Our lead fuel was 89 Standard and 98 Super back then I believe but before that I don't know.

Not to mention we are on the same track with the USA octane difference of our RON and their MON mind ?

Yes total advance is one thing, but how it calibrated through a rev range and difference in vacuum advance types how they are set up to work.

Late HQ 350 was it about 12 deg at idle ? with a retarded cam for emissions, I wonder if the carby jetting was different as well in them ones.

I wonder what was the last batch casting date was of our HQ 350, as due to the USA pollution laws, there must be a jetting difference I would think.

Holden must of given up the 350 because they would of only got the smog unleaded 350 for the HJ not to mention the price extra over the 308 and then a HJ 308 would of hosed off a smog unleaded 350 any day.

As for Aussie made V8 Chev powered cars, 283 and all, what have you found out.

Was it not for some reason that our late 327 batch differed was due too.

Our last Impala 327 got 10 more HP then the year before that if I remember correctly, how is that ?

Just heard a yank call a Impala an Impeler OMG

GMH also forgot to update the torque figure - it should be 335ftlb.

The answer is compression, the 1968 250hp engine was 9:1 - 290 cast heads are 69-70cc.

I think (but haven't yet confirmed) the 1967 engines are the same compression ratio as the last of the HK 327's and also those 1968 trucks ie just over 8.5:1 - this appears to have got rounded up to 8.75:1. Yes GM and GMH seem to have forgotten to increase this for the 1968 engines. The 1969 327's are quoted as 9:1 - these have 69-70cc heads too but 185's (which are the accessory hole versions of the 290 heads we got here in 1968).

The flat top piston 327's go like this:

75cc head - 8.5:1 or just over if head is like 74.5cc (rounded to 8.75:1)
70cc head - 9:1
64cc head - 9.8:1 (rounded to 10:1)

64cc head with lumpy tops (L79) - 11:1.

Edited by user Saturday, 26 September 2015 10:32:26 PM(UTC)  | Reason: spelling

Yes. US GM Engineering documents show this engines as 250hp, 335ftlb gross. The only difference between the US GM figure and GMH's figure for the HK is 1 x exhaust manifold, it will be the same for the Chev and Pontiac. Everything else is the same (except see below) including cam, dizzy, carb numbers etc.

The tricky part is the same US docs show 8.75:1 (as ours do and as you'd expect GMH just copied it), and the volume given for the combustion chamber size of 5.38ci (this is the total measured volume of head, piston below deck and head gasket) gives you about 8.6:1 which as happens in all other GM engines of this timeframe gets rounded up to the nearest 0.25:1. Here is the maths:

CR = (Swept volume +Vc)/Vc = (40.84+5.38)/5.38 = 8.59:1.

The big fly in this though is 5.38 cannot be correct for the 290 cast 69-70cc head. The 1969 327 2BBL 327's rated at 210hp in Camaro (with the 307 size carb) and 235hp in full size Chevy (with the L65 350 2BBL size carb) both are quoted in the same Engineering docs (but the 1969 version) as 9:1 and a CC size of 5.08ci. Same maths above give you CR = 9.04:1 (possibly not rounded to 9.25:1 as these engines were marketed as suitable for Regular fuel). These engines use 3927185 heads which are also 69-70cc heads and are the 1969 replacement for 3917290 heads.

Another check is to look at the HK-HT 307 with 3911032 heads. GMH claim 8.75:1 for this engine, and the same 1968 Engineering docs show a CC of 5.02ci. Formula shows CR = (38.33 + 5.02)/5.02 = 8.64:1 - gets rounded to 8.75:1. These heads are identical chamber size to the 290 cast heads (i'm about to cc some this afternoon to prove it). Thus the Aussie 1968 327 cannot be the same compression ratio as the 307 - it is impossible: Same stroke, same pin height, same deck clearance, same chamber size, just a bigger bore).

So there is only 3 x possible conclusions:

1. The Engineering data for these 1968 engines is based upon 1967 specs where the 4BBL low comp 327 actually had about 8.55:1 compression (figures for 1968 Camaro 210hp 327 (3917293 75cc heads) show 5.43ci chamber, calcs give you CR = 40.84+5.43)/5.43 = 8.52:1. 3917293 heads are the same heads as the 1967 210hp except for the temperature sender boss and hole added, just like the 3917291 is the same replacement for 3890462). However in reality they got the smaller chamber 290 cast heads and the data was not updated.

