Larry's Soft Head

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Steve Baker

I dont get it!

Post by Steve Baker »

OK, I have been lurking and reading his thread and I am now so thoroughly confused I am about to throw my hands up.



First I read this statement which taken in its entirety makes absolutely no since at all and is completely contradictory. Sorry, but the laws of physics can not be twisted like this. No way.
"Because the mixture is more homogenous, it gives a faster burn that lasts longer - the ignited mixture expands more slowly"


Then there is the matter of this,
"What Widmer is claiming, is that by increasing the burn rate, the ignition lead can be reduced, thus allowing the peak pressure point to happen later in the cycle, closer to peak piston velocity and therefore the point of maximum leverage on the crank throw."
ALL the power in a race engine is made in the first inch of piston travel the rest of the time your either opening valve to get the gas out or opening to get the gas in. In some high end engine making well over 2.7 horsepower per cubic inch the exhaust valve opens at 27° to 28° after TDC.


OK what about this one,
"The cylinder pressure vs. crank rotation shows the advantage of the soft head over a typical cylinder head. The soft head yields more cylinder pressure during the time of maximum piston velocity on the power stroke."

If all Comp and Pro stock engines open the exhaust valves at like 27° ( Darrin M or Larry M please confirm) there is no way there is any added cylinder pressure because the exhaust cycle is HALF DONE.

You cant delay an event and make it up on the back sied when there isnt any time to spare as it is. If you hang onto the power stroke for that length of time, how do you get the exhaust out in the time left???




You guys are going to have to explain this to me because this whole " Soft head" deal is a complete contradiction form start to finish.
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Post by putztastics »

Now I'm just a putz but the supersonic exhaust port seems to play a big part. There appears to be a scavenging/flow/reversion advantage with a supersonic exhaust port that allows it to support the same total exhaust flow with less valve open time.
On the exhaust side, everything’s easy. Open the exhaust valve at or near BDC, allow an efficient (sonic) port to efficiently remove the inert gasses, and then seat the valve near TDC.
In the late '70's we found that if you decreased the cross section of the exhaust port to the point where the flow exceeded mach 1, the amount of work necessary to properly scavenge the cylinder was almost nil. By placing the port's smallest cross section well below the seat insert, the flows maximum velocity was now in an area where we could control the sonic shock and use it’s placement to allow the port to literally "pull" the flow out.
To relate to typical exhaust port operation on a flow bench, one normally needs to adjust the pressure drop with each incremental valve opening to maintain the correct test pressure. With the sonic configuration, once port velocity is past mach 1, little or no additional adjustment to the pressure drop is necessary and the flow rate will continue to increase dramatically with each sequential valve opening. Since we’re not using additional pressure to increase flow as the valve opens, we have, not only a very efficient port, but also a port that acts as a vacuum, literally sucking the exhaust out, and eliminating the pumping losses normally incurred.
Somewhere, somebody, has flow tested exhaust ports at a high PSI or inches HG level and has a fair idea what is going on - it wouldn't be that hard to do.

Shoot, building a high pressure exhaust only flow bench would be pretty easy. It wouldn't have to be a traditional "bench" all you would really need is a flow element in-line with the head and data acquisition.

There are used centrifugal air compressors available that will put out 1500+CFM @ 100+psi continuously for under 10K. You could also do the same thing with a much smaller compressor and a big air receiver.
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Post by DavidNJ »

While we are asking questions, aren't all exhaust ports supersonic?

And I thought the drag motors opened the exhaust, off the seat, around 80-100° BBDC.
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Post by MadBill »

This thread: viewtopic.php?t=2598&start=60 shines some science on sonic exhaust flow.
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Post by putztastics »

DavidNJ wrote:While we are asking questions, aren't all exhaust ports supersonic?

And I thought the drag motors opened the exhaust, off the seat, around 80-100° BBDC.
Wondering if they are supersonic is one thing, thinking they are is another,
I don't know how many people have played with supersonic shock wave placement in an exhaust port.

It looks like flow testing was done at actual supersonic the way the supersonic flow characteristics on a flow bench are described.

We ran into a problem with a too small flow meter orifice on an air line at work, when flow went supersonic - it would caused the pressure signal (I think it was the upstream one) to go negative. :!:

Also it looks to me like the exhaust valve is being opened at BDC not before, and being closed at or before TDC, lessvalve open time is possible because of the optimized supersonic exhaust port.

