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Leon's Other 260Z


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#21 JCan

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Posted 02 February 2013 - 01:41 PM

Leon, I am afraid I am going to be a bit long winded now...  Apology in advance...

 

Attached are two screen shots of an excel spreadsheet we assembled for the car we are building.  Given torque as a function of RPM (what we expect to get out of our build) and the gear ratios w can assemble optimum shift points and can plot HP as a function of Speed (assuming I am racing the car).

 

Please take a look at the spreadsheets ---  

 

Since I know my tire diameters, rear end gear ratio, and transmission ratio, and can look up what other people have measured (torque vs rpm) I can take a look at what the optimum shift points are for my car.  The first spreadsheet shows (from right to left) RPM, Torque, HP, then left to right, the speed the car would be traveling if it were in 1st gear, 2nd gear, ... 5th gear by knowing the speed and Engine RPM then looking up the available HP (in the right).

 

First thing, notice the knee in torque at 5500 RPM (I expect the engine I am building will not knee until 6000 rpm, but I am being conservative here).  The loss in Torque causes a loss in horsepower at 6000 RPM.  A wider torque curve would greatly improve overall HP.

 

Your car has webbers ( a 6 pack right? )  Well your torque curve comes up much faster in the low end then mine does using SU carbs.  You can model this here also.!

 

Lastly, lets take a look at the last plot.  In this plot I plotted the available HP as a function of RPM  you can see the HP dips / each represents a shift point.  In addition, I compared the car as is with a different rear end (one with 4.11:1 gear ratio).  Notice the low end HP improvement!

 

What happens if I swap out the stock rear end for one which has 4:11 gears.   Notice we get 160HP at the tires at 20MPH in first gear (4:11 gears) instead of 35MPH at first gear (3.5:1).  This little change should make a BIG difference to quarter mile and off the line times.  Again, note your webbers have more torque at the low end then my SUs so your results may be difference. Which means, if I want my car go go faster, the easiest thing to do is to change gear ratios instead of farting around with trying to eek out another 5HP.

 

This is a long winded way to say:

 

            - The L24/26/28 are magic motors and one thing they have is their ability to be perfectly balanced throughout all RPM.  Take advantage of it! 

                     o balance your motor

                     o understand how your modifications will effect torque

            - Take top down approach to building your car and understand how your car will respond to each modification you make

                     o sometimes your best modification are gear ratios

 

If you want a copy of my spreadsheet, send me an email and I'll forward it to you.  James.Canyon@gmail.com

 

 

Attached Files



#22 Leon

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Posted 02 February 2013 - 03:23 PM

Wow, Jim! I really appreciate your long response and for sharing all your work. Looks like you have a great plan for your build!

 

I also have a quite involved spreadsheet with dyno plots, gear ratios and tractive effort curves, letting me get the most out of the engine and gears. All of that is thanks to the previous owner, who was my Vehicle Dynamics prof!

 

The tractive effort curves show me the optimal shift points, based on the force available at the wheels. The "perfect" shift is when your tractive effort matches with the gear you're upshifting to.

 

Luckily enough, these engines are internally balanced and resilient to 1st, 2nd, and 3rd order harmonics. Gotta love straight-sixes! As you've implied, the crank and clutch will be balanced individually, and the pistons and rods will be weighed to make sure they match each other. Looking forward to seeing you work and meeting sometime!

Thanks again, Jim. ;)



#23 JCan

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Posted 02 February 2013 - 05:06 PM

Vehicle dynamics prof?  Leon, you are a sleeper!  Send me your spreadsheet, maybe I could learn from it!  Also, if you have a good book on vehicle dynamics  I would appreciate the name as I might be able to thumb through it and get a better understanding of automobile engines etc.  ( I did measure in general engineering in college and took the basic engineering courses, thermo, statics and strengths of materials etc).

 

In the mean time, tractive effort curves...  I'll look them up!

