How far can you modify CIS vs. Motronic

duckmcf · 04-06-2006, 09:09 PM

Hi Lads,
I’m looking at buying either an early to mid 80’s SC or Carrera and I just have a question about the scope for engine modifications of each. In reading Mr. Anderson’s wonderful book it seems that if hot cams are to be used neither the CIS nor the Motronic system is really up to it. I understand that the limitations are basically due to the pulses in intake manifold that the hotter cams will induce and that the effect these pulses will have on the air metering devices is disastrous. As such Webers or PMO carbs are a better way to go for a track / club car with S cams.

The problem for me is that I'll want to keep it on the road and as stock looking as I can for insurance and roadworthiness reasons. I’m sure that if I was unlucky enough to be pulled over by the local coppers they would be less than pleased to find a set of fire breathing Webers in there when they were expecting to see an emissions friendly fuel injection system and would probably issue a defect notice just for practice. But on the other hand I’d like to get involved in the odd track day and so eventually I know I’ll go looking for more power and am therefore reseaching this topic before I shell out for a car.

So anyway, how far can these engines be modified before their fuel injection systems reach their respective limits?

PS For what it’s worth I’m based in Australia, so the cars imported here are RoW spec until Jan 1 1986 when unleaded fuel and cats were mandated. After 1/1/86 our cars are basically US spec.

randywebb · 04-06-2006, 09:56 PM

The 3.2L heads flow a lot better.

The DME is far superior to the CIs system.

Any ability to put a 2.6L or 3.8 RS engine in your car??

aigel · aigel's Garage

The 3.2 has a head start, all right, but it also has weaker rods and usually costs more $. The CIS can be built up nicely. There is a tech article on hopping up CIS equipped engines. Do a search. I would go with the best car you can find, not worry about CIS vs. Motronic. A ROW CIS will be close to an US spec Motronic out of the box.

George

911-32 · 911-32's Garage

You can get 260+hp from a Motronic 3.2 with Supercup cams, remapped and SSIs. Do a top end and rod bolts and you have a pretty bulletproof engine with useful power up to 6900rpm. It might struggle with emissions though unless you have a friendly shop. Same engine with 964 cams should make 250hp and will pass emissions.

A Euro engine will make a little more than US spec but not much.

jluetjen · jluetjen's Garage

If you want to get involved in the "odd track day", get either model and just drive it. Even stock, 911's will outperform a lot of non-Porsche cars when it comes to track use. To be honest, if you're just starting out, you won't notice the lack of a few HP from 6000 throu 7000 RPM. By "out perform", I mean that they will handle better at the limit, the brakes will hold up better and the engine will be just as happy on the track as on the street. The most important part of the car to upgrade for track use is the part that's installed in the driver's seat.

duckmcf · 04-07-2006, 04:06 PM

Thnaks everyone,
There's some really good info there that gives me food for thought.

JeremyD · JeremyD's Garage

My 3.4 - Ralph's twin plug 3.5 and a stock 3.2 in green

MURF · 04-07-2006, 05:31 PM

i'm running an 83sc 3.0 with the cam timing kicked up to euro specs [1.5mm] and sport muffler and converted to efi kit from bitz racing ..i'm very happy with the power increase and the drivability..it screams...as fast or faster than my last 3.2

ianc · 04-07-2006, 08:29 PM

I agree with jluetjen. A mid to late 80's 3.2 will give you at least 210 HP, which is plenty fast on the track if you're a novitiate. You can plunk a considerable amount of cash into the suspension and brakes, in addition to honing your skills, before you will really be able to take advantage of more. Buy the newest and best you can afford. Gaining appreciable HP\Torque increases with any Porsche engine is never an inexpensive prospect. HTH,

ianc

Richard Burns · Richard Burns's Garage

Why don't you go along to the Porsche Club in Victoria and check them out. You will find that they have track days and can give you a bit of advise. As for the cops looking at your engine and knowing that it should be say fuel injected as against carbs they are not that smart and when they look at an early say 76 to 89 model P car they have no idea which year model it is or how it should look under the bonnet.