Zmanco

The problem showed up only on the track. I've had this issue with both the stock turbo and some RC Engineering. In the case of the stock turbo, dropping the PWM setting to 20% after 1.5ms seemed to solve it. With the RC Engineering, I tried dropping below 20% and eventually couldn't get enough fuel and went lean. Also, the RCs are only 225 cc/min and my logs showed I was getting to >85% (which is why I put the stock turbos back in). In both cases there were times at WOT where the power would completely fall off and cause MS resets. I had the laptop next to me and saw that the injector PW was still at a normal reading for WOT, so figured the problem was with the drivers overheating and shutting down, but the engine never came back to power until I took my foot off the gas for a few seconds. I suppose if the impedance of the injectors drops further as they get hot that might explain this?

How about when someone says that they received something "for free"? Free can be an adjective or an adverb. It's not a noun.

When people say "I could care less", they should really be saying "I couldn't care less".

Ryan (PrOxLaMuS©) added vortex generators to his car. I think he found the parts on ebay. Search on posts by PrOxLaMuS© with "vortex" in them and I'm sure you'll find it.

I think Armand may be on the right path here. As I read his post I remembered that last summer a friend doing upgrades on his 71 had the same symptoms and in the end it was the length of the pushrod that caused him all his grief.

Tony D, I'm totally open to adding the resistors in, and in fact am leaning towards it. I think I have a heat-related issue with my drivers (I may not have used enough thermal grease). Adding the resistors would be the easiest and probably most reliable way to fix this. Like I said above, I don't yet have an answer to how using resistors on low impedance injectors affects opening time. I suspect it's not a lot of impact, but would prefer to work off fact than supposition. If Z-ya can measure it, that would be great! BTW, I think people are hesitant to use the Datsun resistor pack, at least I am, because I can't easily buy one. But, looks like RS has one that is non-inductive. http://www.radioshack.com/product/index.jsp?productId=2062288&cp=2032058.2032230.2032267&allCount=100&fbn=Type%2FPower+Resistors&f=PAD%2FProduct+Type%2FPower+Resistors&fbc=1&parentPage=family

No worries Ron, I already am familiar with PWM and how it's used with Peak and Hold injectors. This thread keeps going down that path while what I"m really trying to learn is how the opening time for a peak/hold injector is affected if a current limiting resistor is used instead of the MS PWM. In other words, pretend I was using a version of MS that didn't support PWM so had to use a resistor (let's say 6 ohm) with low impedance stock turbo injectors. I'm guessing the opening time would be longer. How much though? If it's only 0.5 - 1.0 ms, then it's no big deal, but if it's a lot longer, then that could be a real problem, especially at higher revs.

On my 73 the front line runs underneath the prop valve, but is not in any way attached to it.

Just to clarify, the front line does NOT go through the stock prop valve (although it might look like it does - check it out up close). The brake differential switch (I think that's the proper name) is mounted on the driver side fender not far from the MC. All this does is sense if there is a significant difference in pressure between the front and rear brake lines and if there is, a switch closes and lights the brake light up on the instrument cluster - like you wouldn't already have noticed that the pedal went down further and your brakes don't work so well Of course, both the front and rear lines need to go through it, but there is no reason to remove it unless it's leaking.

Thanks for the clarifications. My real purpose in asking this question is to learn how adding a current limiting resistor to a low impedance injector will change its opening time. My guess is it will slow down, but by how much?

Good point. I was assuming using the stock FPR. Perhaps someone who sent their injectors out for cleaning/testing can check the report that came back?

I think the NA injectors will run out of capacity as soon as you add the turbo. I was seeing 85% duty cycles with 225 cc (stock NA is only 180) on my NA with cam at 5000 feet elevation at the last track day. I can't see the stock NA injectors keeping up with any kind of turbo without leaning out when it's most likely to cause damage.

http://forums.hybridz.org/showthread.php?t=126218 This thread got me thinking about the pros and cons of using resistors vs. the PWM capabilities of MS. In particular, has anyone measured how using a resistor with a low impedance injector changes (if it does) the opening time of the injector compared to using the PWM capabilities of megasquirt? As I understand it, MS doesn't limit current to the injector for some user-defined period and then switches to pulse width modulation (fancy way of saying it quickly switches the voltage on and off to limit the average current level). In theory the unlimited current should allow the injector to open faster, but I wonder if in practice the difference is significant, or even measurable? I ask because I've found that even with the PWM setting of 25% after 1.5 ms using stock turbo injectors on my NA engine, after long periods of WOT at the track I sometimes see resets. I finally dropped the PWM setting down to 20% and think it's ok, but I wonder how much margin is left. I suspect the power transistors in MS that drive the injectors are overheating and causing the resets. If adding the resistors doesn't have much, if any, affect on opening time, I might just add them as insurance. Anyone else experienced this?

A boy and a girl around 6 or 7 with mom up front almost fell out of the window giving me thumbs up the other day at a stop light. I'm sure they had no idea what kind of car they were looking at, but they knew they liked it. That says something about how our cars have a timeless beauty to them.

