[video=youtube;PXD_AvKbCMg]https://www.youtube.com/watch?v=PXD_AvKbCMg[/video]
Why Are 4 Valves Better Than 2? DOHC vs OHV
- Thread starter NasteeNate
- Start date
****in science!
There's more to it than this.
They had the right idea, but just imagine how much more engineering is involved in designing the cams and how much work it would take to get the timing down just for adding one more valve per cylinder. Shit there's too many lobes on this cam, have to make another cam and separate the lobes. Shit now we have to get all of these on this cam to line up with those on this cam, and then line up on the crank.
They had the right idea, but just imagine how much more engineering is involved in designing the cams and how much work it would take to get the timing down just for adding one more valve per cylinder. Shit there's too many lobes on this cam, have to make another cam and separate the lobes. Shit now we have to get all of these on this cam to line up with those on this cam, and then line up on the crank.
I imagine, in terms of 4.6's at least, the 3v was to have close to N/A 4v power levels without the use of 91 octane.
Also probably cheaper to make ?
To bad ford never made the 5 valve head they developed.
There are very few things in the engineering world that are absolute. Neither is better than the other in ALL applications. :nono:
The question is which is better for the vehicle application in terms of engine design space, weight requirements, torque curve, cost, manufacturing/assembly complexity, B90 reliability and many other factors that are far more important than high rpm airflow and volumetric efficiency.
gas turbines are TWICE as efficient as piston engines but they are a terrible choice for cars for a number of practical reasons.
The question is which is better for the vehicle application in terms of engine design space, weight requirements, torque curve, cost, manufacturing/assembly complexity, B90 reliability and many other factors that are far more important than high rpm airflow and volumetric efficiency.
gas turbines are TWICE as efficient as piston engines but they are a terrible choice for cars for a number of practical reasons.
THIS! Sean Hyland was the first person I asaw to explain it this way. the video is 100% correct, but Hyland's term (assuming he originated it) is more simple.
Last edited:
Psh! Speak for yourself!
granatelli has a turbine powered 78 vette, 880hp and 1160lb-ft of torque :coolman:
Two-stroke > all
Ding ding ding
Fixed it for you!
So we have advantages IN the cylinder combustion chamber. Look how much real estate is required to make a 4 valve V8 engine. A 20' timing chain, guides and tensioners. 4 camshafts and related rocker and lifter parts, a giant cylinder head which creates mass up high in the eng compartment. Plus all these tiny pieces. like an extra 16 valve springs even though they are small. 32 valves requires 32 keepers and 64 locks.
As for the limited valve sizes in a 2v application. You can cheat that in a Hemi by tilting each valve away from the center.
I do love the Coyote engine but credit us due for the Hemi and LS engine for their compact design. Look at the hoodline of a 94-02 Camaro to understand this advantage.
As for the limited valve sizes in a 2v application. You can cheat that in a Hemi by tilting each valve away from the center.
I do love the Coyote engine but credit us due for the Hemi and LS engine for their compact design. Look at the hoodline of a 94-02 Camaro to understand this advantage.
I managed to get 32Vs work with one cam in my truck.
Very true, my 6.6 Duramax has 32VS with one cam.
The HEMI combustion chamber design is a holdover from radial aircraft engines. The price you pay for angling the valves is that your timing options are limited, and your valve train geometry just got a whole lot more complicated, the engine isn't free-running, and you need domed pistons to get any kind of reasonable compression ratio. Not a problem in aircraft engines since most of them were low-compression by design, for automotive engines that is a problem. Your cam follower's base-circle is limited (unless you're designing an aircraft radial engine, then you've got all the base circle you could want) and has to bear the full force of actuating the valve, the larger, heavier spring, and the lifter, pushrods and what-all else is in that geometry train. The current Chrysler HEMI engine is _not_ a HEMI, and it has a gigantic head without any of the benefits of overhead cams and four valves.
mc01svt said it best: Few things in the world of engineering are absolute.
Users who are viewing this thread
