Harv wrote: ↑Sat Jun 20, 2020 9:37 am
ardiesse wrote: ↑Sat Jun 20, 2020 9:19 amMaybe the change to the Y-pipe happened late in HD production.
Yes, the early HD's changed to the HR type rear header at engine number 186K171370.
Cheers,
Harv
Hi Guys.
I reckon the whole X2 header thing has caused more confusion over the years than just about anything else Holden.
Engine no. 186K171370 is mid-HR production, not HR. HD X2 engines are prefixed 179X.
186K171370 is only 1130 engines before the X2 to 186S change in May 1967, this number includes all HR engines, This means that very few X2 engines got the new type rear manifold.
AFAIK all HDs got the two separate engine pipes & the dual inlet muffler, while all HRs got the Y-pipe & single inlet muffler. Parts catalogues, including supplements from that era seem to confirm this.
So in summary, as others have mentioned there are only 2 variations of the rear header, changing at the above mentioned engine no.
The "type 3" (using Harv's list) front header was needed for the 186S (WW Stromberg) auto choke so must have been introduced at (or before) the 186S intro date.
These 2 headers remained unchanged for all 186S as well as 161S & 173S for the LC GTR. For the LC XU1 they simply deleted the choke heat riser tube from the 186S casting, resulting in type 2.
LJ GTR had the stock 202 with the single outlet header, so it missed out on this set-up. Late XU1 got tubular headers (extractors) so they didn't get them either.
The main thing to remember is the all 3 front headers will interchange if you don't need the auto choke, but the rears will not swap without mucking around with the engine pipe(s).
Dr Terry