: Bobbyinski -- Northstar failure



SHERIFF
01-07-05, 08:13 PM
Bobby, will you read the below link, examine the images, and give us an educated guess as to exactly what took place to cause this engine failure please? Thanks!!

By the way, those FORD guys don't like the 300 horsepower Northstar. Because FORD won't put such a powerful creature in their crap box Crown Victorias is my best guess. Just kidding, but they really do bad mouth the Northstar. :D

http://www.crownvic.us/forum/showthread.php?t=10184

elwesso
01-07-05, 09:08 PM
Looks like carbon build up, hence the oil consumption...

http://www.crownvic.us/forum/attachment.php?attachmentid=4881&stc=1

Theres a LOT of carbon on there!

Rick99STS
01-07-05, 11:06 PM
Those Ford guys are just upset because a stock STS will SMOKE a Marauder.

SHERIFF
01-07-05, 11:28 PM
Those Ford guys are just upset because a stock STS will SMOKE a Marauder.
Absolutely! I myself being the owner of both DTS and Marauder, I can tell you the DTS will too. :)

Katshot
01-08-05, 09:13 AM
Only from a dead start. Once the Marauder is moving and able to rev, it's all over. Ford just used the wrong engine in that car IMO. I would've used the SOHC engine myself. Either that, or install a 6-speed in the Marauder.
The pistons don't appear to have been scuffed at all and the carbon isn't that bad. Chances are, the engine was given a fairly good diet of mid-grade or even regular instead of premium and that combined with the "normal" ring issues caused the heavy oil consumption. I'll be interested to hear what Bbob thinks.

ellives
01-08-05, 10:13 AM
Only from a dead start. Once the Marauder is moving and able to rev, it's all over. Ford just used the wrong engine in that car IMO. I would've used the SOHC engine myself. Either that, or install a 6-speed in the Marauder.
The pistons don't appear to have been scuffed at all and the carbon isn't that bad. Chances are, the engine was given a fairly good diet of mid-grade or even regular instead of premium and that combined with the "normal" ring issues caused the heavy oil consumption. I'll be interested to hear what Bbob thinks.

How do you figure "once the Marauder is moving and able to rev, it's all over?" The N* comes into it's own on the top end... not off the line. I continue to see regular posts about N* vs. Hemi and the consensus is off the line 0 to 60 (or maybe even 80) the Hemi has it but after that it's all over.

Katshot
01-08-05, 10:29 AM
Oh PLEASE!
Isn't that Northstar vs. Hemi getting a little old? Been there, done that, Hemi wins. Next!
Have you ever driven a Marauder? Yes, they're a dog off the line but then look out. They are NOT a slow car by any stretch.

Dadillac
01-08-05, 10:58 AM
How do you figure "once the Marauder is moving and able to rev, it's all over?" The N* comes into it's own on the top end... not off the line. I continue to see regular posts about N* vs. Hemi and the consensus is off the line 0 to 60 (or maybe even 80) the Hemi has it but after that it's all over.

I have a little knowledge on this subject. Before i bought my Seville, I owned a 2003 Ram 4x2 with a Hemi. Now, the Ram isn't a car, and weighs more than the Seville, but I know the engine characteristics. Both the Northstar, and Hemi, make most of thier hp in the upper rpm ranges. Both will pull pretty good off the line. The Hemi's hp really kicks in at 3000 rpm. I have noticed the Northstar kicking in at 3500 rpm. After driving both (I know it's difficult to compare trucks and cars), I conclude the Seville would beat the Ram. But, I haven't driven a Hemi powered car, so I'm not sure how fast they are. But to sum it up, both engines do not "wake up" until after 3000 rpm.

Don

Katshot
01-08-05, 11:36 AM
If you have any doubts about the Hemi, just read any one the articles out now about the SRT-8. They should put your mind to rest and assure you that the Hemi is MORE than a match for any Northstar car.

elwesso
01-08-05, 12:12 PM
Its also a litre bigger......

Really they shouldnt call it the hemi since its not really like the old hemi's... Its just a name that has had a big marketing sucess...

I think in a few years we'll see a lot of "hemi"'s failing emissions, since i heard they barely passed.....

Katshot
01-08-05, 06:39 PM
Ya know, I heard that before but I haven't seen anything that backs up that statement. As far as I've been able to read, it's a Hemi.

ellives
01-08-05, 06:44 PM
Ya know, I heard that before but I haven't seen anything that backs up that statement. As far as I've been able to read, it's a Hemi.

