Pistons?

[Dom.kelltt]

Is is best just to put the standard Pistons back in my bis or are there some being produced that are either stronger, shallower (therefor to increase the cc) and/or some that mean I can bore out the block and obtain a bit more power that way?
Any help greatly appreciated
Dom


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[dadandlad]

Hi Dom
I would put the original pistons back unless the bores are damaged
A shorter piston would give you less power as it would lower the compression ratio and also lower the swept volume giving you less cc
Hope this helps
Mark

[Dom.kelltt]

Ahh right, never thought about that issue, thanks for that before I went and bought another,
Thankyou Dom


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[Gadge]

I looked into this myself as I was keen to try and gain some extra HP from a unit that I'm rebuilding. I found a company that was selling forged 85mm Pistons intended for use in aircooled motors. This would increase the cc to 800cc. They also sold 82mm ones which gave 740cc and they weren't a bad price so I was quite excited about it all untill I had a look at the block and realised that it would be eccomicly impossible to get it rebored even by 2mm let alone 5mm (standard BIS Ones are 80mm). The reason being that the liners are pressed into the block and bonded in and can only be 1.5mm at the bottom meaning that any rebore would free them from the block. The only way would be to remove the old liners, rebore the block and refit new bigger liners which looked even more complicated as the block has strenthing ribs right by the liners which would have to be machined away.

The other way to gain cc is to fit a longer throw crank meaning you keep the 80mm BIS Pistons but the longer stroke increases the capacity. Longer throw cranks are available but  the liners would have to be ground back a tad as the crank weight comes very close to it plus as dadandlad pointed out the con rods would be the wrong length and the compression ratio would be abysmal. Buying con rods excatly the size you need would sort this but how much?? In short it could probably be done but it would be very costly and complicated.

[dadandlad]

Ahh right, never thought about that issue, thanks for that before I went and bought another,

No problem and just had a look at your car and realised how old you are so probably best to keep the engine standard for insurance purposes, keep up  the good work you are doing a great job 

[Dom.kelltt]

Yeah, sounds very, very pricey! I'll give it a miss until I've got chance to attempt an engine conversion lol, just wanted to see if it was actually possible for a few quid of you know what I mean,
Anyway, Thankyou both for your help and I'll get on with my engine strip down finally lol!
Dom


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