Valve timing on most automotive engines is such that both intake and exhaust valves are open longer than a full piston stroke.
2007-04-01 10:02:08 · 8 answers · asked by Anonymous in Cars & Transportation ➔ Maintenance & Repairs
yes they are it is called valve lead,valve lag and overlap.
the extra time is to compensate for the time lose in getting the intake air and exhaust gases to get moving,it also helps control valve temps and help scavenge the cylinders
2007-04-01 10:09:16 · answer #1 · answered by doug b 6 · 1⤊ 0⤋
This is false. If your talking about the piston going down on an intake stroke, yes the intake valve will stay open. On some engines the intake valve will stay open for 380 degrees, mostly racing engines. Ok the piston fires and just before it reaches botton the exhaust vavle pops open and wont close untill the piston is just a few degres from top dead center.. Vavle timing and valve over lap gives more power but waist fuel..Becausre some of the fuel is expelled out the exhaust purging and cooling the cylinder. A AA fuel dragster will use 12 to 15 gallon in one 1/4 mile pass.
2007-04-01 17:25:17 · answer #2 · answered by Anonymous · 0⤊ 0⤋
Doug b is correct. Valve lead, valve lag and valve overlap.
Valve overlap is the time period when both the exhaust valve and the intake valve are open at the same time. The exhaust valve needs to stay open after the piston passes TDC in order to use the vacuum created of the exiting exhaust gases to maximize the amount of exhaust gas drawn out of the cylinder. The intake valve opens before TDC in order to use the vacuum created by the exiting exhaust gases to start drawing the intake charge into the cylinder.
And for those that are unsure what a 'stroke' is when relating to the movement of internal engine components:
A 4 stroke engine has one stroke down (intake) one stroke up (compression) one stroke down (power) and one stroke up (exhaust).
Now if you were asking if they are open SIMULTANEOUSLY for more than one stroke of the piston, then absolutely not.
2007-04-01 17:27:55 · answer #3 · answered by Doug K 5 · 0⤊ 0⤋
A full piston stroke, like up and down? That would be false, the valves stay open due to the cam shafts duration.....example.... .250 duration and .450 lift.... a typical small block camshaft specs.
2007-04-01 17:07:06 · answer #4 · answered by Anonymous · 0⤊ 2⤋
I'd say it's almost simaltaneous to the piston stroke, bar a few milliseconds.
The question clearly states a full stroke, not a full cycle.........
2007-04-01 17:14:49 · answer #5 · answered by Seopard 3 · 0⤊ 0⤋
what do you care, if it runs then drive. only a mechanic worries about these things. if you want power install a hotter cam and lifter kit along with timing chain and sprokets. holly carb ,aluminum intake manifold and you're in the ball park.
2007-04-01 17:09:08 · answer #6 · answered by chucky5050 4 · 0⤊ 2⤋
are You passing ASE test on sunday?
that question is far out stupid.since You are not building any engine first.are You? then ask for cam angles, instead
2007-04-01 17:07:02 · answer #7 · answered by Anonymous · 0⤊ 2⤋
Yes.
But just barely.
It's difficult to explain.
2007-04-01 17:10:34 · answer #8 · answered by Mr. KnowItAll 7 · 0⤊ 0⤋