DIY_EFI Digest V4 #216

[Stuart Hastings]

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.

I'm thinking if a lousy carburetor is so expensive, what about using EFI? 
I scanned the DIY-EFI archives for 4.3L, and discovered the preferred 4.3L
EFI is the extremely rare SFI used on the Syclone, and the almost-as-good
second-best is the CIS (one injector, six ports). However, the CIS system
seems to have an aluminum intake manifold, so I don't think I can use it
without the added expense of "fresh-water" cooling. Volvo and MerCruiser
sell V6 engines with TBI EFI, but these are much newer and rarer than
4bbls, so I haven't even bothered asking about junked ones. 

If you're not a boater, please understand that most cheap boats use
low-pressure lake water for cooling, and ignore the consequent slow
digestion of the iron block. Really. In the Real World, most boat engines
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.

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
most EFI systems can be made to run OK open-loop if I'm not concerned
about absolute maximum performance. Most sterndrive systems exhaust
underwater through the propeller hub because a) it's cool and safe, b)
it's quiet, c) water flow will vacuum exhaust from the engine while
running at speed. I don't think the boat exhaust system is a significant
restriction for this V6 engine; does anyone on the list know otherwise?

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.  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. 

I don't know what the Syclone/SFI manifold is made of, but I presume it's
rare enough in junkyards that it's not a realistic candidate. That brings
me to TBI. I gather (from reading the DIY-EFI archives &etc) that
balance-shaft V6 TBI systems are fairly common (read "cheap") in
junkyards; they were used in El Caminos, Caprices, and Astros. I haven't
actually seen one, so I don't know if the intake manifold is Aluminum or
Iron. Said donor vehicles probably all have balance shafts underneath
their intake manifolds, and roller camshafts for reduced friction.
However, I see no reason why a balance shaft manifold won't fit my ... 
"unbalanced" :-) V6 block and heads. Alas, the existing GM roller tappets
won't fit in my block; if I really wanted a roller cam, the easiest route
would be to marinize a "Vortec" engine myself. I'll guess there are a few
V6 aftermarket roller cams, and I'll guess they're pretty expensive too. 
In the long run, it would probably be more cost-effective to trade for a
newer boat. 

Currently-offered V6 sterndrives (MerCruiser & Volvo) are still Chevy V6s
with balance shafts, roller cams, 9.4:1 compression, and 2bbl/4bbl/TBI
fuel systems, and are rated at 190/205/210 propshaft HP when turning
4400/4600/4600 RPM. Assuming the 15HP crank-to-prop overhead in my own
sterndrive, this would suggest approximately 205/220/225 crankshaft HP for
these modern marinized V6s. For compaison, the 1988 non-balance-shaft V6s
had 2bbl/4bbl intakes, and were rated at 175/205 crankshaft HP when
turning 4400/4600 RPM. It also suggests the roller cam and newer heads
("Vortec"?) of the modern engines are worth 30HP all by themselves.

The MerCruiser TBI system claims to have a "water cooled fuel system"; I
don't know what that is, or why it's necessary on a boat (where under-hood
temps are probably much cooler than a typical car). Does anyone know what
this is, and why it's necessary (IMHO, Mercury wouldn't fit this if it
wasn't *absolutely* necessary). 

I'll interject something about my own capabilities here. I'm a programmer
by trade, and while it sounds fun to disassemble ROMs and tweak BL tables
with a laptop while under way, I don't have time for such a big project.
EFI for my boat is only feasible if I can get a stock system from a junked
car that will tolerate the marine environment and "bolt-up" readily.
Ideally, I'd like to buy a complete system from one donor car, including
distributor, intake, TBI, computer, sensors, and fuel pump.  I can
probably deal with some throttle bracket fabrication, new fuel lines, and
I think I can add a fuel pump to my boat's gas tank. However, if an EFI
project gets any bigger, I can't handle it at this stage of my life (I
have four kids, oldest is 8; they are why I have the boat :-). 

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?

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? 

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.

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 ;-) ?

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