AK260

Further to the link I posted above, there is an interesting discussion here .... https://honda-tech.com/forums/engine-management-tuning-124/calculating-ignition-timing-2702491/ I’ve stolen the text of the juicy bit and pasted below: Your questions means many things to many people but There are models (MATHLAB/PHD papers) but you also can estimate your timing curve bearing in some key principles and doing a "analytical review" if that is what you are after (or mean by "calculation") .................................................. ................ For a given engine, and IAT/ECT operating point, Ignition timing is principally a function of the burn rate & VE (torque) Burn rate a linear function of rpm up of a certain break point and swirl/tumble (for a stock ITR is about 4,000rpm - the ignition curve flattens out (Swirl/tumble is proportional to rpm) .................................................. ...................... Just to qualify the above is only talking about cruising to WOT loads (not talking about Timing under Decel, on/off throttle VE is influenced by intake resonance, exhaust scavenging (you can hear your engines sweet spot) The Ignition Curve is a "inverse of the torque curve" - assuming your engine burn rate rises with rpm, you should have minimum timing at peak torque ( I guess someone with a maths engineering expertise can write an inverse function) Bearing the above in mind you can tune your ignition to be pretty close Pay attention to shape of torque curve and tweak ignition accordingly .................................................. .................................................. . Torque - u get this from the dyno U then cant get a idea of the shape of burn rate vs rpm U then tweak the peaks/valley and gradients of ignition curve by eye-balling the torque curve On your DD you get a feel for your engine .................................................. .................................................. ... Look at the stock ITR and D16 maps - u can learn alot (on a D16 OEM timing drops after 4,000rpm) .................................................. .................................................. .... Tuning ignition is way more fun than tuning fuel .................................................. ............................ Google is your friend. .................................................. ............................. There are videos on youtube on MBT/Steady state, but they are always at 3,000rpm/WOT on a chassis dyno - Only on OEM Engine dynos they can hold 8,200rpm/WOT for 10 seconds - This is not not practical for the average Honda-tech forumers or tuner shop (who does no want to break their dyno) - Thus most tuner interpolate with gut feel (which is their un-articulated experience of tuning scores of engines - based on the above (and other) basic principles Do a search and u will find published combustion models (Phd) that can predict MBT within 5%, that have been verified by dyno runs If if u (not a OEM) tuned to MBT on a steady state dyno - your ECT/IAT compensation needs to be spot on for you to be getting MBT all the time (Tune in the day run at night) - and if u are a tuner u would know ECT/IAT move around alot in normal driving

Thanks captain, this is all very interesting stuff. The 22 degs ATDC is the constant regardless of the head / chamber shape and compression. So it would be interesting to see if there is a formulae for taking into account the variables like VE, dynamic comp, chamber shapes, RPM, octane etc. I know a couple of “geeky” engineers at McLaren Cars (which is the recruitment criteria for anyone there) - I will have to put this question to them when we next have a catch up. Edit: this is a VERY good read ... https://ls1tech.com/forums/advanced-engineering-tech/586666-there-formula-calculate-ignition-timing.html

OK so just putting the question of why it goes flat to one side for a moment, here is a thing that I don’t fully get: Conventional wisdom says best timing for these engines is around 34 degrees - yet none of the stock distributors go that far. In fact the majority top out at 27 degrees. My tuner who spent a total of 4 hours on the Rolling Road was adamant that 28 degrees @ 3500 rpm was the ideal. Now I appreciate at 10.5:1 my engine isn’t stock and I also think he was playing it a little safe. But the question is - how has the z world come to the conclusion that the ideal is 34 @ 2800ish and why?

OK - here is another rookie thought for discussion - doesn’t the dynamic compression increase with revs? Wouldn’t that heat the charge more and so easier for flame front to propagate?

So Captain, this is purely my mechanical advance. I have zero base advance, which does mean I have to crank the car a bit when cold but at least it’s WISIWYG and I won’t do something dumb + cranking the extra 5 - 10 secs helps to oil get round before the action starts. The vac curve is a work in progress at the moment. Here is the stock 240z vac curve in 123 speak ... It is basically a recreation of the upper vac curve of this ... Does that help?

