340 Block ID

Tech Question


Ole Johnny Male, Kristiansund Norway, 1969 Dodge Dart 2 drht (GTS replica) 340

Hey Rick!

I am a guy from Norway, who has subscribed to MOPAR ACTION for years. I’mdriving a 69 Dart GTS (replica)with a 340 engine. The engine is std. exceptthe cam, which is replaced with a Crower cam, 282 deg., and an a Edelbrockperformer RPM intake. The car is built for street/strip with a narrowed8-3/4″ rear, 4,10 gear, and S/S springs. EsThe car go steady 8.5s on 1/8mile and 13.00 1/4 mile, but now I want to go faster. So here is myquestion: I have an offer on a race small block Mopar. It seems to be a raceblock but I’m not sure. The casting nr .is 4104230-318-6 built date 5-14-79.In my books that casting nr. is a std. 318 but this block has the X cast inon the right front. And it has 4 bolt mains and solid pan rails. So whatkind of block is this? And how much can it be overbored? Now it has std.340bore, 4.04″. I hope you can help me with this thing, because im not sureabout this block.


Ole Johnny-

It sure sounds like a legitimate late-’70s “X” race block.

Maximum safe bore, w/o a sonic check, is 4.07″. Big bore is not the reasonfor this block’s existence – it’s STRENGTH. A regular 340 block will explodeonce over 500 HP, this one can take MUCH more. Nitrous. 13:1 compression.8,000 RPM. Blower. Nothing this block can’t handle!


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