CBR250 Forums banner

Brendans cbr250 project... still.

48962 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.
1 - 20 of 169 Posts
valves out obviously. VE was measured on a flow bench... something kinda like this http://www.ganges.com/Cylinder_Head_Flow_Test_video_6786164/
but the test wasn't electronic... it was done with pitot tubes and murcury as such...

it wasnt mine though... otherwise I would have had to add that on to the price of my bike :p

the aim when porting it was to obtain high figures from low lift. so abit of time was spent trying different angles on the valve seats... that is a crucial aspect for VE... especially on a High revving engine.

you can see abit of the test rig on one of the photos of the cylinder head on my photobucket page.


To increase the low lift figures (response, overall VE and alot of other crap) the squish pads taking up volume was essentialy getting in the way of my air flow path at low lifts... so they are ground back.

See less See more
;D I'm happy again ^^

if i have some paint left over from painting my other engine... I plan to repaint the master cylinder also.

I'll be sure to give it a try... probably wont give me any regain on resale though... so probably just a waste of effort.
how am I trolling!?!?
why thanks for the insult.

i think you are a top bloke.

infact... i should just give you money because I spent lots of money on a motorbike, which infact is still less than what people pay for a bike from the showroom.

i don't see anything wrong with that because I am retarded. feeling superior now?[hr]
also, you have no idea why I am trying to sell it... or what parts I am keeping/replacing.
richo said:
Who the fuck pays 21k for a bike from the showroom? Only the exotics go for that. And they go a shitton faster and are literally better in every way except perhaps overall weight than a rebuilt 250 that even if restored immaculately to showroom condition is still a prime example of what 20 year old technology looks like!!
so that means anyone who restores or does up an old car/bike is retarded?

so that would include your self for rebuilding your r6.

also, how much is a new r1 retailing for? or what about a toyota corolla?
perhaps i can shine it in a different light.

the sense of accomplishment is pointless if there is always something/someone better? I shouldn't waste time on a cbr... but I cant afford a 1098. I shouldn't bother climbing mt fuji because there is mt everest.

what the heck did i do to deserve this?
i just dont see much motive for buying special polish and effort into it when I am never going to have the oppertunity to appreciate it when I know full well that someone will buy it in the next few months.

they buyer probably wouldn't care about it anyway.
also... i never had 20k at one period in time.

besides... I wanted to build the 250 as best I could as a challenge.

i would feel like a tosser riding a 1098.

same goes for driving a ferrari or porche... when I could build something just as fast.

i feel no sense of occomplishment from buying something... it just doesn't feel like its mine.
sir.b said:
Humbug said:
what the heck did i do to deserve this?
Back to your old tricks...

Humbug said:
and you took the bait ;)

i was just playing along.

i thought it was pretty funny at the time... I don't see why you should take that so seriously
i mean the bike that you are racing... putting in all that time, effort and money into.

if you want to talk about money smarts... you should have put that into your morguage.[hr]
richo said:
Humbug said:
also... i never had 20k at one period in time.

besides... I wanted to build the 250 as best I could as a challenge.

i would feel like a tosser riding a 1098.

same goes for driving a ferrari or porche... when I could build something just as fast.

i feel no sense of occomplishment from buying something... it just doesn't feel like its mine.
You're saying that your 250 will be as fast as a 1098?

Drew's head is going to kerplode:exclamation:
its not always just about that. I never said it would be just as fast... you are just trying to twist my words to incite an arguement.

the point I was trying to make was that I feel accomplished after building something and striving for the best. if it doesn't become the best or equal or even close to, that then gives you the right to call me retarded? you are such a nice guy.
i wasn't trolling in the first place.

i was accused... so i thought... hell with it. just play along, maybe thats what they want.

instead i was flame baited.[hr]
also... whats with the sig sirb?

does it make you feel good about yourself to put others down or to take advantage of someone being bullied?
i wouldn't react so much if you guys didn't make such an effort to insult me. thats exactly how this thread got out of hand.
i wasn't screwing about when i replied to your PM... unfortunatly, a small bunch of people don't give a rats.[hr]
richo said:
Humbug said:

if i have some paint left over from painting my other engine... I plan to repaint the master cylinder also.

