Project 350Z: Building a New Engine - Part 1

by Mike Kojima

Our Project Z was a pretty good example of what a naturally aspirated VQ35DE could do. However, our  VQ had become old and tired. It was worn out from a lot of minimal maintenance street miles, track days, drift and professional stunt driving practice and had started to develop some rod knock.  Luckily we were able to stop before serious damage to the engine internals resulted.  However an engine rebuild was in order. 

Our objective in building this engine is not to build the most awesome NA VQ possible or even to get tons more power, but rather to perform an economic build to address some of the VQ's durability shortcomings, replacing stock parts when necessary with some good quality aftermarket bits.

This way the car would be plenty durable and reliable for lots more track days and drift practices with a new beginner driver!

Want to read more about our Project 350Z?

VQ35DE rods are prone to fail.  Nissan knew the stock rods were weak and improved them some for the later rev up motors and significantly for the latest HR variants.  At more than 7200 rpm or 350 hp, rod life is pretty problematic. Since we wanted our engine to rev to 7700 rpm safely we had to do some upgrading.  We chose to go with some off the shelf rods from K1 Technologies. We feel that K1 rods are an excellent value and are of course much better than the stock rods. The K1 rod itself is machined from a forged 4340 steel billet.  4340 is a heat treatable alloy steel similar to chrome molly, having nickel, chromium and molybdenum as alloying agents to give it roughly double the strength of regular steel with a higher nickel content making it stronger and tougher with a higher impact resistance.  These properties make 4340 an ideal alloy for connecting rods. The rod is first machined then solution heat treated.  This heat treating greatly improves mechanical properties such as the tensile strength of 4340 steel.  Solution heat treating makes the alloy homogeneous where all of the atoms in the material effectively become a solid solution during the treatment making the alloying elements evenly distributed around the part.
Another cool feature of the K1 rods is the use of high strength 3/8" 200,000 psi tensile strength ARP 2000 rod bolts. K1 does not skimp here one bit!  These premium bolts have asymmetrical threads for more thrust engagement for better torque consistency.  
Stock VQ35DE rods are prone to fail at the rod bolts and in the beam below the pin. The K1 rod is an H Beam profile which is resistant to bending and fatigue. The rod is much stronger in the beam than stock  while at 528 grams, is nearly 100 grams lighter than stock at the same time. The rods small end is bronze bushed and the rod machined so the sizing can be held to plus or minus 0.0001 and the weight within one gram per end.  Those are exceedingly tight tolerances!  After machining to shape and heat treatment, the rod is shotpeened which can improve fatigue strength by over 100%.
We selected some of JE Pistons 11:1 shelf pistons.  These are standard off the shelf parts that are in stock and are easily and quickly available.  JE forged pistons are made of tough 2618 low silicon aluminum alloy.  This alloy is tougher than typical high silicon alloys found in cast and some forged pistons.  Low silicon aluminum expands more with heat so they must run wider clearances.  Typically 2618 pistons are noisy, in the worst cases, they sound like a diesel engine especially when cold.  We have found that JE has their skirt profile so speced out that even with a low silicon piston using wider clearances, the engine will run quiet and clatter free, even during initial start up.
Page 1 of 6 Next Page
Bookmark and Share
Monday, July 13, 2015 11:37 PM
Nothing I love more than a Kojima engine build article. Man those PPE headers are nice.
Tuesday, July 14, 2015 6:51 AM
Any power goals that you are hoping to reach? NA VQ builds always seem something fairly outlandish as far as output per $. Will be good to see one built right from the start. Please tell me that one of the parts of the story will be dyno testing the cosworth intake vs. the use of intake spacers.
Tuesday, July 14, 2015 1:10 PM

I hope this isn't just about peak power. It isn't always about peak power, especially under the constraints of NA. Sometimes its more important to get good power faster, or time-to-peak power. A good NA makes decent power, but more importantly does it with less mass, i.e. inertia. So, you rev faster, AND higher. This makes your power more accessible, easier-to-use, and you get it faster. I also believe they are more reliable than boosted motors.

