I don't believe the 6 cyl XC changed colour at all, one old dude I know of that goes on about his XC being a XC & 1/2 4.1L engine is blue in colour and my 3.3L p van was a Jan 1979 build with a blue engine.

I know that the XC V8's did perform better than when the XC first came out, but as for that being when the XC & 1/2 came out I am not sure it is true, but a 5.8L Fairlane could do 195KM/H flat out and the next type due to a carby improvement could do 210KM/H stock.

As for the KW figures the XB is in SAE Gross and the XC I believe is in Net and the XD is in DIN for the 4.9L to go down from 151 to 134 and the 5.8L from 162 to 149.
the 4.1L XC is 92KW 3900 /289NM 1900 8.9:1 Net
The 4.1L XD is 92KW 3900 /295NM 1900 9.0:1 ?
The 4.1L XD is 94KW 4000 /305NM 2000 9.35:1 DIN with Alloy head.
The 4.1L XE is 93KW 3800 /305NM 1700 9.3:1
The 4.1L XF is 103KW 3750 /316NM 2400 9.35:1 lead
The 4.1L XG is 97KW 3600 /297NM 2000 8.77:1 unleaded.
Maybe the later XC got the XD type engine but not the colour, the V8's only went black from the XD on with silver rocker covers.
My mates XD 4.1L alloy head type had a silver rocker cover and I think that the XD 4.1L iron head rocker cover was black and the XC 4.1L was red rocker cover.

Look at the Holden's they used Gross up to HZ and DIN from the 1978 VB Commodore.
Falcon used Gross up to 1976 XB and then Net in the up to 1979 XC and then DIN in the XD from 1979.
So they get their act together in the 80's with DIN figures.

But then again 140KW for a 4.9L Falcon XD verse a Commodore 5.0L at 126KW I don't believe that's true at all because a 1981 Fairlane 4.9L don't out perform a WB 5.0L Statesman do they.

XD-E 4.9L 140KW 4500 /344NM 3200 9.2:1
VC- WB 5.0L 126KW 4400 /361NM 2800 9.2:1
XD-E 5.8L 149KW 4300 /415NM 3000 8.9:1

I have to run to a car show now.

I found some brochures I is a 1974 Transit with 200ci 8.0:1 low compression with the power figures in DIN Gross and DIN Net figures.
Gross 114HP 4600/ 170LB 2000
Net 91.9HP 4000/ 155LB 1800
This runs a 4.62 diff ratio with 14in wheels 3sp manual or auto.

And a 1974 F250 250ci 9.1:1 compression brochure had
Gross 146HP at 4000 RPM / 226LB at 1600 RPM
Net 107HP at 3600 / 200.6LB 1600

The same 1974 Brochure has F250 302 V8 9.4:1 at
Gross 177HP at 4500 RPM / 259LB at 1800
Net 128HP at 3900 / 229LB 1800

The XB Falcon 250 has 155HP and the V8 302 is 240HP as rated in what ? SAE HP nonsense, because how can a 302 pump out 240HP with the 2 barrel carby it has, when the Holden 308 is rated at 240HP with the 4 Barrel.

And I never seen no stock XB 302 beat a stock HQ 308 back in the days, I thought that the 308 were a much more powerful than the 302 once, thinking that all 302 would of been 4 Barrel but then my brother got a XB GS 351 ute and I seen she only had a 2 Barrel on it and a mates 302 ZF Fairlane only had a 2 barrel on it, so bingo the penny dropped.
Even my Dads 1971 400 V8 LTD Galaxie had a 2 barrel carby on it.
A Valiant with a 245 or 265 2 barrel could hose off anything back in the day, bar a 308 or 351.
So I was thinking that the power figures must be crap even back then.

But how do we get the difference in power figures between the XC and the XD V8's
XC 4.9L 151KW to 140KW in the XD nothing is different.
XC 5.8L 162KW to 149KW in the XD ' ' It must be from DIN Net to DIN ? Another newer set standard.