2. US 4BBL 327 low comp actually got 3917293 (75cc) heads which would make it the same long engine minus manifold as the 210hp engine - I get conflicting info from US sources (some say 293's on these, others say 290's). These engines were only made at Flint and Tonawanda (no 4BBL engines from McKinnon Industries at this time). Perhaps Tonawanda 250hp got 290 heads but Flint got 293 heads? This possibility however does not then explain the 10hp and 10ftlb gain over the 1967 engine as it's make the 1968 engine identical to the 1967 other than the journal sizes. I've looked at massive amount of engines from this timeframe now and there is always a justification for extra gross power and torque (the peak quoted gross figures are straight off dyno curves in the Engineering data).

3. The Aussie 4BBL Tonawanda 327 is unique.

I've asked some questions of people in the US but so far they don't seen to get the idea that engines may be different between engine plants, especially McKinnon. The Canadian engine plant didn't become a proper GM plant until they tooled for 4BBL engines in 1969 and became GM of Canada Limited St Catherine's. Prior to that they were only a subsidiary (as in GM only part owner), hence I think until 1969 the V8's built at McKinnon Industries may well have unique casting numbers in some instances (which would explain the McKinnon 307 using the 032 heads where the 290 heads would do the same job). In fact it isn't actually 100% correct to call a McKinnon V8 engine prior to 1969 a Chevrolet engine or SBC engine as McKinnon were building the engines I guess you'd say "under licence" for not only Chevrolet but for Pontaic, Studebaker and Mercruiser and others. This is why they had blank valve covers apparently rather than scripted ones. I think the correct term (quoting from North American Pontiac sites) is SBC "design" (orange engines) as opposed to Pontaic (blue engines) engines.

Byron,

Sometimes it's helpful to go back to first principles. I've gone back to the SBC blueprint numbers to do the calculations. Here are the results:




Regards,

Geoff

Edited by user Monday, 28 September 2015 11:42:55 AM(UTC)  | Reason: E&OE

There was big import duties into Canada earlier in the 60's. Pontiac Canada did it that way to have some commonality of parts between cars like the full size cars and also Beaumont, Arcadian, Laurentian etc. The Pontiacs used Chevrolet chassis as well as the engines. They still imported the bigger and more powerful engines. just built their own base spec.

The last of the 327's got the same inlet from Tonawanda as the HT 350's - which makes sense as the 350 was the normal 4BBL production engine out of Tonawanda for 1969 model year and these HK engines were completed in the 1969 model year (late 1968) in the McKinnon plant but with Tonawanda inlet.

Not sure how the deal with engines worked - I thought they were all imported though.

Nothing wrong with the 1968 250hp Impalas and Pontiacs here - there was no TH400 available in them in the USA either behind small blocks, only big blocks. The TH350 replaced the Powerglide during 1969 model year and you could option the TH400 in full size Chevy and SBC in 1969 model year but after that it was TH350 only. Tuned properly these were no slouch, probably not Galaxy like performance but would be even or better a match for 289/302 auto Fairmonts.

Edited by user Monday, 28 September 2015 7:32:05 AM(UTC)  | Reason: Not specified

Agreed. A small late night spreadsheet error. I've updated the post above. A couple of points:

The 350 and 327 use the same head gasket, a steel shim type 3830711. It is 0.026" thick.
I'm not sure about the 307. It is different from the 327/350 gasket and listed as 3911088. I cannot find any information on it, however even if it was 0.015" thick that still doesn't make the 307 9:1 with 70cc heads. I've added a separate line for it in the spreadsheet, should more information come to light.

I've left the valve reliefs at 5cc for now. There is a lot of opinion on what they really should be:- 5,6 and even 8cc. By the way, if they didn't exist in the 307, and maybe if the head gasket was less than 0.026" it could push the CR up to 9:1, which may explain the quoted CR.

Also interesting that the heads for the 327 are quoted in the parts book as 3928495, which is listed in some US casting lists as "327, 327(250HP), 8.75:1, 1.72/1.5 " and no other information, such as CC volume. I know the part number doesn't always match the casting number, and you have 290 heads, but why would that number be in US listings? It may have been a special number for GM-H, perhaps, and never actually supplied.

The 307 is listed as 3928454, but my HK parts book has a handwritten note against that which says "casting number 3911032". It's helpful when people write these things down.


I do agree with your initial premise however - unless there is something different about the head gasket and/or the valve reliefs on the 307 the quoted numbers for 307 and 327 don't stack up.

Edited by user Monday, 28 September 2015 1:37:53 PM(UTC)  | Reason: Not specified

Holden never got their act together until the red motor in the EH and there Impala and Pontiac were sad compared to what the yanks could get.

Any Aussie Galaxie or Customline would flog any Aussie GMH Impala Pontiac they ever made.
GMH were a real stick in the mud back in the day, them drum brakes on all to the last of the Impala Pontiac

By Chrysler I was thinking of the big tanks like, they got big blocks in them, and very flash to any GMH in the day late 50's and on.

What wasn't imported by GMH? Do you mean the engines?