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Old 02-14-2020, 07:40 PM
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Default My first hemi port job

I had an extra hemi head, so I decided to experiment a little with it on the dingo motor. Iíve also been working on a GX399 carb that Iíve been working on thatís also going to be an experiment.
I got the intake ported on my lunch break today, and I can get my whole index finger through the port to the base and itís pretty much a straight shot from the carb to the valve. what do you guys think?
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Old 02-14-2020, 08:28 PM
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Seems legit

Not much more material to remove lol good work
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Old 02-14-2020, 08:41 PM
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a hair too glossy for my taste..

I'd roughen the surface up again
some rather coarse steel wool pulled through until slightly dull

while one cannot achieve a perfect shark skin texture in the home shop,
it's still directional patterning
which makes the gas flow quicker thanks to reduced drag.

the reason why sand dunes get the close approximation of
magnified shark skin texture in wind direction

'sid
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Old 02-14-2020, 09:30 PM
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Conventional wisdom says that it should have a texture Laminar flow is what Iíve always heard it called, this still has a little texture, but itís very fine. This one is being set up for 25% nitromethane, so itís really more about how much fuel I can get through it than the airflow. Itís an experiment, so Iím trying something a little different.
Iím not even going to post pics of the carb, everything I know about carburetors says that this shouldnít work, but I have a hunch that it might since itís really all about dumping as much fuel as possible into the intake stream. One thing is for sure, weíll all find out together, lol.
Really the only reason that one even messing with this head is that I already have a set of 1.2 billet roller rockers for a hemi that Iím not using. The plan is to put this valve package from NR in it to help with the lift itíll have with a 308 cam and 1.2 rockers.
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Old 02-14-2020, 09:48 PM
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What I know about porting a hemi Predator I only know from others, but it seems to have a bad short turn that benefits from addition of material to help air swing around the bend. It doesn't seem to work as well with a straight port with no short-turn like the inline heads can.
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Old 02-14-2020, 10:04 PM
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Quote:
Originally Posted by karl View Post
Seems legit

Not much more material to remove lol good work
Thank you

---------- Post added at 11:04 PM ---------- Previous post was at 11:01 PM ----------

Quote:
Originally Posted by 65ShelbyClone View Post
What I know about porting a hemi Predator I only know from others, but it seems to have a bad short turn that benefits from addition of material to help air swing around the bend. It doesn't seem to work as well with a straight port with no short-turn like the inline heads can.
Iíve read about that for years myself. I raced big cars for years and always had fast cars, I always did my own head work too. I have had good luck with giving a straight shot to the valve, but a hemi could be different, this is the first time Iíve messed with one.
I like to try things to see if theyíll work, and Iím not out much if I ruined it, in fact I have another hemi head laying around with less run time than this one has, which isnít much.
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Old 02-15-2020, 07:30 AM
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laminar flow is a totally awesome thing,
and extremely hard (next to impossible really) to achieve..
the venturi in the carb alone almost prohibits that btw.
in order to align all flowing molecules the intake manifold would have to be several feet long.
And that's not actually a good idea at all.
since it alos means that heavier molecules would be allowed tosink inside the airstream, creating an imhomogenous mix.

Since laminar flow means that all molecules not only move at the exact same speed,
but also in the exact same direction
(looks amazing with water.. as if flowing water became a crystal rod)
much easier with tiny orifices btw

laminar air flow feels amazing as if dry light water flows over your hand..

Anyways... the next best thing is reducing sidewall drag to prevent additional turbulences
counteracting the airflow
and the directional patterning prevents most of the tiny swirls counteracting the airflow,
instead the stray molecules jet off in roughly the flowing direction
speeding overall flow up and actually help stiring the fuel mix to keep the mix homogenous
for a cleaner and stronger combustion.

I for the heck can't find that awesome video one once did explaining the topic much better than I could.
It was in the early days where I became aware of "port but NOT polish"
(somewhere in the late nineties.. pre youtube)

I remember it was Beetle tuner so a VW Typ4 engine
(maybe Typ1... but I think 4.. anyways some aircooled four cylinder VW boxer)
he made two perfectly identical sets of heads
ported all four heads the exact same way (rough textured ports) and installed them on identical engines..
producing almost identical hp on an engine dyno...
he then took off the heads on one engine again and polished the ports to mirror finish.
reinstalled he lost -I think- five or six horses.
wait was it one engine?.. ah too long ago... anyways he lost a good amount of ponys
by polishing up his ported heads to prove a point.
and while there was no "shark skin" babble back then, he still explaind the reason very well.
(I think that's the first time I heard the name Schauberger... *shrugs*)

Ah well... nevermind
that's one big hole you got,
so pushing through a sincere amount of combustible gas shouldn't at all be a problem
getting a good pop out the business end

'sid
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Old 02-15-2020, 08:04 AM
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I just did my 301 hemi. I was actually amazed at how well the ports were made. This I'm comparing to the B&S on my other engine.

There wasn't really much to do to it besides remove the sharp edge and smooth out the valve guide gusset.

I left the intake rough cut from the burr grinder and took a stone followed by sand paper to the exhaust.

