I started to disassambly my 1968 400 HO engine rusted and frized. As any restored should do, the first thing is to "discover" what type of engine, gearbox, VIN, trans, etc. the car came with. Lockily being my GTO a one owner, the car is 100% original (matching numbers) as I will post the pictures. but the question is, looking at the picture, Is that port a exhaust D port or an oval port, this is because I don't know which type of heads the engine came with. When overhauld the engine, which pistons I'm going to use in relation with compression, flow, cc, etc. I'm posting a sequence of matching numbers, (vin, engine s/n, gear box), and a rusted exhaust HO manifold.
Those are D port heads, and if those are the original exhaust manifolds you've got something special there. Those are what are referred to as the 'ram air' exhaust manifolds. I'm going to attach some images to this email that will show you where to get the important numbers from in order to correctly ID what you've got there.
You need (in this order)
block date code
block casting number
block "engine" code (2 character code)
cylinder head date code(s)
cylinder head casting numbers
Thank you for your reply. In my desassambly process I'm taking photos of every step to document the vehicle numbers. (Just for the record). Since this is my first experience with Pontiac I have a lot to learn. And yes, the car is totaly original and a one owner. I've place "somewere" pictures of the maniforl, but I'll do it againg. Today I took more of the heads, block and manifolds. Any info at all, I'll very much apreciate. By the way, Cliff Ruggles the person that wrote the book about Rochester carbs. told me that my QuadraJet carb was from a 1969 Ram Air Aut Trans. very extrange! See the pictures and tell me what you know. Thank you
How do you translate # 16 ?? Explain me something. When I search for replacement pistons I found 8.0:1 ; 7.5:1, etc. Low compresion. Where does the "extra" CR comes from ?? to obtain a published CR of 10.75:1 ??
Small combustion chambers. #16 heads are approx 72cc. With the stock pistons the cr is around 10.75. In order to run on today's premium you need to get the cr down to 9.5. A good way to accomplish that is to run dished pistons. I've read a good rule of thumb is, 94 octane/9.4cr.
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Last edited by 68greengoat; 11-13-2012 at 12:42 PM.
Ok, from the photos...
The date code on the block appears to be A129, correct? (I couldn't tell for sure from the photo if the last digit was a "9" or an "8"). If it's a "9" that means it was cast January 12, 1969 - making it a year model 1969 block. (A128 would mean January 12, 1968 - year model 1968). 9790071 is a 400 - some had 2-bolt mains, some had 4-bolt mains depending on the application.
The "WS" indicates (if year model 1968) 400-HO GTO - 4 speed, 2-bolt mains, or if model year 1969 it would be a 400 Ram Air III - GTO - 4 speed, 2-bolt mains (but if 1969 the casting number for WS RA-III should be 9792506, not 9790071, so hopefully that block date code is really an "8").
The head date code, B068, indicates February 6, 1968 - again model year 1968. For 1968 HO the tops of the center exhaust ports should have "16" on them.
Ok, compression ratio. First of all, don't go by the factory published specs for compression ratio. The published specs were based on an engine that had been "blueprinted" - i.e. everything machined to minimum/maximum (whichever was most advantageous) factory "blueprint" engineering specs. Such a block would have been zero-decked, the heads milled so that the chamber sizes were at the engineering blueprint minimum - and would have been 10.75:1 compression. The engines that rolled off the assembly line wouldn't have been zero-decked (probably closer to .020 down) and the heads would have been "about" the nominal chamber size of 72 cc's - and would have had a compression ratio of around 9.8- 9.9:1 That's one of the reasons an NHRA class-legal "stock car" is so much faster/quicker than it's street-legal counterpart. Its engine has been built to 'factory blueprint specs'.
To be 'safe' with a factory (or factory spec) cam on today's gas (93 octane) you'll want to aim for a compression ratio of less than 9.5:1 ---- probably around 9.3:1. On a "nominal" 400 (stock bore, stroke, .020 deck clearance, .045 head gasket, 6 cc's in the piston valve reliefs, 72 cc chambers (ALWAYS measure them!) ) I'd recommend swapping the pistons out for a set with an additional dish in them such that their total dish volume including the valve pockets is around 12-13 cc's.
Especially on a street engine, pushing compression ratio to the limit doesn't help power enough to justify the risk (in my opinion). On my 461 that's making over 500 HP, the difference between 9.5:1 and 10.0:1 would only be worth about 8 HP, everything else being equal.
Thank you Bear, but look at the pictures. This is what I found when I took off the heads, that's why the engine was friezed !! There is no piston in # 3 (almost) and # 1 well ... but look at the heads, when I put them up side down, the admission valve just fell. Do you think the heads can be save ?? That's my concern. Today, will continue disassambling the heads and will see what I find. More picts. tonight
I wouldn't try to make predictions about whether or not it can be saved just from photos. My recommendation is to get it all apart, cleaned up, maybe take it to a machine shop and have everything cleaned/hot tanked and checked for cracks, then see what you've got to work with. If that truly is the original engine (did you verify that date code on the block? I'm curious..) then it's worth going to more effort to save it.
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