Help camshaft questions

OK my 305 898 is toast so I am building a 350 for it. My machinist called isky and they recommended a 280 h cam for my boat on 110th lobe separation. Its like 2200 to 6000 rpm. I know this is wrong. Any help guys

Re: Help camshaft questions

There is a member who recently rebuild a 4.3 engine with a fairly aggressive cam setup . . . is handle is "RSBJ". there is also Tail-Gunner, who has some experience is that regard as well.

Here is the thread: http://forums.iboats.com/non-repair...ercruiser-4-3l-need-advice-please-587005.html

The engine is all built and been on a run or two. . .

Maybe these guys will chime in or you can PM them.

Re: Help camshaft questions

jimmy wise said:

OK my 305 898 is toast so I am building a 350 for it. My machinist called isky and they recommended a 280 h cam for my boat on 110th lobe separation. Its like 2200 to 6000 rpm. I know this is wrong. Any help guys

Click to expand...

Ayuh,... Search up a cam that's listed for Idle, to 5000 rpms, 'n you'll be Happy,....

edit;... speed readin', 'n didn't see the 350 part,...

Re: Help camshaft questions

4bbl carb, porting on the heads and a better flowing intake manifold could make some nice power on a 305....

Re: Help camshaft questions

Hi, yup he did say it's a 350.
I'd stay off the highest performance cams. They don't idle well enough for docking and maneuvering around stuff at low speed. The more radical ones will revert (suck back) water at idle and hydrolock. It sounds as if your builder understands avoiding reversion by your 110* lobe separation angle. 110 is a good marine LSA. Reversion occurs when valve overlap gets too great. You really don't know whether there will be reversion til we see the rest of the spec. That will give you the amount of degrees the valves are off their seats and when they are off their seats in relation to each other. Whatever you choose, make it a marine grind. There are some with a recommended rpm range from idle or 1100 to 5400 or thereabouts. Then you are safer.
Your cam is limited by your exhaust too. If you aren't doing a free flow exhaust a big cam is just going to shove a lot of gas into a small outlet. Do some reading on offshore only, lots of folks have built up and modded motors over there. I bet you could find a functional recipe there.

Re: Help camshaft questions

You also don't want to spin the bottom end past 5000 if it's just a 2 bolt main & cast crank assembly. If you go forged crank, 4 bolt mains it can take more rpms. Either way you could improve it with a roller cam and lifters. The roller cam is a performance upgrade. Then if your wallet isn't empty yet, go get some big exhaust stuff, I'd get the switchable exhaust so my neighbors don't hate me. With switchable you can be quiet til you want to go fast. The exhaust through the regular Y pipe will hold you back at higher RPMs.
There are companies making water jacket headers, they are very high performance, very high dollar, and very loud. They can't be made too quiet although there are mufflers available to calm them a little.
If you reach your spending limit before you get it all done just put together what you can now and do more over the winter.
Power costs money, how much you decide on is the fun part.

Re: Help camshaft questions

Thanks guys. My original plan was to use the 305. There was bad rust in two cylinder. It would clean up at 3030 over. That cam was recommended a by isky. I was going to get from 800 to 5000. I don't know why they even recommended that big

Re: Help camshaft questions

What type of boat are you using. Is it a larger cruiser that sits deep in the water below wake speed or is it a runabout..It does make a difference the isky at 280 is a bit of a high risk..quite a bit. What your looking for is duration's @ .050 post those.