This is a great read ... http://www.s262612653.websitehome.co.uk/DVAndrews/timing.htm

I think JB said it perfectly. The only other thing I’be read in addition to what has been said already is that above 3kish rpm the VE increases which helps with better air / fuel mixing and not as much time required for a full burn. I could be wrong so happy to be corrected. I have to dig out the articles again.

In fact, come to think of it, you can use the old bush that comes out of the dizzy for this purpose. The Cardone came with a metal sleeve and I can’t see why it “has” to be plastic! The plastic one in mine had a fair bit of movement, so it doesn’t have to be 100% perfect fit, 99% will do it I suspect it acts more as a guide and to keep things aligned while spinning at speed. Totally cracked me up!!

I posted this on the UK Z-Club forum and it seems on this side of the pond, I’m very late to the party! But for those who haven’t seen it .... This is by far the most entertaining and awe-inspiring bit of engineering I have EVER seen. I’m totally hooked and been binge watching while doing other stuff. The dry humour and unbelievable fabrication skills keep you coming back and make you wonder why we moan about a little rust or fabricating things on our Zs!! It really picks up after the first couple of episodes .... I do wonder what that thing will weigh at the end of the project though! [emoji848]

[mention=19495]captain[/mention] obvious - ooooh! Now I really like that idea. [emoji106] [mention=2635]zedhead[/mention] - very nice find. Never knew such a thing existed! Everyday is a school day. In the UK they are dirt cheap compared with the cost of a 123 toy. https://simplybearings.co.uk/shop/Bearings-Oil-Filled-Bronze-Bushes-Oil-Filled-Bronze-Plain-Bushes/c3_4511_4770/index.html?page=1 Do yourself a favour and while you are about it, turn another to replace the little plastic guide at the bottom of the shaft (which helps locate it into the oil pump drive shaft). Mine was as brittle as an Arizona S30 dash and crumbled with just a stare. Do you fly a Max? Or should i say are you grounded!? [emoji15]

That is a STUNNING bit of kit!! You very lucky man. Have you explored the options for divorce!? You would have a very strong case. ;) Fortunately my wife married someone like her father so she’s used to classic cars, parts all over the house, lots of weekends of spannering and my bad jokes. The latter, only her father truly appreciates. I did cross the line though when she discovered the heat-shield and intake manifold had been in the dishwasher. It did smell of intake and had to be washed empty twice with dishwasher cleaner before normal service was resumed - so I guess she had a point. But the heat-shield did come out “gleaming” on the intensive wash setting; it was worth the beating and bruises. Back to dizzys - the 280z and Zx dizzy bushings can be replaced if you have a way to ream them to the correct size. New un-reamed bushes on the left .... You can see the wear on the shaft just before the advance mechanism. This is my brand new unused cardone item ... The shaft wear is tiny when measure by callipers but makes quite a difference to the movement. So if you go old dizzy, measure the shaft at different points. If you can lathe the whole thing down to the most worn diameter and ream the bushes to match, then you are onto a winner. At this point I decided my life was too short and went 123, it if I had more time and a stock engine then I may have gone down this road.

Brilliant! My car is in my wife’s name (a 40th present to each other) - so when parts arrive all I have to say is: “but darling it’s for YOUR car, I just want it to be the best it can be”!

If I did it again, I would not have bothered with Cardone off RockAuto - it was no better than my worn 280zx dizzy. I have not tried the others but in spite of my comments on some of the annoyances with 123, with the benefit of hindsight, I would say it’s worth buying. Especially now that you know what to look out for during the installation process.

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Wow!! 17 with a 280z? You are one cool teenager! [emoji106][emoji106][emoji106] I only had a Ford Fiesta 1.1 Popular Plus with 40-50BHP. I think lawnmowers have more punch these days. Classic Zs are great cars to learn on as most things are easily accessible and they are pretty simple mechanically.

