Our cranks vs. Fully counterweighted cranks

[olie05]

I've been toying with the idea of going to a stroker crank, and of course I started doing some searching on the topic.

 

In my searching I came across Kameari who appear to be the only company publicly selling "aftermarket" crankshafts for the l-series. This includes an 83mm standard ld28 crank, a fully counterweighted 83mm crank, and a fully counterweighted 85mm crank.

 

Also someone in NC has a moldex billet crank, don't know if this is fully counterweighted or not, but it seems like something you might as well do if you're getting a custom made billet crank.

(source:http://speed.racingjunk.com/category/83/GT/post/1969249/Datsun-Z-Car-vintage-racer.html)

 

From what I have read, it seems that the main reason to go with fully counterweighted is to be able to rev higher. Also, a striking disadvantage is that you are adding more weight to the crankshaft.

 

As an aside, it looks like the rb series engines do not use fully counterweighted cranks, while most (if not all) aftermarket stroker RB cranks are fully counterweighted. TVR's Speed six crank isfully counterweighted. This leads me to believe that fully counterweighted cranks are more reliable in performance applications.

 

Can someone please provide some insight on any other pros and cons of this type of crank vs what we the other 99% of us are running?

[Tony D]

First, lets define 'higher' and 'longevity' and then we can go on to answering your question. I would dispute the contention fully counterweighted lets you rev 'higher', just that it increases reliability when revved to standard rpms all the other cranks make.

 

A standard L-Crank will run over 10K rpm with little prep or problem...how much "higher" are you planning to go?

 

[olie05]

I guess it really depends on where the torque peak ends up... which would come from headwork/cam and probably be influenced by the rod-stroke ratio.

 

I want to build this engine to last, not to blow up, so if i wanted to frequent 8000rpm without breaking apart cranks, would I be able to get away without a full counterbalance crankshaft?

 

(btw it looks like i'm going to end up with a standard diesel crank anyway)

[Gollum]

I guess it really depends on where the torque peak ends up... which would come from headwork/cam and probably be influenced by the rod-stroke ratio.

 

I want to build this engine to last, not to blow up, so if i wanted to frequent 8000rpm without breaking apart cranks, would I be able to get away without a full counterbalance crankshaft?

 

(btw it looks like i'm going to end up with a standard diesel crank anyway)

 

 

Well just as pete brock... I think his engines lasted quite some time at fairly high revs.

 

Though he has some interesting information regarding the early Z cranks, that would pretty much explode the engine once a certain RPM was hit, I think it was like 7500 or something else relatively low. After he finally got nissan to fix the issue (which the did for the production cars as a whole) they were able to run up to 9k no issues.

 

I'd bet that our stock Nissan cranks are probably more relible at 8k than a large displacement 4 cylinder at 8k, fully counterweighted or not. An inline 6 engine is the most inherently low harmonic vibration engine other than a V12. Not too many harsh foces pulling things apart. Plus we have a lot more main caps than other engine types.