Header sizing advice needed
 

Just finished my first engine drop (went REALLY SLOW and carefully), and now I am looking at some upgrades while I have my engine and transmission out.

This site has been great for information (and to tell me I'm an idiot before I do something stupid)!

I have a 1977 911s and as far as parts, it seems to be a transition year that needs parts built specifically for it rather than a range.

I am considering going to some bursch headers to replace the oem heat-exchangers. While I have a 2.7L with CIS right now, I may want to replace my engine at some point with a 3.0L CIS or Carbs.

What size header should I obtain that "might" work on both?

What are the benefits of having a larger or smaller size?

I was thinking of getting the 5/8ths as a compromise size but I wasn't sure if that would mess up my preformance gains on the 2.7L or the 3.0L later on.

Thank you all!

Unless you are going to go with somthing with wild high rpm cams the 3.0 seems to work well with 1.5" headers. There are a number of racers running stock cams and ports making 220whp / 250chp with them in the SPEC911 class it seems. This also works well with a 2.7.

I am asking in part because I might have a line on some cheap 1 5/8ths. However, if my performance on my 2.7L is going to suffer by going larger than 1 1/2 I am willing to wait and spend more money on the smaller size.

I very much doubt I will end up in the high RPM range on any future motor I own.

I wouldn't really look at the 1-5/8 headers unless you are going 3.2 or larger or are going on a serious, serious high rpm track binge. The SSIs are just so good and sized perfect for where you are now and are perfect for low to upper midrange on the 3.0 cars. Plus you get a huge quantity of choices of mufflers.

1 5/8" headers are too big for a mild 2.7: those would be appropriate for an 8K+ RPM 2.7 or 2.8.

Headers that are slightly too big really kills the low & mid-range torque.

Be very careful when removing the stock manifold. The studs break very easily.

You will need penetrating oil, judicous heating, close fitting hex wrench and some light duty metric swearing.

Thanks! That is exactly the advice I wanted. Thank you all for helping me avoid yet another mistake :).