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Just remapped my ignition advance


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Hi all.
Earlier this year I bought a Megasquirt to go on my Stag, the idea being to eventually fuel-inject it.

As a half-way house I've installed the MS and have it running ignition only. This is just a very basic install so far with only 4 connections : ign switched live, an earth, a signal from my Lumenition pick-up and a vacuum pipe for manifold pressure. No temperature sensors so no compensations, just a mappable distributor in effect.

To further keep things simple I've kept the advance weights in the dizzy so I'm using the MS to apply a trim over and above the mechanical advance already in operation. I'm not too bothered about timing scatter from gear backlash / chain effects etc as the idea is to keep things simple for me, and anyway if I chasing the last 1bhp I'd have gone trigger wheel on the crank .. 🙂

So ..  surprise of the day was how much power it made as standard .. a frankly amazing 143bhp! The engine has 90kmiles on it and is completely standard apart from a stainless exhaust, but it's a pattern part not a performance enhancing one.

I will post the graphs up tonight but after going through the ignition it made 149bhp peak and 5-8bhp through most of the rev range. At 2000rpm it gained 15bhp but that's more to do with the incredibly weak mixture at that point, weak mixes burn slowly so this was an artificially low starting power at 2000rpm. On injection or with the mixture corrected at that point i would have expected more power there beforehand.

I stopped the first full power run at 5k in deference to the age of the engine, but later on , and with no issues thus far, I got a bit braver and started going higher. Hence the std graph stops at 5k and the remapped graph stops at 5600


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Yep Neil only 100hp shy of your engine haha!
Going for a simple injection carb / wet manifold method. All the restrictions of the std stag intake I know, but should still give drivability and economy gains compared to carbs / fixed advance.
Hope you're doing well .. looking forward to seeing what your next engine upgrades do on the dyno!

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I am going to build another one for my TR next. In the process of making some inlet manifold flanges at the moment as I want to start doing a bit more flowbench development on another pair of heads.
Would like to crack the 250bhp level next time without using any more revs, a bit more compression and a bit more time on the flowbench should do the job.
I have already fitted a new set of exhaust manifolds and system built to the same spec as the Stag.

I will be in touch when it needs setting up!

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  • 4 weeks later...


I am going to fit an old Silicon Chip designed Programmable Ignition Module after Christmas. That one is quite simple, it just alters the advance against RPM with the addition of a crude vacuum sensor.
I can map the mid-range advance and maximum advance, in this design the distributor weights are wired open and the springs removed, as well as the vacuum advance plate fixed.

What advance did you find works best for you? I'm keeping the Strombergs, so my engine might be similar to yours although a bit less mileage!


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Hi Richard .. always good to see people tinkering with the engines, though I am way behind flyingfarmer ^^ when it comes to pushing the TV8 ! 🙂

My advance table looks very strange being as it is a trim over and above the existing mechanical advance, however I can tell you that on full throttle I'm running around 5 - 7 degrees over and above the std stag advance curve, whatever that may be.
My lower rev advance numbers are artificially skewed though because I'm compensating in the ignition map for an overly weak low rev mixture problem.
Once I have my carb injection-converters on and the mixture is also mapped I will know much better how the true advance curve has been altered.
Good luck with your mappable ignition, do you have any more changes planned ?

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At the moment I'll try to keep mods 'in period' because I want to do some historic rally events and they sometimes like to see period documentation. The programmable ignition is a reasonably easy mod because it hangs off the electronic ignition and lets me try two different maps on one test run until I get it right. Then I can run with either of two maps, say for 95 or 98 fuel. One nice thing is that it uses the distributor in fixed mode - no dynamic or vacuum advance, so I get rid of the ignition timing variables introduced by Mr. Lucas. All the distributor does is give me four pulses per engine revolution and point the spark at the correct plug, the electronics do all the rest.

Neil is always going to be way ahead though!

My low rev mixture is overly rich, I haven't sussed why yet, I suspect the temperature compensators but I haven't worked out how I can permanently remove them.

The more difficult mod is to make an alloy sump guard similar to the ones the works teams used on the 2.5PI rally cars.

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You do not need to take the mechanical advance into consideration at all as your mapped ignition in most states will always be more advance than the mechanical as the distributor always has to be safe at basically without knowing load. Does not even matter at that as it is only rotor arm position that is relevant.


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Just had the first 3D print of my injector converter for the stromberg carbs .. a simple install to spray fuel at the back of the butterfly making it an electronic injection carburettor .. easy to fit .. will have to see how it  performs next year when I get the aluminium version through

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I see a snag on this, Unless yer onto it,!!!!

Yer gonna need 2 v v v bigg injectors t,flow fuel for 6 cyls
and if yer only using a small injector, then its duty cycle will be weel owa
its rated design, mostdont like being over 80% for any lenght of time.
the coils owa heat, an frie

Can up the fuel pressure a bit,that,ll give moer fuel at same duty sett,n
butt still wont really be good enough


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Staged injection would be nice .. possible to fit two pico injectors like I'm using side by side too, but I'm hoping that injector technology is on my side here, that plus the fact that the peak airflow of most stags isnt massive , so one injector per bank should be fine *touch wood*.

And yes the Patton principle is employed, to be fair it's hard to think of any other way of doing a simple install .. it's by far the easiest in terms of machining as it utilises almost all the original hardware, just adds an adaptor carrying an injector. Whereas they employ quite a deep adaptor because they use a side feed GM injector I've used a modern Pico injector which is very short and of traditional top feed design and available is a lot of flow rate versions. The patton stuff looks to be very nicely made/machined.

I'm pefectly prepared to eat my words if mine doesn't work as intended though ..

It's also a chance for me to learn the megasquirt ecu a bit more in-depth than I do at the moment. I would normally had chosen my fave ecu the Emerald K6 but felt it was a perfect opportunity to go megasquirt for a change.
So lots of variables to take in right now .. will let you know how I get on

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  • 2 weeks later...

Just a mention that home market stags have two different advance curves.  Early (Mk1)  engines had much more advance than the later (Mk2) ones.  I noticed that changing from the Mk2 (41525) to a Mk1 (41336) type the engine pulls much more strongly.

I wonder which you have fitted to yours?  Did you add extra advance to the 41525 or the 41336 type?

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