Home
Site Updates
Specifications
Performance
Literature
Contacts
Technical
My Car
Galleries
Sprinting
Days Out
Links
The Blog
Mail Me

Engine


Capacities


The Rover V8 has been available in a wide variety of capacities from the factory plus others available from aftermarket tuners. This is usually achieved by using different stroke cranks in conjunction with the '3.5 litre' bore of 88.9mm diameter or the '3.9 litre' bore of 93.5mm (early) or 94mm (later). All the dimensions quoted here are in metric for the sake of consistency, but the engine was originally all imperial (it started life with a 3.5" bore and 2.8" stroke hence some of the funny metric sizes).

The following cranks are typically available, although this is not an exhaustive list:

  • 71.1mm - Standard 3.5/3.9 litre
  • 77mm - Used in the factory 4.2
  • 80mm - TVR Power amongst others
  • 82mm - Latest factory crank for the 4.6 RV8
  • 86mm - JE Developments amongst others
  • 86.4mm - Real Steel special
  • 90mm - TVR Power

Here is a table which shows how the commonly used capacities are reached using these parts. Note that not many people use the 88.9mm bore:

88.9mm93.5mm94mm
71.1mm352839053947
77mm-42284278
80mm--4444
82mm--4552
86mm--4778
86.4mm4337*-4844*
90mm--5000

* - when used with +020 pistons supplied in the Real Steel kit.


Cylinder Heads


There are 4 types of factory cylinder heads for the Rover V8. These are the pre-SD1, the SD1, the Vitesse, and the RV8 type. There are probably not many pre-SD1 heads in circulation now. Apart from having more restrictive ports they also had smaller valves. The SD1 and Vitesse heads come from the same casting and are almost identical. The RV8 heads have bigger ports but the same sized valves as the SD1 heads. They also have smaller combustion chambers. This is worth remembering as there are many people selling new 4.6 bottom ends but if these are used with SD1 type heads the CR will only be around 8.5:1 unless some machining is carried out. Standard pre-SD1 valves are 38mm inlet and 33mm exhaust. SD1 valves are 40mm inlet and 34mm exhaust, the Vitesse and RV8 having waisted stems. The commonly used big valves that fit on standard seats are 41.4mm inlet and 35.5mm exhaust. Ultra-big valves are 43mm inlet and 37mm exhaust. Standard valves can give close to 300HP while race engines equipped with ultra-big valves can produce approaching 400HP. To reach these power levels the heads have to be extensively ported.

The other heads available in the UK are special castings from Wildcat Engineering. These are a completely new casting with much larger, higher ports that have a straighter path to the cylinder. These heads can be fitted with 49mm inlets and 41mm exhausts. Power outputs of 400-450HP are easily achievable with these if the rest of the engine is built correctly.


Power Outputs


The Rover V8 seems to be the victim of more bogus power claims than any other engine. Sure it is big, but it is old fashioned with a particularly poor cylinder head design. This is reflected in the relatively poor BMEP that can be extracted from these engines. BMEP (Brake Mean Effective Pressure) is the average pressure exterted on the pistons. It is used by all serious engineers to compare the efficiency of engines since it does not depend on capacity or rpm. A figure of 140-150psi is considered to be poor, values of 190+ are very good and the most highly tuned purpose-designed racing engines such as F3000 produce around 230psi. The standard Rover V8 produces 139psi. Discussion with a number of Rover V8 tuners, plus study of some engine dyno printouts, reveals that a good road/competition engine will produce around 165-170psi. Using production based heads only the very best engines (with extensive porting and very large valves) will produce 170-180psi. OK, this is very esoteric, and few people have the BMEP directly available for their engines, however look at the formula for BMEP for a 4-stroke engine:

BMEP = Torque (ftlbs) * 2473 / Capacity (cc)

It is obvious that there is a direct relationship between BMEP and torque output per litre. By plugging the BMEP numbers quoted above in to this formula you can say that a standard engine produces 56ftlb/litre, a *good* road/competition engine produces 67-69ftlb/litre and the very best engines make 69-73ftlb/litre. Bear in mind that these figures are the peak torque. By the time peak power is reached the engine is operating less efficiently and torque per litre will have dropped by at least 10%.

As everybody quotes torque and horsepower outputs for their engines it is thus easy to spot the people peddling bullshit. As an example I know somebody who bought a 3.5 litre engine that was supposed to make 280HP at 5000rpm. 280HP at 5000rpm is 294ftlb of torque. This is 83ftlb/litre. From the above you can see that this a ludicrous claim. Sure enough, the car was a dog and it wasn't long before he was looking for a new engine.


Costs


If you build your own engine and do your own porting then you should be able to build a 220HP 3.5 litre for about 1000. This assumes you need new pistons, a rebore, new bearings, cam, lifters, valves, inlet manifold and carb.

Most people cannot port cylinder heads and if you buy them from a head shop then the cost for the 220HP 3.5 will rise to around 1500.

A number of the top Rover V8 tuners will build you an engine of around 4.2-4.6 litres that produces around 270-290HP for about 3500 if it uses a single Holley or modified standard Efi, around 4500 if it uses quad carbs. At this price the engine will still have cast pistons and standard crank and rods.

Above 300HP the cost goes up exponentially. A tuner-built 5 litre engine with steel rods, forged pistons, dry sump, throttle bodies and full engine management will set you back around 9000-10,000 and will produce around 380-400HP.


© Ian Crocker
Last updated on Apr 20 2001