head work

[sicivicdude]

SCD, is "coking" a typo for "cooking"? I've been looking into the best finish for the combustion chamber. I've read and been told that a textured finish will help prevent hot spots. The only thing I've seen that gave me an idea of how rough is an old guy I know said "400 grit sand paper". I know you spend a lot of time researching things like this, what have you come up with?

Nope, I meant coking which is the technical term for when petroleum products pyrolize and leave ash stuck to a surface.

It's better known in motor oil conditions on high HP forced induction engines (ESPECIALLY turbocharged) when the engine isn't given a proper cool down time and the oil "burns" into the oil passages and turbocharger bearings.

Inside the combustion chamber for a 2 stroke, oil pyrolization is an unintended consequence of having a total loss oiling system where the oil passes through the combustion chamber after lubricating the working components.

It's SUPPOSED that a mirror finish leaves less "nooks and crannies" for the oil to gather into and leave ash. If anyone has any research to prove otherwise, feel MORE than free to share...

 

[sicivicdude]

O sh*t si i can make that arbor inna bout ten mins at work . Thanks man now just gotta find a head . How much off ya think before 110 feul is to be used ? .015 to .020?

It's not exactly like that.... the trouble is, the squish area and combustion chamber shape and size are QUITE antiquated on the blaster head. Basically, it sucks.

You really need to redesign the entire head around MSV calculations in order to maxmize power output and that requires access to (or purchase of) a computer program capable of "crunching" the numbers to determine the Maximum Squish Velocity

If you simply want to shave down the mating surface, you can safely take it off until the squish area meets the mating surface but you don't need an arbor or lathe/mill to do that.... a sander can do that easily. The hardest part is lapping the head mating surface after the grinder has gotten ahold to it... You need a lapping station or machinist stone in order to make sure that it's completely flat for the gasket to take.

 

[YZ Otis]

O sh*t si i can make that arbor inna bout ten mins at work . Thanks man now just gotta find a head . How much off ya think before 110 feul is to be used ? .015 to .020?

If you're going to chuck up a head and shave off .020 to raise compression ya might as well fix the chamber. There is enough info on this forum to make a very good head without mind bending math & complex programs.
Read then Play

 

[dksix]

I have no research to post, just asking questions. Aren't the new high performance synthetic oils suppose to prevent these build up/deposits? I understood that the roughness created more surface area thus increasing the substrates ability to dissipate heat. I wonder if this is one of the trade offs that so often come with performance modifications. Smooth allows less carbon build up and rough dissipates heat better. I can see where better heat dissipation would be a good trade off for people who are looking for the absolute highest performance sacrificing some longevity. At the highest level buildup wouldn't be an issue and nothing but the best fluids would be used but tear downs and rebuilds would be often. Where normally a person would want better life out of an engine instead of a sight performance gain.

 

[sicivicdude]

I have no research to post, just asking questions. Aren't the new high performance synthetic oils suppose to prevent these build up/deposits? I understood that the roughness created more surface area thus increasing the substrates ability to dissipate heat. I wonder if this is one of the trade offs that so often come with performance modifications. Smooth allows less carbon build up and rough dissipates heat better. I can see where better heat dissipation would be a good trade off for people who are looking for the absolute highest performance sacrificing some longevity. At the highest level buildup wouldn't be an issue and nothing but the best fluids would be used but tear downs and rebuilds would be often. Where normally a person would want better life out of an engine instead of a sight performance gain.

Greater heat dissipation through the head would reduce the combustion temperature resulting in a lower thermodynamic efficiency. In the TOP most performance category, removal of cooling capacity is usually undertaken to make the engine run hotter

 

[smallblockmazda]

So find a post on here of how to rework the comb chamber on the head is more taken off inside or what?

 

[dksix]

Greater heat dissipation through the head would reduce the combustion temperature resulting in a lower thermodynamic efficiency. In the TOP most performance category, removal of cooling capacity is usually undertaken to make the engine run hotter

So to make more power one would want to trap heat into the the combustion chamber? I never knew that, I always thought heat was the enemy of performance. Now I'm more lost than ever but that's why I ask questions. I learn something new every day.

 

[sicivicdude]

So to make more power one would want to trap heat into the the combustion chamber? I never knew that, I always thought heat was the enemy of performance. Now I'm more lost than ever but that's why I ask questions. I learn something new every day.

To gain more performance one wants not to trap the heat in the combustion chamber, but in the fire itself.... The hotter and more charged the charge is prior to the ignition event, the more ferocious the explosion will be. Think about what an internal combustion engine is and does.... it intakes air (with 21% oxygen) and mixes an explosive fuel with it. It then puts it into a cylinder and compresses it until the perfect moment and then ignites it. The expansion cause by the fuel burning is what drives the piston downward. The more heat you keep in that charge, the more expansion you'll get.

The trick is keeping the charge happy until the ignition event, the engine from grenading (either from overheating or under lubricating), and putting that power to the ground.

