Difference between a 1978 and 1981 SC?

[shillier]

Hey everyone,

Apart from the engine, what differences will I find between a 1978 SC and a 1981 SC ? I currently have an '81 SC Targa. I've been looking for a couple and found a half decent 1978 Coupe. I'm wondering however, what the difference is between the two years.

Thanks!
Shayne

[real550A]

Some early SC's came with chrome trim.

[aigel]

The 81 should have the 85mph odometer, the 78 not. I am not aware of any differences aside from the engine, engine management and fuel injection.

There is significant differences in the engines and I would lean to a later SC if I had two otherwise identical cars.

George

[Joe Bob]

English or European?

[aigel]

Originally posted by real550A
Some early SC's came with chrome trim.

True. You could get the black trim as an option, while in 80 or 81 all cars came blackened out. I love the blackened out look. I remember when that came out! A lot of car makers did it and sadly many morons tried to paint their chrome - poorly!

George

[Lee]

Early SC has the airpump, but I think most people lost them long ago, and plugged the holes in the cylinder heads. Early cars have no sensor. I think there's a difference in the intake port size. I believe, the early cars have larger ports. I also think that the distributor is curved differently, and is more adaptable to carburetors. I'm pretty sure that bore and stroke are the same. Maybe earlier cars tend to have allusil cylinders more often, but I can't be sure of that. Other than that, I'm not certain of so many mechanical differences...but I could be wildly wrong.

[aigel]

He was asking about non engine differences. Do you know of any?

George

[Lee]

Other than trim, no, not really.

[TerryH]

Originally posted by tcar
Engine diffs are all I know about....

79 or course has the air pump, 80 and on doesn't and has lambda

My ROW 81 has air pump and no lambda. Opposite of US models?

[Carl_Boehme]

78 & 79s came with rubber clutch plate damping system. These failed regularly at 21-23,000 miles because of hardening due to engine heat. I don't suppose there are any of these in service any more. If the 78 you are looking at still has this clutch plate you are looking at clutch replacement.

[shillier]

Thanks guys for the all good info.

I didn't think there was much difference between two years.
I wasn't too concerned with the engine difference as I'm probably going to replace it. However, with the differences between the engines, is it safe to assume that the '81 engine would be a preferred option or would the '78 be preferred for certain applications? I'm just curious.

I also wasn't aware of the clutch difference but no need to worry about that. It's recently been replaced.

Thanks again!
Shayne

[mikemdd]

For what it's worth, I summarize the differences (combined) between the 1980/1981 models vs. earlier (according to Porsche literature).

Below are the changes in 1980:

Fan outside diameter increased from 226 to 245mm
Crankshaft pulley outside diameter decreased from 134 to 127mm
Crankshaft/fan ratio decreased from 1/1.81 to 1/1.68
Fanbelt changed from 9.5X725 to 9.5X710
Valve covers on exhaust side have additional ribs
Intake tube of the oil pump fitted with a suction venturi
Emission changes already discussed
Distributor changed to advance and retard vacuum control
Std equipment now included power windows, three spoke steering wheel, black trim, center console; alarm system optional
Speedometer dial change
VIN number system change

Specific for 1981 changes:

All fuel injection lines made of Steel
Cold start mixture distributor was located in bottom of air distributor housing
Acceleration enrichment microswitch added, as well as 35C temp. switch, and control unit for acc. enrichment
WUR changed, with different warmup characteristics (pressure change and time to warmup change)
Catalytic converter changed intenally, and "cannot be used on older models"
Fuel pump change with replaceable check valve
Fuel filter changed to standardize with others
Fuel accumulator change... increased volume from 20cc to 40cc, with different charging characteristics.
Oil dipstick markings changed, along with change in oil level sending unit
Oil vent restrictor, previously located in the elbow of the fan cowl, is now in the connection on the oil tank "to improve heating for restrictor and less danger of icing up"!
New switch symbols

Pretty worthless information, but that is that.

Mike

[danl]

Originally posted by aigel
There is significant differences in the engines and I would lean to a later SC if I had two otherwise identical cars.

George

As long as we're talking engines now, what are the "significant" differences? I'm not talking about the crankshaft/fan ratio here.... just the important stuff.

