Three-valve heads 1

[SomptingGuy]

Can anyone point me to modern automotive engines that have one intake valve and two exhaust valves?


- Steve

 

[patprimmer]

No and I can't think of one good reason why anyone would do that.

Regards
Pat
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[SomptingGuy]

Me neither. I saw an engine simulation model recently that was built like this, which got me wondering. Maybe the model had a simplified intake system for some reason, but needed the full exhaust?

- Steve

 

[patprimmer]

Maybe a very high boost or chemically supercharged engine where a lot more exhaust flow per unit of inlet flow is required, but that's a real stress.

Regards
Pat
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[factsb4pride]

I owned a 1986 Honda Civic SI that had a 3-valve head. It was a 1.6L 4 banger, but I don't recall the exact engine designation.

 

[PJGD]

It might have been a not-fully-developed model as you suggest, but alternately I can absolutely visualize a boosted engine, probably a diesel, where the exhaust valves are independently actuated. That is exhaust valves with individual ports, one plumbed to the turbo, and the other to the EGR circuit. Then with control over valve actuation you can select whether you utilize the pulse energy for the turbine or to increase the EGR flow. ~50% EGR flow is by no means out of the question for modern diesels.

PJGD

 

[BrianPetersen]

The Civic engine (and every other 3-valve head that I've ever heard of) used two intake, one exhaust per cylinder.

 

[patprimmer]

Two inlets one exhaust is not that uncommon as the intake requires almost 1/2 as much airflow again over exhaust.

Regards
Pat
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[bcs5274]

look at fords 6.8l v-10 3 valve dual overhead cam

 

[SMOKEY44211]

There was a 3 valve version of the Saturn 4cyl but it was two intake one exhaust. Two exhaust valves can run at a higher compression/expansion ratio for a given fuel octane rating because the exhaust valve temp. will be lower. You could achieve a single intake dual exhaust vavle configuration by simply eliminating the lobe needed to provide lift to one of the intake valves in a four valve head.-------Phil

 

[SomptingGuy]

I like PJGD's thinking. Possibly something the OEM's (and independent consultants) are running in their test beds...

- Steve

 

[PJGD]

I believe that Borg-Warner are developing something along these lines with a concentric camshaft within a camshaft which allows one exhaust valve to be advanced or retarded relative to the other. I think they call it VEMS(?).

PJGD

 

[SomptingGuy]

I've been told that Honda's "Wet Dream" engines: the CB250N and CB400N have this arrangement. Sounds dubious. I've been

http://WWW-surfing,

but cannot find any evidence.

- Steve

 

[BrianPetersen]

There was a generation of Honda CB400/450 engines that had three-valve heads, but they were the conventional arrangement with two intake and one exhaust. The generation in question started in 1977 and continued through the mid-eighties.