Engine parts Quality

[Ian Durrant]

To gain an increase in capacity over the 3.9 litre it is necessary to stroke the crank ( ignoring the very slightly larger 3947cc Land Rover bore).
if you use a standard crank and off set the grind on the big end journals you can gain nearly a 1 mm stroke gain which increases the CC and allows the piston to be at TDC fractionally longer and develops better torque.

Micky

I always thought a stroked crank gave better torque because of the lever effect, where the greater the offset of the crank, the longer the lever of the connecting rod to the crank?

[Motorsport Micky]

could the same thing be done with a stag crank ?

dave

To stroke a crank by this method it is important that the standard crank is of such a bearing dia and strength that it can stand the offset being ground into the bearing journal to gain the off set.
Also there has to be access to bigger big end bearings (which need to be a larger dimension to accommodate the different bearing diameter) for example on the 4 cylinder TR we used Massey Fergueson tractor big end bearings at -.060 that's MINUS 60 thou to standard, (...strong coffees for any Stag owners who have fainted). Obviously the cranks have to be rehardened by nitriding or tuftriding so as to maintain an acceptable wear characteristic on the crank and I for one would not consider the Stag crank to be robust enough or suitable for such treatment.

Micky

[Motorsport Micky]

I always thought a stroked crank gave better torque because of the lever effect, where the greater the offset of the crank, the longer the lever of the connecting rod to the crank?

Agreed, but without disseminating all the various affects in infinitesimal detail I thought my comment covered it. The increase in capacity also gives an increase in power and torque, the same as boring the liners out to a larger size.

Micky

[Escape]

The Rover 3.9 and 4.0 are in fact the same engine, different names being given depending on the injection system fitted. The 3.9l is achieved by increasing the bore, 94mm from 89mm in the 3.5l.
Next came a 4.2l with the same bore, but a longer stroke (77mm) was achieved by machining the cranks from the diesel project Iceberg, as described above.
The 4.6l uses a newly designed crank with a stroke of 82mm and the same bore as the 3.9/4.0.
TVR (and others) further increased the stroke to achieve 5.0l and engineering companies (like V8 developments) have continued the work and are now offering up to 5.4l, with both a bigger bore (96mm) and stroke (93mm).
I do want one of those for my Range Rover...

Filip

[wilf]

In general, it is cheaper to gain BHP and torque by fitting the likes of a chevy or ford small block, rather than upgrading a RV8.

Even a pretty standard ( and very cheap!) 350cu in Yank V8 outguns a tuned RV8 by some margin, especially for torque which is what you want in a RR. Obviously there are other issues like headers and gearboxes, but the rule of thumb holds engine wise. I did a lot of work on both engines not that long ago. And ended up going the US route.

[Motorsport Micky]

In general, it is cheaper to gain BHP and torque by fitting the likes of a chevy or ford small block, rather than upgrading a RV8.

Even a pretty standard ( and very cheap!) 350cu in Yank V8 outguns a tuned RV8 by some margin, especially for torque which is what you want in a RR. Obviously there are other issues like headers and gearboxes, but the rule of thumb holds engine wise. I did a lot of work on both engines not that long ago. And ended up going the US route.

Hi Wilf,

I don't believe the enquiry from Dave was to further a desire to swap his engine for a Rover or anything else, he was asking whether some of the Rover technical mods could be used on the Stag and what some of those technical terms meant.
Hopefully he will retain his TV8 with suitable mods, myself if I was wishing for more go from the TV8 I would be asking Tony Hart for his opinions and what he thought could be done, the man has loads more experience than I and many other Stag owners.

PS; if you forward me the petition for Gwondanaland to be reunited I'll sign it lol.

Micky

[wilf]

Micky - you are right about Dave, but I was responding to Filip's comment about wanting a bigger displacement RV8 for his Range Rover.

I think Gondwanaland is a lost cause.............

[Escape]

Not wanting to go off topic too much, but do want to reply to Wilf.
I agree fitting a (bigger) US V8 would be cheaper (although the fabrication required and different gearbox will add to the cost), but I'm not a fan of those. I had a Range Rover based offroad proto with an LS2 from a GTO a few years ago, and the engine never really convinced me. Sure, it was more powerful than the smaller and older RV8 it replaced, but still the same old OHV design with added complexity.
Now the Lotus-designed LT5 from the original ZR1, that would be an interesting option. But not cheap I'd think...
So I'll just fiddle a bit with the RV8 if I feel like it, after all it's not for racing, just for fun, and building is part of the fun for me. Besides, if I were to replace the RV8 in the RR with a Yank V8, the next logical step would be to put the RV8 in the Stag. Which would no doubt start another discussion on here.

Filip

[wilf]

Ah Filip, those old 2V OHV yank engines are simplicity itself, much like the RV8 if I am honest.

I kept away from the LS series, preferring the older generation, carb fed dinosaurs. They really can shove out enormous torque and power for not much money. And with just a little supercharger boost.........

[Westfaling]

I've just had to pull the front off my freshly rebuilt TV8 to sort out a timing chain rattle. But I had a brief period between running-in and the rattle when the sound of the TV8 on song with the top down was so worth it. Wouldn't switch for the world! .. Or maybe that's the cognac talking

[staginhiding]

Felt for you Nick,we've all been there..hopefully sorted now..If not more Cognac

Sam