Welcome to the SR20 Community Forum - The Dash.
Register
SR20 forum logo

Thread: 4CW vs 8CW vibes

+ Reply To Thread
Posts: 21-30 of 32
2009-07-02 06:02:30
#21
I read an SAE article a while back about this subject, but I feel like a big part of this debate should focus on flex, and not just vibration. a 4cw crank is not used in many production engines revving over 7000rpm. Flex of the crankshaft is also worth considering and the lack of a girdle makes the problem worse.

Harmonics is just a part of the puzzle, but look at all the production engines making awesome bhp/liter and the 8cw design is used almost religiously. I feel like the 8cw may have more benefits, and the real reason for the 4cw is because the accountants want to save a few bucks.
2009-07-02 19:36:08
#22
It's interesting that Cosworth, a company that knows something about racing and engines, went with the 4cw crankshaft for the Duratec and Subaru. Here's the link:Crankshafts - Cosworth USA
2009-07-02 19:40:17
#23
Originally Posted by 5speed
It's interesting that Cosworth, a company that knows something about racing and engines, went with the 4cw crankshaft for the Duratec and Subaru. Here's the link:Crankshafts - Cosworth USA


I think 5speed has a very valid point there.
2009-07-02 21:25:15
#24
nismo ran 4cw cranks in their race motors too.

it's interesting how race teams don't run their motors in stop and go traffic with the expectation that those motors will last unopened for 100k+ miles.

While it's always fun to compare race motor/teams to cheap commuter car owners there has to be a limit to their comparisons.

the bottom line is that there is really no point in swapping cranks one way or another. the only people that will drive their car hard enough to warrant checking bearings already know how to do that.

Years ago Steve Foltz was doing a ton of road racing in his VE (4cw) and noticed abnormal bearing wear after about 2 seasons, he stated that if he would have kept the car he would have swapped cranks.

Nismo ran the 4cw cranks but they were trash after a few races, and replaced with another 4cw crank.
2009-07-02 21:55:40
#25
Nismo only ran 4cw cranks in their race KA motors and few others. There are few advantages to a 4cw crank, I didn't notice much difference in how quickly the revs climbed, but I'm sure there is one.

Aftermarket KA cranks have 8cw, and engines that are MADE for revving high have fully cw cranks also. 4G63, SR20DE, 20V, K20 (real vtec ones), Toyota 3SGTE, 5SFE, The 2JZ, 2ZZ, etc.

If the only difference is wear, then I am glad I have a setup that will last longer.
2009-07-02 23:17:22
#26
Originally Posted by Coheed
Nismo only ran 4cw cranks in their race KA motors and few others. There are few advantages to a 4cw crank, I didn't notice much difference in how quickly the revs climbed, but I'm sure there is one.

Aftermarket KA cranks have 8cw, and engines that are MADE for revving high have fully cw cranks also. 4G63, SR20DE, 20V, K20 (real vtec ones), Toyota 3SGTE, 5SFE, The 2JZ, 2ZZ, etc.

If the only difference is wear, then I am glad I have a setup that will last longer.


Like I stated earlier, the factory found a lot of advantages to the 4cw, fuel economy, power, throttle response. It stems from reduce crankcase windage.

Go onto the freeway at 60mph(have someone drive, lol) and stick one arm out the window. You will feel a resistance force on your arm call drag. Now stick both arms out, you just double the drag/resistance. Imagine what happens to the counterweights spinning at 8,000 rpm with the oil flying around. The 8cw crank will have double the drag. Racers go to great length to reduce windage. It's one of those parasitic loss that affect power, fuel economy, throttle response

Since you have turbo, you might not feel or appreciate the throttle respone,but for NA people we do. You have 400+hp it's not a big deal for you to lose 5hp from windage, but it is to us. We need all the hp we can get.

Btw, the Nissan won the BTCC championship in the late 90's with the 4cw.

I'm not saying one crankshaft is better than the other, just that I would not go out of my way to change to 8cw crank.
2009-07-03 00:03:26
#27
i think we are all arguing the same point.

Race motors have no business in these discussions since no one in this forum is on a factory backed race team.

If you are going to find a way to make more power your crank should be the last think you think about swapping out on your car.

if you have your motor apart then that's another story. Personally I went with a gtir crankshaft and 2 crank scrapers so windage loss is a non-issue with zero-clearance teflon
2009-07-03 00:22:07
#28
i think the problem is that the 4cw crank is balanced to be used with the cvt flywheel and not a regular flywheel or an aftermarket...if you balance the 4cw with the regular flywheel the crank pulley and the clutch plate you should not have any problem, dynamic balancing should eliminate any vibration
2009-07-03 16:13:40
#29
Originally Posted by 5speed
Like I stated earlier, the factory found a lot of advantages to the 4cw, fuel economy, power, throttle response. It stems from reduce crankcase windage.

Go onto the freeway at 60mph(have someone drive, lol) and stick one arm out the window. You will feel a resistance force on your arm call drag. Now stick both arms out, you just double the drag/resistance. Imagine what happens to the counterweights spinning at 8,000 rpm with the oil flying around. The 8cw crank will have double the drag. Racers go to great length to reduce windage. It's one of those parasitic loss that affect power, fuel economy, throttle response

Since you have turbo, you might not feel or appreciate the throttle respone,but for NA people we do. You have 400+hp it's not a big deal for you to lose 5hp from windage, but it is to us. We need all the hp we can get.

Btw, the Nissan won the BTCC championship in the late 90's with the 4cw.

I'm not saying one crankshaft is better than the other, just that I would not go out of my way to change to 8cw crank.



Nissan did not win on a 4cw crank. It was an 8cw crank cross drilled an weighted. The sumps were dry and vacuum fed. There was no windage in that sump. In fact i even remeber the blocks being machined out to accpet the massive counterweights they had on the cranks. I even think it was possible they ran a shorter stroke crank. From my memory the counterwieghts were almost semi cricles, literaally. Probably about 130 degrees worth.
2009-07-03 16:30:42
#30
I know of quite a few VE's that run up to 100 shot wet on the stock sub assembly and they are not experiencing bearing failures and the like, so it can't be that horrible.

I can't say how it will hold up to daily 9.5k abuse, but there's only one way to find out I guess. Then again, if you are revving that high it means you have a built motor, and everything SHOULD be balanced!
+ Reply To Thread
  • [Type to search users.]
  • Quick Reply
    Thread Information
    There are currently ? users browsing this thread. (? members & ? guests)
    StubUserName

    Back to top