gmnhra

just in from rudy at gt perf...
the cause of the wierd boost readings appears to be a broken crane roller lifter (an exhaust, which would explain some back pressure) ....of course it took the cam out with it but at least there is a mechanical explanation to the wierd behavior....

thanks for everyones input

gary

FindMe

And you couldn't feel it in the boat, or accelerating? That's a good explanation concerning the added backpressure... one I will put in the ol woops-it file and never forget. I guess if any of my motors broke things like that, I would have seen it before, so I best knock on wood cause I must be lucky as hell... CDF12 nailed it, good job! On a side note, I have had nothing but trouble with Crane cams and lifters (rollers and flat tappet) and will not install them in a motor for anyone... if thats what they want and demand it>>> SEE YA. It doesn't take many of those types of profit losses to get my attention. Kinda funny though, because I have never had a failure with a Crane Gold roller rocker, and recommend them.... go figure. Talk about confusing customers...lol Best of luck to you, and thanks to all of you, for the valuable lesson I learned on this one. Seems like it's always something, but I have to learn something every day... so does this mean I can go drink Beer now? lol

CFD12

Thats exactly what happened to me. 2 broken lifters and a cam on its way out. We didn't notice the lack of power because the blower was just installed (found the weak link) When the same rocker arm came loose twice we knew what was going on. On a side note my motor has high hours.

blown formula

For FindMe:

On carb versions of PC's the vacuum/boost gauge is plumbed into the "box" containing the carb. The Pc is a blow thru system as opposeed to a "pull-thru" system. The PC uses a pressurized /blow thru carb. It does produce vacuum at midrange. Boost is only reached in the upper rpm/throttle opening range where maximum power is wanted......maybe that's why PC's don't stress outdrives as much as the positive displacement types as maximum boost is made AFTER the boat is on plane not during "lift-off" getting there!!
The EFI version also shows vacuum in midrange, the wider the throttle the less vacuum (or more boost) is indicated. The gauge is plumbed into the intake plenum.
I have used both types and I actually prefer the carb version for several reasons.....