So enlightened us as to what you've read.....

BeelzeBob
01-09-05, 12:55 AM
From the limited information and pictures I can't tell if anything is wrong....

Sounds like the engine was using some oil...??...enough has been said on that to fill a book already.

One down side to issueing a service bulletine and service parts (like the replacement pistons and service ring pack) is that suddenly everyone has the problem and needs the "new parts".... The assumption is that because updated or service parts are offered then it means that all the original parts are "bad" and the engine needs to be torn down whether it has an issue or not...real or imagined.

There is not "heavy carbon buildup" on the piston. There is very little actually. Some of you need to look at pistons from engines that have been used...i.e..run...to know what normal parts look like before saying things like that. All engines creat a little carbon on the pistons. Perfectly normal. Normal to light I would say on the piston in the picture.

All the parts in the picture look fine. Hard to believe the engine was using 3 quarts per 1000 miles...???....with the piston looking as dry as that. And somehow it ran 70K and then suddenly started using oil....

My guess it was a slow day in the shop.

BeelzeBob
01-09-05, 01:02 AM
Ya know, I heard that before but I haven't seen anything that backs up that statement. As far as I've been able to read, it's a Hemi.

The new "hemi" is closer to a small block chevy wedge head than an old original "hemi".... Just look at the combustion chamber and compare it to the old hemi. The only thing in common with the current "hemi" and the original "hemi" is the clever use of the name for marketing purposes.

This was thoroughly debated on another thread as copied below:

If you even take a glance at the cylinder head design of the new "hemi" you can see that it bears little resemblence to the hemi of old. Almost none at all. That is why people say (including me) that the new DC engine is not a "real" hemi. I guess to the old farts (like me) the only true "hemi" is a real hemispherical combustion chamber...and the new "hemi" is more a wedge combustion chamber with lots of squish area. No one in their right mind would design a true hemisperical combustion chamber these days. They just do not work. They were fine in the late 50's early 60's and make great nostalgia discussions but the legends are overblown. The old "hemis" that REALLY made HP had modifications to them that made them actually less and less a true hemi.

Before any one gets too worked up over this realize that this whole thing is just marketing anyway. Using the "hemi" name is a very clever idea that has worked tremendously well for DC. Hemi has a certain ring and recognition that is very effective. There is no legal requirement for calling the engine a "hemi" and you can spin the story and design however you want so , of course, if you believe the marketing guys at DC the new engine is every bit a true hemi. Talk to any engineer, however, and they will quickly show you it aint....LOL.

The old hemi had a combustion chamber that was almost a perfect half shere. Cut an orange in half and lay it on the top of the piston and that was the combustion chamber shape. The intake valve was on one side toward the intake and the exhaust was on the other side of the chamber. The spark plug was in the middle. This flows nice by moving the valves on either side of the chamber toward the intake and exhaust but makes a terrible chamber for combustion due to the fact that the chamber is so huge that it takes a large dome on the piston to make the compression high and then, at TDC, the resulting chamber that is left looks like the skin of the orange....it is a very narrow band that is a fairly large shere that takes FOREVER to burn. Very slow burn and VERY detonation sensitive. That is why those old Hemis at 12.5:1 needed racing fuel to make power or else you had to retard the spark so badly they feel on their face. That type of chamber just does not work anymore. It was alittle better than what else was out there at the time but it is poor by todays standards. That is why any and every engineer in the industry kind of smirked when they saw the new engine called a "hemi" as anyone that understands engine design knows that a hemi would never be competitive in todays world for emissions, fuel economy, etc....


When you name or market an engine there is always some level of commonality with most anything that can be used to spin a story. Take the Indy racing engine of several years ago that was called an Aurora....listen to the marketing guys and there was a long laundry list of commonality....DOHC, aluminum, bed plate block design, chain driven cams, etc.....even the cam covers said Aurora. Trouble is, no production dimenions interchanged, no production parts fit, etc.... it is just a marketing story.

If you take all the current "hemi" things that are quoted as being "common" with the old hemi you can see that those items are very conventiently selected. They seemed to leave out the part about the newest "hemi" having the displacement on demand design THAT A V-8-6-4 CADILLAC HAD IN 1981. True. Fact. Cannot escape that. Do they call it a Cadillac or V-8-6-4...???? Heck no. No story there. Call it a "hemi" and look for any possible way to spin the story. LOL.

