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Hemi's: any make, any size....What do you think?

smokin_olds442smokin_olds442 Posts: 41
edited March 6 in Chrysler
I've seen many hemi's and hemi-like engines in my time, some good and some bad. I'd like to know what everyone else in the muscle car realm has to say about it, good or bad. Personally I'm a big hemi fan. The only thing about hemi's is that they have less low end torque than a swirl or quench type combustion chamber type engine...but a little more top end horsepower. I guess it's a little bit of give and take.
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Comments

  • andre1969andre1969 Posts: 21,590
    ...is the 341-2bbl that's under the hood of my '57 DeSoto. Now it's not exactly a high-performance setup; it's rated at 270 hp gross. But still, it has no trouble getting two tons of DeSoto moving, and it actually performs better and gets better fuel economy than some lighter cars with smaller engines that I've owned. For example, I've had three cars with 318's...a '68 Dart, a '79 Newport, and an '89 Gran Fury. In around-town driving, the DeSoto gets slightly better fuel economy than any of them, and only the Dart is quicker from 0-60.

    One reason I've heard that Hemi-powered DeSotos and Chryslers from this era are fairly rare is that people would buy them for the engine, junk the body, and then throw the engine into something else and use it for drag racing. Of course, the build quality on the '57's also ensured that they'd get junked a little prematurely :-(
  • moparmadmoparmad Posts: 197
    Nothing is more beautiful...any size,any make.
    I don't know if a Hemi inherently lacks torque or if they just seem to because they were nearly always built for maximum performance,and maximizing horsepower always hurts low end torque.
  • andre1969andre1969 Posts: 21,590
    I could see the 426 Hemi possibly hurting a bit for low-end torque, since it was designed to be a race car engine that was barely streetable. Still, didn't the '68 Dart Hemi hold some kind of speed record that still stands today?


    I know when the Hemi first came out in the early 50's, its main advantages were more horsepower at a lower compression. Way back when, there was no high octane gasoline, so they could only make compression ratios so high. I know in the example of DeSoto's first Hemi, the 276.1, it had 160 hp. In comparison, I think Oldsmobile needed an engine of around 330 CID to get the same hp.


    All that changed by aroud '55, as high HP engines started popping up everywhere, and the Chrysler 300 became the first American production car to break the 300 hp barrier. The next year, it broke the 1 hp per cubic inch barrier, with an optional dual-quad 354 that pumped out 355 hp. It was also available with a wide array of axle ratios, on up to a 6.17:1 (IIRC). My old Chrysler history book notes that such a beast should do 0-60 in about 5 seconds, although I've never seen a road test to back that up.


    For anyone that's interested, here's a Hemi link... http://www.powerplayhemi.com/. It lists a lot of specs for all the early Chrysler Hemi and Poly engines. There are a few typo's though...for example, for the '57 DeSoto Firedome and Fireflite, they duplicate the hp figures in the torque column.


    The main thing that killed the early Hemi, I believe, were weight and mechanical complexity. A Chrysler 392 weighs 737 lb, and the DeSoto 330/341/345 weighed 669 lb. I don't think fuel economy or reliability was ever a concern, it's just that the corporate big-blocks that followed were just lighter and cheaper to build. And that's the bottom line, whether it's Chrysler, GM, Ford, or anybody. Cheaper always wins out.

  • I've heard a lot of talk about Chrysler hemi's but nobody talked about Fords hemi's. The 429SCJ(super cobra jet) had true hemispherical heads, while the 428 was called a "semi-hemi". And the reason for hemi's having lower torque is not because the way they were tuned but the shape of the combustion chamber. This hemi design burned much more of the air/fuel ratio and was not only more powerful but more efficient too, as said earlier by andre1969. These hemi engines had high volumetric efficiency but low BMEP(Brake Mean Effective Pressure) and that's why torque was low(in technical terms).
  • andre1969andre1969 Posts: 21,590
    ...but what about the 2.6 "Hemi" from Mitsubishi that Chrysler stuck in its K-cars for a few years? ;-) They even had the nerve to put a badge on the side of the car that said "2.6 Hemi". Does anybody know if that thing actually had hemispherical combustion chambers?

    Oh yeah, I never heard about the Ford 429 hemi...so it actually went into production? Didn't Oldsmobile build a prototype 455 with Hemi heads?
  • Well the 429 wasn't called a hemi as was chyrsler's 426, the 429 was known as the SCJ(super cobra jet) and had around 355bhp. The Mustang bodies they were put in had to be factory modified so that the wide 429SCJ could fit in the engine bay...wild!
  • modvptnlmodvptnl Posts: 1,352
    A few corrections if you don't mind. The Boss 429 was a Semi-Hemi head. It had a slight cresent shape in the combustion chamber. The CJ or SCJ NEVER had the Boss heads. There NEVER was a 428 semi-hemi. All 428's and most 427's were simple wedge heads. The SOHC 427 I'm not 100% sure on but it may have been closer to a hemi.

