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

55 messages,  Last post on Apr 27, 2002 at 10:18 PM

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Messages Page 6 of 6

#46 of 55 Could Solenoid-Operated Valves Change the Picture..? by spokane

Mar 01, 2002 (11:45 pm)

Your reasoning certainly seems right, Modyptnl. With respect to variable valve timing, if the electric solenoid-operated valve concept comes to fruition, don't you suppose a set of engine computer algorithms will allow an engine to be either powerful or economical on demand - but could re-open many of the engineering questions associated with swirl, flame propagation, combustion chamber shape, etc.?
 
VW's marketing of "undersquare" is curious. As I recall it, Honda touted its 'Compound Vortex Controlled Combustion' (CVCC) technology prematurely in about 1980. When that engine actually reached the market, it was labeled "CVCC", but did not utilize the compound vortex fluid flow concept.

#47 of 55 Disagree again........................... by dustyk

Mar 03, 2002 (5:28 pm)

..... You have built strawman arguments using embellishing vernacular. I never said that a hemispherical combustion chamber is "soooo superior" or "sooo much better," nor did I say that there were no negative aspects to the design. In fact, I have yet to quantify the difference at all!
 
>> Of course the Hemi of the early 70's could be made to meet emissions. But at what cost??? Again, using your terminology of all things being equal, take a low compression smogged 440 and a low compression choked up 426 Hemi and the 440 would have the same if not better performance at lower, car/truck, applications. In other words no need for a hemi at these lower performance needs. Can you honestly tell me that if a hemi head provided better performance in these applications that Chrysler wouldn't have adapted the hemi to the 383/440 line up? << Despite your complete rejection, this bears repeating again. By 1972 with tighter federal emissions standards, CAFE, Chrysler's 426 being legislated out of NASCAR, the significant cost difference in building a hemispherical combustion chambered head, it just didn't make sense to build a (or the) hemi. Conversion of another block to a hemispherical combustion chamber would've added a bout 200 lbs to engines that were quickly being made in less numbers and going out of fashion. By 1974 sales of big block motors had fallen precipitously. The writing was on the wall for auto manufacturers in 1970. Engines would need to get smaller, lighter, and they would be put into increasingly lighter platforms in order to meet the future federal standards. For the degree of benefit, modifying a current design to make it a hemi just wouldn't have been logical. Put Chrysler's perennially tentative financial condition into the equation, and even more the reason. As part of the agreement with the US government for loan guarantees, Chrysler had to discontinue big block motors in 1980 anyway. >> The piston on a true hemi will have a mis-shapen dome with valve cut outs. It has flaws. It needs to rev to utilize it's better air flow. I don't know anything about the early hemis you keep bringing up. But again, if sooo much better, why did they die out?<< The '51 through '59 Chrysler hemis were phased out simply because they were too expensive to manufacture. Even the polyhead motors were more expensive and with the exception of the 318A, were gone by 1960. The lighter weight and cheaper wedge combustion chambers were easier to cast, more tooling and machine friendly and hence, produced higher investment recovery numbers. The piston shape of a "true hemi" would be a pure, symmetrical, unadulterated half sphere. So a "true hemi" has never been built. As far as adding valve reliefs the same law of physics would apply to any combustion chamber utilizing them. Air-flow across these depressions produce ebbs and back currents to various degrees in ANY design. There is no explanation as to why this would be different in a hemispherical combustion chamber, nor for that matter, why corrective design applications wouldn't apply. Your "it needs to rev to utilize it's better air flow" statement is self serving. It apparently assumes small valves, short valve lifts, and short durations are not compatible with or would not be used in a hemispherical combustion chamber. If so, that's patently incorrect. In fact, the hemi chamber has a propensity for broad torque and power curves, and I can see where valve component dynamics could be optimized for the hemi that could deliver performance not otherwise be as easily obtained in a wedge chamber. >> It was/is a difficult engine to control flame travel on if it is to have any performance. How can you debate this?<< Flame propagation maladies are present in just about any executed design. Wedges have them, too. In fact, I happen to have helped in solving a major flame propagation issue while at GM in the late '60s. GM's (actually, Chevrolet) inline 6 cylinder engines were probably the worse ever for this despite being wedge chambers. The problem was so acute that poor flame front control was responsible for so much manifold inversion that early versions had a pronounced tendency to pull the throttle plate closed during engine advance resulting in throttle flutter. Now I claim no specific authority on the hemispherical combustion chamber since my days at GM were dedicated to projects not related. However, your repeated contention about flame propagation doesn't make sense. The hemispherical combustion chamber has several advantages over a wedge design unrelated to flow. It is inherently high in volumetric efficiency. The chamber roof is open allowing for streamlined ports and less crowding around the valve edges reducing overall induction resistance. In the Chrysler-executed 426 version, the chamber shape formed at TDC has less chamber surface area in relation to volume contributing to less heat rejection and lower carbon build-up. It is a combustion environment requiring short flame travel, not long, and this characteristic contributes to increased combustion consistency and commensurately increased combustion efficiencies at lower flow rates. Dusty

