Head swap, Hemi for torroidal

[best]

Head on the left is our new KTM style toroidal 25cc head.
Head on the right is DT200 Hemi style 23.5cc, and includes a poor squish angle.
This head has been run for months on Triplecrown's stuffed intake and 1mm exhaust raised ported cylinder.
This cylinder was run with no basegasket to lower it 0.030" or about .75mm.
This is all part of ongoing, one step at a time testing.

Burn pattern on the hemi was toward the exhaust and off centered.
A sign of unbalanced transfer ports. Some power being lost here.

Both heads were cc'd to give the values above. Both show no signs of detonation with proper jetting.

So how did they work?

Well, adding the basegasket to the hemi head lowered its compression and made is noticeably softer on low rpm and mid range. Powerband came on in a burst now, and it is definitely stronger on top end, even with the lower compression. I spun it around a track for a quarter hour, hanging out the back end enjoying the new founf over-revs from the raised cylinder. Bottom end has lost its former strength and over all it is a better trak engine than trail engine.

So, off comes this head and on goes the 25cc KYM Toroidal style. Even LESS compression. What are we going to get? This head has the better 11 degree squish going for it. Started on first kick, heck for headgasket leaks (feel with your hand around the cylinder) and off we go. Bottom end still soft but better than the hemi, mid range noticeably stronger. Enough mid range that it doesn't have the big powerband burst. Top end is still strong but not as much overrev as the hemi. A hoot around the track, hanging tail a gear up from the increased mid range, and higher speeds overall. This head feels like a success but I'd suggest the volume is too large. Gotta build one about 20-22cc.

I only had about 15 minute runs of back to back track time on it, but Triplecrown has been out on it all day. Interesting to hear his views.

 

[dksix]

Are you getting any numbers on cylinder pressure between chamber sizes?

 

[Triplecrown421]

the Toroidal head works awsome, after using a basegasket the Hemi head had lost some important low end but had a very potent powerband up top.

The toroidal seemed to open up the mid to top nicely helping the power roll on before the powerband engaged. The rpms seem to drop off alittle sooner then the hemi did but brought that power down some. i like the toroidal head it livened up the bike alot.

 

[Triplecrown421]

earlier today when i went out this morning i was running my basegasket with hemi head. went riding for 3 or 4 hours with that doing some nasty hill climbs dirty wheelies and 0-60s like no tomorrow. at about 4 i stopped home and Best turned to me and says-
"you running that new head yet"
i reply- "No old man, im out riding i aint doing that right now"
Best- "Dammit boy, were tryin this out" as hes walkin over to my bike with a 13mm and new head.

i noticed on one hill specifically that had a jump at the bottom. coast the bike up the jump as i landed would crack it wide open in second and Haul ass up the steep incline. with the hemi before i notice i had to feather the clutch acouple times to get the bike secure into the band. with the torroidal head i noticed when i cracked it she hooked up and almost bobbed the front tires the whole way up.

 

[Awk08]

good stuff guys, real world, ass dyno testing at it's finest !!!!!

someone needs to use this as a sig qoute, thats some funny shizzle ............

Best turned to me and says-
"you running that new head yet"
i reply- "No old man, im out riding i aint doing that right now"
Best- "Dammit boy, were tryin this out" as hes walkin over to my bike with a 13mm and new head.
.

 

[best]

Best turned to me and says-
"you running that new head yet"
i reply- "No old man, im out riding i aint doing that right now"
Best- "Dammit boy, were tryin this out" as hes walkin over to my bike with a 13mm and new head.

I'm glad he doesn't take offense of my direct manner...

No compression test done, and sorry to say no squish value taken.
This engine is a test mule, quite worn out really, so while compression values might be useful to compare from head to head, they will not be very useful to you and what you are getting. Neil was in a hurry and the engine was hot, I "jus gotter done!" I can get a squish value later. The head was cut with the basegasket in mind for an overly safe squish I had no hesitation in "throwing it on". I do believe it will work with no basegasket too, but will be close enough it will have to be squish tested.

