☰
×
Login Register an account
Top Submissions Explore Upgoat Search Random Subverse Random Post Colorize! Site Rules Donate
8

Why 4 valve engines don't need as much lift as 2 valve engines.

submitted by usedoilanalysis to cars 2.4 yearsJan 18, 2023 20:36:47 ago (+8/-0)     (cars)

There's 2 intake valves, their area is combined, so is their lift. There are some flow losses, particularly at lower RPM(for the 4 valve engine), but all things considered, a 2 valve engine needs roughly twice the valve lift as a 4 valve engine to get roughly the same airflow.

When hotrodders talk about a .600 lift cam, they're talking about a cam that operates the pushrod 6 tenths of an inch. The rocker ratio plus the pushrod displacement gives you the effective valve lift.

On a overhead valve engine, there is no pushrod, only rockers/follower, or direct cam to valve action.


12 comments block

sort by: hot new top old low

[ - ] voatersaredumbasses 1 point 2.4 yearsJan 18, 2023 22:17:36 ago (+1/-0)

You mean an overhead cam engine. All engines after the Ford flathead v8's are overhead valve.

Overhead valve engines have pushrods. Overhead cam engines do not.

[ - ] usedoilanalysis [op] 0 points 2.4 yearsJan 29, 2023 22:24:05 ago (+0/-0)

Yeah.

[ - ] Name 1 point 2.4 yearsJan 18, 2023 21:25:37 ago (+1/-0)

Neat. Now if only someone could explain to me why a two or three valve engine is more inclined to make torque than a four valve….

[ - ] Crackinjokes 0 points 2.4 yearsJan 18, 2023 21:40:15 ago (+0/-0)

I don't know why that would be true. Why do you think it's true.?

[ - ] Name 0 points 2.4 yearsJan 18, 2023 21:53:21 ago (+0/-0)

Ford triton V8. I was hung up on high revving rice burners at the time and was surprised that Ford’s cutting edge engine only had three valves. Looked into it and a lot of very torquey motors only have two or three valves. The four valve motors were so shitty on torque that they had to use technology like Hondo’s VTEC to compensate.

[ - ] autotic 0 points 2.4 yearsJan 18, 2023 23:13:49 ago (+0/-0)

Maybe not the valve count directly but the correlation of low valve count to x-plane crank and engine thus tuned for lower rev power?

[ - ] deleted 0 points 2.4 yearsJan 19, 2023 01:54:10 ago (+0/-0)

deleted

[ - ] usedoilanalysis [op] 0 points 2.4 yearsJan 22, 2023 07:36:48 ago (+0/-0)

They're not. 2 valve works better at low rpm because less "curtain area" than a 4 valve. Having more torque at lower rpm doesn't mean you make more torque everywhere under the curve.

[ - ] mikenigger 0 points 2.4 yearsJan 19, 2023 03:25:41 ago (+0/-0)

who cares, ya'll be drivin' electric shavers in 10 years

[ - ] Crackinjokes 0 points 2.4 yearsJan 18, 2023 21:39:49 ago (+0/-0)

But don't the valves actually get pushed into the cylinder rather than out. So the lift is not actually lift the valves are being pushed into the cylinder. Because the wave valve seal against the top of the cylinder head is they have a bevel on the inside that's slightly pyramid shaped so when the explosion happens the valves are pushed against the top of the head and they seal more tightly. So it seems as though that amount of lift on a two cylinder engine I'm sorry to valve engine wouldn't be as important as the diameter of the valves in terms of clearing air flow and clearing exhaust gases etc

[ - ] autotic 1 point 2.4 yearsJan 18, 2023 23:16:37 ago (+1/-0)

Low lift, shorter stroke, less turbulence. Higher lift, longer stroke, more turbulence across the valve.

[ - ] usedoilanalysis [op] 0 points 2.4 yearsJan 22, 2023 07:33:50 ago (+0/-0)

The shape of the chamber and ports matters more than valve diameter. The valve is the biggest restriction in the intake and exhaust system.

The seat and valve are a throat, air enters almost sideways. Valves lift off their seat.