 

[dksix]

To gain more performance one wants not to trap the heat in the combustion chamber, but in the fire itself.... The hotter and more charged the charge is prior to the ignition event, the more ferocious the explosion will be. The trick is keeping the charge happy until the ignition event, the engine from grenading (either from overheating or under lubricating), and putting that power to the ground.

But with a hotter charge, don't you lose density? I'm sort of new to engine performance and just trying to put things together in my head before I start modifing things myself. Just trying to get all the information I can from the people who's done it.

 

[sicivicdude]

But with a hotter charge, don't you lose density? I'm sort of new to engine performance and just trying to put things together in my head before I start modifing things myself. Just trying to get all the information I can from the people who's done it.

You're compressing the charge before the ignition event mechanically using the piston so density isn't an issue. Once the explosion has happened you want less density. The less dense the charge is the more volume it is trying to take up pushing harder on the piston. Harder push on the piston means more power to the crankshaft.

 

[best]

So find a post on here of how to rework the comb chamber on the head is more taken off inside or what?

About 30 years ago I put a Ford 302 engine into a Mazda 808 sedan.
Is that what you mean as "smallblockmazda"?
This is not the car, but is the type of car it was:

My son and I dropped his Blaster cylinder 0.020"-0.040" (cannot remember at the moment) and got detonation with the stock chamber, so just shaving the head was not going to be the answer. By reshaping the chamber we were able to drop the head without detonation.

This is the configuration he had it cut to in this drawing:

The goal is to get the piston very close to the head without hitting it at high rpm when the rod stretches and all the clearances are taken up. About 0.040" is the closest you would dare get the piston to the head at static. The reason you want it close is to create turbulence in the cylinder and allow maximum cylinder pressures without detonation. The stock chamber does not do it. Notice how the bowl is opened up in this photo?

Thanks Blasterdemon7 for the great comparison pict.

As for surface finish, there is a thought that a mirror finish reflects heat back into the fire and resists carbon build up (coking). There are people claiming that a rough finish creates a boundary (laminar flow) layer that insulates heat from the head. Some folks spray the piston and head with a ceramic paint to do the same thing. I am a mirror finish supporter myself.

The heads in this picture are off my KTM 125. The one on the right is a rough surface head with several thousand kms of highway travel and off road use. Jetting is set up quite lean and synthetic oil is used. No tendency for the head to carbon up. The piston was not this clean, quite carboned up.
Notice the different chamber shapes? Left favours high rpm power, right favours mid range without sacrificing too much top end.

 

[smallblockmazda]

Yup ive got a 88 b2200 w a 302 in it!

 

[best]

Yup ive got a 88 b2200 w a 302 in it!

It was quite a job getting it in the old 808. Everything fit well until it came to putting on a starter. I eventually had to make an offset housing for a small diameter starter to clear the steering linkage. I put 302/289/351W into all sorts of vehicles over the years. This one is a 351C 4bbl with 4spd, 3.50L gears Torker intake and custom headers to make it fit (sorry for the weathered photo :

 

[smallblockmazda]

talk bout old photo ! this ones gotta ton of room . did my old toyota w a chevy v8 swap bout 2 years ago. i got pics of both and will have to upload them . my mazda is my daily and the toyota was my old daily till i got a wild idea of a solid axle swap a v8 and 44s! so you wanna take that ridge and stretch it out further?basically?

 

[best]

talk bout old photo ! this ones gotta ton of room . did my old toyota w a chevy v8 swap bout 2 years ago. i got pics of both and will have to upload them . my mazda is my daily and the toyota was my old daily till i got a wild idea of a solid axle swap a v8 and 44s! so you wanna take that ridge and stretch it out further?basically?

We are going to get in trouble for going off topic, so I'll try to get back on topic.
That old photo gives you an idea of how old I am and how many years I have been going fast.
My off 2 stroke road history goes back to a 1974 CR250 that I stuffed and ported and piped (made my own) while I was in high school,
so I have a lot of time for the teenagers on here.
As for off-roading full sized vehicles, I was lucky enough to get on a military driving course that saw weeks of fording,winching, bridging, and every other off-road technique for getting standard pattern military vehicles through unbelievable places. I owned a few Dodge and Ford trucks, an early Bronco, of course the old army Jeeps.
You might find my family hauler from 20 years ago interesting (sorry for any broken links, the page is 15-20 years old. Is the internet really that old?):

Steve's old 4x4 van web page

Anyway, my present passion is KTM 2 stroke dirtbikes until my son got me into Blasters.
I am kind of sorry that I did the engine swap, I really like the Blaster motor and transmission. Nice engineering.
It ain't perfect, but responds to mods well. What other engine can you double the HP for less than a day's pay?
I am really enjoying helping my son to make his Blasters fly. And of course, a head mod was part of making that happen...

 

[smallblockmazda]

Can i take the quench and stretch it out without concaving the bowl? Or does.it need to.be concave?

 

[best]

Can i take the quench and stretch it out without concaving the bowl? Or does.it need to.be concave?

