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240 vs 280 for RB26DETT project, your opinion ?


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Hi Guys,

 

As a project car I am looking into a 240z or 280 now, even 260 is an option. I have used this forum to find most of the differences between the 2. But still can't decide which chassis would be the best start. I want a RB26dett swapped in.

 

Car will be used as street car for fun and occasional race car, certainly not a daily car. Initially I preferred a 240z, series 1 or 2, since those are the originals, less weight, less extra's etc. But the 280's are easier to find in good condition (all I care about is the body, rest (engine etc) will be swapped anyway), and they have a stiffer (but heavier) chassis to start with.

 

Some cosmetic differences could be changed, such as the 280 bumpers, since i prefer the 240z look.

But in terms of the RB26DETT swap, what would the better route? 240 or 280?

Other then finding the 280 easier in good condition, what are the REAL benefits for such a project?

 

Any opinion, ideas or comments are appreciated.

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I debated about this a lot before doing my RB and I too preferred the look of the older bumpers.  It is easy to obsess about the little differences from year to year.  I would focus more on condition and less on which model.  It is easy enough to back date a 280 to closely resemble a 240.   It is less easy to do thousands of dollars in rust repairs on a 240 that was not a good restoration candidate but you talked yourself into buying it because you were mesmerized buy the chrome bumpers.  johnc has a great sticky in the chassis section on what improvements need to be done to make a z capable of handling a high horsepower motor.  There really isn't much more that you don't have to do to a 280 that you will have to do to the 240.  I did the RB26 with upgraded turbos and other modifications.  That motor is total overkill for a Z chassis and results in an excessive and costly amount of unusable horsepower.  You should consider an RB25, but if you have to have the RB26 it would be hypocritical of me to question your judgment because it was pretty awesome.  :)

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Any chassis will require chassis stiffening. The 240 more so then the 280 but either will be twisted into a pretzel by a rb without it. In my first version of the rb 260 the bone stock rb26 i had in it started to twist the chassis. The evidence was above the 1/4 windows. Waves and cracks in the body told me i need to put in a decent cage before i did anymore damage. 

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For purposes of mating the rb, a key difference between 240 and 280 is the stock transimission mount.  Based on my experience and memory, the 280 stock trans mounting points in the tunnel make for a better platform to build a cradle style trans mount for the rb25 trans.  In my Series 2 240z, the trans mounting points are two ears on either side of the tunnel.  The stock trans cradle mounted to threaded inserts on the underside of each ear.  The rb trans mount sits back a few inches (depending on mounts) from the intersecting line of the stock mounting points.  I made a crude mount out of box steel.  The mounting points are offset; that places a moment force (torque) on the mount both from the normal force of the trans itself and from the torque of the engine under load.  Looking at what others have done mounting the rb trans into the 280z, this problem is avoided.

 

As far as power goes, my stock rb25det powered S30 boarders on stoopid fast.  Its somewhere in the 260 hp at the crank range.  It doesn't take much in a 2,400 pound car.  

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Im making probably easy 625whp at 14psi on a rb30/26 240z with the bad dog frame rails and a nice rust free chassis that i stitched welded. So far so good on the chassis but I do plan on putting a roll bar in it. I havent mounted slicks on it yet but i am running 295 kumno XS series which are kinda sticky for street tires. Plan on running about 25 psi in a higher gear/mph and will probably upgrade to the Zforce wide rear flares and 17x13" tires.

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