8CW vs 4CW crank on VE - SR20 Forum
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post #1 of 33 (permalink) Old 03-17-2006, 01:21 PM Thread Starter
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8CW vs 4CW crank on VE

Often come accross posts of people recommending the 8CW crank for VE's, but have not seen many posts of people who have actually done this.

My searches has also brought up arguments against fitting the 8CW crank, since the N1 has been running a 4CW for so long without any problems while still revving past 8500. And mention of the 4CW crank being well enough balanced from the factory to handle 9k rpm abuse.

I post the question:

How many VE's have actually failed because of the 4CW crank, and at what RPM?
How many VE's are running 8CW cranks and is the drop in power/revvability worth it?

ps: Does the 4CW 20VE crank share bearings with the RR 20DE motor?
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post #2 of 33 (permalink) Old 03-17-2006, 03:31 PM
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I dont have any answers to your questions but I will say this. Why would Nissan switch to a 4 CW crank on this motor that revs higher than the DE If the crank was not capable of doing it. I think somebody started a rumor that this crank was bad and now nobody wants one, IMO It's BS I've seen that crank take 9.5k. Dont waste your time switching!
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post #3 of 33 (permalink) Old 03-17-2006, 03:53 PM
 
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i also have the same Q.
like you said, the crank is balanced from the factory. and i know that isnt going to be an efficient reason for harmonics or crankshaft vibration.
Any time you remove excess weight from a reciprocating rotational assembly in an engine you will raise the limit on its max RPM and it will also reduce the amount of force it takes to move those parts. its simple physics.

the less weight that has to be moved will move faster and with less force.


Brandon
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post #4 of 33 (permalink) Old 03-17-2006, 04:10 PM
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IIRC the issue was the strength of the 4cw crank opposed to the 8cw crank. For boost it was recommended to change to the 8cw crank for its strength, someone correct me if i am mistaken.
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post #5 of 33 (permalink) Old 03-17-2006, 06:21 PM
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Has anyone had a 4cw VE crank fail on them using UR pulleys?

I know that a few people are running the UR pulleys with the 4cw VE crank and hasn't had any problems YET.

Planning to build a VE down the road. I've got a DE 8cw crank I want to use. Want to run the UR pulleys safely.

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post #6 of 33 (permalink) Old 03-17-2006, 07:17 PM
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Miko said that the early cars had 4cw cranks. Latter some switched back to the 8cw crank.

Steve
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post #7 of 33 (permalink) Old 03-17-2006, 07:51 PM
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the last gen 16ve in the N16 have an 8cw crank

I have one sitting on my floor. Nissan tried the 4cw cranks and switched back to 8. nissan standards for warrenteed motors are much higher than anyone on this board. Nissan decided that from a reliability standpoint the 4cw crank wasn't as good as the 8.

YMMV
(i decided to heed nissans warning and go with an 8cw crank...lucky for me i have one out of a gtir

ps the ITR also ran a heavier 8cw crank than the normal gsr if that means anything to any of you...

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post #8 of 33 (permalink) Old 03-17-2006, 09:14 PM
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Reason a 8CW crank 'can' be better

My 8CW Tomei crankshaft with a long stroke design can rev to 11,000rpm with the right camshafts... With the aerodynamic CW's and fine tolerances for bearings and balancing, it is very smooth.

I guess it all depends on the engine builder...

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post #9 of 33 (permalink) Old 03-18-2006, 05:15 AM Thread Starter
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still seems like a lot of differing opinions on this.

I guess what we have to ask ourselves is:

Is the 4CW such a reliability concern at 9000 rpm?
How much power loss does the 8CW produce over the 4CW and does this justify the added reliabilty?

How would a set of beefier GTI-R rods do in terms of added reliability and power?
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post #10 of 33 (permalink) Old 03-18-2006, 11:53 AM
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Here's a couple questions.

Does anyone know the weight difference on an 8cw vs. 4cw SR16VE crank?

What year did the SR16VE change from 4cw to 8cw?

In SCCA GTL racing the 4 cw may be an advantage because of the restricted HP at 175 and RPM at 7500+/-.
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post #11 of 33 (permalink) Old 03-18-2006, 07:06 PM
 
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Quote:
Originally Posted by DimeDave
Does anyone know the weight difference on an 8cw vs. 4cw SR16VE crank?

I can tell you the weight of the 4cw crank.
I got an ave. of 31lbs
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post #12 of 33 (permalink) Old 03-18-2006, 09:05 PM
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Static weight of the crankshaft should be irrelevant...

