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Jim Wolf Technology's Turbo Nissan QR25DE Powerhouse - Part 1

By Mike Kojima

Due to some rather unfortunate decisions within Nissan's corporate structure, the QR25DE engine has found its way, probably by default to the top of Nissan's product line up as its flagship performance 4 cylinder engine.  The QR25DE is found in the B15 Sentra SE-R and Spec-V as well as the ultra hideous Sentra B16 SE-R and Spec-V.  In North America, the QR is also found in the Altima, Rogue and as a base Frontier truck engine.

 

 Nissan QR25DE rod vs SR20DE
It is easy to see how the SR20 rod shown above on the left is much stronger than the QR part.  Look at the general lack of robustness of the QR25DE part on the right and note the thinner rod bolts. The stock SR rod can easily withstand 20 psi of boost and over 400 hp stock.  That cannot be said of the stock QR parts.

We have a love/hate relationship with the QR25DE.  We felt that Nissan completely missed the boat with the engine's first iteration which was released in 2002.  The engine had a lot of torque and a wide powerband, but the power output trailed it's competitors such as the Honda K20A, K24, F20 and F22. The QR did not have the delightful high revving fistfuls of power that these Honda engines made, nor the boat anchor robustness of the Toyota 2AZ-FE. The engine's low, class trailing 6100 rev limit simply hamstrung it from a power perspective and made the engine very unrewarding to drive.  The engine was surrounded by controversy from its first release, starting with Sport Compact Car Magazine's discovery and publication that Nissan had seriously stretched it's power claims.  This was confirmed by owners who independently dyno tested their own cars.

QR25DE open deck block
The QR25 has an open deck.  Although this offers improved cooling, open decks often suffer from cracked cylinder walls, poor head gasket sealing and cylinder flexing when subjected to high boost and increased rev limits.  We are not planning for high boost levels or really high rpm so we did not bother to sleeve and close up the block deck like many Honda tuners do.  Sleeving blocks with integrated decks also creates issues with block structural integrity and flex which often hurt bearing life and ring seal so we are going to first try to see if we can make the engine live without sleeves.

The QR25DE seemed to have been released before development was complete as the QR initially was plagued with horrendous design related quality and reliability problems that were so bad, they completely tainted the halo image that the Sentra SE-R had made with enthusiasts over the years.  The QR's problems were unheard of as Nissan has historically always had a reputation of releasing solid, industry leading engines with exceptional performance and durability.

QR25DE block vs SR20DE block

Compared to the late great SR engine family, the early Nissan QR25DE has a spotted history as a performance engine.  In the performance world it has earned a reputation for being fragile and the many recalls that Nissan has had for serious problems from blowing head gaskets to blowing rods out the side of the block has furthered this reputation.  The engine's redeeming features are a cylinder head that flows extremely well, a light overall weight and a strongly supported crank and lower end. A fragile engine is not going to work for our time attack Spec-V so we are going to address the engine’s weak points and see if we can turn the QR into a solid performer capable of racing levels of performance and reliability.

QR25DE VS SR20DE rods and pistons
When comparing both side by side, its easy to see that the SR20DE rod and piston on the bottom are much stronger than the QR25DE parts on top.  Compare the thickness of the rod beams.  This is not entirely a result of poor engineering.  The SR20DE was designed to be a robust turbocharged engine while the QR25DE was designed to be lightweight for its displacement.

 In 2006 Nissan revamped the QR with many improvements, mainly those which strengthened its reciprocating parts allowing a higher 7000 rpm redline.  This much improved engine also made considerably more power.  This is how the engine should have been in its initial release and if it had been so, the B15 Sentra SE-R Spec-V might have become a lovingly adored vehicle like its predecessors.

Nissan QR25DE block
The QR block makes extensive use of external ribbing to strengthen it without excessive weight.  The QR25DE at 2500cc is 500 cc larger in displacement than the 2000cc SR20DE while weighing less, a significant feat.

Jim Wolf Technology, perhaps the top Nissan tuner is North America was drafted for our engine development program.  JWT brings over 25 years of Nissan experience to our program. We immediately decided that the engine had to be turbocharged for reliability.  The QR25DE has a long 100mm stroke and a short 143.05mm rod with an 89mm bore. Its 1.43:1 stroke to rod length ratio is the worst of any production engine by far.  Obviously this engine was designed for low end torque with no regard for controlling piston speed. 

QR25DE bedplate
The QR block features this bed plate which firmly holds the crank in place.  This is much stronger than the traditional main bearing caps that most engines use and is a feature usually found only in racing engines.  The bedplate supported bottom end is one of the QR's best design features.

To make power naturally aspirated would mean significantly increasing its low 6100 rpm redline.  Long stroke/short rod engines have difficulty staying together at high rpm.  The RTR World Challenge SE-R would go through 3 engines per race weekend.  As we don't have a factory works team budget; to ensure reliability, we decided not to exceed 7000 rpm.  With such a low redline we would have to turn to forced induction to make power.

