PDA

View Full Version : 3.5 with 3.9 crank


Dazzarat
3rd September 2012, 05:44 PM
gday all

im looking at upgrading my 86 range rover it has a 3.5 EFI i have been told that a 3.9 crankshaft gives it more bite and i am wondering how much work is involved in this conversion

thanks all :D
101RRS
3rd September 2012, 05:49 PM
Not sure what you are trying to achieve as the stroke is the same on both engines - so if a 3.9 crank can go in you still end up with a 3.5 engine. The main difference between the two engines is the bore - the 3.9 is larger.

Garry
langy
3rd September 2012, 06:24 PM
Besides, the crank in the 3.9 is subtly different to the 3.5. AFAIK it won't fit. There used to be a stroker kit to bump the 3.5 up to 4L, but that was generally only in the UK. If you want extra go,swap the short engine over to a 3.9 block - all the other bits bolt on ok. Pick a Disco 1 between 91-93. ( They have the little 3.9 sticker on the side)
BigJon
4th September 2012, 08:19 AM
Essentially the only difference is the length of the keyway on the snout of the crank.
Dazzarat
16th January 2013, 03:56 PM
thanks guys i think il just find a 3.9lt seems easyer :D
BigJon
19th January 2013, 01:20 PM
Be aware that 3.9s have a tendency to slip liners which 3.5s don't.

When I get the time / money / motivation I will complete the rebuild on my 3.5 which is getting a stroker crank but staying stock bore.
d@rk51d3
19th January 2013, 03:02 PM
Be aware that 3.9s have a tendency to slip liners which 3.5s don't.

When I get the time / money / motivation I will complete the rebuild on my 3.5 which is getting a stroker crank but staying stock bore.

I always thought the same, but a mate just pulled the heads off his 3.5 a couple of days ago, and found several liners displaced.

It would be prudent to top hat any rover v8 you plan on rebuilding. Just not as feasible financially on the smaller engines.
Homestar
27th January 2013, 06:32 PM
Be aware that 3.9s have a tendency to slip liners which 3.5s don't.

When I get the time / money / motivation I will complete the rebuild on my 3.5 which is getting a stroker crank but staying stock bore.

Or you could sell me the crank you have stashed away...:angel::D
BigJon
27th January 2013, 07:12 PM
Or you could sell me the crank you have stashed away...:angel::D


Nah, I read the thread about the 5.2 build... I think my Rangie needs something like that. If I am going to tophat I may as well go big bore!