Forgive me for stating the obvious but jack it up and have a look. Make sure all suspension bolts / nuts are present, check for broken spring, dead or leaking strut, broken anti roll bar mounts, damaged ARB etc etc

Have you measured the length of the rotor arm from it’s centre point out and the same distance on your cap from the centre electrode out - using a digital micrometer? Here is another thought - take the entire distributor assembly off. Put the cap on. Spin it by hand and see if you can feel scraping. Next, clamp the dizzy vertically in a vice. Get a variable speed hand held battery drill, set to low speed and lowest screw-driving torque - such that the drill will stop easily if it encounters resistance. Now with a large flat screw driver bit in the chuck pushed into the bottom of the dizzy, spin it gently, then faster and faster. That way you can get a feel for any grinding, speed at which it occurs and how much resistance there is. Make sure you put some cloth into the tab at the bottom of the dizzy between it and the drill bit to ensure the bit doesn’t foul it. Remember, 3k rpm is 25 rotations of the distributor per second, so when confident with the drill, get some speed on. If indeed the rotor is getting caught, then it is probably advancing the timing to a crazy point that causes stalling. Having said that, (don’t ask why) on the old engine I’ve had an advance of 58 degrees at 3k rpm and no engine load without stalling or spluttering. Under load, that would have caused serious knock / damage and potentially would have stopped the engine running. Does yours spit through the carbs as it stalls? I would say if your shaft is wobbly enough to cause this issue then you should see metal particles everywhere inside the cap and potentially damage at the pickup / star wheel part where the tolerances are tight. If not, then the grinding may be caused by something else in your distributor. I agree with Jon that your cap looks normal / like mine did. Don’t confuse the oxidisation / electrical plasma wear on the electrodes for physical scraping.. Let’s assume the cap and rotor are fine, so: If it’s just happening when revving up, could the advance mechanism be faulty / have broken springs? Potentially, the advance weights are flying out too far, scraping the inside of the dizzy body and causing way too much advance. Doing the above drill test with the cap off would show this up as your scraping sound. Also, put up a video of your shaft’s wobble (preferably the distributor shaft, not the one that will get you banned!) and let’s see how much it’s wiggling by. As you say, there are clearances / tolerances built into these things so the wobble you could see on my video - as horrible as it was - never caused grinding. I’m showing you mine again, don’t be shy, show us yours ...

My 6-3-2 MSA header worked beautifully on both the mainly stock L26 (just ported) and highly modified L28. Never connected with anything other than high speed humps - as it does hang a bit low at the front, particularly if your car is lowered. That I also understood to be a heat-shield to protect your gasket. I did have to “adjust” it for the ZStory Race/Sport header and it’s a VERY solid bit of metal!! The lump hammer was out.

Actually that’s a fair point - I once forgot to put the clips on the cap and driving around I was wondering why the car wasn’t going as well! To this day I’m amazed it didn’t smash itself apart !!! But it did run and rev up.

Cap and rotor made by Bosch. The rubbish ones that came with it: 1 failed in use - centre electrode fell out, the second one was broken out of the box so not even used.

Try this ... https://www.classiczcars.com/forums/topic/55728-float-sync/

That’s great news buddy! There are lots of people that would benefit from your product. BTW last one I tried your website, it wasn’t working - is it down or is it my end not behaving?

Yellow zinc plate them and you have $1.5k + on that bench!!!

Check the size of tour cap as mentioned above - it could be that your 280z cap is just that bit different to the 280zx one. The vac line provides a “load sensing” function. When wide open throttle, the vac drops to zero and advance becomes “base timing” + mechanical advance. When the throttle is closed or part closed the vacuum increases and the distributor adds vacuum advance. This is because the mix is leaner and needs more time to burn. That last bit sounds counter intuitive but think of it this way: you have two plates with a dusting of gun powder that you will light with a match from the centre of each plate. One has a light dusting (lean) with large air gaps between particles, the other has a thick dusting (richer) with much smaller gaps. The one with the larger gaps between each particle will need longer to fully burn across the plate (hence you need more advance). So when cruising, or idling, you have more vac, leaner mix and therefore need more (vac) advance to get a full burn.

Well chap, my tuner who prepares race cars said it was, hence my path to the 123 dizzy as the play in the shaft can cause spark scatter / inaccurate timing at high engine speeds. At 6k rpm that thing is spinning 50 times per second!! The RockAuto Cardone remanufactured one I bought wasn’t much better. While the bushes can be quite easily replaced (there was a guy in the US that made them) the shaft itself gets worn. So unless you can get a new shaft, you will always have some play. I’m a geek so for me it eventually mattered. The only way to get rock solid high speed timing IMHO is crank triggered systems but it all comes down to what you want from your car and how much perfection matters ;) I’m learning the hard way that sometimes, good enough is good enough! But for me it’s more than about driving the car, it’s about giving myself “something to constantly tinker with” - read headaches!!! ;)