#48 of 55 If you say so. by modvptnl

Mar 03, 2002 (11:32 pm)

There have been many designs since the hemi. Including many more expensive OHC and 4 valve heads. Why wouldn't manufacturers embrace a design that is so wonderfully efficient? Especially with every last bit needed for CAFE? Why is the OHC from dodge a wedge? That surely has to be more expensive to build than an OHV.
 
Your big block not being needed theory is silly in that there were still large sedans and trucks and motorhomes still using them in large numbers. The 440 did as good if not better job than a hemi in those applications.
 
A hemi chamber,of course, is parabolic. The piston isn't what is hemispherical. There are a few current head designs(the Ford OHC's come to mind) that have swirl inducing bosses to enhance low speed mixing. So again, your streamlined open roof with unobstructed ports can actually be a detriment for low speed mixing.
 
Why would the "new hemi" have 2 plugs?(if indeed it is a hemi) The bottom line, again, is a domed piston will have more flame travel problems than a flat or even dished piston.
 
I'm curious to what your response is to your comment the big block chevies and Fords being phased out shortly after the hemi when they are still in production in one form or another.
 
The bottom line is that if it was such a great, efficient VE design it would be more widely used. C'mon, how can it be more expensive to produce than a DOHC 4 valve or even an OHC 2 valve.
maybe because it just doesn't work when more efficient, lower rpm power is needed.

#49 of 55 Okay................... by dustyk

Mar 04, 2002 (8:56 pm)

>> There have been many designs since the hemi. Including many more expensive OHC and 4 valve heads. Why wouldn't manufacturers embrace a design that is so wonderfully efficient? Especially with every last bit needed for CAFE? Why is the OHC from dodge a wedge? That surely has to be more expensive to build than an OHV.<< I believe the hemi chamber is more efficient. If the Dodge OHC engine you are referring to is the new 4.7 V8, information that I've read indicates it's a polysherical combustion chamber, not a wedge. >> A hemi chamber,of course, is parabolic. The piston isn't what is hemispherical. There are a few current head designs(the Ford OHC's come to mind) that have swirl inducing bosses to enhance low speed mixing.<< The chamber isn't a true hemisphere either. As far as swirl goes, are you saying that swirl cannot be induced in a hemispherical combustion chamber? >> So again, your streamlined open roof with unobstructed ports can actually be a detriment for low speed mixing. Why would the "new hemi" have 2 plugs?(if indeed it is a hemi) The bottom line, again, is a domed piston will have more flame travel problems than a flat or even dished piston. << Combustion chamber design technology is not static. Two plugs per cylinder could be employed for other reasons, similar to the Nissan and others. If a domed piston is fitted to most wedge chamber designs, I would agree that flame propagation might be a problem. But apparently you are not familiar with the actual shape of the hemi chamber used in the new 5.7. Please example some documentation that supports your contention that all hemisherical designs must suffer in this area. >> I'm curious to what your response is to your comment the big block chevies and Fords being phased out shortly after the hemi when they are still in production in one form or another.<< First, Chrysler was out of the medium and large truck business by 1975, motor home chassis by 1977. No need for big block motors, especially in the pitiful production numbers Chrysler had then. Chrysler stopped producing big block motors for their cars and trucks in 1978. As for cars, Ford dropped the 429 in 1973, I the 427 and 428 were gone soon after. The 400 was dropped in Ford and Mercurys in 1978, Lincoln dropped both the 400 and 460 in 1979. Chevrolet dropped their big blocks cold in 1977, Buick, Pontiac and Olds dropped theirs (403) and Cadillac theirs (425) in 1979. As for trucks, Chevrolet/GMC dropped the 400, replaced with a lower compression, lower HP version of the 454 in 1979. Ford dropped the 360 in 1974 and the 400 in 1982. The 460 was introduced into the Ford HD truck line in 1978. Both of these examples are the result of the first federal emissions standards impacting trucks and the manufacturer's consolidation of power plants. It was easier in the late 1970s and early 1980s to overcome the ravages of emissions with larger displacement designs, and then only in trucks. I might add, these engines sometimes required significant investment in cylinder head redesign to meet emissions anyway. It didn't make sense to offer a broad range of power in incremental packages. Everybody reduced engine line-up. The fact that they or their offspring are produced today is totally irrelevant to the events of the 1970s. First, they have experienced significant changes in head, intake, and exhaust design to meet emissions and increase efficiency. Second, they are here today because gasoline is cheap and rear-wheel drive trucks are in vogue. But my point anyway was specifically Chrysler, which obviously had no need for big block motors of any type. >> The bottom line is that if it was such a great, efficient VE design it would be more widely used. C'mon, how can it be more expensive to produce than a DOHC 4 valve or even an OHC 2 valve.
maybe because it just doesn't work when more efficient, lower rpm power is needed.<< More than two full decades elapsed between the last production 426 Chrysler hemi and the DOHC trend in American production engines. We've seen low numerical axle ratios, the Wankel, diesels, turbo charging, 2-4-6-8, water injection, come and go in American cars. Since the last 426 hemi great advances have been made in materials and production technology which puts an array of designs within easier and less expensive reach. The hemispherical combustion chamber design theory was never popular with Ford and GM, even though both would produce them. Chrysler was in almost constant turmoil, internally, and greatly distracted. To their credit they consolidated scarce research resources to improve the wedge combustion chamber design and for a number of years their "small block" motors met emissions without the costly add on devices (air pumps in particular) that robbed power and performance from their competitors engines. For the same reasons Chrysler quit making them, neither Ford nor GM wanted to invest in a chamber design they had little research experience with and would cost more to tool and produce than current designs. Dusty