 

[dksix]

How did you cut the shape?

 

[Triplecrown421]

we have a friend that owns a machine shop, he dos all our work.

 

[dksix]

we have a friend that owns a machine shop, he dos all our work.

More detail, please. That would be a hard cavity to cut on a manual machine, but could be done.

 

[mud runner]

at about 4 i stopped home and Best turned to me and says-
"you running that new head yet"
i reply- "No old man, im out riding i aint doing that right now"
Best- "Dammit boy, were tryin this out" as hes walkin over to my bike with a 13mm and new head.

sigged 151555151515

 

[best]

Oh great, domestic violence in posterity....

Glenn Doherty, Heritage Machining Services, 32 Calkin Dr, Kentville, NS B4N 3V7 (902)678-1354
email heritagemachine@ns.aliantzinc.ca
Website: www.heritagemachining.ca

Did the work manually.

 

[joeak47]

That would be a hard cavity to cut on a manual machine, but could be done.

Thats not hard to do on a manual machine. Believe me.

 

[dksix]

Thats not hard to do on a manual machine. Believe me.

Explain, just so I understand. Maybe I'm seeing the shape to be complicated than it really is.

 

[best]

The shape is essentially a deep straight sided bowl. Still 50% squish area, but sides cut straighter and only a small radius in the corners. The roof is typically shallower than a Hemi head to keep volume down and for a clean wash and compact burn. Sometimes the plug is actually extended into the chamber, closer to the piston or at least the center of the chamber.

The simpler heads are an angled cut for the sidewall and a flat roof. Simple cut with a carbide tool and the roof to sidewall radius is just left at 1mm or so.

 

[dksix]

OK, I'm straightened out now. I've gotten an information over load on these chamber shapes. I realize now that the first head was a straight walled and the 2nd is a hemisphere or bowl shape. Somehow I thought you were trying an irregular shape, like an egg shaped chamber. Thanks, Best for the post. I got it now and agree, the sphere is an easy cut.

 

[zedicus]

i always wanted to velocity stack the spark plug. a short barrel would give the wave front of the flame more downward movement. only thing is timing would have to be altered as having a barrel on the flame front would naturally retard it some. plus the chamber shape would need to be almost a continuation of the squish to keep from lowerinng compression too much.

 

[Triplecrown421]

i always wanted to velocity stack the spark plug. a short barrel would give the wave front of the flame more downward movement. only thing is timing would have to be altered as having a barrel on the flame front would naturally retard it some. plus the chamber shape would need to be almost a continuation of the squish to keep from lowerinng compression too much.

so you mean like a funnel shaped head starting at squish and barrel ending at the tip at the plug all flowing with one smooth angle?? i wonder if the flame would wonder in the barrel like zig zag.

 

[zedicus]

yeah, even if it did zig zag some it would be auto correcting on it own just because it would have to burn away from the point of ignition. i dont know rather a complete funnel shape, or a straight barrel with a flare at the end would be the best. but a directional forced charge is always more effective then allowing omni directional. look at the wave from a directional antenna, or the fact that when they demo buildings, every charge is small and precision shaped.

maybe a riffled barrel with the plug in one end and a short broad flare right at the very end just over the piston.

 

[zedicus]

and that slight swoosh that some people cut into domes on ebay and try and pass them off as 'ultra hp 250% gain just mount this and youll instantly be the fastest thing on the planet' thing really is not comparable, over the tiny shape and huge open end of the dome that pattern does almost nothing. while over the slender longer barrel that would be needed to direct a flame front you could actually get some improvement out of it.


basically i want to fire a gun at the piston instead of having a open sided stick of tnt try to knock it over.

 

[Triplecrown421]

I C. The stock shape is almost like what your saying. altho its more of a cone shape, we all know that works like sh!t. i wonder how much better a barrel shape would be...

yea those 240 heads that have the ripples around the stock chamber??? this what you mean?? ive never tryed them but i could guess it sh!ts the bed aswell. the ripples are designed to help scavanging but on a 2 stroke they dont fallow all the factors that should be brought into play. poop design no thought....