# Induction Timing

#

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**Induction Timing**

INDUCTION TIMING MODIFICATION

I am writing this as an instructional post on how to determine what the crankshaft induction timing is and how to modify the crankshaft to increase this timing. The method I use here is how to calculate with a good degree of accuracy what the induction timing is. Most use a degree wheel to check timing profiles; there is nothing wrong with that. I personally prefer to also have the calculated method as well to verify that I am reading the degree wheel correctly. I completely devised this calculated method and I have a good feeling that professional engine modders use this or a very similar method. If any of you know a better method or notice anything wrong with my method, please post. As I said, I totally came up with this method on my own and realize that I could be wrong since I am not a professional engine modder. Any of you professional modders who have any knowledge you are willing to share, please post. I too am looking for guidance on this art and/or confirmation that my method is a professional grade method. I want to know any flaws in my method and the correct or better ways of doing this.

Before we begin, let me warn you: be sure of the induction timing profile you want before you do any of these modifications. This procedure is irreversible and you can only increase an engine sinduction timing, not reduce it. If you botch it up or increase the induction duration too much, you will ruin your engine permanently.

TOOLS:

*We will need a caliper capable of measuring the thousandth of an inch and/or the hundredth of the millimeter. I personally use a dial caliper. Be sure to purchase a caliper with long inside measuring blades since you will have to take a measurement deep down the carb hole of the engine block.

*A good Dremel rotary tool with all sorts of grinding stones, fine sander discs, polishing bits, and polishing compounds are a must.

*Masking tape will be necessary to help in marking how far to cut and protect surfaces that you do not want touched by the rotary tool when working on the crankshaft and engine block.

*A scientific calculator with trig functions and is also capable of calculating arc-functions (or â€œinverseâ€ trig functions). Be sure to set your calculator to degree mode for all the calculations.

*Keep all of your cleaning supplies out! Once a piece has been modified, it must be thoroughly cleaned before being reinstalled into the engine! I find it best to only have one piece out at a time and to keep all other parts away from the work area to prevent metal shavings and grinding stone debris from entering them.

Lets begin. The very first thing to do is dismount the engine, clean it externally, disassemble it, and clean each component as thoroughly as possible. To increase the crankshaft induction, the two pieces that must be worked on are the engine block itself and the crankshaft. The crankshaft and engine block I am using as an example in this thread is one of my K4.6 engines that I have completely disassembled.

Now, with the block and the crankshaft in hand, we can measure the necessary dimensions for this project. I suggest you print the diagrams below and as you measure the dimensions, write the measurement next to the letter that represents it.

Let us start with the crankshaft itself. The first dimension we need to measure is the outer crankshaft diameter. With the caliper, measure the outer diameter. This is marked as D in Diagram 1 below. The K4.6 uses a 14mm crankshaft, but it will not be exactly 14mm; it could be 13.95mm instead. Be sure to measure it for the exact measurement and write it down.

Step A: Now we need to measure Htot (see Diagram 1 below). This is done by putting one of the flat sides of the caliper so that the two edges of the induction port are against that flat side and the other side is on the opposite side of the shaft. Write down this number, this is Htot.

Step B: Next we need to calculate the radius (marked R on the Diagram 1 below). This is done by doing very simple arithmetic.

The radius, R is equal to the diameter, D, divided by 2.

Step C: Next we need to calculate the H1. This is also done by doing very simple arithmetic.

H1 is simply Htot (the measurement from Step A) minus R (calculated in Step B).

Step D: Now, we need to calculate the angles so we can calculate the total induction duration. This is where you will need your scientific calculator. To calculate the angle, we need to do a very simple trig and algebra operation. This is how it is done (see Calculations 1 below). These calculations will also give us W1.

* Make sure your calculator is in degree mode! This essay is written for se with degrees; otherwise, you will have to convert from radians and convert to radians constantly.

D1: Theta 1 (Theta is the circle with the horizontal line drawn through it) is the angle calculated. Use your scientific calculator to calculate this:

D1A: From the measurements you wrote down, divide the measurement, H1 (calculated in Step C) by R (calculated in Step B). Write this number down.

D1B: Take the ArcCosine of the number calculated in D1A. The result will give you the angle, Theta1. Write this number down.

D2: Now we can calculate W1 accurately.

D2A: Take the Sine of Theta1 (calculated in D1B). Write this number down.

D2B: Multiply R (calculated in Step B). This is W1 and write this number down.

