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Posted: 10/6/2004 12:09:03 PM EST
Link Posted: 10/6/2004 12:12:24 PM EST
Link Posted: 10/6/2004 12:13:31 PM EST
Link Posted: 10/6/2004 12:15:19 PM EST
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?
Link Posted: 10/6/2004 12:17:09 PM EST
[Last Edit: 10/6/2004 12:20:54 PM EST by gus]
That graphic leaves out one important detail, at least in terms of the old race Hemi's - the piston dome. I suppose the new engines have flat top pistons to keep the compression ratio down, but the old race Hemi's had BIG domes and around 12.5:1 compression. `60's street Hemi's had the dome partially shaved off and a 10.25:1 ratio. That dome was one of the reasons the centrally located spark plug was such a good thing because the flame would propogate down around the dome. Non-Hemi's usually have the spark plug off to the side, and with high compression pistons the flame had to propogate across the piston, and the compression dome caused all kinds of problems with incomplete combustion and detonation.
Link Posted: 10/6/2004 12:17:30 PM EST
So, it's a HEMIspheric chamber eh?
Link Posted: 10/6/2004 12:17:58 PM EST

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.
Link Posted: 10/6/2004 12:19:41 PM EST

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



That's a cross section of one cylinder. There are hemi engine designs that aren't old Mopars (although they started it all). Most DOHC engines (like on many motorcycles) have many of the same advantages and design features.
Link Posted: 10/6/2004 12:20:22 PM EST

Originally Posted By gus:
That graphic leaves out one important detail, at least in terms of the old race Hemi's - the piston dome. I suppose the new engines have flat top pistons to keep the compression ratio down, but the old race Hemi's had BIG domes and around 1.25:1 compression. `60's street Hemi's had the dome partially shaved off and a 10.25:1 ratio. That dome was one of the reasons the centrally located spark plug was such a good thing because the flame would propogate down around the dome. Non-Hemi's usually have the spark plug off to the side, and with high compression pistons the flame had to propogate across the piston, and the compression dome caused all kinds of problems with incomplete combustion and detonation.



Yeah, I think it leaves that out.

Link Posted: 10/6/2004 12:21:58 PM EST

Originally Posted By purplecheese:

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.



Correct! In Australia, there was a Hemispherical 6-cylinder.
Link Posted: 10/6/2004 12:23:37 PM EST

Originally Posted By Redcap:

Originally Posted By purplecheese:

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.



Correct! In Australia, there was a Hemispherical 6-cylinder.



Early `70's Dodge Colts' (Mitsubishi) had true hemi design too - and it was a tiny little 4 banger.
Link Posted: 10/6/2004 12:25:15 PM EST
[Last Edit: 10/6/2004 12:25:32 PM EST by gus]

Originally Posted By GTTacoma:

Yeah, I think it leaves that out.





My point being that the domed piston was one of the big reasons for bothering with the hemispherical chamber.
Link Posted: 10/6/2004 12:25:44 PM EST

Originally Posted By gus:

Originally Posted By Redcap:

Originally Posted By purplecheese:

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.



Correct! In Australia, there was a Hemispherical 6-cylinder.



Early `70's Dodge Colts' (Mitsubishi) had true hemi design too - and it was a tiny little 4 banger.



See I knew they existed, I just couldn't remember them!
Link Posted: 10/6/2004 12:26:56 PM EST

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



ever look at a honda or BMW head?
Hemi hasnt been a Mopar only thing for decades, its just marketing hype
Link Posted: 10/6/2004 12:29:37 PM EST
Except the new "Hemi" isnt a true Hemi.
Otherwise, cool pic.
Link Posted: 10/6/2004 12:31:42 PM EST
Link Posted: 10/6/2004 12:34:29 PM EST
Jaguars had hemi heads all the way back to 1953, and maybe earlier.
All the 6 cylinder Jag engines were hemi, and double overhead cam.
Many European engines such as Ferrari, Alfa Romeo, Aston Martin, and others also used hemi heads back into the early 1960s, and possibly earlier too.

Link Posted: 10/6/2004 12:36:55 PM EST

Originally Posted By Specop_007:
Except the new "Hemi" isnt a true Hemi.
Otherwise, cool pic.



