996 4s - diy 3.9 x51, reworked heads, schrick etc

[diceman]

Nice work!

 

[Tim_s]

Been a while since I've updated this, things have slowly been ticking along. For one, went for a service at Cameron and got some pics, see below. On 3k ish miles on the engine now.
I've also figured out what's going on with the rev limiter kicking in too soon and the slight annoyance on transients. Turns out there's some noise on the crank VR signal - so datalogging at high rpm it's spiking a bit kicking in the rev limiter, and on and off throttle it's a little fuzzy. Not detectable on the rev counter, only datalogging. As annoying as this might be, I'm happy to have figured out what's going on. Interestingly maxxecu doesn't exhibit the high rpm issue so presumably has a more robust VR conditioner circuit than the factory dme, but it does suffer from the same noise on and off throttle.
Anyway, I tried changing the sensor, no luck. So reluctantly off came the gearbox to have a look at the flywheel and sensor interface. All looks good, but new stuck a new dmf in there while I had the box off. Car's still in bits so not had chance to test if I've fixed it or if more troubleshooting required. I contemplated a lightweight fw while in there but decided against it for driveability, noise, harmonics etc. Researching did make me realise the 997 3.8 has a harmonic balancer so I've bought one.
Making the best of having the gearbox off, I also bought a quaife ATB. I went for an ATB as have a blackline in a bmw and find it perfect for road use. Annoyingly I misinterpreted 'with flange retainers' on the quaife tech drawing and ended up with the diff for flanges with snap rings, not bolted. Quaife have been pretty unhelpful and I've not managed to find any cheap used ones so have decided to machine in a snap ring groove into my existing diff flanges. But porsche don't have any stock of snap rings and keep pushing the update date, so I've bought generic ones. Off to use a friend's lathe tomorrow to have a go at this, hopefully then can get it back on the road! That and I slightly damaged a carrier bearing removing it and so had to buy a replacement, and have a smidge more backlash than before, so am reshimming by 0.1mm to get it back to spec. I weighed the quaife vs the original, a 700g penalty for the quaife.
In the spirit of 'while there', I also acquired some pfc 350mm v1 front disks for £300, 9kg vs 11.9kg for the originals, so a handy 6kg saving and bolted right on with 10mm steel washers to space out the calipers. I also replaced the brake line under the car and the rear link pipes and acquired some brand new wheel arch splash guards cheaply.
Weight savings over factory now at approx 125kg.
Remaining on the list are a coolant pipe replacement at the front which has been weeping a little, and pondering what I can do exhaust-wise to get a better flow path and larger diameter manifold primaries and see if I can go significantly lighter than the 21kg in the backboxes (8kg for each box + 2.5kg for the brackets to hold to the engine).

 

[bananaz]

That 4S is having a happy Christmas this year!

 

[Mark Vine]

I had not seen this thread before , having only joined this year. I read with interest as it makes my thread a little boring. I have just had my indy remove my engine for rebuilding into a 3.9, however, you have my greatest respect in doing the work yourself. My days of removing the gear box and engine are behind me now, age is not on my side, nor the tools that you need to do the job.
I look forward to getting my car back and seeing the difference.

 

[Tim_s]

That 4S is having a happy Christmas this year!

Certainly is!

I had not seen this thread before , having only joined this year. I read with interest as it makes my thread a little boring. I have just had my indy remove my engine for rebuilding into a 3.9, however, you have my greatest respect in doing the work yourself. My days of removing the gear box and engine are behind me now, age is not on my side, nor the tools that you need to do the job.
I look forward to getting my car back and seeing the difference.

I don't know about that, most of my thread is my rambling about stuff I've cocked up or isn't working! I've been reading your thread with interest, I'm sure it will be cracking when done.

Few small updates here, the bolted diff flanges are shorter than the ones with snap rings and so my plan of machining snap ring grooves in was never going to work! So a set of snap ring style flanges ordered from 9apart and duly machined and fitted to the car. I'm not very impressed with their fitment in the quaife, the crown-wheel side flange bottoms out prior to sitting flush with the diff face (hard to describe, see pic). It does however clamp against the snap ring without any play. On the other side the flange sits in a bit deeper but as a result there's perhaps 1mm play before the snap ring. I'm sure it won't impact anything functionally, but a little disappointing. That and the snap rings needed reshaping and annealing before I could get them to fit, the quaife doesn't have enough lead-in before the splined bit so they get caught and won't go in. Annoying, but hopefully they're still held in well enough.
At least it's all back together now and the backlash is pretty perfect with a 0.1mm larger shim. I've measured off the diff flange and extrapolated out for the smaller distance.
I briefly fired the car for the first time in a few months, it sounded great with a purposeful bark, I'm looking forward to driving it again!
A few other pics of harmonic balancer and one or two I forgot to add to the previous post from its visit to Cameron.