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The chrysler engine was available with 12 to 1 compression by 1966 & the twin plug heads were in use by the early 70's
My 1976 Direct Connection 'Special Parts Catalog' lists the alloy D6 twin plug head as part number P3614487
Chrysler was well aware of the advantages of high compression & the twin plug layout in the mid to late 60's

In 1964 they had a prototype four valve, twin overhead cam 426 Hemi in the test cell. This one used the toothed Gilmer belt for camshaft drive, which was years ahead of the industry. [They had Bendix EFI as an option in '58 too]
Only one engine was ever made, & it is in private hands today. It was being developed to counter the Ford 427 SOHC engine, but the production two valve pushrod hemi whiped it's arse anyway, so development was not continued.

Now we have the Chrysler 6.1 hemi. The legend lives anew.

http://www.autointell-news.com/News-2004/August-2004/August-2004-3/August-18-04-p2.htm

Look at the latest hemi 6.1!!!

That is the first write up I have read on the new hemi. I new they were out, but hadn't come across any articles about em. Imagine throwing on a big lyshholm screw supercharger, and a pair of holley dominators. That would clean anything at the lights. Might start saving, one of those would look just right in my charger.

try classiczcars.com they might help you there....

Does anyone know where I can get an F54 L28 Block in Australia?

Would like to attempt the 3.1 Stroker Engine

You know whats weird Dodgey that the early toyota 2t or any early t series engine used the hemi design. Then toyota improved the design in the 3t turbo version because of the limit in compression the design had and used twin spark plugs back in the late 70s in racing and early 80s in production. Meaning that Chrysler Dodge or whatever chev arrss kicking company has 25 years later done the same thanks to toyota figuring out that twin plugs and slightly less valve angle with higher ports will allow high comp to be used without piston clearance and interferrence issues.
However the 3ttge was turbo not NA to make full use of high boost.
Toyota also made the 3t a twin cam and added 2 small exhaust valves therefore 3 valve per cylinder.
Heres a quote from Dragdat about the 3t
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from link
http://datsun1200.com/modules/myalbum/photo.php?lid=971

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The "production" 426 was not a "true" hemi either as it became necessary in the design stage to cant the cylinder heads 5 degrees inwards to allow the engine to fit into the engine bay.
Now you gotta know that this is one big big lump when it will not fit into a full sized US car.

It was with the introdugtion of the D5 "replacement" cylinder head that engines so fitted, became true Hemi's.
Those early lumps of pig iron from the 50's were "true" hemi's

This hemi is again 100lbs lighter than a gen3 that means 141.2 kgs or so which means that regardless of its looks
1. its halve the weight of the old one so rod lovers will shed 150kgs to go under a ton.
2. It finally run high comp for NA(the oldie kicked chev in the rear even thought it ran to 90 per cent of its potential due to clearancing problems inherited in design.)

"Cylinder Head
The advantage of a hemi design of combustion chamber is that the valves (and most importantly the intake valve) are always moving away from the shrouding effect of the cylinder walls (Fig 2) as they lift off the seats. However, the new hemi is not actually a true hemi as per its 426-inch predecessor. The hemi style of combustion chamber was put to good use during WWII when the output of supercharged aero engines could basically decide the fate of nations. For a two-valve combustion chamber, the hemi layout not only allows the largest valves to be accommodated but also to have the highest flow efficiency. The downside of a true Hemi configuration is that it does not respond well to a high compression ratio that inevitably requires a combustion-inhibiting, high-domed piston. For an engine with a typical bore/stroke ratio, this means it works great with a supercharger and CRs less than 8.5:1, but not as a normally-aspirated unit with 10:1 or more. To get around this problem the new Hemi has the sides of the true hemi form filled in. With the two spark plugs it is equipped with, this allows all the advantages of a true hemi, including blower capability, along with the ability, if required, to successful utilize high compression ratios."
3. "The new Hemi did extremely well here. At 250 thousandths lift, the stock head was nearer a $10,000 Winston (Nextel) Cup head than it was to even a good modified parallel-valve head."
4. With coming versions it large bore size will be accomodated with an equal stroke to make over 6 ltrs easily.
5. twin spark plugs
6. dimensionally much smaller due to improved exact die casting! imagine a stock 200hp (300hp worked) 4 cyl that weighs in at 70kgs-90kgs!!! a great little pushrod of almost 3 litres and fits snuggly in a 1k bonnet.

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Thats funny from someone who drives a car with a 71 cube [1.2L] engine. What the hell. Our Datsuns might be small, but we love them

I am not aware that the "little" hemi is available in anything other than a Dodge branded vehicle, so for the moment at least, it's a Dodge hemi.

From an efficiency standpoint, i don't think there is much of an argument. It's lighter, more powerfull & runs much cleaner so i guess that they took a GREAT design, & made it even GREATER. Thats a tough act to follow.

I like the early engines because of their classic look & i am building my car within a classic era. I want to keep everything pre 1970 if possible.Quote:

Thats funny from someone who drives a car with a 71 cube [1.2L] engine. What the hell. Our Datsuns might be small, but we love them