Although I like Matt's idea best, another approach is to drive with the tuning window open (TuningVE Table 1). At the moment you want to make an adjustment, press the "F" key which locate the cursor on the cell closest to the current settings being used. You can use a combination of "shift" and "up arrow" or "down arrow" to adjust the VE value on the fly. I find it a quick and dirty way to make near-real time adjustments while driving. But be careful not to take your eyes off the road. With laptop on the passenger seat, I can feel the keys without looking. I'd suggest practicing before going out on the road with other cars.

I was a bit off in how I was reading the delay in megalogviewer. The correct way is to drive with a light steady throttle and then nail it to WOT. Then go look at the log and count how many cycles there are between opening the throttle all the way and the AFR changing. For me it turns out to be 2-3 cycles. Previously I was looking at how long it took for the AFR to change when I suddenly closed the throttle. I think the problem with that approach is that by closing the throttle there is no longer much exhaust flowing and hence it's not a true sample of the delay.

Yes - been there, done that. But you may find that it's not the seal itself, but the seals that go between the rear main bearing cap and the block. When I rebuilt my engine the first time, I did a poor job getting the cap sealed. I thought it was the rear main seal and replaced it in the car, but that didn't solve the leak. Luckily (yeah right) I had a chance to rebuild it a second time, and this time paid extra attention to getting those seals in. Haven't had a leak since. I'm not trying to talk you out of it, just saying that it may not be the rear main seal. And I don't think it's practical to R&R the rear main bearing cap with the engine in the car.

What do you think of the centerforce clutch? I've read both good and bad. The consensus I think is that it's ok for a mostly stock NA, but doesn't hold up much better than a stock clutch to hard launches. Just curious how you're liking it so far. $120 for a new 3 core radiators sounds like a very good price!

I'm no turbo expert (being NA myself), but if you're starting with a NA motor recently rebuilt, do you know what type of pistons were used? If they're dished then I suspect you could probably run mild boost, but if they're flat top, then I doubt you can run much if any. Turbo experts - chime in.

The stock compressor from a later (80 - 83 zx) and its bracket will install nicely on the driver side so you don't have to mess with the alternator. You should be able to find one in a JY in the Bay area. That's what I did with my '73 and the original dealer-installed system. On the freeway it's cold enough to drive with the windows up and remain comfortable. While you're at it, put a 90's Honda Civic blower motor in to increase the airflow. It moves more air and makes less noise.

60-65 psi when cold doesn't sound high to me at all. I see ~70+ (based on the gauge which we all know is less than accurate) when cold and when the RPMs are up. Are you concerned that 60+ psi is higher than you used to see before the rebuild? Perhaps your bearings and/or oil pump were worn giving you lower than normal oil pressure, and now that your engine is in good condition again, this pressure seems too high? Based on the numbers you state, I don't think your oil leak is due to excessive pressure, probably improper installation of the seal. The rear main seal is a pain to install.

On this site and others I've seen the turbo injectors listed as having 265 and also 280cc/min flow rates. For my N/A motor either way it's enough, but the anal retentive side of me would like to know which is the correct value. What's the consensus?

Thought I'd post an update. I went ahead and installed the MSA front camber bushings. On the alignment rack it turned out that the left could go all the way to 1.1 degrees neg while the right could only go to 0.6 neg. So we dialed the left back so they would both be the same. Turns out I have more in the rear than I thought (-1.4 left, -1.9 right). I must have some tweak to the chassis - big surprise in a 35 year old car with 230k miles on the chassis. I took it back out on the same track and things were much improved. While the tires were cool the car was very balanced. It was only loose when I wasn't smooth or made sudden changes with lift throttle in turns etc, - things I know I should avoid My initial tire pressures were 28 front/24 rear. As the tires got hot, the push came back, but nowhere near as much. I put 2 more pounds into the front and I think that helped a little, although it's hard to tell. Tire temps were within 15 degrees across the tread. One big difference is tires: previously I was running Yoko ES100, now I'm running Kumho MX which definitely have more grip. I think if I could get that last half degree of neg camber up front I'd be very happy with the car's balance for my use. I suppose the simple fix would be to slot the right front strut tower. But I'm thinking I may take it to a frame shop and see if they can't improve things. All in all, I'm very happy with the results of the camber bushings, and the improvement was well worth the modest $$$ spent. On a side note: I have to say that now all the big work of "building the platform" is behind me, I'm really enjoying fine tuning the car and my driving to get the most out of it. For example, I found that by braking and turning a little earlier on a few 3rd gear sweepers, I could carry more speed out as well as not abuse the tires as much. I guess "slow in - fast out" really is true

At 4500 rpm, the engine takes ~13 msec for 1 revolution, or ~26 msec per complete combustion cycle. I'm guessing that you may be running out of time to get enough fuel delivered with those injectors, even though the graph says your PW is only 19.5. This assumes you are running 1 squirt and simultaneous firing. Plus, at the top of your rev range, your duty cycle is 99%. I think you're right - you need to go bigger.

I think some people have gutted the drum prop valve to remove its function from the circuit, but not have to deal with finding metric threaded unions for the brake fittings that would be needed if you took the whole prop valve assembly out.