High CR pistons and squish heads chat…

Fast Eddie

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So what's your problem? The vast majority of heat transfer from the piston is from conduction via the rings, con-rod and engine oil which is what I said previously. I didn't say MOST heat transfer is via the oil or via the rings it is a combination of the above.
The article linked in post #51 sites that the piston skirt transfers heat to the barrel via the oil filled gap. Therefore piston to barrel heat transfer is not only via the rings. Remember we were (at that point) talking specifically about piston to barrel heat transfer, not piston to conrod, or engine oil cooling, etc. That’s my only point here. I dont have a ‘problem’ !
 
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If anybody would be so kind to post some pictures for me i could supply some (of single heads though and one or two of the domiracer a couple years ago) to make my point clearer.

Cheers and have a good day.

Christian

@Fast Eddie

Hi there and good morning,

Unfortunately I'm these days somewhat tackled up in work (my real life job).
I will try to look the chapter up in gp Blair's books and try to write a short summary as soon as time allows me.
 

Fast Eddie

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Here’s a Triumph head modified to a bathtub type shape. Dave Degens was one of the early pioneers of this.
In my experience this could only be done once, if you dropped a valve etc and had to repair it, the heat from welding really softened the head.
I would imagine that today, with laser welding, this would not an an issue.
This squish design allowed me to build an 850cc Triumph twin with over 11:1 CR that ran sweetly on pump fuel (the head in the pics is not mine)…


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@Fast Eddie

If done correctly there would be highly likely also no problem with modern TIG welding techniques.
Usually when I weld my combustion chambers the HAZ surrounding zones stay well below 100°c (water/spit as operation temp verifier).

Quick ot: I plan already for months to post some thoughts on reducing heat input during Ac (aluminum) on linkedin as it seems to me (I'm an ex 6g aluminum weldor and by now IWE having started Tig welding at kosman back then still in SF) a contradiction in itself that so many welding shops have NASA like Inverters and at the end you have some poor dude sitting there welding with a green tungsten with a big big rounded blob at the tip, heating everything up like a pan of paella.
Christ sake it's like buying a 6er m-series and using only first 2gears.

Ok sorry for the break out and back to topic, will behave again
 
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Fast Eddie

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Fair point Christian, I am only the crudest of amateur welders so have nothing to add!

Thinking back, the head of mine that went soft actually had a hard life, it was a kind of development head that probably had at least 2-3 different versions of squish design applied, then it had at least 2 reasons to be repaired, so the 50 year old casting suffered a lot !
 
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Fast Eddie

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If anybody would be so kind to post some pictures for me i could supply some (of single heads though and one or two of the domiracer a couple years ago) to make my point clearer.

Cheers and have a good day.

Christian

@Fast Eddie

Hi there and good morning,

Unfortunately I'm these days somewhat tackled up in work (my real life job).
I will try to look the chapter up in gp Blair's books and try to write a short summary as soon as time allows me.

That would be great Christian.

I blew the dust off of a few on my shelf earlier, by PE Irving, AG Bell, J Robinson, and all are quite explicit about the virtues of a functioning squish band to reduce knock and facilitate a (potentially substantial) increase in CR. Citing this as being due to: reduction of temperatures, increased turbulence giving better mixing, and improved combustion chamber shape that better concentrates the charge around the source of ign.
 

lcrken

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@Fast Eddie

If done correctly there would be highly likely also no problem with modern TIG welding techniques.
Usually when I weld my combustion chambers the HAZ surrounding zones stay well below 100°c (water/spit as operation temp verifier).

Quick ot: I plan already for months to post some thoughts on reducing heat input during Ac (aluminum) on linkedin as it seems to me (I'm an ex 6g aluminum weldor and by now IWE having started Tig welding at kosman back then still in SF) a contradiction in itself that so many welding shops have NASA like Inverters and at the end you have some poor dude sitting there welding with a green tungsten with a big big rounded blob at the tip, heating everything up like a pan of paella.
Christ sake it's like buying a 6er m-series and using only first 2gears.

Ok sorry for the break out and back to topic, will behave again
Hi Christian,

I would like to encourage you to post your thoughts here on reducing heat input, or anything else regarding welding on aluminum (heads in particular). Or posting a link to anything of that sort that you post on another site. My welding skills, such as they are, are based on a combination of a few months of on-the-job instruction in a Navy facility some 60 years ago, plus lots of reading from welding text books, and more lately some really interesting stuff on youtube, plus years of welding whatever I needed to for my own projects. Definitely not a pro, but not a novicer either. But I've experienced no end of difficulties in welding in the combustion chambers of Norton heads, so any advice would be welcome. Never too late to learn.

