cam profile mod gains

[metcap]

for best performance whats the earliest intake cam timing opening before TDC and whats the latest exhaust closing?

[JadeEstevez]

I know nothing about the cam grinding process... but how do they make longer duration cams just by grinding a stock camshaft? Wouldn't you need more material to hold the valve open longer instead of grinding the material away? O__o

[JDM hachi]

From what I know, it involves, in a nut shell, "grinding the part opposite the cam shaft lobe to a smaller diameter". this allows you to alter the shape of the lobe. If it helps you visualise it: don't think of the cam as a certain size, rather think of it as a....??..um..??..ratio of ramps on a circular shaft.

matty.

[JadeEstevez]

Woah... You blew my mind! O___o

[andrew_mx83]

By taking meat off the base circle, and adjusting the lash to (effectively) bring the valve up higher the lobe of the cam and therefore your lift is now increased by how much was taken off the base circle.
With all this extra meat on the lobe you can now afford to grind some of this away to reshape the lobe and change the ramp rate and duration.
So you end up with more lift, and more duration which can both be customized to some degree by the cam grinder.

[JadeEstevez]

Oh. So basically are you just making the lobe 'pointier' then working that to a good usable cam lobe? O__o Sorry for the NOOB questions.

[andrew_mx83]

yeah pretty much. the key is that you bring the valve lifter higher up so the lash (clearance) still remains in spec, therefore the valve starts to open as soon as the lobe starts to ramp up.

[Celica RA45]

its also a shitter idea taking off base circle if its dohc motor as the shims might have to be 2mm thicker right through
its always better to buy a blank camshaft and then grind said profile to this

[JadeEstevez]

I didn't think you could get blank camshafts, let alone one for the 18R or 18RG.

[Celica RA45]

well then get them hard faced which is welding up the lobe and then redressing it back to a more desired cam ,might take 10 thou off the base circle ,much better than going from 2mm up to 4mm on the base circle .
it will cost more but worth it try clive cams for hard face he has 304 and 288 2tg and 18rg rally spec cam profiles

[JadeEstevez]

Welding more material on sounds risky though?

[Celica RA45]

not at all i get it done all of the time on my altezza cams as no 1 makes blanks for these ,yet

[JadeEstevez]

But it just sounds like it would be a weak point and the welded part would just break off from the amount of force the cam has to go through.

[metcap]

for best performance whats the earliest intake cam timing opening before TDC and whats the latest exhaust closing?

no one can help with some hard facts or educated guess?

[Celica RA45]

they use a material called starlite its harder than cast iron and works ok with the buckets as well.
on lobe centers hot cams 100 lobe center then try 105 then 110 for a slight warm cam

same with exhaust as well
but i need cams done at 50 thou duration to work the best set up