Create starter map from factory manual specs

Nige · Post by **Nige** » Fri Jan 22, 2010 9:28 pm

I hope this is the place to post this. It isn't exactly a map, but a means to create one from the specs in the factory manual. Appologies if I've missed where I should post it, or if there's one of these already available.

I recently needed to convert the specs in my factory manual for use on the Megajolt. I created a simple spreadsheet to help me out, so I thought I'd post it here as it may help somebody else out.

The attachment is a zip file that contains two spreadsheets, both are the same, but one is in .odf format for us OpenOffice users and I've also saved a copy as .xls for those of you that use Microsoft Office. As it was created in OpenOffice, I can't vouch 100% on how it will look in Microsoft Office, especially the chart, but as the chart is simply eye candy, it doesn't effect the results, but the functionality should be the same in either.

All this does is take the centrifugal and vacuum advance specs from your factory manual, adds the static advance and creates a grid of values for the Megajolt. It has a simple inHG converter as in my experience (old cars) the specs are generally in inHG. This will take a inHG value and show its equivalent in kPa and Absolute pressure for the Megajolt. It can also be advanced, or retarded by a certain percentage. I guessed this would help if a small overall advance retard might be needed for say higher, or lower octane fuel. I know this a simplistic view, but that is what this sheet is for, to get a starter map sorted from the specs that can then be tweaked further.

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First enter your factory static advance value, then find the centrifugal and vacuum advance specs in your factory manual and enter them.

Centrifugal advance:
Edit the RPM reference values to the same as the ones used in the manual, then enter the centrifugal advance values at those RPMs in the column to the right.

Vacuum advance:
Edit the kPa reference values to those used in your manual and in the column to the right, enter the values at those kPa's

The correct reference RPM and kPa values as well as the map values will be filled in in the lower map grid.

NOTE: You may need to convert inHG in your factory manual to kPa, then to absolute pressure for the Megajolt. I've included a converter in the spreadsheet an
d it is based on the following except it rounds to the nearest whole number.

1 inHG = 3.38638866667 kPa (lets round that down to 3.4 kPa)

If your spec lists a value as 14 degrees at 7 inHG...

7 (inHG) x 3.4 = 23.8 kPa. To convert that to absolute pressure, 102 (atmosphere) - 23.8 kPa = 78.2 (round up/down) 78 kPa megajolt reference value.

Final values to enter would be 14 degrees at 78 kPa.

The conversion 1 inHG = 3.38638866667 kPa was taken from: http://www.convertunits.com/from/inch+o ... kilopascal
The conversion to Megajolt values from kPa was taken from : http://www.autosportlabs.org/viewtopic. ... =inhg#6740
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This helped me quickly build starter maps based on the high, mid and low areas of the range in the specifications of my Spitfire Mk1 (1963) before tweaking commenced.

I've re-tweaked the spreadsheet tonight, so if you come across any problems with it let me know and I'll get it looked into. The values already entered into the sheet are the ones that I initially used for the spitfire.

Hope it is of some help to somebody and if the chart is broken in Microsofts Office, maybe somebody could fix it (surface chart best) and re-post it here. Sorry, I don't own Microsoft Office, so can't test it.

***UPDATED***
I've just uploaded the latest version of these sheets. The Microsoft office version has now been tested and updated for that platform.

I've added two 2D charts. One to graphically show the curve for the mechanical advance and another for the vacuum. This means that the layout is also slightly different. Update any value and watch your curve change.

The values in the spreadsheet are the values that I'm currently playing around with for my mk1 spit.

***UPDATE-2*** (6 April 2010)
I've just uploaded the latest version of the sheets.

I've improved the converter to include a drop down selection of what you're converting from and added PSI to the list of what it can be converted from/to.

There are a few other cosmetic changes too. I've colour coded the inputs...
Blue = RPM and kPa reference values to be input
Yellow = Actual degree values at the above (Blue) reference values
Green = The converter input value
Red Text = Drop down unit list to select value to convert from
Red Background = Cells where referenced kPa is in boost territory (turbo)(greater than absolute 102kPa) will have red backgrounds

I've removed/moved a couple of headings and changed the vac-adv chart title to ABS kPa.

Apart from the improved conversions, the basic functionality is the same, but it's now easier to edit and navigate with these small cosmetic changes.

***UPDATE 3*** (18 April 2011)
Thanks to Spandit there is an update to the xls version of this spreadsheet. With his modification, you can paste the values directly into the Megajolt software, or create a new file.

For details of the changes and to download the file that he's attached, you should check out his post further down this thread. (for me it is the first post on page two of the thread).

Nige

speedmerchant · Post by **speedmerchant** » Mon Apr 05, 2010 12:36 am

That is really cool and helpful. My car is a turbo, what would it take to modify the spreadsheet.

