Tail shaft and ims upgrade

[Slowxr6t]

Hi guys, I have boosted up the power of my 15fgx xr6t, stock it had 258rwkw with just a k and n in stock airbox, now after it's been on my hoist for 11 weeks and undergone some internal and external spanner surgery and it's going and all tuned again shes making 382rwkw at 15psi on dyna pack hub dyno. My concerns are 1 the tailshaft. I'm running stock size 245 tires so it spins pretty easy but hooks up in 3rd gear in the zf in the dry. I'm not into power skids and burnouts, but enjoy getting a wheel going as we all do lol. Is my tailshaft going to break? Do they snap on the thin bit before the diff or does the tube twist and break? I'm a bit paranoid about it, if I have to replace it, I think I will get a carbon fibre driveshaft. Also will my axles be fine at my power level? The car has done 30000ks and before any mods when I accelerated hard then quickly backed off there was a thud in the back end, like it was squatting under power then unloaded and went thud, not badly but definitely noticable every time you do it, even does it in town now if you feed it some then back off. What's the noise boys? I'm guessing the bushes holding the diff. Is there any downsides/negatives with the IMS upgrade? Apart from the price. It's not a bad noise, should I just leave it alone until it really gives grief? My main concern is the tailshaft and the damage it will do if it lunches itself. My car made 414rwkw at 18psi but we backed it off to be kind to the drivetrain and the pistons. Opinions please fellow barra modifiers, cheers guys. 

[cat007]

Howdy,

 

382rwkw on 15psi!? Nice work - what turbo?

The thud in the back is the diff bushings. Stock they are too soft so allow the diff to bang around inside the bush. They wear out and really should be replaced with something better. There's loads of info around about diff bushes. Mine were done about 20km's ago and really need to be done again I think as I hate that sound.

 

Something that will break the driveline, is doing a big kickdown pull, I.e. flooring it and letting it kick down to second or even third. The torque load up when this happens is huge and without being able to spin, something will likely break.

[Slowxr6t]

Hi cat007, my turbo is a Garrett 35r with .70 compressor housing and I plumbed a turbosmart 45mm external gate onto the 1.06 external gated turbine housing, it plumbs back in under the car into the 4inch dump I made, its 4inch off the turbo right up to the stock 3 inch flange under the car, the rest of the exhaust is stock, no cat! Car made the grunt easy as just by freeing up the exhaust side, I'm happy as. I did lots of other stuff to it. Ask if you're interested. Cheers

[k31th]

The IMS diff hat solution is great aside from cost, effort to install and mild increase in NVH from regular driveline processes.

 

tailshaft usually breaks on FG's by twisting between the centre bearing and diff mount CV... but that'll only usually happen at the drag-strip when you're on slicks of some sort and you get plenty more grip than usual and you're trying to launch on boost.

[Slowxr6t]

Thanks k31th, what is NVH? Excuse my ignorance.

[k31th]

noise, vibration and hardness. basically all of the things that luxury car manufacturers want to avoid

[cat007]

The IMS hat-trick is a good solution but yeah it is pretty pricey.

Going to something like the SuperPro bushes, will that eliminate the 'BANG' from the rear if you lift off after a head torque load? I.e. hard acceleration in 2nd or 3rd and then lift off suddenly.

 

I too would rather not twist my tailshaft. What sort of RPM and boost would be safe to launch on the track while running 245 'street' tyres that are not slicks? I want to get my 60' down but would like to drive home haha

[k31th]

Yes, with new bushes you'll remove the banging in the diff bush area as you're basically hitting the diff bolt onto the bushing housing when the bush is cracked/broken which causes that banging. Your choice of bush(es) just gives you a range from "comfort" (soft and smooth) to "hard" (lots more NVH but best power transfer - can then break the diff bolt if you have a bush that's too hard).

 

basically whatever you want with regard to street tyres as if you go too much rpm/boost then it'll just spin them rather than gripping enough to break your tailshaft.

[Slowxr6t]

What about with comfort bushes in the ims setup, so not real harsh, has anyone tried it, or does the diff need to be pretty solidly mounted to reduce problems? Iv got standard suspension and I'm not going any firmer. Dont want it to become a dog. What extra nvh is there, under what driving conditions?

[k31th]

it's fine to use whatever choice you like with the IMS setup as the bushes aren't under anywhere near as much lateral force which means it's not going to destroy them (or at least significantly less likely to destroy them). that's kinda the point of the IMS setup, though, to prevent the diff bushes from being destroyed.

 

there's a little more diff normal operation rollover noise under all driving conditions over the stock diff hat setup.