Just curious, what is the difference between sierra IRS and a live axle in weght terms?

Only for the fact that my Avon with a full tank (approx 28 litres) weighed 490kg with Blade engine. (without me though)

bar throwing out the seats I can see much more weight loss without resorting to expense.

Fortunatly I'm a skinny git even though 6'4" and therefore I wont add toooo much

the most significant difference is unsprung weight, not over all weight, which might even be similar. not sure. depends on the rear uprights i suspect.

More variation between different weights of live axle-
An "english" MK1 Escort style banjo axle is a lot lighter than the salsbury "atlas" style axle from a 2 litre Cortina.

With english axles you can also get a light alloy diff carrier to cut the unsprung weight even more.

My X Flow with IRS just SVA'd came in at 560 dead with full tank of fuel
How does this compare with other non bike engined cars ?

Like JoelP said, sprung vs unsprung weight is the key, they probably weigh similar on the scales, but when you are out driving the setup with less weight that is just hanging there (a full axle vs axle carriers), can greatly improve handling, if done right. A live axle has an advantage, it keeps the wheels parralell to the ground at all times, but is heavy and cannot react to the suspensions needs to move as fast, IRS is lighter and will be able to keep up with changes in the road surface better, but if they are designed incorrectly will not keep the maximum tire patch on the road and you will lose traction. A good compromise is the dedion axle, especially for hommeade cars, it is simple enough to do at home, almost as it has less unsprung weight as a live axle, and will keep the wheels at the right position in relation to the ground at all times.

Table of car weights here:

http://www.fluke-motorsport.co.uk/weight/complete.html

Having considered this in the past i came up with the following which you may find helpful. The numbers are from my own measurements and calculations plus other peoples supplied info, so accuracy is not 100%.

live axle
axle casing inc brackets, standard diff, trailing and lateral links, coilovers, prop, brakes.
unsprung 56kg / sprung 7kg / total 63kg

dedion
std diff, trailing links, coilovers,lateral linkage, disc brakes and calipers,driveshafts and joints (narrow), propshaft, dedion tube an alloy ears
unsprung 37kg / sprung 37kg / total total 74kg

IRS
std diff, driveshafts, hubs/uprights(alloy), wisbones (std bushes), brakes, coilovers, propshaft, additional chassis work
unsprung 37kg / spung 46kg / total 83kg

Hopefully this is of some help.

Like I said earlier, a properly done IRS will provide better lap times, it will just handle better and be able to keep up with the changing road surface. Although I dont see how the dedion and the IRS weigh the same.

nice example stressy.