Step E: Now we need to take the measurement of the induction port down the hole where the carburetor sits; this is the induction port of the block (see Diagram 2 below). We need to measure the width of this port. This width is shown as W2 in Diagram 2. This is where the caliper with the long inside blades is required. Once you measure this, write this number down.

Step F: Now we need to calculate W3. This is simply W2 (measured in Step E) divided by 2. Write this number down.

Step G: Now we need to calculate Theta2. (See Calculations 2 below.)

G1: Divide the W3 (calculated in Step F) by R (calculated in Step B). Write this number down.

G2: Take the ArcSine of the number calculated in G1. The result will give you the angle, Theta2. Write this number down.

Step H: Now we can calculate the induction timing; Theta TOT (See Calculations 2 below). Theta TOT is simply 2 times Theta1 plus 2 times Theta2. Be sure you multiply Theta1 and Theta2 by 2 before you add those together!

Now that we know how to determine the induction timing, I will discuss how to modify that timing profile to a longer duration. We know from Calculations 2 that Theta TOT is 2 times Theta1 plus 2 times Theta 2. To increase the induction, the easiest way to do this is to increase the angle Theta 1. We will do this by modifying and opening up the crank induction port. If you know a new induction timing that you want advance you current induction timing to, this is how to do it.

Step I: From calculations 2, we know that Theta TOT is 2 times Theta1 plus 2 times Theta 2. To get the new induction timing, we need to use algebra to manipulate that equation. See Calculations 3.

I1: We name the new induction timing that you want, we will call that Theta Tot NEW.

I2: Theta 1 is what we need to modify to get the new induction timing. We will call this changed angle Theta 1 NEW.

I3: Replacing Theta Tot and Theta 1 in Calculations 2 with Theta Tot NEW and Theta 1 NEW, we can manipulate the equation with algebra; see Calculations 3.

I4: Theta 1 NEW is Theta Tot NEW divided by 2 minus Theta 2. Plug in the values for Theta 2 (calculated in Step G above) and Theta Tot NEW (the new induction duration you want your engine to have) and calculate Theta1 NEW. Write this number down.

Step J: We can now calculate the dimensions we need to grind down to once we know Theta 1 NEW. We must now refer to Diagram 3. All of the original dimensions we calculated for Diagram 1 are included as a reference. We will need to grind down the induction port to open the induction timing more; see Illustration 1. In Illustration 1, the shaded area is the part of the crank induction port that needs to be ground down.

Step K: We need to calculate H Tot NEW. To do this, we must first calculate H1 NEW. See Calculations 4 below.

K1: H1 NEW is the cosine of Theta 1 NEW (Step I above). Write this number down.

K2: Now we calculate H Tot NEW. H Tot NEW is simply H 1 NEW plus R (R was calculated in Step B above). Write this number down.

NOTE: Do not begin to cut yet! We must now calculate the arc distance from the top of the existing port lip down to the new lip. See Illustration 3 and Diagram

I am writing this as an instructional post on how to determine what the crankshaft induction timing is and how to modify the crankshaft to increase this timing. The method I use here is how to calculate with a good degree of accuracy what the induction timing is. Most use a degree wheel to check timing profiles; there is nothing wrong with that. I personally prefer to also have the calculated method as well to verify that I am reading the degree wheel correctly. I completely devised this calculated method and I have a good feeling that professional engine modders use this or a very similar method. If any of you know a better method or notice anything wrong with my method, please post. As I said, I totally came up with this method on my own and realize that I could be wrong since I am not a professional engine modder. Any of you professional modders who have any knowledge you are willing to share, please post. I too am looking for guidance on this art and/or confirmation that my method is a professional grade method. I want to know any flaws in my method and the correct or better ways of doing this.

Before we begin, let me warn you: be sure of the induction timing profile you want before you do any of these modifications. This procedure is irreversible and you can only increase an engine sinduction timing, not reduce it. If you botch it up or increase the induction duration too much, you will ruin your engine permanently.

TOOLS:

*We will need a caliper capable of measuring the thousandth of an inch and/or the hundredth of the millimeter. I personally use a dial caliper. Be sure to purchase a caliper with long inside measuring blades since you will have to take a measurement deep down the carb hole of the engine block.

*A good Dremel rotary tool with all sorts of grinding stones, fine sander discs, polishing bits, and polishing compounds are a must.

*Masking tape will be necessary to help in marking how far to cut and protect surfaces that you do not want touched by the rotary tool when working on the crankshaft and engine block.