Nissan SR20DE crank vs QR25DE crank
The QR crank on the bottom, is only half counterweighted compared to the fully counterweighted SR crank pictured on top. The SR crank's counterweights are easier to see here.  A fully counterweighted crank is less stressed by torsional vibrations at high rpm.  A bad feature of the QR crank is the lack of overlap between the rod and main journals.  This means that the crank is stroked to the limit and is weak in the area between the journals.

 

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Comments
AlexSpecV
AlexSpecVlink
Wednesday, January 20, 2010 3:25 PM
Great article! Though, correct me if i'm wrong but i think its only the 2007+ with the updates to the QR. I have an 06 Spec V and my limit is still 6100 and i still have the Balance shafts (trying to save up for the JWT Kit).

Will the 07+ crank fit without modification to a 02+ block? Also are the pistons/rods that JWT prototyping here being made specifically for the QR with an 07+ crank? Will they work for the older QR crank?

I'm glad to finally see someone starting to get some support to the QR and to help those that own one to find their weakpoints beforehand.
Ben
Benlink
Wednesday, January 20, 2010 4:11 PM
Ugh! I know they work well when built right but.... I am really hoping the QR gets the ax soon. I already jumped ship for a K20A3.
Mike Kojima
Mike Kojimalink
Wednesday, January 20, 2010 4:30 PM
Alex, my bad, I made a mistake, it is 2007 and later. The late model crank needs a different signal wheel and we will get into this later.

Our base block is a older one so it will all fit.
Big J
Big Jlink
Thursday, January 21, 2010 2:33 AM
The cranks, headgaskets, connecting rods (way better design), pistons (higher compression), rings, bearings, etc. will all swap w/o issue. So will some other trick stuff in the head. I'm sure that'll be getting written up later.

The cool parts are found in the QR25DE with the "6MT" designation. The crank is specific, as are the rods, and pistons. The new "6MT" rods have bolts designed to take the higher tensile loads due to the jump from a 6200 redline to a 7000 rpm redline, and the cross section is much better also.

Isaiah
Isaiahlink
Thursday, January 21, 2010 4:14 PM
Best Engine Ever Made!!
urbanjacup
urbanjacuplink
Friday, January 22, 2010 3:03 AM
Mike you're definitely the leader of the QR Cult...those familiar know the potential is there, with a lot of work...Nissan mislead consumers with the SE-R badge back in 2002 and continue to with the B16...Its no longer a badge with a standard, its just a badge that might sell more cars...

Still, you'll find a small contingent of owners who have done some pretty interesting builds with the QR. Along with yours, my interest remains and continues my love hate relationship with this car...

cbjmw45
cbjmw45link
Friday, January 22, 2010 8:46 AM
do you guys know if there is info on a successful swap of the new qr into a b15? if anyone has any info please send my way. i am would be interested in attempting this before trying to piece together my current engine when it finally needs a rebuild\upgrade work. mike great article and thanks for all your dedication put forth to educate the community.
Mike Kojima
Mike Kojimalink
Friday, January 22, 2010 8:55 AM
Its been done many times before.
sticky667
sticky667link
Friday, January 22, 2010 9:34 AM
I think he was asking about the entire lump...rumor has it that the block casting and mount points are different.

side question: Do you know if Clark ever messed with any N/A QR parts? I've finally got those QR20 pistons and the crown is pretty large compared to the stock QR25 piston. Justin calculated ~12.4:1 on a stock B15 motor.
Mike Kojima
Mike Kojimalink
Monday, January 25, 2010 1:23 PM
Big J is the guy you want to ask about that. He is mulling over destroked QR's. He is on this forum all the time.
sticky667
sticky667link
Monday, January 25, 2010 5:50 PM
ya we talk pretty frequently, just curious if Clark ever did anything with an N/A motor
trailbrake2088
trailbrake2088link
Monday, April 05, 2010 7:12 PM
I can't understand why people hate the b16 so much? I love it. Anyway how did they increase the rpm's on the new qr25's with such a high piston speed?
Mike Kojima
Mike Kojimalink
Monday, April 05, 2010 7:16 PM
Um, the article explains all that in quite a bit of detail....
CrickiKaze
CrickiKazelink
Tuesday, February 08, 2011 10:25 AM
I would love to get a simaliar combo on the pistons and rods but fo a higher compression
Jim Soul
Jim Soullink
Wednesday, August 27, 2014 4:22 PM
Hey, great artical mike!!! I wonder did you use the 02-06 block or the 07+ block. If u used the 02-06 motor did the 07+ head fit on the older block and did the intake runners fit on the old block. Would I be able to use the block up and install it on the bottom end. Is the 02 crank forged as well as the newer one. Are the jwt pistons available to buy. There's alot of great info on this write up, i'm just trying to find out all precise info on the parts im trying to get and what will work for my turbo build. Already have turbo kit, ems, fuel pump, injectors. I have the 02 spec v im trying to build the motor up now to handle the power. Thank you for any input in advance.
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