Random Tech Questions

[Hot Pocket]

HP, I understand what you are looking for. You have a basic 'book learned' understanding of the workings in a combustion engine and you want to expand on that by being able to see how the parts truly interact with each other. While I agree it's good to have a solid knowledge base of what you are working on, until you get your hands dirty you will truly never understand.

How many of you that are telling him to go read more have ever laughed at somebody for being 'book smart' and not truly knowing how something works first hand?

@Sharpe

I'll take it next semester!! Thanks for the recommendation

[uglyota]

Hotpocket, two letters is all you need to know about camshafts. Repeat after me:
R
V
( freddy)
Seriously though, howstuffworks.com actually has a pretty solid body of information on how engines work. Search pushrod V8 or something. Doing a timing belt or chain job on a few different motors will force you to learn most of what you are asking. To get you off on the right foot, try to understand how the strokes on a 4-stroke engine work. Then understand how the crankshaft and camshaft work together to make the valves work. Then understand how the camshaft and distributor work together to add fire to the mix, then try to tie it all together and you'll have a better understanding than if you were to just take a motor apart or look at a pile of parts

[robertf03]

duration is the degrees from rise to fall, lift is the amount it goes up, seperation angle is the angle between intake and exhaust.

crankshaft spins twice as fast as cam, 2:1 ratio on the timing chain.

that should cover it all


sae meeting tonight at 7:30 if you think this really is your thing.

[uglyota]

Yo fleminarsky...I heard once that the numbers can only take you so far...it's the profile of the lobes that really matters. The dude was pretty renowned for building sweet yota cams, fwiw. Agree or disagree?

[robertf03]

like valve open dwell angle and duration? I agree, but you don't see those #s in jegs or summit. I think something that closes quicker than it opens would be best for sub 3500 rpm v8's, but the I haven't seen too many detailed discussons about this from the car world. Everyone assumes a symmetric lobe. Maybe its because crazy profiles are hard to do without roller lifters.

[tigweld]

duration at .050 lift is is what describes the ramp rate. super fast ramp rates really= high spring rates for pushrod central cam engines.

[robertf03]

duration at .050 lift is is what describes the ramp rate. super fast ramp rates really= high spring rates for pushrod central cam engines.

yeah but it still leaves out details. all that the duration tells you is when it starts and stops moving. these two profiles could have the same specs on paper, but would be used for very different RPM ranges since lift at .050 would start at roughly the same angle, but the duration at max lift would be different

[tigweld]

lobes have to be somewhat egg shaped or the lifters will get ripped out of the bores or the lifter will wear really fast. that is why .050 lift duration works for most people. flat tappet cams with over about 240 degrees at .050 go flat really easy because the ramp rate is to high for a flat lifter. a roller could probably do a weird shaped lobe like you have pictured but it would eat rollers because to get a spring rate that would hold the lifter on the lobe it would have to be really high. being able to control the rest of the valvetrain package's weight is the main reason you don't see really crazy lobes on lower performance cams.

[agjohn02]

have you never seen a roller cam lobe next to a flat tappet lobe? they are very different. the goal is to open and close the valve as quickly as possible with the type of lifter you are using. flem's drawing is exactly what the comparison is like between a roller and flat tappet camshaft.

[agjohn02]

hotpocket, i honestly learned most of what i know about engines from reading HOT ROD on the crapper in high school. its written in layman's terms and an excellent place to learn. get a subscription, its cheap.

[mudtoy67]

hotpocket, i honestly learned most of what i know about engines from reading HOT ROD on the crapper in high school. its written in layman's terms and an excellent place to learn. get a subscription, its cheap.

ED!!! GET IN HERE!!

[tigweld]

have you never seen a roller cam lobe next to a flat tappet lobe? they are very different. the goal is to open and close the valve as quickly as possible with the type of lifter you are using. flem's drawing is exactly what the comparison is like between a roller and flat tappet camshaft.

no flems drawings are not like a any lobe you will ever see. ive seen plenty of huge (.700+ valve lift) roller cams none had concave lobes. i have seen almost square lobes but no concave ones.

[agjohn02]

no flems drawings are not like a any lobe you will ever see. ive seen plenty of huge (.700+ valve lift) roller cams none had concave lobes. i have seen almost square lobes but no concave ones.

pretty sure that's just him sucking at paint, not trying to draw a concave lobe. that would just be dumb.

[tigweld]

as long as it is not noncave then duration at .050 lift numbers accuratly describe the ramp rate, that is all I am getting at.

[agjohn02]

i don't agree. it does not tell you the time at max lift. a flat tappet and a roller cam could have the same duration and lift numbers but have vastly different lift profiles.