Hot Rodding an A4 - Page 3 - SailNet Community
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post #21 of 34 Old 11-23-2011
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Sloop Jon,
I hear you and I think you have some very interesting ideas. It sounds like an interesting project to try. I don't see why it wouldn't work, but I do agree that in their natural state Atomic 4s are wonderful little buggers. Mine is in a twenty five footer, so it's all I need for sure! But in your case, it might just keep you from digging your bow in like that!

1968 Morgan 24/25 S/V My Fair Leslie
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post #22 of 34 Old 11-27-2011
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I have never owned one but have read they are pretty reliable in stock form, possibly because they are not stressed very hard? Do you want to swing a bigger prop or get more revs? From what I remember, flat heads used to be subject to heat issues, burnt valves and seats, high head temps, and pinging, not something you want in a continous heavy load situation. If you do it let us know how it worked out.

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Also, cracks between exhaust ports and cylinders are common on flat heads. If the head is shaved too much, could have valves hitting top of combustion chamber.
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post #23 of 34 Old 11-27-2011
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Also, cracks between exhaust ports and cylinders are common on flat heads. If the head is shaved too much, could have valves hitting top of combustion chamber.
One of the many flat heads we owned, a Continental 226 CI 6 cylinder out of a Willys pickup, had burnt valves, seats, and as above developed cracks between the valve seats. Also, the head continually warped, leaking coolant into the cylinders, lots of white smoke on start up, and everything was stock. Finally took it out and shoe horned a Ford 302 V8 into the truck. Twice the power, smooth, reliable and sounded good also!! Poor little Atomic 4's, don't abuse them with hop up modifications, it would be considered cruelty to engines, bad boy for even thinking about it.

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post #24 of 34 Old 11-27-2011
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Hypo A4

I guess there is no point in asking "WHY"? We all know that way too much is barely enough. I'm thinking porting and polishing the flat head is a waste of time and energy. You will need custom cast cross flow heads (hemi heads). Given the number of functioning A-4s, you could talk edlebrock into designing them. The biggest problem I see is the fact that we are talking Sailboats, presumably displacement hulls, with a top speed limited by water line length, so i'm thinking you are trying to improve your 0-6 knt time? So we are back to trannies and 4.11 rear ends. Maybe with a 36" prop? What kind of hull are we talking 'bout? For anything other than a full keel, you will have to consider wheelie bars ,er, floats. The other option is increasing waterline length. Have you looked into wrapping the waterline around the boat a few times? That way you could have a longer water line with out increasing LOA and those pesky marina fees. I believe that the tryptophans in left over turkey can have psychotropic side effects.
On the otherhand, a K&N filter with a cold air intake mounted on the seahood may give you exactly what you are lookig for!

Is this what winter does?
Lou
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post #25 of 34 Old 11-27-2011 Thread Starter
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I guess there is no point in asking "WHY"? We all know that way too much is barely enough. I'm thinking porting and polishing the flat head is a waste of time and energy. You will need custom cast cross flow heads (hemi heads). Given the number of functioning A-4s, you could talk edlebrock into designing them. The biggest problem I see is the fact that we are talking Sailboats, presumably displacement hulls, with a top speed limited by water line length, so i'm thinking you are trying to improve your 0-6 knt time? So we are back to trannies and 4.11 rear ends. Maybe with a 36" prop? What kind of hull are we talking 'bout? For anything other than a full keel, you will have to consider wheelie bars ,er, floats. The other option is increasing waterline length. Have you looked into wrapping the waterline around the boat a few times? That way you could have a longer water line with out increasing LOA and those pesky marina fees. I believe that the tryptophans in left over turkey can have psychotropic side effects.
On the otherhand, a K&N filter with a cold air intake mounted on the seahood may give you exactly what you are lookig for! Is this what winter does?
Lou Fair Haven NJ


Actually, answering WHY is easy. What made me think of it was reading a thread about props. Apparently an optimized A4 prop is 9X7 - that is barely more than the blade in my wife's hand mixer. I was simply thinking about some mild mod's that would increase the torque to a level that would allow it to swing a decent sized prop while still keeping the RPM down.