The biggest problem I've had with welding the heads is the endless amount of oil and carbon that seems to permeate the castings. It seems like no matter how well I clean them, I'm still basically burning out the contaminants and then grinding out the area and trying to get a clean weld with new filler.

Ken
 
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I tig welded potential breakout spots on one of Ken's alloy cylinders before boring it for the RGM 920 sleeves.
Because it had never been in use there was no oil impregnation and it welded nicely.
It did require re-machining of both the head joint surface and the base joint surface as there was fairly severe warpage from welding heat.

Glen
 
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When you create a bathtub combustion chamber by welding and adding metal near the valve seats you will shroud the valves and impede flow - losing HP at high RPM. The loss shows up in dyno tests. Its a nice idea but at a sacrifice to peak power. The image below shows two 3/8" shafts representing the valve height near full lift. It shows that adding material to crowd the combustion chamber near the valves will restrict flow.

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You have to be careful with piston dome design. The factory short stroke 77mm Omega piston below weighs a whopping 330 grams bare.
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By comparison the 77mm domed piston below weighs only 210 grams bare.
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@jseng1

Jim im sorry to say that's a misconception, as shrouding of the valve depends on several factors like:
Seat angle (30-55)
Tulip angle
Used cam profile and lift
etc.
Picking up the concern it is a well known fact to some tuners that the combustion chamber is the lead out of the last upper seat correction angle, so thus if combustion chamber shape is correct you get actually slightly better flow figures as the flow remains more homogenous.
Not easy to find correct shape and depending flow but oh well so is life.

Besides sans meaning to sound sarcastic, i'm pretty sure that some of the west coast icons of tuning namely Jerry branch and Cr Axtell had different views on weld ups.
 

Fast Eddie

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Here is an assortment of some different chamber and squish shapes from Christian.

Christian is keen to emphasise that most of the pictures were taken before final touching up etc.

He‘s also keen to apologise for the fact there is some none Norton content included !

Unfortunately the descriptions weren’t attached logically to the pictures on my iPad, so the best I can do is post the list of descriptions, and the pictures. Perhaps Christian can come in with more details?

The pics show:
hemispherical squish
flat squish with high dome
conical squish
domi squish head with flat squish

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@lcrken @worntorn
Hey guys thanks for the replies i was actually worrying that I got way off topic with my ranting in a sect like manner bout Tig welding.

Well considering that modern TIG welders of the likes of miller dynasty, Lincoln aspect (which i own) and fronius (of my dear Austria) have several available wave forms, very high arc frequencies, ac balance and on top of that independently adjustable phase amplitude i usually like to weld as follows.

Clean the crap outta the chamber of necessary with acid and pre grinding.

Set the frequency ultra high to narrow the Arc as with high frequency you get a narrower arc which leads to more focused heat input.
Furthermore a very pointed lanthanum (grey) tip in a slightly bigger diameter to give the pointed tip more heat capacity and thus resistance

Use the least possible amount of cleaning action thus very little positive phase balance. (80-85ish)

Use square wave in order to get immediately the full force of amperes and not some mellow yellow sinus Dr. Feel-good that boils the crap out of the surrounding material.

As for that, up to this point use recommendend amplitude settings, and use if necessary the least preheating necessary, less for the weld but to avoid tension cracks due to uneven heat dilation.

Now to my private experiments:

Use 50/50 or even higher pos/neg balance which sounds at first counter productive, but using the amplitude skew, use very lil cleaning amplitude as you just need it for breaking the oxide layer.
And in comparison give it the maximum negative amplitude with very high frequency.
That way you get an arc that somewhat resembles in it's characteristics a surgeon knife with muchos penetration (in a very reduced time), sufficient cleaning action but due to low positive amplitude reduced heat input.
Only thing is one really needs to watch out to weld fast and concentrated and keep an eye on controlling the weld puddle as the arc is so strong that it almost pierces in /through the puddle.
So one has to move very fast which also leads to reduced heat input and thus in my experience reduced haz.
More i can at this point unfortunately not verify or state as this topic is a current focus of my private investigation (with oscilloscope among amp meter) in which i would like at the end to find applicable welding parameters for advanced aluminum welding with highly reduced heat input (all the welding articles brag about it but mysteriously nobody does it or states how to, funny huh?)
Furthermore I usually weld most of my cast aluminum stuff with 4047 as i found that using my petsonalb WPS's i almost never experienced distortion.

Hope my ramblings made sense and didn't sound to esoteric.

