Same part number across them, even in tha 1974 HQ parts catalogue as far as I can tell.

HT-HG 350 auto and HQ were all 2 bolt. Only HT-HG 350 manual were 4 bolt engines. We actually know the very first HT GTS 350 manual car had a 4 bolt engine, it was the car at Bathurst Holden that they cut a hole in the sump to show CAMS they were 4 bolt engines. The very first HT 1837M was probably a 2 bolt as it was a 327.

The McKinnon HG GTS350 was more powerful, but not by the margin it would appear as when it was tested when new they compared it to the original HT GTS350 tests of the hobbled cars.

Standard spec for HT350 + HG350 is 0.410 exhaust and 0.390 inlet, and the angles mentioned above. The manuals and autos were the same.

Here it is here:
http://www.compcams.com/...etails.aspx?csid=1&sb=2

I was just quoting GMH's material for the original post, and the cam in the link is the same part number as in the HK-HQ parts books. The original figures at the top say "without ramps" but I don't know what lift they start the timing at. 2 thou sticks in my head though.

HQ service manual says:
Inlet:
38deg BTDC inc 10deg ramp
92deg ABDC inc 20deg ramp
Exhaust:
88deg BBDC inc 10deg ramp
52deg ATDC in 22deg ramp

So removing ramps gives you 28/72, 78/30 which is the same as I quoted. Late HQ may well be retarded. Holden V8's were at stages too.

307 was the same part number, even in the HT release parts catalogue. Might explain why a 307 went so well when fitted with the 327's exhaust and inlet/carb. The cam would be significantly bigger to a 307 than it would to a 350. 283's would have used an earlier camshaft, i'd probably have one here somewhere out of an old 1960's GMH Chev or Pontaic as I have a few original engines in the shed.

No, they are all the same. Well the 1968 cars are anyway. Later get the different engine. As far as I am aware the 186 heads weren't a "option" as such, they were offered to those that owned cars for a cost. Bit like the 15" alloys given the XY GT-HO owners in 1972.

I think it's that the Aussie one gets twin exhaust and the USA one is only a single.
This is only worked out in SAE HP of the time.

Edited by user Tuesday, 15 September 2015 10:26:46 AM(UTC)  | Reason: Not specified

As Dr Terry says exhaust doesn't come into it. Engines were rated on a dyno with no accessories. The 10hp is easily accounted for by GMH rating the engine on 97 fuel and with an extra 2 deg of advance and the advance curve starting a bit earlier. You could also option N10 dual exhaust on mot 307 powered Chevrolet and Camaro.


N10 dual exhaust was priced as an option for HK 5litre ($60 retail inc tax on the HK Passenger options price list dated July 30 1968 ready for HK Monaro/Brougham release and $56.21 retail inc tax on the HK Commercials options price list), just not easy to option - from memory you had to use the special instruction section of the order form to do it, and probably had to have some clout with the zone office as well. It was simply the GTS327 exhaust on any non-Brougham 5litre HK. Afaik not as easy to do on HT as the 350's exhaust was different at the engine pipes. It will have been a very rarely exercised option as the Doc says. Bit like a Saginaw 4spd behind a 6cyl in HK passenger - I only know of one of those.

Edited by user Tuesday, 15 September 2015 2:34:40 PM(UTC)  | Reason: Not specified

GM used a dyno for the engines. I have dyno curves out of the Engineering Specifications for most of the 1967-1974 SB and BB Chevrolet engines and the peak gross hp and torque figures are spot on. It is proper gross SAE hp. They even used SAE net for trucks from before 1968 which includes El Camino which has the same engines as Chevrolet and Camaro, so I have also net figures for our HK GTS327 engines and most HT-HQ 350 engines as fitted to El Camino.

I have also found some interesting stuff about the HK GTS327 type 1 engine that explains why it went so well given the seemingly truck like specifications GM and GMH published for it. Will go into it in more detail later.