.5 over bore on 2.25?

[mearstrae]

I beleive that the 2.25 and the 2.5 have the same pistons, the change in cubic inches is achieved by the stroke. 2.25 [bore:3.562" and stroke:3.5"], 2.5 [bore:3.562" and stroke:3.82"]. If I remember right there was a change in the main bearing arrangement between the two, so some change in the rods would have been necessary. Possibly someone else has better spec's on this.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[dabawei]

I beleive that the 2.25 and the 2.5 have the same pistons, the change in cubic inches is achieved by the stroke. 2.25 [bore:3.562" and stroke:3.5"], 2.5 [bore:3.562" and stroke:3.82"]. If I remember right there was a change in the main bearing arrangement between the two, so some change in the rods would have been necessary. Possibly someone else has better spec's on this.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

Sounds great if I am planning to rebuilt my 2.25L engine on S2a then I can consider following (straight forward) changes:
1) change piston rod with 2.5L
2) mill cylinder head to have 8:1 compression
3) change camshaft of 2.5L engines

Any one can advise?

[Terrys]

Sounds great if I am planning to rebuilt my 2.25L engine on S2a then I can consider following (straight forward) changes:
1) change piston rod with 2.5L
2) mill cylinder head to have 8:1 compression
3) change camshaft of 2.5L engines

Any one can advise?

Re:#1, The increase in stroke comes from the crank throw, not longer connecting rods. I'm not certain how the two rods differ in dimensions though.

[mearstrae]

eeek... It isn't that simple. Yes, the rods are longer to accomodate the change in the longer crank shaft throw. So, just using the longer rods would probably put the pistons through the head.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[superstator]

eeek... It isn't that simple. Yes, the rods are longer to accomodate the change in the longer crank shaft throw. So, just using the longer rods would probably put the pistons through the head.

Wouldn't a longer crankshaft throw require a shorter rod? I was under the impression that was how most "stroker" kits worked - bigger crank, smaller rods, and sometimes modified pistons so the skirts don't clip the crank at the bottom of the stroke.

[mearstrae]

Shorter rods would bring stock pistons lower in the bore and may cause conflict with the crank counter throws at bottom dead center. Using shorter rods would work if the piston pin position was changed for the longer crank throw. A longer rod with stock pistons would conflict with the deck [head] at top dead center. It's just that the overall length [piston and rod combination] would have to be such that it met the demands of the cylinder and crank dimensions. You'll see some really short pistons in stoker racing engines for this reason.

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[mearstrae]

I think that after some research this all becomes moot points. The 2.25 is a three main bearing engine and the 2.5 has five mains. Some 2.25's had five mains as part of the Harrier Project. So, unless you can change the 2.25 to the 2.5 crank, to gain the cubic inches, this may all be for nothing. It's hard to find exact spec's for L.R.'s internal bits to draw any educated conclusion as to what refits to what. [I'm glad to stick with the V-8s, everything is so much simpler, as there is all the information and parts that anyone could want...]

'95 R.R. Classic LWB
'76 Series III Hybrid 109
'70 Rover 3500S

[mongoswede]

run the stock lump or stick to simple head swaps or cam swaps to keep things on the cheap side. If you start reengineering the stock engine you will spend a ton of money for maybe 30 hp?.....and it will still be an underpowered inefficient lump compared to todays engines. If you want to get crazy you are better off putting the energy into an engine swap of one sort or another.


keeping in mind that the stock rover is built for that engine and a more powerful engine will strain the gearbox and axles, and the things on the wheels that generate heat when you push the brake pedal. So...be forewarned it is a dangerous rabbit hole to go down.