Take what I say with a grain of salt, I'm on the ragged edge of what I know, probably more like in no man's land. :?
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Re: I dont get it!

Post by SWB »

[quote="Steve Baker"]
Then there is the matter of this,
"What Widmer is claiming, is that by increasing the burn rate, the ignition lead can be reduced, thus allowing the peak pressure point to happen later in the cycle, closer to peak piston velocity and therefore the point of maximum leverage on the crank throw."
ALL the power in a race engine is made in the first inch of piston travel the rest of the time your either opening valve to get the gas out or opening to get the gas in. In some high end engine making well over 2.7 horsepower per cubic inch the exhaust valve opens at 27° to 28° after TDC.
[quote]

Even if you had your exhaust valve closing at TDC on the exhaust stroke, your timing figures gave you 333 degrees of exhaust duration. In reality I think what you're saying is that the exhaust valve is opening 27* before BOTTOM dead center, which is quite different and certainly gives you a lot more time after the first inch of stroke.

You can laugh at my statements all you like, but when you hear about cup and pro engines (from reputable sources on this board) which have a full RPM ignition lead of only 24-26 degrees and making maximum power that way, I think you'll see there is some kind of advantage to it.

I agree that Pat's statement about the 'short but long' burn event is wrong. I don't think you can blame Widmer for what Hotrod published however.

I've read and known about the whole Endyn thing for years now and I can say that I can still not prove any of it wrong. If it challenges your way of thinking then you can either refuse to accept it, or you can open your mind and ask "what if?". I choose to do the latter because I find it helps me push my own products to a higher level. Sitting around saying it can't be done is the best way to not ever do it.

Don Terrill said it when he said that we are our own worst enemies. If we don't think it will work we don't even bother to try it... Maybe you'll fail, but even at that you may learn or at least confirm something in the process and that has to be worth something.

SWB
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Post by DavidNJ »

putztastics wrote:
DavidNJ wrote:While we are asking questions, aren't all exhaust ports supersonic?

And I thought the drag motors opened the exhaust, off the seat, around 80-100° BBDC.
Wondering if they are supersonic is one thing, thinking they are is another,
I don't know how many people have played with supersonic shock wave placement in an exhaust port.

It looks like flow testing was done at actual supersonic the way the supersonic flow characteristics on a flow bench are described.

We ran into a problem with a too small flow meter orifice on an air line at work, when flow went supersonic - it would caused the pressure signal (I think it was the upstream one) to go negative. :!:

Also it looks to me like the exhaust valve is being opened at BDC not before, and being closed at or before TDC, lessvalve open time is possible because of the optimized supersonic exhaust port.

Take what I say with a grain of salt, I'm on the ragged edge of what I know, probably more like in no man's land. :?
I showed Larry's 1999 article to a friend in the industry who used to work for a major manufacturer's advanced engine engineering group. He mentioned the supersonic flows.

While I don't have empirical data on exhaust velocity, EAPro shows it going to around 1500ft/sec in a configuration similar to a 2bbl late model engine.

At sea level and normal temperatures, the speed of sound is about 1100ft/sec. At elevated temps that would rise to 2300-2700ft/sec. However, if the molecular weight and specific heat of the gas. The speed of sound for carbon dioxide is slower, for water vapor higher. Does someone know what this figure would be for exhaust gases?
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Re: I dont get it!

Post by automotive breath »

SWB wrote:.... I agree that Pat's statement about the 'short but long' burn event is wrong. I don't think you can blame Widmer for what Hotrod published ...
I think the guy that wrote the Soft Head article intended to say the burn is faster but the gas expansion is slower.

Larry says it better in his own words.
Less Work = More Power
"If the combustion process is quick and complete, there will be very little burning when the exhaust valve opens, and the exhaust gas temperature will be very low. A quick burn also permits us to use less ignition timing advance to complete the combustion cycle and, therefore, the engine is doing less "negative" work since we’re not trying to compress as much ignited and rapidly expanding mixture. Unfortunately we can’t light the mixture at TDC and still complete the burn by BDC (with gasoline), but we can run only 5 - 15 degrees advance and create a thorough burn cycle. Then, by keeping the exhaust valve shut to a point very near BDC, we can gain a little more work from precious cylinder pressure. At these crankshaft angles the mechanical "push" is admittedly small due to the rod angle, but, as we only produce power on one of four strokes, we opt to take maximum advantage all the pressure available".


