E30 Zone

i recently bought another nice lil e30 which the nice lil man said had been converted to a 325 from 320 but the problem is somedays it seems to pull like a 2.5 and otherdays i doubt it is more then a 2.0, how can i identifiy if its a 2.5 or 2.0ltr? it has a 6 branch manifold on it and a full stainless but just dont seem to have any power somedays

also the nice man has welded the diff and the car rev's so high, is this bcoz the diff or has it got a short box or something?

many thanks
Ashley

Its could be a M20B25 with a M20B20 gearbox prop and diff.

Engine should have markings on the block saying 2.5

bottom of the block by the sump inlet side theres a small flat should say 25 6 k or 25 6 e if its a 2.5
might need some wire brush action tho and prob a torch

thank you both for your help