Hi all, Im in the middle of building a 400 on propane for my truck. Truck specs will be 1994 k2500, about 6 inches of lift, one tons, 44s, nv4500, and possibly a doubler. What I have for the engine build so far is 11.5:1 compression ratio, 5.7 scat rods, forged pistons, RHS pro 220cc iron heads, and a comp 12-239-3 4x4 camshaft ( 218 / 226 @ .050 .462 / .480) It will be topped off with a single impco 425, would like to go duals but I would like to give the single a try first. I am second guessing my cam choice, Do I have enough cam to feed 400 cubes and to take advantage of the heads I have? I am thinking the single mixer will be the limiting factor on this engine. This truck is being built for some southern wheelin, I probably wount spin it over 5 grand though. What do you guys think?

If anything is mismatched in that build it's the cyl heads. Those are huge runners for a truck unless you're spinning the bejeezus out of it, which you said you aren't gonna do. I said this in another thread, but I recently discovered on the dyno that a single 425 will act all sorts of goofy when you try to run them at high rpm. They go off the chart rich at about 5200rpm on a 433 cid engine. They can't get enough air past the air valve so they start pulling fuel down the line from the vaporizer/regulator. Yours is going to sart doing that right about the time you would start to make use of your big intake runners. My suggestion would be to run a smaller runner head if possible.

Yeah, I was affraid I went to big on the heads. :shaking:

I don't know what you do most with your truck, but it will probably work fine. Propane is pretty forgiving since it stays vaporized in the intake runners. Your compression ratio and cam selection are great for propane and a good selection for a 4x4 that needs to retain some bottom end torque. If you can trade the heads to some circle burner for some 180ish runners you would be happier.

Ok, thanks for the advice. May be looking for a new home for the heads.