#50 of 55 We'll just agree to disagree then. by modvptnl

Mar 04, 2002 (11:03 pm)

A lot of your big block info is waaaay off. To drop a 429 in favor of a 460 doesn't mean anything. Ford still used the 460 in LTD's until '78/79. The whole car line was down sized, not just the motors. The 402 AKA 400 and 454 is the same family. Ford 400??? Why are you bringing up a small block??
 
"I might add, these engines sometimes required significant investment in cylinder head redesign to meet emissions anyway"


 
BINGO!!!! If the hemi would have been more efficient for these applications it would have been incorporated!!!
 
<The chamber isn't a true hemisphere either. As far as swirl goes, are you saying that swirl cannot be induced in a hemispherical combustion chamber?>
 
Please explain, the 426 was the ONLY true domestic hemi. The Ford was a crescent shaped dome(called the semi-hemi) in the Boss and GM never made one(not sure what you mean by GM tried). Ironic statement IMHO in that if swirl were induced by changing the shape of the chamber you don't have a hemi any longer.
 
This last statement made is probably what I've been trying to say all along. The basic canted valve dome type chamber can be utilized with smaller valves or swirl inducing technology or maybe even multi valve technology. But once you start messing with the chamber you can call it a hemi or hemi magnum or whatever you'd like but it wouldn't be a true hemi in the 426 tradition......because it just wouldn't work, then or now.

#51 of 55 Well........................... by dustyk

Mar 06, 2002 (7:46 pm)

