Lancia Integrale crankshaft strokes and rod ratios

[1NRO]

Guy,

Recently I've been looking at some of the eight weight cranks that are available for the turbo engine and would like your opinion please.

Three strokes are available 86mm, 90mm and 96mm all requiring different lengths of rod. As I calculate rod ratios (roughly) they will be 1.73, 1.61 and 1.46. Nothing too accurate and not allowing for compression height change which is another question I have for another day.

Having scoured the WWW and read what books I have, I have taken a liking for the 86mm, this requires obviously the longest rod. My understanding (clouded by many opinions and info overload) is I'll benefit in the higher engine range (at the expense of lower) with a safer high rpm with benefits such as lower piston velocity and reduced friction due to a reduced rod angle. Better combustion, higher cylinder pressure and increased chamber temperature and syptoms bandied about. My concerns are for the reduced capacity, increased potential for detonation and harming the VE. What if any of this rings true? What else am I missing? Possibly I'm just WRONG thinking this for a turbo engine!?

The shorter stroke as I understand improves torque in the low range with a delayed maximum cylinder pressure (less prone to detonation) I'm concerned for total cylinder pressure and reduced combustion as well as harming the ability to rev. What if any of this rings true? Maybe this is the route for a turbo engine?

Maybe, if only for my sanity, leave well alone and stick to the 90mm stroke.

I realise that its a long way down the list of priority when it comes to a race engine and jobs to do but I don't want to miss a trick or leave a stone unturned. Even if it means living on meagre rations for a while longer :-)

Thanks

Nik

[Testament]

Guy,

Recently I've been looking at some of the eight weight cranks that are available for the turbo engine and would like your opinion please.

Three strokes are available 86mm, 90mm and 96mm all requiring different lengths of rod.

Aftermarket crankshafts for the twincam? where are these available? how much$$$?

[Guy Croft]

Sorry to be boring but in my professional opinion you'd have to walk a very long way to find a 'quantifiably better' setup than the standard setup, be it a std crank or race one. And yes, I know the topic gets 'done to death' on the internet, when it comes to bolt-on solutions some folks love to chase the 'holy grail'. You know what I mean?!

I could publish tedious technical justifications involving lots of maths but truly, there's no point. The only maths worth pursuing is how far your engine budget will stretch to cover more, er.. tangible things.

GC

[1NRO]

Guy,

Thats OK, I realise it is a topic that goes round and round with no end.

The basis of my thoughts is a mistrust of the standard crank when asking it to do things that is doesn't normally do (high revs) I consider the cross drilling a weakness.

Nik

[Guy Croft]

Your fears are groundless - it's plenty strong!

I ran a 2 liter genuine 200bhp NHRA with early (131) crank (with twice as many cross-drillings) to 9500 consistently (same crank ran 2 years), member Greg at ACE Motorsport runs his Integrale to way over that, I have the dyno curves, I'm sure he'd say the same. Cannot quote his power for confidentiality reasons but it's,er.. high..

That nitrocarburised forged EN40B 2 liter crank is mega-strong and an all-time classic design. Way stronger than any billet copy.

GC

[1NRO]

:-) Thats good enough for me, saves me fasting for quite as long as they don't come cheap as you'll know.

Nik

[Evodelta]

Quote Nik:

"Thats OK, I realise it is a topic that goes round and round with no end. "


For the money they cost you would hope so!

[1NRO]

HA HA, very funny!

I beg to differ though, if there were no ends what would you bolt the pulley and fly wheel too ;-0

[Evodelta]

Hmmm, by 'no end' I thought you were implying Ad infinitum!

In all seriousness though:

Guy,

Is not the 8 weight crank that Nik talks about going to put less strain on the other components, aswell as itself? It looks like a standard crank with one counterbalance that is to one side of the crankpin will try to bend to one side or twist at high Rpms? Surely having a counterweight to either side of the crank pin will allow far more equal loading and more harmony amongst the components? I dunno, your thoughts are as ever appreciated and I've attached a couple of pics to show what we are talking about.
I'll have to dig out my notes and see how much these weigh in comparison....

Martin.