Displacement

[zentac]

Reading the PJ thread got me thinking....

Displacement = (PI/4)*(Bore^2)*(Stroke)*(Cylinders)

So the Standard engine has a bore of 81mm, PJ`s had 81.25

Standard engine = 0.785398163 x 6561 x 80.8 x 6 = 2498
PJ's engine = 0.785398163 x 6601.5625 x 80.8 x 6 = 2513

so the oversized bores would only give (280/2498)*2513 = 281.68ps
so a standard engine would have 276bhp and PJ`s would have 277.8bhp a lot of work for not a lot of gain.

On that basis
81mm bore = 2498 = 276bhp (Standard)
82mm bore = 2560 = 283bhp (2.5% increase in power)
83mm bore = 2623 = 290bhp (4.9% increase in power)
84mm bore = 2686 = 297bhp (7.6% increase in power)
85mm bore = 2750 = 304bhp (9% increase in power)
88.7mm bore = 2995 (3 ltr) = 331bhp (12% increase in power)

Im not sure how far the VR4 can be bored out but it makes interesting reading

[Nick Mann]

PJ had bought a V6 block and started playing. I don't know the whole story, but it sounds like he was experimenting with how much you could sensibly remove from the cylinder sleeve. I don't know if the 0.25mm increase was the first bore, the maximum bore or just a clean the walls from previous damage operation.

He was looking at increasing displacement and I don't believe he would have gone to all that trouble to be satisfied with 15cc's!!

From looking at the block in the VX bunker, there is also room for changing the stroke. That could give a bigger increase than boring, but would you need a different crank or could you get away with grinding the journals? Another question I'm sure PJ had asked someone. But who?

[Kieran]

Most of his 'Tuning' work was done by Nobles? Maybe they'll have a pointer or 2?

[zentac]

Now here is an interesting thing Ive just found out while looking at CAPS. Mitsubishi sell oversized pistons, 0.5mm and 1mm

[Rally205]

And looking at things from the other direction. If you were to keep the standard bore and then increase the stroke you would need a stoke length of 97mm to achieve a capacity of 3 ltrs BUT you end up with an extremely undersquare engine which is great for torque but not for higher rpm.

I would need to look at a block to see how far you could bore and stroke it whilst keeping it undersquare and getting the max capacity from it.

Anyone got one? :inquisiti

[SGHOM]

Anyone got one? :inquisiti

might have ?? /yes :thumbsup:

[Rally205]

Cool. Will need the main bearing caps and bolts aswell and some of the old bearing shells. Do you need to use it again or can I cut it up?