R23 & wasted spark

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R23 & wasted spark

Post by edgedj » Thu Nov 22, 2012 11:53 pm

Does anyone know if the combination of r23 cam and a wasted spark ignition system (EDIS in my case) is likely to result in a backfire in the inlet like I'm experiencing?

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Re: R23 & wasted spark

Post by Lotus-e-Clan » Fri Nov 23, 2012 8:08 am

I run Canems wasted spark with a GB72 (46/72/72/46) so can't give a definite answer but the wasted spark is on the exhaust stroke and any back fire SHOULD be through the exhaust (if there is fuel present). The only time I ever get a backfire is through the exhaust, and that's only after I've (rarely) cocked up the start and flooded it such that unburnt fuel is present on the exhaust stroke and the wasted spark cracks one off like a shot gun!

Back fire through the inlet sounds like your ignition map timing is is off colour, or your inlet valves aren't sealing on the firing stroke, or you have a flooding issue on the early part of the overlap when the exhaust valve closing /inlet opening (see next paragraph). The inlets of an R23 (48/76/76/48) should close 76 deg ABDC ..In other words you have 104 degrees of closure before TDC on the compression stroke and the earliest you can fire the ignition is 50 deg BTDC on the compression stroke so should get no back fire though the inlets on the non-wasted part of the ignition program.

The inlets will start to open @ 48 deg BTDC on the end of exhaust stroke (overlap) but there should be hardly ANY mixture coming through at that point especially on part-throttle and some of that might escape out of the closing exhaust valve. So you would need a combination of VERY rich jetting (or leaking pump jets or too high a float level), low exhaust gas velocity (poor exhaust extraction design) to catch the wasted spark on the exhaust stroke and for it to come out through the inlets.

If your cam timing is too advanced then the inlets might be opening even earlier than 48 deg on the exhaust stroke which will add another negative factor into the mix allowing too much fuel through on the final part of the exhaust stroke especially combined with flooding/jetting issues.

Food for thought anyway.
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Re: R23 & wasted spark

Post by benwick3 » Fri Nov 23, 2012 10:34 am

Have run R23 with wasted spark (Weber Alpha)and no problems as described. Worth checking both cam and ignition timing. Only problem I've had with wasted spark was when the trigger wheel moved on the bottom pulley due to failure of the retaining screws.

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Re: R23 & wasted spark

Post by edgedj » Fri Nov 23, 2012 7:41 pm

Thanks for the advice guys, much appreciated. Great to hear that it can run wasted spark. I think the problem is huge over fuelling because my engine is producing hardly any vacuum so the megasquirt map based system is very confused. My camshaft is a custom Kent cams item loosely based on an r23 with less overlap for my turbo.

I did have a timing issue due to a dodgy timing wheel bought off ebay which confused the edis ignition. The spaces were too big.

I think my sole problem now is a leak on the inlet/exhaust gasket playing havoc with the manifold pressure. Fingers crossed!

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Re: R23 & wasted spark

Post by benwick3 » Fri Nov 23, 2012 11:33 pm

Dave,

Forgot to point out that the Weber Alpha uses a tps. One other useful thing is to retain a tdc mark and reference pointer so that you can check the timing with a timing light. That's how I found that the trigger wheel had moved.

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Re: R23 & wasted spark

Post by Lotus-e-Clan » Sat Nov 24, 2012 9:20 am

Yes TPS is the only way to go with a race cam and twin 40s on a n/a engine.

I have a vacuum meter in the dash and anything over 15% throttle means NO vacuum so the only way to plot a fully meaningful ignition map is to use TPS, then the ignition advance matches the load much better. But if you are running a turbo then you do need a MAP sensor. Perhaps utimately you need both MAP and TPS.

Over fueling and poor gas extraction/lack of vac sounds like the reason you are getting a pop through the inlet on the wasted ign cycle.

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Re: R23 & wasted spark

Post by edgedj » Thu Nov 29, 2012 4:57 pm

can anyone confirm that I should get a relatively steady vacuum needle at idle. I appreciate there may be a loss of resolution with the hotter cam but at the moment mine is dancing around like crazy at idle - I suspect it's exhaust leaking over to inlet causing the issue...
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Re: R23 & wasted spark

Post by pimpdriver » Thu Nov 29, 2012 5:48 pm

Dave
I have always put a 0.6mm mig tip in the vacuum line as a restrictor and a cheap plastic fuel filter as a damping plenum chamber. It really makes a difference to the signal the ecu sees.
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Re: R23 & wasted spark

Post by Dave ' Linwood ' Lane » Thu Nov 29, 2012 6:07 pm

You do need a restrictor in the vacuum gauge pipe , mines adjustable for some reason , vacuum required for the gauge is so small I can pull the pipe off the gauge and it doesnt even effect the tickover.
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Re: R23 & wasted spark

Post by james » Thu Nov 29, 2012 6:50 pm

Odd, mine always worked fine without a restrictor. :?:
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Re: R23 & wasted spark

Post by Lotus-e-Clan » Thu Nov 29, 2012 7:17 pm

My vacuum gauge is connected to all four inlet tracks via the DHLA venturi vacuum tappings on the car body. With one inlet connected you expect to see it swing wildly at idle (unless damped as Eric has done).

