Dual spark plugs or squish?

[dorset]

so there is an initial primary turbulence around a transverse axis between the valve seat and the piston top? always?


anything visual like this available for OHV?


https://www.youtube.com/watch?v=jdW1t8r8qYc

skip to 1:44


kevin

[dannobee]

That's more swirl than tumble in that video. Swirl is used more on wedge heads and the mixture spirals down against the cylinder wall if viewed from the top. Tumble rolls into the cylinder like a wave breaking. As the mixture enters an open intake valve, it encounters the side of the cylinder wall and rolls like a wave if viewed from the side. Either of these is used to help the air and fuel mix to become a more homogeneous mixture that stays in suspension until it's burned. What you don't want is fuel to fall out of suspension and hang around the ring lands where it doesn't contribute to power output.

More like this video
https://www.youtube.com/watch?v=SIUmQJwVfuw

[englertracing]

I like the quench porsche chambers putmov posted, but I think to make that work you need a shallower valve angles

I don’t think it’s either/or between those two designs, unless one is going for extreme compression ratios. I think that even with the wide valve angles, one could “move” some of the metal from the piston into the cylinder head and create an engine that can be run at higher rpm safely. It is true to get the most out of the design by being able to run a flat-too piston, a tighter valve angle is probably required.

Well on the small bore you surely don't want to shroud the intake valve,
With shallower valve angle you can have less shrouded and more quench area, and a smaller dome
No pics of trucked up chamber but looking at his pistons the quench is small and the chamber is deep. The quench is only blasting the side of a dome anyway. Pretty grim really.

[Truckedup]

I like the quench porsche chambers putmov posted, but I think to make that work you need a shallower valve angles

I don’t think it’s either/or between those two designs, unless one is going for extreme compression ratios. I think that even with the wide valve angles, one could “move” some of the metal from the piston into the cylinder head and create an engine that can be run at higher rpm safely. It is true to get the most out of the design by being able to run a flat-too piston, a tighter valve angle is probably required.

Well on the small bore you surely don't want to shroud the intake valve,
With shallower valve angle you can have less shrouded and more quench area, and a smaller dome
No pics of trucked up chamber but looking at his pistons the quench is small and the chamber is deep. The quench is only blasting the side of a dome anyway. Pretty grim really.

The chamber wall is tight to the side of the piston dome as shown in the photo of the piston and a . The chamber is just like a Mopar hemi.. the squish area is small band around the cylinder but before after on my street Triumph proves is quite effective at lowering octane requirements and sharper throttle response.
Drastic changes to the valve angle and chamber shape sound good but in reality it's not too practical. The factory 4 valve pentroof head would be legal in modified production , expensive , rare and no one uses them for some reason..
There are supposedly better head designs used on Nortons, BSA and the pushrod Honda CX 500 and 650, but the majority of records are held by Triumphs..

[ptuomov]

Keith Duckworth’s barrel turbulence aka tumble swirl aka tumble is what I think drives the combustion efficiency of hemi and semi-hemi heads. One of early examples:

https://www.grandprixengines.co.uk/Note_26.pdf

I’ve become convinced that combustion efficiency can be greatly improved by directing the flow with a straight long-side port roof aimed at an angle perpendicular to the exhaust valve stem and thus parallel to the exhaust valve face and then maintaining this “barrel tumble” flow with the piston crown shape. Squish itself is less important to combustion for hemi, semihemi, and pent-roof cylinder heads.

[dorset]

i dont have the rules with me but for LSR in mine and truckedups modified production venues i believe the motors have to have the same numbers of valves as stock.

either way the aftermarket four-valve heads dont bolt on to the stock barrels but come with custom 700cc jugs that cannot be run in the 650 class.

very pretty though. ive never seen flow or dyno data for them.

http://www.vintagebikebuilder.com/vinta ... -head.html

[ptuomov]

I'm sure many forum members would be interested in seeing photos of combustion chamber and piston from both of you!

