Nissan QR25DE Torque Plate

Extreme Engine Tech: Jim Wolf Technology's Turbo Nissan QR25DE Powerhouse Part 2

By Mike Kojima

When we last left off on our QR25DE project, Jim Wolf Technology was well on the development path for our motor with new rods, pistons and the removal of the balance shafts.  JWT still had a few more tricks up their sleeves to help the motor make more power and to improve its reliability that we will get into in this installment.

Follow our project here!

Modifed Turbo Nissan QR25SDE
This groove leads to additional holes in the main bearing to give the rod bearings and crankshaft a more continuous supply of oil.  The bearing has been polished and WPC treated as well.

QR25’s are known to have problems with spinning rod bearings.  The rod bearings are on the small side in diameter and width and don’t have much surface area to bear load and to support full hydrodynamic lubrication.  JWT did several things to improve this situation and hopefully cure the problems.

Modifed Turbo Nissan QR25SDE
The rod bearings were polished and WPC treated.  Tests show that WPC treatment can increase the bearing load capacity by as much as 25%.

First off as discussed in our last installment, JWT eliminated the balance shafts.  This helps ensure that the oil pump gets only unaerated liquid oil instead of foam.  Cutting off the balance shafts' oil supply means that there is more oil available to be fed to the rod and main bearings.  Next JWT modified the oil passages feeding the main bearings.  As the rod bearings are fed via passages in the crank from the main bearings, oil flow from the main bearings is critical.  In stock form, oil is fed from a single hole in the main bearing to the hole in the crank that feeds the rod bearing. We also used the late model rod bearings.  The quality of the rod bearings was upgraded after a rash of failures of stock motors under warranty.

Modifed Turbo Nissan QR25SDE
These grooves in the main saddles help feed those additional holes in the main bearing over more degrees of crank rotation.  This gives the rod bearings much more oil.

JWT machined a groove in the main bearing saddle in the block and drilled additional feed holes in the main bearing so the rod bearing can have an uninterrupted flow of oil to it for nearly 360 degrees of crank rotation. Next the rod bearing feed hole in the crank was chamfered and tear dropped.  This helps ensure that oil can find its way into the hole instead of getting squeezed out of the sides of the main bearing.  Hopefully these mods will cure the QR’s penchant for destroying its rod bearings.


Page 1 of 5 Next Page
Bookmark and Share
Tuesday, July 27, 2010 10:11 PM
Great article as usual Mike !
Wednesday, July 28, 2010 4:04 AM
Awesome write-up, I cant wait to see this beast fully done up. I love the idea of mapping the boost in the lower gears, can it be done in any turbo set-up?
Wednesday, July 28, 2010 5:13 AM
Well written as usual, but I have a few questions.

1.) Does undercutting the main bearing not give you the willies? How much experimentation did JWT do to prove this is safe?

2.) Similarly, did you use the later model oil pump to accommodate for the lost oil volume from the oil squirters? How much oil do they actually flow? At what pressure do the Honda squirters open up? Longevity mods seem counter intuitive in a race engine with no harmonic damper...

3.) Can you actually buy an Altima without AC? I didn't know you could buy anything without AC any more, lol.
Wednesday, July 28, 2010 5:42 AM
My question is regarding the replacement of the crank damper with a lightweight pulley. Everything I've read from reputable sources suggests that running an inline-4 without a tuned damper can be disastrous for the life of the main bearings.
Wednesday, July 28, 2010 6:53 AM
Don't get Mike started about light weight pulleys LOL! There's actually a thread in the MotoIQ forums where we discussed this quite a bit.
Wednesday, July 28, 2010 6:55 AM
I am with ab0z on this one. Everywhere I read, people say that removing the OE crankshaft pulley (which in most cases has damper inside), ruins the crankshaft bearings quicker.
Can you shed some light on that Mike?
Wednesday, July 28, 2010 7:23 AM
Mike has been using them for years without problems.

Mike Kojima
Mike Kojimalink
Wednesday, July 28, 2010 7:27 AM
All good questions, Without writing a whole bunch, on an inline 4 don't worry about it unless it spends a lot of time past 8k which most OEM dampers are not tuned for anyway. The RTR World Challenge Sentra didn't have a damper and had an even smaller pulley.

Grooving the backside of the bearing saddle will not hurt anything, we don't do stupid stuff, Nissan also did this on the 54C SR20DET.

