964 c4 power upgrades

[Tony pitts]

Hi.. first time poster, I’m just about to take delivery of a 964 c4 cabriolet and would like some advice on upgrading the power, maybe Another 30 bhp, is this reasonably easy to achieve and how should I go about it? Thanks Tony

 

[Dekker]

Some simple upgrades are to de-cat it and fit a bypass to one of the boxes.
I did a primary bypass on my Cab and the sound was glorious but after 10-15K the 2ndary box was shagged and I was told this often happens. Pity as the primary exhaust is quite heavy and anything that lightens the car is going to add performance. It was measuring 108dB on stationary track testing.
I now have a G pipe to omit the 2ndary box and still have a cat on my C2 Coupe and just get in on 105dB track days. Sound is deep and throaty and everyone tells me it sounds great but it's not very loud inside the car. It's supposed to add a few bhp but not done a before and after test to know for sure.
Another is fitting a heater blower bypass. This will help on weight loss as well as fitting RS carpet ware and getting rid of the heavy sound deadening on standard cars.
Getting progressively more expensive is to fit an after market 993 style exhaust system, this lets the engine breathe better as the 964 exhaust right bank passes over to the left side and joins prior to going through the single cat whereas the 993 has separated the exhaust and cat to each side of the motor and both join in the rear exhaust box. This is reputed to add the major part of the power difference of 20bhp between the 993 and 964.
Next would be getting rid of the dual mass flywheel and fitting the RS or GT3 flywheel and clutch. This will probably cause tickover problems and stalling which maybe sorted via changing some settings on the DME or through fitting a Steve Wong chip. The latter has an extensive line of chips covering various 964 mods so. My idea was to wait until the flywheel is changed, new exhaust and maybe a better cone filter intake box before buying the chip.
If not done before it's a good idea to get the brake calipers refurbished and the shock absorbers replaced. Shock absorbers don't last 75K and some less 50K. This will enable you to set the ride height better by getting rid of the large space between the top of the tyre and the wheel arch on a standard car. You should be able to drop it 30mm without a problem and then get it set to the RS specs for toe in/camber etc.

 

[C2dweller]

Worth getting the motor dyno’d too - to be sure you’re starting at the right kind of numbers. They are generally very good with age.

As an alternative to exhaust upgrades you could also look at inlet upgrades - hot film conversions are well documented and can yield the kind of numbers you seek.
kr Lee

 

[Tony pitts]

Thanks for that.. much appreciated.
best Tony

 

[Alexander_Drobik]

Hmm, you get some small improvement by extra tuning on the standard set-up, the later plastic induction system was better than the earlier metal one. You have to be careful with the exhaust, quite a number of mods gave next to nothing but sounded louder - the exhaust length is important on Porsche engines. If you have a Cab, why do you want a few extra horses? If the engine is in fine fettle, tappets adjusted right, clean air filter etc, I doubt that you would notice 20-30 extra bhp. If you wanted to have a meaningful increase, you need to change the engine management system and ditch the air flap unit. I would not go for an RS flywheel, on the C4 the kick-back from the front mechanicals is noticeable if you are soft cruising around; there was a reason why they stuck a really heavy dual mass damper onto the C4.... a single mass flywheel is a good compromise. Back to the engine, a re-chip would give you about 20 bhp with a hot-film, and a Motec setup would give you 40-50bhp with the standard exhaust. Don't try a stander set-up or a hot-film with a lightweight RS flywheel - you will stall 1 in 3 times. Note, if the car is post 92 (I think 92 not 91 but pls check) or registered post that, it needs cats to pass the MOT. The 4 or 5 bhp that a cat bypass gave you is not really a big step towards power and you could fail the MOT. Good luck.

 

[T911UK]

Are you thinking the single mass flywheel and the RS lightweight flywheel are 2 different things?

 

[mcgc0]

Loose any uneccessary or unused weight - quickest and cheapest option. You can throw thousands at this and only gain 40-50hp tbh. Don't forget, more power doesn't always equal faster car (lap times).

Had some of the above upgrades done over a period of years previously on a Redtek engine (RS flywheel, new EPROM, cat bypass, cup pipe, motorsport engine oil etc). Anything else a bit pointless imho. Currently dyno'd at 295 hp and happy with that. My M030 968S still faster on the twsity bits too...

Be interested in what you do though. Keep us posted.

 

[Dekker]

Worth getting the motor dyno’d too - to be sure you’re starting at the right kind of numbers. They are generally very good with age.

kr Lee

Who do you use to dyno your car Lee?

Hmm, you get some small improvement by extra tuning on the standard set-up, the later plastic induction system was better than the earlier metal one. You have to be careful with the exhaust, quite a number of mods gave next to nothing but sounded louder - the exhaust length is important on Porsche engines. If you have a Cab, why do you want a few extra horses? If the engine is in fine fettle, tappets adjusted right, clean air filter etc, I doubt that you would notice 20-30 extra bhp. If you wanted to have a meaningful increase, you need to change the engine management system and ditch the air flap unit. I would not go for an RS flywheel, on the C4 the kick-back from the front mechanicals is noticeable if you are soft cruising around; there was a reason why they stuck a really heavy dual mass damper onto the C4.... a single mass flywheel is a good compromise. Back to the engine, a re-chip would give you about 20 bhp with a hot-film, and a Motec setup would give you 40-50bhp with the standard exhaust. Don't try a stander set-up or a hot-film with a lightweight RS flywheel - you will stall 1 in 3 times. Note, if the car is post 92 (I think 92 not 91 but pls check) or registered post that, it needs cats to pass the MOT. The 4 or 5 bhp that a cat bypass gave you is not really a big step towards power and you could fail the MOT. Good luck.

Good points regarding the flywheel, I know the early C4's had a single mass flywheel. It's not something I have knowledge about personally, just what I've read on the forums over the years. Is the GT3 clutch and flywheel a light one like the RS?

My M030 968S still faster on the twsity bits too...

Many cars are faster than the 964, but they don't look as good [].

 

[Alexander_Drobik]

Yes, the very early C4's had a single mass flywheel - around 20lbs from memory. The 90/91/92 cars had dual mass, 2 suppliers. The RS had the lightweight flywheel. There were also a number of US flywheel options. Main point is don't try to run a C4 with an RS flywheel without an ECU change. There was a good reason why the factory nearly doubled the weight and installed dual-mass/load of rubber flywheels on the C4 - it really did dampen the front axle dynamics; remember on the C4 the front axle is always connected, when you power off the front kicks back. Also, you need a 4 wheel drive rolling road to test the power, and you should never tow a C4 with the front wheels lifted off the road.

 

[Tony pitts]

Cheers Alex... taking the car to parr early in the new year so will get prices on all the above suggestions
best Tony

 

[Dekker]

Cheers Alex... taking the car to parr early in the new year so will get prices on all the above suggestions
best Tony

Don't forget to come back and tell us what you found out.

 

[Tony pitts]

Will do and thanks again.

 

[T911UK]

Oh yeah, forgot about the 89 C4 flywheel