whats best for performance? chamber and piston design

[N-gin]

What would be better?
A flat top piston with a flat squish and grooves.

Flat top piston with chamber at ?° squish.

?° piston with ?° chamber

Or a Mega-Sphere chamber with the matching dome piston?

Performance meaning the most efficient burn, all other variables equal.
Head flow
CCP, DCR, SCR, Valve size, port size, bore, stroke, cam, exhaust, etc

[Jaycee1964]

hemispherical chamber with Domed piston is most efficient. 

[vdop]

Dished> flat top> dome if and only if you can achieve the same compression. So that's pretty much irrelevant with our huge combustion chambers.

[prodrag1320]

in a perfect world,a flat piston with a very small combustion chamber would be the best.in a HD head to get higher compression,a 20* or 30* piston with the same machined into the shelf part of the head works best

[TorQuePimp]

What would be better?
A flat top piston with a flat squish and grooves.

Flat top piston with chamber at ?° squish.

?° piston with ?° chamber

Or a Mega-Sphere chamber with the matching dome piston?

Performance meaning the most efficient burn, all other variables equal.
Head flow
CCP, DCR, SCR, Valve size, port size, bore, stroke, cam, exhaust, etc

Depends on the chamber

[aswracing]

Kirby is absolutely correct. You look at all the really high performance motor designs, and there's a definite trend to shallow valve angles with flat, compact chambers and flat top pistons.

But the 58 degree included angle of a Harley head is just not conducive to that. So you have a deeper chamber, and with squish bands you get some shrouding of the valves. The angled dome piston is the solution. Angling the piston dome up to about the valve angle gives maximum valve unshrouding. That's why 30 degrees is more or less the accepted optimum angle (stock valve angles are 27 & 31)

The problem with angling this steeply though is that you give up squish band surface area, unless the dome is made very tall to compensate. And of course tall domes take the motor out of the realm of pump gas.

The solution is to turn around and dish the middle of it ...



This is a small sampling of the 30 degree pistons in our lineup, but you get the idea, we do these for almost every application. This design gives plenty of squish surface area without raising compression too high for pump gas. This of course gets paired with a matching cut in the heads:



Because this removes most of the shelf the air has to go around as it enters and exits the chamber, breathing is improved. You see this more with large valves, in fact, in an XL head with a bathtub chamber, try to go past about a 1.900 valve and the flow bench numbers hit a wall unless you angle the squish bands like this. Shrouding isn't as bad on the Twin Cam head but it's definitely there.

Another advantage to angling domes is that the fuel being squeezed out of the squish band has a straight shot at the flame front, without coming out horizontally and running into a protruding dome the way you get with a traditional domed piston. When the charge comes out and hits a dome, it has to turn, and that inevitably causes some separation.

30 degree domes are nothing new, they've been widely used in race motors for forever.

But again, this gets back to Kirby's point ... all this is a crutch for the problems caused by the wide valve angles. Here's an example of how to do it better. One of my personal bikes is a Buell XBRR ... 56 of them made ... 82ci, came factory with 2.250 intakes and 1.750 exhausts and putting 150hp to the back tire ... here's it's chamber:



The valves are stood up, the ports are much straighter (you can look down either of the 62mm downdraft throttle bodies and see the intake valves), and the chamber is much more compact.

The coolest thing about that motor though is it's itty-bitty flywheels:

[Admiral Akbar]

 

Way cool..   Tapered / angled squish is the best way to go also..   Those heads are works of art,, Like the flywheel..

Max

[Ohio HD]

Definite motor porn!   

[irishrover]

Looks a lot like a HTCC head and piston. I bet that motor spins up fast with that small counter weight on the crank

[TorQuePimp]

  That is sportster stuff.

  Axtell,Mackie,Hemi engineering and I am sure others do/have done/are doing all sorts of different angled squish configurations and nothing you see is exactly ringing a bell....speaking strictly twin cam,pump gas,everyday all day no PMS type builds.

  Would be nice if someone resurrected STD's TC head in a builders format with options like no combustion chamber,shrunk up ports,and whatever else....plenty of 5 axis machines out there to make chips and see what could be done.

[gordonr]

That is an impressive head set up aswracing. Do you have a pic of the piston? On another note It is funny, where are valve size police?

[gordonr]

  That is sportster stuff.