Not trying to start a flamer here, just stating the facts. Nor am I descrediting the new or old "hemi" nor DC for captilizing on the marketing appeal of the "hemi" name. The new "hemi" is a nice engine that makes a lot of power, is very very flexible in it's design and displacement range. GM does the same thing with the "small block chevy" The new LS1 style engine bears little or no resemblence to the old small block. It it had been designed as a clean sheet of paper engine and the old small block would have never existed it would be just another engine. But it certainly markets better as a "small block chevy". And if it wasn't you wouldn't be hearing about the 50th anniversery of the small block....LOL

It is all a marketing game so don't get upset over it.

BTW...if you look at most cam-in-block or pushrod engines the valves are side by side along the longitundinal dimension of the block. Meaning that if you drew a line down the center of the cylinders on a bank the exhaust and inlet valves are oriented on that line. On the older and original pushrod engines it was ground breaking technology to cant the intake valve toward the intake port and the exhaust toward the exhaust port....gasp. That is where the term canted valve engines came from. Then different valve angles were discovered and experimented with including cocking the valves to the side as well as canting them toward the exhaust and intake. This is the design change that got the original "mystery motor" big block chevy lore started. Porcupine heads they were called due to the valves sticking up at odd angles and not side by side. The original hemi was just a further reach on this topic as Chrysler moved the valves side by side on a line crossways of the cylinders intead of oriented longitudinally. This allowed them to be closer to the respective ports, put the valves at the more opportune angles for the respective ports and allowed shorter intake and exhaust ports. It also allowed the plugs to be in the center of the combustion chamber. Trouble with this is that, with only two valves, and with large enough valves to allow flow, the chamber had to be HUGE to package the valves. See discussion above. The other problem with this is the extremely awkward valve train mechanism required to actuate the exhaust valve on the other side of the head canted the "wrong" way. Look at the old hemi rocker arms and you will see what I mean.

BTW more.....a spark plug with mulitple electrodes is NOT the same thing as having dual plugs in the chamber....LOL. By having dual plugs the burn rate of the chamber can be changed significantly (shortened or faster) by initiating the combustion from opposite sides of the chamber. The burn rate is how long it takes the charge to burn from the plug toward the farthest reaches of the chamber. This is governed by physical dimensions of the chamber so by putting more than one plug in the chamber the distance from any given plug to the farthest reach of the chamber is reduced..making the burn rate of the chamber faster (good). You can put 20 electrodes on the plug and it will not change the burn rate of the chamber. LOL.


Main lesson here. Read the ads and car rags with a large grain of salt. Do NOT get your automotive engineering or engine design education from marketing sorts. Few of them even understand what they are trying to convence you of and fewer yet understand what they are trying to explain to you. They are trying to sell cars. Period. If "hemi" works...use it. LOL.

SHERIFF
01-09-05, 01:05 AM
Thanks! And yes, I agree, it was very limited information available. Just pictures of an engine torn apart. I had never even thought about maybe the shop simply needing the "work". :)

Took you long enough to get here! I thought we were going to have to send somebody to bond you out of jail or something. (just kidding) :D

BeelzeBob
01-09-05, 01:31 AM
Funny how the Ford lovers seem to enjoy seeing a Northstar apart....LOL

They must not hang around Ford dealers much to get pictures of the Ford engines apart....LOL.

Spyder
01-09-05, 01:32 AM
Awesome post on the hemi...once again, thoroughly enjoyed the learning, great info and such. :)

haymaker
01-09-05, 01:44 AM
Yep, Chevy tried to chime in with the big block they called it the semi-hemi. The valve train was always wearing the valve guides into an oval shape when running a high lift camshaft sometimes within a few thousand miles then the oil seals couldnít stop the oil at the stem-guide area after that the oil would be sucked or leaked into the combustion chamber fouling the plugs along with some exhaust smoke at start-up. If I remember correctly the street hemi ran like 34-36 degrees total timing but the Chevyís were more like 40 degrees total timing. When I had my N* down I noticed how much the combustion chambers reminded me of the old street Hemi except for the depth of the chamber and the two extra valves. I still have some of the old Hemi tulip intake valves out in the garage.
Nice post bbob.

