MY 83 3.0 dilemma

[favrok01]

OK
I have a 83 3.0 engine back from rebuild it has higher compression, 964 cams, and stainless valves (to list the changes)

[the dilemma]
I have a 83 complete top intake with the 43mm runners.
I also have a 78-79 Complete stainless airbox top intake with 48mm runners.

which one should i use?

and if i use the 78-79 intake do i need to change any wiring at all?
i was told i did because the 78-79 didn't use a o2 sensor or brain so i would have to change things

[jdowty3]

Have the intake ports on the heads been ported to match the 48mm intake runners? If not, either use the 43mm runners or have the heads ported and use the 48mm setup.
Maybe JW can chime in about any wiring\sensor type differences.

[favrok01]

bump

[KobaltBlau]

Are you measuring the OD? the runners/ports are normally referred to by ID, as 34mm for 80-83 US and 39mm for 78-79.

If I were in your position, when I had the engine rebuilt I would have had the heads ported to 39mm so that I could use the larger runners.

However, if you didn't do this and the ports are still 34mm I wouldn't slap the bigger runners on the smaller ports, I would use the 34mm runners. otherwise you will have a "step" at the entrance to the intake port.

[favrok01]

Your totaly right but the rebuilder wont answer me wether he did this or not. But on my first thread someone had mentioned it maybe causing some HP becouse of air velosity.

[techweenie]

Originally posted by favrok01
Your totaly right but the rebuilder wont answer me wether he did this or not. But on my first thread someone had mentioned it maybe causing some HP becouse of air velosity.

Since you don't have the intakes on the engine, why couldn't you measure the head port IDs yourself?

[favrok01]

actually the 38mm are on now but i am waiting for a FD to get the engine running

[favrok01]

bump

[Superman]

According to my understanding, the ports would need to match, and the ENTIRE intake systems need to be used. In other words, the later SC's used a different FD, different runners, different everything. They also used a frequency valve and a computer. The earlier SC's are of the K-Basic variety, using no frequency valve, a different FD, etc. If the intake ports match, the earlier SC systems make more power. But if not the later runners and FD will work best.

Yes, air velocity is significant. While the later SC systems have narrower intake runners, this also causes intake air velocity to increase. That higher intake air velocity helps to better "pack" the combustion chamber under certain circumstances.

[favrok01]

thank you, this is exactly the type of info i was looking for
i will just wait, install the 78-79 FD get the car runing and go from there.

[Gunter]

Let us know how the basic Jetronic from a '78-'79 works with the bottom of a later SC engine.
In other words, after you plug in the 14-pin connector, will the engine just fire up?
Or are there some wiring changes necessary?

[favrok01]

Good question a few people have asked that same question. Saturday will be the answer.

[Gunter]

How are things progressing? Having fun yet?