    Now the bad news. The Hemi is NOT an efficient design. It uses a domed combustion chamber in a parabolic shape and because of this can utilize very large valves which of course is great for high rpm horsepower but not the best for low rpm velocity. Because of this giant combustion chamber some weird piston shapes had to be made to get any compression. With valve notches and such, flame travel is compromised. Witness top fuel hemis, even with exotic fuels and big boost #'s they run 2 plugs per cylinder for ignition. Of course the hemi is a GREAT high RPM race engine but due to lower octane fuels, emissions and such it's not the most efficient design.

    Many people mistakingly think the current crop of 4 valve, centrally located spark plugs are hemis. Most of these heads are "pentproof" chambers which is a flater more efficient design.
  • if the plugs are centrally located in the chamber then yes it is a hemi-resembling design, and yes the hemi's were more efficient...they burn more of the fuel/air mixture than wedge heads and therefore have greater volumetric efficiency but low BMEP that is the reason why they have high rpm horsepower and not as much torque as the wedge design.
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  • modvptnlmodvptnl Posts: 1,352
    What does "hemi resembling" mean?? Good try on back pedaling. A hemi is a HEMISPHERICAL true domed combustion chamber PERIOD. If it has any inturruptions in this parabolic chamber it is NOT A HEMI. The modular motors are WEDGE designed(except for the DOHC which is a pentproof chamber)Even though the plug comes in from the top of the SOHC the plug location is NO WHERE NEAR CENTRAL. The modulars have small bores and on the 2 valve heads a centrally located plug would be next to impossible. If you can, find a JULY isuue of MUSTANGS AND FAST FORDS. It shows a good picture of some 5.4, 2 valve heads off a Lightning. They are most obviuosly wedge chambers.
  • moparmadmoparmad Posts: 197
    The 426 crate Hemi makes 465 horsepower and 486 ft pounds of torque. From 3000 to 5000 rpm it never drops below 480 ft pounds,the chart doesn't give numbers below 3000 rpm but it doesn't appear to be dropping quickly below 3000.
    The proof of the pudding as far as the Hemi being ahead of its time is probably best reflected in the fact that here we are arguing about how efficient a 50 year old head design is. Obviously there is a little hype with the Hemi or Chrysler would have brought it back years ago,but just as obvious is the fact that even if it isn't that big of a help it certainly must not hurt either or it would remain dead.
    BTW... The latest numbers I've seen on the 5.7L Hemi for production are 330 horsepower and 375 ft pounds of torque!
  • modvptnlmodvptnl Posts: 1,352
    Yes the Hemi was an excellent head making tons of power but remember when this was!!!! 100 octane gas was .25 a gallon and there were no emissions to worry about. The "new" hemi I haven't seen yet. I will be VERY surprised if it's a TRUE hemispherical combustion chamber. Also realize that GM's LSI wedge head with relatively small bore is making more power than the "NEW" hemi and it's a 4 years old design. Ford's 5.4 with "modern" dohc 4 valve heads made 385 HP N/A. The hemi had it's day.......it's over now, sadly.

    BTW the Ford 514 crate motor makes 600 HP with good old "MODERN" wedge heads. Heck, the crate 392 stroker Ford motor out powers that hemi!!!
  • ndancendance Posts: 323
    Seems to me that the 'hemi' is mostly a marketing concept. Why anyone would care what the shape of the *combustion chamber* is, of all things, is beyond me. (My weary old memory banks seem to think that 426's idled really poorly, why?, poor camshaft design or an inefficient head design at low rpms?). With the amount of computer power available to modern mechanical engineers, I'll bet that they can cook up far more optimal designs than the kind of plug and pray techniques of the '50s and '60s. I'll also bet that killer port and chamber design result in shapes that are *not* obvious at first glance (just think of all the inserts built for heads (ZL1 for instance) which *shrink* the port size but actually increase flow).

    Kind of like assuming that smooth surfaces result in higher efficiency necessarily.
  • moparmadmoparmad Posts: 197
    The reason the 426 Hemi idled poorly had to do more with the cam than anything else. From the factory it had 284 degrees of duration and .490" lift on the intake and .481 lift on the exhaust,that is quite large for a street cam.
    The numbers I gave were for the first step Mopar Performance Hemi,the 528 Mopar Performance Hemi develops 610 horsepower and 650 ftlbs of torque,and it runs on 92 octane pump gas. If you include Ray Barton and other engine builders the power levels can go basically as high as you want to pay for. But this holds true of any engine doesn't it.
    As far as the new Hemi remember that these are numbers for the first incantation which is a truck engine and even though it doesn't put up the horsepower it delivers on the torque big time.
    I think the other misconception here is that the new Hemi is exactly the same as the old Hemi. I'm sure that it is a modernized version of the Hemi and is changed very much from what it once was. Also the flow of the head has more to do with the port design than the shape of the combustion chamber. One of the advantages of the Hemi head was that it lined up the head with the intake manifold better allowing a straighter shot for the port,this might seem like it would hurt the low speed velocity of the charge but remember that the ports can be tuned by varying their size and shape.
    The Hemi was banned by NASCAR which is what killed Fords Hemi,they no longer needed it to be competitive. It also killed the Chrysler DOHC Hemi which was in development to combat the Ford. The reason for the ban was simple. The Dodge and Plymouth aero-cars(Daytona and Superbird)were routinely breaking the 200 mph barrier,which given the limited knowledge of aerodynamics and the four wheel drum brakes was far from safe.
  • ndancendance Posts: 323
    I'm not sure that cam timing is the culprit.