Katshot
01-09-05, 09:48 AM
Yeah, I remember that post from before, very nice. But since I've never actually seen one of the combustion chambers from a "New Hemi", I can't say with any degree of certainty that you are correct. If, and when I actually DO see one, I'll chime in on it. But until then, I'll just go along with the 99% percentile that takes D/C at their word. Maybe I'll stop over at the Dodge dealer to satisfy my curiousity next week.

eldorado1
01-09-05, 03:13 PM
Got a northstar? You've got a hemi. http://cadillacforums.com/forums/images/smilies/hammer.gif (in the purely technical definition sense of a hemispherical combustion chamber)

dkozloski
01-09-05, 05:10 PM
A true hemispherical combustion chamber engine with a flat top piston works out to be a very low compression ratio engine unless it has a very long stroke. The only examples I have seen with anywhere near a square bore stroke ratio are large, highly supercharged, radial aircraft engines. As such even the old '50s Dodge "Red Ram" was not a true HEMI with its domed pistons. Marketing hype forever.

ellives
01-09-05, 05:38 PM
Chrysler (at least in the last 10 to 15 years) has been more about marketing than real substance. In the case of the current "Hemi" craze, at least there is a real product there as far as horsepower output, even though it's clearly nothing more than a modern, high displacement, high horsepower engine that could be built by anyone. Heck even Nissan is doing it. They just don't call theirs a Hemi.

dkozloski
01-09-05, 06:01 PM
The marketing prose in the '50s was pretty interesting. The Buick "nailhead special", refering to the small exhaust valves, was called "pent roof". The 348 Chevy had no combustion chamber in the head at all. The bottom of the head was totally flat with the valves highly pocketed, which seems counter-productive, but in fact was an ingenious way to improve valve opening rates. The top of the block was not 90deg. to the bores but was cut off at an angle thus forming a wedge shaped cumbustion chamber against the flat bottomed head. Because the valves were pocketed they could be operated with a cam with pretty conservative opening ramps but the valves would not start to flow until the opening rate was well established. Thus the duration could be much longer than normal without destroying bottom end performance. The same on closing. The 348, 409, and 427 would all wind as well as a 283 with the Duntov cam; easily reaching 7500 RPM without valve float. These were the engines with the weird sculpted valve covers.

ljklaiber
01-09-05, 06:19 PM
Leaving all the wedgie, Hemi nonsense aside..The NS is a DOHC, 4valve , all alloy engine that is "MODERN"> Since I kept my bore scope..(looks in through spark plug hole) ....when I sold out of my shop, I can say that that piston in the photo looks about the same as my 95 SLS with 146K.

My problem is with the dumbass that laid suspension components on an alloy block in the other photo. Real pros at that shop. COLLECT YER CHECK! CYA!

CoupeDevilleRob
01-09-05, 06:30 PM
I'm sick of hearing all these Crown Vic guys rag on Caddys. My friend is one of these freaks and I have to put up with it constantly. His 01 Vic has to be one of the worst put together cars I've ever encountered. There's something like three seperate rattles in the dashboard, the door panels squeak and creak, and the front end squeaks incesantly. And there is an assortment of vibrations and shakes that come and go. All this on a car with 31,000 miles. Granted my Caddy has a few squeaks and rattles, but its 22 years old and has 107,000 miles. They're just bitter that for whatever reason they had to settle for a Crown Vic/Grand Marquis instead of a Cadillac.

That felt good, had to get that off my chest.

dkozloski
01-09-05, 06:37 PM
ljklaiber, I agree completely. In this area, work of this quality is called a dirt-floor overhaul even if the floor the parts are sitting on is concrete. In a first class shop the floor has tile with rubber matting or the floor is end-grain hardwood. The benches have rock hard maple, Formica, or similar non-metallic tops. Two thumbs down.

ljklaiber
01-09-05, 06:37 PM
FYI! I might add that the City, County , and State Cops here in SE Georgia all drive Ford Crown Vics. I , as an old guy get to lean on them a bit at the AllNight restaurants. SLS can handle any of them

"sneaky Pete races have ALL been in favor of my 95 SLS. Belive it or not the Taller gearpoint works against STS types who light up their their tires and have to play catchup. Not the cars fault. FWD is not bad at all when you get used to it. RWD unloads on the light end and they can't recover. JMO!

danbuc
01-09-05, 06:44 PM
Most states use the crown vic now, since chevy no longer has the contract for the 9C1 caprice, which I might add was an awesome car. Newark, Nonly uses old, busted up caprices, mainly cause the town cant afford the new crown vic's :helpless: . I heard a story a while agao about a proble that the crown vic's had with rear end colisions. Aparrently, they had a tendensy to explode when hit directly in the rear. There was a cop writing a ticket when jeep smashed into the back of his car and both exploded into flames killing them instantly. I then heard that Ford filled the rear bumper with fire retardent foam, in order to prevent this. This has got to be the most idiotic idea ever. That like having a recall on a car for a cracked chassis and fixing it with duct tape. WTF were they thinking? :hmm: . Typical ford I guess, oh well. Not my problem. :D

ljklaiber
01-09-05, 06:46 PM
You got dKosloski! Down here we call it 'dirtball' bar B Q. No excuse for a bare block being use d as a parts stand.

