15 replies to this topic

[Benzo4gT]

Evening all, as a person who is a bit crazy and anal about things, I decided to pull apart the td05 20g today and see what it looked like. I have had a bit of experience with dremmely goodness and am now also armed with a die grinder. I bought some super long and fine burrs, and one tiny match head sized one, all proper good quality ones, and I got some stones and flap wheels. These are before and afters. Oh, and it spins with a puff of breath for a couple of seconds, maybe they all do, not sure, but I've been getting a bit of exercise and joy huffing down the hot side

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[croket]

That looks pretty good would be interesting to see if it flows much more , especially like the outlet before and after shots

[Benzo4gT]

Thanks mate. I think it would flow better, but not anything much, I might pick up 3-5 hp tops over the whole inlet to cylinder head. I just like do eliminate cast lines from everything, all mitso stuff was so mass produced they didn't bother to smooth the surfaces.
I have actually taken the high polish off the outlet and put 400 grit finish on it, the reason being the Boundary layer effect. Although it seems counter intuitive to think that a slightly roughed surface will flow better, the air flow directly on a mirror finished surface is zero because the flowing air affectively sticks to the surface. But the difference between high polished and 400 grit flow on a surfaces of a the intake tract, including ports etc. is 1% or less, that is assuming the surface was smooth to begin with.
Taking the cast lines out will make most of the difference along the way to the valves.
I would love to get into it more, I find it fascinating.
Sorry to get nerd all over the place.

[croket]

I read up a bit when i did my kx 250 two stroke engine and found in most peoples experience it was better not to have high polished but thats on a na twostroke so kinda different i guess. What i read was its good to have a bit of texture to get the air sorta tumbling or whatever.
Im not as clued onto that kinda stuff as you are by the sounds of it hahaha
I will post up the intake on my gt pumps 20g for you to see its nicely ported by them which is a bonus

[Benzo4gT]

Haha, I wouldn't say I'm too clued on, probably just enough to get myself in trouble trying to learn
The 20g conversion on mine was done by GT pumps as well I believe,(but I didn't get the port job) would be good to see yours.

2 strokes are cool, the ports are slots on opposite sides and you can change the powerband by port shape and overlap, and or a different exhaust expansion chamber. I ported my 60hp Mariner outboard when I rebuilt it, just a tickle though, but it goes like hell! It's a 2 cyl 2 stroke, I think it's from the late 70's and about 648cc or something.

I've tried getting stats on port flow for pressure on 4 strokes, but the info is always based on atmo stuff, with atmo they depend on port velocity which is why bigger ports sometimes lose power, but I figure with forced induction it would be a different story . I'll keep searching and learning I guess. I have 2 4g63 heads atm, one is stage 1 ported, which is just a bit of bowl work, gasket match and sanding the cast lines out.
The second one I've ported out quite a bit larger but still keeping the same overall shape of the port, I will have flow figure for std, vs my ported one in about a month, should be interesting hehehehe.

[evo-gsr]

Ben...only the exhaust housing on your turbo is a GTPUMPS job.
The compressor cover is genuine Mitsubishi gear which was machined out to suit the 20g compressor wheel, which came from GTPUMPS too.

[CYBORG-X]

see how its all shiney smoothe... that's bad, im unsure about your skill or previous experience porting, so I apologise if I insult. the surfaces should always remain a corse dull finish, this stops the 'rain on glass' effect. what you have done is great, you need to either run a tree hone down the port or hit with a heavy sand blast to finish it. ideally you use a fine scroll roll inside of any ports.

[evo-gsr]

Whys that Josh?

What is the rain on glass effect??

Edited by evo-gsr, 08 September 2013 - 11:34 AM.

[CYBORG-X]

long story short, with a rough surface the air passing through forms a tiny layer of turbulence around the edges of the pipe/port, but this allows the air to pass through extremely quickly. if its smoothe, the air sticks to the surface like rain on glass, causing friction in the air passing over it, thus slowing it down.

[OLDIE]

I would think that Extrude Hone would be the better way as it can remove casting dags in places you can't get to in the snail.
Has anyone had this done and the cost along with results would be good.

[croket]

Haha, I wouldn't say I'm too clued on, probably just enough to get myself in trouble trying to learn
The 20g conversion on mine was done by GT pumps as well I believe,(but I didn't get the port job) would be good to see yours.