Neither is any other "hemi" ever built, except maybe the original `50's hemi's. The new one is more of a Hemi than, say, a Boss 429 though (often called a "semi-hemi"). Ford DID make a very few 427CI SOHC hemi type engines, but they were so flawed in their design that they are barely worth mentioning. Nothing like 10 feet of timing chain to improve valve timing and stability, eh?
Link Posted: 10/6/2004 12:36:55 PM EST

Originally Posted By purplecheese:

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.



Technically Honda and Toyota both offer hemisepherical combustion chamber engines with angled valves and the spark plugs sticking straight down. The design is almost 100 years old, dating back to 1904. Chrysler first built a hemi-head engine during WWII for a V16 airplane motor. Dodge has the HEMI name trademarked, but the old patents are all public domain now.

Remember the Alamo, and God Bless Texas...
Link Posted: 10/6/2004 12:40:09 PM EST

Originally Posted By MillerSHO:
Not to be rude to the poster, but "nothing to see here people, move along."



My point was, Howstuffworks.com has a cool in-depth history of the HEMI engine series and the specs.
Link Posted: 10/6/2004 12:42:13 PM EST

Originally Posted By GodBlessTexas:

Technically Honda and Toyota both offer hemisepherical combustion chamber engines with angled valves and the spark plugs sticking straight down. The design is almost 100 years old, dating back to 1904. Chrysler first built a hemi-head engine during WWII for a V16 airplane motor. Dodge has the HEMI name trademarked, but the old patents are all public domain now.

Remember the Alamo, and God Bless Texas...



Correct! It's a design. Chrysler patented it for the US market, and had the balls to market it despite the high cost of production (in the 1950's). Much more machine work involved for the low tech of the day. In today's world of CNC and digital machining centers, it's no biggie.
Link Posted: 10/6/2004 12:49:16 PM EST
Many new developements have controlled detonation with non-hemispherical combustion chambers. The Hemi thing was just marketing. There is a lot more to an engine than just combustion chamber shape. The ZR-1 Corvette engine was able to achieve an 11.25:1 compression ratio on street fuel by using a clover leaf combustion chamber. Planerench out.
Link Posted: 10/6/2004 12:51:59 PM EST
[Last Edit: 10/6/2004 12:55:07 PM EST by gus]

Originally Posted By Planerench:
Many new developements have controlled detonation with non-hemispherical combustion chambers. The Hemi thing was just marketing. There is a lot more to an engine than just combustion chamber shape. The ZR-1 Corvette engine was able to achieve an 11.25:1 compression ratio on street fuel by using a clover leaf combustion chamber. Planerench out.



True, today. Not true in 1951, or even 1981. The current Hemi thing is largely marketing. The original Hemi thing was for real. That's one reason why 100% of top fuel dragsters still use the original (1950's) basic design to this day - they aren't allowed any electronics to manage detonation, and nitro motors LIVE on the edge of detonation.
Link Posted: 10/6/2004 1:05:48 PM EST
Link Posted: 10/6/2004 1:47:41 PM EST
toyota 3tc inline 4 cyl hemi...one of the most durable 4 bangers ever, great for racing ,and for all you v8 guys it had pushrods too..
Link Posted: 10/6/2004 2:13:29 PM EST
In the early 90s I remember Honda experimenting with a hemisperical heads and oval or elliptical cylinders on a bike engine and getting unbelievable horsepower. Anyone got anything on that?
Link Posted: 10/6/2004 2:15:00 PM EST
Hemi = Overrated.
Link Posted: 10/6/2004 3:54:24 PM EST
Don't know about over rated. I could care less about the new Chrysler hemi. I do remember the sound of the original Street Hemi as several of my friends owned them. Now if Chrylsr brought that out in a new car I'd be 1st in line to buy it.
Link Posted: 10/6/2004 6:57:28 PM EST

Originally Posted By gus:
Ford DID make a very few 427CI SOHC hemi type engines, but they were so flawed in their design that they are barely worth mentioning. Nothing like 10 feet of timing chain to improve valve timing and stability, eh?



Barely worth mentioning? You are nuts. 427SOHC was the pinnicle of Ford Racing in the 60's and had a significant part in the factory wars between Ford and Chrysler especially in the A/FX and top fuel classes. One of the baddest crate motors you could buy over the counter. 658 H.P. with 8V. Motor would have owned Nascar if it had been allowed. Timing chain was 6-7 feet long but there is a Gilmer cam drive available.

