CIS Injection and Engine Compatibility?

[SeaDweller]

I have a question or two for my own edification.........

I recently purchased a US version '83 3.0L engine for my '78 Euro SC. Because I had a new engine wiring harness among other things, we decided to take the entire CIS injection assembly off of my '78 Euro engine, and put it on the '83 US engine. The engine I bought is free from emmissions equipment.

I noticed that most, if not all of the CIS components have different part numbers when going from '78 to '83, and some are indicated as being specifically for a Euro model car. Parts like the WUR, airbox, intake runner sleeves, etc. are all different.

Are the '78 and '83 longblocks pretty much the same, except for a little higher compression?

Am I going to run into any problems putting the CIS assembly from a '78 Euro engine on an '83 US engine?

If I have to replace a component, what should I buy, the part for a '78 Euro motor, or an '83 US motor?

Did the '83 US motor (longblock) have any design changes that might not be covered by my '78 CIS?

Anything else I should be aware of?

Thanks!

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Michael
'78 911SC Euro

[Superman]

In short, I suspect you will have little trouble. These engines are all the same displacement, and so the volume of air they pump would be about the same. Later SCs are higher compression, but earlier SC heads have bigger intake ports. I would think the component with the greatest potential for not working on a different SC engine would be the Fuel Distributor, since they are designed for an engine that pumps a specific volume of air. Since SC engines all pump about the same volume of air, I would expect these distributors to be relatively interchangeable. If you can, you might want to retain all the parts from both motors in case you do need to swap them.

You might also consider using the earlier heads on the later motor. This way, you'd have higher compression with bigger intake ports. If you then go with a more aggressive cam and race pistons, you would have one of the strongest possible SC engine combinations.

The only other difference I am aware of is the later SC engines have an improved scavange pump pickup screen compared to the earlier engines. Early SC engines sometimes experienced an oil starvation problem during intense racetrack running.

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'83 SC

[john walker's workshop]

it's a good swap because you simplify the system. the intake runners and sensor plate are bigger on the early engines. the head port size of the 83 engine is smaller, so you will have to port the head to match the intake size. you could do it with the engine assembled if you're careful. cover up everything but the one port you're working on. there will be lots of aluminum chips. rotate engine to close the intake valve on that cylinder so no chips get in. the port is tapered smaller at the top, so all you have to do is basically straighten it out. make a template of the intake runner bore and transfer it to the head and scribe a line around the port. a porting tool with an aluminum cutter bit and bee's wax to keep the aluminum from sticking in the cutter is all you need, other than a air blower.

[SeaDweller]

Thanks guys..........

What are the ramifications of not increasing the port size?

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Michael
'78 911SC Euro

[john walker's workshop]

the airflow will hit the protruding edge of the head port and will not flow smoothly, robbing you of the power you could have had. it's a considerable improvement.

[Superman]

Okay, this is suddenly very intriguing to me. When I do my top end rebuild, I am planning to install 20/21 cams and backdated exhaust. I was not planning to port the heads. I had heard that porting the heads might only take away some low-end torque because the smaller port speeds up incoming air (vanturi effect) and packs the combustion chamber better at low RPMs.

Now I hear that porting may help make power. Should I port?

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'83 SC

[john walker's workshop]

78/79 SCs ran quite well in spite of having larger ports than 80-83. you would have to use the 78/79 complete intake system to make it worthwhile.

[SeaDweller]

Quite interesting..........

So considering the modifications that could be done to a later model SC engine ('83 for instance) to increase HP without the expense of tearing it down, backdating the CIS injection and going to early exchangers (or SSI's) seems to be the most cost efficient.

If the original '83 engine was around 204HP, what gains could be expected from using the early CIS and backdated exhaust (or SSI's)?

Thanks!

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Michael
'78 911SC Euro

[john walker's workshop]

i did that on a 80 recently. complete b+b exhaust, early intake, heads ported to match, stock otherwise, and it was a screamer. you could get 20hp from the exhaust alone.

[SeaDweller]

Schweeeeet...er, I mean, very nice.....



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Michael
'78 911SC Euro