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DIY Turbo Discussion greddy on a 1.8? homebrew kit?

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Old 01-05-2009, 04:59 PM   #41
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I've not messed with the variable cam controls, but my guess is that the single pulse sync signal is not comprehensive enough for cam control feedback, and probably should be on the part of the cam gear that isn't moving about all the time. It is capable of controlling two cams independently if the need arises, hence two high speed feedback signals.

The traction control must read the front wheels in order to know ground speed so that it can determine the slip on the driven wheels. If it were a drag car then I could just read one front wheel and the speedo gear. But since I want traction control to work while turning sharply I'll need more information.

I've seen plans for a twin mercury switch circuit that will change which front wheel it's reading from depending on which way the car is turning, but I was hoping for something more elegant. With the strong LSD I'm using, the speed sensor in the gearbox should usually indicate an average of the two driven wheels. However I know that I do occasionally lift an inside rear wheel off the ground, and it would be very cool to be able to log this and see if I would benefit from tightening up the diff or softening the rear sway. I'd like to be able to continue pouring on the power as long as the wheel with the weight on it is still doing some work reguardless of how much faster the one in the air is spinning.

Another benefit of having a wheelspin parameter is that instead of setting a separate boost curve for each gear (which is fairly surface dependent), I can simply tell it to run full boost and it'll cut back the power automatically at say 15% wheelspin.
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Old 01-10-2009, 09:38 PM   #42
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Originally Posted by DammitBeavis View Post
At a steady RPM, any prediction algorithms would be doing nothing but a little averaging.
I see, I read your post as "while reving from to" not "in the range from to" hence my comment.

The tests aren't surprising really, but it is interesting to hear it. When I did the timing light test I could floor it in neutral and it would be rock solid and barely move. This is ms2 with 36-1 wheel on the crank.

Fred.
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Old 01-10-2009, 10:10 PM   #43
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Just thought I'd share this since I was skeptical if it would work. I needed to move my sync signal to within 90 crank degrees after a crank pulse in order to make it work with my new setup. I used the least scientific and most half-assed method of doing it and it worked out great.

I was aiming for ~45* after the crank pulse (precision wasn't necessary), so I simply marked a point on the crank signal wheel 1/4 of the way between the teeth with a tape measure and lined the mark up with the sensor. I removed the cam sensor and stuck a sharpie marker in to make a dot as centered as possible on the cam gear. Then I removed the cam gear, measured the height of the existing nubs, and ground them all smooth. Next I drilled a hole where the sharpie mark was and tapped it for a M6 bolt which was approximately the same width as the factory nubs. I then put the bolt in from the back, and used a dremel to shape the tip that stuck through to the approximate dimensions of the other mark.

It fired right up and worked. In fact, it worked so well that the sharpie method got me to ~46*, so I was only 1* off my target!
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Old 01-10-2009, 11:06 PM   #44
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Joe had both set ups on his car, but I don't know if he can go back and forth in software.
At the time I did the conversion, I was able to switch back and forth between the 36-1 crankwheel and the CAS by moving a jumper external to the MS and changing the software settings. I can't do that anymore, since my CAS is presently taking up space in a landfill somewhere. (Or perhaps, since I threw it away while in CA, it was shredded, mechanically sorted, and then recycled. Who knows, maybe in a year or two I'll wind up drinking out of a can that used to be my CAS.)

I did, however, perform a back-to-back comparison of timing stability on the CAS and on the crankwheel. This was done by locking the timing to 10BTDC in software, and opening the throttle by hand while illuminating the reference mark on the crank pulley with a timing light. With the CAS in control, I observed greater than 5 of jitter at a constant RPM of... shoot, I think it was ~5,000 RPM or so. (been a while.) I then switched to crank-trigger mode, and observed a jitter of ~1 at the same RPM.

The timing belt, at that point, was about 2 years old (roughly 10,000 miles) and was properly adjusted. I'd imagine that an engine with an older (and presumably looser) timing belt would yield even poorer timing stability when triggering off the cam.
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Old 01-10-2009, 11:16 PM   #45
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Quote:
Originally Posted by Joe Perez View Post
At the time I did the conversion, I was able to switch back and forth between the 36-1 crankwheel and the CAS by moving a jumper external to the MS and changing the software settings. I can't do that anymore, since my CAS is presently taking up space in a landfill somewhere. (Or perhaps, since I threw it away while in CA, it was shredded, mechanically sorted, and then recycled. Who knows, maybe in a year or two I'll wind up drinking out of a can that used to be my CAS.)

I did, however, perform a back-to-back comparison of timing stability on the CAS and on the crankwheel. This was done by locking the timing to 10BTDC in software, and opening the throttle by hand while illuminating the reference mark on the crank pulley with a timing light. With the CAS in control, I observed greater than 5 of jitter at a constant RPM of... shoot, I think it was ~5,000 RPM or so. (been a while.) I then switched to crank-trigger mode, and observed a jitter of ~1 at the same RPM.

The timing belt, at that point, was about 2 years old (roughly 10,000 miles) and was properly adjusted. I'd imagine that an engine with an older (and presumably looser) timing belt would yield even poorer timing stability when triggering off the cam.
And I'll chime in and say "I saw the same thing" on my NB, though not quite as sever. With the trigger wheel setup, I was able to run slightly more advance in places where before, it would *sometimes* knock, and now, it doesn't. Makes it more accurate and predictable. Trigger wheels FTW!
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Old 01-11-2009, 12:54 PM   #46
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Quote:
Originally Posted by Joe Perez View Post
I did, however, perform a back-to-back comparison of timing stability on the CAS and on the crankwheel. This was done by locking the timing to 10BTDC in software, and opening the throttle by hand while illuminating the reference mark on the crank pulley with a timing light. With the CAS in control, I observed greater than 5 of jitter at a constant RPM of... shoot, I think it was ~5,000 RPM or so. (been a while.) I then switched to crank-trigger mode, and observed a jitter of ~1 at the same RPM.
The interesting question is how still was the timing relative to CAM timing? I think on a friend's bone stock MS-I it's pretty good. Sure, this is mostly useless, but interesting - again saying it's not MS-I but rather the timing belt that's the issue.


Quote:
Originally Posted by rb26dett View Post
The tests aren't surprising really, but it is interesting to hear it. When I did the timing light test I could floor it in neutral and it would be rock solid and barely move. This is ms2 with 36-1 wheel on the crank.

Fred.
Same thing, it's illuminating to look at the cam timing. I've done this, and might be inspired to do it again.


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Originally Posted by DammitBeavis View Post
I used the least scientific and most half-assed method of doing it and it worked out great.
Heh, congrats on the 1* timing accuracy, that's great. When working with the MS-II, I ended up being convinced the signals on the crank were inverted from what they really were, and to get the phase right I made a variable trigger phase device:


I just cut a piece of computer case out, put some holes in it, and moved the sensor some degrees from where it normally lived. It didn't fix my problem, though it did exactly what it should do, and hence pointed me to the read issue which I later fixed. :-)
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