OCG35

iTrader: (2)

you mean "heads" not "headers" right?

KhanMan

iTrader: (2)

Yes that is what I mean. I guess I rushed it a little.

nismology1

idrive_MD

iTrader: (8)

glad this thread popped up, I've always been curious about this myself, not so much being put into a Z/G, but with all these 240SX+VQ swaps I've been waiting to see if anyone would take the plunge. All i've seen really are vq30+vq35 parts, straight up vq35de's or vq30+vq35HR parts and then up from there everyone jumps into Infiniti V8's or LS1/2.

I even thought the same when companies started making stroker kits, I thought to myself, "wouldnt it just be cheaper to use a 4ltr Frontier VQ bottom with a Z top on it?"

I nominate somone with much more money, time and resources than me to do this!

Skrilla

iTrader: (15)

unfortunatly I haven't been able to compare the hr to the DE but since both motors still have wider bores than strokes the rods speeds shouldn't be an issue. While rod speeds measured against bore and stroke are not exact, it still gives you a good picture. I've done far more extreme on less sofisticated blocks.

Skrilla

iTrader: (15)

I would have to disagree on 2 points since rod ratio is in direct correlation to high rpm ability NOT combustion chamber filling. High rpm combustion chamber filling is necessary for high rpm power which is done by large bore short stroke and nothing at all to do with rod ratio. Rod ratio is simply engine geometry at work. The vq35 at 95.5 mm x 81.4 mm vs. the vq40 at 95.5 × 92.0 mm rod ratios are 1.771(vq35) and 1.813 (vq40) respectively making the vq40 rod ratio inferior to the vq35. The good news is the result is so negligible that upgrading to the vq40 would still provide a huge improvement to tq and hp. The engine efficiency would decrease by such a miniscule amount it’s not worth mentioning. The new possible power would grow from 287 (or 276ish in new SAE rating) to about 310hp (or 300ish in new SAE rating) at 6500 rpm redline(stock of coarse for the vq35de). An extra 1000 revs would be night and day in terms of power and safe provided you have the valve train that can handle it. Since this would involve a hybrid motor might as well do the valve springs at the very least. This would definitely be worth looking into

On a side note, My 97 talon I revved to 7800 rpms with 87.5mm bore and 101mm stroke. The rod ratio was so horrible it would make you cry. The block was from a '98 dodge stratus and naturally aspirated it choked, literally, beyond 6500 rpms. The only reason it was viable was from the turbo. Fortunately the vq40 still has a rev happy design so this isn't a problem that would occur and I wouldn't see why it couldn't continue to make power up to 7500 rpms with the vq40 block and vq35 heads and some reflashed ecu

NismoZ123

iTrader: (2)

Couldn't you install just the 3.7 or 4.0 liter crank, and/or rod and/or piston set.

And keep the existing block/heads...? Much easier to work with I'd think.

http://www.nismo.co.jp/en/products/c...RS/380rsc.html

nismology1

So how exactly can a higher rod/stroke ratio be better for high RPM ability yet not have a direct effect on cylinder filling?


I will respectfully disagree, although not in principle since we basically agree on how rod/stroke ratio affects where an engine is naturally happy. I will attemp to the above question though. A higher rod/stroke ratio results in, unequivocally, longer dwell time at and near BDC. This gives the inertial intake charge more of chance to fill the cylinder without the piston starting to push back up in the bore. It also efftively reduces side loads on the piston and increase dwell time at or near TDC which gives the flame front more time to travel to the edge of the cylinder before the cylinder comes down the bore. All three of these factors help make an engine what it is. There's a reason nissan went with a taller block and longer rod with the HR/VHR series.



You can't say one is categorically better than the other. Just depends on what you want.

nismology1

.....

Skrilla

iTrader: (15)

Good point, that statement is so true, these kind of talks can be very informative. I didn't really consider this for a couple reasons though. I've found the nature of wide bores/short strokes helps wiith the cylinder filling, as does dwell, however in cars with variable valves that can control their overlap and duration. There is signifigant enough blow through from intake and exhaust valves staying open simultaneously that when the exhaust valves are slammed shut the air is slammed into the cylinder. This is the case with the DE. Most modern cars with variable valve technology have now fixed this problem

I would have to disagree. We happen to be discussing how the high rpms of the 3.5DE cylinder head would affect the 4L block, so the smaller rod ratio is unequivocally the best option for what you want lol.

nismology1

Wider bores tend to be accompanied by larger valves. Shorter strokes tend to have longer rods. Both aid high RPM power production.


Well most cars still don't have cam-changing VVT technology implemented. It's either variable phasing or (in rare cases) variable lift but the duration stays the same. But I'm not quite understanding what you're saying about the air being slammed into the cylinder. Pardon my ignorance. :P



Again, nissan went with a longer rod in the HR/VHR for a reason. You are still somehow under the assumption that a lower rod-ratio is better for high-RPM power.

Jeff92se

iTrader: (4)

I'd assume you could get your motor up and running with the oem ecu tune and then dial it with an Osiris tuner or and the dyno shop?