turbo cbr 600 f3 valve springs ??

[xinoka]

Sorry for the lame questions but its the first time that I m boosting one engine and I have some doughts on this engine limits.

How much rpm it can andle whith and whithout boost (10 psi max) ?

Is there aftermarket valve springs kit for this engine or from other engine (f4i?) ?

I have milled pistons deck to lower the c\r for testing http://img464.imageshack.us/img464/6679/pistonrectificado007ll5.jpg
Dont worry... have 3 sets left whith all the rest http://fsae.com/groupee_common/emoticons/icon_wink.gif

[xinoka]

Sorry for the lame questions but its the first time that I m boosting one engine and I have some doughts on this engine limits.

How much rpm it can andle whith and whithout boost (10 psi max) ?

Is there aftermarket valve springs kit for this engine or from other engine (f4i?) ?

I have milled pistons deck to lower the c\r for testing http://img464.imageshack.us/img464/6679/pistonrectificado007ll5.jpg
Dont worry... have 3 sets left whith all the rest http://fsae.com/groupee_common/emoticons/icon_wink.gif

[John Stimpson]

I wouldn't fret too much about your valvesprings... It is great that you are paying attention to them however, because a spring issue can and will totally screw you.

I assume that based on restrictor, you won't be turning the engine as hard as the OEM intended (which is about 14krpm). My experience is its about pointless to turn the restricted CBR's past about 12kprm.

That said, OEM springs should totally be up to the task. Because you're boosted though, spring force will be down. In which case, I would simply shim the springs a little (no more than 1mm or so) to gain back a little force.

Kudos to you for not being afraid to mill your pistons. Members of my team were crapping razor blades last year when I started milling on our new set of Wisecos!

What pistons are those? They don't appear to be OEM "MBW" ones.

[VFR750R]

Valve springs are uneffected by boost. As long as the valve is open the pressure will be more or less equal, and on intake closing, as soon as the valve touches the seat it will start building compression below the valve above intake pressure regardless of aspiration type.

Increased cylinder pressure does increase loads on the exhaust valve during exhaust opening, but not the spring. During intake stroke, pressure is slightly lower then exhaust pressure, but only by the difference in intake and exhaust manifolds which is small in a road race turbo application.

The one place to consider is after choke, the intake pressure starts to fall off but the exhaust doesn't unless you work with your wastegate control. But, again, it's not enough to overcome seat pressure on the exhaust side.

P.S. I hope your dome isn't too thin.
P.P.S. I don't recommend shimming valve springs above factory callout, install height is a critical feature of the valvetrain. Better would be to rate springs, only take the best ones and set them up on the short side of the install height, but no less.

[John Stimpson]

How can you say valvesprings are unaffected by boost??

Any positive manifold pressure is going to act on the intake valve, trying to open it. Valve seated "pressure" (a misnomer, but commonly accepted term) is going to be less than the design intent.

I set up a heavily blown DOHC 5.4 Ford V8 a couple years ago, equipped with OEM springs, which seat at around 350N. At about 1bar boost, it made 450ish rwhp, whereas it should have made 750ish. The torque curve was aiming for the roof, but then just flattened out at around 4500. After scratching my head a little, I outfitted the engine with some better springs with around 450N seated pressure, and found my 785whp that was the hope to begin with.

I'm with you on shimming valvesprings, and of course installed height. However, the biggest affect is going to be spring surge, which you are not going to get with a shimmed spring, running several thousand rpm below what the springs are originally designed to handle. Also, springs fatigue quicker when shimmed, but again, not really a constraint based on the relatively short lives of our engines (100 hours is a LOT of run time)... Of course, I am partially assuming maximum restricted engine speed of about 12krpm for the CBR engine.

[John Stimpson]

I might add that tens of thousands (probably hundreds of thousands) of engines have delivered millions of happy service hours with shimmed valvesprings, so its a very viable solution, so long as you know what you're doing.

[xinoka]

I forgot to mention that this project has nothing to do with FSAE so no restrictor!
Yes they are OEM and I milled all the positive dome living 1mm more thicker at the center.
Can someone calculate my c\r plz because I dont know dome volume,etc,etc http://fsae.com/groupee_common/emoticons/icon_confused.gif

So shiming the springs is worthless since my ecu http://www.dynaonline.com/english/sportbike_dyna2000.htm can rev to 16krpm ( doenst mean that I have to go so far ) and boost it to 5psi max for now.

WebCam http://www.webcamshafts.com/have dual valve springs,titanium retainers for this engine...have someone already use this? Does it worth the money?

Thanks

[VFR750R]

If you have 15psi of boost, right before the valve closes the intake pressure is 15psi and so is the pressure inside the cylinder. The moment it closes, the same pressures are there either side of the valve...so the valve sees the full amount of seat pressure. This moment is the only time seat pressure is required to prevent bounce, after that a much lower pressure is needed to hold a stationary valve in place.

I would guess in your case John, given the square area of the valve, the boost was enough to overcome the seat pressure and was bleeding into the cylinder during the exhaust stroke, which on a supercharged engine is still roughly atmospheric pressure inside the cylinder.

My calcs say 350N is about 78lbs on the seat. At 1 bar (15psi) it would lift a valve with a diameter of 2.6 inches. And I'm sure that is larger then the 5.4's valves, but still dangerously close considering that intake and exhaust pressure waves can be as much as half an atmosphere themselves.

My point was more based on turbocharged engines, where the entire engine is seeing a higher pressure, not just one side.

[VFR750R]

Is that 1mm thickness left? That's like .039" right.
On NA restrictor plate engines with FSR pistons you can run close to .100". A boosted full skirt piston...I can't say it won't work, but good luck.

[Wesley]

We can't calculate your compression ratio any more than you can, in fact, especially not since we can't measure your piston.

Properly:
To do it - get a burette from your chemistry lab (or a graduated cylinder will do in a pinch) and install one piston in a block. I'd oil the piston and bore all the way around with heavy weight oil or grease to get it to seal. Put it at TDC, and bolt a piece of plexi over the cylinder (use the head bolt holes) and drill a small hole in the center. Using any convenient non-corrosive fluid, you can dispense some into the plexi and measure your installed volume at TDC. You should then be able to solve for your CR. The plexi should fit since you've milled the dome off the piston. It won't work with the stock ones unless you get thick plexi and mill a pocket of known volume in it.

Dirty and not very precise:
Alternatively, weigh a piston before and after milling. The subtracted weight times the density of the alumium will give you an idea of the volume of metal removed directly from the combustion chamber.

[xinoka]

http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif http://fsae.com/groupee_common/emoticons/icon_smile.gif
Thanks for all the help!!!

ps: speechless about this forum...