Also your camera date is a year out of whack Every time I put my batteries in the charger i loose my date. So I turned off that function years ago.

I was just out running my 383 through the gears. Not a cloud in the sky and 50's. I right now using a custom Comp Cams SR with 236/242 112 installed the equivolant to 4 degree retarded. 1.65 in 1.6 E rockers @ 11.24 compression

73383 - I didn't remember that you were such an experienced a mech. That's why I ask those questions.

 

G

I don't consider myself an exper. mech, but I do know how to turn a wrench, I am a profesional body man. I grew up in a body shop and have been around cars all my life. I hotroded some in the late 60s when double hump heads, duntov cams, and chrome reverse wheels were the ****. I had a 67 vert in the late 70s. Then had kids and sold my toys. I'm now going through my second childhood. I now manage a bodyshop that works on European made mostly. My 73 has parts and pieces from, Porsche, BMW, and Mercedes in it somewhere. The coolest thing about this time around is the amount of aftermarket products out there to choose from.
Since I only learned how to post picks yesterday, here are some before, during, and after shots of my baby.

I don't think you are really ever finished with one of these

 

Motorhead

I found a compression ratio calc. on the keith black web site. It seems you made a mistake on data entry. Where you enter the intake closing figure it is the closing point at .050 lift plus 15 deg. This makes a huge diff. the number on the crane cam should have been 57 (42+15) versus 77 you entered, I tried to copy and paste but it would not come out, anyway on the crane came my static was 9.221, dynamic was 7.809. Still not great. I have not been able to find comp cams intake and closing numbers for .050 lift, I'll call them monday for that. But from this info I suspect my old 280h was between the 8.0 and 8.5 nimber.

cyl head 64cc
piston head 19cc dish
gasket .040
gasket bore 4.1
cyl bore 4.040
deck clearance .020
stroke 3.75
rod length 6.0
Intake Closing Point (degrees)
ABDC @ 0.050 lift plus 15 degrees 57

This gives me 9.22 static and 7.80 dynamic not 6.8


If you know where I can find the comp cam # at .050 lift let me know

 

I pulled the cam today and every thing looked good, all the wear paterns were where they should be. I checked the cam it was the correct one I even put the mic on it. The only problem it seems is I was getting a lot of reversion. All runners on the intake were black some worse than others. Below is the best pic I could get. Since I have only read about this problem and never seen it, if anyone has please chim in.

Dennis

 

The closing point they have is 15 degs after the .050" duration numbers. This is just a ballpark figure that most mild cams will be closed at. When you get into roller cams and higher performance cams the intake for the most part takes more than 15degs past .050" to close as you can see by the measurment @ 0.004" for your second cam, the roller cam here it is :

Cam Timing: TAPPET @.004
Lift: -----Opens ----------------Closes ----------ADV Duration
Intake ---35.0 BTDC -------77.0 ABDC ---292 °
Exhaust-- 83.0 BBDC ---------37.0 ----ATDC-------- --300 °

This is what 427Hotrod meant when he posted "I see similar .050 numbers on intake, but it's got 20* more advertised duration. That looks like a pretty lazy lobe for a roller to me...."
You could actually add 1 or 2 degrees because at .004" the valve is not closed yet making you DCR even lower than the 6.834 I calculated the first time.

 

If you are getting a lot of reversion you might want to change your rear gear to cruise in a higher RPM range.

 

Motorhead I am confused:
At the bottom of the crane cam card it gives the opening and closing points at .050 lift.
------------------------------------------------------
Cam Timing: TAPPET @.050
Lift: Opens Closes Max Lift Duration
Intake 8.0 BTDC 42.0 ABDC 107 230 °
Exhaust 56.0 BBDC 2.0 ATDC 117 238 °
-------------------------------------------------------

If this is not correct, the how do I figure the right numbers at .050 lift

Also does the above pic look like reversion to you.

Thanks
dennis

 

No that is correct, what is not correct is on the Keith Black website where it states you add 15 degrees to the .050" degree and the valve is closed.

The calculation .050" + 15 deg is not correct for your cam as you can clearly see by .004" numbers where it tells you the valve is still open and you are at 77 degrees now. To fully close it would be 78 - 79 degrees ABDC

Not sure if you are getting confused here by looking at the specs, it says intake closed but it is stil .050" open at this point.

And yes you have reversion in the intake, you have over 70 degrees of overlap ( intake and exhaust both open and piston is heading north ). That much overlap is ususally reserved for big solid roller cams, mine doesn't even have that much. This is what is meant by lazy ramps

 

Motorhead

Still confused, your calculator says the same thing at the bottom left corner. I tried to copy, but would'nt work. but it states

----------------------------------------------------------------
Intake Closing Point
(degrees)
ABDC@0.050 lift plus 15
degrees
--------------------------------------------------------------------
Am I reading this wrong, I see it as Intake closing a 42+15=57

I don't mean to be a pain, I just want to get it right this time.

Dennis

 

Ok here it is. Intake closing is usually given in terms of X number of degrees after bottom dead center. To make thing equal and easy to compare between cams a measurement of .050" was adopted in the cam manufacturing world. So you get for your roller cam 42 degrees ABDC. At this point your intake valve is not closed itis still open .050"

THe guys that wrote the DCR calculator know this but they also need to determine when the valve is actually closed to calculate dynamiccompression ratio. Since there is no way to accurately determine when the valve is actally closed on all cams from the .050" measurement they have given you an estiimated 15 degrees to add to your .050" meaurement so now the valve is supposed to be closed shut. Problem with this is that will only work on stock to mild cams. Bigger cams and roller cams will take much more than 15 degrees past the .050" to close.

That is one reason the cam manufacturer also gives you a .004" measurement. With this measurment you can more accuratley "see" the cam lobe profile as well as more accuratley detemine when the intake valve is completly closed. As you can see on your cam card the duration ABDC @ .004" is 77 degrees. This means the valve is still open ,004" at 77 degs past bottom dead center. To actually close the valve it will take another one or two degrees so the number you would put into the DCR calculator is 78 or 79 degrees.

So with this in mind how can it be shut at 42 + 15 = 57 Degs ?

Anyway this is how I see it, if you want to use their method of 15 degrees + .050" method then feel free. I could actually be wrong about this but I think I am right. I did not have a .050" measurement to use as it was not supplied on my card. Instead I had a .015" measurement and I wanted to use the DCR on the Silvolite site. So I assumed that they were looking for the duration at which the intake is closed and I after some calculations I determined I needed to add about 4-6 degrees after .015" spec. to get the valve closed. It gets worse with my solid roller I have a .018" lash adjustement that isn't even taken into consideration