Real talk about saw porting theory (no arguments)

[Czed]

I don't at all.

Never did myself thought i might be missing something.

 

[jmssaws]

Anybody got a 5105 recipe?
I'm porting one now and can't find my notes to save my ass

 

[jmssaws]

Nevermind I found it.

 

[EvilRoySlade]

Can someone clear my head? I've been staring at my 365xt with a degree wheel. I've heard raising exhaust and transfers is what they need, increasing strato duration, leave strato, gut strato. Intake, barely gets mentioned other than DO NOT go wider (no skirt).
In fully stock form, I'm at: Ex-99, Tr-116, In-74 and .030" squish.
I see I have 17* blowdown. If I raise exhaust I lose compression time on the upstroke right?

Where I get lost is if the strato ports are left operational, how can you increase duration on them? Seems to me that you could not exceed the intake duration, or better yet, they need to be the same.

 

[mdavlee]

They have good torque as is. Raisins couple degrees will only lose 5-10 lbs of compression. If you do a gasket delete along with this you'll be even on compression gain/loss. Feeding more air into the case to purge exhaust with the stratos can't hurt. If I remember right you lower them or open the window on the piston.

 

[MustangMike]

I am strictly an amateur, but I think deleting the base gasket then sanding to squish band to get .020 would be a good improvement for that saw.

 

[EvilRoySlade]

I am getting the base cut to use gasket and have squish around .020-.022. All ports will be at least brought back to stock but I plan to adjust accordingly. It's an easy enough saw to practice on without a RT angle so I figured why not.

If the intake is closed and the piston is coming down couldn't you be pushing out of the strato ports if they close after? I hope that makes sense.

 

[EvilRoySlade]

They have good torque as is. Raisins couple degrees will only lose 5-10 lbs of compression. If you do a gasket delete along with this you'll be even on compression gain/loss. Feeding more air into the case to purge exhaust with the stratos can't hurt. If I remember right you lower them or open the window on the piston.

I was surprised to see how much piston was above the transfer floors already. It must be how they got the timing. If I drop the floor a bit it would increase strato duration and leave transfer the same. Yes?

The little bits I have seen seems that 99 on exhaust has peak torque quite low in the RPM range, like 7-8000. I'd like it more about 10,000. Without experience I understand that 1-2* higher (98/97 respectively) yields higher torque RPM. Or do I need to hit the books again?

 

[mdavlee]

I am getting the base cut to use gasket and have squish around .020-.022. All ports will be at least brought back to stock but I plan to adjust accordingly. It's an easy enough saw to practice on without a RT angle so I figured why not.

If the intake is closed and the piston is coming down couldn't you be pushing out of the strato ports if they close after? I hope that makes sense.

The strato ports feed right into the cut outs correct? I'm blank on how they look right now.

 

[srcarr52]

I am getting the base cut to use gasket and have squish around .020-.022. All ports will be at least brought back to stock but I plan to adjust accordingly. It's an easy enough saw to practice on without a RT angle so I figured why not.

If the intake is closed and the piston is coming down couldn't you be pushing out of the strato ports if they close after? I hope that makes sense.

Cutting squish and dropping the jug down will increase strato and intake duration. 0.010" is approximately 2 deg duration. Intake duration is always longer than the stratos.

 

[EvilRoySlade]

The strato ports feed right into the cut outs correct? I'm blank on how they look right now.

Yes. Stratos open at intake to piston about 28* before piston opens to transfers.

 

[EvilRoySlade]

Cutting squish and dropping the jug down will increase strato and intake duration. 0.010" is approximately 2 deg duration. Intake duration is always longer than the stratos.

Shaun thanks. It just dawned on me to pull the gasket and time, even though it'll be at .013" squish it's still data.

 

[Lightning Performance]

What about flame travel flat top vs pop up ?

Oooo lol.
Flame travel is longer on the popup. It yields more pressure on the piston based on more surface area but there is more to the story. The flame must change direction on the popup so the time travel is even longer. The cylinder pressure tends to splay outward and thus puts more pressure towards the ring lands, hence a better ring seal is had most times. Detonation is directed away from the piston center and toward the cylinder walls. This can be good and bad. Good to direct it away from the center but bad for a thin jug wall. Trade off are occurring and it does change things just a bit. The piston can run a bit hotter based on the fact that it is now thicker in the center. That can also be a good and bad thing. Are you more lost now or have you been found? lol
Yet, there is still more to the story.

