Topic: CB500/4 racer resurrection - airbox finished, didnt quite work....

[turboguzzi]

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

well mirko, if you have time you can have a look here, there are tutorials too..... maybe once you master it i can send you my 3D's

https://sim-flow.com/download-simflow/

[MessnerMoto]

nice yoss... actually I will need it soon for myself

I need to get used to that app

[turboguzzi]

This whole experiment turned out to be super educational and somewhat constructive, ending up with about 5-6% flow increase, even if it has fallen short of my target of 10%.... I produced in these weeks some four plaster "flow boxes", three 3D printed port cores with different shapes and overall tried some 10 different configurations/variations.

First big lesson is that at least IMHO, it is almost impossible to judge the value of a port just by looking at it, pocking fingers in or what have you.... sometimes enlarging an area by 1-1.5 mm would worsen the flow by 10 CMF!
The other interesting lesson was that just "raising the floor" can easily make things worse. It's super critical WHERE do you raise it and by how much. Again, cant think of any other way to find out rather than make many variations and see what works on the flow bench.
I ended up with two final candidates, one is just a smal development of the current port (pink casting) by enlarging the throat to 90% of the 27mm valve + further enlargement of the two passages around the valve area, creating two "side bowls" before the seat and taking care that they are fully symmetrical (they werent before). this port peaked out at 92CMF compared to 87 before the work.
The other port shape that worked well is quite radical. It didnt manage to improve flow in the high lift range, but did meaningfully improve flow in the 3-5mm lift range. This is the only port shape that worked with raised floor but the main issue is that it required also lowering the roof of the port and that would be quite a difficult thing to do. It's goes very wide and shallow around the valve and has noticeable less volume, so could give in my opinion better throttle response and better use of inertia charging during overlap. Maybe one day and with access to a 5 axis mill i will give it a try...
Now it's back to cleaning all the plaster dust in the workshop and start applying the changes to the actual head.

[Tintop]

Good information TG, thanks for letting us look over your shoulder.  Wondering if the roof had to be lowered after the floor was raised to move the middle of the air stream back into the flow sweet spot?

[MRieck]

 Any experimenting with port length?

[turboguzzi]

Good information TG, thanks for letting us look over your shoulder.  Wondering if the roof had to be lowered after the floor was raised to move the middle of the air stream back into the flow sweet spot?

hei TT, very hard to put into words.... blue surface is my current port (mostly modified around the valve stem area), green surface is the "high velocity" port.
in second pic you can "peek inside" and see how much smaller it is while still flowing about the same.

mike, the ports you see in the casts and 3D are pretty much minimum length i can do them, cant really get the carbs closer to the head than this. Didnt try longer ones. That could be a variable to test by different stack lengths.

[Tintop]

Thanks for the screen shots TG.

[turboguzzi]

porting project pretty much done, lets start with exhaust side? i widened quite heavily the area around the guide and carved quite a lot into the hump behind it as stock it really chokes the port.
finished to very glossy 320 grit finish so carbon build up will be low and hopefully heat reflection higher.
Last step is preparation of these bungs in order to D-port the exit as theres nearly no flow in that area. the bung is going to be fixed to the floor with an M6 allen from bellow.

[turboguzzi]

inlet is done too, seat was opened to 90% valve diameter (27mm X .9 = 24.3 ). Was kind of worried itll be a difficult job, went quite smooth with the good control the die grinder gives.
similar approach to the port itself of working quite a bit around the guide, only here the side walls open up and then kind of venturi into the seat area. Still left to finalize the exact height of the bung to fill up the floor a bit.

[turboguzzi]

Almost reached my target of +10% degree increase in flow, so time to stop playing around and put the thing back together. The ports you see in the pictures above ended up giving with 9mm lift 94 CFM @ 28"H20, something like 7 CFM over the 87 i started with, so that's a cool 8% increase. Mind you, over the stock port (green line) it's a good 30% increase or more...

Tried every possible configuration of creating inserts to give the inlet port more of a "D" shape but nothing worked, all what i tried lowered the flow, so giving up on this feature.

The insets for the exhaust work well, so they are going in, even if i dont have reliable CFM numbers to aim at as my flow bench is not really built to blow air, i'm measuring the exhaust by vaccum on the exit rather than pressure from bellow the valve.

[MessnerMoto]

I really like and support scientific approach. Data don't lie

[bwaller]

Great work TG. How's the leg?

[turboguzzi]

plate has been removed 11 days ago, so far so good. but operation was a bit more invasive than i thought... he had to make a 7" cut form top to bottom to lift the plate up from the bone as it was starting to stick already... was hoping Doc would be able to slide it off from a small cut...
so have now a long cut with some 20 stitches holding it together.
ugly but improving fast.
changing bandages tomorrow, will post a shot

[scottly]

The insets for the exhaust work well, so they are going in, even if i dont have reliable CFM numbers to aim at as my flow bench is not really built to blow air, i'm measuring the exhaust by vaccum on the exit rather than pressure from bellow the valve.

Six of one, half a dozen of the other. The pressure below the valve is higher than the exit by 28" H2O.

[turboguzzi]

yes, i know, pressure delta is pressure delta, but still seems like many flow benches have a "blow" mode for EXH work.

[scottly]

It's easier to reverse the flow, if the bench allows, than to reverse the head?? Perhaps your readings were affected by a poor seal from the exhaust port to the suction side of the bench?

[crazypj]

inlet is done too, seat was opened to 90% valve diameter (27mm X .9 = 24.3 ). Was kind of worried itll be a difficult job, went quite smooth with the good control the die grinder gives.
similar approach to the port itself of working quite a bit around the guide, only here the side walls open up and then kind of venturi into the seat area. Still left to finalize the exact height of the bung to fill up the floor a bit.

