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Z20 build


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#41 flatcat19

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Posted 23 November 2017 - 01:37 PM

I'm not going to win this argument.

 

I won't claim that long rods are the answer to world hunger, but when building an engine package that dots all the i's and crosses all the t's, everything needs to be addressed. A Ford exec famously said about the K-code 289, something to the effect that these are for people who want no stone left un-turned in the hunt for power.

 

Don't knock it til you've tried it. More importantly, don't discourage others.


You can't hang if your nuts haven't dropped...it's physics


#42 datzenmike

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Posted 23 November 2017 - 02:45 PM

Not discouraging anyone. Want to know if this theoretical gain is worth chasing for a few HP. Racing engine builders do some crazy stuff for a few HP that most would easily say is 'not worth the trouble'. If you look up the rod/stroke controversy it's certainly unclear. They say anywhere between 1.5 and 1.8 is fine. The pros have lots of esoteric theory but not much fact about it. So we're back to 'racing engine' vs what most people build. In the real world if you were rebuilding your L20B with a Weber, an L16 exhaust, a ported closed chamber head and a mild cam head just how much gain would you see by finding 6" rods and pistons from a 200sx? I'm guessing not much unless you go multiple carbs, header, cam bla bla bla and turn it up above 7K. So in a way I would be discouraging some from the bother and expense if the end does not justify it. I'm not building a 'racing engine' just to take advantage of a longer rod is all.


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#43 flatcat19

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Posted 23 November 2017 - 03:11 PM

When you have less than 90hp to start...only a few extra hp is a huge gain.


Anything that helps the dick swell, amiright?

You can't hang if your nuts haven't dropped...it's physics


#44 datzenmike

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Posted 23 November 2017 - 04:28 PM

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#45 Stoffregen Motorsports

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Posted 23 November 2017 - 06:27 PM

Mila Kunis makes everything alright. Thanks Mike.

 

If you think they might not be worth the trouble, consider the trouble. At the worst, you're looking into a set of custom pistons. A lot of guys do that anyway as OEM's or good aftermarket pistons become hard to source. It boils down to pennies when taking into account the whole engine package. A good set of aftermarket pistons will cost you $200 to $300. A custom off-the-shelf piston (which is the case for long rod L4 pistons, since so many engine builders have paved the way with their own R&D, and many piston MFG's have those designs on hand) will run about $400 to $500 for the set. For the extra $250, it's worth it. As I said multiple times in the past, it smooths out the power curve, so your actual gains are not unsubstantial (double negative).

 

A set of used N85 rods (making a long rod L20B, Z20, 2200, 2300, etc) can be had for pennies if you score at the wrecking yard.

 

Flatcat said it better than I would have, any swelling of the dick is a good thing. Amiright, amiright or amiright?



#46 wayno

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Posted 24 November 2017 - 11:08 PM

This mod is probably the most important to ensure a long engine life. It's very easily accomplished by shortening the slots in the distributor cam so the mechanical advance is limited. You can weld the holes a tiny bit and file them smooth to get the proper total advance.

 

Springs should not be the only thing that limits total advance.

 

I don't know what Jeff charges to go through a distributor, but I bet it wouldn't cost more than a hundred bucks to get the advance limited.  If you can find a SSS distributor cam, that's a bolt in operation. When I was at Rebello, we charged about $150 for a full distributor recurve and rebuild.

 

I could likely do something like this, and then test it on one of my drivers engines till I got the advance where I wanted it, i will have to go back thru all these posts to find out what the total advance should be as I think I read that somewhere.

I expect it would be better guess rather than do nothing at all, I can always pull it apart and weld more or file what I did down till I get it where I need it.


 

 


#47 Stoffregen Motorsports

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Posted 25 November 2017 - 08:57 AM

Your total ignition should be about 32 degrees. Initial about 12 degrees. I simply remove one of the springs that hold the centrifugal weights, but then you have to make sure there is enough tension on the one that's left so the distributor cam doesn't flutter at low engine speeds (When the centrifugal force is low).

 

Doing it the way you described is totally fine, a little bit at a time, but if you wanted to get it right the first time, simply print out a paper degree wheel from something you find online. Slip it over the distributor cam and move the mechanical advance then look at the paper degree wheel to check how much movement you get. Should be about 20-25 degrees of travel. Maybe less.



#48 wayno

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Posted 25 November 2017 - 09:51 AM

Your total ignition should be about 32 degrees. Initial about 12 degrees. I simply remove one of the springs that hold the centrifugal weights, but then you have to make sure there is enough tension on the one that's left so the distributor cam doesn't flutter at low engine speeds (When the centrifugal force is low).

 

Doing it the way you described is totally fine, a little bit at a time, but if you wanted to get it right the first time, simply print out a paper degree wheel from something you find online. Slip it over the distributor cam and move the mechanical advance then look at the paper degree wheel to check how much movement you get. Should be about 20-25 degrees of travel. Maybe less.

 

OK, so how I seen it in my head was welding the end of some slots(never had one apart), but then you say to just remove a spring which at first totally confused me, then I realized that if one was already out then the other one would only let it advance half as much, is this correct?

Is there a way to either tack weld it or a way to make the one without a spring solid where it cannot move at all maybe half way out so the balance is not as messed up?

Is the balance more important at low or high RPMs in this situation, in my head I see it being balanced at high RPMs as better as I suspect it spends most of its time there anyway.

Are all Nissan distributors basically the same, I have a couple junk distributors I don't care about I could pull apart, also is the napZ distributor the same as the Matchbox or is it advanced electronically by the ECU?


