Merged header choice

[RUSS74GHIA]

I've ordered a 42mm Thunderbird header, but my stockist won't be placing an order with their supplier for a week or so.
They've offered me a very good deal on a 45mm they've got on the shelf, but I'm of the opinion it may be a little big for my application:
1915cc
Twin 40DRLA 34mm vents
Engle W-125/1.25 rockers, dble springs, 40x35.5 valves
9.3:1 CR.
Car will be street/strip use. If it's a 50/50 choice i'll go with the larger one it as it'll be useful to have if i ever go for more cc
Any thoughts?

[andy M.]

42mm would be 1 5/8" much better suited to a 1914, I ran a 1 3/4 header for a while and when I switched to 5/8 header it ran 2 tenths faster

andy

[TexasTom]

There's a great article in the latest HotVWs about this EXACT topic ... I suggest you read it.

If it were Mine, I'd be installing a 1 1/2" (38mm) exhaust header (max) on that engine, given head and cam choices.
The 45mm system ( ) you speak of for this application would be the exhaust of choice if you planned on making best power in the 3500 to 9000 rpm range.

Find that issue of HotVWs! It will be worth it!
TxT