Converting from Mech Injection to Carbs on a 3.0 SC

[Alaska911]

I am planning on restoring a 1983 3.0 SC engine and would like to convert it from the Bosch Injection to PMO carbs. Any advice on this would be greatly appreciated. Thanks

[Spud]

First things first, an 80 SC has CIS, not Mechanical injection.

[jpnovak]

There are many things to consider if you want to convert to carbs. Yes, the PMO kit will work. YOu will have to have the linkage, manifolds and carbs. you should convert to a low pressure fuel pump. I am personally not a fan of choking down the output of the CIS pump, although some have had good results.

You will also have to recurve or replace the distributor. The 83SC does not have enough mechanical advance. YOu can use a 78-79 dist. Steve W at Rennsport can recurve.

The carbs will have a bit better throttle response but fuel mileage will go south. To really take advantage of the carbs, cams and pistons would be suggested. I guess you don't have to worry about emissions in AK but that could be a concern. I would also worry about freezing up in that cold climate unless its only driven in the summer.

What are your goals for the car?

[Alaska911]

To answer your question jpnovak. I have a 1977 911S with a 1983 3.0 SC motor that is need of a rebuild. It is basicly a clean canvas so anything and everything is possible. It is only a summer driver so cold starts is not a factor. I am starting the restoration on the car next month and I am trying to fiqure out how to get the most out of my motor. I am up to any suggestons on what would be the best combination for the motor. I don't want to break the bank building this thing but I don't mind spending a fair amount of money of this winter. This will be a summer driver and I am looking for maximum performance.

[jpnovak]

OK maximum performance. I might suggest a high performance 3.0. Here are some keys to this motor.

high compression JE Pistons (9.5:1 for single plug, 10.5:1 if you twin plug) Check to make sure have Nikasil not alusil cylinders to fit the JEs.
Mod_S cams
Port the heads to matach the flow characteristics
40mm PMOs
SSI or backdate exhaust.

Should be a great motor.

Search the archives for more information. YOu may also wish to build a 3.2 short stroke by installing 98mm pistons.

Of course, a 3.6 would have more torque and more power.

[Eagledriver]

You can get good performance out of an sc motor with just converting to carbs and using a better exhaust. Our race group has a spec class with lots of 3.0 SC motor in it. We use stock SC motors with carbs and headers/sport mufflers and get 230 to 235 horsepower out of them. Makes for a nice reliable race motor. This is without changing pistons or cams.

-Andy

[dd74]

Originally posted by Alaska911
I am up to any suggestons on what would be the best combination for the motor. I don't want to break the bank building this thing but I don't mind spending a fair amount of money of this winter.

Alaska - I was in Anchorage around this time last year. What a city. Reindeer hotdogs everywhere I turn, good seafood, and the sun practically never goes down. Great city, and I guess you have the only Porsche, huh? 'Cause I didn't see a single one.

Anyway, if you're going to maximize your dollars, I would stay away from carbs entirely. Why? Because you also have to dyno test the carbs to get them jetted properly for whatever other mods you'll do to the motor. So, set aside some $$$ for dyno time (is there a dyno in Anchorage?), in addition to money for pistons, head work, cams, etc., etc. And you get about 50 more hp for the cost of another SC.

Maximizing your dollars is a different scenario altogether. You can short stroke the 3.0 to 3.2, swap in some 20/21 grind CIS sport cams, get a good valve job done on the motor, adapt some SSI heat exchangers (you'll need the heat - even in summer), and a good exhaust, and you'll have maybe 20-30 hp less than a carb/piston/S-cammed 3.0, but with more reliability because you'll still have the CIS.

BTW: who's going to do the work? You or a Porsche shop?

[Shuie]

Do you have to pass emissions tests or inspections to keep the car on the road? If so, forget about the carbs.

There is a ton of info out there on rebuild configurations. It can get confusing and overwhelming quickly. If you DIY, make sure you are well informed and have a clear plan in mind before you start buying any parts.

Doing everything yourself will be a lot of fun, require a large time and tool investment, and a lot of homework on your part. You can spread the cost out a little better this way, but dont trick yourself into thinking you are going to save a bunch of money and still be able to do it right. You might save a little money, but nothing about these cars is cheap in the end.

Sending the motor out to someone like Supertec will take all of the guesswork out of the process and insure that you end up with a good motor at a fair price with minimal downtime.

You can build a nice reliable and relatively fuel efficient street motor and by keeping the CIS. A CIS 3.2 or even a 3.4 will still look like a stock 3.0.

3.2 short stroke from Henry at Supertec

82 911SC engine base, ARP rod bolts, 79 big port heads, 79 big port intake, 98 mm JE piston (9.5 to 1 cr.), Web 20/21 cams, 79 ign. dist, Taylor plug wires, tensioner up-date, 2.7 euro fuel dist, .022 warm-up regulator, SSI heater boxes. This engine is in a 74 911 so the injection was cleaned up to work best with a hand throttle.
No dyno sheet but it runs great.

rdanes 3.4

'79 3.0 case which has been boat tailed
74.4 crank ('88 3.2 crank)
Mahle, Max Moritz, 98 mm P&Cs @ 9.8:1 compression
Pistons have a ceramic coating on the crown and dry film lube on the skirts.
Cylinders are half mooned
Pauter light weight billet rods and bolts
20/21 Web cam
5 angle valve job
Ti retainers and EBs HD valve springs
ARP case studs
New ejectors and seals
Big bore throttle body
Light flywheel
single plug
magcor wires
Back dated heat
CIS injection
SSIs and a Dansk 2/2

[Brother]

Did you ever make the switch to carbs?