If you were in a gunfight, would you rather have 6 rounds on a .45, or 16 rounds on a Glock?
Mike Kojima
Mike Kojimalink
Tuesday, July 14, 2015 4:17 PM
Read the second paragraph.
Tuesday, July 14, 2015 7:46 PM
I'm curious to hear how the spec clutch holds up. In my years of internet surfing, I haven't been left with a very positive image of them.
Tarik Laaraj
Tarik Laarajlink
Tuesday, July 14, 2015 9:21 PM
This a capable motor.
Not sure why you chose this over an hr though?
Mike Kojima
Mike Kojimalink
Wednesday, July 15, 2015 12:38 AM
We considered an HR swap but it was too expensive for a car that is basically a somewhat low buck thrasher track day, drift day stunt practice car. It is not a competition car that needs to be ultimately fast. The HR swap would require an engine, a wire harness and an ECU which would need to be adapted to the car. It would also need a different hood and some minor fabrication. We also considered changing to HR heads but it would be just as impractical.
Wednesday, July 15, 2015 9:52 AM
What would the HR swap need fabrication wise?
Wednesday, July 15, 2015 8:18 PM
Too bad you couldn't throw some ported heads on. More low hanging fruit that doesn't sacrifice reliability or longevity. I don't pay much attention to what these make, so I'm curious to see a full pull. I suspect it'll be a nice improvement. Any reason you didn't go with the Spec aluminum pressure plate? It has a replaceable wear surface like the flywheel. I put a full aluminum setup on my Z06 and love it, no drive ability issues at all.
Mike Kojima
Mike Kojimalink
Wednesday, July 15, 2015 9:35 PM
Exhaust and intake for dual TB's and MAF plus hood
Mike Kojima
Mike Kojimalink
Wednesday, July 15, 2015 11:06 PM
Answer is read paragraph 2, it's a budget build with durability in mind. Headwork adds to the cost and lag time of any project. Finding a good cylinder head person that can turn things around quickly is hard. Also the HR head flows so much better, it's silly to waste much money on the DE head and if the budget was too low for a HR swap....
Friday, July 17, 2015 11:49 AM
I can see having to do some fab work for the intakes... but can't you just get the headers from PPE for the HR? I know the y-pipe is interchangeable between the DE and HR, so with the right headers it should bolt right on. Then the hood is just bolt on...

and for the intakes, you can prolly start with something aftermarket made for the HR and do a couple mods to get it to fit
Mike Kojima
Mike Kojimalink
Friday, July 17, 2015 4:46 PM
To be clear once again this was a budget build and the owner of the car did not want to spend the money for an HR swap.
Saturday, August 08, 2015 10:04 AM
I can't wait to see how this turns out. I've been wanting to build my NA DE for so long now. This article will be a very helpful guide.
Tuesday, September 27, 2016 4:02 AM
Hello. What was the result of switching the JWT C2 intake cam for a JWT C8 ?
I would like to do a cam work for my 350Z, don't know what would benefit the most between JWT C2 intake & exhaust or C8 intake and C2 exhaust.
Mike Kojima
Mike Kojimalink
Tuesday, September 27, 2016 10:42 AM
If you check out the later article when we dyno it, you can see the power gains, we were octane limited. The C8 needs pistons with more valve relife. The C2 is the biggest with the stock pistons.
Tuesday, September 27, 2016 12:46 PM
I saw the whole article and it was very interresting.
I am on a budget, and my goal is to make the car more enjoyable all accross the powerband but i do not plan on changing the internals ( exept cams.)
I think i will go for JWT C2 only then. When you had only these, were you happy with the overall gains ?

Thank you for the quick answer btw, more than 1 year after the last message i did not expect it tbh.

What would you think my power output would be with
- Motordyne 5/16 spacer
- JWT c2 cams
- PPE headers
- invidia gemini

Thank you very much anyway :)
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Partners:

© 2018 MotoIQ.com