I just picked up a 79 Howard mini day cruiser... 540 BBC, 871 BDS blower. As far as I can tell (the boat is in storage right now) I have 2 Holley 850 double Pumpers on it. There not boost reference, and the original owner told me that before he changed the cam to a little more lakeable cam... He found that cylinders 7 and 8 had small amounts of damage due to leaning. It was jerked out of the boat and sent back to the engine shop and they replaced the pistons, ceramic coated them, and put a different cam in. He bore scoped for a couple seasons to ensure there are not any lean spots on the pistons since. HOWEVER!!! I am always looking at improvements. I have only bean able to drive this thing once (let alone see it a few more) since the purchase but I am assuming that without "blower" carbs (non boost reference pv's) it most likely has the power valves blocked off and the jets are x stages richer. So here is my thinking on all this. When you set non blower Holleys to run on blowers, I hear you usually go about 6-8 stages richer on jets (pv's blocked off). This would create nice AF ratio under WOT, however, idle and cruise will be extremely rich. This would cause the engine to not be as "lakeable". So if a happy medium was found that made the engine idle and cruise good but lean at WOT... then ceramic coating/cam change solves a possible lean at WOT then I am good right??? That's a rhetorical question... Only a wideband or reading plugs can offer that answer but I want to know if my logic is even close. Now lets just say I've got all this thinking pretty good so far. So if I was in the market for buying some boost reference carbs to better match the AF ratio at idle/cruise/and WOT then what carbs would be the best choice? It looks like Holley makes a blower carb, I don't like BG stuff to much, I am temped to call up BDS and get some from them but I've heard really great things about Quick fuels also. Now so far the only carb I have found that is both a "marine" and a "blower" carb is from Quick fuel. I'm not sure BDS coats there carbs to resist water corrosion or has the overflow port for the fuel. I bet BDS could make whatever I want but there already more expensive than the Quick Fuel so now I'm thinking Quick Fuel. Any thoughts on carbs? Do I even need to worry about getting "blower" carbs?
I just need to wait till summer and get this thing out and look at what I specifically have (carb model, jets, pv's, etc), but I'm chomping at the bit here to gain as much knowledge as I can before boating season starts.
I've talked with the original owner and he said I might want to look into the systems that have fuel injectors at the base of the intake manifold along with the fuel from the top. Is there such a thing as carbs on top and FI ports to "make sure" AF's are correct? My thinking is that if you have FI ports at the base then you would have to have like a EFI bird/buzzard catcher system on top? Also It looks like that all the lower intake manifolds that have these FI ports also have the burst disk port which is cool, but they also seem to have restricted or non standard coolant passages. For instance if it were used in a street car, there is not a thermostat boss. This style of lower intake seems to not be what I am looking for...
ALL I WANNA DO IS MAKE SURE I DON'T LEAN OUT CYLINDERS AND STILL HAVE A WELL MANNERED 800 HP MONSTER! lol
All day long I see pics of twin Holleys on 871's and all is well. No leaning, no super rich mixtures at everything but WOT, but maybe I'm just looking at a picture rather than knowing any real data about that engine. I refuse to belive that all these years before "blower" carbs that there is no such thing as a good safe all around tune for a blown engine.
I live in Montana, so an engine dyno? No way. Not within couple hundred miles at least. So if I want to verify top notch AF's of each cyl, what's the "approved trade method" for tuning my carbs for a blower? Hard passes and pulling plugs? Shoving my homemade 02 up the water exhaust? (never had to use it on a boat before)
This is the first supercharged ride I've owned so I am newer to all of this. I have tuned many carbs to get awesome mileage and great color on the plugs. When possible I use my O2. Almost all of them are NA engines though. What I'm worried about is leaning specific cylinders out. It seems in boosted engines you can have drastically different mixture in each cylinder. Right? Or is this foul thinking? Do BDS blower intakes for a 540 have inherent flow issues? Do Cams on blower motors have a bigger play in leaning out specific cylinders?
I have so many questions
I hope not to overwhelm... sorry.
You guys are the experts! And I thank you in advance for all the info!