Some barely worth mentioning SOHC drivers:
Pete Robinson, "Tinker Toy"
Connie Kalitta, " Super Mustang"
Phil Bonner," Daddy Warbucks"
Hubert Platt,"Georgia Shaker"
Dick Brannan, "Bronco" factory built funny car
Dick Loehr, "Stampede"
Ohio George Montgomery, "Malco Gasser"
Jack Chrisman, "Chrisman’s Comet" first nitro funny car
"Dyno Don" Nicholson, "Eliminator I " almost unbeatable in A/FX during the 1966 season.
"Fast Eddie" Schartman
Don "the Snake" Prudhomme
Mickey Thompson "Mach-1"
John Force
Gaspar "Gas" Rhonda, "Gas Rhonda"
Les Ritchey
Bob Tasca
Tom "THE MONGOOSE"McEwen


Link Posted: 10/6/2004 7:39:32 PM EST

Originally Posted By gus:
That graphic leaves out one important detail, at least in terms of the old race Hemi's - the piston dome. I suppose the new engines have flat top pistons to keep the compression ratio down, but the old race Hemi's had BIG domes and around 12.5:1 compression. `60's street Hemi's had the dome partially shaved off and a 10.25:1 ratio. That dome was one of the reasons the centrally located spark plug was such a good thing because the flame would propogate down around the dome. Non-Hemi's usually have the spark plug off to the side, and with high compression pistons the flame had to propogate across the piston, and the compression dome caused all kinds of problems with incomplete combustion and detonation.



Some of the Hemis from the 60's had two spark plugs per cylinder.

As for claims of the Hemi being 'overated', the reverse is closer to the truth: The 426 CID versions were 'rated' for around 425 HP, but typically produced well in excess of 550...
Link Posted: 10/6/2004 7:55:07 PM EST
[Last Edit: 10/6/2004 7:56:02 PM EST by MoparMike]
Check out the 528 Hemi Crate engine.

Edukashun rekwestud: Is the reason that the new Hemis arent true Hemis is because they dont have a hemispherical piston as well?

And yes, I realize the irony of having someone named "MoparMike" asking that question, legitimately seeking info.
Link Posted: 10/6/2004 8:18:19 PM EST

Originally Posted By gus:

Originally Posted By Planerench:
Many new developements have controlled detonation with non-hemispherical combustion chambers. The Hemi thing was just marketing. There is a lot more to an engine than just combustion chamber shape. The ZR-1 Corvette engine was able to achieve an 11.25:1 compression ratio on street fuel by using a clover leaf combustion chamber. Planerench out.



True, today. Not true in 1951, or even 1981. The current Hemi thing is largely marketing. The original Hemi thing was for real. That's one reason why 100% of top fuel dragsters still use the original (1950's) basic design to this day - they aren't allowed any electronics to manage detonation, and nitro motors LIVE on the edge of detonation.



It wasn't the computer but the combustion chamber shape that allowed such a high compression ratio with the fuel available. The hemispherical chamber is the most efficient for a complete burn in a short duration (read rpm) due to the flame front only being able to travel so fast. Detonation has little to do with it. Hot spots in the combustion chamber (also possibliy causing preignition), lean mixture, and timing problems are the cause of detonation. The hemi is not the most efficient shape for exhaust scavenging as it is a rather neutral flow shape. Some swirl imparted by the placement of the valves creates optimum shape for a given engine speed. Finally, the placement of the spark plug in the direct center of the chamber wastes space that could accomodate larger valves. Planerench out.
Link Posted: 10/7/2004 2:03:34 AM EST

Originally Posted By Atencio:

Originally Posted By gus:
Ford DID make a very few 427CI SOHC hemi type engines, but they were so flawed in their design that they are barely worth mentioning. Nothing like 10 feet of timing chain to improve valve timing and stability, eh?



Barely worth mentioning? You are nuts. 427SOHC was the pinnicle of Ford Racing in the 60's and had a significant part in the factory wars between Ford and Chrysler especially in the A/FX and top fuel classes. One of the baddest crate motors you could buy over the counter. 658 H.P. with 8V. Motor would have owned Nascar if it had been allowed. Timing chain was 6-7 feet long but there is a Gilmer cam drive available.

