increase the valve float limits

[JsMich]

hi there, i've search a lot to find this answers, but I only found pieces of the answer.

what is making valve floating happen sooner on certain engine??

it seems that the valve spring have a lot to do with it, but i'm sure their's more.

my project is a 4 cyl (frankeinstein h23 block w/ h22 vtec head) for racing, and here's what I have in mind;
- turbo
- aftermarket valve spring, of course,
- titanium retainers, valve (in/ex), connecting rods, wrist pin,
- camshaft that enable high flow on the vtec lobs, with p/p of all in/ex port
- a rod/stroke ratio of 1.75 (6.545" rods w/ 3.74" strk), are those rods too long??

ok that said i've been thinking, what can make my engine hit higher rpms??
is their anything to do with the pistons skirt to help stability, their going to be custom anyway??
should I keep the balancer shaft, or will the mass and the 5 gear needed to make them turn will be a problem at high rpms?
does all the gear weight, flywheel,... have a thing to do with the stability at higher rpms??

the reason I want high rpm (11K + and making power through that) is that I want to use the full potential of every gear

 

[ejit]

I think you should take a step backward and try some fundamental research before designing your own motor. Let me guess: you read somewhere that 1.75-1 is the "ideal rod ratio"? So you began by multiplying your existing stroke by 1.75 to get your new rod length?
Your block is only 8.655" tall. With the existing rod, your piston's compression height is only 1.214" tall for zero deck. If you increase the rod length to 6.545", the piston will be .24" tall, which is physically impossible.
The concept of the "ideal rod ratio" only applies to motors developed on a clean sheet of paper. There may be an ideal ratio, but it will be different for every motor and every application. To use an existing (limited) head at higher RPM than the design limits, the ratio normally goes up - even worse in your case.
The first time that motor turns 11,000 RPM will be the last time. 11K is 34.8 m/s average piston speed, far beyond any Formula 1 motor. What do you know that they don't?
The motor would not develop any more power at that speed in any case - the head simply stops flowing.

 

[JsMich]

no, i've used this logic, i'm decking my block 1" over, and the stock block is more, so by staying with that same crankshaft I wanted to use the maximum of that block without playing too much with the c-h of the piston, which may make my piston weaker, and it arrives at 1.75, I could have taken a 1¼" deck plate, but that would make a longer rods which I don't think is good for high rpms.

how do you calculate your piston speed?? is it in relation with the strk of the engine??

 

[ejit]

With 1" added, the rod length is possible.
Piston speed in m/s = stroke X revs/1181. This is only the average, a better limit is piston acceleration which gives the highest instant load:
Z = (N^2)*S*(1+(1/2n))/2189
Where Z = acceleration in f/s/s
N = rpm
S = stroke in inches
n = rod ratio
Values over 200,000 f/s/s are very dangerous.
Really high rpm motors have rod ratios exceeding 2-1, provided that reciprocating weight in the rod's small end can be kept to a minimum. However, high "n" values move the point of maximum cylinder pressure closer to TDC, which will reduce maximum safe compression and maximum boost (in favor of breathing), so it's a compromise.
I think 1.24" may be a bit conservative for CH, but you need more thickness above the top ring for boost protection, it varies with bore size, I'm not sure how much. What boost level did you have in mind?
Please remember that even with light weight valve components, a very big spring will still be required for high rpm, and this means high seat loads, breakage, short seat life and somewhat reduced choices of lobe shape, since acceleration must be tightly controlled to prevent float, and this must be given design preference to maximum area at specific points of crank rotation, etc.
The usual method is to simply do the head as well as possible, larger exhaust valves (up to the limit of the casting for high boost), flow the head and determine cam profile from boost level and "split" (i.e., lobe difference between I & E, based on flow differential). Max safe rpm level is typically 28 m/s even for brief service; that's about 8800.

 

[JsMich]

wow that's the kind of info I wanted, thanks

i'll redo some of my math and see a better way to get my goal!!

as for c-h, what would be a good height, i've thought about 1,1"

I have another question, I suppose that this kind of speed is making damage when the rotating mass is too high for the material used to hold all those pieces together?

so is their a formula that would imply the weight of rotating components??

boost in minds are 20-25psi max w/ 9:1 static CR
the block and all of the pieces that will go in my engine will be, treated for more lubrication (I've thought about Swain Tech for this) and they will be cryoed

the seat will be changed as the valve guides, in fact i'm only using honda block and head as a base for a completly new engine

 

[ejit]

1st place I'd ask for the minimum CH (although I think 1.1" is do-able) is

http://bbs.theoldone.com/forum/

I don't think rotational inertia will be a problem using the existing journal sizes. You may want to reduce the counterweight OD and take some metal off the rim for aero and gyro effects.

 

[JsMich]

the server seems to be dead!!

 

[ejit]

Sorry, there was a message recently about the board being down for maintainance but I (duh) didn't read it.

 

[JsMich]

do you think it will be reopened??

 

[enginebob]

"The motor would not develop any more power at that speed in any case - the head simply stops flowing."
I read this above.
A bit confusing for some maybe. I think you meant the port flow is at it's maximum capacity?

Causes of valve float can be spring pressure, cam profile, weight of valve train are most common.

 

[JsMich]

i'm now thinking about destroking that engine to a 2.0L engine, so that would be a swap from a 95mm stroke to a 81.5mm stroke, might loose some torque, but I think that if I crank up the boost little more it will overcome that issue, but i'll gain a lot on top end which is what I want!

just need a place to make a good custom crankshaft!

 

[ejit]

http://www.theoldone.com/forum/default.asp