 

 


#49 Stoffregen Motorsports

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Posted 25 November 2017 - 10:22 AM

No. The way it's laid out inside, there is a distributor cam, which has two wings on the bottom. Each wing has a slot to guide the pin connected to the two weights (one weight per one slot). Then there are two springs, one connected to each weight. The springs don't limit the travel, they set the speed at which the travel occurs, so if you remove one spring, the advance happens more quickly.

 

The reason there are two springs is to allow the timing to creep up on total advance instead of having it come in early. This was undoubtedly a way to control emissions. The balance, as you call it, from the factory does not take full advantage of the engine's desire to have more timing at lower RPM's. It's too limiting, or stiff.

 

I suggest you take one apart and have a peek for yourself. All you need to do is remove a breaker plate and have a look. Once you see for yourself, it will make sense.

 

I forgot you had a matchbox distributor, and I can't remember ever using one, so I'm just guessing that the mechanicals inside are the same.



#50 datzenmike

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Posted 25 November 2017 - 10:56 AM

The Z series NAPS have vacuum and mechanical advance identical to the L series. Only the later '86 Z24i got the CAS.
 
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Above this is the magnetic rotor and single piece dual output module.

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.


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#51 Stoffregen Motorsports

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Posted 25 November 2017 - 11:03 AM

Thanks for the pics, Mike.



#52 datzenmike

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Posted 25 November 2017 - 01:26 PM

Some later modules have 4 connections. One for power, two for the negative side of the coil and a 4th that when grounded by a vacuum switch disables the exhaust side plugs to reduce engine noise under heavy load. Now normally a dual plug system needs less advance so suddenly switching to single plug would also reduce power, it would run retarded, but the module somehow increases the timing on the remaining intake plugs to compensate.

 

Seems like you could wire this is in regular advance, set your timing and have a vacuum switch that turns on the retard mode during hard acceleration or boost applications to prevent pinging. The difference is built in I would immagine and may be 5-8 retard degrees?

 

The Mileage Option Z20 has a special knock sensor in the block and a detector circuit that retards the timing. This one may vary the retard, I don't know.


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#53 wayno

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Posted 25 November 2017 - 06:45 PM

OK, so I have to shorten them slots a little on the outside as doing it on the inside could throw other things out of sync like the idle timing.

If I were to guess I would say around a third of the slots need to be welded up, maybe a quarter, and then the metal faces need to be cleaned up, nice and smooth as possible, then use some kind of degree device to see where I am, I want 12 to 15 degrees welded up.

This is likely something I could do to the work truck also, it knocks if I have it advanced any more than 2 degrees when I time it, if I were to weld up maybe 8?/10 degrees I could likely go back to the stock timing specs.


 

 


#54 datzenmike

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Posted 25 November 2017 - 07:31 PM

Why not just turn the timing retard a couple of degrees?
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#55 wayno

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Posted 25 November 2017 - 08:43 PM

Why not just turn the timing retard a couple of degrees?

 

Were talking about 10.9 to 1 compression ratio on the LZ20 according to you, most on here that have raced or do race say I am going to have to do something as it is going to knock/ping.

The work truck just barely knocks sometimes/intermittently, that is what I can hear, I expect it knocks/pings and I don't hear it and I am at 2 degrees before TDC now, when the cam was timed wrong I didn't have these issues except when it was very hot outside, then it would barely knock when going up slight grades, if I floored it or let up it would quit knocking/pinging, now when I floor it it just keeps on knocking/pinging, I suppose I could dial it back to 1 degree BTDC or TDC, or maybe I can take some of the mechanical advance out of it and be able to set the timing back to where I am used to it being, 6/8 degrees BTDC, as it doesn't seem to be working all that well the way it is, as I drove it with the cam timed wrong for several years without issues.


 

 


#56 wayno

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Posted 25 November 2017 - 11:40 PM

Well I pulled apart a Z24 distributor this evening and it didn't come apart easily, likely because it has been out in the scrap pile for a while.

Lot of stuff in there but I finally made it to the Plate/weights/springs, even with the springs loose that plate don't like to turn, but I would imagine when it is spinning it worked fine as the weights were easy to move with my finger.

That is not a lot room to work with in them oval holes, they are 3/8ths of an inch long and the pin is an 1/8th by itself, so that is a 1/4 inch movement of which I have to fill just slightly over a 1/16th inch of it.

Also when the weights move out do they change the timing evenly or is there a curve?

Looking at it, to me it looks like the farther it moves the less/slower the timing changes.


 

 


#57 datzenmike

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Posted 26 November 2017 - 06:45 AM

Some have dual springs wayno. A shorter one that adds to the main spring as it extends so the advance isn't linear. Also the weight and shape of the weights affects the advance curve. As the weights move they rotate and swing a lesser? mass outward.


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#58 Stoffregen Motorsports

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Posted 26 November 2017 - 08:26 AM

I think you should check what you have before you make any changes, Wayno.



#59 distributorguy

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Posted 27 November 2017 - 11:43 AM

High compression like that I'd set it up for 16 BTDC at idle, 30-32 total mechanical by 3200 or so rpm.  Its difficult to get that right without an accurate Sun machine that has a recently calibrated tachometer.  

Likely you'll need to weld about .040" in the shorter slot.  Maybe a hair more. 

Our race engine runs 24 at idle, 28 total.  The practice motor at 11:1 is set up as I described above.  Scalded cat!  

 

Quick calculation:

the advance weight pin travels in the slot .0143" per degree of distributor advance.  The distributor will advance half of what you see at the crank due to the doubling effect of the timing gear set.  So for 8 degrees in the distributor, = 16 mechanical at the crank multiply that figure by 8 and weld up the difference from your slot with the weight in still in it.    



#60 datzenmike

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Posted 27 November 2017 - 01:54 PM

High compression needs a shorter burn time so less advance. Or do you mean 8 crank/16 distributor degrees?


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