2 strokes are cool, the ports are slots on opposite sides and you can change the powerband by port shape and overlap, and or a different exhaust expansion chamber. I ported my 60hp Mariner outboard when I rebuilt it, just a tickle though, but it goes like hell! It's a 2 cyl 2 stroke, I think it's from the late 70's and about 648cc or something.

I've tried getting stats on port flow for pressure on 4 strokes, but the info is always based on atmo stuff, with atmo they depend on port velocity which is why bigger ports sometimes lose power, but I figure with forced induction it would be a different story . I'll keep searching and learning I guess. I have 2 4g63 heads atm, one is stage 1 ported, which is just a bit of bowl work, gasket match and sanding the cast lines out.
The second one I've ported out quite a bit larger but still keeping the same overall shape of the port, I will have flow figure for std, vs my ported one in about a month, should be interesting hehehehe.

Here ya go this is my 20g photo not the best its from my phone

[Benzo4gT]

see how its all shiney smoothe... that's bad, im unsure about your skill or previous experience porting, so I apologise if I insult. the surfaces should always remain a corse dull finish, this stops the 'rain on glass' effect. what you have done is great, you need to either run a tree hone down the port or hit with a heavy sand blast to finish it. ideally you use a fine scroll roll inside of any ports.

I have actually taken the high polish off the outlet and put 400 grit finish on it, the reason being the Boundary layer effect. Although it seems counter intuitive to think that a slightly roughed surface will flow better, the air flow directly on a mirror finished surface is zero because the flowing air affectively sticks to the surface.

Already with ya mate, 400 grit is not shiny, just smooth. I probably should have posted up the dulled off pics,(sorry) but I get the surfaces of anything I port shiny enough so I can see any defective spots, including head work, then I'll pull it down to 400 or down to 240 or so depending on where I'm porting. I couldn't get this type of finish in the snail though so it is a lot rougher than 240. The effect of slightly roughed surfaces helps dispel the boundary layer as previously said, but as to what the perfect number of roughness is under boosted conditions for air, I have not found yet.
All of the info I've found so far about turbulent vs laminar flow is either based on fluid dynamics of is about aircraft wings.
Taking the casting lines off is certainly worth something though.

In wiki regarding polished surfaces, under Cylinder head porting it says this; "Flow bench testing shows that the difference between a mirror finished intake port and a rough textured port is typically less than 1%. The difference between a smooth to the touch port and an optically mirrored surface is not measurable by ordinary means."
Flow bench testing is done at about 10 to 28 inches of water pressure (2.5 to 7 kilopascals) or just over 1 psi. What happens on the layer of the surface when 25psi is put through might be different.

I've heard the stories about guys that have had high polish jobs done and lost power, but in reality I think they just had a crap port job to begin with, or mismatched valve timing by people who don't understand port velocity vs flow and how it affects primary and secondary pressure waves.

I think there is a ton more to all of this, a lot of which I have not been able to get any quantifiable real world evidence on as all the big boys are very tight lipped.
Just my 2c

[CYBORG-X]

good to hear you bang on the money!!! as for extrude hone, its expensive, considering you have to go in and shape it and remove the high spots first anyway...

[micky_vr4]

Have you had a look at Engineering Toolbox?

Check this link for a worked solution to the pressure loss in an air duct (it can be varied for different pressures and piping roughness coefficients):
http://www.engineeri...ubes-d_459.html

If you can follow that then you're doing well

[Benzo4gT]

Awesome link mickey, I'll look into that, this is the kind of stuff that has me fascinated!
I think I can get my head around it.
My Grandfather worked with Rolls Royce during WW2 in some sort of development as far as I know, he was a mechanic with the airforce in Darwin with the RR merlin engines. He was an amazing mechanic, the guy could just listen to an engine and work out what was wrong with it and what it needed as far as tuning goes.
So I'm hoping to figure out port velocity in relation to plenum size, scavenging effect of exhaust in relation timing of both intake and exhaust valves. It seems the tuning potential is infinite. I suppose that's why MIVEC (or any variable valve timing) was developed, best of both worlds.
Alfa Romeo had a centrifugal helical variable timing setup early 80's or late 70's I believe.
It would be nice to know the physics behind it all so I could tune my engine to suit my driving style perfectly, but then part of me just says throw boost and fuel at it and hammer it

[Django]

you can essentially 'see' the rolling effect with the air you guys are explaining about with the mirror finish when spraying a car. When the clear is on and you wet and dry, you can see the water bead off the paint and when it's been smoothed, it 'sticks' to the paint.