1981 244 DL (B21F) exhaust mod/cam question

[percussionist]

Have a 1981 244 DL B21F engine, naturally aspirated (US 49 state version). I've done an exhaust mod that has started a running argument with another Volvo geek. I went to a shop and cut the header pipes just at the point they entered the collector pipe. Increased the pipe size from 44.5 mm to 50.1 mm, then ran them directly into a high-flow cat. From there, into 57 mm pipe, then to a straight through muffler at 63.5 mm.

This represents a "4-1" exhaust system, with the cat becoming a collector. The result has been noticeable improvement on the low end, with more power starting at 2K-2.5K rpm, and much better response 3K-4K. This is about 500 rpm earlier than before the mod. My next mod was to be a somewhat hotter cam. My friend says that a hotter cam will "suffer" because the Volvo B21 has to have a 4-2-1 exhaust system to scavenge the most power, and to take the most advantage of a higher performance cam, I need to re-do the entire exhaust system.

Any thoughts?

BTW, interesting forum. Glad to be here.

 

[obi_waynne]

How aggressive is the cam you are fitting? I guess that up to 275 degrees you should be fine.

4-1 Exhausts tend to work best on high rpm engines and 4-2-1 exhausts are generally better for most typical fast road cars but there are always exceptions. It would be interesting to see what the improvement would have been on a 4-2-1 exhaust with a 50.1mm pipe on it for comparison.

 

[percussionist]

Thanks for the reply. I was looking at an Enem V15 NA cam, which is spec'd at 256 duration both in and out, and 11.9 mm lift both sides, 38 degrees overlap. I have been told (repeatedly) that doing what I did with the two-inlet cat in place of the collector pipe ruined the flow of the exhaust, particularly for the top end. What I don't understand is why it runs so much better at the low end now...