Author Topic: CB500/4 racer resurrection - airbox finished, didnt quite work.... (Read 36647 times)

livefast_dieold · « **Reply #75 on:** January 23, 2019, 11:36:02 AM »

Amazing!!!

I've been swamped at work the past 2 weeks, but next week I'm coming for a beer to see your experiments :-)

CR750 · « **Reply #76 on:** January 23, 2019, 01:01:24 PM »

Hey TG,

Looking all scientific and stuff, props !

Just a sidenote, if you care for the little difference it makes.

maybe quickly splash some woodglue dilluted with water on the gypsum where the actual port cavities are, to recreate the aluminium surface properties.
The glue dilluted with water is thin enough that it will be pulled into the material when brushed on, yet it does not create a superslick smooth surface (keeping the somewhat rough appreance of the gypsum replicating the aluminum;

a) this seals the surface making it more comparable to aluminum (Gyspsum is poreus material)
b) this will make carving out the material also more controllable, and it will prevent smaller edges and so on from collapsing to quickly ( material is also bit more ' held together' for lack of better words when carving with a dremel or such )

I use this trick often on making MDF molds ( glue some mdf boards together to create a block - then treat it with this mixture) and then use CNC milling to make 3d molds out of them. The MDF sucks in the mixture into the material for a few cm, leaving a really nice material for detail milling ! You can also use waterthin epoxy for the same trick, but for you're situ that would be overkill and more expensive.

(Also when you make the gypsum molds, use a marble to make round dents in the first halve ( put marbles in the top when it's curing. Then when you cast the second halve, remove the marbles from the first, and you have super nice excact indexes for your two molds halves, if you follow what I am saying.
And when casting the purple mold, - I think you do not have a vacuum to remove the bubbles - smack the cup many time on the table surface with it's bottom before pouring then most bubbles will rise to the surface. and old innertubes of motorbike cut in rings make super nice big elastics for holding mold halves together yet easy to remove )

turboguzzi · « **Reply #77 on:** January 24, 2019, 03:56:27 AM »

Hi CR, tnxs for the tips! I am an industrial designer so quite aware of the little tricks in model making. Actually plaster casting was introduced to me in my 1st yr. course at design school (late 80's) and silicon molds is something we do often at work. nowadays i'm more into managing a studio rather than hands on model making, so did some mistakes in the first try but it's all coming back to me.

So did a first mod of valve seat opening to 0.9 valve diameter (27mm x 0.9 = 24.3 ), which would seem to make a lot of sense when you realize the port throat goes down to less than 23mm before the seat.... that change alone means increasing the minimum port cross section area by more than 10%. Win-win situation right?
Well, if you needed proof that air flowing in ducts has a twisted mind of it's own and it's all counter-intuitive, here it is: there was almost no change in flow!
Two potential explanations
The stock port small throat diameter creates a venturi effect that actually helps with flow past the valve so i need to restore back the venturi effect that the stock port had (the so called “add bowl”), the opening of the seat has made the port to look more like a simple dump and even if bigger, it flows worse.
or, the restriction is somewhere else and the enlarged seat will show positive results only after i find where the restriction is and remove it.
All in all quite interesting and good fun to solve.

MessnerMoto · « **Reply #78 on:** January 24, 2019, 11:12:08 AM »

nice work as always.

You should 3d scan your port model and do everything in 3d and using some FEA software.

That would be much faster and also it would allow you to do porting using CNC

turboguzzi · « **Reply #79 on:** January 24, 2019, 01:07:48 PM »

i dont disagree with you but i am not a freelancer with full control of my time like you

this guy did exactly that, nowadays called CFD rather than FEA, but he is working at just one port (not four) and has access to all the gear through university.

for my reality plaster is quicker, doable and besides that it's a classic racer...

his nice stuff is down the long page

https://www.supermotojunkie.com/showthread.php?148704-2013-CRF450R-supermoto-conversion/page2

MessnerMoto · « **Reply #80 on:** January 25, 2019, 02:25:50 AM »

Eh if you are in Belgrade we could send your mould to a shop for scan. It would be finished in half a day and it would be very cheep