 

My spreadsheets are rudimentary as I made them up in an effort to ensure the car I am building does NOT have tremendous HP from 0-60 (as after all I am handing it to my 16 year old son) yet allows me to add a few tweaks once he gets older to increase the fun factor!  (notice the gear ratios are really high, I used SU carbs, the cam is a mild cam which destroys low end torque - yes the bad side is that after the engine hits 35mph, the car should be a rocket however brian's primary driving will be below 50 mpg (mostly streets).  

 

 

Jim 



#24 Leon

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Posted 02 February 2013 - 05:34 PM

Vehicle dynamics prof?  Leon, you are a sleeper!  Send me your spreadsheet, maybe I could learn from it!  Also, if you have a good book on vehicle dynamics  I would appreciate the name as I might be able to thumb through it and get a better understanding of automobile engines etc.  ( I did measure in general engineering in college and took the basic engineering courses, thermo, statics and strengths of materials etc).

 

In the mean time, tractive effort curves...  I'll look them up!

 

My spreadsheets are rudimentary as I made them up in an effort to ensure the car I am building does NOT have tremendous HP from 0-60 (as after all I am handing it to my 16 year old son) yet allows me to add a few tweaks once he gets older to increase the fun factor!  (notice the gear ratios are really high, I used SU carbs, the cam is a mild cam which destroys low end torque - yes the bad side is that after the engine hits 35mph, the car should be a rocket however brian's primary driving will be below 50 mpg (mostly streets).  

 

 

Jim 

 

I'll PM it to you. ;)

 

Race Car Vehicle Dynamics (Milliken and Milliken) is the chassis bible and Internal Combustion Engine Fundamentals (Heywood) is the engine bible as far as I'm concerned. Both are fantastic books.

 

I hope your son drives the Z responsibly, you're putting a lot of thought and work into this. I like your design intent!

 

Here's a good example of a tractive effort curve:

 

trans%20Gear%20Tractive%20Force.gif



#25 JCan

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Posted 02 February 2013 - 06:22 PM

Interesting topic.  Ive been reading about tractive effort and tractive resistance at:  http://www.thecartec...tive Effort.htm  .  It is going to take me a couple days to absorb what I am reading.  Basically we are optimizing the amount of Force (N) applied to the wheels and picking the optimum gear ratios to deliver this force on a level road taking into account rolling resistance  air friction, and effective wheel diameter (rubber tires are lossy as compared to steel wheels).  

 

You know, I have always thought of the 240z as a variable displacement engine.  IT seems to me that one could design an optimum gear ratios for fuel economy AND also take account the cars max performance.  Therefore we could have one set of curves with the optimum RPM being low (2500 rpm) optimizing for economy and a traditional set of curves with higher RPM say 6000 RPM optimizing Force applied to the wheels, (tractive effort)

 

Regarding Brian (my son).  I think he has a level head and is rather deliberate with his actions.  As he has completely reassembled each part of the car (with help from me of course) he has a lot of pride in it and doesn't want to damage it.  Brian will only drive the car for the next two years, as when he goes away to college, the car will stay here (we do not allow our children automobiles at college).  Once he graduates, I will put the car in his name and he will be free to upgrade it as he sees fit...

 

Thanks for the introduction to great resources (Books) and this topic of Tractive effort.  I am sure (over the next couple of months) to add this newfound information to my understanding of the car.



#26 Leon

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Posted 02 February 2013 - 10:51 PM

Tractive effort curves represent all RPMs, it's basically the engine's torque curve. Hopefully my PM helps!

 

Setting the ratios to match fuel economy and optimal TE at max RPM is probably not possible unless the engine has a totally flat torque curve. A properly done L-series will have a fairly flat torque curve but optimal ratios for max TE and max mpg will still be different. Maybe not by much, but different. Setting gears for mpg will create wider gear ratios (higher load at lower RPM = good mpg) and a deeper overdrive (again, lower RPM and higher load) than something designed for the track. To clarify, the engine operates more efficiently at higher load, a wider open throttle being the main reason.

 

I'm sure you can sense the difference when driving various cars with manual gearboxes. Economy cars are geared noticeably differently from sports cars. My Accord hates accelerating but gets great mpg because of wide ratios.

