Oldskoolrob
Active Member
Hey groovers - is it stamped on the block wether it's 3.5 or 3.9? I can't remember.....
Identifying 3.9 blocks
- Thread starter Oldskoolrob
- Start date
Oldskoolrob
Active Member
Thanks - but I'm kinda chasing if you could pass off a 3.9 as a 3.5. Let's say hypothetically you had a project car you could only legally put a 3.5 into...
........hypothetically
........hypothetically
There are "early" 3.9's where you could swap the blocks out and all ancillaries should bolt-up P6B-like, the engine number would be the giveaway but other than that you'd need to take the heads off and measure bore and stroke to verify... and there are later 3.9's, generally called "interim" or 4.0's so as not to confuse these with the earlier engines, that have the lugs cast into the block for cross-bolting; these use the serpentine belt drive for water-pump, alternator, power steering/Air and have a crank-driven oil pump and in my application ( an "interim motor" with a serpentine belt and x-bolted ) it's going to be a fairly tough argument with an inspection agency that my car remains a 3.5.... to muddy the waters I believe there were some military vehicles + 4WD's that were interim motor 3.5's... as for legality, you're in OZ and at the mercy of ADR's ( Aussie Design Regulations ) so you'd need to consult those fairly carefully Someone who is a walking encyclopedia of the Rover V8 development over time will no doubt chime in
G
G
jp928
Well-Known Member
As for state of Vic in Oz, you are allowed to up engine power by certain amounts before you need to get an engineering inspection - currently 20%. So if you went from a 10.5:1 CR 3.5 giving 158hp to a 3.9 (unknown CR?) giving 190hp you would be right on the edge - 158hp +20%=189.6hp. Dont know the hp figure for the other CR types - interested in the figure for 9.25:1.
I seriously doubt many inspectors would know off the top of their heads how to read Rover engine no codes. I plan to put a 3.9 (38d...) in mine later and all I will do is notify Vicroads of an engine no change, and show them the no if asked. Even if you had a 4.0 or 4.6 type, how would they get to see the cross bolting, or the unused bosses on a 3.9?
When I had the Subaru engine changed a few years ago (one of a bad batch of 2.5 Turbos from early 2008) I took a letter from Subaru with the new no to Vicroads - when they asked if they could see the no to check it, I said that would require some dismantling, so they passed on that.
I seriously doubt many inspectors would know off the top of their heads how to read Rover engine no codes. I plan to put a 3.9 (38d...) in mine later and all I will do is notify Vicroads of an engine no change, and show them the no if asked. Even if you had a 4.0 or 4.6 type, how would they get to see the cross bolting, or the unused bosses on a 3.9?
When I had the Subaru engine changed a few years ago (one of a bad batch of 2.5 Turbos from early 2008) I took a letter from Subaru with the new no to Vicroads - when they asked if they could see the no to check it, I said that would require some dismantling, so they passed on that.
The 9.25:1 engines were quoted as 143HP or 106kW in the owner's manual that came with the car. I agree with you, unless an inspector is a Rover aficionado, I dare say they would likely have no idea, either about engine numbers or the subtle differences between the engines. It will have the CR stamped next to the engine number but not the capacity.
Ron
Rover only differentiated between early and late models JP. So the early models and some of the late models (series 1 and series 2 up until 1974) were 10.5:1 engines. The 9.25:1 and the 8.5:1, certainly the former were released from 1974, and both continued until 1976. Camshafts for early models were different to later models, but the later models regardless of their compression ratio all used the same camshafts.
Ron
I don't know if there was a distinction between the high compression and low compression 3.9 litre engines in terms of camshafts. I know that they were a symmetrical design, but that is about it. If you like the specs of the one that you have seen, sounds like the one to go for in that case.
Ron
Ron
mikecoombs
Active Member
The cams were the same on the early engines however the distributors came in multiple variations. The advance springs, Mechanical advance stop and vacuum unit being the major difference. The carbs could also have differences ie. in needles and springs.
I have only just seen your post; I use an MG-B overflow bottle that takes a ( pressure ) radiator cap that is mounted on the inner fender above radiator height; the radiator having a zero-pressure cap
The motor is too close to the radiator with the 3.9 to run fan blades on the water pump so I’ve got twin electric fans
Graham
jp928
Well-Known Member
Back to the original question about identifying 3.9 blocks - my 3.9 has a date cast on it (94), and a part no (HRC2411, made by West Yorkshire Foundry - 'WYF'), as well as the engine no. It came with a serpentine front cover, which I have disposed of as unsuitable for a P6B. It has undrilled bosses for the cross bolts. The heads on it are the smaller combustion chamber types -casting HRC2479, dated 03/94. If you have these casting numbers you can verify their age and type better. Despite having the smaller chambers designed for composite gaskets this one came with shim gaskets fitted.
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