"On the exhaust side, everything’s easy. Open the exhaust valve at or near BDC, allow an efficient (sonic) port to efficiently remove the inert gasses, and then seat the valve near TDC. Piston to valve clearance isn’t an issue here, as we have all that "space" over and around the exhaust valve"
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Re: I dont get it!

Post by lil289 »

SWB wrote: I've read and known about the whole Endyn thing for years now and I can say that I can still not prove any of it wrong. If it challenges your way of thinking then you can either refuse to accept it, or you can open your mind and ask "what if?". I choose to do the latter because I find it helps me push my own products to a higher level. Sitting around saying it can't be done is the best way to not ever do it.

Don Terrill said it when he said that we are our own worst enemies. If we don't think it will work we don't even bother to try it... Maybe you'll fail, but even at that you may learn or at least confirm something in the process and that has to be worth something.
SWB
Very well put. It's been two decades since that article came out and it still fascinates me how far ahead he was and how little we know about what's really going on. Sure his basic idea came from others like Michael May but so what? Larry was able to put that together along with his knowledge of porting, valve seats, exhaust cross sections, valve events, etc, and make it all work.
putztastics wrote:supersonic exhaust port seems to play a big part. There appears to be a scavenging/flow/reversion advantage with a supersonic exhaust port that allows it to support the same total exhaust flow with less valve open time.
Yes, plus the fact that with his combo, the EGT's are much lower so there is less volume of exhaust gas that needs to be purged.

From his archives:
http://www.theoldone.com/archive/piston ... design.htm
I cast some small block Chevy heads back in the mid 80's, and although I did rotate the deck to lessen the 23 degree valve angle, and reduce chamber volume. The plug position was optimised, and of course the ports were adequate, and the inlet ports were properly biased to promote swirl. The pistons were "unique" in shape...all I'll say is they had no dish, except two .120" valve reliefs. They were certainly of the domed variety. Those small blocks were 358 cid. engines with 1.75-1 rod length to stroke ratio, very short cam timing...235 degrees @ .050", and the intake manifolds were some of my Edelbrock "specials" with Murray Jenson prepared Holley 830 cfm carbs. Those engines had "over" 16-1 static CR, and dynamic compression was so high we had to use custom starters run off 24 volts. They were installed in some Camaros and two pick-up trucks. They all ran 91 octane unleaded pump gas. They never detonated, the mileage was 37 (combined) for the cars and 25 for the trucks. The Camaro's had Turbo 400 automatic transmissions, and from off idle you'd swear that there was at least a 454 under the hood...the throttle response was almost too quick. Those "loaded" cars all ran 12's with ease. The trucks had pulling ability that no body imagined, and were a dream to drive, especially compared to their street counterparts.
12's and 37 MPG combined city and highway??? Can someone please test this!!! Imagine yourself in an old heavy 12 second classic car waving at the smarty pants in his hybrid vehicle as he pulls into the gas station and you keep motoring on by. :D

Getting back to the fast or slow burn thing...
Steve Baker wrote:First I read this statement which taken in its entirety makes absolutely no since at all and is completely contradictory. Sorry, but the laws of physics can not be twisted like this. No way.
"Because the mixture is more homogenous, it gives a faster burn that lasts longer - the ignited mixture expands more slowly"
As strange as it may seem, the more I ponder Larry's statement, the more it seems to make sense. Could it be that by using his swirl ports and keeping the fuel well mixed with smaller droplets, that perhaps the combustion event rises slower and steadier than usual yet burns more thoroughly such that by the time the exhaust valve opens most of the work has already been applied to the piston (low EGT's), as opposed to the norm where the richer and more uneven AF ratio is still burning and still working hard pushing down the piston (high EGT's)? With the normal way, despite higher cylinder pressures during the tail end of the power stroke, you can't open the exhaust valve late to take advantage of this otherwise you'll suffer major pumping losses on the exhaust stroke. So the burn is "faster" in the sense that the entire combustion event is shorter than usual and yet the burn is also "slower" because as Larry says, "the ignited mixture expands more slowly."
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Re: I dont get it!

