Just picked up a 78 400 from a TA with tranny for $100.00 and I am thinking about building it up for my 68. So all said how should I build it will it bolt to the 68 mounts? My understanding is they all interchange. I want to put the original motor up and away and play with something I don't care about. Looking to go .060 and run on 94 octane street driving with 3.55 gears will budget around $3000.00. Anyone have any recomended machine shops around Columbus?
A 78 block will only have the three bolt mounts which won't directly bolt up to the firebird 2 bolt motor mounts. You will need some adapters that are available. I have no experience in using the adapters so somebody else will have to chime in.
Blocks up through 69 had two bolt mounts. 70-74 have five bolt holes, fit the old 2 bolt and newer 3 bolt mounts. 75 and up have just the 3 bolt holes. (or about those years)
You can't do much with the block to lower compression. Pontiac managed the CR in the cylinder head.
You're seeing the light and planning your build then finding the parts, rather than the other way around.
400 compression is a bit of an issue because few of the factory heads are true bolt-ons that will result in the right compression for today's pump gas. Most of the available heads will either need to be surfaced to reduce the combustion chamber volume, or you'll have to get dished pistons from any of the many vendors who carry them.
Are the heads you have 6X-4 or 6X-8? (The -4 or -8 ID is stamped on a boss below the rocker cover rail between the two left-side spark plug holes.)
They are 6X heads but can not make out -4 or -8 they are the stock heads off the 78 block. I have been doing a lot of reading and just ordered Jim Hands book. Really did not want to build up the #s matching motor to play with but if I can redo the 6X heads to drop comp to around 9 to 1 then I would feel better about it. Any help on picking parts based on exp would be great.
Pull the Craigslist ad if the block in the car is original. Not worth risking a numbers-matching combo (heads and block) just to avoid using a set of adapters.
A stock '78 400 would have some pretty low compression, depending on the heads (6x-4 vs. 6x-8). One way to kill 2 birds with one stone is do a stroker kit. Not only will the added cubes make more power, but will raise the effective compression ratio with those same heads.
This 6x-4 heads should measure 95cc or less, while the 6x-8 will measure at least 100cc. On a stock '48 400 that equated to a 8.1 and 7.6 compression ration respectively. Depending on the stoker kit, you can raise that by a full point or more. Gee, right in the ballpark where you wanted to be... 2 birds, baby!