 

Sounds like your son has a great head on his shoulders and you did a fantastic job of raising him. :2thumbs:



#27 Leon

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Posted 03 February 2013 - 12:25 PM

When I picked up the Z, the PO gave me a bunch of paperwork and documents along with it, including old manuals. A 1973 FSM was one of them, and despite its ravaged condition it's nice to have. Then, last week I saw an ad on CL for a 260Z FSM! The owner (REALLY nice guy!) drove up to my place last night and hands me not only the 260Z FSM but also a 280Z FSM. The generosity was much appreciated!


Attached File  DSCN1676.JPG   108.47KB   38 downloads



#28 Perfect240z

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Posted 04 February 2013 - 11:29 PM

Lucky dog!

#29 EvilC

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Posted 09 February 2013 - 02:58 PM

Remember I was joking about picking up 260z cars at the same time?

 

http://forums.hybrid...-final-version/


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#30 Leon

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Posted 10 February 2013 - 04:51 PM

Remember I was joking about picking up 260z cars at the same time?

 

http://forums.hybrid...-final-version/

 

That is sweet, Clive!



#31 EvilC

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Posted 10 February 2013 - 05:06 PM

Thanks!

 

Will be fun.


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#32 Six_Shooter

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Posted 10 February 2013 - 05:16 PM

If you ever want to sell that '73 FSM, let me know, I'd love to have one to go along with my '73.


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#33 JCan

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Posted 10 February 2013 - 05:18 PM

Leon... your going to sell it to me... right?  (just kidding)



#34 Leon

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Posted 10 February 2013 - 06:31 PM

If you ever want to sell that '73 FSM, let me know, I'd love to have one to go along with my '73.

 

Leon... your going to sell it to me... right?  (just kidding)

 

:lol:  If I decide to sell it, I'll let you guys know!



#35 spitz17

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Posted 11 February 2013 - 03:17 PM

Great pick up Leon. Can't wait to see it in person sometime!


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#36 Leon

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Posted 11 February 2013 - 03:26 PM

Great pick up Leon. Can't wait to see it in person sometime!

 

Thanks Glenn, can't wait to put it back on the road!



#37 Leon

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Posted 23 March 2013 - 11:14 AM

It's been a while...

 

I found a machine shop for the engine rebuild, turns out every Z owner I've met recently take there engines there (Baca's Machine Shop)! I've also sent the tail-light bezels off to be re-plated about 3 weeks ago, should be another 2-3 weeks until those are back. In the meantime, I'll be painting the tail light panels and stock mirror to close-to factory color. They were painted satin black by the PO.

 

Today I paid for a Datsun Comp 3.9 R180 CLSD after searching for STi R180s for a little while. Hopefully I'll see it in my driveway within a week. Should make for a nice, classic street combo: L28 with triple 45s, late ZX 5-speed, and 3.9 CLSD. :D



#38 JCan

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Posted 25 March 2013 - 08:52 PM

Leon.

 

WOW - CLSD plus 3.9:1 plus higher gear ratios from the 5 speed... very nice!

 

Regarding your tail section and grill section.  I had mine powder coated satin black.  They turned out looking just like new.  and the cost was rather inexpensive ~ $50.  

 

I'll show off a picture below.

 

Jim

 

 

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#39 Leon

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Posted 26 March 2013 - 06:38 AM

Nice Jim, looks awesome especially with the silver paintjob!

 

Just last weekend I picked up some spray paint from the local auto parts store, it's some sort of dark grey. I forgot what they called it but I believe it's a trim color for Nissans. It looked close enough to me when I was looking through the paint section. I figured if I don't like the color, I can just repaint! Powdercoating sounds like it might be a nice option that I hadn't thought about, so thanks Jim. ;)



#40 Leon

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Posted 30 March 2013 - 12:39 PM

Diff came in on Thursday! I finally had some time to unpack it and put it up on the bench after doing some cleaning this morning. I got a tip from a local racer as far as diff shops go. Apparently, the place to go is SF Differential in South City, so I may be paying John a visit. :)

 

DSCN1832_zps2b8c8d04.jpg

 

DSCN1834_zpsdebf71f5.jpg






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