DIY_EFI Digest V4 #216

[Pat Ford]

On Thu, 8 Apr 1999, Stuart Hastings wrote:

> Date: Thu, 8 Apr 1999 13:28:51 -0700 (PDT)
> From: Stuart Hastings <stuart at hal.com>
> To: diy_efi at efi332.eng.ohio-state.edu
> Subject: Re: DIY_EFI Digest V4 #216
> 
> I'm interested in improving the performance of my boat.
> 
> The boat engine is a 1988-model Chevy 4.3L V6, with a 2bbl carburetor. 
> This is an early 4.3L V6, with no balance shaft, and no roller tappets. 
> Outboard Marine Corp, my engines' "marinizer," rated it at 175 crankshaft
> HP or 160 propshaft HP. (Current practice is to rate boat engine HP at the
> prop.)  OMC also offered this engine with a 4bbl carburetor, and claimed
> 205 crankshaft HP for it. I checked with OMC, and the carb/intake is the
> ONLY difference between these engines. OMC has confirmed that the 4bbl
> setup will add 30HP to my engine.  (I recall compression as
> 8.4:1(?unsure), and OMC specifies 89 octane gas.) My particular engine has
> about 220 hours, and seems to have been well cared-for;  compression is
> still about 165psi in all cylinders.
> 
> I've done some preliminary queries, and discovered I can buy a used 4bbl
> carburetor + manifold for about $350, plus shipping and miscellaneous
> expenses (gaskets, carb rebuild kit, new throttle linkage). Probably $450
> total by the time I'm done.

by boat standards that is cheap


> die of neglect long before they rust away anyway. A side-effect of
> "raw-water" cooled engines is their use of very-low-temperature
> thermostats; since the cooling water is almost unpressurized, a 160F
> thermostat lessens the likelihood of steam bubbles and burned valves.

any warmer and you start getting mineral deposits

> 
> Another unique boat engine problem is the exhaust. Most marinized car
> engines have water-jacketed exhaust manifolds, because anything as hot as
> an exhaust manifold is a fire hazard on a boat. I think this means that an
> EGO is pretty much out of the question on a boat engine, but I presume

on a 5.7 magnum I worked on on of the runners was un jacketed for about 4"
and an o2 sensor

> 
> I presume that adding an aluminum CIS intake manifold to my
> raw-water-cooled engine will turn it into a giant battery :-) with
> accellerated galvanic corrosion.

you can get away with al and fe if you add a zinc anode

>  It's possible to fit these engines with
> a (misnamed)  "fresh-water cooling"  system, consisting of a heat
> exchanger, extra plumbing, automotive coolant, and a 180F thermostat, but
> that's another $300-$500 investment. The higher running temperature is
> good for combustion efficiency, oil life, and engine durability, but many
> such boat engines will require an oil cooler too (still more $$). This is
> all a little extravagant for a motor that runs about 50 hours per year in
> fresh (non-salt) water.

it also extends the boating season

> 
> Since the point of this project is to increase HP, there's no point in
> pursuing it unless the generic GM TBI system would supply 200+ crankshaft
> HP from my unbalanced, non-roller-cam V6. 
> 
> 1. Are GM 4.3L V6 TBI systems capable of 200+ HP?
> 
> 2. Is the GM 4.3L V6 TBI manifold made of Aluminum or Iron (or Plastic?).
> 
> 3. I presume the standard TBI in-tank pump needs some baffling; what
> *exactly* is required? Can I swipe the tank-wall fitting (probably steel)
> from a TBI car and modify it for my boats aluminum gas tank?

how deep is the tank if it is tall you can get away with a fuel fitting
down low on the back

> 
> 4. Automotive carburetors typically vent bowl fumes externally. Marine
> carbs vent bowl fumes into the carb intake (above the butterflys), so
> fumes don't collect in the bilge and explode. I presume that a
> properly-installed TBI system won't leak gas or fumes into the bilge.
> Correct? 

yeap

> 
> 5. My Prestolite non-electronic "marine" distributor has fine metal
> screening glued over the bottom vent holes. Can I "marinize" an electronic
> TBI distributor by duplicating this screening? A distributorless system
> elegantly avoids this, but then I presume I need the flywheel pickup that
> may or may not fit my heavy, clutchless marine flywheel. And my marine
> bellhousing probably doesn't have any provision for a crank sensor either.

that screen is a flame arrestor, if you have an explosive bulge something
else is more likely to spark the bang

> 
> 6. Are there any blatant misconceptions in my thinking, outlined above?
> 
> 7. If an appropriate TBI system exists (cheap, powerful,
> marine-compatible), what donor cars should I look for?
> 
> 8. Would I be smarter to grit my teeth and buy a used 4bbl for $450?
> 
> 9. Would I be smarter yet to forget the whole project, because the
> existing 2bbl works fine, and an additional 30HP (17%)  won't improve the
> boat's performance by very much ;-) ?

can you get to hull speed? once at hull speed it takes huge power to get 
any real speed increase ( I don't remember the exact # but it was 
something along the line of %40 more power for %10 more speed) 

the added power would help getting a skier up 

> 
> My research so far has been a few Fuel Injection books, and the DIY-EFI
> archives, and the DIY-EFI stuff is much more useful. I'm very impressed
> with the depth of the technical discussions on this list; thus far, the
> price of my research has been inversely proportional to its value :-)  . 
> 
> Thanks in advance,
> 
> stuart hastings
> stuart at hastings.org
> 
> 
> 
> 
> 
> 

Pat Ford                           email: pford at qnx.com
QNX Software Systems, Ltd.           WWW: http://www.qnx.com
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