For example:
Theorectically, if the 8CW crank has its CW's close to the crankshaft centreline, then the rotational inertia of the 8CW would allow it to rev harder and more reliably than say if the 4CW crank CW's are further from the crankshaft centreline, which would also allow the CW's to vibrate more(as indicated by link I posted above)

Essentially, a side by side analysis would be required of 'all' possible crankshafts would be required to evaluate which crankshaft would be better suited.

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post #13 of 33 (permalink) Old 03-18-2006, 09:19 PM
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Quote:
Originally Posted by Sabre 200 Gxi
still seems like a lot of differing opinions on this.

I guess what we have to ask ourselves is:

Is the 4CW such a reliability concern at 9000 rpm?
How much power loss does the 8CW produce over the 4CW and does this justify the added reliabilty?

How would a set of beefier GTI-R rods do in terms of added reliability and power?
It's not that complicated. I would with out a doubt say the 8cw is better. Just because Nissan Cheaped out for a couple years should not make you throw logic to the trash and doubt the 8CW is not better.

Steve
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post #14 of 33 (permalink) Old 03-18-2006, 10:05 PM
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The 4cw crank will be fine for normal street use with stock valvetrain, as you'll tear up the upper end floating valves before you hurt anything underneath. As the Aussie noted, the 8cw crank will flex less and allow significantly higher red line with hd valve springs and other tough valve gear. This from Andreas. 8cw crank will make you no difference whatsoever with stock valve gear. And yes, the 2nd gen VE, yet few and far between on the used JDM market, has an 8cw crank. Apparently if you wish to tear yours apart, you can plop a DET crank right in. If you have the valve train to do 9k you probably would do well to do an 8cw crank. The HD rods, why do you even need to ask the question?

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Last edited by jerryeads; 03-18-2006 at 10:08 PM.
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post #15 of 33 (permalink) Old 03-19-2006, 12:06 AM
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I am convinced (but no proof) that a 8CW crank would have helped my roadcourse VE that saw 8000RPM regularly during 30 min sessions. On the street I don't think it's a big deal at all.

Steve
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post #16 of 33 (permalink) Old 03-19-2006, 05:13 PM
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How about adding a girdle?

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post #17 of 33 (permalink) Old 03-19-2006, 05:59 PM
 
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Quote:
Originally Posted by iamhappy46
Static weight of the crankshaft should be irrelevant...

For example:
Theorectically, if the 8CW crank has its CW's close to the crankshaft centreline, then the rotational inertia of the 8CW would allow it to rev harder and more reliably than say if the 4CW crank CW's are further from the crankshaft centreline

The static weight of the crankshaft is Relevant. it may not be the most important, but it makes a difference.
and your right about the 8cw having more rotational inertia, but it will reach its rpm slower and take longer to drop it off.

It really depends on your application. if its going to be driven on the street and see the track here and there the 4cw should be fine, but if it going to be on a track more often then not then use the 8cw to your advantage to keep the RPMs where you need them.

mine will be kept mainly on the street and for that reason im using the 4cw, i already have it and it more suitable for my application.
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post #18 of 33 (permalink) Old 03-19-2006, 10:28 PM
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Actually, if the 8CW crank has its weight closer to the crank centreline, it will have LESS rotational inertia, therefore would accelerate quicker and drop off quicker...

The 4CW crank has more weight further from the centreline to maintain balance and would the equivalent of you spinning on the spot while swinging a bowling ball around on a rope... compared to the 8CW crank where your holding the bowling ball in your hand...

Sure, the 4CW crank does have some advantages but I truly believe the 8CW crank is superior.

Esentially, their static weight/mass sould be about the same

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post #19 of 33 (permalink) Old 03-20-2006, 01:05 AM Thread Starter
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Application is for 90% street use and the other 10% is 1/4 mile. Although sometimes the street driving I put the car through is harder than the punishement it takes at a track....

I already have a DE girdle witih DE bolts. (VE ones too short once girdle is added)
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post #20 of 33 (permalink) Old 03-20-2006, 04:20 PM
 
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Quote:
Originally Posted by iamhappy46
The 4CW crank has more weight further from the centreline to maintain balance

youre right. i totally forgot about that, but there is less weight on the CWs.

I agree that the 8CW has superior balance, but isnt the only way to go for your application.
I am currently rebuilding a 20VE and have the block completely disassembled. ive checked all the bearings (rod & main) for wear and all were perfect for the exception of a few improperly seated.

the engineers that build these engines do so for a reason. it may have slight repercussions way down the road that cant be foreseen, but the 4CW had a reason to be used. the same cranks were used in the VZ-R N1s which are meant to be a track ready car. these engines are designed to rev fast and run hard.

Last edited by DisBeBrand0n; 03-20-2006 at 04:55 PM.
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