GrannySShifting

iTrader: (10)

Trying to figure out what the limits are of the intake and exhaust valve clearences. ANyone ever sliced a head in half and seen at what point the valves actualy come in clearence issues with the piston?

Fireball

iTrader: (21)

Jason @ Thunder told me it happens ~ 8* after TDC for the intake (or 8* before for the exhaust)

as for specs...

161.8* @ .200 (cam lift)

Cam doesn't reach .400 lift

racer7088

Jason is right. Most cam's are closest around 10 degrees plus or minus a little from TDC. You would check the exhaust 10 degrees BEFORE TDC and the intake 10 degrees AFTER TDC to really be sure with the timing chain slack taken out and real springs on. With checking springs you will have less than you will really have and on some deals the intake will have a little more anyway because of the lifter plunger sinking a teeny bit when the lifter hits the ramp buy don't bet on that. The exhaust is likely to hit at extreme speeds too as the pistons is chasing it closed and it bounces on the seat whereas the intake valve chases or opens into the piston. Another words you can run a little less on intake than exhaust usually but the heavier intake may actually float first depending on the lobes. You just have to test if you don't have a spintron.

distortion_69

iTrader: (20)

I'm curious to know as well.. obviously the cam doesn't reach .400 lift, but the valve does.. I'm curious to know what the duration figure is at .400 as well. Is there a calculator with the specs on my cam sheet to calculate what mine is?

Thanks,
Josh

racer7088

Well divide your valve lift by the rocker ratio to see what lobe lift equals .400 valve lift. Like .400 / 1.7 = .235 lobe lift and see what your duration at .235 lobe lift it by degreeing it there.

distortion_69

iTrader: (20)

Yeah, obviously I can see where the cam is by dividing by the rocker arm ratio.. I was just hoping there was an easier way to tell the actual duration numbers. No worries I guess I already really knew it'd require more than an opening and closing point to determine what it is at certain points in the rotation. That being said, are there any write ups for doing this, and if there is I'll go ahead and take a little bit to do one that I'm installing in 2 weeks just for my personal curiosity I donno if posting the results would be a good idea But it'd be interesting to compare cam motions lobes to some of the more popular xe-r cams. Probably not that big of a deal, but the newbie in me is curious.

Thanks,
Josh

GrannySShifting

iTrader: (10)

yes yes yes, im retarded, lobe will never fit a .400 cma lift in stock bottom end lol

So, say at a 108 installed centerline a 240ish duration intake lobe, whereabouts on cam lift would 8-10 degrees ATDC be? The piston is opening as the intake valve is opening so given stock rod length, stroke etc 8 ATDC is what in cam degrees? Or where you talking about 8 ATDC in cam degrees not crank degrees? Its the simple stuff that screws my mind all up lol. point of this is, if its hitting on the opening and closing flanks of the lobe around .50-.200 cam lift, you can run larger area up top, with slower off the seat timing for more p/v, and more stable at hi rpm

Heres a hypothetical 288/236/162 duration at .006/.050/.200, vs a 289/240/162 which would have more intake valve clearence installed on the same int. centerline. Obviosuly the first 288/236/162 have the same or better. Now which would have more the latter, or a 289/240/157, as a general?

I run slow(er) exhaust lobes so I dont think there would be much bouncing on those