  Axtell,Mackie,Hemi engineering and I am sure others do/have done/are doing all sorts of different angled squish configurations and nothing you see is exactly ringing a bell....speaking strictly twin cam,pump gas,everyday all day no PMS type builds.

  Would be nice if someone resurrected STD's TC head in a builders format with options like no combustion chamber,shrunk up ports,and whatever else....plenty of 5 axis machines out there to make chips and see what could be done.

I was following STD last year to see if twin cam heads were in the near future from them but didn't get a straight answer.

This is my modded TC STD hemi. 2.180int 1.750ex. My experience with hemi chamber is its advantage of having deshrouded valves. With this setup Im at 400cfm through the whole stack





The bad part about building a hemi is the lack of off the shelf piston availability. It not cheap.

[turboprop]

Nitro Billy (current owner of STD) and Jim (HMFIC at STD) will be in Cinci in a few weeks. Be sure to stop by their booth and discus the need for STD TC head castings.

[Hillside Motorcycle]

When Axtell introduced that single 30* J&E design for the 80" Evo head, we used a "Potty mouth"-ton of those.
Always seemed to work good, but not really anything that jumped up and alerted us to it being the Holy Grail, by any means.
Just another way to square a circle.........figuratively.....
Scott

[Admiral Akbar]

  That is sportster stuff.

  Axtell,Mackie,Hemi engineering and I am sure others do/have done/are doing all sorts of different angled squish configurations and nothing you see is exactly ringing a bell....speaking strictly twin cam,pump gas,everyday all day no PMS type builds.

  Would be nice if someone resurrected STD's TC head in a builders format with options like no combustion chamber,shrunk up ports,and whatever else....plenty of 5 axis machines out there to make chips and see what could be done.

Oh.. I don't know.. There is some Bassley/STD / Axtel evo stuff that has made excellent numbers..  Not sure I could dig it up as the stuff was too pricey for my habit.. Paul Morris might have some examples..

Tapered squish still needs everything else right to make the numbers.. 

Max

[aswracing]

When Axtell introduced that single 30* J&E design for the 80" Evo head, we used a "Potty mouth"-ton of those.
Always seemed to work good, but not really anything that jumped up and alerted us to it being the Holy Grail, by any means.
Just another way to square a circle.........figuratively.....
Scott

Got a set of those in my FXR.

Couldn't agree more.

[strokerjlk]

All the 20-30 deg perimeter dome builds I have been involved with , do really well.
It's a little harder to hit your compression , and most come in a little low unless the cylinders and pistons are checked together for cc's .
I have tuned several that came up short on compression ( as what I would have liked )
But they always pull up great numbers . Mackie . Axtell, Wfo Larry .
A 95 ci cranking 170 , a 117 cranking 170 or evan a 110 cranking 240 ccp run out fine and have no PMS .
You can really see the diff , when you set back a see the tuning requirements.
Takes more money and effort , but it pays off .

[prodrag1320]

When Axtell introduced that single 30* J&E design for the 80" Evo head, we used a "Potty mouth"-ton of those.
Always seemed to work good, but not really anything that jumped up and alerted us to it being the Holy Grail, by any means.
Just another way to square a circle.........figuratively.....
Scott
[/quot

here too

[Bakon]

Is this why the HTCC 95 piston with the reverse dome worked pretty well but the bigger HTCC stuff that looked more flat top, didnt put out the numbers? Some recoomended a 20 degree Axtell to gain more with heads cut like above to match them.

Those are some nice looking heads and pistons. what compression for 103 (107) set?

[PanHeadRed]

"Performance .......... the most efficient burn"

Not always the same answer.....

most efficient burn?.........sphere.

What would be better?......the one that makes the best ju-ju in the cylinder while the piston is moving up and down.

[John/1]

Hi
83 cc chamber for a 4.25 bore with a flat top piston 12.5 to 1 on a 131 ci.Cylinder head has not been milled.Notice how valve are not shrouded [attach=0]

[attachment removed after 60 days by system]

[TorQuePimp]

what head is that ?

[Admiral Akbar]

"Performance .......... the most efficient burn"

Not always the same answer.....

most efficient burn?.........sphere.

What would be better?......the one that makes the best ju-ju in the cylinder while the piston is moving up and down.

Yeah.. With the spark at the center.. Need a long electrode on the plug..

Max

[N-gin]

So how do you determine the best ju-ju for the performance enthusiasts?
Is it how they ride?

[gordonr]

what head is that ?

Cool head. Looks similar to an Ultra Pro.