*A scientific calculator with trig functions and is also capable of calculating arc-functions (or â€œinverseâ€ trig functions). Be sure to set your calculator to degree mode for all the calculations.

*Keep all of your cleaning supplies out! Once a piece has been modified, it must be thoroughly cleaned before being reinstalled into the engine! I find it best to only have one piece out at a time and to keep all other parts away from the work area to prevent metal shavings and grinding stone debris from entering them.

Lets begin. The very first thing to do is dismount the engine, clean it externally, disassemble it, and clean each component as thoroughly as possible. To increase the crankshaft induction, the two pieces that must be worked on are the engine block itself and the crankshaft. The crankshaft and engine block I am using as an example in this thread is one of my K4.6 engines that I have completely disassembled.

Now, with the block and the crankshaft in hand, we can measure the necessary dimensions for this project. I suggest you print the diagrams below and as you measure the dimensions, write the measurement next to the letter that represents it.

Let us start with the crankshaft itself. The first dimension we need to measure is the outer crankshaft diameter. With the caliper, measure the outer diameter. This is marked as D in Diagram 1 below. The K4.6 uses a 14mm crankshaft, but it will not be exactly 14mm; it could be 13.95mm instead. Be sure to measure it for the exact measurement and write it down.

Step A: Now we need to measure Htot (see Diagram 1 below). This is done by putting one of the flat sides of the caliper so that the two edges of the induction port are against that flat side and the other side is on the opposite side of the shaft. Write down this number, this is Htot.

Step B: Next we need to calculate the radius (marked R on the Diagram 1 below). This is done by doing very simple arithmetic.

The radius, R is equal to the diameter, D, divided by 2.

Step C: Next we need to calculate the H1. This is also done by doing very simple arithmetic.

H1 is simply Htot (the measurement from Step A) minus R (calculated in Step B).

Step D: Now, we need to calculate the angles so we can calculate the total induction duration. This is where you will need your scientific calculator. To calculate the angle, we need to do a very simple trig and algebra operation. This is how it is done (see Calculations 1 below). These calculations will also give us W1.

* Make sure your calculator is in degree mode! This essay is written for se with degrees; otherwise, you will have to convert from radians and convert to radians constantly.

D1: Theta 1 (Theta is the circle with the horizontal line drawn through it) is the angle calculated. Use your scientific calculator to calculate this:

D1A: From the measurements you wrote down, divide the measurement, H1 (calculated in Step C) by R (calculated in Step B). Write this number down.

D1B: Take the ArcCosine of the number calculated in D1A. The result will give you the angle, Theta1. Write this number down.

D2: Now we can calculate W1 accurately.

D2A: Take the Sine of Theta1 (calculated in D1B). Write this number down.

D2B: Multiply R (calculated in Step B). This is W1 and write this number down.

Step E: Now we need to take the measurement of the induction port down the hole where the carburetor sits; this is the induction port of the block (see Diagram 2 below). We need to measure the width of this port. This width is shown as W2 in Diagram 2. This is where the caliper with the long inside blades is required. Once you measure this, write this number down.

Step F: Now we need to calculate W3. This is simply W2 (measured in Step E) divided by 2. Write this number down.

Step G: Now we need to calculate Theta2. (See Calculations 2 below.)

G1: Divide the W3 (calculated in Step F) by R (calculated in Step B). Write this number down.

G2: Take the ArcSine of the number calculated in G1. The result will give you the angle, Theta2. Write this number down.

Step H: Now we can calculate the induction timing; Theta TOT (See Calculations 2 below). Theta TOT is simply 2 times Theta1 plus 2 times Theta2. Be sure you multiply Theta1 and Theta2 by 2 before you add those together!

Now that we know how to determine the induction timing, I will discuss how to modify that timing profile to a longer duration. We know from Calculations 2 that Theta TOT is 2 times Theta1 plus 2 times Theta 2. To increase the induction, the easiest way to do this is to increase the angle Theta 1. We will do this by modifying and opening up the crank induction port. If you know a new induction timing that you want advance you current induction timing to, this is how to do it.

Step I: From calculations 2, we know that Theta TOT is 2 times Theta1 plus 2 times Theta 2. To get the new induction timing, we need to use algebra to manipulate that equation. See Calculations 3.

I1: We name the new induction timing that you want, we will call that Theta Tot NEW.

I2: Theta 1 is what we need to modify to get the new induction timing. We will call this changed angle Theta 1 NEW.

