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Author Topic: CB500/4 racer resurrection  (Read 5350 times)

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Offline turboguzzi

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Re: CB500/4 racer resurrection
« Reply #100 on: February 05, 2019, 09:38:23 am »

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/

Offline MessnerMoto

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Re: CB500/4 racer resurrection
« Reply #101 on: February 07, 2019, 12:51:48 am »
nice yoss... actually I will need it soon for myself

I need to get used to that app

Offline turboguzzi

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Re: CB500/4 racer resurrection
« Reply #102 on: February 20, 2019, 01:01:58 pm »
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.

« Last Edit: February 20, 2019, 01:07:11 pm by turboguzzi »

Offline Tintop

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Re: CB500/4 racer resurrection
« Reply #103 on: February 20, 2019, 02:00:52 pm »
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?
1977 CB550/4 Cafe - Speed Warrior / BOTM 03/11
1980 CB750F (project)
Whittaker GBF Vintage Racing Sidecar (XS750 power) - ITG / 151's / CMR Racing Products (SOLD)
1976 CB400 SS - stock / BOTM 04/11 (SOLD)
1973 CB750 K - basket case (SOLD)
77 CB550 Cafe build
550/750 Filter Thread
Sidecar Rebuild Thread

Offline MRieck

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Re: CB500/4 racer resurrection
« Reply #104 on: February 20, 2019, 02:56:38 pm »
 Any experimenting with port length?
Owner of the "Million Dollar CB"

Offline turboguzzi

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Re: CB500/4 racer resurrection
« Reply #105 on: February 21, 2019, 06:16:44 am »
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.

Offline Tintop

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Re: CB500/4 racer resurrection
« Reply #106 on: February 21, 2019, 06:04:41 pm »
Thanks for the screen shots TG.
1977 CB550/4 Cafe - Speed Warrior / BOTM 03/11
1980 CB750F (project)
Whittaker GBF Vintage Racing Sidecar (XS750 power) - ITG / 151's / CMR Racing Products (SOLD)
1976 CB400 SS - stock / BOTM 04/11 (SOLD)
1973 CB750 K - basket case (SOLD)
77 CB550 Cafe build
550/750 Filter Thread
Sidecar Rebuild Thread

 

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