Thread: serpentine and hotwire conversion 3.5

Id like to change everything over to the 3.5 including the serpentine setup , manifold and plennum. I am capable of putting the 3.9 crank into the 3.5 if I have to for the serpentine setup but Id rather not if I dont have to , I believe the crank snout is different . Also will the 3.5 rods fit the 3.9 crankshaft ?
I think I can just remove the 3.9 computer and hook up a 3.5 disco1 computer into the car and it will run the 3.9 injection at appropriate fuel metering for the 3.5 .
Does anyone know if the exhaust manifolds for the 3.9 will fit straight up to the 3.5 . (I can change the heads over if I have to )
I love the 94 rangie and am after something a little different if im going to do a engine swap I may aswell go a bit custom , It never sees off road its used as a highway tourer .

The 3.9 crank is the same as the 3.5 . You just change over the timing case. The different cranks apply to the later oil pump engines which do not have a distributor. This applies to "interim" engines up to December 1993 build date.
I would think the 3.9 injection will be quite happy on the 3.5 as the MAF is the main sensor and one of the benefits of a MAF is that they adapt to a wide variety of engines. However a 14CUX from a 3.5 Disco should plug right up.
YES the exhaust manifolds are the same.
So just check the build date of the car . If it is after January 1994, then there are a few differences in the engine.
So it just looks like a straightforward job of not having to dismantle anything except the timing case.
I have the "How to Power Tune Rover V8 engines " which details all the changes , so I can look it up for you.
Regards Philip A

Got the car stored on a property but I do have the vin if that helps with Identification .
SALLHAMM3MA654905 Engine number 38D28823B
I will google these numbers to see if I can find build date without going to the car .

Thanks for your help Philip

The keyway in the 3.9 crank nose is longer so to use the serpy setup you either get the key way on the 3.5 lengthened or fit the 3.9 crank .

That engine # is a normal 3.5/3.9 crank as in the bearings are the same .

The 3.9 heads will work better on the 3.5 , if you want higher comp ratio use tin gaskets and if you want the std 3.5 ratio use an equivelent thickness gasket as a 3.9 composite gasket .

Felpro make a composite gasket that is similar in thickness which is right for a 3.5 .

Will performance be improved if I swap over the 2 camshafts aswell as heads . If i get a little better compression with the 3.9 heads on the 3.5 then I might get a little better performance .

Don`t know by all accounts a 3.5 low compression factory cam works pretty well in a 3.5 .

I think the last of the sd1s 3.5s rover car was similar numbers to a 3.9

If you use the serpentine front end, definitely use the 3.9 heads. They already have the extra threaded bolt hole for the alternator/aircon bracket, and the extra threaded hole for the power steering pump bracket.
In fact, the 3.5/old 3.9 heads probably don't even have the casting for the third power steering bracket bolt. Mine didn't and I had to make up an additional support bracket to stop the power steering pump mount flexing when serpentine belt tension is applied.
I would use the crank that is in the best condition, and if that turns out to be the 3.5 crank, just get the key way milled out to take the longer key steel.

Also make sure you keep the big end bearing caps matched to their original conrods, the conrods matched to their cylinder number, and the main bearing caps matched to their original block. It's easy to mix them up when you have two engines in pieces and you move parts between them :-)

The keyway in the 3.9 crank nose is longer so to use the serpy setup you either get the key way on the 3.5 lengthened or fit the 3.9 crank .

According to the book, this is not correct. The keyway is the same length up to December 1993 build. the longer keyway is for the oil pump not the serpentine front.
There is effectively no difference in the 3.5 and 3.9 heads up to december 1993 engines. I do not know about the drillings for accessories. Up to December 1993 they had 14 bolt head s with tin gaskets.

Will performance be improved if I swap over the 2 camshafts aswell as heads . If i get a little better compression with the 3.9 heads on the 3.5 then I might get a little better performance .

AFAIK the cams have the same timing but the 3.9 is advanced 2 degrees for better low down torque. You will gain no performance by using the 3.9 heads as they are exactly the same.

You can tell if it is pre or post Dec 1993 build . The post jan 1994 will have bosses cast for the cross bolted mains on the sides of the block and a crank driven oil pump.
Regards Philip A

Originally Posted by PhilipA

According to the book, this is not correct. The keyway is the same length up to December 1993 build. the longer keyway is for the oil pump not the serpentine front.
There is effectively no difference in the 3.5 and 3.9 heads up to december 1993 engines. I do not know about the drillings for accessories. Up to December 1993 they had 14 bolt head s with tin gaskets.


AFAIK the cams have the same timing but the 3.9 is advanced 2 degrees for better low down torque. You will gain no performance by using the 3.9 heads as they are exactly the same.

You can tell if it is pre or post Dec 1993 build . The post jan 1994 will have bosses cast for the cross bolted mains on the sides of the block and a crank driven oil pump.
Regards Philip A

You are talking about the wrong engine with your book quotes .

The 3.9 engine this fellow has is one as the engine number he quotes a B suffix which makes it a crank driven pump and 10 bolt 28cc heads and it has the longer keyway and just so`s you know the 2 go together ,the serpy and the crank oil pump .

The KA model 92/3 has a ribbed belt for the alternator only and has 14 bolt heads and doesn`t have a longer key .

The vin number he quotes tells you it`s the last of the model an MA 1994/5 .