I haven't poured over the 300+ topics to see if these questions have been asked and I'm not gonna.

1. I know that the 170 was designed to take torsional stresses from the chassis. Can I count on the 225 and the aluminum motors to take the same stresses?

2. How can you tell, by looking, if an engine is an aluminum block or a cast iron one? Different paint jobs?

The aluminium block Slant Six was carefully tested to take all the stresses of passenger car use.

The easy way to tell an aluminium block from a cast iron engine.... the cast iron block has expansion (freeze) plugs and the aluminium block does not.
A magnet will also tell you what the block is made of.
DD

You said...

"... the 170 was designed to take torsional stresses from the chassis"

Do you mean through the engine mounts? Can you elaborate? Never heard that before.

If the block is painted, sand off a small area to bare metal and scratch along it with a penny pushing in hard. If the block wears on the penny, it's iron. If the penny scratches off small silver shavings, it's aluminum.

But you can also tell by the numbers, and someone else will chime in on those.

In 1960, some Chrysler engineers bought a Lotus Eleven and modified it to take a 170 slant six. It is known as the world's fastest Eleven as it topped out at 186mph.
They claimed that the motor was designed to be ridged enough to take torsional stresses. The modified chassis stopped at the aluminum adapter plate between the motor and the Warner T-10 transmission and then picked back up for the front suspension somewhere near the front of the engine. You can find an article about this on Slantsix.org and the Lotus Eleven Register.
I have been thinking of building a LoCost Lotus Seven replica and doing the same thing. Hence my interest in whether the later slant sixes also had this rigidity.

I looked into making a LoCost a while back( and after several episodes starring Patrick McGoohan), and started some calcs and mock ups...the only bummer of it is the engine leans to the passenger side and might be problematic on the suspension and weight (hence...time to hang the pipes and a longer ram intake on the other side to balance)....After looking it over for a while, I shelved it I think the easier swap would have been to use an AMC 4.0L to keep things even.

Good luck on your project, it should be a cool ride!

-D.Idiot

I've been fascinated with the Lotus-Valiant for awhile myself, believe I recall seeing it once at Riverside as well.

Looking at pictures I've seen of the aluminum block, and the couple I've seen first hand (and knowing a bit of structural design), I'll hazard a first impression that it won't take the same torsional loadings the iron blocks will. The 225 & 170 iron blocks are essentially identical patterns however, with deck heights as a primary difference, so should be very close in that respect.

As to any metalurgic changes in the iron ones over the years; I don't know.

By the way, the chassis didn't completely stop at the engine, rather surrounded it and used it as part of the structure. Sorry I don't have a better picture, but this should do. Click on it, the link's a bit larger.

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Thanks for that tip. I couldn't tell by the pictures I was looking at and had the impression that there was nothing between the front suspension and the engine/trans adapter plate.

i have an excellent alum.block with main caps

It sounds like, for my purposes anyway, I should avoid the aluminum block. Too bad. Thanks.