And then I have another problem with the Holden figures in 1999 with the 179KW 5.0L V8 the VT show the same figures as the VS do, but the 179KW VS only comes with a crappy single exhaust and the VT is twin exhaust and I have driven both and the heaver VT flogs the VS.
But from the 2003 VY Series 2 Holden uses ECE Power figures, this being more evolved than before test, so we have this progression evolving.

The old SAE figures could be diddled easy and the facts prove it was done and that's why USA brought out the Net HP standard to catch out the cheating done as the emission laws called for more realistic values.

Sure the SAE were mainly correct as they go but they could jet the engine up and fiddle with the timing from standard to get better results, but for one thing I agree on as Byron has pointed out, that he likes this old SAE standard because it makes pointing out the old Chevy engines easy as to what engine it truly is to identify.

So in the end I see the figures are all as they claim in respective to what they are under, but I prefer gaffs plotting out the torque and power so I can understand what it going on better than just rubbish like maximum figure.

I found that my 235KW VY SS ute could out perform my mates VY Series 2 SS 245KW ute and another mates 250KW VZ SS ute and that's just by using the same gear in runs, I found that the torque had more to do with performance higher up in the gearing ratios, the 245 and 250KW engines make their max torque at higher RPM and a bit more but if I could get gaffs of them I am sure my 235KW must be making more at some points in the rev range.
The VZ SS sedan came with a lower diff ratio 3.73 than the VY 3.46 ratio, now why was that I wonder ? because the truth is she did not perfume as well due to the stricter ADR Law, most likely retarding the cam timing to comply and this makes the HP go up but lose some torque down low mid range by rights.
The VZ SS ute got the 3.46 diff ratio and that make went and got 3.9 ratio put in, this helped in some ways but not after 210KM/H my VY would just kill his for dead and we had dirt bikes in the back, his straight in line and mine sitting sideways, his had ran out of grunt in 5th gear at that speed and mine could wind out to 260KM/H in 5th and his 6th gear was useless.
I think I could only do around about 180KM/H in 6TH.
I thought that the 250KW was going to kill my 235KW wen we first went out, but I wanted to see by how much, but my 235KW had him Roo Ted, so he tossed in the 3.9:1 diff and only got me from 1st and 2ed gear.

AS for bikes gearing I had a stock Kawasaki KLX650R and mate a XR500 with cam and high comp piston they were about the same in taking off and to top speed, but I worked out that if I went 1 tooth less on the rear sprocket it should perform better and it did, old mate never ate that many rocks and it was due to using the torque better of the big 650, but on my Suzuki RMX250 I put 1 tooth more on the rear and she performed better.
I would sit down and do the math and try work out what's best to do with the gearing and what I felt would work and I had to because most riders were mainly only little short arse 6ft or less and I was not having them beat me, f that for a joke.

I Agree.

It is odd that Ford would not do what GMH did once DIN figures were quoted, and quote both dual and single exhaust power figures. Most Commodore and WB around then did.

I guess those end of XC engine change figures could be like the HZ 5.0L, where it changed compression (from 9.7 to 9.4:1) with release of VB engines but it is not well documented - you have to really dig into GMH literature to find any mention of it in HZ, and even then figures remain as SAE net whereas VB is quoted differently.

Only really early HZ will have HX engines, like just pilots. They changed a fair bit, but not much changed during HZ apart from the use of XT5 (blue) blocks around VB release and the compression dropped on 5.0L. The first A9X or two got a HX style engine too, and the rest were HZ style.

I don't think it is unusual to find red blocks with 3.3 on them. I've seen lots of them. There isn't much different between XT4 and XT5 engines in terms of blocks, the XT5 V8 blocks were introduced with VB volume production, may well be that 6cyl were similar, or at least some of the patterns were changed early. It happened with late WB 6cyl too, if you go and look at late WB 6cyl engines they are VK blocks painted blue.