Some barely worth mentioning SOHC drivers:
Pete Robinson, "Tinker Toy"
Connie Kalitta, " Super Mustang"
Phil Bonner," Daddy Warbucks"
Hubert Platt,"Georgia Shaker"
Dick Brannan, "Bronco" factory built funny car
Dick Loehr, "Stampede"
Ohio George Montgomery, "Malco Gasser"
Jack Chrisman, "Chrisman’s Comet" first nitro funny car
"Dyno Don" Nicholson, "Eliminator I " almost unbeatable in A/FX during the 1966 season.
"Fast Eddie" Schartman
Don "the Snake" Prudhomme
Mickey Thompson "Mach-1"
John Force
Gaspar "Gas" Rhonda, "Gas Rhonda"
Les Ritchey
Bob Tasca
Tom "THE MONGOOSE"McEwen





I say hardly worth mentioning because it was only useful on a drag strip, and the whole deal lasted, what two or three seasons? At least half the drivers mentioned switched to Chrysler Hemi's, and most of the rest fell into obscurity. This is not really meant to be a slam against the SOHC, because with a few more years development it could have been a hell of an engine. It had some other weaknesses in the bottom end that needed to be resolved before it was capable of really competing against the Chrysler in nitro racing, and the cam drive problem was never sufficiently resolved. Plus, it was super expensive compared to the Chrysler which was often simply lifted out of some old `57 Dodge and rebuilt for the drag cars. The Ford hemi was banned from NASCAR racing at the same time as the Chrysler engine was, and Chrysler's design returned when they released it as a street production engine (something that would have been nearly impossible with the SOHC engine). NASCAR eventually banned the Hemi again, and in my opinion it was done to give Chevrolet a chance at maybe winning a race someday (up till then it was all Chrysler and Ford). The very same thing happened in NHRA Pro-Stock.
I might add, Chrysler was working on its own OHC prototype Hemis, but dropped it for the same reason - cam drive issues.
Link Posted: 10/7/2004 2:05:38 AM EST

Originally Posted By MoparMike:
Check out the 528 Hemi Crate engine.

Edukashun rekwestud: Is the reason that the new Hemis arent true Hemis is because they dont have a hemispherical piston as well?

And yes, I realize the irony of having someone named "MoparMike" asking that question, legitimately seeking info.



Mostly it's because the combustion chamber isn't truly hemispherically shaped, which isn't as important when using flat top pistons.
Link Posted: 10/7/2004 2:21:37 AM EST

Originally Posted By Planerench:

It wasn't the computer but the combustion chamber shape that allowed such a high compression ratio with the fuel available. The hemispherical chamber is the most efficient for a complete burn in a short duration (read rpm) due to the flame front only being able to travel so fast. Detonation has little to do with it. Hot spots in the combustion chamber (also possibliy causing preignition), lean mixture, and timing problems are the cause of detonation. The hemi is not the most efficient shape for exhaust scavenging as it is a rather neutral flow shape. Some swirl imparted by the placement of the valves creates optimum shape for a given engine speed. Finally, the placement of the spark plug in the direct center of the chamber wastes space that could accomodate larger valves. Planerench out.



The new cloverleaf shape wasn't even a wet dream during the time frame I'm referring to. Yes I know that swirl is a big deal in aiding complete combustion, which is a BIG deal in preventing detonation. The old Chevy "rat" engines were "wedge" designs, much like similar engines from Ford and Chrysler in that era. Wedge engines, using domed pistons, had big problems with incomplete combustion due to the flame front being disrupted by the dome. This causes parts of the chamber to be rich, while other parts become lean, thus the detonation problems. I raced wedge engines for 15+ years and that is the problem encountered by everyone that raced them. That is why fully race prepped pistons had the domes smoothed and rounded as much as possible - to minimize interruption of the flame front, and to avoid sharp edges that could become hot enough to cause detonation.
As to exhaust scavenging, in the time frame I'm referring to NO other engine could compare to the Hemi due to its true crossflow valve layout.
Finally, the Hemi already had the biggest valves out there. The real problem Hemi's faced where valves were concerned is that they faced each other and valve timing was critical to avoid collisions between the intake and exhaust valves. In all, the biggest weakness in Chrysler's design was that due to it being a pushrod engine it had HUGE long exhaust rocker arms which could flex, or worse yet break, and that is one of the most common failure modes to this day for racers using the old Hemi engine design. Chrysler Hemis still 100% dominate nitro racing, and hold all the class records for SS/A and SS/AA, as they have since about 1968.

I'm talking apples, you are discussing oranges.
Link Posted: 10/7/2004 2:43:19 AM EST

Originally Posted By gus:

Originally Posted By Redcap:

Originally Posted By purplecheese:

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.