Now I'm sure there's those that could put it on a flow bench and do a better job, but for my needs, an hour or so with the Dremel made me happy
ēMERGEDē
Too bad you can't make it look like this.
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Old 02-15-2020, 08:15 AM
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I was always told don't polish. Here's an article with lots of info and pictures. Looks like they finish with 320 grit sand paper. If they don't polish an F1 engine Im sure there is a good reason.

https://www.f1supernews.com/2013/09/...nd-pneumatics/
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Old 02-15-2020, 09:47 AM
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Quote:
Originally Posted by Whitetrashrocker View Post
I just did my 301 hemi. I was actually amazed at how well the ports were made. This I'm comparing to the B&S on my other engine.

There want really much to do to it besides remove the sharp edge and smooth out the valve guide gusset.

I left the intake rough cut from the burr grinder and took a stone followed by sand paper to the exhaust.

Now I'm sure there's those that could put it on a flow bench and do a better job, but for my needs, an hour or so with the Dremel made me happy
Thatís interesting, I can get my whole finger through the port, so wet sanding it with some fine paper wouldnít be a problem.
I guess I didnít understand what laminar flow really was, my understanding of it was that the texture in the port would catch a small amount of air and cause the air and fuel to flow easier than it would against a perfectly smooth surface. Thatís why Iíve always left the sand marks 90 degrees from the flow. I figured that would be how youíd catch that air. My stuff had always be among the fastest for what it is anywhere Iíve raced, but Iím always looking to improve, so this would be a good time to try something different.
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Old 02-15-2020, 10:06 AM
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Mammoth, that was a cool article. It amazes me the R&D, and the machining that goes in to something like that. The flow molds were a beautiful touch. Really let's you see what's going on inside.

FHB, with out all the science involved.
Polish the exhaust so the expanding air can get out faster.
The intakes leave rough. The tumbling air over the rough surface will help keep the fuel atomized and from sticking to the walls.
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Old 02-15-2020, 10:22 AM
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Quote:
Originally Posted by Whitetrashrocker View Post
...but for my needs, an hour or so with the Dremel made me happy
I was told a rotary tool is the wrong tool for that job..
since all marks end up perpendicular to the flow,
while they should be parallel to the flow,
that's why pulling/pushing steel wool (or even emory cloth) through gives a better suiting finish for the job.
well so I was told..
now looking at that article above... those look perpendicular and much smoother than I anticipated.
haven't read the article yet just flew over the images and crossread a few lines to get an idea..
hmm... but yeah I'd assume F1 racing teams know perfectly well what works and what doesn't
then again.. aren't F1 engines DFI?
if so, there'd be no need to stir the air/fuel mix in the intake (since there's only air anyways)
*shrugs*

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Old 02-15-2020, 11:48 AM
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For a kart with an industrial engine I'm pretty sure anything helps performance. Now when you wanna play with the big boys our tactics don't gain much.

Besides isn't this about trying things? Gotta learn somehow
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Old 02-15-2020, 12:16 PM
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My understanding is that the ports can’t be made too big on these motors, there just isn’t enough material that can be removed to kill the velocity. This one will be on 25% nitromethane, so there will be a tremendous amount of fuel flowing through the port. Nitro is an oxygen bearing fuel, so airflow isn’t as important as just dumping fuel in it.
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Old 02-15-2020, 02:40 PM
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Looks good. I got some advice from a legit engine builder. Take the long side radius out about 50 thousandths up to the bowl.

Also the short side “corners” can have a bit more material taken out of them. They are too round.
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Old 02-15-2020, 03:49 PM
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Looks good. I got some advice from a legit engine builder. Take the long side radius out about 50 thousandths up to the bowl.

Also the short side “corners” can have a bit more material taken out of them. They are too round.
It’s been opened up quite a bit more than .050 everywhere, lol. I cut a whole lot of material out of that port.
I think I see what you’re talking about on the low side corners right where the short turn starts. I may open that up a little and square it off some. How that got so round was all of the material that I cut out of the port floor, that’ll give you an idea of how far it’s already been opened up.
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Old 02-15-2020, 09:09 PM
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https://youtu.be/vkSntQWiQDU
Interesting video I found on porting these little heads
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Old 02-16-2020, 12:00 PM
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Quote:
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what do you guys think?
Im going to reverse this , is my hack job FHB approved? GX200 head ,hemi bottom end.

Took about .050 off the head with the blade grinder, lapped flat. Straight on the block, good for 12.7 to 1 compression.
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Old 02-16-2020, 12:25 PM
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Quote:
Originally Posted by karl View Post
Im going to reverse this , is my hack job FHB approved? GX200 head ,hemi bottom end.

Took about .050 off the head with the blade grinder, lapped flat. Straight on the block, good for 12.7 to 1 compression.
What in tarnation?

It it the lighting or does the long radius side look pretty gnarly?
How did you deck the head and get flat again? I used a mill and still had to sand on a surface plate for a while to get it straight.
Your good!.
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Old 02-16-2020, 06:39 PM
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Quote:
Originally Posted by karl View Post
Im going to reverse this , is my hack job FHB approved? GX200 head ,hemi bottom end.

Took about .050 off the head with the blade grinder, lapped flat. Straight on the block, good for 12.7 to 1 compression.
Looks like itíll move a whole lot more than an unported one would. What kind of bits did you port it with?
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