With all four inlets interconnected (no restrictor(s)) I get a steady 11 inches Hg at idle (1350 rpm) with GB72 cam timings not too far off your R23.

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Re: R23 & wasted spark

Post by edgedj » Thu Nov 29, 2012 7:26 pm

Lotus-e-Clan wrote:With all four inlets interconnected (no restrictor(s)) I get a steady 11 inches Hg at idle with GB72 cam timings not too far off your R23.
Mine is swinging wildly between 0 and 5 inches - also one of the cylinders runs much hotter than the others. I've just taken my stainless steel manifold off and it doesn't look too clever, not very flat at all. So I'm currently grinding and filing it flat to get a better seal on my new gasket (in the post)

Trouble is, I've done a bad thing for debugging, I've changed just about every variable with this one engine swap (engine build, new cam, new fuel rail, new ecu, new fuel pressure reg, the list goes on!). So I have no baseline or place to go back to :oops:

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Re: R23 & wasted spark

Post by Lotus-e-Clan » Thu Nov 29, 2012 7:31 pm

I should have added that on one inlet the highest vacuum reading was 8 or 9 inches. It went up to 11 only after connecting all four. So your 5 inches is maybe a bit on the small side ( :wink: ) and will increase when you sort the manifold.

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Re: R23 & wasted spark

Post by pimpdriver » Thu Nov 29, 2012 10:44 pm

I have always run the restrictor and damper on my cars and had very stable idles. I helped to install megasquirt on an R21 cammed, fuel injected, van down south earlier this year. On eventual start up ( bit of a wiring problem ), the idle vacuum was going from 50 up to 90 on a quite rhythmic basis with 4 cbr600 throttle bodies all connected up to one vacuum Pipe. Having no mig tips about, a piece of wire insulation was stuffed up the vacuum pipe and the idle then varied from about 60 to 80 :) . Installed a fuel filter plenum and the idle varied from 70 to 72. :D That to me seems to suggest they work :lol:

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Re: R23 & wasted spark

Post by Lotus-e-Clan » Fri Nov 30, 2012 8:08 am

70 inches damped vacuum at idle is a SIGNIFICANT increase over 5 to 11 inches un-damped at idle. :o

Which makes me wonder if there is a direct, linear, real time relationship with damped vacuum and engine load. :?

I suppose if the full range of damped vacuum data is mapped appropriately it may serve the purpose of mapping load to ignition advance. But if there is a significant delay in the change (or loss of linearity) of damped vacuum with ACTUAL engine load, then the resultant change in ignition advance might not match the real time engine load.

All a bit theoretical so put me right Eric on what happens in practice using damped vacuum...I must be missing something obvious, or I've over-analysed the dynamics of the difference in damped and undamped vacuum? :lol:
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Re: R23 & wasted spark

Post by pimpdriver » Fri Nov 30, 2012 10:24 am

Pete
Sorry about that, my fault by using numbers without saying what they are :oops: :oops: . The values I used were kPa ( kiloPascal ) which megasquirt uses for load sensing.
0 kPa is total vacuum and approx 100 kPa is atmospheric pressure. The kPa value expected at idle varies depending on engine and cam. I used to get about 35 kPa at idle with a sport cam and weber 28/36, approx 68 kPa at idle with an R20 and cbr600 throttle bodies (turbo engine), approx 75 kPa at idle with an R21 and twin Webers and approx 78 at idle with an R22 and twin Webers. As you can see the usable range of load sensing diminishes as the cams get more radical, which is why throttle position is probably better for the R series cams ( or a system that uses both).

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Re: R23 & wasted spark

Post by Lotus-e-Clan » Fri Nov 30, 2012 11:07 am

I see! :lol:

And there I was thinking your engine building /gas sealing skills must be soooooo much better than mine! :roll:

What a relief! 8)

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Re: R23 & wasted spark

Post by james » Fri Nov 30, 2012 11:29 am

It'd be extremely difficult to achieve 70"Hg, at least on Earth - atmospheric pressure can only suspend a column of ~30"Hg. :wink:
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Re: R23 & wasted spark

Post by edgedj » Mon Dec 17, 2012 11:50 pm

Screen Shot 2012-12-17 at 23.30.09.png
Getting a bit further with this... I sorted my trigger wheel issue which was causing a complete lack of spark at higher rpm with a new and better manufactured item. Now I'm left with the engine running well over 3kprm or on boost. But below 3kprm it's not happy at all, running so rich it actually misfires.