Adding piston coolers are not for longevity, but survival on a turbo road race engine that does it for more than a quarter mile at a time. We are using the latest version of the oil pump and that engine uses coolers.
Wednesday, July 28, 2010 12:59 PM
will the oil coolers from the later model QR bolt up to an earlier model QR? Or do you have to modify the block?
Mike Kojima
Mike Kojimalink
Wednesday, July 28, 2010 1:24 PM
You have to machine the block to use them.
saturn racer
saturn racerlink
Wednesday, July 28, 2010 8:38 PM
how much of a pain in the ass would it be to increase the deck height via a spacer, sleeves, and a custom timing chain cover and chain? would such an undertaking be worth it? OS Giken does it with their RB stroker kits, but those are timing belt engines.
Thursday, July 29, 2010 5:41 AM
Are those the piston squirters from the DET, KA motor? Where did you source them from?

Nice article, great approach (as if I'd know lol). . Like a lot of people I was pretty pissed when the QR25 showed up in place of a SR20VE or even a revised KA24DE, seems as much motivated by emissions, economics/shared platform issues with the huge #'s of Altimas out there. Very interesting how you are addressing each strength/weakness of the QR25 I'd never have the resources to do this, which keeps me completely away from owning car with any performance aspirations with a QR motor, that and its notorious long list of problems. Too bad because the Spec V chassis seems pretty good. But I don't buy Nissan for lack of reliability, stock QR just seems like a gentrified attempt addressing the KA24DE power/weight/flow issues and avoiding using an SR20VE - which would have made that a kick-ass car OEM. Things like the egg-beater balancers, etc. all seem to be addressing shortcomings of the original design (crank/lower end design, weak rod bearings, etc). The KA24DE was a better motor in some ways, reliability not the least of those. Heavier, yes, but having seen some pretty high powered KA builds there, at least other than weak pistons (which you'd pull for FI anyway), it's a tough motor. The car would really have been an OEM screamer if they offered the Altima SE-R version of the VQ35DE...which probably makes zero marketing sense given the arrival of the 350Z and the V6 Altima.
Mike Kojima
Mike Kojimalink
Thursday, July 29, 2010 5:57 AM
Going to a deck plate introduces a whole new set of reliability issues although it would be cool to have a taller deck in this motor, a decent rod ratio would make it less thrashy and longer lived. I don't like sleeves, they are hard to seal and add a bunch of integrity issues to the block. It seems like 50% of sleeved motors eventually spring leaks or at least must be torn down and redecked, sometimes several times before they settle.

The K Motor has a lot of problems as well, mostly deck seal with more than 20 psi in things more rigorous than 1/4 mile and dyno passes. Next is block failure due to harmonics at more than 7500 rpm with real use. At more than 500 hp they get pretty sketchy. Matt Powers has to take it easy on his turbo K drift car, at more than 500 hp it is super unreliable.

Thursday, July 29, 2010 6:00 AM
Sorry, that came out kind of accusatory. I guess I was asking more how experimental THIS motor was regarding the main bearing undercuts. I'm sure you guys and Jim Wolf wouldn't want to field the demands from 500 dudes wanting undercut main bearings if they weren't willing to do it to a customer motor.
Mike Kojima
Mike Kojimalink
Thursday, July 29, 2010 9:40 AM
The backing plate of the bearing is steel and around 0.080 thick, its pretty strong. The groove area is small and its on the top side where its not going to have a huge compressive load. Plus this has been done on many other OEM applications by other manufactures. The SR20VE does this s well.
Thursday, July 29, 2010 12:52 PM
@ Steve: In this case the squirters are sourced from a Honda B18C. In the article Mike also mentions that the squirters that later model QR motors came with could be used as well.
swed 66
swed 66link
Wednesday, October 06, 2010 12:33 AM
Hello, nice building you are doing. I have a question regarding the head gasket
have you purchased it from a Nissan dealer in the U.S., with the three layers? you have the part number? In Sweden we get it with two layers of Nissan Europe. I work at a Nissan dealer in Sweden and part number I ordered
Best regards Sune
Saturday, November 20, 2010 6:21 PM
What is considered late model on the rod bearings in the qr25?
Mike Kojima
Mike Kojimalink
Saturday, November 20, 2010 6:41 PM
B16 or 2007 plus
Kyle 01
Kyle 01link
Friday, July 14, 2017 11:56 AM
Hey, i was wondering how this build ended up? I was looking for part 3 and could never find it.
Post Comment Login or register to post a comment.

MotoIQ Proudly Presents Our Partners:

© 2018 MotoIQ.com