STS 310
01-10-05, 10:58 PM
I cant understand why someone would buy a crown vic as a personal ride.

EEEEWWWWW.

I went to the crown vic board and all the pics are all of have cars that are dirty and, well.....

I wont go there!!

Those guys WORSHIP the marauder. LOL................

BeelzeBob
01-10-05, 11:07 PM
Got a northstar? You've got a hemi. http://cadillacforums.com/forums/images/smilies/hammer.gif (in the purely technical definition sense of a hemispherical combustion chamber)


I would characterise the Northstar chamber as a pent-roof chamber,not a hemi. A hemi is hemispherical. Both the Northstar intake and exhaust valves are in the same plan...so they form a pent roof not a hemi.

Even the old "hemi's" were not totally hemispherical...but close.

BeelzeBob
01-10-05, 11:10 PM
If I remember correctly the street hemi ran like 34-36 degrees total timing but the Chevy’s were more like 40 degrees total timing.


The street hemi's were severely detonation limited. They really wanted 45 degrees of timing...but there was no gas good enough. On the drag strip and racetrack, where gas was not the limiting factor, the standard tuneup on the old hemis was way over 40 degrees of spark. The hemi chamber is actually terrible for detonation. It is very large and the spark plug is a long ways from all the end gas in the chamber. Worse yet, when the piston crown is bumped up to raise the compression (necessary with the huge combustion chamber) it starts to block the combustion chamber off so that it gets thinner and thinner and the burn rate gets slower and slower and the propensity to detonate gets worse and worse.

STS 310
01-10-05, 11:21 PM
The street hemi's were severely detonation limited. They really wanted 45 degrees of timing...but there was no gas good enough. On the drag strip and racetrack, where gas was not the limiting factor, the standard tuneup on the old hemis was way over 40 degrees of spark. The hemi chamber is actually terrible for detonation. It is very large and the spark plug is a long ways from all the end gas in the chamber. Worse yet, when the piston crown is bumped up to raise the compression (necessary with the huge combustion chamber) it starts to block the combustion chamber off so that it gets thinner and thinner and the burn rate gets slower and slower and the propensity to detonate gets worse and worse.

See, I can barely understand that (comprehenssion is there) but, it makes sense. What were the variables, or was it push for the "something new technology".

Or the greatest, "Through it out there, and hope it works approach."

BeelzeBob
01-10-05, 11:34 PM
I heard a story a while agao about a proble that the crown vic's had with rear end colisions. Aparrently, they had a tendensy to explode when hit directly in the rear. There was a cop writing a ticket when jeep smashed into the back of his car and both exploded into flames killing them instantly. I then heard that Ford filled the rear bumper with fire retardent foam, in order to prevent this. This has got to be the most idiotic idea ever.


You heard a story like this...???....LOL The propensity of the Police Crown Vic to catch fire when rear ended has been on all the news shows, CNN, 20/20, Prime Time, etc...for several years.

In Ford's defense, any car with the fuel tank in the rear (like cars used to be made) is susceptable to fuel tank damage when rear ended in a severe high speed impact. You just cannot avoid the fact that the fuel tank is in the rear, the rear of the car is going to crush when rear ended and the fuel tank is likely to be involved. That is why most cars have gone to mid mounted fuel tanks. The architecture of FWD cars makes this easy. RWD cars with driveshafts makes this harder. Not impossible, but harder. The Crown Vic is an old platform that was designed LONG before severe rear impact issues came along and it has the fuel tank in the rear. It is almost impossible to relocate the tank without completely redesigning the car so....

