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MG Midget and Sprite Technical - Megajolt - temperature & advance correction

Chaps with megajolt or similar

I am scratching my head a little bit figuring out how to use the advance correction facility based on engine temp.

I have mapped my engine temp sensor to Deg C and it is showing fine in the MJ.

The MJ splits the range of 0-255 into bins of 25. This can be converted to Deg C, which gives bins of roughly 14 deg C.

Deg F Deg C
0 -18
25 -4
50 10
75 24
100 38
125 52
150 66
175 79
200 93
225 107
250 121

Now I am guessing that this feature would only be used at values less than 80 deg C, as at normal operating temp we move into our normal operating map.

My question is, how much extra advance would an engine need as it moves from 20 up to 80 deg C? By the table above there are 5 bins (in deg C, 10-24, 24-38, 38-52, 52-66, 66-79) so the extra advance can be reduced as engine temp increases.

Also, could it be used as a safety precaution if the temp rises to above 107 deg c?

Thanks
Matt
Tarquin

In the lack of any other response I'll put in my tuppeneth from my use of MSExtra+
I wouldn't worry too much, maybe a few extra degrees advance (say 5 or 6) at 20C and none at normal operating temp maybe retarding the same sort of amount at 110C (assuming normal op temp at 90C).
At the end of the day it won't make huge differences and as you suggest, wont even do much during most of your driving.
I didn't even bother using temp correction and never felt I needed it.
Bob T

Hi Bob
I had hoped you would chime in.
The engine starts fine when cold. I suppose I could put a bit extra advance in, and if it starts to kickback when cranking reduce it a little.
In fact I don't know what ignition advance is used when cranking? Does MJ/EDIS use a different advance than the normal map?

I just thought as the feature was there, I would use it. And I've got the bits to add the temp sender into the coolant system (metro bit I think, a spacer which goes under the thermostat housing with a boss for a sender unit, £3 off ebay NOS, bargain).

Would the MJ aux input be better used for inlet air temp?
Tarquin

Here's the air intake temp correction for my Kseries. Note:

- add a little fuel (% scale) when intake temp low, as air more dense
- similarly, reduce fuel at high intake temps, as there's less weight of air going in...
- reduce advance at high temps, since the hotter intake will lead to faster swirl and faster burn; otherwise will pink or even detonate.

pt2 to follow...

A

Anthony Cutler

BTW - I don't have any additional advance for starting; the Emerald implies this is needed, but IMO it's just wrong - really you should retard to start, as engine turning so slowly, and the *last* thing you need is advance to push the engine backwards. Anyway...

Here are the coolant temp corrections I use:

- add fuel and timing for low coolant temps: air is dense, some fuel might drop out onto the manifold walls; and less likely to detonate
- in theory, you could reduce fuel at high coolant temps... but conversely normally you keep the fuel the same or even add fuel to provide cooler combustion to increase safety margin, esp. at high revs
- for ignition, increase advance at low temps (since detonation is less likely), and reduce advance at high temps, when pinking/detonation is more likely

- see also startup enrichment aka choke - also temp dependent.

HTH

A

Anthony Cutler

Thanks Ant, thats what I thought.
I will keep hold of that if I ever put megasquirt on the V8. Only got Megajolt on the 1380 at present.

It's a bugger that the MJ can only accept 1 auxilliary input.

Thanks
Matt
Tarquin

In terms of fuel correction, MSExtra will calculate and adjust automatically so not really a major issue to worry about even in the future.

Matt, I don't think you should worry about any temp correction for now. just get cranking advance at about say, 10deg and get the table in order. Just isn't worth installing the extra sensors unless you're gonna go fuel too? ;-)

HTH
Bob T

This thread was discussed between 07/08/2011 and 08/08/2011

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