250 HP Slant Six - No Turbo

joesnow said

I am told to bore to use 2.2 turbo fordged pistons, late 80's cast crank "lighter", 198 rods or after market lighter rods, good head work "mill, port, big valves, ect.",offey intake, holley 4bl, good cam, clifford header, manual steering, electric fan, good converter, gears, suspension, traction, =
low 13.00's Its being done. http://www.slantsix.org/ssrn/issues/ssrn52Nov08.pdf

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A long rod with a cast crank (and the cast crank block - they changed the main journal size) is going to need custom rods as 198 rods will not fit.

The Mopar Performance manuals once listed a 12 second slant six formula. I don't fully trust it, but with the vehicle weight they listed of 2350 lbs (major league gutting), that would mean probably around your horsepower target. Some of the key details:

4 barrel carburetor - most likely on a Clifford manifold. They suggested 390 cfm but that may be on the low side.
12:1 compression
A camshaft with a 284 degree advertised duration, 221 degrees at 0.050", 0.528" lift
Serious head porting with oversized valves
Rear gears steeper than 4.11:1, and a very high stall converter if running an automatic

And one they didn't mention: A lot of time spent dialing in the carb jetting, getting the ignition curve just right, and optimizing the head porting. Guys like Dr. Dodge at slantsix.org will be a bit help here. I know sometimes you can get sarcastic responses there - particularly if you stated you wanted 250 rear wheel horsepower, to stay naturally aspirated, and to do so cheaply. You're going to have to compromise on at least one of these goals, and some of the members on slantsix.org may be a bit less tactful about saying that.

(Although they're quite friendly compared to how some forums can react to newbie questions. Try asking "I found this turbo kit on eBay, is it a good buy?" on miataturbo.net. Who'da thunk a bunch of Miata drivers would react that way? :D)