Kind regards

Christian
 
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@Fast Eddie

Thank you so much for your help.
Will try to explain to my best!

First picture domiracer head with reshaped chambers and as mentioned before no loss of flow due to reshaped chambers.

2nd picture
Big single with conical squish

3. Picture
Piston that belongs to picture 4
Head with flat squish and smoothed out dome in order to avoid resistance in burn through.

Pic4
Combo with piston

Pic 5 and 6
Head with hemispheric squish complimenting dome shape.

Picture 7
Good example of a head that was welded in a very quick time and remained outside the head gasket surface below approx 100°C.
My personal favourite is the conical squish head as it gives the highest compression (to compensate for late intake closing) ratio with the mixture located where you want it with long duration (late Ic) race camshafts.

Hope ya guys like the pic's as already mentioned i'm not a GQ photographer so my pictures get taken when it serves me so some heads where in a non finished halfway through state.

Have a good evening
 
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lcrken

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Thanks for the response, Christian, and the welding suggestions. I'll have to pull out my junk test head and see if I can improve my results.

Also, thanks for the interesting combustion chamber pictures. Maybe getting a little OT, but it's a subject that's historically been of great interest here on the forum, so no fault.

As you said, some of the best known specialists back in the day had serious disagreements on the best way to improve efficiency in Norton heads (as well as others). I had the opportunity to hear Axtell's (firmly held:)) opinions on Jerry Branch's technique, and to observe examples of both. I chose to follow Axtell's advice in this area, for a number of reasons, and was very grateful for it, but that's another story. And neither of them followed Paul Dunstall's principles. Jim Messler, one of the factory Norton tuners had his own ideas on the best mods for Commando heads, also very different from the above experts. I have one of his short stroke 750 heads with giant valves in a full hemi chamber, but fairly small ports. It worked extremely well for me for many years on a 920 race bike. I've also seen one of the bathtub chambers he was doing later in his career. I don't have pictures of it, but as I recall, it looked a lot like the ones produced by George at MEZ Porting, shown below, but with a more oval bathtub shape. I recall once talking on the phone to eccentric tuner Kenny Augustine about his ideas on Norton heads, but I don't recall the details, except that he had some interesting things he wanted to try. I don't know if he ever got the chance to do so and see the results. I'm pretty sure the other Norton tuners back then (Leo Goff, etc.) all had their own take on the best way to go, but I don't have any experience with them or any info on their methods. More recent (at least relatively) specialists like Steve Maney and at least a couple of European tuners, have also experimented with trying to improve on the original Norton head design. And there's always our own Jim Comstock, who has had his way with many a Norton cylinder head, and Jim Schmidt, who has put a lot of time and energy into applying the Harley XR750 port design philosophy to the Norton head. And how could I leave out Canadian Norton wizard Herb Becker, whose work has been explored on this forum several times. There's clearly more than one way to successfully set up a Norton twin. It fascinates me that research is still going strong on such an old design, and the availability of new, improved Commando heads, originally from Fullauto, and soon to be from John Snead, offers another resource for experimentation. Good time to be a Norton lunatic.

bathtub2.jpg


Ken
 
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Fast Eddie

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Folks…

I changed the title of this thread… so the squish head chat is no longer off topic… go for it…!
 

lcrken

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In that light, here's a link to a similar thread back in 2011


Ken
 
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The like the chamber below and it looks like it would work well.
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Tighter chambers that crowd the valves may restrict the flow and result in a loss of top end HP - you don't know until you've done the flow tests. The proof is in the results. Show me the flow and dyno results and the heads associated with those results. I've heard of only a few racers with bathtub heads who were happy with a performance improvement and I've made pistons for bathtub heads (see small central dome 750 piston below). I've also heard that they can lower the top end HP. It may be fun to experiment with different configurations but I want to see an actual improvement throughout the RPM range.

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Herb Beckers modified bathtub 920 head on left in photo below (94 HP and 154mph on the saltflats with no streamlining)
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Son of Siredward

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Sir Eddy's head to support the 12.8/1 Pistons... De-stroked crankshaft rolling the left hand throw backwards 90 degrees for a 270/450 firing order.
6.5 inch rod length yields a 2.774 rod length to stroke ratio at 497cc making HP to 10,250 RPM!

Major Squish into this combustion chamber supported by “Singh Grooves” to help turbulence.
Built for one thing, TOP SPEED!


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Son of Siredward - those are the kind of results I like to hear about. Do you have a flow chart to compare it with an unmodified chamber with the same size ports and valves?
 
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