Who would like to continue with some more points here???

Insomnia is a good and bad thing. You have more time to be "well read" but read will never make you a better hack of a grinder. It will make your bench racing faster ;-)

None of this has a damn thing to do with intake velocity or exhaust exit port volume or does it...

Is this a fact or fiction? The popup slows down the burn time?

 

[paragonbuilder]

Oooo lol.
Flame travel is longer on the popup. It yields more pressure on the piston based on more surface area but there is more to the story. The flame must change direction on the popup so the time travel is even longer. The cylinder pressure tends to splay outward and thus puts more pressure towards the ring lands, hence a better ring seal is had most times. Detonation is directed away from the piston center and toward the cylinder walls. This can be good and bad. Good to direct it away from the center but bad for a thin jug wall. Trade off are occurring and it does change things just a bit. The piston can run a bit hotter based on the fact that it is now thicker in the center. That can also be a good and bad thing. Are you more lost now or have you been found? lol
Yet, there is still more to the story.

Who would like to continue with some more points here???

Insomnia is a good and bad thing. You have more time to be "well read" but read will never make you a better hack of a grinder. It will make your bench racing faster ;-)

None of this has a damn thing to do with intake velocity or exhaust exit port volume or does it...

Is this a fact or fiction? The popup slows down the burn time?

Couldn't sleep either.
Interesting thoughts!
Bring on the theory, I'm listening.
Are you coming to any gtg's this year?


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[Lightning Performance]

Mostly facts not thoughts. I did not figure that out myself. It was explained and passed on to me by someone who has passed on to the big dirt nap.
Maybe

 

[tickbitintn]

Glad I'm not the only one that can't sleep!!

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[Lightning Performance]

Did we start a trend? wtf..,

 

[drf256]

It yields more pressure on the piston based on more surface area

More surface area, yes. It does not change the column of pressure exerted down on a piston. I don't care what shape the dome is. Force=Mass x Acceleration, period. A 50mm bore pushing down on any shape piston will yield the same force if the pressure is the same. It probably cools better though.

A pop up may change charge direction in some engines because Some of the charge will hit the pop up and be pushed upwards towards the chamber more. It also may create a wider squish area and more squish velocity if it's machines just right with symmetric squish between the chamber edge and the top edge of the pop up dome before it turns flat. But too large a squish area ain't good either. The charge trapped there isn't burned, it's lost.

As for flame travel, I believe all of the charge is ignited within the first few degrees surrounding TDC. The smaller the combustion chamber, the more preheated the charge and the more central the plug, the faster the travel will be.

The piston crown can induce swirl which will decrease detonation and result in more complete charge burn by creating a more heterogenous stoichiometric charge in the chamber. There was a bunch of experimentation in the 80's with custom 4 stroke pistons with some wacky looking domes to induce swirl.

My main issue with pop ups is that they need to be machined anytime a new slug is needed for an engine. It will create more work for a builder, which may be good or bad.

There are some jugs with near perfect numbers where a pop up will help. Others with near perfect upper transfers where a popup and band cut combo will ensure good numbers and flow.

Like anything else, it's a useful tool. The last jug I machined was crying for a popup, but I didn't do it. Kicking myself a bit for that now. I dropped the jug and cut the band, then raised everything back up. Now I need to open the chamber for less compression. All because I wanted my friend to be able to use an off the shelf piston whenever he needed to.

My .02. Explain why I'm wrong.

 

[Lightning Performance]

Your far from wrong and trapped charge is very good point. It is wasted space and fuel. I beg to differ on the surface area. A lil bit is gained but not much as you stated. More area = a bit more push.

I never did buy into the stock piston argument. Once we tinker with them nothing is stock so why worry about the piston being an OE drop in?

In fact I hope to try out a popup in my next ms361 build.

The burn rate will depend on the compression ratio, the cylinder temp and the fuel octane and available O2

 

[paragonbuilder]

Personally, I find the replacing a piston reasoning faulty. I heard it a bunch though. In my opinion, if it creates a better or stinger motor, that's what we are looking for. How often do we really need to replace our pistons? And any machine shop can easily do that if we needed to replace it.


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