31 replies to this topic

[Exmantaa]

OK, one for the engine experts;

 

It apears to be that the 2.0 Ecotec engine (B207/LSJ/Z20NET) has/had 2 different crank designs.

The early ones with a 1/2 counterweighted crank (4 weights) and the later version with a fully counterweighted 8CW crank... (build details will be disclosed later.  )

Also not sure if the later 8CW version is forged or cast...

 

So, besides the overall weight weight issue, which design is better for a modified 7,5-8K SC engine? Read that most stock high rpm engines (Honda etc.) tend to all have a fully counterweighted crank to reduce crank vibrations and bearing life. Same 8CW design for the old C20XE redtops.

 

So, which one to use? The forged 4C or the (maybe cast) 8CW version??

Edited by Exmantaa, 09 January 2014 - 12:02 PM.

[Winstar]

OK, one for the engine experts;   It apears to be that the 2.0 Ecotec engine (B207/LSJ/Z20NET) has/had 2 different crank designs. The early ones with a 1/2 counterweighted crank (4 weights) and the later version with a fully counterweighted 8CW crank... (build details will be disclosed later.  ) Also not sure if the later 8CW version is forged or cast...   So, besides the overall weight weight issue, which design is better for a modified 7,5-8K SC engine? Read that most stock high rpm engines (Honda etc.) tend to all have a fully counterweighted crank to reduce crank vibrations and bearing life. Same 8CW design for the old C20XE redtops.   So, which one to use? The forged 4C or the (maybe cast) 8CW version??

I'm not an expert on rotational dynamics but OEM's don't change things for no reason. Either it's cheaper (cast not forged, it allow them to loose the balancer shafts) or it was deemed that is was necessary (to meet a higher rpm limit or durability problem)

[fezzasus]

 

OK, one for the engine experts;   It apears to be that the 2.0 Ecotec engine (B207/LSJ/Z20NET) has/had 2 different crank designs. The early ones with a 1/2 counterweighted crank (4 weights) and the later version with a fully counterweighted 8CW crank... (build details will be disclosed later.  ) Also not sure if the later 8CW version is forged or cast...   So, besides the overall weight weight issue, which design is better for a modified 7,5-8K SC engine? Read that most stock high rpm engines (Honda etc.) tend to all have a fully counterweighted crank to reduce crank vibrations and bearing life. Same 8CW design for the old C20XE redtops.   So, which one to use? The forged 4C or the (maybe cast) 8CW version??

I'm not an expert on rotational dynamics but OEM's don't change things for no reason. Either it's cheaper (cast not forged, it allow them to loose the balancer shafts) or it was deemed that is was necessary (to meet a higher rpm limit or durability problem)

 

I agree with Rob, with the catch that the cost of a redesign may well negate the cost savings so i'd expect any change during a production run to be to increase durability.

 

Other view is could be that most OEMs have more than one supplier to protect themselves against shortages. It may be simply that you're comparing two different suppliers, or engines made in two different manufacturing sites

[siztenboots]

7327 crankshaft?

[Exmantaa]

Just to add to this, both cranks in same engine design, both with same balancer shafts.. (maybe different man. plants) The change in design was around 2006 and older Saab crank number NLS...

[FLD]

I've had both cranks and they both look cast but have rolled fillets etc.  It might be that the crank with a greater counterweghting allows for a greater discrepancy in piston weights as the majority of the rotating weight is at the crank so the difference is smaller.  Thus the cost of the greater counterweighted crank is more than accounted for in the savings made by having a wider tolerance on the pistons. 

 

Also from what I've heard / read (no personal experience) the 4 CW crank is much harder to balance often needing heavy slugs adding.  Might be pish but its what I've heard.

[Exmantaa]

I've had both cranks and they both look cast but have rolled fillets etc.  It might be that the crank with a greater counterweghting allows for a greater discrepancy in piston weights as the majority of the rotating weight is at the crank so the difference is smaller.  Thus the cost of the greater counterweighted crank is more than accounted for in the savings made by having a wider tolerance on the pistons. 

 

Also from what I've heard / read (no personal experience) the 4 CW crank is much harder to balance often needing heavy slugs adding.  Might be pish but its what I've heard.

