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Vacuum Advance / Ignition Mapping


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Starting to look at ignition timing now, particularly after I realised I wasn't running the ignition map I thought I was! Turns out I mustn't have saved the map when copying across from Megajolt to Megasquirt, and had been running a really conservative default map.

Anyway, now that I'm running EFI, I can consistently run 16.5:1 AFRs at cruising loads, which from what I understand needs even *more* advance than 14.7:1. So what I'm thinking is that I can start off with whatever effective value the factory distributors would give on a vacuum advance unit, and then work on increasing it from there.

Looking at the maps that other people are using, the cruise areas seem really conservative. Rob's map was around 24-33 degrees in this area, and Paul Geithner's is fairly similar, albeit a little bit higher at higher rpm cruising areas.

Wasn't the factory vacuum advance giving an effective timing of something around 35-45 degrees?

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Thanks Alec, good idea.

Drove the car today with the map I used to have, much better! The engine feels so much stronger, and the throttle response feels more like I remember it being on carbs - albeit now with much more power and smoothness because it's injected. It's funny how the ignition map changes the throttle feel so much.

I'm more keen now to get hold of a knock module for the MS3, particularly as tuning EFI for 16:5.1 on cruise is getting into unchartered territory. People are reporting success with it on all manner of engines, I just need to think of a good location to mount the sensor.

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Your can do it "seat of the pants" by inching the timing up in the cruise areas until you get pinking then take about a degree out.  Really need someone else driving the car or a clued-up passenger to drive the laptop to do this.  If you can get a few points you'll soon get a feel for what the engine wants and be able to start filling in the gaps.  Bear in mind that if you do this on a cool damp day it'll probably pink like hell on a really hot day, so don't overdo it.

The best way is on the RR.  When I took the PI recently he was able to set the RR to hold the rpm, watch the laptop display so he knew he was keeping the throttle opening the same and also keep an eye on the RR torque readout.  I would then advance the timing at that point until the torque peaked then back it off a little (maybe 1/2 degree).  Pinking actually begins a little after the torque has peaked usually.  Picked up some useful gains - as much as 20% in a couple of spots and the engine feels much more lively at part throttle.

At very low manifold pressure and low rpm you'll probably find the limitation is what you can drive smoothly.  You can put enough timing in to make the car really jerky to drive.

Not sure how worthwhile the knock module is on a N/A, road driven car but I'll be more than happy to read about your experiments  ;)

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