2jz block bored out with 1jz crank?

[Marotta1]

Just boring out will not get you much displacement gain at all. The benefit of using a 2jz block would be you could use longer rods with the same short 1jz stroke. In so doing you could build yourself an even higher revving motor than a regular 2jz, or just a less stressed motor. Longer rods with the same short stroke put less stress on the crank and rods due to lower rod angles. It's a smoother/smaller less jerky motion.

You can get the same or sometimes higher piston speed with less stress on components. Long rods with short stroke can reduce peak piston velocity & acceleration and thereby inertial loads on the rod and crank bearings. There can be less cylinder sidewall stress as well. A long rod can minimize rod angles and thrust load and friction losses at the piston skirt.

[Poodles]

Would require custom pistons, and overall it's a waste.

[IJ.]

"Siman school of automotive design and engineering".....

[rayray]

with rough calculations there IS a rod angle difference of about 12-14% and about a 2-3% difference in crank angle (based off what info i could find on 1j/2j rod lengths) when comparing this long rod 1jz vs a standard 1jz. this will decrease the stress on some parts and on cyl walls somewhat...

but again, without increasing stroke or bore (again assuming stock 1j crank and standard bore on a 2jz block), you are talking about one helluva an expensive 2.5L engine. if you want to have anywhere near 3L, you're probably better off modifying a 2JZ crank or making a new one altogether to utilize a longer rod and shorter stroke using 2JZ components.

and by changing all of this, you are also affecting other characteristics of the engine as well

[rayray]

i found this too, which may or may not help your decision. i don't know if this calculator is accurate, but i found mine to be within a degree or two chicken scratching on the back of receipts.

http://2.3liter.com/Calc2.htm#PistSpeed

according to that calculator there is probably going to be less than 4% improvement in negative piston acceleration and a slight increase in piston accerlation during positive piston acceleration at/near TDC at 9000rpms. unless you plan to rev the piss outta the thing, it is likely you won't see much of an improvement in reality.

also keep in mind, with stroke being constant, a short rod will have faster piston speed near TDC and slower at BDC. a long rod will be the opposite with it being slower up top and faster near BDC. so changing the rod and so forth will also change other characteristics of the engine... not just making the engine "higher revving"

my 2 cents is that although intriguing, the costs totally outweigh the benefits... but that's just me

[Poodles]

It's still more mass moving around as it's a longer rod. It's completely pointless.

[rayray]

another good read http://www.stahlheaders.com/RodLength.PDF

[Mark Conte]

a 2j block with (assuming unmodified 1jz crank) is basically a taller 1j with no difference in stroke of that of a standard 1j

if you keep bore on the 2j and 1j the same in this case, and the only thing changing between the two is the crank, the only thing you're changing is the length of the stock 1jz rods to suit the deck height of the 2j. you end up with a taller, heaver 1j that will have identical stroke and bore of a stock 1j.

if you're aiming to get more stroke with a 1j, you're better off starting with a 2j. if you want a short stroke with increased displacement, bore out a 1j.

Usually the deck height of a 2JZ is 8.621" FYI (give or take around 1-3 thou)

and it's not just the bore that is changed on a 2j block to achieve 3.4L. if it were that simple everybody would have a 3.4L. rod length and stroke (as well as bore) is changed.

theoretically even if you used 90mm bore pistons in a 2j, you would only achieve 3.28L

the same theoritical 90mm bore magical piston in a 1j would only get you a whopping 2.74L... again changing bore only.

Rod length on "3.4" liter 2JZ's stays the same @ 5.590", the stroke goes up to 94mm - 3.701" and the pin goes up to a honda-spec 1.181"

[rayray]

didn't know the rod length on a 3.4L stayed the same. so the center to center is identical to stock? well i guess if you're moving the pin instead that makes sense. i assumed the opposite