Lightest engine and gearbox options

Fly in the ointment from me.....If you want light and lots of geeeewhizz then has to be a bike motor.

[snapper]

Don't use the Freelander diff unless you have a bike engine.
The ratio is 3.2 to 1 giving you 120 mph in 3rd, 145 mph in 4th and 175 in 5th at 6,800 rpm.

With the aerodynamics of the Roadster being what they are (brick like) you would probably hit peak road speed in 3rd and have quite slow acceleration.

There are not a lot of light options for the diff but the 7" will be lighter than the 7 1/2" and both lighter than a fixed axle

[ACE HIGH]

Why not look at a Harley Davidson 1340 or 1500 cc bike motor.I believe that torque is more important than Horsepower and while there engines are around 85 hp unstressed they are very well made,I am not up to date with the latest Harley motors/gearboxes,do any of them have a reverse?,not as silly as it sounds as the big Harleys are around 300/350 kg and must be a problem at times to manouver when stopping.Maybe they make them bigger than 1500,or perhaps the bigger Honda cruisers,they would present some cooling problems but would be light weight,which is the way to go,not excessive horsepower .David

[deezee]

When building a sports car, your best putting in a sports engine. Harley bikes are built for cruising and not acceleration. The 80 lb/ft torque of a slow revving VTwin is embarrassing compared to the 150 lb/ft from a stock zetec.

[Balidey]

Originally Posted by snapper

Don't use the Freelander diff unless you have a bike engine.
The ratio is 3.2 to 1 giving you 120 mph in 3rd, 145 mph in 4th and 175 in 5th at 6,800 rpm.

There are not a lot of light options for the diff but the 7" will be lighter than the 7 1/2" and both lighter than a fixed axle

I thought that Westfield used the Freelander diff in their cars?

As for engine choice, I think it will be eventually be the lighter all alloy Ford item, so the Duratec / Zetec SE will be the ones I will be looking out for. Not sure on capacity just yet.

I am not 'anti-bike-engines' its just I think its more sensible to me at the minute to go car engine.

[deezee]

Both the Duratec and the Zetec SE required a fair bit of mucking about to get them running. Plus they are more expensive than a plain old Zetec. If your car weighed in a 600 kgs @ 100bhp (165 bhp/tonne) for the SE and 635Kgs @ 140bhp (220 bhp/tonne) I'd go for the plain cast 2L Zetec.

[Balidey]

Good point, well made. Thanks.

[ACE HIGH]

NZ's most successful home made sports car was an air cooled Lycoming aircraft engined special with a home made 3 speed gearbox,engine around 4 litres,max revs around 3900 rpm,built around 1956,max speed about 140 mph ,developed to about 160mph.weight about 700 kg.This car could out accelerate many exotic formula 1 racers of the day and when one hears it racing it sort of just chugs around,the diff ratio was about 2.1 to 1.The point is:there are horses and horses and while the Harleys are cruisers with poor road holding they can accelerate OK.I believe that an 86hp Harley would give a much better spread of power than the 125 hp Toyota I had in my Chevron 7 and coupled with the light weight I believe it would have gone faster.Google ralph watson lycoming for a look at an interesting vehicle and an incredible engineer.David

[Bimbleuk]

Originally Posted by deezee

I suppose instead of the Ford option, try a 20v 4AGE from a MR2. Its a 1.6 supercharged knocking out around 170bhp. All aluminium engine. Use the aluminium RWD gearbox from Toyota again and it will save a fair bit of weight.

The MR2 mk1 had the 1.6 16V 4AGZE which was supercharded and iron/ally. Don't bother its old tech and very heavy with all the cast iron bracketry and inefficient Denso blower.

The Mr2 mk3 had the all ally 1.8 1ZZ-FE. Not too heavy but only about 140BHP and quite bulky like most of the all ally engines.

The blacktop 1.6 4AGE 20V engine from Japananese imports only is one of the lightest and most compact small engines (excluding bikes of course) you can fit. 150-160 BHP and around 90kg if you include the manifolds and standard individual throttle bodies (fitted as standard). Due to a light flywheel and lightened internals compared to all previous 4AGEs.

However you will still be hard pressed to beat the Rover K series engines for lightness. Again a bit more bulky due to the all ally design but about the same or lighter than the Zetec SE and up to 1800cc.

I found the very early Sierra diffs are about the same weight as the Freelander diff at about 17-18kgs. All later Sierra diffs I believe are at least 22 kgs or above. The only draw back is the driveshafts are unique to the early diffs as the input diameter is smaller for the driveshafts.

[deezee]

Originally Posted by Bimbleuk

The MR2 mk1 had the 1.6 16V 4AGZE which was supercharded and iron/ally. Don't bother its old tech and very heavy.......

However you will still be hard pressed to beat the Rover K series engines for lightness.

I can appreciate that its not the most advanced engine out there, but half the "engineering" on new engines is for emissions, which hardly matters to home made sports cars. Also, like I've mentioned before, surely bhp/tonne is the figure that important here and the 4AGZE is well over 50 bhp/tonne better than the K series

Besides, don't you have a Toyota engine in your car