The fix that Ford is implementing on the police packages is to add armor to the fuel tank and to add the foam to the bumper area. The foam is energy absorbing foam....like as in styrofoam....not some sort of flame retarding foam....like foam from a fire extenguisher....LOL LOL

The Crown Vic with the rear mounted fuel tanks is a very safe car in my estimation and it is the same crown vic that has been driving around on the streets for decades with no apparent fire problem. The car easily passes all the rear barrier standards and that includes fuel tank leakage and damage assessement...

The PROBLEM is the cops tendency to park their cars in high traffic spots and to use their cars as traffic blocking devices. They are also frequently stopped alongside the expressway with high speed traffic inches away while they write a ticket. They CONSTANTLY put their cars in positions just begging for them to get hit....from behind....by high speed traffic. And then they cannot understand why they catch fire. This is a huge DUH.....for law enforcement in my opinion. I see police cars used as barriers and needlessly parked in compromised positions all the time that make me cringe. Somehow they think that the flashing light on their roof makes them immune from someone hitting them. Guess again. If they planned on making the car a "target car" on purpose they should have ordered cars with closed cell foam bladders in the tanks instead of blaming Ford.

Remember the chevy "side saddle" fuel tank fire debacle that just disappeared with the "Prime time" stunt...??? The Ford police car rear impact fires is a close second in terms of stupidity but everyone is afraid to tell the cops this.

My rant....police stop a truck for speeding at 3:00 AM on the interstate near Detroit. While sitting behind the 18 wheeler the police car is rear ended and jammed into the truck by another 18 wheeler whose driver had a momentary lapse of concentration/moment of drowsyness/whatever. Unfortunately , just where he veered onto the shoulder there was a police car (needlessly) parked. So...instead of the rumble strips waking him up and alerting him so he can pull back into the lane he kills the cop. Cop is a hero in the local papers. I think he is no hero and needed his head examined instead. Stopping a truck by the side of the interstate in the dark and creating a traffic hazard for half and hour or longer is WAY WAY more danger than was created by the truck running 75 MPH at 3:00 AM. Even if they did need to stop someone like that, wait for an exit ramp and stop them off the highway. The use of police cars for battering rams and as blocking devices and leaving them exposed to high speed rear impacts all the time makes one want to avoid having your cars used as police cars for all the bad publicity they get. End of rant.

STS 310
01-10-05, 11:46 PM
Politics.

Nuff said.

SHERIFF
01-11-05, 12:00 AM
I see police cars used as barriers and needlessly parked in compromised positions all the time that make me cringe. Somehow they think that the flashing light on their roof makes them immune from someone hitting them. Guess again.
BINGO! We have a winner. Nuff said! :)

BeelzeBob
01-11-05, 01:33 AM
See, I can barely understand that (comprehenssion is there) but, it makes sense. What were the variables, or was it push for the "something new technology".

Or the greatest, "Through it out there, and hope it works approach."


Remember that the hemi was a mid 60's technology engine. The location of the valves across the chamber rather then side by side made the heads flow great (for the day) so they just lived with the chamber design. When you put two large valves across the chamber like that the chamber has to be pretty large to allow a high enough roof to accomodate both the valves and allow the spark plug in the middle. Combine those features with a large bore for big displacement and the geometry of the chamber reeks of detonation. The hemi was detonation limited in just about every form which is why it reached its power limitations on street fuel very quickly.

Detonation is the spontaneous combustion of the end gas in the chamber. As the spark ignites the charge and the mixture burns across the chamber (it is a progressive burn....not an explosion all at once) the end gas in the chamber is subjected to more and more heat and pressure....to the point that it can spontaneously combust if the fuel octane rating is not high enough. To prevent detonation you want a compact chamber that doesn't take long for the burn to cross and lots of turbulence in the mixture to speed up the combustion rate. With a small or compact chamber the end gas is not exposed to the heat and pressure for nearly as long so it is more resistent to detonation given a fixed octane rating. The hemi violates all of these. The chamber is huge. It has very little squish areas for generating misture motion. Due to the dimensoins of the chamber and the low turbulence and slow burn the end gas was heated and compressed unusually long and it would detonate frequently unless high octane fuel was available. To make matters worse, when the dome was added to the piston, the combustion volume became thinner and thinner....the "peel of the orange" description is very accurate. The flame travel thru the thin cross section of the chamber was very slow so the detonation tendencies got worse and worse. Not a good design for combustion but it was a good design for flow in those days so it made a splash...mainly because of the large cubic inches for the day.

dkozloski
01-11-05, 02:18 AM
Aircraft engines and fuel dragsters that use hemispherical combustion chambers get by with it by using dual ignition systems (dual sparkplugs) to shorten the distance the flame travels. Total advance for an aircraft engine is about 25 Deg. If you lose one magneto the power drops way off and things get hot.

