Anybody have the specs and/or PN on the GM valve springs used with the 3927140 "off road" camshaft. I think that these springs are sometimes referred to as the "Z28" springs.
Joe
Joe
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Re: Valve Springs
3927142: 110 lb @ 1.70", 358 lb/in, coil bind 1.16"
3911068: 80 lb @ 1.70", 267 lb/in, coil bind 1.15"
With proper setup the production 068 spring will rev to 7000-7200 with a OE mechanical lifter cam and about 6500 with OE hydraulic lifter cams. I recommend setting installed height to yield nominally .090" (.050" minimum) coil bind margin based on maximum computed valve lift at 1.44:1 actual peak rocker ratio.
"Z-28 spring" is a misnomer as all Z-28 engines were built with the 068 spring. The 142 spring was designed specifically for the 140 cam, but can be used to extend the rev range of production cams.
Always use the minimum force spring with attention to proper setup to achieve design revs. Greater spring force increases internal engine friction and increases the chance of excess lobe wear. The worst case is a high force spring and lots of low speed engine running time.
Duke -
Thanks Duke *NM*
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PS: Z-28 Misnomer
Right, kinda like "Kleenex" is tissues to many people. To my grandparents, and my father, the refrigerator was the "Frigidaire".
To a lot of folks from our parents/grandparents generations, the "machine" meant many things, generically, especially the sewing machine, washing machine, and vacuum cleaner.
There are a lot of people who, to this day, employ olde tyme language when speaking of common things. My favorite is Emeril. Ever the showman (and IMHO, a lousy cook, with no knife skills.........how the hell did he get to be called a "chef") who likes to use such terms as "ice box" and "tin foil".
On another Corvette forum, we referred to K.Y. Jelly as "Kentucky Jelly". But we won't go there, on this here forum.
JoeComment
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Re: PS: Z-28 Misnomer
Hey Joe,
When I was 16 and knew everything I dropped a #140 cam that I bought from a local racer into a 67 Camaro with a mostly stock 327, and 3.08 gears.
Man, that cam sounded fine rumbling through the parking lot at high school, everyone thought that Grumpy Jenkins was pulling in. I ended up with a car that was so slow it wouldn't fall off a bridge.
BLComment
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Re: PS: Z-28 Misnomer
Lordy, Bryan. Methinks that car would not have been very streetable ("slow") even with a set of 456's or even 488's installed. Just an educated guess, but I would think that that cam doesn't "come on" until about 4500RPM.
With your 308's it was definitely a dog. Yeah, it sure must've sounded nice though. Those mean sounding Duntov, 30-30, and LT1 cam designs were great in their day, but will get shut-down by most post 1984 Corvettes, good running 5 liter Mustangs and "tricked-out" rice burners.
Such old, 50 year old technology is quaint, but dated. Today's "fast action" camshafts (ie: hydraulic, or preferrably solid roller)should run circles around the best 50 year old camshaft design..........and be streetable at the same time.
JoeComment
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Yes, indeed.
Over the past 5 years or so, I have been messing around with short duration, high lift hydraulic cams for my BB engines. You may lose a few HP from about 4500 RPM up, but you gain so much in torque from idle to 4500 that on the street you can't beat it. The heads are SUPER important too, unfortunately the older castings flowed big numbers but the port velocity was low (ie: dog at low RPM) and the mixture motion was lacking (poor combustion efficiency).
If an engine only operates at 20% efficiency, boosting volumetric efficiency from 80% to 85% is a 6% improvement (ballpark guess) with a "racing cam". But improving combustion efficiency from 20% to 22% is a 10% improvement - by using a modern design factory head. The late 1990's Vortec heads are GREAT! For the BB, instead of 36 to 40 degrees ignition advance, you only need 28 to 30 degrees for max power (can you say increased combustion efficiency) .
MarkComment
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