Post by Ape »

lil289 wrote:
SWB wrote: Sure his basic idea came from others like Michael May but so what?
There is no what as there was no criticism on widmers accomplishments, but mays studies might be interesting on their own and allow further info on the subject, and so far widmer seems to be one of the only ones that has more info about mays stuff, besides the scarce info there is.

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Post by hydra »

Think about it this way,
If Michael May's design really did work, it would have seen much more popular usage. I did quite a bit of research about it a couple of years ago, and I recall reading that a lot of OEMs tried it, and while it supposedly worked very well, nothing ever became of it. I wonder why that is, especially when you consider that the May's head was supposedly cheaper to manufacture than an inclined wedge head :roll:

Now, according to Harry Ricardo (whom I consider to be a far more reliable and respected source than either Michael May or Larry Widmer) in Internal Combustion Engines it IS possible to have too much swirl/turbulence/quench or combustion that is too fast. From memory, the ideal rate of pressure rise is ~30psi/crank degree. Any more than that and combustion becomes noticeably rougher and power is actually LOST...

Personally, I think Larry Widmer is a quack. Statements like "They never detonated [at 16:1 compression], the mileage was 37 (combined) for the cars and 25 for the trucks" don't exactly help either...

That's all I'm going to say about this matter, you can either take it or leave it.
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Post by Ape »

hydra wrote:Think about it this way,
If Michael May's design really did work, it would have seen much more popular usage. I did quite a bit of research about it a couple of years ago, and I recall reading that a lot of OEMs tried it, and while it supposedly worked very well, nothing ever became of it. it IS possible to have too much swirl/turbulence/quench or combustion that is too fast.
well as said there is not a lot of info available perhaps even less outside europe, fact is that besides the named facts by ricardo and i might add G.P.blair who is also analogue in that opinion about detonation etc. that May did not just development work. During the 70´s to 80´s he did very very successfull ford V6 R&D that also ran into the zakspeed capris (http://www.geocities.com/simontmallett/zakcapri4.html. )
Besides the fact that he supposedly still does development work for some rather large european car manufacturers. So i would assume that it might be a matter of taking or leaving it, but as said there is relatively lil info on the subject, and reasons of manufacturing or not for oem, is not a valid argument to me judging by the way BMW as an oem treated the apfelbeck (radial diametral) cylinder head design. But this would get off topic.

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Post by hydra »

Ape,
There's a book by Jan Norbye (can't remember the name right now) published in the early 80s that devotes 3-4 pages to May's fireball head. That was the most extensive source of info I found on Mays' design. They made it sound very promising, like it was the next "big thing"... VW had a prototype running at 14:1 compression, and things were looking good at the time, but nothing ever became of it.

My main beef isn't with Michael Mays and his design. I know that he's an accomplished engineer and has lots of experience under his belt (he helped develop the Porsche Type 547 "Fuhrmann" Carrera engine for one), and I respect that. My problem is with Widmer and some of the more ludicrous claims he makes...
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Post by MadBill »

[quote="DavidNJ...At sea level and normal temperatures, the speed of sound is about 1100ft/sec. At elevated temps that would rise to 2300-2700ft/sec. However, if the molecular weight and specific heat of the gas. The speed of sound for carbon dioxide is slower, for water vapor higher. Does someone know what this figure would be for exhaust gases?[/quote]

That information is also in the thread I quoted a few posts back.
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Post by Ape »

hydra wrote:Ape,
There's a book by Jan Norbye (can't remember the name right now) published in the early 80s that devotes 3-4 pages to May's fireball head. That was the most extensive source of info I found on Mays' design. They made it sound very promising, like it was the next "big thing"... VW had a prototype running at 14:1 compression, and things were looking good at the time, but nothing ever became of it.

My main beef isn't with Michael Mays and his design. I know that he's an accomplished engineer and has lots of experience under his belt (he helped develop the Porsche Type 547 "Fuhrmann" Carrera engine for one), and I respect that.
That was the reason why i was somewhat amazed about the previous post as i knew you must know the older style mercedes heads (i think of the 5 cyl.??) that have a somewhat similar design to the fireball.
Thanks for the book tip will try to get a copy. Or do you think you could perhaps copy those 3-4 pages?? I would be very gratefull, as i allready tried to get in touch with mr. may unfortunately without any good results.
And his former associated company "schwabengarage" doesnt have any info on the subject.

kind regards
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