1987 3.2 Carrera Backdate project - Sladeys hotrod

[Gary71]

Oh and remember if you wind up the rear rates way more than the front you increase the relative rear roll stiffness so it will oversteer even more!

...and I'm not sure you need any more of that!

[haasad]

Mindful that with this conversion the rear shock towers would seem to be taking more load will they need bracing or other reinforcement ?

Andy

[sladey]

Tuthills fitted hollow 27s in my SC, keeping the fronts standard, and it seems to work well on road and track.

I re-read the backdate stages of this again last night. It's one of the threads which prompted me to push the button on a 911 purchase, so thank you for that.

You're welcome Al

OK funnily enough on the spring rates I ordered a set of 160's last night. I just got a call from Merlin Motorsport saying they will be another day before they get them in (which I thought was very good service) . Whilst talking about it he said the 160s would be very soft - if it was a kit car with weight up front then it might be what he'd expect. He was clear that he couldn't advise me on it though (which is fair enough). Talked it through and I've gone for 250. It's a guesstimate but hopefully shouldn't be too far out. The guy said if I put masking tape on them when I install them then he'll take them back and swap them if they aren't right - which again I thought was good service.

On the shock tower support - yes that does need doing - I've ordered the laser cut ones from Elephant racing - not cheap but they look cool. I won't be installing them straight away - I'll be dropping the engine in the spring to take it to Mike bainbridge to look at an oil leak - at that stage I'll weld the strengthening in. I don't think it'll hurt not having them on for a short period - I won't be doing any trackdays or anything

[dragonfly]

Would comparing to 964 spring rates offer a useful comparison, as they have coils?

[Bruce M]

The calculation in the link above appears to make some guesses over the material used to make the bars. Different steel alloys and different qualities. So those figures are useful as a relative measure between bars (illustrating the 4th power for diameter) but less so for the absolute measure.

A useful test is to measure how far the hub moves vertically from unladen to fully laden with both suspension types and try to match them or up rate by a known percentage. You have to allow for preload however.

[hot66]

Have you spoken to chuck at Elephant to see what he recommends ?

[sladey]

300 is his fast road recommendation

[911hillclimber]

If it helps:

My Lola race car has coil over and weighs a lot less than the 911, 560Kg to be accurate.

The rear coil-overs are at 20 deg inclination and the spring rate is 300 (each) at the rear.

Thus, the 911 with 300 will place a lot more weight on the spring.

This might serve a road spec 911 well.

My road/hillclimb 911 with a heavy 3.2 engine/box has 30mm 3 Litre Turbo rear bars which equate to close to 300 also.

It is magic on road or hill.

[sladey]

Thanks for that - I'm used to the compliance I get with the 25mm and like it - I don't mind going a bit stiffer but am optimistic that the 250 I've gone for shouldn't be too far out

[911hillclimber]

I think you will be v happy with the spring rate.
Setting the damping rate to control them will be the fun part, and critical too for the best performance.

I will be v interested to see how you get on with them, a nice mod and refreshing to see.

A compliant chassis on the road is a very good thing, and will add a lot of controlled speed.
A stiff rock-hard suspension is a distinct hindrance.

I don't think you need to do too much to the 911 to make a good improvement and loose very little as a result.
I found Bob Watson knew all the right tricks. and i for one would not hesitate contacting him at Nick Moss' Early911 place.

[sladey]

I've actually got bilstein sports at the rear - been on for about 6 years now and really like them

To fit the coilover conversion I have to have a groove machined into them

[911hillclimber]

Yes, for the lower snap ring. The body will be thin wall tube so tread carefully and choose a good machinist.

I know Mike Bainbridge has a good tame machine shop he uses for tricky stuff though he has a trusty lathe also.

He knows what he is doing.
I thought the dampers were adjustable, they obviously are not. Bob had mine re-valved to suit the 30mm torsion bars and the set are fantastic.

[sladey]

Interesting stuff - thanks for that

[Gary71]

Have you considered something like this?

http://www.demon-tweeks.co.uk/motorspor ... es-slip-on

I wouldn't fancy trying to machine a thin walled damper tube.

[911hillclimber]

Indeed, a better DIY prospect, slip over and run a nice MIG weld round the base.
I looked at those a long way back when I was still serious about hillclimbing the 911.
Decided an impreza was faster, and indeed it was significantly faster.
bloody great on AST Coil overs with 3 way damping.