Correct! In Australia, there was a Hemispherical 6-cylinder.



Early `70's Dodge Colts' (Mitsubishi) had true hemi design too - and it was a tiny little 4 banger.



There was also a 4banger HEMI in an Aries for a year or two.
Link Posted: 10/7/2004 3:19:28 AM EST
Also remember that the Chrysler Hemi design was not just about combustion chamber. The block design was just as important. Because of all the power potential, Chrysler engineers knew that they had to have a block that would live under the extreme power that was produced by the design. That is why the chrysler 426 Hemi block is the strongest configuration. It has deep skirted walls (below crank centerline) to encase the crank bearing caps, which were then CROSS bolted. This was to prevent walking and distortion, therefore reducing crankshaft and bearing failure. The water jacket and gallery design was different too. It was WET all the way around the exhaust ports. There are many other design features that are overlooked by the "it's all hype" crowd, that make the 426 Hemi, THE ultimate design.
Link Posted: 10/7/2004 3:43:53 AM EST
The power of marketing trade names is strong... Technically speaking, all Hondas are 'Hemis'.

For some idiotic reason, when people think back to the legend of the 426 Hemi. The somehow misattribute the power to the combustion chamber design, and totally ignore the two giant 4 barrel carbs sitting on top of the thing...
Link Posted: 10/7/2004 3:55:46 AM EST

Originally Posted By cwd10:
Also remember that the Chrysler Hemi design was not just about combustion chamber. The block design was just as important. Because of all the power potential, Chrysler engineers knew that they had to have a block that would live under the extreme power that was produced by the design. That is why the chrysler 426 Hemi block is the strongest configuration. It has deep skirted walls (below crank centerline) to encase the crank bearing caps, which were then CROSS bolted. This was to prevent walking and distortion, therefore reducing crankshaft and bearing failure. The water jacket and gallery design was different too. It was WET all the way around the exhaust ports. There are many other design features that are overlooked by the "it's all hype" crowd, that make the 426 Hemi, THE ultimate design.



+1 Looks like you've done your research
Link Posted: 10/7/2004 4:04:32 AM EST

Originally Posted By gus:

Originally Posted By GTTacoma:

Yeah, I think it leaves that out.





My point being that the domed piston was one of the big reasons for bothering with the hemispherical chamber.



Perhaps, but ironically, a hemi doesn’t naturally lend itself to high compression ratios because a hemi head--one designed with large valves anyway--has a huge volume. One way to cope with this is to have incredibly long piston strokes; another is to dome the pistons, and yet another is to “quench” (I think it’s called) the combustion chamber between the valves which is what the new hemi does. Unfortunately to keep with a true hemi head like the 426, either doming the pistons or increasing the stroke causes the reciprocation assembly’s weight to grow, which ain’t good for going fast.

Because wildly increasing the stroke makes for a very large increase in reciprocating weight, the Chrysler injun-ears naturally “popped” the pistons because of its lesser weight effect. However, there’s another limit to placing weight far above the piston’s wrist pin: if it gets too heavy, the piston tends to become unstable and wears the heck out of the cylinder (street-engine concern) and, the top of the piston tends to break off at very high rpm (race-engine concern) unless it’s really beefy...which increases its weight. It’s a vicious circle of compromise.

The old hemi pistons weren’t spherically (I don’t mean hemi-spherically) domed--they couldn’t be because the domes would interfere with the valves; even in the 10.25:1 street-hemi-engine, but, especially so in a racing engine. So, the domes formed a necessarily odd shape with the valve relief, which worked directly against the benefit of having a hemi head--not that big of a deal, but piston weight was a big deal. There’s a practical compression limit with using a true hemi head.

Another benefit seldom cited in hemi talk is that the intake valve on the 426 hemi moved directly up and down so it tended to “whip” less and its size could be made quite large so as to flow more air. The exhaust valve was also naturally well positioned to aid flow and because the two valves were pointed much more toward one another than with a “wedge style,” the scavenging effect--a cam/valve timing trick--was extreme with the hemi. But, that darned dome on the piston had to be dealt with even more if the scavenging effect was to be fully realized.

