Why a CIH engine, whats the benefit?

[CoriolisSTORM]

Sorry guys, pardon my ignorance, but what's the Cam in head design's advantage over other types? What are the pros and cons of it? I just kind of want to know all that I can about it, I'm sort of not up to date on this configuration (the only ones I have any experience with are the OHV AMC/Chrysler/Jeep engines and such, the 4s and 6es). Pardon my ignorance, I'd just like to know some things about the design and such.

[baz]

the cam in head is a half way house between an over head valve and an over head cam
it cuts out the push rods of one without the height of the other but keeps the rockers with adjustment so its easier to maintain than shimming the valves on an ohc

[namba209]

Drawing on what little I know about engines, the big thing about the CIH engine is no pushrods to bend or break. Secondly, because the cam is in the head and under the rocker arms it doesn't need to be much taller than an OHV and is shorter than an overhead cam engine which has the cam along the side of the valves, I think. Other members feel free to add if I screwed up. HTH.

[baz]

over head cam has the cam above the valves Ron not along the side thats why the head is so tall

[jeff denton]

I'd say that a CIH has an advantage over cam in block in that it has no pushrods, meaning less weight for the cam to "throw" up and less for the spring to "shove" back down.
It's disadvantage to the overhead cam would be that it still has lifters riding on the cam lobe, this is heavy compared to having just a lever (rocker) being moved by the cam lobe.
The point made about the CIH having a lower profile is a good one, but just think if its cam were up a little higher, then a rocker/lever with a roller riding on the cam would be awesome, as in a Sea Doo engine.
So rather than start another huge re-design of the head, I'd point out the the CIH engine's best attribute is that it is what came stock in our cars and we love it for what it is and make do. Or just rip it out and stick a RamJet 572 in it but that dicussion would cost us half our friends and send this to a different forum...

[namba209]

Originally Posted by baz over head cam has the cam above the valves Ron not along the side thats why the head is so tall

Thanx Baz, I really wasn't sure what the actual configurtion was. I haven't seen an engine with the valve cover off to be sure, so I guessed.

[GTJIM]

Advantages:
1) compact, light valve train all contained in the head
2) use of 1.5ish ratio rockers mean cam can be smaller in diameter than a true OHC
3) rockers make valve adjustment far easier than the shims of a true OHC
4) hydraulic lifters easily used
5) unique "Opel" configuration with lots of them made
6) with roller rockers and suitable springs/cam motor can rev to near 10,500 rpm !!

Disadvantages:
1) sliding, very short 'push rod' in end of rocker - wear point.
2) ports all on one side of head as position of cam prevents crossflow porting
3) wedge combustion chamber
4) complex head casting which can lead to cracking
5) only available in cast iron
6) Rockers fracture if used for extended periods above 6,500/7,000 rpm

[tekenaar]

Originally Posted by GTJIM Advantages: 1) compact, light valve train all contained in the head 2) use of 1.5ish ratio rockers mean cam can be smaller in diameter than a true OHC 3) rockers make valve adjustment far easier than the shims of a true OHC 4) hydraulic lifters easily used 5) unique "Opel" configuration with lots of them made Disadvantages: 1) sliding, very short 'push rod' in end of rocker - wear point. 2) ports all on one side of head as position of cam prevents crossflow porting 3) wedge combustion chamber 4) complex head casting which can lead to cracking 5) only available in cast iron

. . . and not mentioned before, but worth mentioning here is that one of the primary, stated design goals of the CIH engine was to produce a reliable, sustained "Autobahn" RPM valve train using primarily existing GM, read Chevy, designs. Remember, GM bean counters had the final say-so on almost everything "new" at the time!

[baz]

i always wonder if the engine could have been made with a triumph dolomite sprint type of head ? 16 valve but with one side working direct to the valve buckets like an ohc and the other side working with rockers like the cih so both sides run from the same 8 cam lobes