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3.0 heads on a 2.5 block - problems?

6K views 32 replies 5 participants last post by  Brian_S 
#1 ·
what issues will i face running a pair of 3.0 heads on a 2.5 block? heads will have 3.0 camshafts and 3.0 injectors. i understand the compression bowl is a slightly different size on the 3.0 heads and presume this will see marginal difference in performance/fuel efficiency (for better or worse?). can this be rectified with an adjustable fuel pressure regulator?

furthermore, are there any other concerns at all other than performance related questions? i mean, is there a danger of destroying the engine?! :eek:
 
#30 ·
yeah waterways are the same, but that gasket is going to burn through in no time. the lip really is quite big. the compression bowl seems to be the only difference tbh. oh well, it was a worthwhile exercise insofar as at least we now know conclusively the difference between 3.0 and 2.5 heads and how feasible mixing and matching 3.0 heads with a 2.5 block is! haha! hope others find this thread useful anyway lmao
 
#31 ·
when i put the 1.6 head on the 1.3 i used the 1.6 gasket for the same reason your worried about the lip, its the displacement in the head that really matters, just use a 3.0 gasket,

i'd try it just to see if it all works but its allot easier and not allot of work with an 8valve engine lol


Regs
Rich
 
#32 ·
just to add a bit more info to this thread, i was chatting to someone about it and they advised that the T vents in the heads must match the block (oil pump). these are the torx headed 'bolts' about mid way along the upper edge of each head (you can just see one in the pic below).

these act as an oil flow restictor to the cam bearings and cam followers.....when the oil pump capacity was improved on later heads the T vents were changed to match. if you put later heads onto an early block you must also use the original T vents. the T vents are different in length, as the later ones have smaller dia cross drillings. maybe someone can confirm this?

 
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