All this sounds like the hemi was lame, (IMO, it was extremely well injun-eared) but there’s one little thing one can do to any engine that makes it come alive, and especially so with a hemi head--supercharging! With supercharging, lower compression ratios are tolerated with substantial increases in power, but with extreme power increases, with very high boost pressure, the compression ration needs to be low. So, with the hemi’s large valves and large ports, flow was of course greatly increased when running at high boost pressures. And, naturally, when a low compression ration is needed, the hemi’s piston dome problem goes away and the hemi becomes a high-horsepower-making monster.

Thanks for reading all this.
Link Posted: 10/7/2004 4:05:47 AM EST
"For some idiotic reason, when people think back to the legend of the 426 Hemi. The somehow misattribute the power to the combustion chamber design, and totally ignore the two giant 4 barrel carbs sitting on top of the thing..."

Then why is it that you can go to any Mopar car show or race, and see dozens of original 426 Hemi's making a lot more power with a SINGLE, 4bbl carburetor?
Link Posted: 10/7/2004 4:14:39 AM EST
Good info there, injun-ear but you're placing too much emphasis on the design compromise, and forgetting the practical realities. I personally have worked on street and race hemi's with high compression, and they make GOBS of power. Not to mention the top fuelers which are making in excess of 8000 horsepower with better than 16 to 1 ratio's AND nitro, AND a blower. No matter how you try to explain away the power and efficiency of the Hemi, the reality of it keeps coming back to bite you. It just works. Just ask all the guys loosing races to Hemi's. Not just top fulers either. Look at NSS and other classes. The Hemi will live on as the ultimate design. History has proven that.
Link Posted: 10/7/2004 4:25:44 AM EST

Originally Posted By cwd10:
Good info there, injun-ear but you're placing too much emphasis on the design compromise, and forgetting the practical realities. I personally have worked on street and race hemi's with high compression, and they make GOBS of power. Not to mention the top fuelers which are making in excess of 8000 horsepower with better than 16 to 1 ratio's AND nitro, AND a blower. No matter how you try to explain away the power and efficiency of the Hemi, the reality of it keeps coming back to bite you. It just works. Just ask all the guys loosing races to Hemi's. Not just top fulers either. Look at NSS and other classes. The Hemi will live on as the ultimate design. History has proven that.



I had intended to go into more detail about the street hemi and how it was a race-engineered engine adopted to live on the street. The compromise I meant to highlight was really with the street hemi.

I didn't mean to insinuate that a street hemi couldn't be modified to be very-very powerful, but I did try to illustrate the compromises involed withe the design. Clever/brilliant design is a marriage of compromise--design is compromise. The hemi--both old and new--are brilliant designs.

Top Fuel is utterly unique in the engine world. The engines live for a few minutes--seconds at high power--between resurrections.
Link Posted: 10/7/2004 4:27:30 AM EST
Well said.
Link Posted: 10/7/2004 4:34:10 AM EST

Originally Posted By purplecheese:

Originally Posted By Maynard:
Forgive my ignorance, but Hemis are V8s right?

Why do they show it as an inline engine?



Hemi's have come to be associated with the Chrysler/Dodge corp. I don't think that the Hemisphyrically Chambered Engine is limited to just the 8 cylinder, though I have yet to really see anybody outside of ChryCo offer such a beast (I know they exist, but my memory lacks there).

This is just a BASIC drawing of how it work, not a full schematics, so take it as that.



Willy's Jeep had an I-6 "Hemi" in the early 50's IIRC. It may have also had a camshaft that 1 lobe worked both the intake and exhaust valve. So it had 6 lobes, 1 per cylinder, to run the engine.
Link Posted: 10/7/2004 4:52:43 AM EST
[Last Edit: 10/7/2004 5:30:08 AM EST by gus]

Originally Posted By cwd10:
"For some idiotic reason, when people think back to the legend of the 426 Hemi. The somehow misattribute the power to the combustion chamber design, and totally ignore the two giant 4 barrel carbs sitting on top of the thing..."





Balony. If that were the case, the NASCAR Hemi (single 4bbl) would have never been competitive. Furthermore, the 440-6Pack, which had 3 2bbl carbs, had a higher flow rating at 1350CFM than 2 Carter AF's as used on the Hemi, which was under 1300CFM. The high CFM inlet system is on the Hemi because it's needed, the inlet system is not the main reason for all the power, although it is a part of it.



Then why is it that you can go to any Mopar car show or race, and see dozens of original 426 Hemi's making a lot more power with a SINGLE, 4bbl carburetor?


