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12v. I would need modified 3.0 sized pistons to maintain compression right?

Would I need 3.0 heads or can the 2.5's be modified? Larger valves etc.?

Still looking for the 2.8 here.

well there are 2 ways to go about the 2.8L gleich replica as far as i know, i've posted it here before.

1) yes, keep the 2.5 motor as gleich did. in his first state of tune (190hp) he kept the valves stock, but switched to forged 90mm 10.5:1 pistons to bore out the capacity. the second stage of tune included wild cams and bigger valves for more than 240hp at the crank.

2) use a 3.0 engine complete as you suggested swapping in the 2.5L crank. i believe by playing with the small end bushing of the rod you can restore lost compression with the shorter stroke of the 2.5 crank.

Would the 2.5 crank work with the 2.5 connecting rods and 3.0 pistons?

If your using the 2.5 crank and 3.0l p/sleeves, you have to get your cr right.This is done by ofsetting your small end in the rod by 1.84mm upwards.Check my rod pic in "my engine is dead "You will see the ofset s/end.

At least as far as 12 valve motors are concerned the 2.5 and 3.0 rods are the same

Even the multivalve motors have the same rod-just stronger..

Barry

Same rod...but stronger? How? Because no more oil hole on the small end?

Not just the oil-hole... the casting is different, new material etc...

What would the compression be if the 3.0l crank was replaced by a 2.5l?

If I understand what has been said correctly, using the 2.5 crank in a 3.0 block will work physically but will result in a lower compression ratio. This can be corrected by ofsetting the gudgeon pin to raise the piston height.

Looking at this from anonther direction, what about using 3.0 liners and pistons in a 2.5 block? If rods and piston hieght are the same for both capacities, is this a simple way of achieving the 2.8l capacity without needing to modify stock components, or am I standing on my head?

Grant Richardson

Grant, if you went that route you'd need to have the block machined to accept the 3.0 liners and the valves would still be the smaller 2.5 versions. Dropping the 2.5 crank into a 3.0 engine with the small end rod bushes altered as Barry suggests sounds like a simpler and cheaper method. You'd also benifit from the bigger 3.0 valve arrangement so it'll breath better - right little screamer probably!

Barry, I understand the CR would drop if you don't re work the rods, but what CR do you actually get by dropping a 2.5 crank into a 3.0 without making any alterations?

This is the same question I asked - I have though about skimming the blocks & liners to bring the compression up.

how about 3.0L block with standard pistons, and refit 2.5 heads?? will the smaller cc head raise the CR enough??

Could lead to bad squish band area though? Barry any input!!

Steve R wrote: Barry, I understand the CR would drop if you don't re work the rods, but what CR do you actually get by dropping a 2.5 crank into a 3.0 without making any alterations?

Also wondering same thing
What are the small end rod bushins made out of? Perhaps I could have ones that offset 1.84mm made...or are they avaliable somewhere?

Aaah,A revived topic..nice.

On a S.A. spec motor,small chamber volumes,low dome pistons,the cr works out to 8.12:1 .

Do remember that Euro and us spec engines had large volume chambers and high dome pistons compared to the S.A. spec.
So do the math here..It should be pretty similar though.

The bush used for the small end offset is made from bar stock.Its not something off the shelf..
If you have a competent machine shop the guys will know how to sort this out for you..

Just looking at a post above regarding 30l crank and 2.5 pistons..The pistons will protrude above the sleeve by 1.85 mm in this combo...