    428 CJ specs:
    lift: i = .480, e = .490
    dur: i = 270, e = 290

    L72 spec:
    lift: i,e = .520
    dur: i = 316, e = 302

    (I'm assuming that duration was measured in a similar fashion, of course).

    428 CJ's (it *has* been a while, so maybe my memory is fogged) are really darned docile. Since I've only owned cars with the LS6, L89, and CJ motors, I can't really say how an L72 is to live with. I remember that magazine writers of the day (70/71) picked on the 426's for rough running. Now that I think of it, maybe the dual carb system is at fault, some sort of feedback loop with the idle circuits fighting with the distibutor advance fighting with the geometry of the gas flow through the engine.

    I admit, it drives me kind of crazy to use Grand National racing as any sort of metric on engine design. Although it is *real* racing, the sanctioning body (ie France) makes it impossible to really compare designs since they've cooked up 40 years of Mickey Mouse restrictions to keep the makes dead-even competitive.

    Now that the cars are 'stock' cars in name only (as compared to the '60s and before), they might as well drop all pretense and use real racing engines. Of course, all that would happen is Mercedes (or Porsche, or Honda, or ....) would show up, place their powerplant in some already dominant team's car, and win every race.
  • ndancendance Posts: 323
    that ultimate horsepower is largely a function of money more than of engine make (in terms of production based, US built, pushrod V8's). I'll bet that the prostock engine builders could start with practically any basic design (even Oldsmobile!) and build competitive horsepower levels. Of course, by that time they've redesigned a chunk of the oiling system, had their own heads machined from factory blanks or whatever, etc. etc. A nice example is the AMC engines used in the Trans-Am. Add Penske + Traco and, voila'. Instant race engine.

    I think that, in general, a 'good' high performance engine is one that a dummy like me can easily track down parts for, is reasonably priced, and I can understand. (The understand part is what keeps me away from 911's. . In terms of late '60s/ early '70s cars, it's real instructive to drive, say a Boss 302 on the same day as a '72 911S. They run about the same in a straight line, but the Mustang really is a POS in every other way).

    I suppose when you get right down to it, the optimal high-performance V8 available today (at least for lighter cars) is the Chevrolet ZZ4 crate engine. Really a smoking deal and pretty much unbeatable for the money. Slam that baby into a 914 (with the later gearbox of course) and you're livin' large.
  • mcsapmcsap Posts: 15
    It seems to me that Chrysler was the only company that took a racing engine and offered it as an option in production cars. There are a lot more 331/354/392/426 engines out there than any other "hemi" from any other company. I belive a minimum of 500 was required to be considered production back then.
  • Oh, hemis were quite common in Europe way before Chrysler but they were all I believe racing engines. Hemis in production cars prior to Chrysler would have to be Duesenberg and Stutz, and of course Miller and Offenhauser used this principle for racing. Chrysler's approach was different than the Euros or most racing cars because Chrysler did not use overhead cams, prefering the simpler idea of unequal length pushrods. It was a clever solution to keeping costs down, but of course without the overhead cams the engines didn't rev as high. But will all that displacement, high revs weren't necessary for the applications.
  • dustykdustyk Posts: 2,931
    ......usually contribute to increased torque. All other things being equal (bore, stroke, offset, camshaft timing, lift, duration, valve size) they produce more torque.

    Now, the 426 street hemi found in those "B" bodied Plymouth's and Dodge's of the 1960s felt a little weak on the take-off because of longer cam durations. When camshaft duration is increased above 270 degrees it'll have the same effect on any engine.

    Dusty
  • modvptnlmodvptnl Posts: 1,352
    I'll respectfully disagree. The MAIN advantage of a true Hemi is that you can use monstrous valve sizes because of the domed chamber. This and the HUGE ports afforded by the design will actually HURT torque, especially at lower revs because of the reduced port velocity.

    Of course, using forced induction and high rev horsepower the Hemi is still a valid design but the pentproof design used on modern 4 valve heads is a better all around design because of piston shape and a few other more favorable traits.
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