I3: Replacing Theta Tot and Theta 1 in Calculations 2 with Theta Tot NEW and Theta 1 NEW, we can manipulate the equation with algebra; see Calculations 3.

I4: Theta 1 NEW is Theta Tot NEW divided by 2 minus Theta 2. Plug in the values for Theta 2 (calculated in Step G above) and Theta Tot NEW (the new induction duration you want your engine to have) and calculate Theta1 NEW. Write this number down.

Step J: We can now calculate the dimensions we need to grind down to once we know Theta 1 NEW. We must now refer to Diagram 3. All of the original dimensions we calculated for Diagram 1 are included as a reference. We will need to grind down the induction port to open the induction timing more; see Illustration 1. In Illustration 1, the shaded area is the part of the crank induction port that needs to be ground down.

Step K: We need to calculate H Tot NEW. To do this, we must first calculate H1 NEW. See Calculations 4 below.

K1: H1 NEW is the cosine of Theta 1 NEW (Step I above). Write this number down.

K2: Now we calculate H Tot NEW. H Tot NEW is simply H 1 NEW plus R (R was calculated in Step B above). Write this number down.

NOTE: Do not begin to cut yet! We must now calculate the arc distance from the top of the existing port lip down to the new lip. See Illustration 3 and Diagram

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**RE: Induction Timing**

Im sorry for delaying this for so long, My intial post that I just put on today is only how to calculate the induction timing. I am at the moment writing the modification portion as I post this; but please forgive me, all my pics I had prepared for that portion were lost when my main computer crashed. I instead have to redo everthing on word as far as drawing the pics; my brother took back his camera I was using for this essay. Once I get the induction port modification part doen, I will edit the original post to add it in. I will also add more diagrams and calculations as well.

Knowing how to figure intake induction is critical; without it, figuring out the desired induction will be nothing but absolute guesses. Such guesses will do nothing but present the potential of ruining your engine.

Knowing how to figure intake induction is critical; without it, figuring out the desired induction will be nothing but absolute guesses. Such guesses will do nothing but present the potential of ruining your engine.

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**RE: Induction Timing**

Hi SAVAGEJIM

Am i missing something?I've read through more than a couple of times and i can't understand how we can calculate the crank timing when there is no reference to crankpin/piston posistion,surely this will only give us the duration?[sm=confused_smile.gif]

Ant.

Am i missing something?I've read through more than a couple of times and i can't understand how we can calculate the crank timing when there is no reference to crankpin/piston posistion,surely this will only give us the duration?[sm=confused_smile.gif]

Ant.

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**RE: Induction Timing**

This is meant to work on the induction timing only. The above method I described tells how to calculate only the induction timing, not the sleeve (lateral intakes, boost, or exhaust) port timings. I intend to put up another essay calculating those, but I will need more diagrams that are more detailed and complicated for me to draw.

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**RE: Induction Timing**

I don't think you understand what i'm saying.Disregarding the sleeve for a moment.Wouldn't the crank timing figures be quoted relative to the piston posistion as in;the crank window opens at x degrees abdc and closes at x degrees atdc?I don't understand how we can calculate the crank timing without any reference to crank pin posistion relative to the crank window?

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**RE: Induction Timing**

Yes, that is true. I just gave instructions to calculate the induction timing, not its reference to when it opens and closes relative to the piston position. For the oment, the only way I can think of to determine when the induction port opens and closes in relation ABDC or ATDC is by the use of degree wheel.

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**RE: Induction Timing**

Ah so now i see why i'm confused.I would call the opening and closing points(relative to piston posistion)the induction timing and the period between these points the induction duration.

Ant.

Ant.

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**8**Join Date: Oct 2002

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**RE: Induction Timing**

ORIGINAL: SAVAGEJIM

For the moment, the only way I can think of to determine when the induction port opens and closes in relation ABDC or ATDC is by the use of degree wheel.

For the moment, the only way I can think of to determine when the induction port opens and closes in relation ABDC or ATDC is by the use of degree wheel.

With trig you're converting piston travel (linear movement) in the bore to rotational angles but this is extremely messy compared to just using a degree wheel. For one thing you have to measure the centre to centre distance between both ends of the rod to get the ratio of rod length to stroke. It's only advantage is that if you wanted to change the cylinder timing then it tells you how many thou to grind off the upper edge. Like I said....messy!

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**RE: Induction Timing**

Pretty good write up there.

I am going to dremel out the crank on a Traxxas 3.3 motor.