[dorset]

i put up a couple way back on page 1 for my 650

viewtopic.php?p=873716#p873716

the pistons are JE slugs cuztom cut to 11.75. the highest triumph ever did stock was in the old TT racers of the 60s at 11:1. there were essentially no changes to the hemispherical chamber from 1963 to 1972 except for a increase in intake valve size i think. 90 degree valves, splayed ports, just a huge fishbowl.

in 73 they bored to 724cc and by 76? had gone from the original undersquare 71 × 82 to 76 x 82, 744 i think it is. the head castings interchnge but have different headbolt patterns. my 650 head is actually a 750 casting designed for tbe 724cc motor but drilled for the last 650cc production runs. one year only. ive got spares in case i blow it up. again.

it would be interezting to see a hemi head welded up with zquish pads into something that channelled the flame better using a custom piston top. thats beyond my budget at the moment but i occasionally buy lottery tickets.

[PackardV8]

It would be interezting to see a hemi head welded up with zquish pads into something that channelled the flame better using a custom piston top. thats beyond my budget at the moment but i occasionally buy lottery tickets.

Better win the MegaMillion. A friend tried to do an aluminum head shadetree. He had a buddy who was a certified professional aluminum welder. The welds were beautiful, but the valve seat bores warped, the valve guide bores warped, the head surface, as expected, warped. He couldn't find any machinist locally who would tackle finishing the chambers and getting the seats and guides back to blueprint. Finally, he shipped it off to The Guy for his engine and after $1500, what he got back was only close; not the magic he'd hoped for. The excuse, "I don't guarantee other people's work. You should have bought my $2500 head."

[englertracing]

http://www.vintagebikebuilder.com/vinta ... -head.html
wow this could be a real special....
probably end up with 5 grand in it......

[ptuomov]

http://www.vintagebikebuilder.com/vinta ... -head.html
wow this could be a real special....
probably end up with 5 grand in it......

I think that porsche melted all of their concept four-valve air cooled heads in testing... and they were very comfortable using oil and fuel to cool things. I’m not saying it won’t work, I’m just saying that significant technological uncertainty remains!

[Krooser]

The modern Hemi fires the second plug 5 degrees after TDC to clean up emissions and allow the use of a simpler, and cheaper, cataylitic converter. Total advance is at about optimum at 20 BTDC.

[dorset]

Better win the MegaMillion. A friend tried to do an aluminum head shadetree. He had a buddy who was a certified professional aluminum welder. The welds were beautiful, but the valve seat bores warped, the valve guide bores warped, the head surface, as expected, warped. He couldn't find any machinist locally who would tackle finishing the chambers and getting the seats and guides back to blueprint. Finally, he shipped it off to The Guy for his engine and after $1500, what he got back was only close; not the magic he'd hoped for. The excuse, "I don't guarantee other people's work. You should have bought my $2500 head."

gah

that is not the preferred outcome for me. truckedup and i are both at about the same spot on the envelope for these old things, and im pretty sure more horsepower for either of us comes at an inevitable cost. i already blew mine up once when an ARP rod bolt let go, but ive been able to resurrect it.

we're both at the point where i think more speed comes from trying to get the frontal area small and cutting turbulence on the sides. neither is easy

[Truckedup]

i dont have the rules with me but for LSR in mine and truckedups modified production venues i believe the motors have to have the same numbers of valves as stock.

either way the aftermarket four-valve heads dont bolt on to the stock barrels but come with custom 700cc jugs that cannot be run in the 650 class.

very pretty though. ive never seen flow or dyno data for them.

http://www.vintagebikebuilder.com/vinta ... -head.html

Yes ,same number of valves. For sure the Factory Triumph TSS 8 valve head is legal in 750 pushrod, maybe the aftermarket heads also other than stock production.

[Dutchman]

Side squish bans I have done in the past on evo big twin stuff years ago. In a drag racing app they performed well. Not a difficult task .
A lathe with 15 in swing should do the job with a face plate and a piston fixture.
I would buy a blank .750 dome set of Pistons, figure the angle I wanted of the squish band,35degrees comes to mind ,set the tool post to that angle,indicate the chamber on the face plate and cut the squish bands in the head,repeat for the other cylinder. Then remove the face plate and put the piston fixture in,not touching the tool post from the last chamber cut,cut the piston angles in the domes.
This is so the piston is a exact match to the chamber and the head gasket becomes the distance for the squish.
Done this a few times but now there is other ways to achieve decent squish on a Harley,the Brit stuff is like racing a Harley 30 years ago. Nothing is readily available .
Hope this is some help.