Patrick's 1986 944 Turbo by 333pg333

8 minute(s) of a 264 minute read

Steve, I'm sure you're right in what you're saying and thanks for putting that all down. Here are some observations from the engineer to add to the mix. I knew something was up....

"Hi Patrick,

I’ve been analysing some of the data in more detail and what I have discovered is the following.

We have been using 45mm of rear damper travel at the track. This probably equates to around 70mm of wheel travel.

Unfortunately the car needs to have more droop travel through some of the higher G force turns. The inside rear wheel is lifting off the ground, this is the jacking effect that Paul was talking about, at the time we thought it was being caused by too much rebound damping and we removed some.

Factory setup have the droop controlled by the bolts retaining the outer torsion bar bush, your application probably has the rear droop controlled by a spacer above the piston within the damper so some damper or rear suspension setup mods will be required before the next outing.

If you look at the data particularly suspension position [position each corner in a new graph on the page] you will see that the lr suspension pots flat lines during some corners at around -22.

At this time the rear wheel is starting to lift of the ground and the rear will start to become unstable. 

Your video also confirms this as you have to correct your line on entry , you were travelling 16 klms quicker than the previous lap and the gpsmap shows you wider on entry before the apex which all added to the event.

The rear end appears to be rolling more that the front but a more accurate measurement of motion ratios would be required before you could call this a fact.

Everywhere that the lr suspension starts to bounce off the full droop point is where you were complaining about a lack of rear grip so we need to rectify this before next outing. 

If there are no spacers within the damper then we may need to get extended rose joints, Im a bit surprised that this has occured given that you bought the dampers to suit this application.

Mark

Rsport Race Engineering"

I also wonder about the rear inside lifting. Perhaps he means on the track that day as opposed to just at that corner before the crash. However even if that was the case it may mean that the inside wheel was not actually lifting off the ground but still could have been getting pretty light. Also, as has been noted, I slip initially and correct before the main 'let go'. There are also some bumps through there which could have easily unweighted part of the car. Not everything has been discovered yet I feel. I want to resolve this before taking to the track again. Collin, I don't have the ride height but it was not slammed low at all. I suspect it wasn't all that much lower than normal ride height but don't have the actual measurements.

4/27/12

Going to inspect a shell we have to see what other parts we can scavenge off it. There's not a whole lot left. Kinda like going back to that chicken in the fridge for the 4th time! Doors and rear 1/4 panel I'm thinking. Most of everything else is already gone...even the 1 piece roof!

5/5/12

Still not sure yet what lies beneath but from what we can see it 'appears' to be mostly surface or panel damage. The shocks look straight, the shock pots didn't break, the wheels look straight, the roof is straight, windscreen intact...tie rod bent and sway mounts seem to be the most obvious undercar issues. Might just have been really lucky and hit the tyre-wall at the perfect angle. 

Also note the shot of the rear rh wheel. I hadn't paid much attention to this in the past but the builder and engineer are very much convinced that there is not enough droop or suspension travel. Bit hard to compare with the body kit on there but in the flesh it certainly doesn't look like it drops down much. What would 'normal' travel be? 5"...more, less?

Does this rear 1/4 panel look usable in terms of the cuttoff point? 

Oh, got a basic torque read too. Doesn't cross at the normal 5252rpm. Guess that's just a scaling thing. Not sure if it can be re calibrated to the 'normal' position or if it would change the actual curve. Looks like about 365ft/lb on the 'optimistic' pull. Doesn't seem a great deal of tq either way. I suppose that's also just dyno to dyno.

5/8/12

I just don't know and it's driving me quite a bit insane not knowing what the definitive cause was. I'm still thinking it's more than one reason but can't claim to know the exact combination. Going to be a few more weeks before work even resumes on the car. More time for it to rattle around in my head for days/weeks on end. More YaY!!!

5/12/12

I'm kinda sick about the whole thing tbh. Took so much time and money to get it there only to have that happen. Not knowing the full cause and quite possibly never will further exacerbates the frustration. 

Now I have a guy in the UK who is a cage builder saying that I should probably not re use the cage in my car even if the chassis/body is repairable. I don't believe he is trying to sell me anything, merely pointing out his observations. Said that in super slow motion video cages deform and can go back to 'normal' without being recognisably affected, but he says the metal can have fatigue or weakening. 

So either I'm faced with fix body but cut out cage and start again. Or body no good & re-tub. Realistically a painful and expensive process down here. Or just a plain old rebuild a totally new car. None of these options appear attractive. Could fix body and turn blind eye to possible cage issues which doesn't sound smart. Not sure how to test if cage has been affected? If floor, mounting points and suspension pickup points all look good perhaps it's ok? Just have to wait a few more weeks until panels stripped and assessment can be made. Frustrating and daunting.

I'd like nothing more than to do this and halfway done already. Just not going to happen like this just yet. My builder is super busy at the moment so work won't start for another week or 2. I will put to him concerns or questions about re using the cage. I am pretty sure he'll agree with you, but are we all being a bit ignorant and maybe the cage guy in the UK knows more than we do? If the cage happens to be visibly deformed I'm not sure if you can replace certain parts or have to start from scratch? Because we haven't pulled the panels off yet I don't think I can make a call on the overall outcome, but I do have parts heading this way already. Looking at seats now but want to wait to hear outcome of damage first. Re tubbing is not easy even though you've mentioned it. Building a whole new car is not an option right now, so just have to wait to see how this one looks underneath.