Walt T
Lieutenant
- Joined
- Mar 16, 2002
- Messages
- 1,369
Re: Carburator Help???
I'll try to explain why such large carburetors are used and my advice is seemingly contradictory. For best performance, select a carburetor that is rated 10-30% higher than the engine CFM requirement. Use 10 to 30 higher on single-plane manifolds . If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 20 to 50% higher. Why go to higher cfms than needed? Because of the engines volumetric efficiency. And every engine's VE is different. This is why you can build two engines identical, hook them up to a dyno and one will produce more than the other. <br />Putting a Dominator on a stock BBC Mercruiser jet will not give any benefit other than the sellers profit margin. A BBC in a jet application built for 7,000 rpm will use a completely different induction system and will benefit. Simply looking at pictures of boats in 'Hot Boats' magazine does not represent true research. I'm sure you can find small blocks with dominators on them, but that doesnt mean it's the right carb for you. It's very difficult to convince the average guy to spend his money where it counts such as the jet pump first when he is dazzled by the awesome looking engines.<br />When you overcarb your engine you want to believe it is better because you just spent a bunch of money. Even though you know it isnt any faster, and is actually slower, you arent gonna say that. That behavior simply enforces the myth to other guys that don't really know any better and go out and buy the same thing. The pursuit of more performance is full of myths and misinformation and has resulted in a colossal waste of dollars by folks just like us who can't really afford to throw away 500 bucks on a carb. If you think I'm full of it, that's fine I really couldn't care less. After all it is YOUR money. <br />Use common sense. This is my advice to the original question by Boatnaround:<br />Spend your money on the jet pump first. You'd be suprised.
I'll try to explain why such large carburetors are used and my advice is seemingly contradictory. For best performance, select a carburetor that is rated 10-30% higher than the engine CFM requirement. Use 10 to 30 higher on single-plane manifolds . If the engine needs 590 CFM, select a carburetor rated in the range of 650 to 770 CFM for a single-plane manifold. A 750 would be right. An 850 probably would cause driveability problems at lower RPM. A 1050 probably would cause actual loss of HP below 4500 RPM. For dual-plane manifolds use 20 to 50% higher. Why go to higher cfms than needed? Because of the engines volumetric efficiency. And every engine's VE is different. This is why you can build two engines identical, hook them up to a dyno and one will produce more than the other. <br />Putting a Dominator on a stock BBC Mercruiser jet will not give any benefit other than the sellers profit margin. A BBC in a jet application built for 7,000 rpm will use a completely different induction system and will benefit. Simply looking at pictures of boats in 'Hot Boats' magazine does not represent true research. I'm sure you can find small blocks with dominators on them, but that doesnt mean it's the right carb for you. It's very difficult to convince the average guy to spend his money where it counts such as the jet pump first when he is dazzled by the awesome looking engines.<br />When you overcarb your engine you want to believe it is better because you just spent a bunch of money. Even though you know it isnt any faster, and is actually slower, you arent gonna say that. That behavior simply enforces the myth to other guys that don't really know any better and go out and buy the same thing. The pursuit of more performance is full of myths and misinformation and has resulted in a colossal waste of dollars by folks just like us who can't really afford to throw away 500 bucks on a carb. If you think I'm full of it, that's fine I really couldn't care less. After all it is YOUR money. <br />Use common sense. This is my advice to the original question by Boatnaround:<br />Spend your money on the jet pump first. You'd be suprised.
