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post #1 of 7 (permalink) Old 04-12-2011, 04:57 AM Thread Starter
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Megajolt Maps

OK let me start this by saying that I'm fumbling around in the dark a bit.

My spider is running Megajolt with twin 40's. I did 3000 miles on it last year and found it was a bit low on power on was was effectively a base map with a maximum advance of 37. I have just rebuilt the head and bolting it all together again it effectively feels the same.

Here in the UK there is an engine management guru Dave Walker who produces the Emerald 3D system. In his book he suggests that 8v engines should run far more advance than 16v engines and puts in two maps. The 16v one is very similar to the one I have but the 8v one runs advance up to around 50 (from memory)

It looks like the 37 advance is in the midrange of around 3500 rpm and mid throttle, if I'm reading it correctly lots of advance at small throttle openings and less full throttle.

Does anyone know ? I will copy the timing into a megajolt table and post them below.
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post #2 of 7 (permalink) Old 04-12-2011, 06:49 AM
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37 deg of advance isn't far off of what the distributor will give you, so it should be ok. Or at least close.

Have you checked to make sure that you are getting what you are asking for? So if you request 10deg, you are getting it?

Check your marks on the flywheel, and use a light to make sure you are getting what you are asking for.

Other than that, at WOT (assuming the carburation is correct, and the throttles open up all the way), 37 deg of advance is about right.

Part throttle, OTOH, you can advance that to get better mileage- experiment with part throttle settings.....
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post #3 of 7 (permalink) Old 04-12-2011, 02:55 PM Thread Starter
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Thanks,

I changed Map from the first one to the second ...
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post #4 of 7 (permalink) Old 04-13-2011, 04:35 AM
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Are you running boost? If not, why does the load side of the table go past 200 (let alone past 100)?

One other thing- 2500-4000 rpm can be upped some- I wish I had a parts book handy, but IIRC, the distributors reach max advance pretty quickly, so you should be able to add some spark in that area.
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post #5 of 7 (permalink) Old 04-13-2011, 07:35 AM Thread Starter
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No boost - that was just in the megajolt software table so I didn't change it. Should I re-set all those values with a maximum of 100?
I've got TPS not MAP and the values ( I thought) correspond to the voltage readings on the TPS. The calibration gives a reading of 255 which corresponds to 5.Ov

Like I said - I can bolt all the bits together but it would help if I knew what I was doing !

I'm an absolute demon at setting up points and timing.

Regards
Leo (playing with technology - badly)

Last edited by 348azeus; 04-13-2011 at 09:15 AM.
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post #6 of 7 (permalink) Old 04-13-2011, 11:48 AM
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Being that it said load, that normally is a measure of MAP. If you leave it as TPS, you'll be fine. Still double check when the engine isn't running that the Y corresponds to TPS and not MAP...

Since you are WOT = 255, then the original graph has you limiting spark to 25 deg overall. that would be to little.

The new one should be better. All in all, if you have a distributor curve availble to you, the highest TPS line should match to the curve- that would be a good start. (And remember distributor speed = 1/2 engine speed....)

But you should also make sure you are getting what you ask for, so check that it's delivering spark when you are telling it to deliver it. 0 = 0, 10 = 10, 33 =33 (or wherever the high mark is).
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post #7 of 7 (permalink) Old 04-13-2011, 03:01 PM Thread Starter
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Thanks,
you have just doubled my knowledge of mapping !

I will revisit the table - as I notice that i miskeyed base rpm at 1400 instead of 1000.

I'll do a few tweaks and report back. i've a gut feeling that my 12mm C&B's and 45's are are bit too wild for tractable road use even with mapping.
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