Kerb weight
 

I am trying to find out what the kerb weight of a navigator with a 2 liter GT6 engine full fuel tank (std spitfire) is to work out the correct spring free height and Lbs required for the front end. I have seen mentioned 600kgs, is this a guesstimate, has anybody had their car weighed?

Pretty sure that Mr T has had 602 on a weighbridge.

Thanks oxford 1360, if that's the case then 150 lbs spring will have about 10 1/4 inch free length. Mr T mentioned he was going to fit a set of 150 lbs springs wounder if this was done and what free length they ended up.

From what i have read you need to have the lower A arm parallel to the ground when under it's own weight, the coil spring will then be about 7 inches in a compressed state so it all hinges on the kerb weight.

If any body has other ideas then please put them forward.

Yep, there's a VOSA weighbridge half a mile from my house and I know the manager, so he was happy to let me queue up amongst the HGV's. My straight six powered Spyder is 680kg's with a full tank, about the same weight as the fuel tank of the truck that followed me onto the scales...

I've now fitted early Spitfire 150lb front springs cut down by one coil. Coupled with an uprated front arb, these have massively improved the ride and handling and have preserved the stance I like too. The 150lb springs weren't easy to source but I reckon the Mk iv/v 180lb springs would be fine. Anything harder might give you faster lap times on the track but will make the car more difficult to drive on the road as the front wheels will hop off the tarmac instead of riding out the bumps. The thing with tyres is that if they're not touching the road they can't be gripping it. :(

I also read that the lower 'A' arm should be parallel to the ground for best results. I achieved that by cutting half a coil out of the 150lb springs but found that the nose went very light at relatively modest speed (about 50mph) making the car wander around and needing constant steering correction.

Cutting another half a coil out completely cured that issue and has left the lower 'A' arm rising slightly up from the chassis towards the wheel. I've driven over some pretty rough roads round here and have suffered no bump steer or bottoming out of the suspension so I'm happy with the result.

Good luck with your setup, I wouldn't get too technical with it, trial and error will give you the results you're looking for easily enough. :juggle:

Well Mr T, you have re-assured me no end with your last post.

I followed your example and cut a fair lump off my springs in order to get the stance I was looking for, and like all before me, knew that the lower wishbone should be parallel to the ground.

It was however just like yours, it rose slightly from the anchor point towards the wheel.

The only difference here is that my car will be a lot lighter than yours, so the ride could be a tad rigid methinks.

Would be worth finding some 150lb springs then, unless you fancy ending up on first name terms with your dentist...

Mr T in a previous thread you mention the weight of your spider being 780kg's, was this a typo.

It's 780kg's with a full tank. That puts it between the S1 Elise at 725kg's and the S2 at 860.

Even with my unstressed straight six only pushing out 79bhp that still gives me over 100bhp per tonne, and it feels quick enough on the road.

I do have a spare engine sitting in the garage that might just get upgraded when funds allow...

Something that is mentioned in few threads is to cut a compression spring down, this was a big no no while serving my apprenticeship as it leads to premature sagging due to stressing of the steel and bowing effect as the spring seat is no longer ground flat at the point of seating.

With this thought in mind it may be wise to locate a spring the correct free length/lb's for the vehicle weight or slightly shorter then add a spacer ring to the spring top seat to make up the short fall.

Oops, my mistake, looking back it is 780kg's.

It would've been quite easy to shave a couple of hundred kg's or so out of the car at the build stage - no luggage box, aluminium floor and side panels instead of ply and 'glass, alloy wheels, no heater, K series 4 pot motor etc. - so a sub 600kg version wouldn't be too hard to achieve.

A stripped out, single seater spaceframe chassis'd version with a modified VVC motor could easily turn out under 500kg's and over 400bhb/tonne. :flame: Just a thought...

Oh, and to put that weight into perspective, the stripped down '57 Porsche 356 Speedster weighed 794kg's.

I am planning to upgrade my existing engine in situ for a bit more power. I'll be replacing the cam later today with one from a Mk2 Vitesse, which should give me another 6 or 7 hp. I'll see how that affects performance then add in a pair of 1.75" Strombergs that are sitting in the garage for maybe another 6 or 7hp, followed by a Witor flow balanced manifold for perhaps another 10. The chap who dyno'd it for me also recommended bypassing the inlet manifold heating pipe for a couple of hp. If I end up with 100bhp I'll be happy, but more would be better. :)

Isn't that always the way...

Interesting point Mr T about bypassing the inlet manifold heating pipe, i suppose to prove this one i could rig a valve up to switch on and off while on the dyno. The 1.75 carbs and manifold will make the biggest improvement, did you strip the engine at the initial build stage to check all was well, here's a link http://sdrv.ms/1bXwKRr to the workshop manual for the GT6, i also have a tune manual which i downloaded for free off the net i will see if i can find the link for that. Here the link http://www.triumphexp.com/article/tr...phs_Vizard.pdf

Happy reading.

Another point I've read is to chuck the standard fan and replace with a thermo controlled electric fan which gives about 4bhp and better slow running cooling.

There is one major factor in the weight issue and that's the bloke behind the wheel so less pie's for me and lettuce sandwich for dinner, umm can't wait.:preggers:

It may be useful for a sticky thread to be started where we can post info on kerb weight and bhp etc of our cars, just a thought.

I've just added a link to this thread to the "Sticky" if it will help.

Already have the electric fan fitted.

Already on a diet...

1.75" Strombergs came with adaptors for the 1.5" manifold and needles fitted suitable for the Vitesse motor, but I want to strip them down, clean them and replace a few seals before fitting them.

Engine had allegedly just been rebuilt when I bought the car so I didn't strip it myself. Have a feeling the head gasket has failed as I've been losing coolant with no apparent leak. There's no 'emulsion' under the oil filler cap but the coolant's got to be going somewhere. Should find out later today when I start a partial strip down to change the cam. That'll also give me a better idea of the general condition of the insides of the engine.

Will take photos of course. :biggrin1:

In case you've got a few quid burning a hole in your pocket It's also worth noting that Canleys do a wonderful range of "stuff in alloy".

So you can replace oem steel bits with a considerably lighter alloy part.

Obviously this doesn't' get around the "who ate all the Pies" issue, but having less money may end up with you also spending less at Greggs? :)