Stroker Crank

[Oldtimer_Basis]

Okay, I think, I already know the answer... I ask anyway:
Is there a Company that builds Crankshafts with more Stroke than stock? Offset-Grinding is not an Option for me, because I´ve heard too many Horror-Stories about that. The other Question would be: What is the maximum recommended Bore for the 912?
It´s not that I´m not happy with the Performance. It´s just that I like to have a ready to run Spare-Engine lying around... and I usually head for max Displacement, when I´m building one... if not, I always feel like I´m giving away Performance for nothing
The only Exception is my TR7 Coupe - no one ever seemed to have build a Stroker-Crank for it and you cannot bore it to mentionable Dimensions because of the tight Cylinder Spacing...

[bash]

Lotusbits do a 2.5 and I believe they were looking at a 2.7 litre. However because of conrod angularity harmonic balance becomes a big issue over that size. Some other manufacturers who fitted contrarotating balance shafts fudged around this problem up to about 3litres but obviously thats not an issue that can be solved here. Its all to do with the piston travelling at different speeds within 1 stroke. Because of geometry issues a piston travels further in the first 90 degrees of the crank rotation than it does in the second 90 degrees of crankshaft rotation giving secondary vibration issues. Have a look on utube theres a couple of animations on there that demonstrate this.
Im sure peter or tim know more about this than me.
Bash

[Pete Boole]

Yep - Lotusbits offer a 2.5 stroker crank. They have just developed a better counterweighted version as well. The liners are pretty thin - I can't imagine over-boring them and retaining enough strength.

Pete

[Oldtimer_Basis]

hmm... 3 Litres does sound cool
Yes, Bash, the Problem is based on the Mass-Accelerations of the 2nd Order... 4 Cylinders straight tend to hop, and that can only be solved by an additional Counterweight, that is working against the Crank. Porsche and some others solved that by using a kind of "Camshaft" on the Side of the Engine, that counteracts these Masses.
Usually, I ignore that. It is not really bad for the Engine, it just feels awkward.
Soooo... do you have a Name or two of the Brands, that offer these 3 Litres Cranks?

[bash]

Not for a lotus, they dont exist.
Bash

[Hawaiis0]

Lotus bits can now do 2.6 litres I've been told

[Pete Boole]

2.5 + forced induction!!

Pete

[Oldtimer_Basis]

@Pete: Call me neurotic, but I get nervous Twitches, when Plastic and excessive Heat combine

[Pete Boole]

Never really a problem in the Esprit!! But I was thinking supercharging

Pete

[Oldtimer_Basis]

Well, this is my very first Lotus-Engine. "Playing around" with the Rotating Assy, the Head and stuff is Okay for me to familiarize myself with it. Forced Induction is a different Story, I only do that with Engines I know. Heat Dissipation, Rigidity of the Block... all big Questionmarks for me with that Engine...