Talk:Hemi engine

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I think we should make this page a summary of Chrysler's Hemi technology and fully split out the 426 Hemi and new Hemi. It's a bit confusing.

Should Hemi just point here, or should it explain hemispherical heads in general? —Morven 04:37, Aug 8, 2004 (UTC)

I think we should have a page for hemispherical heads, pointing here and at other hemi (small h) engines like the Jaguar XK6 and Mitsubishi V6 and Chrysler Australian straight 6. The new Hemi and old Hemi and "early" Hemi are all different enough that each could have its own page, I'm sure. I'm going to split out the Mazda engines like this too. --SFoskett 14:41, Aug 8, 2004 (UTC)

Contents 1 Compression ratio 2 hemispherical vs. Chrysler Hemi 3 crossflow 4 All engines are hemispherical

[edit] Compression ratio

I'm curious how the compression ratio of a hemi-head engine compares with other gasoline engines. It would seem to me that a full hemisphere would take up a lot more space (of course, I suppose "hemi" doesn't necessarily mean a full hemisphere is in there), and the piston wouldn't be able to rise far enough to compress the gas/air mixture to the level you see in other engines. Anyway, just something I don't know much about. —User:Mulad (talk) 18:53, Sep 2, 2004 (UTC)

Hemi engined cars had domed pistons to compensate. One of the ways to vary compression ratio is to dome or dish the piston top. —Morven 20:48, Sep 2, 2004 (UTC)

P.S. the "New Hemi" isn't a full half sphere; it's shallower, so that domed pistons are not needed. Domed pistons make the combustion flame-front have to go further, which means pollution-causing incomplete combustion —Morven 20:51, Sep 2, 2004 (UTC)

[edit] hemispherical vs. Chrysler Hemi

I think we need to split this article. Chrysler Hemi engine should refer to those models that Chrysler called "Hemi" and the regular Hemi engine article should be a general overview of the design with links and information on Porsche, Mitsubishi, Chrysler, and other Hemis. Thoughts? --SFoskett 16:29, Jun 1, 2005 (UTC)

Yes, agreed. Chrysler Hemi engine should refer to the three different Chrysler hemi designs. We are currently lacking a page on the 426 Hemi, I believe; one should be created. Hemi engine should be a general page about the concept.

Dr_gonzo should learn to be less gonzo, at least in terms of using a spell-checker. —Morven 18:40, Jun 1, 2005 (UTC)

spell checkers cramp my style. Dr-Gonzo.

[edit] crossflow

or "crossflow cylinder head"??? the Crossflow cylinder head article says nothing about hemis. --Gbleem 05:45, 27 July 2006 (UTC)

It certainly doesn't, just like an article about animals may not mention ring tailed lemurs 202.27.209.71 08:21, 25 February 2007 (UTC)

[edit] All engines are hemispherical

Aren't all engines more or less hemispherical (as opposed to the archaic flat head design), given that the head is usually cone shaped to a large degree.

I think this is all a bit confusing, as

From what I've heard "Hemi" means:

1. to have two valves per cylinder
2. these valves must be in a strait line, and obviously, in the head
3. the spark plug will be between them
4. perhaps the engine will have to use push rods?

And although these engines are supposed to be "the sex", as they won nascar, nascar is restricted to ancient, 2 valve engines.

Also, it doesn't take a genius to realise that, at 10:1 compression, by sliding a piston in a cylinder, having anything really resembling a hemisphere at the end is going to take a stroke so long when the piston is at the bottom, the space in the cylinder will resemble a saussage (which certainly isn't a good shape in terms of thermal efficiency) 202.27.209.71 08:21, 25 February 2007 (UTC)

I see we don't have an article on Wedge head. In fact, valves "in a straight line" is a funny concept; obviously, any two valves will be in a straight line, but if you mean the valves are parallel, that's kind of the opposite of a hemi, that's a wedge head. Imagine a triangle with two long sides and one short side; one long side is the top of the piston, the other long side is where the valves are in the head, the short side is the other side of the chamber in the head; often where the spark plug goes. A hemi is more likely to have valves canted in different directions, i.e. on opposite sides of an isoceles triangle, if not an actual hemisphere. Variations such as the old chevy "semi-hemi" 427, where the valves were definitely canted apart, but not a true hemi, etc. Gzuckier 19:00, 26 February 2007 (UTC)

I'm not really up with the play on different engine configurations, my 86 suzuki swift single overhead cam pushing intake and exhaust valves via rockers had a hemispherical head. I'm not sure about how single overhead cam engines that push the valves directly (no rockers) work (I can only assume the valves would be parallel with a spark plug between them) or dual overhead cams, but it was my understanding that all (non-archaic) rocker engines had non-parallel valves and a moderately

[1] This page seems to suggest that the only advantage is larger valves