Best,

Jeff

Nige · Post by **Nige** » Mon Apr 05, 2010 9:43 pm

That is really cool and helpful. My car is a turbo, what would it take to modify the spreadsheet.

just change the kpa values (directly under the kPa label) to include the range above atmospheric (102kpa). I should really change the label from Vacuum to Pressure as it is for both really. I only run an NA motor and only use values up to a maximum of 102kpa, so it didn't occur to me.

In the InHG converter just use a negated (-) value for pressures above atmospheric. Might also add a psi value into the converter.

Nige

Gassed'58 · Post by **Gassed'58** » Tue Apr 06, 2010 12:42 am

Interesting posting, having a good play with this. Thanks for taking the time to create this .

Nige · Post by **Nige** » Tue Apr 06, 2010 6:25 pm

Nige wrote:
That is really cool and helpful. My car is a turbo, what would it take to modify the spreadsheet.
just change the kpa values (directly under the kPa label) to include the range above atmospheric (102kpa). I should really change the label from Vacuum to Pressure as it is for both really. I only run an NA motor and only use values up to a maximum of 102kpa, so it didn't occur to me.

In the InHG converter just use a negated (-) value for pressures above atmospheric. Might also add a psi value into the converter.

Nige

Sorry, replying to my own post.

I've now improved the converter in the sheet and it will now convert to/from. inHG, kPa, Absolute kPa and PSI. See the updated first post above for details and download.

Nige

Nige · Post by **Nige** » Tue Apr 06, 2010 7:10 pm

speedmerchant wrote:That is really cool and helpful. My car is a turbo, what would it take to modify the spreadsheet.

Best,

Jeff

I've made the sheet a little more boost friendly with an update, or two. Checkout the update-2 version and description of the changes in the first post.

Nige

speedmerchant · Post by **speedmerchant** » Wed Apr 14, 2010 4:01 am

Rad!

Jeff

speedmerchant · Post by **speedmerchant** » Wed Apr 14, 2010 4:06 am

This needs to be a "sticky"

Jeff

Phil English · Post by **Phil English** » Wed Jul 07, 2010 2:31 pm

Great Stuff! many thanks for posting this, I have a Reliant Kitten fitted with a 999cc Fiat Fire engine, Mods include 1.1 Punto head Skimmed and ported, 262 degree fast rd cam, cbr400rr carbs with tps & megajolt, my problem was finding a starting point for the mapping, this thread soon sorted that,

spandit · Post by **spandit** » Sun Apr 17, 2011 9:09 pm

Superb thing - but I'm still a bit confused.

I have a graph from the manual with the centrifugal advance (I presume, as there is no vacuum advance fitted to my engine). I've entered these into the spreadsheet.

I've also put in the figure of 13 in the static advance (because it says "Automatic spark advance at distributor shaft = 13")

Should I put all the vacuum figures to zero then?

Nige · Post by **Nige** » Sun Apr 17, 2011 9:23 pm

Hi,

If you don't have a vacuum unit on your engine, then I guess that you should set the vacuum settings to zero and it won't matter what the kpa values are set to as it won't be effecting the mechanical values.

It does seem strange to have no vacuum advance if it isn't a race engine that's going to be at full throttle most of the time though. Vacuum is for economy whilst driving as when you lift off the accelerator when cruising a leaner mixture is fed in and the spark can be advanced much more to ignite the mixture earlier.

Nige

spandit · Post by **spandit** » Sun Apr 17, 2011 9:25 pm

It's a military engine - perhaps they didn't want extra complication and weren't too concerned about economy?
Do I need to enter the dwell angle anywhere?

Nige · Post by **Nige** » Sun Apr 17, 2011 9:31 pm

Ah yes, I guess the military aren't known for worrying about fuel economy.

There is no dwell input on the sheet as I don't believe the megajolt has an input for it. I moved on from the megajolt last year, so can't remember for sure. I now run the ignition part of a megasquirt as it allows it to fire through the origininal distributor to keep the original look with the modern electronic ignition.

I do still use the same sheet for the megasquirt, I just adapted it.

Nige

spandit · Post by **spandit** » Sun Apr 17, 2011 9:38 pm

Ah well, thanks anyway. It would be quite easy to modify the sheet to format the output for pasting directly into an MJLJ file to save all that typing - I can do it if you wish and post it back on here

Nige · Post by **Nige** » Sun Apr 17, 2011 9:42 pm

That would be great!

I'm no spreadsheet expert, it just scratched my itch at the time. If it would help anybody else, I'm sure the modification would be welcome. If you do post it back, I'll get a notification as I'm subscribed to the thread. I'll modify the text in the original post to let those that just glance at the start of the thread know that theres a modified one further down.

Thanks,

Nige