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Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953
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   Forward Look NON-Technical Discussions -> 1955-1961 Forward Look MoPar General DiscussionMessage format
 
56D500boy
Posted 2020-03-31 4:25 PM (#596299)
Subject: Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953



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After enquiring about detailed articles about the first "hemi" (double-rocker) Chrysler engines, I was directed to some SAE papers. I haven't bought those yet but I did buy a 1951 Chrysler Firepower brochure and a 1953 Dodge Red Ram brochure. They arrived yesterday. I trust that someone here will enjoy seeing the contents of these brochures as they help to explain why we got double-rocker engines in the 1955 to 1958 Forward Look cars.

I will add the Chrysler Firepower info here and then add the Dodge Red Ram info in a second post.





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56D500boy
Posted 2020-03-31 5:44 PM (#596307 - in reply to #596299)
Subject: 1953 Dodge pre-Forward Look Red Ram Double Rocker Engine Brochure



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Location: Lower Mainland BC
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As promised (or threatened) the 1953 Dodge Red Ram Engine brochure:







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firedome
Posted 2020-04-01 10:40 AM (#596327 - in reply to #596299)
Subject: Re: Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953



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Interesting stuff! Nice to see it properly referred to as the Double Rocker engine, that's what Chrysler always called it.

The Poly - single rocker - is also, deservedly, getting more respect, it basically differed mainly in the single rocker heads, but the opposed intake and exhaust valves gave most of the same benefits of combsution gas flow at much less expense than the hemi. It's also an excellent design.

Cost and weight were their Achille's heel. Interestingly, the graph that shows the 'hemi" compared to 331 (Cadillac) and 304 (Olds, or 303 as Olds called it) calls attention to the hp advantage of the "hemi", however both of the lighter, simpler yet durable GM engines were far more influential in the long run: the Olds 303, 324, 371, and 394 engines all varied from the 303 architecture simply by bore/stroke and minor valve changes, and in production from 1949 to 1964. The Cad 331 begat the 365,390,429, again with the same architecture and only very minor changes from 1949 to 1967. Their economical but efficient wedge head design was eventually adopted by Chrysler's B series engines starting in 1958. The later 2nd Gen "hemi' Was not related to the older hemis, as they used the B engine blocks with new "hemi" heads developed by Bob Rodger (a NY native)

Edited by firedome 2020-04-01 10:45 AM
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56D500boy
Posted 2020-04-01 1:05 PM (#596334 - in reply to #596327)
Subject: Re: Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953



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Location: Lower Mainland BC
firedome - 2020-04-01 7:40 AM
Interesting stuff! Nice to see it properly referred to as the Double Rocker engine, that's what Chrysler always called it.


Thanks for the comments Rodger. I was thinking of finding some factory technical info on the polyspherical heads because, I agree, $ per hp, they were pretty good, probably better than the "double rocker" Not sure about the cost to make the engines but the 1956 315 D500 double-rocker made 260 hp and the 1956 315 single rocker Super-powered Super Red Ram made 230 hp (with factory 4 bbl carb and dual exhaust)

I found this video on the "single rocker" Poly the other day. I thought that the guy (Uncle Tony??) did a good job explaining the differences, etc.

https://www.youtube.com/watch?v=YU0Eo2f0vKg

This image of a "poly" (single rocker) head shows how they were still able to have the valves arranged similarly to the double rocker, creating almost the same kind of cross flow.





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Powerflite
Posted 2020-04-02 12:08 AM (#596355 - in reply to #596299)
Subject: Re: Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953



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Thanks for posting these Dave. I really enjoy reading through them.

But I beg to differ Roger. In terms of influence, the hemi design begat the poly, the poly design was copied by GM in the 409, and later in the big block Chevy, as well as the LS motors that they use today. The double rocker hemi also inspired many other motors like dual overhead cams etc. So it is really the Chrysler motor that is more influential. It's just that where cheap is the name of the game, the hemi has a harder time competing. With computer aided flow simulations coming into play, and other technical advances, the wedge design was able to be improved considerably to almost meet the performance of the hemi motor, but that came much later. Also, if Chrysler had decided to continue using a hemi motor in '59 for high end cars, it would likely have been a version similar to the 426 hemi, as the larger bore spacing and the bottom end of the block is a natural progression for Chrysler to use on it's larger motors. So the newly cast hemi motor would have received it as well. They couldn't continue using the 392 block design because they had reached the max bore size on it and couldn't reasonably increase the displacement without increasing the stroke even further, which they didn't want to do.

The main thing that GM did right was to make each engine have the same bell housing pattern and simplify engine swaps. That decision doesn't make a lot of sense from an engineering & sales perspective, but it made a huge difference in the popularity of their cars long after they were sold. It enabled them to build a solid base of fans that remained loyal to them because of how easy it was to upgrade your dumpy little grocery getter into something you could have fun with. And sticking to that theme from the '50's all the way into the 2000's has done a lot for them.

In terms of light and cheap, Ford did a much better job than GM. Their small block motors are a lot lighter than GM or Mopar. And they are more narrow so they easily fit into many small car chassis. So why weren't they more successful than GM? The mustang kept them afloat for many years, but was not as popular as the myriad of GM offerings like the Corvette & Camaro.
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Handygun
Posted 2020-04-02 9:34 AM (#596362 - in reply to #596299)
Subject: Re: Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953


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Bob Rodger wasn't part of the 426H.
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57burb
Posted 2020-04-02 1:53 PM (#596367 - in reply to #596355)
Subject: Re: Pre-FL Double Rocker (aka "Hemi") engine information from 1951 and 1953



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The Hemi was a nice and powerful engine. But any theoretical performance improvement inherent in the combustion chamber design was not justified by the expense and complexity of manufacturing it. The architecture also dictated a lot of additional weight to get that exhaust valve waaaaaay over there opposite the intake.

To really take advantage of that centrally located spark plug, you need aggressive cam timing, high compression, carburetor CFM, RPM, and excellent fuel quality. That's the kind of thing that led race car and aviation engineering development toward hemispherical combustion chambers, but those same "racey" attributes are not desirable in a mass produced automobile. Hence, development of Poly V8 engines that were quickly followed by B/RB and LA engines that delivered similar performance for street cars while costing and weighing MUCH less.

The Hemi design really only shined in the 300s, Adventurers, and D500s because they rectified the tame cams and low compression required by the pedestrian versions of each engine family.

The Hemi became a legend when drag racers crammed supercharged air and nitromethane into their engines. They quickly realized the only engines that could survive that kind of abuse were the big Chryslers. It also helped that they were tough, plentiful and dirt cheap at the time, a winning combination!

Being honest, the double rocker was not a hugely influential design. It was itself derived from prewar aviation and racing designs. The cam-in-block architecture with pushrods kept one foot in the past. The Hemi combustion chamber design was greatly improved by engines such as the Ford SOHC that had them paired with overhead camshafts actuating the valvetrain with less mass. But they were even more complex and expensive to produce! Great for racing, not great for a family car. It was really the '90s with Honda VTEC and the '00s with DOHC V8s where true hemispherical combustion chambers were successfully brought to the masses.

Going backwards, the GM LS engines are more similar to the '49 Olds Rocket V8 with their inline valves and pushrods. They are also very strong, lightweight and cheap to produce while breathing well. That simple architecture and cheap power making potential has served them very well in regards to popularity with enthusiasts.

Edited by 57burb 2020-04-02 1:55 PM
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