But speaking of your port work.... My wild guess is that you need to add material not remove it. To increase Venturi effect. I dont have experience so wild guessing

turboguzzi · « **Reply #81 on:** January 25, 2019, 02:31:17 AM »

that's exactly the plan, it's called d-porting
question is of course how much and where

some idea you can get from this 3D i built, red is the current port, violet the new one
actually did already some tests yesterday, initial results are good

MessnerMoto · « **Reply #82 on:** January 25, 2019, 03:23:14 AM »

yes something like this.

can you post that 3d picture from the side view so I can see difference from 2d perspective

CR750 · « **Reply #83 on:** January 25, 2019, 01:13:42 PM »

Interesting

I think we are with three industrial designers here. Mesner, you and me

share the same job and passion it seems.

turboguzzi · « **Reply #84 on:** January 26, 2019, 08:28:20 AM »

here is how i make the plaster ports
empty mold first, the second is ready for covering with silicon grease sprayed to separate the two halves
going to go more radical with this set, lets see..

MessnerMoto · « **Reply #85 on:** January 26, 2019, 11:15:03 AM »

Quote from: cr750 on January 25, 2019, 01:13:42 PM

Interesting I think we are with three industrial designers here. Mesner, you and me share the same job and passion it seems.

Actually I am programmer by profession, but I am changing profession like you see

Quote from: turboguzzi on January 26, 2019, 08:28:20 AM

here is how i make the plaster ports
empty mold first, the second is ready for covering with silicon grease sprayed to separate the two halves
going to go more radical with this set, lets see..

yoss post side view picture.... change the angle of the port if you are going to add material. You will have most of the gains there

turboguzzi · « **Reply #86 on:** January 26, 2019, 02:58:12 PM »

as you are a relatively youngster in the forum, you might not be aware that i changed the angle by 10 degs some 12 years ago

http://forums.sohc4.net/index.php/topic,19554.msg
pointless to go beyond 10 degs as there isnt really room under the frame for the carbs to be more tilted, and the classic CR that we are allowed to use cant work at more that 10 degs tilt either (float issues...)
just dont tell me to build a new frame as a solution for that

The funny thing is that now that i got a flow meter i discovered that the 10 degs hardly make any difference, really really tiny gain. air is like that, sometimes it doesnt really follow intuition.
dont have the pc with cad with me now...

MessnerMoto · « **Reply #87 on:** January 27, 2019, 01:47:01 AM »

Quote from: turboguzzi on January 26, 2019, 02:58:12 PM

as you are a relatively youngster in the forum, you might not be aware that i changed the angle by 10 degs some 12 years ago
http://forums.sohc4.net/index.php/topic,19554.msg
pointless to go beyond 10 degs as there isnt really room under the frame for the carbs to be more tilted, and the classic CR that we are allowed to use cant work at more that 10 degs tilt either (float issues...)
just dont tell me to build a new frame as a solution for that
The funny thing is that now that i got a flow meter i discovered that the 10 degs hardly make any difference, really really tiny gain. air is like that, sometimes it doesnt really follow intuition.
dont have the pc with cad with me now...

didn't now that you already added 10 degree. Yes there is a problem with carb probably at some point I was not thinking.

How do you plan to add material to ports ?

napoleonb · « **Reply #88 on:** January 27, 2019, 01:57:35 AM »

There was a chap in the Netherlands who raced Aermacchi's who made a custom retainerplate for their bowls (Jan Kampen).
So they went from horizontally mounted with a 90 degree header to vertical directly onto the cylinderhead with the float bowl still horizontal.

Nothing you can't fix TG...

turboguzzi · « **Reply #89 on:** January 27, 2019, 06:22:05 AM »

true, but there's really no space under the spine frame to push the carbs higher and a custom frame is definitely not on the cards. there's also not enough meat under the valve spring cavity to push the port itself higher (see pic). so it's really about optimizing the port shape, quite a lot to do just there honestly.
bear in mind that before people started transforming aermacchis to full side draft like your guy, those engines had a really ugly 90 degree bend in the manifold. and even after that carb mod, the head is essentially just a pure sidedraft like ours, just rotated fwd 90 degs

then, just thinking of producing such adapters for four carbs sound painful in terms of potential new problems to solve, fuel sealing, float heght, special jets.

any project has to account to what's feasible for you and the return on investment. i could also technically design a new head and machine it in CNC or cast it with enough hrs./$$$, not something i have.
my head is already modified as in the blue lines BTW, (red lines is stock), i am quite aware that getting 10% or even 5% more flow is not going to be easy.
if it doesnt work then ill only be out of 150$ /30 hrs invested so far.

turboguzzi · « **Reply #90 on:** January 29, 2019, 04:03:13 AM »

Following 754 suggestions and having some time to kill till a set of new molds was drying, gave those spacers a try

Weight of them together before hourglassing them was 75 grams....