That's a ton of great information. I guess I got real lucky when I did my 550 back in 1979, looked a lot like your port shape, wider around valve guide. Very interesting about exhaust port filler, are there details of dimensions in posts somewhere?

[turboguzzi]

i'm fine tunning plug size at the moment,

just like with inlet porting, the exh plug us very sensitive to dimensions,

biggest challenge is to make the clay stick to the polished port when the vacuum is sucking on it!!!

[turboguzzi]

gee, cant believe i've been stuck since april! manged to contact directly Hi-Speed pistons in Taiwan and finally got a new set of rings, so work can continue...

the old rings with three season on them looked fine, end gap and tension felt ok, but seemed stupid to me not to put a new set.

So pistons are mounted, this sunday Ricardo will join me to lower the engine into the frame so things looking good and pace picking up again, but I will certainly miss the season ender at Misano in october.

BTW, didnt answer crazypj question about the exhaust plugs... managed to rig the flowbench to measure also the exhaust and after much testing, I wasnt getting more than a few % improvement so at the end decided not to add them.



 

[turboguzzi]

engine is back in frame and while tightening the mounting brackets noticed that the right side rear top one was really not sitting well, the offset of the stock OEM is too big piece making it sit all twisted. the frame was checked for straightness so guess it is the famous very loose frame tolerance that japan was known for in the 70's.... just like forcing the frame to clamp on a slightly too short swingarm pivot, it doesnt feel healthy to put those bending forces on the bracket. having time in my hand till cyl block is back from honing, I made this 10mm alu bracket and turned a spacer according to the right space available.
No more forcing it, and on top, new one is 60grams, old steel one 120!  If any one wants a replica, i've got the 2D cad....

[scottly]

guess it is the famous very loose frame tolerance that japan was known for in the 70's.... just like forcing the frame to clamp on a slightly too short swingarm pivot

My '82 FT had a gap of over 1.5mm at the swingarm pivot, which distorted the bracket welded to the frame. The clue was that the pivot bolt was tight until it had been backed off several turns. I used a .062" washer to fill the gap.

[turboguzzi]

brent and tim asked for some more details of my 38mm  FrankenFront, so here you go

the fork legs are off a late 80s gpz600, think it was called ninja600r in USA. mine had antidive only in one leg, some have on both.

they are pretty light, lighter than the honda stock 35mm and have modern features like double teflon bushings. I blocked off the antidive and removed from the bottom of the tubes the one way valves that acted on the simple tube dampers.

inside these, i placed a rare set of new (!) late 90s cbr900 cartridges which have adjustable damping.  found them in a swap market for 50 euro still in their original honda cartons...

in the legs i didnt do much other than turning off on the lathe a plethora of ears sticking out that had no use.

Another thing i did was to replace the super heavy steel tube caps with aluminum ones with the same thread.

Last, i shortened the springs to get my preffered 0.9kg/mm rate and turned nylon spacers to compensate.

I wanted some really light triples without the expense of CNC0ing my own. ended up with 1st gen ZX6R triples that have a neat double bolt fixing in the bottom one as well as an aluminum stem. cant find the numbers but i think that triples alone were more than 1kg less than the honda's.

as these are for a 41mm tube, turned some 41-38 spacers to hold them. more work on the lathe was to adapt the tapered set of honda ID size bearing to the OD of the stem. form the top triple i sawed off the ignition cyl bracket.

last, the stock dust cup above the top bearing wouldnt work, so turned one form nylon to fit.

Yes, quite some hours spent on the lathe, but love working on it!

Not sure the fork bridge is really necessary but at least it keeps the fron fender above the wheel

[simon#42]

why didnt you shorten them?

[turboguzzi]

i'm bulidng a chopper now, actually need to bring the triples up....

yeah, good question. this is static setup so just simulating for now the front ride height as it was before with the 35mm fork. Need to see the static sag with complete bike + fuel and myself. Then need to get out to the track and see where i end up in terms of front ride height and sag.

IF i can cut some cm. of tube, then it's easier said than done... I dont have at the moment a good solution to threading those fine internal threads for the caps. it's something like a nasty M34 x 1mm pitch. if you have such a tap, let me know with an internal thread bit on the lathe it is not going to be much fun.

might be easier to do a plain cap held with a circlip.

my calc says that for the 40mm sticking out there are 70 grams per leg to be saved, 140 total. nice but not going to loose sleep about it. will see later where i end up.

BTW, head torqued down...

[MRieck]

Almost reached my target of +10% degree increase in flow, so time to stop playing around and put the thing back together. The ports you see in the pictures above ended up giving with 9mm lift 94 CFM @ 28"H20, something like 7 CFM over the 87 i started with, so that's a cool 8% increase. Mind you, over the stock port (green line) it's a good 30% increase or more...

Tried every possible configuration of creating inserts to give the inlet port more of a "D" shape but nothing worked, all what i tried lowered the flow, so giving up on this feature.

The insets for the exhaust work well, so they are going in, even if i dont have reliable CFM numbers to aim at as my flow bench is not really built to blow air, i'm measuring the exhaust by vaccum on the exit rather than pressure from bellow the valve.

Why didn't you go with the 28.5 intakes and .9 ID.....you would have achieved greater than 10% increase. I haven't seen any seat shifting etc and that is after the engines have had the snot beat out of them. A larger seat can be installed if you are worried about seat thickness after increasing the ID. I have no idea if there are shops around where you live that R/R seats and finish them.
As a side note...having the seats bored on the Serdi accomplishes 2 things....it is quick and the ID's are the exact same for each seat. The valve job comes out really nice especially the 30 degree cut.