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Brendans cbr250 project... still.

48959 Views 168 Replies 29 Participants Last post by  Humbug
inlet: 99% VE
Exhaust: 100%VE



valve guides taken right back etc... pics of headwork to come later.

but for now...



I'll do a write up on engine specs in the next few days.
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ok, now before you go flying off the handle i am not attacking you........

what kind of fuckin 2nd rate cylinder head engineering joint did you go to?

number 1, volumetric efficiency is supposed to be measured with the valves in place and the valves opened to max lift. a measurement of VE with nothing in there is a waste of fuckin time, of course its gonna be at or near 100%, there is nothing in the bloody way.

number 2, i strongly believe that by porting off the lumps around the valve stem [and all of the protruding valve stem mind you] you have detrimentally effected the VE by increasing the cross sectional volume in the middle of the port while not concentrating on making it a gradual neat taper. if you suggest that you did, i call lies. i dont see any material build up inside your ports [high temp epoxy usually] for that to be true. honestly, did you do that porting job yourself? if not, please name them, i would love to give them a call and ask a few questions about their methods. i mean if they are going to butcher your ports like that and then do a valve out VE measurement and tell you "hey guy, we are fuckin awesome, look at this 100% figure!!" and keep a straight face, they are either deadshits or dumbshits...

i suggest you get it all taken back and get it re-measured if you want a reading that you can actually stand behind and say is accurate...

/constructive criticism
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of course you had the valves in. otherwise your engineer is a fuckin retard. good to see you know oh-so-much about the maths behind it but dont even know how to read or comprehend basic english. its not like i've got such an awfully illiterate writing style...

that being said, i didnt mean volume i meant area [so i made a typo, sorry...] and i certainly didnt mean velocity i did actually mean the overall VE of the ports.

what i am trying to tell you is that if you took as much meat out of that area as has obviously been removed you have created a larger cross sectional area ALL along that part of the port. this would mean that according to bernoulli's principle, that since the OEM ports were designed to have a steady and gradually decreasing cross sectional area [to steadily increase velocity to peak at the valve seat] that your now larger centre section of your port will have a sudden decrease in velocity [due to less pressure] followed by a dramatic and abrupt [rather than gradual] increase in velocity as the port suddenly chokes off before the seat. whilst i understand that air is compressible, do you understand the ramifications of this? this WILL cause a large turbulent low pressure area in the centre of the port which will mean that you will almost certainly not get as much air into the cylinder as you would if the cross sectional area had remained at a gradual taper. if you do not believe this, then you fail to grasp the most basic part of the function of the ports. fair enough, the stock ports look ugly, but they are damn efficient and are more than likely at or near 100% to start with on this motor especially considering the high power:capacity it churns out. out of curiosity did you get a baseline VE figure to work off before your changes?

regarding my porting job, unlike you i didnt have daddy's money to throw at an engineer to use a flow bench and to do all my work for me but i did do a shiteload of reading up on port geometry and and regarding the "balancing" problem you suggested. im not completely fuckin retarded to just randomly port out material without ensuring all the ports are as close to identical as possible. i did a volume check on each port and they were all within .25ccs of the baseline port i did. that was a bastard. i also did not significantly change the port geometry [especially the short turn radius] because having sectioned a head, i know exactly how little meat there is to the water jackets. the exhaust ports were almost completely unchaged apart from the mirror finish and the port matching to the header flange, which had its own step which would have helped prevent reversion on overlap.

i do realise that even if your head makes the bike perform worse you will still come back and say "OMG its awesome" because you are completely unable to admit when you have ever done anything wrong, ie, every single time you have been banned. let alone this, when you have paid for someone to do your work for you so trying to tell you that anything even remotely detrimental has been done is an exercise in futility. all you wanted was to come on here and say "i is the greatest, bask in my fat wallet glory and feed at the teat which is my mechanical prowess"

though in all honesty, i would love to be proven wrong and know that everything ive read and been taught is wrong and that you can just ignore large parts of fluid dynamics that don't suit you and just take the bits that work for you. i didnt know engineering was like religion...

in any case, how many cc's have you increased the squish volume by? have you calculated how low you have dropped your compression ratio to? have you thought about how much that will affect your overall horsepower gains? looks like at least 1cc at a minimum. thats an increase of 20% which is going to be a metric shitload less compression, moreso since you have definitely taken more than 1cc off each piston face fly cutting your pistons.
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sigh, brendan this ends here...

you originally came to me asking for advice over msn, at every point you resisted every single suggestion i had because you know better. you decided to fly cut the pistons even though i told you how thin the piston face is and how easy it is to hole them as is. i told you that changing the port geometry the way you wanted to was not an ideal thing to do and you decided to pay someone to do it anyway. then you started being a rude little cunt and i blocked you and you then started spouting your ideas on the forum and i for one did not want bad ideas flowing through this forum unmetered. i only ever interjected because i saw what you were going to/had done was not correct or the optimal solution for the outcome desired and felt that others should see the other side of the coin. but you [and surprisingly some 3rd parties it would seem] took that as direct assaults on you as a person rather than the specific aspect i was referring to.

i do find it ridiculous that it would seem that the only way to placate you is to let you do things that are not neccessarily as AWESOME as you have been led to believe, post it on the forum as the holy grail and let that stand as gospel without any critical evaluation whatsoever beacuse to criticise you at all is harrassment.

you are a child and have a lot of growing up to do, as suggested by many others, if you can't handle people with differing opinions then maybe you are too infantile for this forum...

and thats saying a lot considering the quality of the ppl around here lol...
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just to clarify a point brendan...

you obviously don't seem to understand what i was meaning about the removal of the valve stem guide and its surrounding material. you also seem to think i am attacking you without any basis for this.

this is not so. unlike you, i have sectioned a cylinder head so that i could not only see the ports from side on, but i also took measurements and lo and behold, the honda engineers must have designed these ports with some sort of crazy number magic or something because even with the valve stem guide protrusion, the diameter measurements of the ports steadily decrease smoothly from port start to port finish.

lets pretend that we can straighten out the port into a nice straight smooth taper. my leet paint skills can help here...

the left pic illustrates [using arbitrary figures] a straightened port decreasing in diameter steadily, with the obstruction in place. fair enough, the obstruction will get in the way but with air being so fluid and all, it would still manage to get through with minimal disturbance, with boundry layer effect as well as the fact that at peak revs the port velocity should be approaching the speed of sound and all. obviously there will be some ill effects but the valve stem guide is that long for a reason, to prevent lateral movement of the valve encouraging a better seating position each time it clamps shut.

on the right we can see what would have been done to your ports by removing the entire obstruction. all of a sudden there will be a larger diameter than the previous segment followed by an abrupt change to a much smaller diameter. that area WILL become a low pressure point in the port which WILL significantly affect the airflow characteristics.

whilst i am sure your friend who did the job for you knows his shit and machines off the valve stem obstruction in car heads [which is usually accompanied by an overall opening of the leading length of port to suit] doing it to the level shown in your pics in these tiny ports is less than ideal.

in any case, this will almost certainly be construed as a direct attack on your as a person rather than critical evaluation of something you have done and no doubt be accompanied by all and sundry reasons to explain why this is incorrect.

which is why i will giggle. because you can quote as many higher principles of fluid dynamics at me, but when your theory violates the most basic elements, it cannot be right...
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