tomato

I'm sad ths car is going to 2wd...as a sunroof delete 964 C4 owner I was looking forward to a few choice C4 modifications...again thanks for posting Colin.

I did ask about fitting a 993 6 speed box into my Gulf backdate but was told it was only possible on a 964 C2. Can't remember why.

Looking forward to progress on this thread!

tomato

BTW I met a guy who always deleted sunroofs on the many new 911's he had, liked Guards Red and Cashmere interiors. Is the first owner of your C4 Nick Faldo perhaps?

NineMeister

Well, the way I see it is that if you are set on increasing performance a 6 speed C2 conversion is THE choice modification for a 964C4, but I do appreciate what you are saying. Shame you did not ask 9m about the conversion of your Gulf BD, you could have avoided the misinformation.

One other option that works brilliantly well in a 964C4 is to convert it to 6 speed with a 993C4 gearbox, torque tube and front differential, the package saves 50kg and eliminates the in-built understeer of the permanently coupled 964 4wd system. Yes it can be done, it's no more complicated than the job I am doing here and would make a huge difference to the handling balance of the car - in a good way.

NineMeister

Ah, great question. By inference you are also asking me the question of whether I have ever taken an interest in who owned my 964 before me, the answer to that one being unfortunately, no. I suppose I could write to DLVA to find out but that's not the type of guy I am, because in spite of whoever was uncovered as a prior owner the C4 would still be converted to a 964C2 6 Speed because it's now mine and that's exactly what I decided to do with it from the moment I handed over the deposit!

kos11-12

Hi Colin,
could you please tell us what parts are needed to covert a 64 C4 to 993 C4,
thanks
K

StanUK951

And what happens to the electronics? PDAS, is it the same? Longitudinal / lateral sensors? Etc.

NineMeister

All goes in the bin Stan. The only control system the 993 system uses is a passive slip-sensitive viscous coupling for the front differential and that's it. Wonderful.

In a nutshell to convert a 964C4 to a 993C4 system you will need:
993C4 gearbox
993C4 Torque tube
993C4 front differential
964C2 or RS rear driveshafts
Adapter flanges to convert 964C4 front driveshafts to fit 993C4 differential

NineMeister

A little bit more progress today with the installation of the engine and gearbox.

The original 140k engine was leaking oil and due a rebuild, so rather than live with this until I'm ready to rebuild it we decided to fit a spare 964 engine from another 964C4 that I acquired for a project. This spare engine had a specialist rebuild at 80k and has now clocked just under 100k so in theory it should be a good runner. We've checked and adjusted the valve clearances & tweeked the camshaft timing whilst the covers were off, fitted the RS clutch & flywheel and then bolted on the 9m 964/993 6 speed gearbox.

The photos show the original engine with C4 box and the new engine with the 6 speed going into the car.

jack.pe

Colin,

Thanks for this interesting thread.. I'm sure lots of the C4 guys are thinking along these lines. When you know please do tell us the rough cost for parts and labour for:

1. A conversion to 6 speed box and C2 configuration
2. A conversion to the 993 C4 system

Also this may have already been explained on other posts but would it not just be possible to take out the centre diff on the C4 and weld/lock together the two output shafts so power just goes to the rear? if the electronics are an issue then just junking them and replacing the rear diff with a mechanical locking diff? If possible presumably this route would be cheaper and simpler? albeit without the benefit of the 6 speed.


Jack

Mikke_Possu

Thanks Colin to share this. This is definitely interesting and I have to read the whole threat again to understand this C2 conversion properly.

NineMeister

I will put together prices as soon as I can pick out the complete labour content from the conversion.

I have also looked into converting the 964C4 box to a C2 and no, I don't think that welding will offer an acceptable solution. It is definitely possible, in my opinion only by manufacturing a double internally splined solid sleeve to replace the transfer differential. Two factors put me off going down this route, the first being the cost of designing and manufacturing the part, the second being the additional weight of the C4 shaft & gears in comparison to the C2 versions. I came to the conclusion that commercially it was just not worth the effort.

jack.pe

Thanks Colin and apologies on calling you ken in the previous post!

Appreciate there will be some extra weight compared to a C2 box but surely out of the extra 100kg a C4 has this would still get rid of 90% of that weight? everything forward of the centre diff could be junked right?

I think a sleeve as you mention would the way to go but would that be a complex thing to make? Also would the C4 active rear diff still work or would it have to be replaced with a mechanical locker?

Thanks and will wait for the cost estimates with interest.

NineMeister

That's OK John, I've been called a lot worse!

I can't argue with your logic that retaining the C4 box with modification would make sense, the problem is simply the cost of designing and manufacturing an expensive component to do the job that has a very limited commercial value. If I owned my own machine shop and wanted one myself the design, tooling and machining costs would be nil and the part would be made by now, it's as simple as that. For my car I wanted the 6 speed and was not prepared to compromise.

The rear C4 diff could be retained, although you might have/prefer to fit a passive mechanical pre-load adjuster to replace the hydraulic slave unit, hence deleting the active control system which would probably not work in 2wd mode.

Andy Roe

Would you also have to replace the ABS system when converting it to a C2 (or a 993 C4 drivetrain) or can you retain the C4's system for that? (I thought it was connected to the PDAS system?)

NineMeister

Please have patience, we will be getting to this as soon as the mechanical installation is finished.