 

 

You had/have both cranks as in both 2.0 versions?? (not talking about the cast 2.2 stroke crankshaft...)

 

I'm pretty sure the old 4CW 2.0 crank is (said to be) a forged item and the material looks rather different than the 8CW version.

Just adding to the confusion...

[FLD]

Ah yes, I'd missed that bit sorry.  It was a 2.2 8CW and a 2L 4CW crank I had.

[techieboy]

I'm pretty sure the old 4CW 2.0 crank is (said to be) a forged item 

 

Everything I've ever read says the same.

[Rosssco]

 

I'm pretty sure the old 4CW 2.0 crank is (said to be) a forged item 

 

Everything I've ever read says the same.

 

 

Says so on this:

 

https://www.verboom....upercharged.pdf

[Winstar]

the GM build shows that the LSJ and LNF crank dimensions are same I wonder is the LNF needed the counter weights and they just decided to use a single design for both engines?

Edited by Winstar, 09 January 2014 - 02:32 PM.

[Exmantaa]

Yes, the GM documentation for the LSJ speaks of:

[font="arial, helvetica, sans-serif;"]"Forged steel with induction hardened fillets"  [/font][font="arial, helvetica, sans-serif;"](now I remeber what the colouration on the fillets was)[/font]

[font="arial, helvetica, sans-serif;"]But this is all about the old 4CW crank. Newer 8CW is a bit of a mystery...[/font]

 

[font="arial, helvetica, sans-serif;"]And yes the newer DI LNF (engine A20NHT) has the same forged 4CW crankshaft as the earlier LSJ/B207, but still unsure which crank design is better suited for a high rpm machine. The Turbo LNF is not really a screamer, but has mucho's torque. [/font]

 

 

Edited by Exmantaa, 09 January 2014 - 02:41 PM.

[vocky]

the 8CW can run at a lower engine speed for reduced emissions 

Edited by vocky, 09 January 2014 - 03:39 PM.

[Exmantaa]

Isn't that why they also introduced the dual mass flywheels??

[techieboy]

Thought that was for a smoother gear change and increased drivetrain protection.

[Exmantaa]

Drifting from the main path; 4CW or 8CW better for +7.5k SC use...

 

(I remember the Mad Doc once had those supelightweight cranks. Almost no counterweight left and did they not destruct an engine??)

[FLD]

Drifting from the main path; 4CW or 8CW better for +7.5k SC use...

 

(I remember the Mad Doc once had those supelightweight cranks. Almost no counterweight left and did they not destruct an engine??)

 

He machined off the counterweights completely!  I think that by removing opposing weights you can keep balance but obviously the tollerances get tighter as you lighten the whole assembly.  Surely for a high revver you need super balancing so either crank would do.  The lighter crank will just get there faster.

[vocky]

take both cranks to the balancing place and ask them which will balance best, I believe you should have the same counter weight as the rods and pistons create, so it's perfectly balanced.

 

Personally I would use the 8CW as it should be smoother, but the 4CW cranks seem to do just fine 

 

That said the mad docs engines possibly failed due to using standard z22se rods and pistons, rather than the size of the CWs

[alanoo]

I remember than Renault switched in 2004 the Clio RS crank from 4cw to 8... but it was only in preparation for their Cup 182 race engines and they never had an issue AFAIK with the 4cw version (and we are talking of a 7600rpm 93mm stroke crank).

 

Vocky may be right, the main reason may very well be emission related, I'll try to ask my engineers friends

[Dominique]

I really can't think of an other reason for introducing 4 more counterweights than to iron out residual crankshaft vibrations. (torsional vibrations, combustion impulses)

An other advantage is the improved load distribution on the main journals. Though I never heard this being a problem area, unless running with oil level too low. 

 

Not sure if GM saved production money as the 8 counterweight is a more complex shape to fabricate, well...unless its casted. 

Looking at the counterweights of the crankshaft from the newly delivered B207R engines though, I'd say its forged.

A forged crank will generally have a rougher look with rounded edges, while a cast crank will show sharp, well-defined edges. The casting process results in greater control of the net shape in the fabrication process.

 

Installing the 8 counterweight crank still doesn't feel right. I've spend too much money already in getting weight off that car ... 

saying that, there's no actual figures on both crankshaft weight anyway. . . decisions...