Thread: Hemi Engines

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Im just trying to learn a little about different engines. What i was wondering is if anyone could tell me the difference between the 426 Hemi and the 426 Hemi Wedge. Thanx.
Don

Not "hemi wedge", just wedge. Hemi has two rows of valves at an angle to each other, wedge has all the valves in a single row.

Hemi is a nickname for hemispherical.

Combustion chambers in heads have some shape. All kinds of shapes have been tried over the years. Since a sphere is the smallest surface area for a given volume, it was natural for someone to try a domed or "hemispherical" chamber layout. It offered advantages in theory since the spark plug could be located in the top of the "dome" and the flame travel would be somewhat equal in all directions. Putting the valves in a single row created layout problems in a hemi (or domed) chamber so two rows were used, one for intakes and one for exhausts. The hemispherical chamber was supposedly more efficient in the days before swirl designs, etc The original hemi motors from the early fifites were impressive with their wide valve covers (to hide two rocker shafts).

Wedge is another combustion chamber shape. It allows the valves to all be in a single row....simpler and cheaper to build. Chevrolet and Ford engines have wedge chambers.

Chrysler made both styles of heads and used them on engines that had 426 cubic inches. The heads are not interchangeable.

Now, the word HEMI is a marketing ploy....just like Super Sport, Cobra Jet, etc.....the new hemi shares Zero parts with a real hemi Chrysler....in the late sixties, saying "it's a hemi!" meant something......instead of just a big plastic badge on the fender.

Originally posted by robot

Now, the word HEMI is a marketing ploy....just like Super Sport, Cobra Jet, etc.....the new hemi shares Zero parts with a real hemi Chrysler....in the late sixties, saying "it's a hemi!" meant something......instead of just a big plastic badge on the fender.

I think the new so called HEMI's do have the hemispherical combustion chamber because the spark plugs go into the tubes like the first and second gen Hemi's did.

Matt, that is correct....but the "hemi" advantage is gone....it isnt the fire breathing monster that the old one was.....we have four hemi trucks here at work and the owners like to squeal the tires...

The problem with the Hemi design is they wouldnt pass emissions due to nox problems. the modern hemi resembles the hemi of old with the sides of the combustion chamber filled in.

the new hemi has the primary advantage of the old one in the vastly superior air flow afforded by the cross flow valves...and the fact that you can run much larger valves and subsequently larger ports because of this arrangement vs traditional wedge heads...the new hemi heads flow almost as good a a rat motor, despite the small bore...

...plus, the hemi's valves open "on-center" meaning they center themselves in the bore and away from the head for virtually zero shrouding.

I don't know...when a run of the mill hemi displacing some 345ci pushes my friend's 5000+lb truck to high 14's, I don't really think that it's lacking in any department...

...and then, there is the srt-8's engine

MMmmmmm, 425 Hp on pump gas. Amazing how everything old becomes new again. Like the gas crisis.

If you want to know about Hemi's, I find this a good source.

http://www.allpar.com/mopar/hemi/hemi.html

We ran a 354 hemi back in the early sixties. I love the big critters, but they are serious HEAVY. If I recall, a 392 with accessories was close to 800 pounds.

Bear in mind, at my age memory ain't the best thing I have going for me, so please don't send me any nastygrams if that 800 figure isn't totally accurate.

Jim