I'm certain that MAP can be made to work with a finely tuned VE table, so long as it can get a clean MAP signal. See the attached screenshot from TunerStudios MAP logging, which logs the MAP signal every 0.128ms (no that's not a typo!). It's clear to see that the engine is pulling 78kpa vacuum at idle, but the reversion pulse from the R23 results in an average much closer to 100kpa. The key to this might be to get Megasquirt to read the MAP signal at the bottom of that curve, which it can do but central to getting precise measurement timed with the combustion stroke on cylinder # 1 is having the engine detect that event, rather than just wasted spark. With EDIS wasted spark, Megasquirt knows how fast the engine is spinning and can count cylinders but can't differentiate between any of the cylinders, or even tell which is an exhaust or combustion stroke.

So my next move is to modify an imp distributor to provide a camshaft signal (high accuracy not needed, it just helps the ECU identify cylinder # 1), which consists of a single toothed steel disc and a second VR sensor which is aligned just before ignition on cylinder # 1. After that, I can do fully sequential injection and inject each cylinder at the perfect time before each inlet valve opens.

If it were simple, it wouldn't be interesting right? :D
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Re: R23 & wasted spark

Post by Lotus-e-Clan » Tue Dec 18, 2012 2:27 am

What does the "real time" ignition map look like below 3krpm when it's logged during running (assuming you can log it)?

You need plenty of advance below 3krpm on part throttle (about 30-32 degrees most of the time). For example, twin 40 DHLAs with an R23 need the No6 emulsion which is designed to be quite weak below 3krpm - hence why you need plenty of ignition advance. If your ignition advanvce is unstable /retarded below 3 krpm then WBO2 AFRs will read rich even if fueling is relatively reduced because the poor igniton timing will result in unburnt fuel /rich AFR reading.

Personally I'd use a TPS signal for ignition as it is "nailed" to throttle opening and not "reactive" to it like a vacuum signal. If you've got to have vac /boost readings for a turbo then maybe you need both TPS and MAP to sense all situations correctly (TPS off boost, MAP on boost)?
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Re: R23 & wasted spark

Post by edgedj » Tue Dec 18, 2012 12:13 pm

the problem with alpha-n is in part a bit of OCD in me which says that speed density is the way to go and partly because I have a very large throttle which is a concern in terms of resolution at low openings. also I have an air idle valve which bypasses the throttle plate and that would really not work if I were basing load on the throttle.

I need a large throttle body for the boost but this results in tiny cracking open values on the throttle giving quite large amounts of power off boost.
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Re: R23 & wasted spark

Post by ImpManiac » Tue Dec 18, 2012 5:41 pm

It sounds to me as though your system needs TPS and MAP sensing, Dave. :) Does your ECU accept inputs from both simultaneously?

I also think that Eric's 'vacuum reservoir' could be an interesting experiment for your installation. The damping that it ought to introduce could be helpful for your application with the manifold pressure fluctuations accentuated by your choice of camshaft. :idea:

Of course, this poor off-idle performance may well be an artefact of the R23's extreme valve timing. Perhaps there is not much that can be done to improve matters with that camshaft and your large throttle butterfly. :!: Just a thought. :wink:

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Re: R23 & wasted spark

Post by edgedj » Wed Dec 19, 2012 1:37 am

Yes I can do blended TPS and MAP, I do tend to agree that,I'll end up there in some form. All this work will make it run better at the boundaries between and if say I have to have TPS below 2krpm then that's better than 3krpm.

The vacuum canister is only providing an average I think. Megasquirt has its own software averaging which is configurable that can mimic such an analog device easily. The problem is that the average is wrong and what I really need is the minimum vacuum, to do that I need phase detection and sequential injection, which is no bad thing anyway.

I'll post when the next step is done, if that fails then there are some awesomely clever ITB solutions with a map sensor per TB.
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Re: R23 & wasted spark

Post by ImpManiac » Wed Dec 19, 2012 12:17 pm

edgedj wrote:I'll post when the next step is done, if that fails then there are some awesomely clever ITB [independent throttle body] solutions with a map sensor per TB [throttle body].
Interesting. :wink: I look forward to finding out about these at some point. :mrgreen:

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Re: R23 & wasted spark

Post by edgedj » Wed Dec 19, 2012 2:22 pm

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Re: R23 & wasted spark

Post by ImpManiac » Wed Dec 19, 2012 2:43 pm

That is genuinely clever and useful. :) :) It also makes sense from an intuititon point of view.

