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4 minutes ago, Captain Obvious said:

Yup, I'm an electrical engineer.

And I don't usually read the directions either.  LOL 

 

 

I went to Georgia Tech.....tried M.E., but when I got to Fluid Mech and Thermodynamics, I switched to Industrial Management. I needed to work on my selling skills 😜

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Haha!! I understand completely.

I went to Penn State, and the EE department forced all the other disciplines to take one introductory electrical class for non-EE majors. Every one of the other disciplines had to take it, and every one of the students universally hated it. So... By the time I got there, the ME department had retaliated and made the other disciplines take one introductory ME class for non ME's. It was thermo and fluid flow, and of all the classes I ever took, I think I despised that one the most.

Now that I have identified so many automotive related applications, I'm sure I could get much more out of it. But at the time, it was pure torture.

It was even rumored that sometimes people would swap... Your ME friend would take your thermo test for you and you would take their Intro to Circuits tests for them. Not that I ever participated in anything like that, of course.   :ph34r:

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Yeah, That's the Kameari tensioner that I see mentioned in threads about this topic, and the only problem with it seems to be the price. Nice piece of engineering:
jj32-10_4.jpg

 

So in summary, here's the issue in a nutshell...

When you remove material from the bottom of the head, it brings the centerlines of the cam and crank closer together. With the cam and crank closer together, the valve timing becomes retarded and the chain has more slack.

One solution to these issues is to shim the cam towers upwards and use either longer valves or thicker lash pads.

Another solution is to account for the timing change using an adjustable cam pulley, and adjust for the chain slack with a different tensioning design, such as the Kameari tensioner.

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32 minutes ago, Reptoid Overlords said:

I am having a bit of a time finding the cam towers /valve spring shims..

Sent from my N9130 using Tapatalk
 

What do you need, specifically? I have a ton of parts I'd love to get gone. Unfortunately they are earley towers, N47 is the most recent. Let us know!

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56 minutes ago, Reptoid Overlords said:

I am having a bit of a time finding the cam towers /valve spring shims..

Sent from my N9130 using Tapatalk
 

datsunspirit.com

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Man I didn't even think about Datsun Spirit. And with all those beautiful engine build threads. I was looking through Motorsports online site(another good bunch)and only saw spacers for. 040 on the cam towers.

I'm looking for cam tower spacers/valve spring spacers/valves to match. 080 shaved P79 head.

Sent from my N9130 using Tapatalk

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I ended up going with the cam tower spacers and valve spring shims from Datsun Spirit.  The polished valves look real nice, but I opted for OEM style 44mm/35mm valves from Rockauto.  When I e-mailed Datsun Sprit's contact on their webpage with some questions about what to get, I got a reply from Eiji himself.  On a Sunday no doubt. 

http://datsunspirit.com/shop/cam-tower-spacers-080-2-0mm-copy/

http://datsunspirit.com/shop/swirl-polished-valves-44mm-35mm/

image.png

image.png

 

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I had 2mm shaved off my N47. I simply lined up the sprocket triangle to position #1. To do this I ended up moving 1 full link.  The tensioner took up the slack. It was on a well worn engine.

I would recommend repositioning the slack side chain guide to take up some slack if possible.

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I didn’t know that you could take 2mm off of an N47 head. Are you sure you got valve clearance with an .080 cut? 

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51 minutes ago, Diseazd said:

I didn’t know that you could take 2mm off of an N47 head. Are you sure you got valve clearance with an .080 cut? 

It runs nice.  Pistons are dished. 32cc Compression with C Cam is ~ 190psi.

 

cc2.jpg

chamber.jpg

DSC09877.JPG

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Now that the dust has settled with my broken camshaft project, I'm trying to get back to my F54/P79 motor.

I was messing around with the handy-dandy Atlantic Z engine calculator app found here:   http://www.atlanticz.ca/zclub/techtips//calcs/engine builder/index.html     and I can't get it to give me the correct compression ratio. The FSM says the F54/P79 combo (used in the later ZX NA cars) yields a compression ratio of 8.8:
_ZX specs1.jpg

But using the calculator app, I don't get that result. I get 8.43 instead:
_enginecalc1.jpg

I get 8.43 instead of 8.8. What am I doing wrong? I know some of the numbers (like the head gasket thickness) is off a little, but not enough to explain my delta.

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It does look like an error in the FSM though, the calculator is close for the dished pistons, using 1.25 mm for the gasket.  7.353.  One of those CR's has to be wrong.

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I got the chamber volume "off the web". That 53.6 is the number that "everybody uses". Of course, because of that, I cannot attest to the accuracy.

So I've been messing around with the calculators a little more, and I believe they messed the math up some. I've got an excel spreadsheet with my own measurements and calculations and I get pretty close to that 8.8 using data that I measured or derived myself. When I use my measurements in my spreadsheet, I get 8.86. I have not measured the chamber volume myself, so some small differences there could explain the remaining discrepancy.

I do not think they are calculating the uncompressed volumes correctly. Also, my measurement of piston stick-up above the block deck back-calculates to a significantly different pin height than what they're using.

Edited by Captain Obvious

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I just did the calc and it seems very close to the tool.

Some subtle points are:

  • On compression stroke, the volume of the gasket is reduced by the piston protrusion into it.
  • On the Intake stroke, the piston top is not 79mm down from the block but 79 mm down from its top when protruding.

Here are my calcs. Attached is the XLS.

image.png

image.png

P79 Comp Ratio Calc.xls

Edited by 240260280

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Yes, I understand those subtle points, and that's where some of the problems are. For example... If you change the pin height spec in the calculator here>>   http://www.atlanticz.ca/zclub/techtips//calcs/engine builder/index.html 

The compressed volume changes, but the un-compressed volume does not. It's a bug. It's not accounting for the fact that the piston height at the bottom of the stroke is raised as well.

I'll clean up my spreadsheet some and maybe post my numbers.

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Well if you're going into the code... Here's the other things I came up with.

First, I think the pin height used for the L28 flat top pistons is incorrect.  When I put my pistons at TDC, they stick-up out of the block by .021 inches. I'm assuming Nissan's target was 0.5mm there. So whatever you need to do with the pin height to make that piston pop-out number work out to 0.5mm.

Also, I measured the thickness of a used head gasket to be 0.047 inches (1.19 mm). I measured the thickness of a brand new one to be about .052 (1.3mm), so there's some crush there when the head is torqued down.

Other thing I found is that the piston holes in the head gaskets are elliptical, not round. I measured the holes on a used gasket to be approx 3.440 by 3.505 inches (87.4 x 89mm) . Sure you can average those two numbers to something in between to make the end result close to correct, but I think it would be better to use real numbers.

I also measured the holes on a brand new L28 head gasket and got approx. 3.447 x 3.516  (87.5 x 89.3mm), so the piston holes close down some as the gasket gets crushed. That makes sense too.

Anyway, if you're going under the hood, there's some other things to think about.

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So while were talking about this stuff... Has anyone here actually measured the chamber volume of the P79 themselves? The online calculators use 53.6 cc, but can anyone here attest to the accuracy of that number?

I've not measured it myself, and I don't currently have the equipment.

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