No, 3947040 are Tonawanda's 1968 version of the Saginaw plant's 3917291. Both are the same thing just from the two US SBC foundries just different casting number and mark. 3947041 is the 1969 version with the accessory holes, again the Tonawanda version of the Saginaw 3927186.

No, 041 is the Tonawanda version of a 186 Fuelie, which is why they are on HT GTS350 manual engines. The HDT engines at Bathurst 1969 had Flint engines hence why they had 186 heads. These are all 64cc heads.
The Canadian GTS327 heads are 75cc low comp 188 heads. Tonawanda GTS327 290 heads are 69cc.

I think the Flint '186' heads were available as an over-the-counter replacement part for 350 manuals but not likely as a performance upgrade, just replacement part. I'd be very surprised a cam upgrade was available from Holden. GM at the time listed only one higher performing hydraulic cam and it powered the the 350HP 69 and 70 year model Corvettes and some 325HP passenger cars. 224deg/224deg @50 114deg LSA 450/460 lift rings a bell. This would be the only cam upgrade offered at the time but I doubt Holden would have gone down this path.
Adrian

Nope to all. 041 are simply Tonawanda heads, just like 040 from 1968. They are identical and interchangeable with 186 and 291 respectively from Saginaw (Flint assembly). Same part numbers. Same thing with 290 and 032 heads, 290 are Tonawanda and 032 are McKinnon Industries. They too are identical. After 1969 this stopped as there was a big restructure and all foundries and engine assembly came under the one dept rather than being separated. Essentially the first step towards GM Powertrain I guess. After 1969, St Catharine's engines are true Chevrolet engines. 1969 and prior (called McKinnon Industries at that stage) engines from Canada aren't Chevrolet engines as McKinnon was not a Chevrolet facility at that stage - they built SBC design engines for Studebaker, Holden, Mercruiser, Pontiac etc. This is why the rocker covers are blank (HK-HT 307 for example).
GMH had 3 x factory blueprinted engines sent over from the USA for the 1969 HDT cars. They were Flint sourced, just used Flint casting numbered parts, and this is why the 186 heads appear in the HT parts catalogue amendment. It is simply Harry Firth arse covering to make sure if someone spotted a difference they were covered. You can even see this if you have a copy of either that amendment or I think the HG parts catalogue, GMH used the 3927186 cast number as the part number. These heads use the same part number as the 041 heads - there was no need to do this other than to arse cover.
The only higher performance heads used are the St Catharine's cast 370 heads on the last HG 350 manuals, These share the larger 172cc inlet ports with the old 461X heads, all other fuelies had 164cc inlet ports.

There was no GMH sanctioned can upgrade afaik. I can tell you though that a dead stock HT 350M engine fitted with 186 heads and the 350/350hp hydraulic cam puts out about 325hp (25hp increase over stock engine). The 350/350hp Corvette engine had in addition to this 2.02/1.6 valves and lumpy top Pistons from memory.

"There was no GMH sanctioned can upgrade afaik. I can tell you though that a dead stock HT 350M engine fitted with 186 heads and the 350/350hp hydraulic cam puts out about 325hp (25hp increase over stock engine). The 350/350hp Corvette engine had in addition to this 2.02/1.6 valves and lumpy top Pistons from memory."

The 350/350 Corvette engine and the 325/350 passenger car engines were the same bar the 2.5 rams horn exhaust compared to the 2.0 passenger car manifolds. Same pop top pistons, cam, valve size etc.

Edited by user Friday, 19 August 2016 11:02:28 PM(UTC)  | Reason: Not specified

The air filter and cam and head up grade are mentioned on this forum some years ago.