>>the 460 in LTD's until '78/79. The whole car line was down sized, not just
the motors. The 402 AKA 400 and 454 is the same family. Ford 400??? Why are
you bringing up a small block??<< My information regarding the phase out of various engines was obtained by Chilton's. They do not list a 460 in LTDs in 1979. Only Lincolns. The various engines mentioned were to demonstrate the decline of big displacement power plants by all manufacturers. If you remember, your claim is that the 426 hemi was dropped because the hemi couldn't be a daily driver and was hard to meet emissions. My response has been consistently that the 426 hemi didn't have a future because of cost, low production numbers, and at a time when large displacement motors became dishonorable. While Chrysler's position was more acute, it is plain and simple that large engines by all companies were quickly losing favor for the same reasons: disinterest in high performance engines, decreasing fuel consumption, reducing manufacturing costs, meeting emissions. >>("I might add, these engines sometimes required significant investment in
cylinder head redesign to meet emissions anyway" ) BINGO!!!! If the hemi would have been more efficient for these applications it would have been incorporated!!!<< Silly response. Why invest in expensive methods to accomplish this when wedge designs would meet emissions with less cost? To make a 318 or 360 small block Chrysler into a hemispherical engine in 1972 would have been illogical. The added weight of the increased mass in cylinder heads alone would have been a negative (the 318 and 360 were already heavy enough), much less developing new tooling and manufacturing lines. It was cheaper to make the wedge chamber engine meet emissions, not because the hemi chamber wasn't capable, but because they were already wedges! Even if it would've been MORE difficult to meet emissions WITH A wedge, it would have been cheaper to stay with that design to reduce tooling and manufacturing costs. Proof that a hemispherical combustion chambered engine meets emissions and low-speed driveability requirements, there has been a hemi engine in production and used in both cars and trucks from 1974 to 2000. Maybe this company hadn't heard that it couldn't be done! >> Please explain, the 426 was the ONLY true domestic hemi. The Ford was a crescent shaped dome(called the semi-hemi) in the Boss and GM never made one(not sure what you mean by GM tried). Ironic statement IMHO in that if swirl were induced by changing the shape of the chamber you don't have a hemi any longer.<< In the early seventies Oldsmobile made several versions of "W" engines incorporating very radical valve and cam arrangements. One of the first engines was a hemispherical combustion chamber with a typical two valve per cylinder layout, then progressing to a four cam, four valve motor. Each variant got a number (W40, 41, 42, 43, etc.). The combustion chamber was purposely not referred to as a "hemi" even though the head chamber shape contained the same angular profile as Chrysler's 426. Ford produced "hemi" kits in the early fifties. These converted the Ford flathead, as I recall, to a hemispherical combustion chamber. If you cruise the web, you'll find these, I believe. >> This last statement made is probably what I've been trying to say all along. The basic canted valve dome type chamber can be utilized with smaller valves or swirl inducing technology or maybe even multi valve technology. But once you start messing with the chamber you can call it a hemi or hemi magnum or whatever you'd like but it wouldn't be a true hemi in the 426 tradition......because it just wouldn't work, then or now.<< Haven't a clue what you're trying to say here. In reference to the new Chrysler 4.7 motor, I cannot find any Chrysler literature source that calls it a "hemi." In fact, several independent sources use the phrase, "not a true hemi." But beyond that your claim is just that. Swirl is required in a wedge chamber because there is a large dead area on the other side of the valves furthest away from the spark plug bulkhead. That flame front cannot reach that area reliably and combustion efficiencies cannot be raised without flow restricting swirl techniques, especially in a conventional design where the valves are placed in the middle of the chamber roof, side-by-side. A hemispherical chamber that places the spark plug in the chamber epicenter has a more equal and much more symmetrical flame pattern. In addition the plug is cooled by the mixture stream. It is true that flame propagation will not reach the extreme lower edges in a STATIC CHAMBER. However, turbulence-producing piston profiles are able to scavenge these small areas the same as swirl inducing techniques used in wedges, except without the inherent induction losses. Now, you have continually referred to the 426 "hemi" as if it is the quintessential hemispherical combustion chambered engine. It may be quintessential, but it, too, is not a "true hemi." Everyone who knows anything about hemi motors knows that the 426 CID motor manufactured by Chrysler from 1966-71 contains a near trapezoidal chamber roof. The motors you appear to know nothing about are the "true" hemis built by Chrysler from 1951-59.

#52 of 55 Ford's 460 by andre1969

Mar 06, 2002 (7:53 pm)

Last year for it in passenger cars was 1978. It did not make it into any of the downsized "Panther" bodies. The 400 hung around for 1979, but only in the Lincoln Continental 4-door and Mark V coupe. They were just boat anchors by then, down to something like 166 hp.

#53 of 55 we're splitting hairs now by modvptnl

Mar 06, 2002 (9:08 pm)

Your comment that the 429 was dropped in '73 was why I mentioned the '78/'79 460 LTD's.
 
Look, we'll NEVER sway each other's opinion. It's just that if the hemi was so much more efficient at all engine operating parameters, it would have made a resurgence a long time ago. Efficiency to me in a production (not race motor) translates not only to the PEAK power produced but the all important emissions and CAFE while doing it.
 
There has been so much spent to extract a good balance between performance, emissions and economy that if the hemi were to have an advantage it certainly would have been on new LS1's or the 4 valve Ford motors or the OHC chrysler and Ford motors. You can't tell me that a hemi with all its advantages would be more costly to build than any of these motors(with the exception of the LS1, even though it is a fresh, clean sheet design)
 
As far as a flat head Ford with a hemi head....I can't even envision this simply because of the non-OHC layout.

#54 of 55 GMengineman1 by gmengineman1

Apr 27, 2002 (9:19 pm)

When I was much younger I was part of a racing team that ran a twelve port Wayne Hrning head equipped GMC 302 c.i.d. in line six cylinder engined roadster. The thing was a torque monster (for it's day). The two competitors who gave us fits were 1) a Ardun valve in head conversion Ford (originally a flathead V-8) and a built up Dodge 341 c.i.d. hemi engine. Both were strong. Both were fast and both won consistently at the 1/4 mile drag races at L.A.D.S. Raceway and at Colton (both in So. Calif.) My money still rides on the hemis (when built right) to get the win consistently. Those 392's and 426's are awesome!
Another engine that still impresses me is the Mopar 340 w/ six pak.

#55 of 55 by speedshift

Apr 27, 2002 (10:18 pm)

I know about the ARkus-DUNtov heads but what was a Hrning head? A crossflow conversion? Did the stock Jimmy head only have three exhaust ports?

Messages Page 6 of 6

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