can someone please explain the difference between the 2.4 and 2.5 engine. looking at specs i see no difference . same bore, same con rods, same crankshaft. i say that because listed part numbers are the same. some years ago i built an engine using parts from two bad engines, using the block, pistons from one, con rods and crank from another. head was resurfaced valves checked for straight and reseated,valve clearences checked and correct. compression was low but equal across cylinders. leakdown test 3% across engine. i find myself wondering if i mismatched parts between 2.4 and 2.5 engines. to cause low compression across the board, it seems like the crank and rods would have to be the culprit. but all part # listings i have found list the same part # for both engines. both engines came from the same year model s40 with the same engine code in the vin. any help appreciated

 

there's multiple iterations of the I-5 with different displacements, NA or Turbo and different turbo sizes. A good resource to start with is the "volvo modular engine" wiki which breaks down key changes introduced with the iterations. You can match up the iterations by engine code (ie the B codes which in turn match to the VIN code).

 

thanks, i will check into that.

 

curious what years/model are you looking to compare?

 

i was trying to get to the difference between the 2.4 and 2.5 engines. i think perhaps in mixing two bad engines, i somehow came up with a low compression unit. the car in question is a 2008 s40. i had an engine with a bad crank and good block and one with good crank and rods. installed the good crank and rods into good block. replaced rings and all bearings. resulting engine has low compression but same across the board. leakdown test at 3%, indicating rings are sealing. checking part # on line show no difference for crank, rods,or pistons. both engines came from 08 s40 with same engine id in vin #. but i do not know the history of these cars, might not be original engines. i think, with rings sealed, something must be wrong with the stroke, but only found same part # for crank and rods. only 1 listing for 2.4 piston rings and bearings. compression at 115-120 on all 5 cyl. spec at @150+. i was very carefull to put rod and pistons back in original order. again all help appreciated.

 

generally speaking, for gas engines there's three flavors of the "white block" - NAs which have a higher compression, the high pressure turbos (typical to T5 models) and the low pressure turbo (typical to say a 2.5T). the basic blocks and heads are of a similar design but will vary the head and pistons to get the different compression ratios, bore etc. So if you were to compare a HPT engine out of a T5 you'd find an 8.5 compression ratio and an 81mm bore x 93 mm stroke. The 2.4T (aka the LPT) you'd have a 9.0 compression and an 83 mm bore and a 90 mm stroke. I am not sure if the cams are different. Now if you were to compare a 2.4 engine to a 2.5, there are similar HPT vs LPT nuances but the 2.5 generally has a bigger bore for the extra displacement. In terms of an engine swap, I suspect most accessories will bolt on but keep in mind the ECUs / tune are different for the LPT and HPT and the NAs are totally different from an accessory perspective, plus have a 10.5 compression (no bueno for a turbo application). So given the differences in bore etc there's no cobbling two engines to make one here unless they are similar configs to start with.

As to your compression issue, I'm not sure what would make a consistently low compression across all five other than a) the engine was cold when the test was done so the rings didn't seal well. I'd redo on a warm engine if possible, then follow up with a wet test to gauge the ring's health. Second, I'd check cam timing. If you are one notch off, the engine will run but that may be enough to lower the compression to your results. Third, I'd check the engine for other signs of poor maintenance that would lead to worn rings. If you drop the pan, is there lots of sludge etc and is the pick up clean or dirty? My concern would be that the whole bottom end is worn out, not just the rings.

 

thanks for your reply. this is an na unit. in order, compression test done on hot engine. leakdown test at 3% which is factory spec, indicating rings were sealed and as stated the same across the engine. cam timing was checked and verified both by myself and a professional mech. the third question, i rebuilt the engine with all new bearings and rings.ring end gaps were checked. the head was surfaced by a prominent eng rebuilder, the valves checked for straight and reseated. valve clearances were corrected. block, pistons, and head all came from the same engine. only crankshaft and rods came from second engine. since all compression was essentially the same across the engine, i was looking for a common cause. the only thing i can come up with is that for some reason, the stroke was lessened. in researching part numbers i was unable to find a different crank or con rod to explain the problem. still a mystery to me. please keep ideas coming, the answer is out there.

 

ok since you mentioned its a rebuild, I'd expect 180 PSI on an NA (150ish is what the turbos would show) so assuming cam timing was set correctly (including the preloading of the VVT gears) then its feasible that a wrong rod, piston or crank type could impact compression. Could also be a wrong head (ie too many cc's in the combustion chamber). Hope that's not the case but I'm gonna noodle on this issue :-) I'm wondering if its possible that the cam/crank timing is 180 degrees out and what that would do to compression.

 

thanks again for reply. the head used was the original to the block. it had been resurfaced which, if any thing ,would have raised compression. original pistons carefully put back in original places. i have replaced cam belts on several volvo engines, and as i said, had it verified by a pro. i am a 50yr mechanic although not an auto mechanic for about 20yr. i previously purchased a 2000 s40 that had spun the belt and bent all 16 valves [4cyl engine] i learned a lot about the volvo modular engine and was successful in repairing it and drove it for several years. i purchased this 2008 s40 with a damaged engine. upon removing the head, i found a hole clean thru #2 cyl wall. looking around i found another 2008 s40 with a hole in the oil pan. that engine, when torn down, had ruined the crank, but cylinders were un damaged . so, i combined the two, installing the good crank and rods in the good block with new bearings and rings. the key seems that compression is low the same across engine, and after much thought, i can only see the crank/rods as the problem. what frustrates me is that researching part numbers i only find the same numbers for all 2.4 variants. by the way, the engine runs quite well, if a little weak. please keep responses coming.