[Jay S]

1980 TA that is Awesome!

No worries Pastry. If I wrote something wrong I would rather be called out on it than leaving it wrong.

[70GS455]

Originally Posted by Steve C.

In the past I had been told by the Crower tech department two different answers, rated at .005" tappet lift and .006" tappet lift.

So about two years ago I called Louis, reported to be the head cam designer at Crower on this subject. I asked at what tappet lift do they rate their hydraulic flat tappet cams at..... in essence he said it did not matter and suggested not much happens regarding air flow until above 1000 rpm or so anyway and then gave an explanation. And he further commented that it will vary with their different cams, they are not all the same. He actually asked, are you trying to use it for input into the "Wallace" program !

He asked what cam was I interested in, so for an example I mentioned the 60919. He looked up his master design profile numbers for it. He said that specific cam is designed at .005" tappet lift for 301 degrees duration. He further reported it has 139 degrees at 0.200" tappet lift. He said the most important are the .050" and .200" numbers. He further commented it could be as much as 306 degrees and 142 at .200 lift, and to be honest I did not fully understand his reason or I misunderstood on those numbers. So take that with a grain of salt here !

But in his detailed discussion he did confirm my comment that the amount of duration actually delivered at the valve under running conditions will vary. The hydraulic lifter gives under running conditions for a host of reasons... rpm, oil temperature, weight of oil, etc.

He confirmed the lobe lift is 0.3130", but when I asked about the lobe separation he stated it was 112 and not 113 as sometimes touted.

Don't shoot the messenger here... it was a lengthy conversation and this is in short and I hope I got it correct. I wish I had a transcript !

Also mentioned in the thread when we discussed this it was pointed out to keep in mind during manufacture the grinding wheel size will be a minor factor in the end result. Usually they are within 1 degree of design. Also the master pattern will be most accurate to a certain size core. Example, a Pontiac journal size is not the same as a small block Chevy. Many catalog specs are based on a Chevy size and the grinder has to take this into consideration.

.

From having degreed various cams in the past and looking at all sorts of numbers, the tappet is moving roughly 2 crank deg per thou at .006", on older non fast ramp profiles. So at 0.006, the 301 at 0.005 becomes approx 4 deg less or roughly 297 advertised.

Sent from my SM-T817V using Tapatalk

[LeighP]

I’d heard all the stories about the poor low torque of the 041 cam. I bought my 68 off my friend’s widow......has a 428 Manual with RAIV cam and 850 Holley.
It displayed the low torque at low RPM that is a hallmark of the RAIV. I decided to change the plugs as the car sat for some time after my friend’s death.
I replaced the NGK plugs with my preferred AC Delco plugs.......
Low and behold, I got easier starting, better cold idle and I also got a noticeable increase in low end torque.....the car will carry a higher gear through a corner than it used to. All together better to drive.
I certainly wouldn’t say the RAIV is a bad cam.

[77 TRASHCAN]

Originally Posted by LeighP

I’d heard all the stories about the poor low torque of the 041 cam. I bought my 68 off my friend’s widow......has a 428 Manual with RAIV cam and 850 Holley.
It displayed the low torque at low RPM that is a hallmark of the RAIV. I decided to change the plugs as the car sat for some time after my friend’s death.
I replaced the NGK plugs with my preferred AC Delco plugs.......
Low and behold, I got easier starting, better cold idle and I also got a noticeable increase in low end torque.....the car will carry a higher gear through a corner than it used to. All together better to drive.
I certainly wouldn’t say the RAIV is a bad cam.

455???