reground cam - making sense of the specs quoted

[gb500]

i had my 200ci six cam reground here in australia.

now the cam specs listed for the grind are :

260deg adv, inlet 20 BTDC /60 ABDC ,203deg @50 ,valve lift 0.412
260deg adv exhaust 65deg BBDC/15 ATDC 203 deg @50,lvalve lift 0.412


now i have the cam back and it came with a check sheet of the lobes ie inlet 1 and exhaust 1 as ground

now i can understand that a regrind may be slighty out:

but the spec check sheet has :at 0 valve lash/clearance

inlet
no figures for 0 lift
at 006 lift = 263.55 deg duration
at 0.10 lift = 254.62 deg
@0.050 = 213 deg

exhaust
no figures for 0 lift
at 0.006 lift = 264.66 deg duration
at 0.010 lift = 254 .77 deg duration
@0.050 lift = 212.9 deg

so it seems it has an extra 10 deg duration at 0.050 over advertised and an extra 4 deg at 0.006 lift.


my question is : hyd lifter must have some 'give /compression' each time they open close as the little ball shuttles back and forth in them - any body got any idea what this give would be ? new hyd liftres supplied are sealed power HT900 ( need to check they are the identical as to whats allready there)

0 thou ( cant believe that)
4 thou ?
6 thou?
8 thou ?


if its 0 thou then my adv duration is even more than 260 deg.

if its between 0.006 and 0.010' the the cam duration is approx at 260 deg.

easy to understand with solid lifters as the lash/clearance is mechanically set and can be taken off

or is it just not an accurate cam grind ?

enquiring minds want to know

at the end of the day i will put it in and drive it cause the motor cost $50 for some thing that had been rebuilt by ford of australia.- probably 25 odd years ago - but has sat in a disused car for all that time- still has the hone marks on the bores

brett
melb

 

[gb500]

sorry noticed a typo:

no figures for 0 lift
at 006 lift = 263.55 deg duration
at 0.010 lift = 254.62 deg
@0.050 = 213 deg

 

[Lazy JW]

....


if its 0 thou then my adv duration is even more than 260 deg....

Yup. Sort of. When you dial in the cam (you do intend to do this? ) you will see the lifter start to rise long before the "advertised" numbers. That is what is called the "ramp" of the cam; it gently starts to open the valve rather than slamming things open/shut. The same thing happens on closing.

This sounds like it will be a nice street cam.
Have fun,
Joe

 

[gb500]

yep sure will dial in the cam- got my dial guage all ready!

my understanding of the ramp was as you say ,to gently start the lifter moving ,- but i understood that this also took up the lash.until you got to the adv duration

brett

 

[Lazy JW]

Not with a hydraulic cam; they keep the lash at zero all the time (theoretically). They do "flex" up and down a bit inside, losing a bit of motion in the process, but all in all they are a good thing for the street.
Joe

 

[gb500]

wow - solved

moral of the story is
' always double check (and check again) with vendor'!

turns out he has 'included' wrong sheet with the cam- no wonder it didnt make sense- but assures me the grind is what i asked for!

he will send in the 'correct ' sheet



and here he had me thinking i was a bit hazy in my understanding the world of cams and specs

hmmmmm

brett
melb