Tony D Posted March 22, 2005 Share Posted March 22, 2005 I finally had a chance to do my pulley mod as in the sticky. Linky: http://www.cardomain.com/memberpage/735451/9 FINALLY I have a timing mark that MATCHES my timing light! WooHoo! Finally I am getting a full 40 degrees advance during the high vacuum, high rpms sections of the map. The engine is MUCH freer on the top end of the rev range as the adjustability of the CAS screw only allowed me to get maybe a total of 28 to 30 degrees total advance. So I moved the pin hole to line up the Timing Wheel one bolt rotation advanced. I found that a 13/64'th transfer punch will work perfectly for transferring the hole from one timing wheel to the other (I sandwiched two together, one in the stock position, the other advanced on top of it, bolted to an old pulley), and using the same sized drill bit also allowed a nice tight fit on the factory Nissan Dowel in the back of the pulley. The ONLY thing I did differently, was I lined up the trigger to the CAS line 8 "nubs" off from the place it set after finding TDC and marking it on the other side of the pulley. This 8 "nub" offset allowed me to set "120" on the spark Trigger Angle (what I figured was it was the roughly 72 degrees difference, plus the 30 degrees from the 8 "nubs" and some Kentucky Windage in aligning the CAS on the Bracket). This puts the timing mark RIGHT at 9 degrees at an 850rpm idle speed, and well in advance of the scale's 30 degrees during a rev-up. I have set no offset in the other screen. I will now work on the lights to get legal, and then start doing some road trimming. For once I can do something on the car, and it is actually verifiably tracked in the MSSTune. Again, WOO HOO! IMO, I would not even TRY to dick around with adjusting the 81CAS, while the engine is out of the car, pull and modify the pulley, get your TDC marks set up on the altered timing plate, and bolt it all together before installing it in the car. I pulled the radiator to get to this stuff because I did it in-car. Putting the 81 CAS back to "TDC" is something you will have to do BEFORE you pull the pulley off also. Marking it after the mod is easy using typical TDC finding methodologies. I am really suprised by how much better the car runs with the extra advance available! Moby, feel free to use as you see fit to incorporate the photos in your sticky if you want... Quote Link to comment Share on other sites More sharing options...
mobythevan Posted March 22, 2005 Share Posted March 22, 2005 Great info. I added it to the sticky with only very minor editing thanks Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted March 22, 2005 Share Posted March 22, 2005 thanks for info-i bought a preasembled megasquirt and i am installing it into my 77z/81zxt .i dont know if i am going to use 81zxt stuff or buy new hall sensor and trigger off of flywheel like xander.i found info on the circuit using gm 4 pin hei module to output correct rpm signal for megasquirt.i have 2 of the 81zxt cas sensor units. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 23, 2005 Author Share Posted March 23, 2005 Went for a drive today, got tons of intermittent ping while on boost. Thought for a while it was soething "too good to be true" on the conversion, then looked at my spark bins, and found an alternating "36" in every other bin along the full load (170KPA) line! D'OH! Went back and made one pull with the laptop on in "follow mode" and sure nuff, rrrrrrPing! rrrrrrPing! rrrrrPing! changed the bins to the "24" and "26" they should have been, and on the return trip pulled hard, and not a hint of spark knock! Like I tell everyone, always start tuning a system at low boost, and on the stock bottom end, one error like that on high boost and it would have been BOOM! LOL How they got changed I have no idea, I must have had them in ther for a test earlier, and forgot to change them back after the test. Whew! Quote Link to comment Share on other sites More sharing options...
mobythevan Posted March 23, 2005 Share Posted March 23, 2005 I must have had them in ther for a test earlier, and forgot to change them back after the test. I do that kind of stuff about every other week. I've got to get better about keeping a log book or something. Quote Link to comment Share on other sites More sharing options...
Tony D Posted March 28, 2005 Author Share Posted March 28, 2005 Just a Bizzare second thought I have had while observing the modified plate in action. Seems Nissan put the TDC mark at a different place than their paddles. The paddles were advanced for the CAS in the first place. But while your TDC mark that I made actually reflects piston position, I ended up sing the paddle position for timing on the other side. THAT is why the timing is dead on with the paddle, and wherenver I try to trim to the TDC mark I made (like Nissan) I can't get the thing to run! It is better using a paddle for timing readings anyway---it's far easier to read. Unless you make two marks reflective of TDC, and the exact same offset on the CAS side of the pulley it's almost impossible to tell where the timing mark will end up. My advice from this point would be to mark the TDC simply for reference in the future, but know that timing directly off the paddle over on the CAS side of things will make your life easier. Even if it does look like you are firing 60 degrees advanced based on your TDC mark... :rolls eyes: I may play some more, but it works all as written, maybe I'm overthinking the mechanics involved here anyway... Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 5, 2005 Share Posted April 5, 2005 okay sorry if these are silly questions... I have an '81 CAS setup on my turbo motor, and have thought up until now that this precluded me from using MS w/o upgrading to the '82-83 distributor. So, I am gathering from this post that you CAN use the '81 CAS with MS, but am I correct when I say that it sounds like to do so you have to do quite a bit of modding to it to get it to work? Or was this something you did by mistake and had to correct, meaning I could run MS with just my stock setup? Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 6, 2005 Author Share Posted April 6, 2005 It depends... I used the 81 CAS to prove you could, because nobody else had... From what I could tell the most advance you can get on the stock CAS adjustment bracket is about 35 to 40 degrees. This is 10 to 15 degrees too little for "full" N/A mode advance. During boost it shouldn't matter as you are only running around 25 degrees BTDC, so a max advance of 30 degrees should be fine... BUT... For cruise and partial throttle coasting, you want bins that may be as high as the low 40's BTDC for maximum fuel economy and response. To accomplish that you have two choices with an 81 CAS. 1) modify the bracket. I was not about to take all the bracketry off and see if I could make something work or 2) Take the front pulley off, drill ONE hole, and bolt it back together after aligning the trigger wheel using the new hole. The modification is VERY easy, and you should check your damper ANYWAY because the thing revs to 7K EASILY in the first two gears, and doing that will eat up the rubber in the dampener. By doing the modification, you will get full N/A advance, and allow full advance under all conditions. The engine RUNS with the 81CAS fully advanced, but you never really know where it is running, and I didn't like that. With the five bolts holding the timing disc to the pulley, the math was easy. Move it one bolt in any direction and you alter timeing 365/5 degrees. Or 73 degrees. If you take your original timing set at 24 degrees, and DON'T CHANGE ANYTHING, and do this modification, your spark angle should be VERY CLOSE to 97 degrees. I moved my CAS 8 "bumps" off of dead true (for some stupid reason), which is supposed to be 24 degrees. So add that to the 97 I already screwed into it, and it comes out to almost EXACTLY the 120 I put into the offset window on the setup screen for megasquirt. With that setting, when I fired the car, it took right off, idled correctly, and when I hooked up the timing light the mark was DEAD ON to the spark table for the rpm I was supposed to be switching between (9 and 14 BTDC). I have played with the numbers and it introduces an error in the timing light for initial timing and how the engine runs, so it must be correct. It is a VERY easy modification, and FAR easier than swapping the spindle and over to the 82/83 CAS... At least IMO... The CAS is identical in output between models, so it's up to you which one you want to use. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 6, 2005 Share Posted April 6, 2005 Tony D - about that last sentence, are you absolutely sure about that? Not asking in an argumentative way... the reason I ask is, some small bugs I've had since day one of this turbo swap... man I have tried everything that I could think of plus tons of things suggested by guys here to remedy, and nothing worked, and nothing made sense. Then someone noticed that I had mentioned I was running the '81 CAS, but am running an '82 ECU, wiring harness and AFM. They suggested that this might be my problem, and I think said that they had heard elsewhere that though you can get the car running by mix and matching like this, it wont run quite right. I had always figured they supplied the exact same signal until someone suggested this to me... this has nothing to do with my MS questions or anything just wondering if you've somehow tested or really do know they supply exactly the same signal? This would lift a small weight off my mind and again, keep me from feeling like I HAVE to eventually swap out to an '82-83 dizzy... agreed I did NOT look forward to the prospect of changing out the shaft and all that. But then... not exacly looking forward to pulling off that pulley either and I wouldn't DARE rev my engine to 7k are you kidding me?!? I have the redline on my Autometer tach set firm at 5500... but at any rate at least now I know it can be done, running the '81 CAS I mean, and that I probably dont need to worry that that is causing me any problems with my current setup either. So now I'm even MORE interested in running MS... well, more than interested, just severly funds-limited Quote Link to comment Share on other sites More sharing options...
Tony D Posted April 7, 2005 Author Share Posted April 7, 2005 Well, the diagrams in the FSM are identical, and the explanation of their operations are identical in the FSM's. From this, i took a four channel O-Scope, and went to comparing the waveforms between the two units when I was having "problems" with my install. They were identical. I have several 82/83 ZXT CAS units that I powered up and tested both by spinning by my fingers and by an electric drill to simulate actual engine running conditions. My Milwaukee Magnum turns 500rpm, so it was very nice for approximating the waveform at 1000rpm engine speed. JeffP had told me they were the same an interchangable, and from the O-Scoping, I tend to agree that there is not difference in the output from the modules. HOW they derive the information is VERY different, but the waveforms on the output are identical. As for RPMS, make sure you set your hard limiter and soft limiter up before your first drive. The thing will pull in first like it never has before! Go MS, you will be glad you did! I think you can even run an "emissions program" that will get your through CA Smog if you keep the stock wiring look about the engine bay when you do the conversion. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted April 8, 2005 Share Posted April 8, 2005 sweet... thanks for the info Tony especially that you really TESTED yet another MYTH and PROVED it to be FALSE!! So that is one less thing for me to worry about, I mean about running the '81 CAS on an '82 ECU setup. Now if only you could figure out what IS causing those last couple bugs... but ah well I gave up on them long ago... hey... it starts right up, every time, runs, and get's me where I want to go, very quickly if so desired so why mess with it? about MS... well.. it is still high on my list of "things I plan to do with this car.... some day"... just that all work on the car, barring maintenance, has come to an almost-complete stop... I'll FINALLY be adding a full 3" mandrel exhaust hopefully soon within the next week or so... then in another couple months hopefully I would like to do eurethane bushings. Then... whenever time and money allow, I'll turn back to looking at power mods and possibly either doing a MS or z31 setup. Quote Link to comment Share on other sites More sharing options...
randy 77zt Posted April 9, 2005 Share Posted April 9, 2005 my 77/81zxt has had a few different ecms for other 81-83zxt and they all worked.but i am installing megasquirt and i am using a prefabbed hall sensor and magnets made by cherry.magnets will be installed on flywheel. Quote Link to comment Share on other sites More sharing options...
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