Deciding on an engine

There are several main factors that will determine your engine choice:
Race/Road - Where will you be using it?
Vehicle weight - What car is it for?
Size - Is the engine bay big enough?
Money - What's the budget?
Transmission - How is the power getting to the road?

These things all seem pretty obvious but its easy to forget one or more and make the wrong choice. So how does each affect which engine you should use?

Race/Road
If you are racing then check your regulations first, your options may be very limited. For both road and track easy of driving will make the car faster but the main difference is the rev range you will want to be using and the amount of fuel used. As a rough guide, on a track a good usable rev range is 3500 to 8000 rpm. On the road that bottom end needs to be much lower to make it easier to drive in traffic. As the cam timing has to be optimised for a specific rev range this means more torque and low down power but less peak power at high revs.
In practice, the lower on-cam rev range produces a faster driving car under circustances where the full rev range cannot be used - ie on the road. Higher rpm means increased engine wear, higher temperatures and significant extra strain on transmission components.

Vehicle Weight
The vehicle weight makes a difference when looking at which engine is most suitable. A simple formula can give an indication of which engine option is more suited.

C - Car Weight (no engine or transmission)
E - Engine & transmission weight
P - Power output

Power/Weight ratio: R = P/(C+E)

When C is small (lightweight race car), E makes a very big difference to R. When C is large E has less effect.
Make sure to do this calculation including the ancilliaries, gearbox, starter, flywheel and clutch. The results can be surprising.

Size
Although you can guarantee someone will take the time to squeeze almost any engine into any car, it normally involves a lot of work and a level of compromise that can defeat the original aim. Related to the size is also the problem of moving the centre of gravity. In the C23, the engine is placed well toward the centre of the wheelbase so increasing the mass of the engine has a small effect on handling. On many road cars the engine sits in-line with the front axle - increasing the mass well away from the COG will change the balance and could ruin the handling.

Money
A common mistake when building a kitcar is to pick and build a car around an engine you already own under the assumption that it will save you money. It almost never works. The cost of a basic production engine will likely be less than 10% of the total costs of building the car. When assessing the installation cost you must look at the whole engine and transmission package. At the very least you are likely to need:
Basic Engine
Wiring Loom
ECU
Throttle-bodies / carbs
Camshaft
Starter motor
Alternator
Clutch
Clutch slave cylinder
Gearbox
Radiator
Exhaust system

If you want to build a high performance engine then additional costs are involved:
Machining
Con rods
Oil cooler
Rolling road session(s)

Don't forget to factor in the running costs - a high compression engine will need fully synthetic oil with frequent changes and may require octane boosted fuel.

Transmission
An engine doesn't work on its own - a lightweight engine is only a benefit if a suitable gearbox can be used that keeps the total package weight low. The gearbox must be able to handle the torque, the cost of a clutch, flywheel and adaptor plate should be considered as should a starter motor. The position of the selector shafts/gearshift can be quite critical in getting a slick and usable shift.

Conclusions
During the development of the C23 we tried several different engine and gearbox combinations. We looked at all of the above factors and created a multitude of spreadsheets to work out what engine and gearbox package gave the best combination of power/weight/size and cost. The differences between the options are in some cases quite small but as a total package the Duratec/Audi combination is a real winner. As a standalone engine the Duratec engines give outstanding performance for cost.

Review
Race/Road - The Duratec offers a very wide power band with low-rev torque that benefits road and race. The 2.3L option makes for a very fast road engine with the minimum of tuning parts and keeps high reliability. The 2.0L engine makes very impressive power with a top end of 8000rpm and upto 250bhp available without head machining, perfect for racing.
Vehicle Weight - Duratec engines have high-torque output and low weight. Designed to move cars in the 1500kg range the Power/Weight ratio in all vehicles under 1200kg is very favourable although vehicles at the top end of this category might benefit from larger capacity engines such as V6/V8 units.
Size - Duratecs are compact design that will fit most LSIC and Mid-engined apps. Upto 225bhp the short exhaust header system gives the best results whilst also being very small making exhaust routing much easier than Rover or Honda alternatives that require longer header and branch manifold to work effectively.
Money - For an inline mid-engine rear-wheel drive layout, the Duratec/Audi solution is the most cost effective high-power solution for both road and track use. The main reason is not the engine cost, which is comparable with alternatives such as the Honda K, but the total package cost. By utilising oem components in a custom adaptor the transmission cost comes in at about 70% of the alternatives without over-stressing the gearbox and keeping a fast synchromesh box. An organic clutch can be used even for racing.

We offer a fitting service and we're always happy to offer advice.