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Re: R23 & wasted spark

Post by edgedj » Fri Mar 08, 2013 10:58 pm

quick update on this, I chickened out and went for an R17 cam instead - it's lovely. Seems to rev to 8500 happily and that's enough for me. The R23 did clean up and run very sweetly after 5krpm but really that's not great in Jersey with the 40mph speed limit.

Having said that, I do now have sequential injection working thanks to the efforts to get the R23 running, so not all lost.

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Re: R23 & wasted spark

Post by Lotus-e-Clan » Sat Mar 09, 2013 7:46 am

And the R17 will rev further if you open up the chokes (but then the bottom end suffers obviously). 8)

My original Chesman R17 unit on a SINGLE 40 with mahusive chokes and larger auxillary venturis (I wish i could recall the exact sizes) was eager to go to 10 k rpm. :D BTW I think going by the lack of discussion about auxillary venturis, tuners probably miss a trick and only increase their choke sizes when looking for more top end.

OK you're on full EFI so big chokes etc aren't particularly relevant. :oops:

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Re: R23 & wasted spark

Post by edgedj » Wed Mar 20, 2013 11:58 pm

Lotus-e-Clan wrote:OK you're on full EFI so big chokes etc aren't particularly relevant. :oops:
Heh yes absolutely, my choke size is about 60mm but it's not a choke it's just an air door! Time will tell how mine reacts to the rev range but it's looking like tailing off in power beyond 9krpm. Here is a video of me largely pootling around but occasionally opening it up.

http://www.youtube.com/watch?v=ufgWY7lOQJM


Since this video was taken I've tuned the ignition map by basing it on the low CR van ignition settings from the workshop manual for low load settings and it's much smoother, also I've tuned the fuel more. The blend from off boost to on boost is now harder to distinguish which leads me to believe that I've improved the power off boost
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Re: R23 & wasted spark

Post by Lotus-e-Clan » Thu Mar 21, 2013 7:57 am

Wow!

Can see the accelleration in the vid via the rushing scenery as the nose rises! 8)

BTW I assume your R17 is timed in @ 107 thou ATDC.

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Re: R23 & wasted spark

Post by edgedj » Thu Mar 21, 2013 9:25 pm

it is a bit fun, I'd love to get it out on a motorway like I used to do with my old Stiletto turbo, that was most surprising in 3rd and 4th gear having a big shove available at 90mph is a great feeling in an imp! Sadly it's a 40mph island wide limit for me in Jersey.

I've timed the cam at 0.105" at TDC, as per this page and a few more:

http://www.imps4ever.info/tech/camshaft.html

Anyone know if I'll get better results with something else? Engine is 998 with 8.98:1 CR
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Re: R23 & wasted spark

Post by Lotus-e-Clan » Thu Mar 21, 2013 10:02 pm

107 thou is better than 105 thou for an R17 .. according to Andy Chesman... and for a n/a engine....at least that's where I set my R17 cam....I'd experiment a bit on cam timing to suit your forced induction ... you might find a sweet spot for your set-up? 8)
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Re: R23 & wasted spark

Post by edgedj » Tue Mar 26, 2013 6:22 pm

I've just fitted a speed sensor to the rear driveshaft, confirmed accuracy via GPS and done a 0-60 run. From the datalog hit 60.6mph at 5599 rpm in third gear after 5.6 seconds. Perhaps I should just stick with 7psi boost...
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Re: R23 & wasted spark

Post by Lotus-e-Clan » Tue Mar 26, 2013 6:53 pm

...or you could hit 60 mph @ 8250 rpm in second ....

I wonder which would be quicker .. one less gear change v midrange torque from the turbo?

Sounds good, but keep going because I can get 6 secs (possibly sub 6 on a good day) in my n/a 1040 heavy road going Clan (8250 rpm in second). Maybe you should be aiming for nearer 5.0 secs with a turbo? 8)

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Re: R23 & wasted spark

Post by edgedj » Tue Mar 26, 2013 11:04 pm

I could but I fear that my clutch will not last many more starts like that! I think also most of the losses are at the zero to 5mph point and that's all about mistreatment of a road car and reduces the lifespan of everything in hugely disproportionate manner.

The log shows I lost 0.6 secs in the change from 2-3 and Ii was seeing no loss of power in the gearchange in second, so perhaps just one more run leaving it in 2nd would be worth the risk to the clutch :twisted:
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