has anyone did timing mods by math? where you just measure the engine, then add the formula and get a timing to mod the engine to?

or is it, you just cut away till you no longer get any increase in performance then mark down what degree you stop seeing the increase?

1. That's what engine simulation software is used for.

2. If you have a dyno that would be another way to do it.

They have a timing degree wheel you can by for the little two stroke motor that's how the big boys do it. Try Jb mods or AB mods and high performance mods.

I know how to degree an engine, I just need to know how to figure out the modded timing, of an engine.

You can study thermodynamics and then read a 700 page book about it. Look for a book by Professor Gordon P Blair.

The other way would be to spend $5000 on a dyno and a box of engines and go from there.

yeah, but the x-dyno is $6,000 and a box of engines is $300 - $2,000 or theres another dyno thats $10,000 - $12,000 plus the software to run it which is $2,000 - $3,000




giddyuperic, I did a search on JBmods and nothing came up (or at least not on RC engine modding)

JB, what are you actually looking for? To me it sounds like you are looking for KNOWLEDGE and that can only be had by studying, trial and error + money and time.
There are no shortcuts, there is no simple formula where you enter desired hp and torque and the current timing of the engine in your hand.

The absolute cheapest way is to buy the software I have suggested many times here on RCU and just play around with it.


I'm not trying to be a smart-ass. There just aren't any shortcuts. Nobody can in one post here say what you need to do.

well, there is one for induction timing, so I thought there might be one for port timing. but if not, then oh well.

What are you saying?
There is no formula for induction timing that tells you what numbers are the best, because the actual power and torque output of an engine is a combination of everything...

Can you be more specific? I don't get what you are asking.

isn't this http://www.rcuniverse.com/forum/m_59...tm.htm#5995115 where you just measure it then, do some math, and it gives you the degree to cut to, or did I miss understand it?

Yes that is correct. It's just that your original question was unclear.

Yes there is a formula to calculate what timings the ports have based on dimentions (bore, stroke, length of conrod and height of ports).
If you know some basic trigonometry you can easily come up with it yourself, I'm just to lazy to spend time and post it here.

I was hopeing someone already had it rote down, then I could put it in a spreed sheet then I could just stick my measurements in there (bore, stroke, length of conrod, etc) and it do the work for me, since I haven't taken trig yet.

Yeah but wasn't this part of your school work LOL?

well yeah, but that was the day I skipped

just kidding, no it nots, and I'm only taking Algebra, and I'm only a B sometimes C student in it, somethings I can get 100/100 on but somethings I get 60/100 on and then sometimes only a 20/100 on it.

and I think next year I'm taking business math or something like that.

Umm, you're 14 right? Business math!?

yeah, so I don't have to take trig.

yup I'm 14 almost 15.

I was hoping savagejim would post here, since he did the induction timing, so I thought he might have one for the port timing.

hey sman,
y do u find it nessicary to post replies to modding engines when u don't answer anyone u just try to make that person feel dumb and make yourself seem smart. i thought these forums were here to help people, and not to discurage people from triing new things in this sport.

If you read many earlier post from me you will find that's not the case. I'm actually trying to steer him in the right direction.... read between the lines dude.
It's not in my intention to make anyone feel dumb, because I don't think that is the case. He's not dumb.

depends on who you ask

OK dayglo, here we go.

Here's a picture to go with the formuals:


Variables:

R = length of conrod in [mm]
D = Stroke/2 in [mm]
P = piston position relative to center of crank in [mm]
X = crank pin postition relative to center of crank in [mm]
alpha = crank angle in [deg]


Formulas:

In the picture we can see that:

P = X + T

where

X = D x cos(alpha).

To calculate T we need the help of phytagoras formula that says:

R^2 = T^2 + T2^2

Solve for T and we get:

T = SQRT(R^2 - T2^2)

T2 can also be expressed as:

T2 = D x sin(alpha)

which gives us:

T = SQRT(R^2 - (D x sin(alpha))^2

Finally we get the expression for P as a function of crank angle alpha:

P = D x cos(alpha) + SQRT(R^2 - (D x sin(alpha))^2)

Now you can insert: D = Stroke/2 (but I won't do that, it makes it cluttered to read)

Hope this helps.

There's an error in the picture. The angle alpha should be between the black line and the vertical red line, not the horizontal.

so that will will give me the timing to mod too?

This will give how the piston moves up and down the stroke depending on crank angle. No you need to measure what distance from the top of the liner the piston is at TDC to get a reference point for that and then you use the value (P) to add and subract from that when you decided at what point a port opens after TDC for example.

I am not going to do the rest for you.

ok, let me see if I'm understanding this right. this will tell me how far the piston goes up the sleeve, when I decide when I want the ports to open. is that right?

It tells you were the piston (actually wrist pin) is relative to the center of the crank shaft as a function of crank angle.