Now quick and without pulling out you calculator... your guesstimate how many grams have been saved

simon#42 · « **Reply #91 on:** January 29, 2019, 10:28:29 AM »

18 grams saved

Tintop · « **Reply #92 on:** January 29, 2019, 01:24:51 PM »

about 20%?...15 grams

turboguzzi · « **Reply #93 on:** January 29, 2019, 03:13:55 PM »

scale says 12...

admittedly, they look "faster"

livefast_dieold · « **Reply #94 on:** January 30, 2019, 03:03:41 AM »

Went visiting Yossef sunday evening, I think we should start calling him: "the John Britten of Sesto San Giovanni" :-)
I'm amazed by the level of ingenuity he can regularly pull off from his workshop!

turboguzzi · « **Reply #95 on:** January 30, 2019, 03:18:07 PM »

first try with d-porting, just added about 3mm height max so section has now a very flat floor and the "short radius" is also somewhat larger. this is together with some widening of the port around the stem area.
And yes, it's working, around 4-5 cfm picked.
I am still on the steep part of the learning curve, and came across an interesting tell tell sign.
i noticed in some of the tests before this mod that on 8-9mm valve lift vacuum reading was oscillating by some 2 CFM, so got thinking it could be something in the flow bench sealing gone wrong or vacuum motor rpm just hunting.
Reading an interesting post about flow bench testing by an experienced builder, turns out that this is most likely connected to the flow detaching intermitently from the floor at the down turn and turbulence patterns.
Nice to see that with the d-port vacuum oscillations are almost gone, port is "quiet" a sign that this shape keeps the flow attached better. Who would have thought...

MessnerMoto · « **Reply #96 on:** January 31, 2019, 02:29:14 AM »

I know it is not possible because of carbs frame etc but I could not resist to play a little bit

It is 10 more degree

Yoss you haven't answered to me. How you will add material . Welding or something else ?

MessnerMoto · « **Reply #97 on:** January 31, 2019, 03:24:21 AM »

but from what I can copy from new design from Honda there needs to be more gentle Venturi shape

this honda heads are all form 2018

turboguzzi · « **Reply #98 on:** January 31, 2019, 03:54:28 AM »

Hi mirko

that is a 4 valve head, very different porting approach from a 2V.... apples and oranges

the plan is to make the fillers in aluminum and hold them from bellow with a screw. I might or might not add hi temp epoxy to smooth it down.

It's something that has been done before, old bike tuner did this in Rene's 500/4

your sketch with the yellow line is simply not doable without serious re-welding of the head, modifications to frame, etc.

First race coming up in two months, so im concentrating on what is realistically doable in the time frame, i.e. detail re-shaping of the port.

Remember that i still have to start working on the exhaust port, so little time for extreme modifications.

MessnerMoto · « **Reply #99 on:** January 31, 2019, 08:12:02 AM »

Quote from: turboguzzi on January 31, 2019, 03:54:28 AM

Hi mirko

that is a 4 valve head, very different porting approach from a 2V.... apples and oranges

the plan is to make the fillers in aluminum and hold them from bellow with a screw. I might or might not add hi temp epoxy to smooth it down.

It's something that has been done before, old bike tuner did this in Rene's 500/4

your sketch with the yellow line is simply not doable without serious re-welding of the head, modifications to frame, etc.

First race coming up in two months, so im concentrating on what is realistically doable in the time frame, i.e. detail re-shaping of the port.

Remember that i still have to start working on the exhaust port, so little time for extreme modifications.

yes yes I know but one can dream especially if I am not the one that needs to do actual modification

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Author Topic: CB500/4 racer resurrection - airbox finished, didnt quite work.... (Read 36647 times)