The quench (or squish, terms are interchangeable) can be a straight conical cut.
Does not have to be concave to match the piston. Better that it tapers open a bit, whether it does this as an angle or a radius (from the piston) does not matter. The angle of the cut is about 11 degrees according to Sicivicdude (I didn't figure it out) and my drawing below is what I actually had cut, measured after the fact, not what I think would be perfect. As it is, the modified head below (green lines) worked awesome, but I would suggest using the blue lines and measurements for your squish.

Very important you measure the distance between piston and head (quench/squish at cylinder edge). You do not want this any closer than about 1mm or 0.040" (Sicivicdude recommended 0.050"). Some guys push it closer, some guys blow up motors. Stock is somewhere in the 0.120"-0.150" range and I believe my son is running 0.070" right now with wonderful results.

Quench/squish gap is like compression or boost pressure or many other things, they give diminished returns as they approach risk. The jump from 0.130" to 0.080" will be hugely noticeable. The jump from 0.060" to 0.050" barely noticeable but closer to the risk zone.

Have you read this recent sticky?:
Sicivicdude's great thread on squish

You do have to open the bowl up on the Blaster head if you want any improvement in the power. Don't worry about the possible loss of compression, because compression is not as important on a 2 stroke as it is on a 4 stroke (for top end power) and it will be made up by you getting the head closer to the piston (shaving it). There is waaaayyy too much squish/quench area on the stock Blaster head and not enough chamber. Shaving the stock head enough to make a difference will just cause detonation. I know, I tried.

Finally, in Sicivicdude's great thread on squish he mentions 3 ways to measure quench, only use the solder method in my opinion. Solder taped to the top of the piston (clean it if you have to) over the pin and right out to the edges of the cylinder. Turn the crank by hand, gently. Measure with micrometer or vernier.

Long answer to a simple question. A bit pedantic but I do not want to lead you the wrong way.

Steve

 

[dksix]

Best, great post. I noticed that your modded head has a volume of 28cc vs 22cc and 23cc, wouldn't that lower compression a lot? Are you measuring the total volume of the chamber from the gasket surface? How much area does the piston displace from the 28cc? I wasn't aware that compression had less effect on 2 strokes than 4 strokes. After this set up was broken in, what was the pressure reading with the 28cc chamber? How much change did it make after you cut .020" from the original shoulder (volume, chamber pressure and the power the engine made)? You said would would suggest staying closer to the DT200 dimensions, what improvements do you think that would have made?

 

[best]

Best, great post. I noticed that your modded head has a volume of 28cc vs 22cc and 23cc, wouldn't that lower compression a lot? Are you measuring the total volume of the chamber from the gasket surface? How much area does the piston displace from the 28cc? I wasn't aware that compression had less effect on 2 strokes than 4 strokes. After this set up was broken in, what was the pressure reading with the 28cc chamber? How much change did it make after you cut .020" from the original shoulder (volume, chamber pressure and the power the engine made)? You said would would suggest staying closer to the DT200 dimensions, what improvements do you think that would have made?

Let's see, Blaster stock bore at 66mm is an area = Pi*r*r = 3.1412*33*33= 3421sqmm
So that would be 3.4cc per mm shaved off or 0.855cc per 0.010" shaved off.
We dropped the cylinder 0.040" and shaved another 0.020" off the head so the piston now intrudes another 5.1cc into the chamber volume.
Looks like we needed the 28cc chamber to keep the compression stock. That was more good luck than good planning!

To measure the chamber volume I greased the head gasket surface and then set it on a sheet of glass. Then I filled the head through the spark plug hole with water from a graduated syringe (available cheap from a drug store or vet). This does not allow for piston dome, head gasket thickness or piston to deck height. Doesn't have to, it is just a comparison of original to modified.

My son took compression readings, but I cannot remember what they were. Our gauge seems to read low compared to others posting here, somewhere in the 130 range and didn't change enough to talk about after the mod. Sorry for being not so scientific. The additional 0.020" shave made a slight but noticeable difference. I'd suggest more from the improved quench than the 1.7cc compression improvement but they both work in the same direction.

Compression improves mid-range in a 2 stroke, but but beyond a certain point drives heat into the piston and kills top end power. Next time we get a head cut (soon I am thinking) we will flatten out the taper of the quench area closer to that of the piston. If the piston is 10 degrees, we will aim for 11 degrees on the quench surface. Also we may aim for more of a toroidal shape to the chamber to boost midrange with less worry about radius at the quench and chamber juncture. This quench area is about 47% of cylinder area, that is fine.

Here in red is an approximation (due to my limited capacity with Paint!) of what I'd like to do with the Blaster head allowing for the fact we plan to raise the cylinder again:
The cone recess near the plug is not helpful but is unavoidable due to the shape of the stock Blaster head.

 

[dksix]

.......Next time we get a head cut (soon I am thinking) we will flatten out the taper of the quench area closer to that of the piston.

If you would consider posting a thread (sort of a how to) with pics and a write up of the process, I'll donate a head to the cause. I can have it on it's way to you Tuesday, if you're interested in sharing your techniques and some results. I've even got a new top end gasket set I'll throw in with the head. I:II:II:II:II:I