Clearly the 202 let alone the 173 was not big enough to power the HQ when compared to the Falcon 200 / 250 and Valiant 245 / 265 engines. Holdens starting with the EH had the 149 / 179, HR the 161 / 186 and HQ the 173 / 202 engines. I long wondered why they had two engines nearly identical except for a small capacity difference. The final cost would have been very similar and engineering not approving the smaller engine. Was it marketing to sell the smaller engine to fleets or accountants to charge more for the larger engine? I like to know the sales ratio and apart from the EH I suspect it was very low for the smaller engine. The HQ and on (VK) should have had the 202 as the base engine with an option of a 202S. There was a reluctance for private and fleet buyers to go with the 253 / 308 V8. Because of the head bolt pattern the Holden six cylinder head could never go cross flow. But why did they wait until the VC before a 12 port cylinder head? Never an alloy cylinder head as per the Falcon. EFI on the last engines in the VK was all too late. The Phil Irvine alloy cylinder head had the induction coming down vertical to open up space for the induction and exhaust ports. Torana fitted with these cylinder heads as sports sedans keep up with the V8 of the day. Hopefully the photo of Phil Irvine cylinder head sticks in here.