[aigel]

Originally posted by danl
As long as we're talking engines now, what are the "significant" differences? I'm not talking about the crankshaft/fan ratio here.... just the important stuff.

The chain tensioner idler arm is narrow and without a bushing on the earlier 3.0. This can lead to the arm cocking and hanging up - causing chain tensioning failure. Many people claim that this is 90% of the chain tensioning problem, the actual tensioner only 10. Even if you have the chain fed tensioner upgrade, it may have been done using the spacer and keeping the narrow arm. Not a huge deal, but unless you see the inside of the early 3.0, you don't know if the carrera chain tensioner upgrade was done correctly - with replacing the idler arms. If I would buy an updated early engine, I would open up the chain covers and make sure I had the wide arms.

The other difference is the steel fuel lines. Needless to say what happens if a fuel line lets go. Steel is easier to keep up.

I like the fact that there is no air pump on the later SC. Makes for a cleaner engine compartment, especially if you live in an area where you have to retain smog equipment. It also makes for a cleaner engine underside, without all the air injection piping.

I like the fact that the later SC runs higher compression. You can upgrade to a heftier cam more easily that way. If you have the low compression version, you have to be careful not to "bleed off" too much compression with too big a cam. If you talk to John (camgrinder), he will for example tell you to stay away from the 964 cams for the low compression 3.0.

George

[emcdan]

The biggy is the intake runners. The 78'-79' has the larger intakes manifolds. They seem to be highly sought after for those retaining the CIS and upgrading.

Is there anyone out there with the larger runners on the higher compression pistons? And if so, what differences in power delivery or hp have been noticed?

[aigel]

Originally posted by emcdan
The biggy is the intake runners. The 78'-79' has the larger intakes manifolds. They seem to be highly sought after for those retaining the CIS and upgrading.

Yes. The ideal 3.0 CIS engine should have some parts from the early engine and some parts from the late. If it comes to bone stock, I still would prefer the later 3.0.

There are folks in the club that do a mix and match with early and later parts, euro injection etc. to get the best power, without breaking into the next higher competition class. Makes sense if you want to be competitive.

In my opinion unless you compete it is not worth the hassle to redo all that, just to make a few more ponies. If the engine is apart anyway, then it's a different issue. If I ever have to rebuild, I'll do just that.

George

[Carl_Boehme]

I didn't intend to mislead anyone on the clutch problem. When the clutch on my 79 failed at 23k in 1981. Bud Hart said, he would replace it with a 1981 clutch plate which used springs instead of rubber.

I just looked through the maintenance records on my 81 and it has never had the clutch replaced. Hard to imagine that it is an original rubber damped clutch plate wih 145k on the clock.

[78targa]

Don't forget that the Lambda unit was added to the engine and 1980 as a precursor to the DME of the Carerra's. Definately not an engine management system, but in my opinion, worthless electrical garbage that can fail. I would prefer the 78-79 engine over the later SC's for that fact alone. I think there was a better flowing fuel distributor on the earlier SC's, wasn't there? In 1980 didn't the fuel distributor for USA cars become more restrictive?

Note that some earlier 78's also came with 911S components. For example I owned one that had alloy calipers. The 78 didn't have the OXY sensor (at least mine didn't) . Seatbelt latches were a different style...ok, not that important...

Anyhow, just a couple of things to add.

[aigel]

Originally posted by 78targa
Don't forget that the Lambda unit was added to the engine and 1980 as a precursor to the DME of the Carerra's. Definately not an engine management system, but in my opinion, worthless electrical garbage that can fail.

Better than a belt driven air pump and all kinds of tubing over your engine. You will get better gas mileage if you actually analyze what's coming out the other end and feed it back to the FI. Every 911 after 81 has an O2 sensor and none of them had air pumps any more. Electronics are what make modern cars last a lot longer.

George

[78targa]

Hmm, well I guess I tore off all of that other garbage. I also never worried about gas milage either, just horsepower. I'd always take 39mm intake runners over the 34's.

I agree EFI is a better alternative to shoving as much air and fuel as you can into an engine. However I don't think there are enough signal inputs on a later SC engine to give you a well functioning EFI system. The stuff out these days is really good, but in the early 80's it was there to cope with emissions...

Oh, george, holler if you ever need a Lambda unit for an '81...I have one for sale... (really!)