Degree a cam/cam swap

FiatFunk

FiatFunk

True Classic
Hey gang, so I might be getting dumber over time or just forgetful.
I'm having trouble remembering how to degree a cam. I've taken my sweet time getting this car back together and I can't quite remember how I did it on this engine I just installed.
Reason for the change is that I believe the cam I built it up with will not have adequate duration for the high compression I have. CR is 11.3:1 and I currently have Vicks SOHC 2 in place,
Valve Timing – 37-71
Degrees Duration – 290
Lift MM – 10.5
Degrees Overlap – 74

I think I'll have detonation problems with that cam, so I'm wanting to put their SOHC 3 in.
Valve Timing – 40-85
Degrees Duration – 305
Lift MM – 10.4
Degrees Overlap – 80

I should set TDC on the flywheel according to the mark, and then using this online calculator (screenshot below) I understand intake full lift to be at 112.5° Am I right? I remember it being very simple, as the only other time I've done this it was on a twin cam, more complex but I got it right, although I had more cam info than I do here.
So I back the pistons down the holes a little, take off the belt, then the cambox, swap the cams, use the dti gauge on the bucket to establish and mark full lift, and reassemble, setting full lift at 112.5° (half way between opening and closing)

Sounds right?
 

Attachments

  • Screenshot_20240322-083035.png
    Screenshot_20240322-083035.png
    241.6 KB · Views: 25
From the Guy Croft web page circa 2003.. Example is done on the twin cam, near identical applies to the single cam.. sans-one cam or the "other cam lobe" is fixed on a single cam.

Given this cam is supplied by Vicks, call then to verify the "designed" cam overlap/timing. Keep in mind, two crank rotations per single rotation of the cam. Set/mark the cam timing at the cam relative to the cam housing. This is one of the lesser appreciated aspects of the Lampredi SOHC & TC engine design, cam timing can be done direct on the cam off the block. The advantage is not small.
Guy Croft_Cam timing-1.jpg


Guy Croft timing-2.jpg


Guy Croft cam timing-3.jpg



Bernice
 
Last edited:
Rupunzell said:
From the Guy Croft web page circa 2003.. Example is done on the twin cam, near identical applies to the single cam.. sans-one cam or the "other cam lobe" is fixed on a single cam.

Given this cam is supplied by Vicks, call then to verify the "designed" cam overlap/timing. Keep in mind, two crank rotations per single rotation of the cam. Set/mark the cam timing at the cam relative to the cam housing. This is one of the lesser appreciated aspects of the Lampredi SOHC & TC engine design, cam timing can be done direct on the cam off the block. The advantage is not small.
View attachment 82813

View attachment 82814

View attachment 82815


Bernice
Click to expand...
Thanks, I did mark the current cam to journal position at FL as Croft suggests. I remember Croft says you can install the SOHC cam using only FL but better to use LATDC as well. I'll be working on that later today, so will post with pics then.
 
FiatFunk said:
I will probably be wanting larger carbs right away, but it should work I think?
Click to expand...
36 DCNF... 36mm throat diameter, does not indicate the Venturi diameter or aux Venturi size. All three is dependent on engine RPM power band range. Larger is not better, choice is dependent on cams used, compression, individual cylinder displacement, RPM power band and more..

Basic bore / Venturi size selection chart ( 4 cylinder engines exampled) per individual bore/cylinder.
Bore to venturi ratio of 1.25 is good.
Weber DCOE choke size graph.jpg




Will 36mm DCNFs work, yes, might not be ideal for the needs/goals.


Bernice
 
You must log in or register to reply here.
Back
Top