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280 engine mod into 240Z


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I am currently considering rebuilding a 280 motor for my 240 Z.

I have a 280 turbo motor and was seeking information on intalling 240 rods into 280 block and milling dished pistons .105 inch to make flat tops.

Does any member have experience in performing this modification? DISADVANTAGES?

I am planning on using the P90A head (hydraulic lifters) with stock 240 carbs and manifold.

I welcome any and all comments and suggestions to how and what to do to make an inexpensive, fun, and durable motor. I would like to keep this motor all stock or original parts from exisiting model years.

I also need some suggestions on a camshaft for this setup. I can't find any specs on the original turbo cam. Will this cam perform good as a street cam? or should I just count on purchasing a new cam?

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Why do you want to mill down your pistons, is it to save money ? i would advice you not to go that way, if the rods is from your original L24 and it is a matching block, you should keep it as is with the car.

Flat top pistons can be purcased for a price around $200 and you can have your cam send out for re grind at Delta for a price in the $80-90 area, you will not want to use the turbo cam in a N/A motor.

I recently got pistons from Northernautoparts.com send Rick Schroeder a mail and he can give you a quote rickschroeder(a)northernautoparts.com.

Unless you use a BIG cam you will be fine with stock carbs and manifold, maybe get some other needles.


Some cam specs FYI http://www.atlanticz.ca/zclub/techtips/cam/index.htm

Edited by ChrisZ
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I am not tearing down my 240 engine. I have spare 240 rods from another engine. I don't know what I will put this motor into for testing if I follow through with this.

The reason to turn the dished 280 turbo pistons is that normal flat top 280pistons cannot be turned .105" with out getting into the ring groves.

The reason for the 240 rods is because they are .105" longer than the 280 rods. So the pistons will need to be shortened .105 ", they become flat top. Also the piston will have the ring pack moved up on the piston by .105", which is similar to a racing piston configuration.

This makes a 280 long rod motor. Why the effort? cheap stoke parts and should run better than a regular 280 flat topped piston motor. Added hp by improved geometery in the wrist pin rod crank angles.

Also the milling of the pistons is much less than buying new pistons, about $50. Also dished pistons aren't in a huge demand,-- are they?

What I'm interested in is "Is there anyone that has researched or performed this modification before? I'm thinking it is worth a try.

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I get your point on this and i don't think it is worth the efford, if you want a long rod motor that can rev, you should de stroke a L28, using crank and rods from a L24.

What i know is based on searching, reading and more searching and reading and i have also read some place that milling down dish top pistons will take of some of the strenght, still i have no experience, just a thing i wouldn't do.

If you have 9 millimeter L24 rods, they can bring in something like $100, its just what i would do.

I'm supriced that no one else have chimed in on this, maybe you will have a better chance of getting a answer if you jump over the fence to hybridz.com, its more the style there, but please fill us in if you have any interesting news on this subject.


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If you only feel like experimenting go for it. Otherwise why go through all the effort ? You said it makes the pistons more like a ''racing piston'' then you are using a head with hydraulic lifters ? The turbo head is a low compression head also. Why not get some flat top pistons from a f-54 non turbo engine? The turbo cam will work fine with SUs , it will make more torque on the low end but will fade at high revs. Some like the stock turbo cam for a street driven Z with SUs for that reason. I contemplated that cam for my Z.

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The only thing I'd really be worried about is proximity of the top compression ring to the combustion events happening above it.

I measured approximately 6.2mm between piston top and top ring on a spare L24 piston I have lying around. I won't have a spare dished 280 piston to measure until next week, but removing 2.667mm of material is quite significant. You said that if you removed this much material from the dished slug that you'd be closer to a “racing piston configuration” Is this going to be a racing motor with a racing motor's longevity?

Edited by blue 72
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