Below is a pic of the standard crank.

Can I gring the flat spots out to the edge (so the throat looks like a V or would this be going too far.

I am trying to go for more top end power and speed.

I am going to dremel out the crank on a Traxxas 3.3 motor.

Below is a pic of the standard crank.

Can I gring the flat spots out to the edge (so the throat looks like a V or would this be going too far.

I am trying to go for more top end power and speed.

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**RE: Induction Timing**

The flat spots you are talking about on your TRX engine is the focus on the rest of my essay. Grinding down these flat spots to open the induction port more for the purpose of increasing induction duration is what I intend to write about next. But you are right, those are very flat and there is a rather sharp ledge towards the inside of the port. That can use some rounding to help better fluid flow and help reduce turbulence. However, dont round the edge that is up against the outside of the port (next to the surface of the crankshaft), this will modify your induction timing even more.

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**RE: Induction Timing**

G'Day, Just interested to know if you have finnished writing the modification portion yet?

Still very interested to read about it.

Still very interested to read about it.

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**RE: Induction Timing**

Yeah, thanks for showing interest, I thought for a while that interest was not there since this thread sort of fell by the wayside. I have the modification portion written and the diagrams drawn; I just need to proof read it, touch up the diagrams, covert the diagrams to jpeg files, and post. I will have the rest posted on this weekend.

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**RE: Induction Timing**

sweet thats what been looking forward to a really good how to guide.

really want to start doing this but no places actualy give info on this side of it.

been reading your threads for ages just never posted.

keep up good work looking forward to reading it

really want to start doing this but no places actualy give info on this side of it.

been reading your threads for ages just never posted.

keep up good work looking forward to reading it

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**RE: Induction Timing**

Yeah, unfortunately, no one even really wants to talk about any sort of math. Getting formulae out of people or to get them to even try to express thier explanations in physics and mathematical formulae is like pulling teeth. There are a few people who have helped me a ton on these forums and led me to excellent sources and/or given excellent links, but most unfortunately do not even want to deal with the arithmetic or the algebra, much less the trig.

This is why I am posting these threads; I want to bring physics and math to the discussions and inspire people to provide more substantial and well grounded explanations instead of simple explanations and saying the "too many variables" thing.

This is why I am posting these threads; I want to bring physics and math to the discussions and inspire people to provide more substantial and well grounded explanations instead of simple explanations and saying the "too many variables" thing.

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**RE: Induction Timing**

Thanks, Very keen to see what you have there.

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**RE: Induction Timing**

For those of you who are a little more algebra and trig savvy, here is the formula to determin the height of the piston within its stroke when you know a given crank angle:

S=stroke

L=conrod length

The circle with the line through it is called Theta, this is an angle

Theta Crank=angel of crank assuming 0degrees at TDC

S=stroke

L=conrod length

The circle with the line through it is called Theta, this is an angle

Theta Crank=angel of crank assuming 0degrees at TDC

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**RE: Induction Timing**

I'm dreadful at trigonometry and not much better at algebra so I'm going to try to put that formula into a spreadsheet to do the dirty work for me .

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**RE: Induction Timing**

Not a bad idea at all. MS Excel, for example is a great spread sheed and even includes scientific functions (trig, logrithims, and stats functions). Programming it to do these calculations make the angles and dimenstional calculations a plug and play affair. It might be complicated at first to punch in th function formulae, but once its in there, with the above formulae, you can calculate dimensions and angles for any induction duration you want.

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**RE: Induction Timing**

I use a spreadsheet when I check out a new engine to record the vital statistics like bore, stroke, shims, squish clearance etc. When I enter the bore and stroke it automatically fills in for swept volume and piston area for instance. With a few more measurements it automatically gives me the compression ratio so I can play with adding or removing shims to see what affect it has. The hard part is setting up for the right formulas .

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**RE: Induction Timing**

I've added more to the origineal post, I now explain what to calculate and measure for to increase the induction duration. Upon proofreading it once I added it, I realized I forgot to even mention calculating the arclength of how far to cut dorn from the existing crank induction port lip! []

I will draw up that last bit and post that too. [8D]

I will draw up that last bit and post that too. [8D]

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**RE: Induction Timing**

Jim I had not realised you posted the docs, thanks for sharing,

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**RE: Induction Timing**

Further to that formula for piston height compared to crankshaft angle I finally managed to make up a spreadsheet in both Works and Excel. Plug in the rod length (centre to centre), the stroke and the crank angle and it'll pop up the travel of the piston from both TDC and BDC. The crank angle can be filled in as either measured from TDC or from BDC. Personally I prefer to measure exhaust and transfer timings as the degrees from BDC because that's where they do their work.