BeelzeBob
01-11-05, 02:20 PM
Aircraft engines and fuel dragsters that use hemispherical combustion chambers get by with it by using dual ignition systems (dual sparkplugs) to shorten the distance the flame travels. Total advance for an aircraft engine is about 25 Deg. If you lose one magneto the power drops way off and things get hot.


Exactly....which is what the "new" hemi does. Dual plugs on either side of the chamber. That allows the valves to be closer together in the center of the chamber (reducing size and volume) and shortens the flame travel for a faster burn chamber.

The shape of the new hemi head is soft of a hemi but more of a pent roof design with large squish areas on both sides for turbulence/in cylnder mixture motion.

haymaker
01-11-05, 04:47 PM
The street hemi's were severely detonation limited. They really wanted 45 degrees of timing...but there was no gas good enough. On the drag strip and racetrack, where gas was not the limiting factor, the standard tuneup on the old hemis was way over 40 degrees of spark. The hemi chamber is actually terrible for detonation. It is very large and the spark plug is a long ways from all the end gas in the chamber. Worse yet, when the piston crown is bumped up to raise the compression (necessary with the huge combustion chamber) it starts to block the combustion chamber off so that it gets thinner and thinner and the burn rate gets slower and slower and the propensity to detonate gets worse and worse.
I am not a Hemi guy but it has its good points. I cut my teeth on small Chevyís. I donít want to be misunderstood because of all the links to Hemi websites I have included below they are for any of you that donít know what a Hemi is or have never viewed the Hemi valve train or combustion chamber.

Bbob.. What reference do you have for over 40 degrees total timing in a street Hemi? I sure donít remember anyone running that much total timing. Who do you know that was running that much timing in a street or race Hemi? I thought 38 degrees was a bit much. 101-102-octane gasoline was common on the street in those days.

Maybe I forgot how the whole flame travel thing works. I know the Hemi combustion chamber is large but the sparkplug is the center, so that would be half the distance to the other side of the chamber in any direction. One would expect the flame to travel across the entire area outward from the sparkplug with very little restriction. The wedge combustion chamber (although smaller than a Hemi) has the sparkplug all the way over to one side and when the sparkplug fires; the flame must travel across the area to the other side of the chamber which isnít that much shorter than the flame travel in the Hemi. If you look at both the hi-compression Hemi and wedge combustion chambers with the piston at TDC it sure looks as though the flame would travel through the Hemi chamber less encumbered than the wedge chamber.
It was always my understanding, the better the combustion chamber design the less total before top dead center timing hence the Hemi with the 36 degrees and the wedges at 38-42 degrees.


http://www.thehemi.com/forums/viewtopic.php?t=501 total timing for a street or race Hemi.

http://www.geocities.com/dodgedifferent2/hemi.html 427 Chevy, 289 ford and Hemi Combustion chambers comparison.

http://www.hotrodsandhemis.com/ demo showing the difference between wedge and
Hemi combustion chambers in action

http://www.thehemi.com/forums/viewtopic.php?t=419 Picture of the 5.7L Hemi combustion chamber about half way down the page.

http://www.hemi.com.au/hemidefinition.htm drawing of an early Hemi cylinder head.

http://www.thehemi.com/forums/viewtopic.php?t=516 Hemi cutaway picture.

BeelzeBob
01-11-05, 11:08 PM
The real problem becomes , as described, when the piston crown is raised to increase the compression. When the piston is near top dead center the dome sticks up into the chamber. What is left of the chamber that is holding all the mixture about to be ignited is represented by the "skin of the orange" analogy. The actual chamber is a very thin volume that is spread out in all directions. The burn has to progress across this thin cross section...not directly across the whole chamber. By the time the burn reaches the perimeter of the chamber the end gas has had ample soak time at high temp and pressure so as to be very susceptable to detonation.

Not to belabor this but think of the skin of an orange sitting on the table. There is a long way from the center of the skin at the top along the skin to the farthest edge. The "center" is not just the center of a circle but the center of a hemisphere...a very thin layer of a hemisphere. so the flame has to travel outward to the edge as well as pretty far downward to the end of the chamber...and it cannot go straight...it has to follow the curve of the hemispherical shaped skin of the orange.

