250 non supercharged cubic inches is not the best way to move a 4000 pound truck no matter how much HP.
It's been pushed around by a 250 all it's life, so anything will be an upgrade! The six speed with 4.56 or 4.88 gears will also greatly help get the truck up and going. My daily driver has 4.37's, and I really like the short gearing in it.
I believe it is going to be hard to make that much power, especially w/a siamesed stock type cyl head.
You could get 350 HP but I would think you need to up the compression more. But that wont make much of a daily driver w/that much compression of 14:1+ plus you will need a very radical camshft. 1.94" intake 1.60" exhaust.
Sissells (Mike Kirby) can get the pistons you need to fit the cyl head chamber.
Port work, larger valves lumps installed Larry. http://www.t6racing.org/
Mike Kirby, great cyl head work also. http://sissellautomotive.com/
IIRC, Sissells 250 engine w/the 12 port head 10:1 compression made 320 HP @ the crank. Very mild build BTW. But the induction set-up, pretty wild IMO, Blue engine.
Also, IIRC, here is the engine: http://sissellautomotive.com/completeengines.html
http://sissellautomotive.com/cylinderheadpics.html
Guys making 450 HP range 250 CI (Naturally aspirated) in Brazil are running a certain % of nitromethane from what I have been told.
IMO, you would be better off supercharging or turbocharging the 250.
Once you go w/a boosted engine you will never want to be naturally aspirated again. Two cents.
I think for an auto X track, a supercharger might be a better choice.
MBHD Thanks for those links! I've been on both sites before drooling over what those guys are able to do!!
I'd really rather stay N/A. Won't individual runner intakes like used with Webers/Dellorto's reduce the low rpm reversion that causes lower rpm drivability problems in plenum manifolds? Higher compression should help lower rpm torque production, and as I mentioned I'll be running it on E85 which is 105 octane so I'll be able to run pretty high compression on the street. It's 85% alcohol so it should stay cool as well. It's readily available here and is around 50 cents cheaper per gallon than 93 octane.
The Sissell blue engine is awesome, and the intake is very much like what I run on my daily driver VW engine; individual runner intakes with twin two barrel Dellorto's. The low end torque and throttle response is unreal!
It sounds like the cylinder head will be the greatest stumbling block, but I can't afford a 12 port head. What kind of CFM numbers will it take to make around 350 hp?
Here's a pic of one of the carbs and intake from my daily driver VW Bug (small one on the right), and the other is for my stroker build. I really think that IR intakes are the way to go if you want driveability with a large cam. On my VW stroker motor, I'll be running a cam with 301 advertised duration, 268 duration @50, and 12.5 compressioin ration, and it will idle smoothly at 800 rpm. I've heard of V8 guys with similar experiences with IR intakes- huge cams that pull to 7k plus, yet idle and drive as smooth as stock. Can't this work on an 250, or do the siamesed intake ports throw a stick in the spokes?