Thinking about all the 33+ footers around 10K Lbs out there with A4's, swinging a 9X7 prop seems pretty feeble.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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post #26 of 34 Old 11-27-2011
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Actually, answering WHY is easy. What made me think of it was reading a thread about props. Apparently an optimized A4 prop is 9X7 - that is barely more than the blade in my wife's hand mixer. I was simply thinking about some mild mod's that would increase the torque to a level that would allow it to swing a decent sized prop while still keeping the RPM down.

Thinking about all the 33+ footers around 10K Lbs out there with A4's, swinging a 9X7 prop seems pretty feeble.
Ran across this, sounds good? Boat Seem Underpowered?

Dabnis
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post #27 of 34 Old 11-27-2011
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I had thought you were kidding. I did not mean to offend. To drive a bigger prop, you need more low end torque, not high end horsepower. Or, as has been mentioned, you could change the gearing of the transmission. I just picked up Don Street's "Ocean Sailing Yacht" and he talks about the British Sea Gull outboard, which has a really low gear ration and swings a big prop and generates a lot of thrust. In short you want to increase displacement (bore and stroke) to increase torque. Props are most effective, roughly speaking, below 2,000 RPM. Increasing horsepower by the means you discussed, will allow the engine to breath better, rev higher and produce horsepower at the top end, exactly where you don't want it for a propeller. Typically when you increase horsepower, you have less at lower rpms and more at higher RPMs, leading to the "peaky" nature of racing engines. The best torque producers are big single cylinder thumpers. That's why many boats had an optional 10 HP diesels like the Yanmar YSM 12 (1 cyl), vs. the 30 HP Atomic (4 Cyl). Less HP, more torque and a lower gear ratio. This is why tractors have four cylinder engines and Formula 1 cars have v12s and the like. For planing hulls, you can make use of high horsepower, as drag is reduces when on plane and out of the water, but for a displacement hull once you are at hull speed, drag rises dramatically and the bow wave gets bigger, but speed doesn't increase. Both the Macgregor 26M and the Hunter Edge have a planing hull so they can use the 90 hp outboards. My 28 displacement hull will get to hull speed (6.4 kts) with 10 HP. No matter how much additional horse power it won't go faster than 6.4 kts. The YSM in my boat swings a 13 inch propeller, vs. the 9 inch you quoted for the Atomic. I hope this makes sense.
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I had thought you were kidding. I did not mean to offend. To drive a bigger prop, you need more low end torque, not high end horsepower.
None taken. I realize that it is an offbeat idea and I was just trolling for other views. I also realize that low RPM torque is what is needed, that's why I referred to it several times. The ideas I proposed were more in the vein of efficiency improvements, precision assembly etc. rather than the usual "make it bigger" hot rodding. Also, a savvy cam grinder can place the engines torque peak pretty well anywhere. I have no idea at what RPM the stock cam reaches max torque but I doubt it was optimized for marine conditions. The engine WAS of agricultural origin and marinizers rarely, if ever, go so far as changing the cam profile.

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My 28 displacement hull will get to hull speed (6.4 kts) with 10 HP. No matter how much additional horse power it won't go faster than 6.4 kts. The YSM in my boat swings a 13 inch propeller, vs. the 9 inch you quoted for the Atomic. I hope this makes sense.
That extra 3 inches of prop is EXACTLY what I had in mind. Pushing a 10K Lbs. 35 footer against wind & current with a 9 inch prop seems a tad Quixotic.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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post #29 of 34 Old 11-28-2011
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Well like the farmer said the first time he saw ballerinas toe dancing: If they wanted taller girls, they should have hired taller girls.
At some point it is easier and cheaper to sling in a diesel than to custom build a a-4 with a custom transmission. I know with Airplanes, which face similar constraints, they end up installing huge 500+ cubic inch motors to get 250 HP, low enough to run a propeller without a gearbox. Besides if the 9.5 inch prop is getting you to hull speed, what is the advantage of the bigger prop?

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post #30 of 34 Old 11-28-2011
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Perhaps an alternative to modifying the engine could be experimenting with props. I would think one would want to have as much prop surface available as diameter would allow, perhaps a larger diameter with less pitch? If diameter is limited perhaps 4 blades with less pitch? It appears the A4 makes about 30HP?, the problem appears to be getting the power efficiently transfered (thrust) into the water, kind of like having little skinny tires on a car with 300 HP in it?

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