, so very soon we may find out exactly what the common problem seems to be.