TomZ, sorry to hear of your problem. Which piston are you using. My guess is a flat top, ie the high comp.. The 400s long stoke necessitates using a dished piston to keep the comp. down to reasonable levels. I helped a friend get a 400 built last winter and ran into the same problem with the builder. He insisted on flat top pistons, would not listen to us. So, we paid the bill and left with the parts! No point in building something you can't use. Found a builder down in Syracuse and had him finish the work. Used KB Hyperetics with a 30cc D dish for about a 9.1 comp. ratio. Turned out to be one sweet motor, very torquey. Runs on 89 oct. all day long. The SRPs would be stronger of course, but more money. The 400 went into a Formula sport cruiser, so we figured the KBs would suffice. My suggestion, if you got flat tops, start over with the correct parts. Trying to make do with them will only lead to a broken motor. Also refer to Dennis Moores book for a good cam. Way too many engine builders have no idea what constitutes a good marine cam. Chuck

Traviss,

What part number did you use for the pistons? I'm shooting for about 9:1, but I want to look at your pistons in the catalog to see what the specs are for comparison.

Chuck,

That is exactly what I've run into, though with mine the whole job was basically a freebie. They use a totally different (or same depending on how you look at it) way of thinking over there.

I'm going to replace the pistons, rings, and bearings over the winter months. I'll probably have Comp custom grind a cam for me that will match the application. They already recommended that I go this route, but I already had the cam installed, etc. so anyway, I'll be fixing that as well.

There are some pitfalls when lowering the horsepower potential of these stroker motors. As the horsepower comes down the torque seems to skyrocket. I don't think that the Alpha will like that, but hey... it's insured (and fairly new... it was evidently replaced about four years ago) and so far it has been fine.

The Crane H-272-2 works very well in a high (static) compression (9.0:1 to 10.5:1) 383 small-block stroker marine engine. This cam bleeds off lots of cylinder pressure. Here is the cam card. Also, be sure to use the matching valve springs as well. One more thing that you should look at is to make sure that your quench clearance is 0.035" to 0.040". Everything else you have there should work fine.

Tom.. the part number for the SRP pistons are #183103, they are forged and have a dish of 16cc's ( i can't really remember) this part number is for .030" over. The part number will be diffrent for the oversize you have..

Traviss,

Thanks for the part number. If I decide to make the change, then I'll check them out. I've already been to the website.

ForrestC,

So that cam will really help me out? I looked at the cam card and the numbers look comparable to the Comp XM-262 that I ran in the motor that got trashed. Crane lists the cam as being usable over 10:1... I believe that Comp says not to go over something like 9.5:1 or so with their cam (I guess because of the incredible cylinder pressures).

Have you or anyone that you know used that cam in a marine small block?

Thanks!

Tom- in my 383, I used the same cam as Travis (119831).

I went from a stock Volvo 280 (350) to this 457HP 383 (460+ft/lbs). I truely believe that the hydraulic roller (with the steeper ramps) makes the difference. I went with the Edelbrock Performer RPM heads, with some porting & blending.

I am using TRW 10-1 forged pistons, 18/36 timing.

In my old, heavy (slug) boat, I went from spinning a 21" prop @ 4,400 RPMs, to a 23" prop @ 5,000 RPMs...

Tom,
What is the timing set at?
Have you checked the plugs? Does the engine run too lean?
What oct. fuel do you run?
GEOO

Timing right now is set at 31* with 7* initial. The engine sounds really pissed off at idle but performance is quite sluggish the way it is. A milder cam might solve some of this. The plugs were all OK except for one which was ever-so-slightly damaged at the tip of the ground strap. I had a problem with that particular cylinder where an intake valve tuliped. All of the plugs were a nice tan in color, even the damaged one. I run 93 octane from Mobil or Amoco (gas station fuel since I trailer it).

TomZ, I run the H-272-2 cam in all three 383 marine engine that I built and currently run (18 Donzi and 27 Magnum). Compression that these engines run is in the 9.3 to 9.5 to 1 range. I can run 89-octane in any of them and the total advance is 32- to 34-degrees BTC (10 to 12-degrees BTC initial and total in by 3500 rpm). Don't cam your marine engine like a drag car. You want to make sure that there is enough duration to reduce dynamic or running compression, and that the ramps are smooth enough so as to close the valves gently.

BTW TomZ, what is your current compression ratio? I think that must be verified before any "fix" recommdations can be made. If you know your combustion chamber volume, your piston manufacturer can provide you with the correct compression ratio.

The piston manufacturer claims that with this piston compression should be 10:1 with a 64cc head. The problem though is that Vortec heads actually 61cc when measured though GM claims them to be 64cc. My builder says that the calculated compression ratio with a .038 compressed gasket is 10.3:1. He claims that it should run OK on premium fuel. Obviously, that's wrong. Maybe it works OK in the auto world as the engine doesn't see continous load. I've heard it ping, though it was at a time when the gas was being recycled to freshen it up.

I never made it out of the past weekend to check it out like I wanted to. Maybe it's OK and live-able. The cylinder pressure is what bothers me the most and I'm afraid of really ruining something. Will that cam drop the cylinder pressure to somewhere a little more usable?

Thanks!