They make very large capacity single 4bbl carbs today. More importantly, it is MUCH more difficult to get 2 carbs to run well together than it is to get one carb to work by itself. Most bracket and index class drag racers run only one carb for that very reason - easier to tune and it will be more consistant.

Link Posted: 10/7/2004 5:14:49 AM EST
[Last Edit: 10/7/2004 6:26:43 AM EST by gus]

Originally Posted By cwd10:
Also remember that the Chrysler Hemi design was not just about combustion chamber. The block design was just as important. Because of all the power potential, Chrysler engineers knew that they had to have a block that would live under the extreme power that was produced by the design. That is why the chrysler 426 Hemi block is the strongest configuration. It has deep skirted walls (below crank centerline) to encase the crank bearing caps, which were then CROSS bolted. This was to prevent walking and distortion, therefore reducing crankshaft and bearing failure. The water jacket and gallery design was different too. It was WET all the way around the exhaust ports. There are many other design features that are overlooked by the "it's all hype" crowd, that make the 426 Hemi, THE ultimate design.




All true, except that the basic engine block is evolved from the B/RB wedge engines (361,383,413,426,440) which all had the deep wall block before the 426 Hemi. The Hemi had beefier main caps, and they were cross bolted as mentioned above.

Other Hemi advantages that were a result of its 426 wedge origins include having the ignition driven from the front of the cam instead of the rear of the cam (Ford did this on some engines as well), This is important because it eliminates torsional cam flex which is especially prominent when using stiff valve springs. The result is much improved ignition timing stability. Also the oil pump is driven by a very beefy drive shaft and is mounted externally. Where most engines have the ignition drive gear attached to the bottom end of the distributer, B/RB/Hemi engines mount the gear to the oil pump drive shaft and mate the distributer via a slotted shaft. Chevy used the slotted shaft (think screwdriver) to drive the oil pump.

The biggest advantage to old Mopar big blocks is that they had long connecting rods. This is very advantageous in that when the crank is 90 deg off TDC the angle of the rod to the cylinder bore is less than if a shorter connecting rod is used. This gives numerous advantages including reduced friction and cylinder wear, among other things.

This is such an advantage that GM finally introduced their DRCE (drag race competition engine) featuring a taller block design, allowing more advatagious rod length/stroke ratio (usually just called the "rod ratio"). That project was the brain child of Warren Johnson back when he was trying to figure out how to beat Bob Glidden's Pro-Stock Fords (which had long connecting rods, BTW) Of course, the taller custom blocks from GM also have the cam located farther from the crank, allowing the builder to use longer stroke crank shafts and build HUGE displacement engines.The GM street engines of the day were made with a shorter block to keep the overall height of the engine down to appease their styling studio. Ford built some engines of either design philosophy.
Link Posted: 10/7/2004 6:33:42 AM EST
[Last Edit: 10/7/2004 6:34:04 AM EST by cwd10]
All good points, but I left the evolution of Chrysler big blocks out of my post, to try to keep it short. I didn't think it was relevant to the conversation, since this thread was about the Hemi and not Mopar B/RB engines in general. BTW, for a good bit of trivia, the Australian six cylinder Hemi was designed by Chrysler as well. In fact it was designed by the famous Maxwell/Hoover engine team that did the Max Wedge's, Hemi's, slant six and others.
Link Posted: 10/7/2004 7:09:45 AM EST

Originally Posted By gus:
I say hardly worth mentioning ..........



Some good points Gus.

The Chrysler OHC Hemi was developed to counter the 427 SOHC in Nascar. It is my understanding that Chrysler dropped their OHC Hemi design after Nascar stated that Ford could not run theirs.

The SOHC had a good 5 season run. Several of the drivers mentioned raced Cammers up into the early 70's. Some of the others switched over to Boss 429s. Quite a few quit after Ford pulled the sponsership plug in 1970.

The Boss 429 and 385 series Ford Big blocks were to be the replacement of the FE family which included the SOHC. Ford 427's in general were expensive motors to manufacture. When Ford pulled the plug on development in 1970 it kind of killed the potential that the new Ford big blocks might have had. The 427 SOHC fell into obscurity not because of any peformance issues with the cam drive but for the reasons you state, it was an expensive engine and Ford had discontinued the production of all 427 parts. Meanwhile, third party vendors concentrated on the Hemi in the top professional classes( because it was the best motor available...you would never get me a Ford boy through and through to admit that ) and the rest is history.
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