Where this comes in handy is if you want to raise the exhaust timing (for instance) from 70 to 75 degrees. Simply by changing the original crank angle to the desired angle will show how much needs to be ground off the top edge of the exhaust port. The piston height figures for both sets of timing can be put in the area marked Modifying.

If someone is good at algebra (and that's not me ) then SAVAGEJIM's formula could be transposed to give rod length when a particular stroke, piston height and crank angle are known. I'd like that .

I'm attempting to attach both spreadsheets by adding .jpg to the file names. They'd need to be saved and then the file names altered back to the original by deleting the .jpg part.

Oops, that didn't work so save the left one by altering to Wu61250.wks (instead of .jpg) and save the right one as Dz80960.xls

Where this comes in handy is if you want to raise the exhaust timing (for instance) from 70 to 75 degrees. Simply by changing the original crank angle to the desired angle will show how much needs to be ground off the top edge of the exhaust port. The piston height figures for both sets of timing can be put in the area marked Modifying.

If someone is good at algebra (and that's not me ) then SAVAGEJIM's formula could be transposed to give rod length when a particular stroke, piston height and crank angle are known. I'd like that .

I'm attempting to attach both spreadsheets by adding .jpg to the file names. They'd need to be saved and then the file names altered back to the original by deleting the .jpg part.

Oops, that didn't work so save the left one by altering to Wu61250.wks (instead of .jpg) and save the right one as Dz80960.xls

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**RE: Induction Timing**

Those two attachments are not showing up.

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**RE: Induction Timing**

Unfortunately the attachment manager will only do .gif .txt and .jpg files so I had to change the file extensions to .jpg so it would accept them. It can't show a thumbnail because it's not a photo but if you right click to "save link as" or save file as" to download one or the other to your computer you have the chance to alter the .jpg to .wks for the left one and .xls for the right hand one. It's the only way I could figure how to attach them.

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**RE: Induction Timing**

ORIGINAL: downunder

Further to that formula for piston height compared to crankshaft angle I finally managed to make up a spreadsheet in both Works and Excel. Plug in the rod length (centre to centre), the stroke and the crank angle and it'll pop up the travel of the piston from both TDC and BDC. The crank angle can be filled in as either measured from TDC or from BDC. Personally I prefer to measure exhaust and transfer timings as the degrees from BDC because that's where they do their work.

Where this comes in handy is if you want to raise the exhaust timing (for instance) from 70 to 75 degrees. Simply by changing the original crank angle to the desired angle will show how much needs to be ground off the top edge of the exhaust port. The piston height figures for both sets of timing can be put in the area marked Modifying.

If someone is good at algebra (and that's not me ) then SAVAGEJIM's formula could be transposed to give rod length when a particular stroke, piston height and crank angle are known. I'd like that .

I'm attempting to attach both spreadsheets by adding .jpg to the file names. They'd need to be saved and then the file names altered back to the original by deleting the .jpg part.

Oops, that didn't work so save the left one by altering to Wu61250.wks (instead of .jpg) and save the right one as Dz80960.xls

Further to that formula for piston height compared to crankshaft angle I finally managed to make up a spreadsheet in both Works and Excel. Plug in the rod length (centre to centre), the stroke and the crank angle and it'll pop up the travel of the piston from both TDC and BDC. The crank angle can be filled in as either measured from TDC or from BDC. Personally I prefer to measure exhaust and transfer timings as the degrees from BDC because that's where they do their work.

Where this comes in handy is if you want to raise the exhaust timing (for instance) from 70 to 75 degrees. Simply by changing the original crank angle to the desired angle will show how much needs to be ground off the top edge of the exhaust port. The piston height figures for both sets of timing can be put in the area marked Modifying.

If someone is good at algebra (and that's not me ) then SAVAGEJIM's formula could be transposed to give rod length when a particular stroke, piston height and crank angle are known. I'd like that .

I'm attempting to attach both spreadsheets by adding .jpg to the file names. They'd need to be saved and then the file names altered back to the original by deleting the .jpg part.

Oops, that didn't work so save the left one by altering to Wu61250.wks (instead of .jpg) and save the right one as Dz80960.xls

Nice work.

I've been using this method for years now and I wrote a program doing the same thing.