Modding 4.3-cam, gear and prop advice needed

[Boatman296]

Hello, I'm a first time poster on the forum but I've had a chance to view a lot of great information so far.

Today I picked up a '93 Baja 180 that needs some TLC. The interior needs to be re-done but the hull is in good shape. Supposedly the 4.3 and drive were in working order (six years ago). It was winterized at that time.

As part of the total overhaul of this boat as a fun and expensive winter project, I would like to up the ante in the area of hp. I have read the pros and cons of sticking with a 4.3 or bumping up to a V8. I think I can get what I am wanting with the 4.3 for less than $2000. After searching for the best 4.3 mods, it looks like '96+ Vortec heads (and associated valvetrain), Edelbrock intake, slightly larger marine carb and better cam could net 250 hp. Hot Rod magazine took similar parts (a stout 280 Comp cam being the outlier) and made 300 hp on the same motor. I figure a tamer grind should be a better match for boating.

Sooo, my questions-wanting to make good power and torque in a relatively small boat, does the 266 grind (intake 210/exhaust 215, 112* LCA, 0.5 max lift, 1,800 to 5,000 rpm operating range) cam seem okay? The Vortec heads like a split duration favoring the exhaust side. Unfortunately, there aren't many off the shelf cams to choose from. CR looks like it should come in around 9.5 to 10:1. I'm not afraid of using premium gas if I have to.

Then, assuming I can get 250 hp, should I re-gear and re-prop like it is a V8 or am I safe with the stock set-up? I am in the dark to start with regarding what prop it should have because one did not come with the boat.

 

[wca_tim]

Re: Modding 4.3-cam, gear and prop advice needed

Last summer, I did everything you mention except I went with the factory grind marine roller cam rather than an aftermarket. had flat top pistons with stock vortec heads for a little below 10:1 compression ratio. It ran (runs) great on premium pump gas and would keep up with a lot of my friends rigs that had 350s in them. The factory grind roller cam isn't too bad and in fact gives a great torque curve.

if you go v-6 what are you going to do for exhaust? I have a strong sense that with stock manifolds and risers you may have reversion problems if you add much cam. There's also the issue of having to be able to idle low so you can shift into gear without trashing the drive.

The factory marine roller cam should be somewhere about: 197 / 207 (@.5) and .430 / .450 with lsa 112 OR 202 / 213 with similar, perhaps slightly higher lift (@.5). Those are "best guesses", I think I have the numbers for the actual grinds / part numbers somewhere from thinking through that engine last year. I went with the factory grind and was happy with it overall, but it did run out around 4800-500 rpms... It gave great power through the range and peak hp was probably right at 4800. Merc doesn't publish performance spcs in detail, but I've attached a simulated plot that should be fairly close to where I wound up and presumably not far off of what you're contemplating doing.

In the end, it was a good running set-up, but I decided I wanted a little more. the cam seemed incremental, etc... so I replaced it with a stroked smallblock a couple months ago. With the price of fuel, might have been better advised to leave the v6 in... but the grin factor is definately there with the 383.

Hope this is helpful

 

[Boatman296]

Re: Modding 4.3-cam, gear and prop advice needed

Tim,

Thanks for the response. Yeah, I've done a lot of research regarding reversion. From what I can tell, it looks like LCAs less than 112* and bigger durations (i.e. greater than 230) might cause problems. I know the guys with big blocks like lots of lope and lots of duration. It seems like some of the reversion issues happened to this type of boater. I figured the 266 grind would be safer. I was originally looking at the 280 (224/224, LCA 110*) but I figured the rpm range would be to high, torque would suffer down low and reversion might be a problem.

Thanks for sharing your findings regarding your boat. Did you reprop and regear after the mods or did you stay stock? How did it affect your holeshot and WOT mph?