As no doubt many here will know, Chrysler Australia produced an all-new six in the seventies called the Hemi 6.
It came in three sizes, the smallest being a single choke 215 (160hp), the most ordered 245 (2bbl gave 185hp) and the 265, which had options up to triple dual choke DCOE Webers and over 300hp standard.
They were built very light. I'm told they were 160lbs lighter than a Slant 6 (225) and the original design and development work was done in the US.
Rather than having the valves canted in from each side, they were in a line along the head with 17° lean away from the centre of their cylinder. Ports were all on one side of the engine and they ran I E I E I E I E I E I E rather than the usual E I I E E I I E E I seen on most sixes.
I've got a car with one in, goes great (or it did before I put it off the road to restore it) and I have several other engines I'm accumulating. My nephew will be doing a bit of cylinder head experimentation because a friend of mine drag races one and doesn't want to have to buy one of the aftermarket alloy heads now available for them. He also wants to build a really toey 215 to run in a drag class we have here for Holden and Falcon inline sixes of about that size.
Here's a pic of the first model to use the Hemi 6:
This is the 1970 VG Valiant. 45,000 of these were built, but some had the 318 V8 in them, while a very small number retained the slant 6. The Hemi 245 and 215 engines were backed up by drivelines from Borg-Warner, an Australian version of the B-W 35 3-speed automatic with bigger clutches etc or a Borg-Warner 3-speed manual (Pacer models getting a close ratio version) and in the rear was a Borg-Warner 78 differential.
The crank is the same for all three sizes, only the bores are changed. In fact, I'm told that some 245s were machined out of 265 castings. I have a few sitting in my shed, right there alongside the 230 cube flathead sixes I've picked up for another project.
I'll have to get some photos posted of Hemi 6 parts when I get a chance. Unfortunately I'm going away for a week and a half so that will slow me down on things like that.
Here's a few pics of a roughy I have in the shed partially dismantled. This one is a 265 that's been lying around in the weather for a long time. First, the chamber that makes the name:
Here's how the valves are inclined, unfortunately I can't show how the rockers work these, but it's a simple matter really:
The ports are large, trust me. Remember that this head is about 2½" longer than a slant head... and note the I E I E I E I E I E I E arrangement of the ports:
The crank is another major change from the Slant. Seven main bearings, it's an iron crank and one size fits all engines 215 to 265. It's lighter than a slant crank by about 20lbs:
The crankcase... those seven mains, the cam runs in four bearings only:
Note also the similarity to the small block bolt pattern for the bellhousing? The lower bolts differ, and the dowels, they are about 1" further apart than the small block, presumably because of some kind of pressure from transmission maker Borg-Warner. Or there might have been some other reason... I simply don't know.
I mentioned the valve and port order in these engines...
Having that order with a six and having four bearings on the camshaft has led to a problem when adding aggressive valve timing via a hot cam.
The inlet valve on cylinder No 5 and exhaust valve on No 6 open and close at the same time. This pressure on the cam right at the same point as the distributor drive is taken - a skew gear between these two lobes - with these lobes away from the cam bearings means that there can be flex in the cam which will give a minor mis-time to the cylinder firing when those valves open.
Moreover, when there's a flex in this section it must transfer to the next section of the cam, the centre section, where the skew gear drives the oil pump. Hemi 6s are well known for their wearing out of the oil pump drive gears as they get this little bit out of mesh.
One Hemi 6 expert, Andrew Sanders, has developed a method of overcoming this by machining between the distributor drive gear and the adjacent cam lobes and fitting narrow aluminium half-round supports, which he lubricates, in there to prevent the flexure. He told me that the first thing you notice is that the idle's smoother, so there's no doubt it makes a difference.
Another way around it would be to make up a new cam and change the firing order, going from 1-5-3-6-3-4 to 1-2-3-6-5-4. This firing order was used over a hundred years ago on the K-model Ford because Henry wanted to reduce the loadings on the crank so he could make it lighter. It would require new manifolding to be ideal and may require a different harmonic balancer.