A number of the guys I work with used to race hemi engines "back in the old days". In fact, one of the techs that we have was an ex Chrysler racing support tech that retired and then got tired of being retired and came to work for us. He has told me many stories of the pitfalls of hemis and what it takes to make them REALLY run..... Honestly, I have never run or tuned a hemi myself but I trust my sources as they were pretty close to the action in those days.

BTW....it takes better than 101 octane leaded fuel to run the timing that high in a hemi to make power. That is the point. The engine is very detonation limited on 101 octane fuel from what they have told me. The "tune" on 110 octane leaded racing fuel would involve even more spark at 40 degrees. When the chamber was not detonation limited the spark could be increased even more and even more power was made. You just cannot find fuel like that though....

The Reno air racers run spark numbers like that in the Rolls Royce Merlins (which also had a very slow burn chamber) and they get heavily leaded racing fuel that is reported to be 124 octane rating. VP Racing Fuel used to supply this stuff and called it "air race special". Only place it was obtainable.

Excellent Hemi pictures and references in those links BTW. When you look at the picture of the new hemi combustion chamber you can see how much flatter it is and the squish areas added to the sides. It still resembles an old hemi in that the valves are across the chamber instead of side by side in the non-hemi engines...but you can also see that the original hemi was much more hemispherical in shape and far larger.

Another problem with the old hemis was the huge surface area of the combustion chamber and the piston dome. Lot of area to absorb heat....and to heat up the mixture futhering the detonation problem.

DeLorean_Northstar
01-12-05, 03:14 PM
its funny to hear them ford guys bad mouthing a Cadillac. I just recently purchased a 1997 Cadillac Seville SLS with 164,000 miles from the original owner (gold keys and all) for an AWSOME DEAL, and I must say in the almost 6 months that I've owned it, i've had less problems with it than my (sold) 2003 Mercury Marauder financed NEW, owned for a year and 6 months and put 18,000 on it. My Marauder almost got Lemon Lawed due to electrical problems. sold it and got the caddy. I also used to work for a police department garage and let me tell you, you dont know what oil burning is untill you've seen a P71 police interceptor. ive seen cars be decomissioned from police use at just over 60k, granted not very many but its happened. to be fair my brother got a 97 deville with 130,000 that he got for an awsome deal (too good to be true) but found out hes got blown head gaskets. even with blown head gaskets, my brothers deville could take the Maruader. thats gotta say somthing. I loved the Marauder and the only reason I got rid of it was because I couldn't afford it anymore, but I'll take a blown head gasket Northstar over a FORD anyday!

I do admit ..... I still drive my Cadillac wearing the leather jaket that came with the Marauder :shhh:

Stoneage_Caddy
01-12-05, 04:39 PM
Bob , your the first person i heard talk of the porcupine head outside a little blurb on a nascar show ...

can you tell more about it ?

always wondered about that engine ...

i guess it never made it into production ?

SHERIFF
01-12-05, 05:44 PM
its funny to hear them ford guys bad mouthing a Cadillac. I just recently purchased a 1997 Cadillac Seville SLS with 164,000 miles from the original owner (gold keys and all) for an AWSOME DEAL, and I must say in the almost 6 months that I've owned it, i've had less problems with it than my (sold) 2003 Mercury Marauder financed NEW, owned for a year and 6 months and put 18,000 on it. My Marauder almost got Lemon Lawed due to electrical problems. sold it and got the caddy.


BINGO! We have another winner! :)

dkozloski
01-12-05, 06:06 PM
If you want to see what is happening in a combustion chamber just fill a large room with natural gas. When the mixture is correct just touch it off in one corner. The Bureau of Mines guy I talked to said that initially the flame front travels just a little faster than you can run. As the combustion continues it heats and expands the air which compresses the remaining mixture. As heat and compression continues the process gets faster and faster and more intense until the climax which is the explosion. A large gas explosion produces a characteristic drawn out WHHUUUUUUMP!! The local Dairy Queen restaurant blew up one morning at 4:00 AM and I knew instantly what it was. The difference in a combustion chamber is that the process is carried a step further. In normal combustion the flame as seen through a quartz window in a test engine is blue. If conditions are correct the combustion can become so intense that the remaining mixture will all go at once in the process known as detonation. If you are looking through the quartz window you will see a blinding white light. In your car when you hear that plinkling sound like throwing pea gravel at a pipe what you are hearing is cylinder walls and other important parts flexing and springing under the extreme pressures.