I'll be sure to give it a try... probably wont give me any regain on resale though... so probably just a waste of effort.
This is the first post that caused issues. Before that it was just people offering genuine encouragement.

EDIT: It's not our goddamn responsibility to censor our posts so we don't offend you. Harden the fuck up.
i didn't say i wouldn't do it.

i was just stating a fact. thus why i am not so keen to do it.

*edit* then don't get so offended if I'm kidding about by posting a pic of rex hunt.

so why dont you harden the fuck up
i for one am not laughing.

now lets get on with life please... i missed my lunch because I couldn't unglue myself from this T_T
mootavic said:
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.
ok lol... when you asked valves in or valves out... I presumed you ment open... (mind you its pretty hard to flow them if the valves are shut obviously enough) but generally speaking, you don't flowtest heads without the valves in place... thats just silly... i wasn't sure what you were askin to tell the truth... so i took a stab. I admit I fail at english... it was totally the wrong word used... I even said off :/

Regardless, the VE was not obtained via a direct measurement, that is impossible... its actually a calculation. RPM engine displacement and mass flowrate/velocity is all known... so it can be then calculated... That is why it is expressed as a ratio or a percentage. in otherwords... the ports have been opened right up via the removal of some of the valve stem... thats pretty standard practice when it comes to porting. but i will elaborate more on that in a sec...

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...
lol, ok. Now, what I think what you were trying to say is that removing the valve stems detrimentally effected velocity by increasing cross sectional area, in turn decreasing VE as it is no longer sucking the gasses due to vacuum pressure after valve closure~opening... this couldn't be much further from the truth... allow me to explain...

Actually by removing the stems (in this case, please keep that in mind), the velocity was almost kept constant. (actually increased marginally due to increased mass flow rate from porting of the intake ports.) this is not because the stem has a neat taper, but infact, because the stem is quite an obstruction. a neat taper on the exhaust port isn`t as important (in this case as the goal of head performance is different to that of stock, please also keep this in mind) as say on the intake side... this is because increasing mass flow and decreasing resistance was more effective then trying to keep a laminar flow, however velocity is still important factor regardless, so it wasn`t completely disregarded... It didn`t effect the vacuum effect so much on valve closure as the ID of the exhaust is still the same and the exhaust port length is very short. Increasing the volume of the exhaust port dramatically increases low lift flow figures. It behaves completely different now.

So this epoxy you speak of, is called zedspa... Lucky enough I didn`t need it in this situation. (if I bored the sleeves thus increasing displacement I would have needed it to change the overall profile... but I would still have a larger internal cross sectional area. there is enough material on the roof of the port. Don`t worry, too much wasn`t removed.

The company that benched it is called "Ghea Race Engines". The bloke who worked on it, his name is Anthony (founder of the company)... and he knows his shit. Actually he has retired now (last time I checked)... he was getting abit old and the labouring work is hard on old people :p.

I'm not sure if the business is still continuing... but let us know if you found out anything interesting.

In regards to your C/head, as far as I know... you didn`t even bench smokeys head...so it would of taken a miracle to balance them... and all that polishing was a complete waste of time. that would have got you about 1% of 45ps or maybe even less... which is absolute FA. I'm trying not to be so sensitive... but it does seem kinda like you are trying to take a dig at me... swearing and all. but I will overlook that for now.

*edit* just added some bold to highlight something worth lolling about... there is no such thing as cross sectional volume.

*edit*edit* just thought I would point out that tapers in fluid mechanics are designed to decrease turbulence which effects head loss. dont forget that air is compressable, and when it is at a lower density, a volume flowrate increases when the mass flow rate stays constant. I expected you to know that.

*edit*edit*edit* just also thought that I would point out that the floor of the port wasnt touched so that a uniform cross sectional area could be maintained. if i cut that short turn radius... it would have caused problems.
See less See more
banana.logic said:
Hessian said:
Hows the karate going?
funnyly enough, I had Kendo last night.
See less See more

dont worry about it...
1 - 20 of 169 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.